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a_bab
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[*] posted on 3-6-2004 at 06:54


Rogue chemist, thank you very much indeed.
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[*] posted on 3-6-2004 at 19:17


Your welcome a_bab.

Sodium azide scans have now been uploaded. Same spot as before
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[*] posted on 30-6-2004 at 15:21
hey Froot,


hey Froot, I have the same encyclopedia, but it's the 5th edition, i don't know which do you have. Anyways, this is what my encyclopedia says:

Hydrazoic acid is formed (1) by reaction of sodium nitrate with molten sodamide, (2) by reaction of nitrous oxide with molten sodamide, (3) by reaction of nitrous acid and hydrazinium ion, (4) by oxidation of hydrazinium salts, (5) by reaction of ethyl nitrite with NaOH solution and acidifying.
Is this what you mean?
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[*] posted on 1-7-2004 at 09:33


Mine is the third edition. If that info is incorrect surely it would've been rectified by the 5th? Even now that it's been re-worded. :o Is there any way that this procedure for hydrazoic acid is possible?

[Edited on 1-7-2004 by froot]




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[*] posted on 1-7-2004 at 13:02


No. Polverone's answer still stands.

This is a common problem with many short synthetic descriptions. They are too short to be of any use and are misleading. Kirk-Othmer also has many examples of this.

I think that the original articles on hydrazine + NaOH + alkyl nitrites are in Ber., 41 (1908)
Thiele- p. 2681
Stolle- p. 2811

Also see the excellent US patents:
1628380, 5208002, 5098597, and any others that you might find by doing a word or classification search.
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[*] posted on 23-8-2004 at 13:42


For those of you who still want this book, the preparation of the azides section is on the roguesci FTP.
I was not the one who upped it there, one of their members did.
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[*] posted on 24-8-2004 at 09:42


Has anyone managed to get the sodium azide out of a car air bag detonater. I thought it was sodium azide they used but I do not know how much.
The bit I have got is if you pass N2O over the melted sodamide you get sodium azide and water, the water should be blown away. Sodium azide when distilled with 50% sulphuric acid yields hydrazoic acid.
Mick

Boils at 37 0C

[Edited on 24-8-2004 by mick]
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[*] posted on 24-8-2004 at 14:28


Keep in mind that the azides are more poisonous even than cyanides! That's the reason I don't mess with them.
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[*] posted on 26-8-2004 at 09:42


I have also considered the possibility to find an old airbag and "extract" sodium azide from it. I once found a homepage with pictures and everything of an airbag being opened and the sodium azide removed. It contained quite a bit of NaN3, well above 100 grams IIRC. Of course this page is nowhere to be found anymore :(

The sodium azide was present as small pellets, which was dissolved in water to remove insoluble additives such as iron oxide and/or silicates which are added to react with the metallic sodium that is formed when the azide breaks down (into nitrogen gas and sodium metal vapour of course).

The extraction itself was quite straight-forward. I remember something about a screw behind the steering whell that was to be removed before the airbag was opened. This relaxed a spring inside the firing mechanism and made sure, that the airbag could not explode during the opening procedure. I doubt this mechanism can be found in all automobile brands though. I think it's most often an intirely electrical firing system.

The major problem I have encountered is: which cars/models have airbags that actually contain NaN3?. A lot of manufacturers have moved to safer alternatives that are not as toxic. I did some research about a year ago, and it seemed that there was a move towards nitrocellulose or compressed gas as the airbag propellant. If one wants to buy an old airbag it would be nice to know beforehand that it actually contains sodium azide and not a small canister of nitrogen, argon or something else!

Used airbags are also quite expensive as they are in high demand because people accidentally bump into things at low velocity, just enough to set off the airbag thus needing replacement. The spare-part dealers and scrap yards seem to know this, because prices are quite high in my experience. And usually you have to buy the entire steeringwhell and airbag unit just to get the NaN3, making it even more expensive :(
In the end it might me cheaper to make your own azide. It just takes time and decent lab equipment.

Although NaN3 is extremely toxic I wouldn't worry that much about it. Being a non-volatile solid I think you would have to be quite careless to cause any danger to yourself. Wearing vinyl gloves and maybe a dust mask should do it. Of course once you get the azide out of the airbag and start to play with it, one has to be extremely carefull. Certainly keep it out of direct sunlight and keep it dry and away from acids to avoid formation of HN3.

[Edited on 26-8-2004 by Nitramine]
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[*] posted on 26-8-2004 at 14:09


On that note does anyone know how the NaN3 is initiated in air bags?

I have some lab grade NaN3 and you have to heat the hell out of it to get it to deflagrate - it doesn't detonate in my experience, unlike the heavy metal salts. I haven't tried heating a large amount though.

Further to a_bab's question about storage of lead azide, I have a large quantity (50g+ dextrinated) that has been stored in the dark under water, for safety, for over 10 years and it still detonates like the day it was made!

Lead azide has always been the detonator of choice for me - its incredibly powerful and so easily made.
Hint for all those searching for NaN3 - its a commonly used preservative in biology labs.
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[*] posted on 24-9-2004 at 21:24


Nitramine,

Did you ever find an archive copy of the webpage detailing extraction of NaN3 from airbag pellets?
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[*] posted on 26-9-2004 at 00:48


