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Author: Subject: Hydrazine
Praxichys
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[*] posted on 7-10-2015 at 09:33
Progress report 1:


Improvements to GB1153483, in lieu of GB392845 on the manufacture of Hydrazine Sulfate: A Chlorourea-Ketazine Process not involving Cl2.

I decided to give GB1153483 a try, just to see whether their 75% claimed yield held any vestiges of truth.

12.6g (0.2 mol) urea was dissolved in 18.9g water. 1.6g of 50% NaOH (0.01 mol) was stirred in and the mixture was placed in the freezer.

When the mixture had dropped to -10C (it froze), 125g of 12.5% commercial NaClO (0.2 mol) at 0C was added in roughly 10ml portions evenly over an hour. Vigorous stirring and re-chilling followed each addition. The reaction is not very exothermic but any rise in temperature above 5C results in bubbling, undoubtedly signalling the decomposition of the chlorourea intermediate. The bubbling was most pronounced on the first and last additon, suggesting that thermal control is difficult with a low reaction mass, and decomposition of the intermediate is fast at high concentrations. The mixture does not foam.

After the last addition of NaClO, 30.4g of 50% NaOH (0.38 mol) with 0.1g Knox gelatin was added with rapid stirring, causing the light green mixture to begin foaming. The reaction was heated as quickly as possible, reaching 60C in about 10 minutes and causing foam to add another 1/3 to the volume of the reaction mix (total about 300ml incl. foam at peak). The color of the liquid gradually became orange/amber. After approximately a minute of exotherm the foam rapidly subsided, leaving a straw colored, foam-free, hot liquid characteristic of a hydrazine prep.

This was allowed to cool with stirring with a watch glass over the top of the erlenmeyer until it reached approximately 30C. 28.8g (0.4 mol) methyl ethyl ketone was added and the mixture was allowed to stir for an hour for the azine to form, cooling to room temperature in the process.

The azine layer was extracted and immediately run into 19.6g H2SO4 in 20.9g H2O at about 30C. Hydrazine sulfate precipitated immediately. This was stirred for 10 minutes, then heated with stirring for about 30 minutes to drive off the MEK. After a loss of 1/3 of its volume, the mixture was placed in the freezer and chilled to 0C. It was then vacuum filtered and washed twice with 30ml portions of ice water.

The dried filtrate weighed 6.26g, or 21% of theoretical yield, and consisted of dense, pearlescent crystals consistent with hydrazine sulfate.

Some notes:

-All percentages listed are w/w.
-Satuating the reaction mix with NaCl after extracting the azine (30g was added and did not fully dissolve) yielded no more extractable azine, after 24h.
-Theoretical yield would net a volumetric efficiency of 96g hydrazine sulfate per liter of flask volume, including room for foam. The 75% yield in the patent would net 72g/L, 50% would net 48g/L and the current yield was 20.9g/L. The "Mr Anonymous" method requires about 6 liters of volume for at max 236g of product, an efficiency of 39g/L. Achieving the same yield as Mr. Anonymous (ca. 60%) using this method would result in a volumetric efficiency 1.48 times greater. The yield stated in the patent would achieve 1.85x over the M.A. method - a marked improvement in both volumetric efficiency and safety, albeit with judicious temperature control.
- I prefer the ketazine extraction method over direct precipitation. I feel like M.A.'s method has a high level of Na2SO4 contamination.

Things to try on the next run:

- Spread out the addition of the NaClO. Ideally the mix should never rise over -5C. Use a bowl of 30% CaCl2/H2O chilled to -20C as a thermal buffer to surround the flask and absorb the heat. Regrettably, my lab freezer is too small to set up an addition funnel/stirrer inside, so additions are limited to small-volume aliquots.
- Make a schedule of additions starting and ending small, max 10ml.
Schedule, ml/5 min intervals, total 1h10m: 5, 5, 5, 10, 10, 10, 10, 10, 10, 10, 10, 5, 5, 5. A volumetric pipette stored in the freezer will help with this.
- Use fresh NaOCl. The commercial 12.5% has been in my freezer for a year. I went out and purchased 4 gallons of 10% today. The slightly lesser concentration of hypochlorite will also help with thermal management.
- Stir overnight with MEK to fully form the azine. Not sure about rate of reaction on this.
- Use 10% more MEK to make up for unwanted products formed with unreacted urea/hypochlorite in the basic environment.
- Use a separate gelatin solution rather than the NaOH solution. Gelatin clumping was a problem in the NaOH and its effectiveness as a chelator was probably compromised. I feel that this is a big factor, per US1959503(A)/GB392845. It may also significantly increase the foam volume, reducing volumetric efficiency to a point where this method will be inferior to others.

Failing this, I will try a third time with recrystallized urea. It's a pain in the ass to do, so that will be a last resort. I will also double the scale, and split the reaction mass into two equal portions prior to the hydrazine extraction. One will be azine-extracted and the other will be directly neutralized/precipitated with HCl/H2SO4, to check the efficiency of the azine process.

A possibly interesting experiment:

- What happens if all NaOH is added to urea to form essentially cold conc. ammonia first, then add hypochlorite slowly at -10C? What happens when this is done with MEK present in the ammonia?

[Edited on 8-10-2015 by Praxichys]




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[*] posted on 10-5-2016 at 09:38


Quote: Originally posted by vmelkon  
COPPER IS EVIL! Cu2+

Just for your info:

I redid this experiment --- the Nurdrage method : mix 2-butanone and ammonia solution. Then drip NaClO slowly.
The glassware in which I had my NaClO was contaminated by a copper compound.

My yield was 0%.
Definitely, the presents of Cu2+ messes it up.
------------------------
From
http://www.lookchem.com/Chempedia/Chemical-Technology/Inorga...