triazole

1. Procedure
(Note 1)
A. 1-Formyl-3-thiosemicarbazide. Four hundred milliliters of 90% formic acid contained in a 2-l. round-bottomed flask is heated on a steam bath for 15 minutes, and then 182 g. (2 moles) of colorless thiosemicarbazide (Note 2) is added. The mixture is swirled until the thiosemicarbazide dissolves. The heating is continued for 30 minutes, during which time crystalline 1-formyl-3-thiosemicarbazide usually separates. Boiling water (600 ml.) is added, and the milky solution that results is filtered through a fluted filter paper. After standing for 1 hour, the filtrate is cooled in an ice bath for 2 hours, and the 1-formyl-3-thiosemicarbazide that separates is collected by suction filtration and air-dried overnight. It weighs 170–192 g. (71–81%) and melts at 177–178° with decomposition.
B. 1,2,4-Triazole-3(5)-thiol. A solution of 178.5 g. (1.5 moles) of 1-formyl-3-thiosemicarbazide and 60 g. (1.5 moles) of sodium hydroxide in 300 ml. of water in a 2-l. round-bottomed flask is heated on a steam bath for 1 hour. The solution is cooled for 30 minutes in an ice bath and then is treated with 150 ml. of concentrated hydrochloric acid. The reaction mixture is cooled in an ice bath for 2 hours, and the 1,2,4-triazole-3(5)-thiol that precipitates is collected by suction filtration. The thiol is dissolved in 300 ml. of boiling water and the solution is filtered through a fluted filter paper. The filtrate is cooled in an ice bath for 1 hour, and the thiol is collected by suction filtration and air-dried overnight. The 1,2,4-triazole-3(5)-thiol weighs 108–123 g. (72–81%) and melts at 220–222°.
C. 1,2,4-Triazole. Caution! This preparation should be carried out in a ventilated hood to avoid exposure to noxious fumes.
A mixture of 300 ml. of water, 150 ml. of concentrated nitric acid, and 0.2 g. of sodium nitrite (Note 3) is placed in a 2-l. three-necked flask equipped with a stirrer and a thermometer. The stirred mixture is warmed to 45°, and 2 g. of 1,2,4-triazole-3(5)-thiol is added. When oxidation starts, as indicated by the evolution of brown fumes of nitrogen dioxide and a rise in temperature, a bath of cold water is placed under the reaction flask to provide cooling and an additional 99 g. (total, 101 g.; 1 mole) of 1,2,4-triazole-3(5)-thiol is added in small portions over the course of 30–60 minutes. The rate of addition and the extent of cooling by the water bath are so regulated as to keep the temperature close to 45–47° all during the addition. The water bath is kept cold by the occasional addition of ice.
When the addition is completed, the bath is removed and stirring is continued for 1 hour while the reaction mixture gradually cools to room temperature. Sodium carbonate (100 g.) is added in portions, followed by the cautious addition of 60 g. of sodium bicarbonate (Note 4). The water is removed from the slightly basic solution by heating the solution in a 3-l. round-bottomed flask under reduced pressure on a steam bath. To aid in removing the last traces of water, 250 ml. of ethanol is added to the residue and the mixture is heated under reduced pressure on a steam bath until it appears dry (Note 5).
The residue is extracted twice with 600 ml. of boiling ethanol to separate the triazole from a large amount of inorganic salts. This extract is evaporated to dryness on a steam bath under reduced pressure, and the resulting residue is extracted with two 500-ml. portions of boiling ethyl acetate. The ethyl acetate extract is evaporated to dryness on a steam bath under reduced pressure. The crude 1,2,4-triazole remaining in the flask is dissolved by heating it with 50 ml. of absolute ethanol, and then 1 l. of benzene is added. The mixture is heated under reflux for 15 minutes, and the hot solution is filtered through a fluted filter paper. This extraction procedure is repeated. The two extracts are combined, cooled in an ice bath for 30 minutes, and filtered to remove colorless crystals of 1,2,4-triazole (m.p. 120–121°), weighing 28–30 g. after being dried in air. About 300 ml. of the filtrate is removed by slow distillation through a Claisen still-head to remove the bulk of the ethanol. The residual solution is cooled in an ice bath for 30 minutes and filtered to separate an additional 8–10 g. of colorless 1,2,4-triazole, m.p. 119–120°. The total weight of 1,2,4-triazole is 36–40 g. (52–58% yield).
2. Notes
1. This procedure is no longer regarded as the best available for the preparation of 1,2,4-triazole. See Discussion section.
2. The thiosemicarbazide must be of good quality or the yield and quality of 1-formyl-3-thiosemicarbazide will suffer. The thiosemicarbazide supplied by Olin Mathieson Chemical Corporation, obtained as a colorless free-flowing powder, can be used without purification.
3. The use of sodium nitrite helps to avoid an induction period.
4. A large flask is used to contain the vigorous effervescence that occurs upon the addition of carbonate. The final pH should be near 7.5, and it is reached after the addition of bicarbonate no longer causes bubbling.
5. Prolonged heating under reduced pressure should be avoided, since 1,2,4-triazole tends to sublime
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[*] posted on 26-9-2004 at 00:51


4-dodecylbenzenesulfonyl azides

1. Procedure
Caution! Although the mixture of dodecylbenzenesulfonyl azides is the safest of a group of diazo transfer reagents,2 one should keep in mind the inherent instability, shock sensitivity, and explosive power of azides. All users should exercise appropriate caution.
4-Dodecylbenzenesulfonyl chlorides. A 250-mL, three-necked, round-bottomed flask, equipped with a mechanical overhead stirrer, a Claisen adapter bearing an immersion thermometer, a pressure-equalizing addition funnel, and reflux condenser, is charged with a solution of 60.00 g (0.184 mol) of dodecylbenzenesulfonic acids (Note 1) and 8.64 mL of dimethylformamide (DMF) in 60 mL of hexane . Stirring is initiated while the mixture is heated to 70°C using a heating mantle, and 22.1 mL (36.24 g, 0.304 mol) of thionyl chloride (Note 2) is added at a rate to maintain controlled reflux (Note 3). The required addition time is about 1 hr. The dark solution is heated an additional 2 hr at 70°C and cooled to 40°C (Note 4). While still warm (40°C), the mixture is transferred to a 250-mL separatory funnel, and the dark lower layer is separated from the hexane solution (Note 5). The hexane layer is cooled to 25°C and washed with 60 mL of aqueous 5% sodium bicarbonate solution (Note 6). The bicarbonate wash is back extracted with 36 mL of hexane and the combined hexane layers are treated with 3 g of carbon (Note 7), (Note 8) and stirred for 2 hr at 25°C. The carbon is removed by filtration and the cake is washed with three portions (12-mL each) of hexane. The combined hexane layers plus the hexane washes are used to prepare the azide.
4-Dodecylbenzenesulfonyl azides. A 500-mL, three-necked, round-bottomed flask fitted with a mechanical overhead stirrer is charged with the hexane solution from step A. To this solution is added a solution of 11.6 g (0.178 mol based on the total solids from the sulfonyl chlorides above) of sodium azide (NaN3) in 100 mL of water and 2.0 g of phase transfer catalyst (Aliquat 336) (Note 9). Stirring is initiated, and the reaction progress is monitored by thin layer chromatography (Note 10). Approximately 4 hr at 25°C is required to complete the reaction. The two-phase mixture is transferred to a 500-mL separatory funnel and the aqueous layer is removed. The hexane layer is washed with 100 mL of aqueous 5% sodium bicarbonate solution and dried over 28 g of anhydrous sodium sulfate. The drying agent is removed by suction filtration, and the cake is washed with 20 mL of hexane. The concentration and purity of the 4-dodecylbenzenesulfonyl azides are best determined by evaporation of a small sample to an oil of constant weight with visible spectrophotometric assay for the azide (Note 11). The hexane solution of dodecylbenzenesulfonyl azides, when standardized as above (Note 11), can be used as obtained for most applications. However, if desired, careful concentration of the hexane solution under reduced pressure at room temperature affords 58.2–61.4 g (90–95%) of the oily mixture of dodecylbenzenesulfonyl azides; corrected for the assay of the azides the yield is usually 95% (Note 12) and (Note 13).
2. Notes
1. Dodecylbenzenesulfonic acids, a 97% mixture of branched chain isomers, was purchased from Spectrum Chemical Mfg. Corp.
2. Reagent grade thionyl chloride from Fisher Scientific Co. was used.
3. An excess of thionyl chloride–dimethylformamide catalyst is used to prevent formation of sulfonic anhydrides. A stoichiometric amount of thionyl chloride gives a much reduced yield.
4. The progress of the reaction is monitored by thin layer chromatography. A 0.1-mL sample is removed, evaporated to dryness and dissolved in 2 mL of hexane. The solution is spotted on an Analtech silica GF plate (8 cm × 2.5 cm) and developed in hexane/methylene chloride (4/1). Visualization by UV light shows Rf = 0.4 for the sulfonyl chlorides.
5. If allowed to cool to 25°C, the dark layer may solidify, hampering the separation. This very acidic layer is the excess thionyl chloride/DMF complex. It should be handled with proper protection in a ventilated area To facilitate visual identification of the layers, the checkers added about 25 mL of hexane.
6. The pH of the bicarbonate wash is a reflection of the efficiency with which the dark lower layer has been removed. In the course of a dozen runs, this pH ranged from 5.5 to 7.1. If the pH of the wash is below 5.5, a second wash with bicarbonate is necessary.
7. Nuchar SA carbon from Westvaco Co. was used.
8. It is essential that the carbon treatment be carried out within a few hours. Experiments where this treatment was delayed for 16 hr invariably produced an azide mixture of lower purity (85%) and lower yield (80%). Although the sulfonyl chlorides hydrolyze only slightly (1–2%) in wet hexane in 24 hr, that amount of sulfonic acids in the presence of the phase transfer agent catalyzes the hydrolysis of sulfonyl chlorides. After treatment with carbon, the hexane solution of sulfonyl chlorides can be stored for several weeks in the refrigerator with little or no adverse effect on the next step.
9. Aliquat 336 (tri-n-alkylmethylammonium chloride) was obtained from Aldrich Chemical Company, Inc. The material is a mixture of C8 and C10 chains with C8 predominating. There is a slight initial exothermic reaction on adding the phase transfer catalyst. Intermittent cooling with a cold water bath is required to keep the temperature below 35°C.
10. A sample of the hexane layer from the reaction mixture is diluted 10 fold with hexane, spotted and developed as described in (Note 4). Visualization by UV light shows Rf = 0.3 for sulfonyl azides.
11. The assay for sulfonyl azides is adapted from the method of Siewinski, et al.3 The azide content of the hexane solution was assayed as follows to determine the contained yield:
1. Standard Curve:
Stock solution: 80 mg of NaN3 diluted to the mark in a 100-mL volumetric flask with 0.1 N NaOH-MeOH.
Procedure: Into a series of four, 100-mL volumetric flasks, transfer 5, 7, 10 and 15 mL respectively of the stock solution. Into a 100-mL volumetric labelled blank, pipet 10 mL of 0.1 N NaOH-MeOH solution. To all add 2 drops of 0.1% ethanolic phenolphthalein indicator solution, and 20 mL of aqueous 1.5% sodium sulfate (Na2SO4). Acidify each, in turn, to the phenolphthalein end point with 1 N hydrochloric acid and immediately add 25 mL of 1 M ferric ammonium sulfate [Fe(NH4)(SO4)2] solution. Dilute to the mark with 1.5% Na2SO4. Let stand 10 min, then read absorbance at 458 nm. Plot absorbance vs. concentration.
2. Sample:
Pipet 5 mL of the hexane solution containing 4-dodecylbenzenesulfonyl azides into a 100-mL volumetric flask and dilute to the mark with methanol. Pipet 5 mL of this solution into a small stoppered flask. Add 2 mL of aqueous 1 N potassium hydroxide solution and heat at 75°C for 20 min. Allow to cool to room temperature, add 2 drops of 0.1% phenolphthalein solution, and 10 mL of 1.5% Na2SO4. Shake, then transfer quantitatively to a 60-mL separatory funnel. Add 10 mL of butanol (or isoamyl alcohol) to the sample flask, shake, then transfer to the separatory funnel. Shake the funnel, let the layers separate, then remove the bottom (H2O) layer into a 100-mL volumetric flask. Add an additional 10 mL of 1.5% Na2SO4 to the alcohol layer in the separatory funnel, shake, let the layers separate, then transfer the water layer to the volumetric flask. Neutralize the combined water layers to the phenolphthalein end point with 1 N hydrochloric acid, then immediately add 25 mL of Fe(NH4)(SO4)2. Dilute to the mark with 1.5% Na2SO4 solution, let stand 10 min, then read absorbance at 458 nm. Read azide concentration against the NaN3 calibration curve.
12. The checkers determined the yield by evaporation of the hexane solution to constant weight (3–10 hr at 0.1 mm). The yields cited are based on the assumption that the 3% impurity in the starting sulfonic acids is not present in the final product. The checkers found the material obtained upon concentration, to be sufficiently pure for use without further purification.
13. The spectroscopic data for the mixture of four isomeric secondary dodecylbenzenesulfonyl azides (2.5:1.6:1.6:1.0) is as follows: 1H NMR (400 MHz, CDCl3) δ: 0.70–1.00 (m, 6 H), 1.00–1.50 (m, 12 H), 1.50–1.80 (m, 6 H), 2.90–2.50 (m, 1H), 7.25–7.45 (m 2 H), 7.87 (m 2 H); 13C NMR (100 MHz, CDCl3) δ: 12.07, 13.94, 14.02, 14.05, 14.07, 14.10, 20.63, 21.89, 22.50, 22.61, 22.63, 22.65, 22.69, 27.18, 27.48, 27.52, 27.58, 29.15, 29.26, 29.30, 29.32, 29.44, 29.46, 29.49, 29.51, 29.57, 29.61, 29.72, 31.69, 31.82, 31.83, 31.88, 31.91, 36.21, 36.34, 36.60, 36.61, 36.64, 38.06, 38.85, 40.24, 46.11, 46.38, 48.15, 127.55, 127.66, 128.33, 128.93, 129.01, 135.82, 135.85, 154.56, 154.82, 154.87, 156.09; IR (film) 2126 cm−1.
Waste Disposal Information
All toxic materials were disposed of in accordance with "Prudent Practices in the Laboratory"; National Academy Press; Washington, DC, 1995.
3. Discussion
4-Dodecylbenzenesulfonyl chlorides have been prepared from the corresponding acids using chlorosulfonic acid,4 phosphorus oxychloride,2 and thionyl chloride.5 The use of catalytic amounts of DMF in conjunction with thionyl chloride is based on the work of H. Bosshard, et al.6 The insolubility of the DMF/thionyl chloride complex in the reaction solvent permits easy removal at the end of reaction. Extraction with dilute base removes the last trace of acids and the solution is pure enough for the next step.
The method described above for the preparation of the mixture of 4-dodecylbenzenesulfonyl azides is new and based on the work of Bollinger and Hazen.5,7 Sulfonyl azides have been prepared by diazotizing substituted sulfonyl hydrazides,8 and treating sulfonyl halides in methanol-water,9 ethanol-water,10 acetone,2,5,7 or acetone-water solutions11 with aqueous or solid sodium azide.5,7,12 Use of phase transfer catalysis for the preparation of sulfonyl azides is new, simple and effective. It avoids solvent changes and permits isolation of a hexane solution of sulfonyl azides without concentration.
The use and advantages of 4-dodecylbenzenesulfonyl azides as a diazo transfer agent are fully discussed by Hazen, Weinstock, Connell, and Bollinger.7 In contrast to p-toluenesulfonyl azide, that has the shock sensitivity of tetryl (N-methyl-N-2,4,6-tetranitroaniline) and the explosiveness of TNT, the mixture of 4-dodecylbenzenesulfonyl azides exhibits no shock sensitivity at the highest test level (150 kg cm) and 24% of the heat of decomposition measured in cal/g. p-Toluenesulfonyl azide appears as a diazo transfer agent in Org. Synth., Coll. Vol. V 1973, 179; VI, 1988, 389, 414 and its preparation is reported in the first of these. Two explosions during its preparation have been reported.13,14
This preparation is referenced from:
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[*] posted on 26-9-2004 at 00:54


ACETAMIDE


Submitted by G. H. Coleman and A. M. Alvarado.
Checked by H. T. Clarke and E. R. Taylor.
1. Procedure
In a 5-l. flask is placed 3 kg. (2860 cc., 50.0 moles) of glacial acetic acid and to this is added a weight of ammonium carbonate corresponding to 400 g. (23.5 moles) of ammonia (Note 1). The flask is fitted with a one-hole stopper holding an efficient fractionating column 90 cm. long with condenser and receiver. An air condenser 150–200 cm. long may be employed. The mixture in the flask is heated to gentle boiling and the flame so regulated that the rate of distillation does not exceed 180 cc. per hour. The distillation is continued in this way for eight to ten hours, until the temperature at the head of the column reaches 110°. The distillate, which is a mixture of water and acetic acid, amounts to 1400–1500 cc. The receiver is changed, the flame under the flask is gradually increased, and the distillation is continued at about the same rate until the temperature at the head of the column rises to 140°. The distillate, which amounts to 500–700 cc., is largely acetic acid and may be used in the next run.
The contents of the flask are transferred to a 2-l. flask for fractional distillation (p. 130), having a column 40–50 cm. long, and distilled under atmospheric pressure, using an air condenser. The fraction boiling below 210°, amounting to 250–300 cc., is collected separately. The material remaining in the flask is nearly pure acetamide and may all be distilled, 1150–1200 g. passing over at 210–216°. By redistilling the fraction boiling below 210°, the yield may be increased to 1200–1250 g. (87–90 per cent of the theoretical amount). The acetamide thus obtained is pure enough for most purposes, but if a purer product is desired it may be recrystallized from a mixture of benzene and ethyl acetate; 1 l. of benzene and 300 cc. of ethyl acetate are used for 1 kg. of acetamide (Note 2). Colorless needles melting at 81° are thus obtained (Note 3). The solvent and the acetamide it contains may be recovered by distillation.
2. Notes
1. Ammonium carbonate of commerce is often extremely impure, and care must be taken to obtain a representative sample for the determination of the ammonia content by titration with standard acid. The ammonium carbonate used in this preparation contained 27.2 per cent of ammonia, and 1470 g. was used in each run.
2. Crystallization of acetamide, by solution in hot methyl alcohol (0.8 cc. per g.) and dilution with ether (8–10 cc. per g.), has been recommended as the best method of purification.1
3. As acetamide is somewhat hygroscopic, it cannot be exposed to the air unless precautions are taken to have the air dry.
3. Discussion
Acetamide can be prepared by the rapid distillation of ammonium acetate;2 by heating ammonium acetate in a sealed tube and distilling the product;3 by treating acetic anhydride with ammonia;4 by heating a mixture of ammonium chloride and sodium acetate to 240°;5 by the action of cold aqueous ammonia on ethyl acetate;6 by boiling a mixture of glacial acetic acid and ammonium thiocyanate for four days;7 by saturating glacial acetic acid with dry ammonia and then refluxing;8 by distillation of ammonium acetate through a reflux condenser filled first with glacial acetic acid and then with aniline until the temperature of the mixture reaches 220°;9 by passing a stream of ammonia through heated acetic acid;10 and from formamide and hydrogen at 200–500°.11
The procedure described is based on the method of Noyes and Goebel,12 in which equimolecular proportions of ammonium acetate and acetic acid are heated together, the acetic acid having been shown to accelerate both the dehydration of ammonium acetate and the hydrolysis of acetamide.

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[*] posted on 26-9-2004 at 00:58


DIAZOMETHANE
[Methane, diazo-]


Submitted by James A. Moore and Donald E. Reed1.
Checked by D. J. Pasto and E. J. Corey.
1. Procedure
Caution! Diazomethane is toxic and explosive. The operation must be carried out in a good hood with an adequate shield (Note 1).
An efficient condenser (60 cm. or longer) is fitted with an adapter to which is sealed a length of 9-mm. tubing extending nearly to the bottom of a 5-l. round-bottomed flask, which serves as the distillation receiver (Note 2) and (Note 3). The adapter should be connected to the receiver with a two-hole stopper carrying a drying tube if anhydrous diazomethane is desired. The receiver is placed in a well-mixed ice-salt mixture, and sufficient anhydrous ether (about 200 ml.) is added to cover the tip of the adapter.
In a 5-l. round-bottomed flask are placed 3 l. of U.S.P. solvent grade ether, 450 ml. of diethylene glycol monoethyl ether (Note 4), and 0.6 l. of 30% aqueous sodium hydroxide solution (Note 5). The mixture is chilled in an ice-salt bath to 0° (Note 6), and 180 g. (0.5 mole) of N,N'-dimethyl-N,N'-dinitrosoterephthalamide (70% in mineral oil) (Note 7) is added in one portion. The flask is immediately transferred to a heating mantle and connected by a gooseneck to the condenser. The yellow color of diazomethane appears in the receiver almost immediately. About 2 l. of ether is distilled in 2–2.5 hours (Note 8); the distilling ether is practically colorless at this point. The tip of the adapter should be kept just below the surface of the distillate during the distillation. The distillate contains 0.76–0.86 mole (76–86%) (Note 9) and (Note 10) of diazomethane as determined by titration.2 When the apparatus has been protected with a drying tube, the diazomethane is suitable for reaction with an acid chloride without further drying.
2. Notes
1. Diazomethane is not only toxic but also potentially explosive. Hence one should wear heavy gloves and goggles and work behind a safety screen or a hood door with safety glass, as is recommended in the preparation of diazomethane described by De Boer and Backer.3 As is also recommended there, ground joints and sharp surfaces should be avoided. Thus all glass tubes should be carefully fire-polished, connections should be made with rubber stoppers, and separatory funnels should be avoided, as should etched or scratched flasks. Furthermore, at least one explosion of diazomethane has been observed at the moment crystals (sharp edges!) suddenly separated from a supersaturated solution. Stirring by means of a Teflon-coated magnetic stirrer is greatly to be preferred to swirling the reaction mixture by hand, for there has been at least one case of a chemist whose hand was injured by an explosion during the preparation of diazomethane in a hand-swirled reaction vessel.
It is imperative that diazomethane solutions not be exposed to direct sunlight or placed near a strong artificial light because light is thought to have been responsible for some of the explosions that have been encountered with diazomethane. Particular caution should be exercised when an organic solvent boiling higher than ether is used. Because such a solvent has a lower vapor pressure than ether, the concentration of diazomethane in the vapor above the reaction mixture is greater and an explosion is more apt to occur.
Most diazomethane explosions occur during its distillation. Hence diazomethane should not be distilled unless the need justifies it. An ether solution of diazomethane satisfactory for many uses can be prepared as described by Arndt,2 where nitrosomethylurea is added to a mixture of ether and 50% aqueous potassium hydroxide and the ether solution of diazomethane is subsequently decanted from the aqueous layer and dried over potassium hydroxide pellets (not sharp-edged sticks!). When distilled diazomethane is required, the alternative procedure of De Boer and Backer3 is particularly good because at no time is much diazomethane present in the distilling flask.
Both the toxicity and explosion hazards associated with diazomethane are discussed by Gutsche.4
2. If it is desired to determine the yield of diazomethane by titration, the receiver should be calibrated so that the volume of the distillate can be measured without the necessity of transferring to a graduated vessel.
3. The submitters have used equipment having all connections made with ungreased 29 / 42 ground-glass joints. This is contrary to previously recommended practice (Note 1). The submitters feel that ground-glass joints do not represent an added hazard, and that their use expedites the completion of consecutive runs. In the course of many preparations, however, a film of polymethylene was found to accumulate on the joints and prevent a tight fit. This film can be removed by a brief treatment with hot concentrated alkali and vigorous rubbing.
In some forty preparations made by the submitters, one explosion occurred which was attributed to the cracking of the adapter tube during the distillation. The adapter and the drying tube were disintegrated, but the receiver and the contents of the distilling flask were not affected, indicating a local detonation that was not sustained.
The checkers did not use glassware with ground-glass joints. New unmarked flasks and condenser were used which were connected together with fire-polished glass tubing and rubber stoppers.
4. Practical grade 2-(2-ethoxyethoxy)ethanol (Matheson, Coleman and Bell) can be used without further treatment. In a few preparations, the submitters encountered difficulty with the formation of a very stiff gel of disodium terephthalate in the flask during distillation. In one case, this difficulty was traced to the use of an old bottle of 2-(2-ethoxyethoxy)ethanol from another source.
This relatively large volume of cosolvent was found to give optimum yields. The submitters have found that the evolution of diazomethane from a stirred suspension of the reagent in ether and 40% aqueous sodium hydroxide is extremely slow and incomplete.
5. The use of more concentrated solutions of potassium hydroxide gave somewhat lower yields.
6. Caution! It is extremely important that the flask contents be cooled to at least 0°. The reaction is rapid and a considerable amount of diazomethane is generated at this temperature.
7. This material is available from Eastman Organic Chemicals and Aldrich Chemical Company. It is also available from E. I. du Pont de Nemours and Company, who use the trade name Nitrosan for it. The 30% white mineral oil acts as a stabilizer. The material may be stored indefinitely at room temperature. It sometimes turns green on long standing, but this does not affect the yield of diazomethane (private communication from B. C. McKusick).
8. The yield of diazomethane is slightly lower if the distillation is carried out more slowly.
9. The average yield in some thirty runs was over 80%; yields as high as 95% have been obtained. It is probable that a second receiver in series would permit the recovery of a small additional amount of diazomethane.
10. The checkers decomposed the small amount of diazomethane remaining in the reaction flask by careful addition of 100 ml. of acetic acid before disposal.
3. Discussion
Diazomethane has been prepared by the action of base o nitrosomethylurea,2 nitrosomethylurethane,5 N-nitroso-β-methylaminoisobutyl methyl ketone,6 p-tolylsulfonylmethylnitrosamide,3 and N-nitroso-N-methyl-N'-nitroguanidine.7 8
4. Merits of Preparation
The great advantages of the present method are the availability, moderate cost, and high stability of the nitrosamide, and the suitability for large-scale preparations. The procedure is rapid and simple, and the yields are consistently higher than in any other method tried by the submitters.
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[*] posted on 26-9-2004 at 00:59


INDAZOLE


Submitted by Emily F. M. Stephenson
Checked by C. F. H. Allen, C. V. Wilson, and Jean V. Crawford.
1. Procedure
A. o-Hydrazinobenzoic acid hydrochloride. In a 2-l. beaker, provided with a stirrer and a low-temperature thermometer, and cooled in an ice-salt bath, are placed 42 g. (0.31 mole) of anthranilic acid and 300 ml. of water. The stirrer is started, and 340 ml. of concentrated hydrochloric acid (sp. gr. 1.18) is added in one portion; the anthranilic acid dissolves, and its hydrochloride begins to separate almost immediately. After the mixture has been cooled to 0°, a solution of 21.6 g. (0.31 mole) of technical sodium nitrite in 210 ml. of water is added from a dropping funnel, the tip of which extends below the surface of the suspension, at such a rate that the temperature never rises above 3°. The addition requires about 30 minutes; stirring is continued for 15 minutes longer, and at the end of this period a positive test with starch-iodide paper should be obtained (Note 1). The clear brown solution is then diluted with 150 ml. of ice water.
In a 12-l. flask, equipped with a low-temperature thermometer and surrounded by an ice-salt bath, a solution of sulfurous acid is prepared by saturating 2.4 l. of water at 0–5° with sulfur dioxide from a cylinder. A brisk stream of the gas is continued (Note 2) while the cold diazonium salt solution is added in about 150-ml. portions over a 30-minute period and the temperature is maintained at 5–10°; the reaction mixture assumes a dark orange color (Note 3). The cooling bath is removed, but sulfur dioxide is passed into the mixture for an additional 30 minutes. After the mixture has been allowed to stand for 12 hours at room temperature, 3 l. of concentrated hydrochloric acid (sp. gr. 1.18) is added; the o-hydrazinobenzoic acid hydrochloride separates at once. The mixture is chilled to 0–5° and filtered through a precooled Büchner funnel; the product is washed with two 50-ml. portions of ice-cold dilute (1:1) hydrochloric acid. The yield is 50–51 g. (86–88%); the salt melts at 194–195° with decomposition (Note 4) and is suitable for the next step without further purification (Note 5).
B. Indazolone. In a 2-l. round-bottomed flask to which a reflux condenser is attached are placed 47.1 g. (0.25 mole) of o-hydrazinobenzoic acid hydrochloride, 1.25 l. of water, and 12.5 ml. of concentrated hydrochloric acid (sp. gr. 1.18). The mixture is refluxed for 30 minutes. The resulting pale yellow solution is transferred in two portions to a 23-cm. evaporating dish and concentrated on the steam bath to about one-fourth its original volume. The indazolone separates at an early stage of the evaporation but redissolves as the concentration of acid increases. Sodium carbonate is added to the warm solution in small portions until the acid is neutralized (Note 6), and the suspension is allowed to stand for 2 hours. The nearly colorless indazolone is removed by filtration, washed with two 25-ml. portions of cold water, and air-dried. The yield of product, m.p. 246–249°, is 30–33 g. (90–98%) (Note 7).
C. 3-Chloroindazole. In a 200-ml. flask connected by a glass joint to an air condenser protected by a drying tube are placed 26.8 g. (0.2 mole) of dry indazolone and 15.8 g. (16 ml., 0.2 mole) of dry pyridine (Note 8); 46.1 g. (27.6 ml., 0.3 mole) of phosphorus oxychloride is then added, with shaking, over a 10-minute period. Heat is evolved, and acid fumes are generated. The mixture is heated with occasional shaking in an oil bath, which is maintained at 128–130° for 1 hour and at 130–140° for 4 hours. The clear brown solution is then cooled to 70° and poured, with hand stirring, upon 500 g. of cracked ice. This mixture is allowed to stand for 24 hours. The pale buff solid is removed, washed on the filter, first with 100 ml. of 0.5 N hydrochloric acid and then with 40 ml. of cold water, and air-dried (Note 9). The 3-chloroindazole is crystallized from 3 l. of 20% ethanol. The yield is 21–22.5 g. (68–74%) of material melting at 148–148.5° (Note 10).
D. Indazole. In a 300-ml. flask are placed 15.3 g. (0.1 mole) of 3-chloroindazole, 18.6 g. (0.15 mole) of red phosphorus, and 100 ml. of constant-boiling hydriodic acid (sp. gr. 1.7) (Note 11). The mixture is refluxed for 24 hours (Note 12), cooled, and filtered through a sintered-glass funnel (Note 13) to remove the phosphorus; the flask and the solid are washed with two 20-ml. portions of water. The clear filtrate is transferred to a 300-ml. Claisen flask and concentrated to about 40 ml. by heating in a water bath at a reduced pressure. The residue is washed into a 250-ml. beaker with 70–80 ml. of hot water, and the clear solution is cooled in an ice bath and made strongly alkaline with concentrated ammonium hydroxide (about 80 ml. is required). The next day, the indazole is collected and dried; the white solid melts at 143–145° (Note 14).
The product is added to 75 ml. of benzene, and the suspension is boiled until the frothing has ceased, the benzene lost being replaced (Note 15); the resulting suspension is filtered to remove the insoluble material. The clear filtrate is heated to boiling, diluted with 25 ml. of petroleum ether (b.p. 70–90°), and allowed to cool slowly. The yield of white product, m.p. 145–146.5°, is 9.7–10.2 g. (82–86%). The over-all yield from anthranilic acid is 43–55%.
2. Notes
1. If the starch-iodide test is negative at this point a little solid sodium nitrite may be added.
2. This operation should be carried out in a hood or out-of-doors.
3. Small amounts of a red crystalline solid were obtained at this point by the checkers in several runs. This substance can be converted to o-hydrazinobenzoic acid by the addition of 5 ml. of concentrated hydrochloric acid to a suspension of 1 g. of the solid in 25 ml. of dilute (1:1) hydrochloric acid. The red solid changes to the white o-hydrazinobenzoic acid hydrochloride without apparent solution.
4. The melting point varies with the rate of heating. The values given were obtained with a bath preheated to 180°.
5. The free acid may be obtained by treatment of a solution of the hydrochloride with a concentrated aqueous solution of sodium acetate. The powdered hydrochloride (18.9 g., 0.1 mole) is dissolved in 567 ml. of water, and sodium acetate solution (8.2 g. [0.1 mole] of anhydrous sodium acetate in 30 ml. of water) is added. o-Hydrazinobenzoic acid separates at once; the mixture is chilled, and the light-tan acid is removed by filtration, washed with two 25-ml. portions of water, and air-dried. The yield is 13.1 g. (86%); m.p. 248–250°. If a purer acid is required, the crude material may be recrystallized from ethanol (50 ml. per g.); the pale tan product then melts at 250–251.5°.
6. About 20 g. of sodium carbonate is required.
7. The indazolone may be purified further by recrystallization from methanol (24 ml. per g.), with filtration of the hot solution through a layer of Norit. It separates as white needles, m.p. 250–252°; the recovery is about 50%. An additional 10% of material (m.p. 246–248°) may be obtained by dilution of the filtrate with 2 volumes of water.
The submitter reports that the described method of purification gives a better product than is obtained by solution in dilute sodium hydroxide and reprecipitation with acid.
8. The submitter reports that dimethylaniline can be used but that it is less desirable because a small amount of a green by-product is formed.
9. The crude chloroindazole, m.p. 143–145°, is difficult to dry. Small quantities may be crystallized satisfactorily from water (250 ml. per g.). The submitter reports that a good product can be obtained by steam distillation but that even with superheated steam the distillation is very slow.
10. In a run 2.5 times this size, the checkers dissolved the crude product in 190 ml. of ethanol and diluted the hot filtrate with 260 ml. of water; the chloroindazole was obtained in 80% yield.
11. It is essential to use acid of this concentration.
12. This reaction time ensures complete conversion of the chloroindazole.
13. As an alternative procedure, the mixture may be diluted with 70 ml. of water and filtered through S & S No. 596 filter paper.
14. The crude indazole is so difficult to dry that the weight at this stage is not significant.
15. This operation is carried out in an open flask in the hood and at a point remote from flames; the indazole is dried by the steam distillation of the water with the benzene.
3. Discussion
The preparations of o-hydrazinobenzoic acid hydrochloride and indazolone are essentially those given by Pfannstiel and Janecke.1 The procedure for the conversion of indazolone to indazole is a modification of that of Fischer and Seuffert.2 A procedure involving the decarboxylation of indazole-3-carboxylic acid is described by Schad.3
Indazole has been obtained in a variety of ways which are of no preparative value. The elimination of the amino group from aminoindazoles, first utilized by Witt,4 by the action of ethanol or sodium stannite on the diazonium compounds appears to be the only other useful procedure.
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m-NITROBENZAZIDE
[Benzoyl azide, m-nitro-]


Submitted by Jon Munch-Petersen1
Checked by William S. Johnson and W. David Wood.
1. Procedure
A. m-Nitrobenzoyl chloride. In a 1-l. round-bottomed flask are placed 200 g. (1.2 moles) of crude m-nitrobenzoic acid2 and 500 g. (300 ml., 4.2 moles) of thionyl choride (Note 1). The flask is fitted (ground-glass joint) with a reflux condenser carrying a calcium chloride drying tube leading to a gas-absorption trap3 and is heated on a steam bath for 3 hours. The condenser is then set for downward distillation, and as much of the excess thionyl chloride as possible is distilled at the temperature of the steam bath. The residue is transferred to a 250-ml. Claisen flask and distilled at reduced pressure (water pump), b.p. 153–154° /12 mm. (Note 2). The yield is 200–217 g. (90–98%), m.p. 33°.
B. m-Nitrobenzazide. In a 2-l. round-bottomed flask fitted with an efficient mechanical stirrer is placed a solution of 78 g. (1.2 moles) of commercial sodium azide in 500 ml. of water (Note 3). The flask is surrounded by a water bath kept at 20–25°. The stirrer is started, and over a period of about 1 hour a solution of 185.5 g. (1 mole) of m-nitrobenzoyl chloride in 300 ml. of acetone (previously dried over anhydrous potassium carbonate) is added from a dropping funnel. m-Nitrobenzazide separates at once as a white precipitate. Stirring is continued for 30 minutes after the addition is complete; then 500 ml. of water is added and the reaction mixture stirred for an additional 30 minutes. The azide is separated on a suction filter, washed with water, and dried in the air. The yield of crude product, m.p. 68°, is 189 g. (98%) (Note 4). It may be recrystallized from a mixture of equal parts of benzene and ligroin (b.p. 100–140°), when the temperature is kept below 50° (Note 5). The product thus obtained consists of almost colorless crystals, m.p. 68–69° (Note 6), the recovery being 80–90% (Note 7).
2. Notes
1. Eastman Kodak Company white label grade thionyl chloride is satisfactory.
2. Since the product crystallizes readily, water cooling should be applied only at the receiver, not at the side arm.
3. The reaction should preferably be carried out in a hood, as hydrazoic acid may be liberated in small amounts. This compound, which is volatile, is highly toxic, and its inhalation may cause temporary headache and giddiness.
4. This product is sufficiently pure for general reagent use. m-Nitrobenzazide is recommended4,5,6,7 as a reagent for the characterization and estimation of aliphatic and aromatic hydroxyl compounds. It reacts to form nicely crystalline m-nitrophenylcarbamic esters,5,6,8 in which the nitro group may be titrated with titanous chloride. With amines it forms substituted m-nitrophenylureas.9,10
5. At higher temperatures a Curtius rearrangement into the isocyanate may occur, nitrogen being liberated. An alternative procedure for recrystallization (preferred by the checkers) consists in dissolving the crude product in a small amount of benzene (if the solution is discolored it may be treated with decolorizing carbon) and adding an equal volume of ligroin. On seeding, the product crystallizes.
6. The melted compound decomposes with liberation of nitrogen.
7. Using the same procedure, p-nitrobenzazide, m.p. 71–72° (Note 6), may be prepared. The yield of crude product is 90%, and of recrystallized product 70%.
3. Discussion
m-Nitrobenzazide has been prepared by the action of nitrous acid on m-nitrobenzhydrazide, which is obtained by treating methyl m-nitrobenzoate with hydrazine hydrate.5,7 The procedure described here is mentioned by Naegeli and Tyabji11 and is similar to that given for benzazide.12
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TRIMETHYLSILYL AZIDE
[Silane, azidotrimethyl-]


Submitted by L. Birkofer1 and P. Wegner.
Checked by R. F. Merritt and W. D. Emmons.
1. Procedure
Caution! This reaction should be conducted behind a safety screen in a hood. If the system is not completely dry, the presence of toxic hydrazoic acid is probable.
A 1-l., three-necked flask fitted with a stirrer, reflux condenser equipped with a drying tube, and addition funnel provided with a pressure-equalizer arm is dried in a 100° oven and assembled while warm. The warm apparatus is immediately purged with dry nitrogen, introducing the nitrogen at the top of the addition funnel. The flask is charged with 81 g. (1.2 moles) of sodium azide (Note 1) and 500 ml. of freshly distilled diethylene glycol dimethyl ether (Note 2). A simple distillation apparatus is then dried in the oven and assembled while warm under a slow nitrogen purge. The distillation flask is charged with 112 g. of chlorotrimethylsilane (Note 3), and after a forerun of approximately 2 g. the remaining material is distilled (b.p. 57–58°) directly into the addition funnel of the reaction flask. During this distillation it is convenient to disconnect the nitrogen stream from the top of the addition funnel and introduce it into the distillation flask. After the distillation is complete, the distillation apparatus is disconnected and the nitrogen stream is again introduced at the top of the addition funnel. The chlorotrimethylsilane (108.6 g., 1.000 mole) (Note 4) is then added rapidly to the sodium azide slurry, and this mixture is stirred at 70° for 60 hours. During this period the nitrogen flow is terminated (Note 5).
After the heating period is complete, the nitrogen stream is again initiated, and the mixture is cooled to 30°. The addition funnel and reflux condenser are replaced with two gas-inlet tubes with stopcocks. One inlet tube is connected to the nitrogen source and the other to a standard vacuum trap, of at least 150 ml. capacity. A vacuum (15–20 mm.) is applied to the trap after the latter is cooled to −78°, and the product is then distilled at 30° (15 mm.) into the trap. Slight heating is necessary to maintain 30°, and rapid stirring should be continued throughout. Removal of volatile product is complete within 5 hours under these conditions. The entire system is then slowly pressurized to atmospheric pressure with nitrogen, and the product is redistilled through a 5-cm. Vigreux column. From 121 g. of crude flash distillate are obtained 4.0 g. of forerun and 98 g. (85%) of pure trimethylsilyl azide, b.p. 95–99°. During the distillation the pot temperature is maintained at 135–140° with a thermostated oil bath. The pot residue contains 19 g. of diethylene glycol dimethyl ether with traces of trimethylsilyl azide. The purity of the product cut as established by 1H NMR (CCl4) is 98%. A single peak at 13 cps. downfield from tetramethylsilane is observed, the only impurity being siloxane hydrolysis products. Chlorotrimethylsilane is conspicuous by its absence.
2. Notes
1. Sodium azide was obtained from Alpha Inorganics, Inc., Beverly, Massachusetts, and the freshly opened material was used without further purification or drying.
2. Diethylene glycol dimethyl ether from Aldrich Chemical Co. was distilled under a nitrogen atmosphere, and the fraction boiling at 161–162° was used.
3. The chlorotrimethylsilane was obtained from Pennisula Chem-research Corp., Gainesville, Florida.
4. It is undesirable to reweigh the chlorotrimethylsilane in the addition funnel because moisture contamination is possible. An excess of sodium azide is used in this preparation, and the exact amount of the silane used is not critical.
5. If the nitrogen flow is maintained during the heating period, the volatile materials will be swept out and the yield will be reduced.
3. Discussion
Trimethylsilyl azide has been prepared by the thermolysis of 1-trimethylsilyl-5-trimethylsilylaminotetrazole, by reaction of hydrazoic acid with hexamethyl-disilazane, and by reaction of chlorotrimethylsilane with sodium azide.2 With a suitable solvent and anhydrous conditions the last procedure is the method of choice and has been extended to other trialkyl and triarylsilyl azides.3
Unlike hydrazoic acid, trimethylsilyl azide is thermally quite stable. Even at 200° it decomposes slowly and without explosive violence. Accordingly, it is a very convenient and safe substitute for hydrazoic acid in many reactions. A notable example is the cycloaddition of hydrazoic acid to acetylenes, a general route to substituted triazoles.4 The reaction of trimethylsilyl azide with acetylenes is also a general reaction, from which 2-trimethylsilyl-1,2,3-triazoles may be obtained in good yield.5 These adducts are hydrolyzed under mild conditions to the parent alkyl 1,2,3-triazoles.5

Another interesting application of trimethylsilyl azide is as a convenient preparation of trialkyl- or triarylphosphinimines, first prepared by Appel and Hauss using chloramine.6

This synthesis is quite simple and its success lies in the facile cleavage of the Si-N bond.7,8 Trimethylsilyl azide also reacts with aldehydes, giving the stable adducts, 1-trimethylsiloxyalkyl azides, which on thermolysis yield N-trimethylsilyl amides.9

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ETHYL (R)-2-AZIDOPROPIONATE
[Propanoic acid, 2-azido-, ethyl ester, (R)-]


Submitted by Andrew S. Thompson, Frederick W. Hartner, Jr., and Edward J. J. Grabowski1.
Checked by Christopher L. Lynch and Stephen F. Martin.
1. Procedure
Ethyl (R)-2-azidopropionate. An oven-dried, 500-mL, three-necked flask is equipped with an overhead stirrer, nitrogen inlet, and an immersion thermometer (Note 1). The flask is charged with ethyl S-(−;)-lactate (19.2 mL, 0.169 mol) (Note 2), tetrahydrofuran (175 mL) (Note 3), and diphenylphosphoryl azide (40 mL, 0.185 mol) (Note 4). The mixture is cooled to 2°C in an ice-water bath. To the mixture is added 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) (24 mL, 0.157 mol) (Note 5) dropwise via syringe. (Caution: The DBU addition causes an exotherm. The reaction temperature is maintained below 5°C by carefully controlling the rate of addition. For this reaction the addition required 35 min). A thick white precipitate forms during the DBU charge. The reaction is stirred at 1°C for 1 hr, and then it is warmed to room temperature and stirred under nitrogen for 24 hr (Note 6). The resulting homogeneous reaction is diluted with methyl tert-butyl ether (MTBE, 170 mL), and water (100 mL) is added. After the water layer is removed, the organic phase is washed with water (100 mL) and 0.5 M citric acid monohydrate (100 mL). The organic layer is dried (Na2SO4) and concentrated under reduced pressure to ca. 40-50 g of a pale yellow oil (Note 7). The product is purified by simple distillation to afford 12.84 g (57%) of a clear, colorless oil, bp 83−88°C/50mm (Note 8), (Note 9) and (Note 10).
2. Notes
1. A Teflon-coated thermocouple of the J-type attached to an Omega model 650 digital thermometer can be substituted for the immersion thermometer.
2. Ethyl lactate was purchased from Aldrich Chemical Company, Inc., and used without further purification. The water content was 0.8 mg/mL by Karl Fisher titration (Metrohm model 684 KF coulometer).
3. Tetrahydrofuran was purchased from Fisher Scientific Company and dried over 4 Å molecular sieves for 18 hr prior to use. The water content was less than 0.05 mg/mL by Karl Fisher titration.
4. Diphenylphosphoryl azide was 98% as purchased from Aldrich Chemical Company, Inc., and the water content was less than 0.01 mg/mL by Karl Fisher titration.
5. DBU was 98% as purchased from Aldrich Chemical Company, Inc., and the water content was 0.5 mg/mL by Karl Fisher titration. The amount of DBU was calculated to be 0.93 equiv of the ethyl lactate charge by assuming a purity of 98% for DBU and 100% purity for ethyl lactate. Amounts of base over 1 equiv resulted in product epimerization.
6. The reaction typically requires 16-24 hr. The progress of the reaction was monitored by capillary GC after diluting a 0.1-mL sample with 1 mL of methyl tert-butyl ether. GC conditions: Hewlett-Packard 5890 series II GC using an Alltech Econo-cap column (30 M × 0.32 mm × 0.25 μM, catalog # 19646). [The submitters used an HP-5 column (25 M × 0.32 mm × 0.52 mm, HP part # 19091J-112)]. Start oven at 50°C, then increase to 250°C at 10°C per min. The reaction was considered complete after 90% conversion; starting material Rt 4.3 min, product Rt 7.0 min.
7. The vacuum was deliberately bled to maintain 120-130 mm to minimize product losses due to volatility.
8. The yield was based on the DBU charge. The product was contaminated with 4-8% of starting material that codistilled with the product. The following characterization data was obtained: ethyl (R)-(+)-2-azidopropionate: [α]D25 +14.8° (hexane, c 1.00); 1H NMR (250 MHz, CDCl3) δ: 1.28 (t, 3 H, J = 7.2), 1.43 (d, 3 H, J = 7.1), 3.89 (q, 1 H, J = 7.1), 4.21 (q, 2 H, J = 7.2); 13C NMR (75 MHz, CDCl3) δ: 14.1, 16.7, 57.3, 61.8, 170.9; IR (thin film) cm−1: 2120, 1743.
9. Optical purity can be quantitatively assayed by HPLC after reducing a sample to the amine with triphenylphosphine. A 50-mg sample was diluted with 10:1 THF:water (1 mL in a screw cap vial) and treated with triphenylphosphine (190 mg). Gas evolution begins within 5 min; once this subsides the reaction is sealed and placed in an oil bath at 50°C for 30 min. The mixture is diluted with HClO4 (pH 1.0, 1 mL) and washed with dichloromethane (2 × 1 mL). The acidic water phase contains the salt of the amine. A 200-μL sample was diluted to 1 mL and assayed by HPLC using a Crownpak CR(+) column (Diacel Chemical Industries): HPLC conditions; aqueous pH 1.0 HClO4, flow 0.5 mL/min, UV detection at 210 nm. The product had an enantiomeric excess of 96%, major enantiomer, Rt 3.4 min, and minor enantiomer, Rt 5.0 min.
10. The product from the distillation was analyzed by drop weight testing and differential scanning calorimetry (DSC). The drop weight test indicated that the product was not shock sensitive. By DSC, there was a 400 cal/g release of energy which initiated at 135°C. The pot residue showed a slow release of energy which was estimated to be ca. 100 cal/g and initiated at 150°C.
Waste Disposal Information
All toxic materials were disposed of in accordance with "Prudent Practices in the Laboratory"; National Academy Press; Washington, DC, 1995.
3. Discussion
Asymmetric introduction of azide to the α-position of a carbonyl has been achieved by several methods. These include amine to azide conversion by diazo transfer,2 chiral enolate azidation,3 4 and displacement of optically active trifluoromethanesulfonates,5 p-nitrobenzenesulfonates,6 or halides.7 8 Alkyl 2-azidopropionates have been prepared in optically active form by diazo transfer,2 p-nitrobenzenesulfonate displacement,6 and the Mitsunobu displacement using zinc azide.9 The method presented here is the simplest of the displacement methods since alcohol activation and displacement steps occur in the same operation. In cases where the α-hydroxy esters are available, this would be the simplest method to introduce azide.
In addition to α-hydroxy carbonyl compounds, the method can be generally applied for alcohol to azide displacements. This method has been successfully demonstrated on fourteen optically active alcohols.10 Mechanistically, this reaction proceeds in two stages. The first is alcohol activation via formation of the corresponding phosphate, and the second stage is the azide displacement step. The method is most useful for azide displacements of alcohols which tend to racemize using highly reactive groups for activation (e.g., sulfonate formation or Mitsunobu conditions11). When diphenylphosphoryl azide and DBU are used, the alcohol is only mildly activated for displacement as a phosphate. Use of the phosphate thus provides access to azide displacements of alcohols that are too sensitive using standard activation techniques. However, since the phosphate is only mildly activating, the alcohol undergoing displacement should be benzylic, allylic, or as in the present case, α to a carbonyl.
Certain classes of compounds are too reactive for the present method. Ethyl mandelate produced a racemic, protected phenyl glycine derivative. Benzylic alcohols with two methoxy groups (directly conjugating in the 2 and 4 positions) gave azide of 50% e.e.
Other classes of alcohols are unreactive. Ethyl 3-hydroxybutyrate (a β-hydroxy ester) went to the phosphate stage, but would not undergo azide displacement. In this example about 30% of the crotonate was formed because of β-elimination.
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Nitramine
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[*] posted on 4-10-2004 at 12:25


Quote:
Nitramine,

Did you ever find an archive copy of the webpage detailing extraction of NaN3 from airbag pellets?

The webpage doesn't exist anymore. But I managed to find the homepage in my archives. Finally my tendency to save anything that seem exciting have paid off ;)

I have just uploaded the page about extracting sodium azide from airbags here:

http://www.geocities.com/lenodk/NaN3.htm
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sylla
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[*] posted on 4-10-2004 at 12:30


nice spam tokat but it would have been a better idea to write it in a txt and send it as an attachment...

Don't u think ?
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DNA
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[*] posted on 26-11-2004 at 16:51
3 types...


What about the 3 different types of lead azide?
Could you tell a bit more about that?
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JohnWW
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[*] posted on 27-11-2004 at 00:53


I am sure there can be only ONE type of Pb(N3)2, which is that used in detonators. Perhaps you were thinking of other azide compounds, e.g. Pb(N3)4 (very unstable if it could be made!), or PbO(N3)2, or PbClN3.
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neutrino
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[*] posted on 27-11-2004 at 09:01


I thik he might be referring to something along these lines: Pb(N3)2, PbOHN3 (basic lead azide), and maybe a double salt or something with a different crystal structure?

edit: I'm not sure if there is a basic lead azide, but I know there's a basic lead picrate.

[Edited on 27-11-2004 by neutrino]
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The_Davster
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[*] posted on 27-11-2004 at 10:13


There are four polymorphic forms of lead azide. Despite the info being uploaded by me onto the FTP which I mentioned in a previous post, I will post it here because I have gotten a surprising number of requests about this information.

La1.JPG - 116kB




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