2 NH2Cl + N2H4 → N2 + 2 NH4Cl
This reaction is particularly catalyzed by copper. A large excess of ammonia and the addition of complexing agents such as ethylenediaminetetra-acetic acid (EDTA) are used as countermeasures.



lookchem.com is a business network from the Chinese government to earn more money from Western countries with their own asian companies. For professional business profiles only, NOT a website for chemists. Not a good source of information. ;)

The last post: ammonia dissolve better in cold water but what is the reaction mechanism between urea and sodium hydroxide, without hypochlorite ?...
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[*] posted on 17-5-2016 at 07:21


Praxichys - thanks, that is an interesting experiment.

We also tried a variant method from the literature (don't have the exact reference though) which involved bubbling Cl2 gas through a urea solution containing some dissolved gelatine in order to produce chlorourea. The chlorine was absorbed pretty well and a yellow coloured solution resulted. We tried to use about 1.1 x the stoichiometric amount of Cl2 gas needed.

The solution was fairly concentrated - about 30g of urea in 60ml of water, plus about 0.3g gelatine.

Then this was added to a chilled solution of sodium hydroxide (24g in 50ml deionised water). There was a STRONGLY exothermic reaction at this point (easily reached 90C without much difficulty) and some foaming.

Once this died down, HCl was then added until gas evolution stopped, at which point there was a crystalline white precipitate (we assume NaCl) which we filtered off.

The filtrate was then acidified with 50% sulfuric acid and chilled. We got some crystalline hydrazine sulfate, but not much, probably only a few grams.




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[*] posted on 17-5-2016 at 13:37


Quote: Originally posted by Praxichys  

I feel like M.A.'s method has a high level of Na2SO4 contamination.


Uh huh ....I see, you "feel" .....say what ? ! Hmmmph

Try the improved method with the bulk neutralization using HCl followed by the H2SO4 ....that was designed to soothe feelings :D

The interesting thing for followup would be the use of a manganese salt to increase yields as reported by Russians.
See these posts linked

http://www.sciencemadness.org/talk/viewthread.php?tid=1128&a...

http://www.sciencemadness.org/talk/viewthread.php?tid=1128&a...
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[*] posted on 27-5-2016 at 05:32


Quote: Originally posted by Rosco Bodine  
Quote: Originally posted by Praxichys  

I feel like M.A.'s method has a high level of Na2SO4 contamination.


Uh huh ....I see, you "feel" .....say what ? ! Hmmmph

Try the improved method with the bulk neutralization using HCl followed by the H2SO4 ....that was designed to soothe feelings :D

I "feel" things when I can't be bothered to generate data. :D

I only have concerns about contamination because the solubility curves of the two suggest that they probably coprecipitate to some degree. Precipitating hydrazine sulfate from a sodium sulfate or even sodium chloride solution is going to warrant recrystallization at the least. I'd be curious to assay the hydrazine content of that, just to see. It would be virtually impossible to judge the purity of such a mixture by eye since the crystals can be made similarly dense and granular using the precipitation methods given.

The azine extraction method removes pretty much all ionic contaminants by nature. Granted, it does use more glass and has some toxic intermediates, but I'd rather do a L/L extraction over a recrystallization anyway. I do not doubt that your method is optimized for high yield - I just prefer to work it up differently out of concern for contamination.




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[*] posted on 27-5-2016 at 13:25


Also prefered the MEK-azine extraction, really brings peace of mind to know there are no contaminants in there! ;) Besides... during acid neutralization of the entire reaction mixture, the CO2 effervescence is really strong and creates an aerosol which will likely also contain some hydrazine. So this is not something that should be performed without safety measures IMO.
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[*] posted on 27-5-2016 at 20:10


Trace sodium chloride as a spectator ion is a pretty low concern in most reactions where the hydrazine sulfate would be later used. And there is a chance some of the hydrazine is sequestered as carbonate disrupted by acidification, which could benefit yield.
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[*] posted on 10-10-2016 at 08:02


Quote: Originally posted by Al Koholic  
The fumes smelled relatively ammoniacal but also had a distinct sweetish component. /rquote]
In my experience, N2H4 smelled of Ammonia mixed with woodsmoke.
Like a sweet mesquite BBQ undertone. Too bad it's so toxic. :(
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[*] posted on 20-4-2017 at 10:13


Quote: Originally posted by Al Koholic  
As a matter of fact, I ran into exactly the same problems. The bubbling upon supposed neutralization of the hopefully hydrazine solution is most perplexing. I did not notice a green gas but more of a thick cloudy white vapor of some kind during my neutralization. I also used a somewhat large excess of NH3...

Lets think about this...I did not use gelatin or EDTA and still I get the bubbling upon warming of the solution and neutralization. You used both gelatin and EDTA and notice similar bubbling although noting the presence of chlorine by smell which I did not notice. Perhaps some side reactions are occuring in both of our cases with different outcomes? Seems unlikely...

Did you notice a really bad smell when you added the H2SO4 to the solution for neutralization? It was bad in the sense that rotting food is bad...nauseating...not like the pungent sting of Cl2.

[Edited on 3-12-2003 by Al Koholic]
The bleach could have chlorate prehaps. So the gas could be chlorine dioxide


[Edited on 20-4-2017 by The jersey rebel]
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[*] posted on 4-5-2018 at 23:54
Dihydrazine Sulfate


How to prepare Dihydrazine Sulfate(H10N4O4S) ?:)
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[*] posted on 10-10-2018 at 06:27
Protocol: Synthesis of hydrazine sulfate from bleach and urea


I recently made hydrazine sulfate from household bleach and urea according to NileRed's method (posted on Youtube).

TL;DR: The bleach had a much lower concentration than expected but in the end it worked out.

Experimental:
About 500 ml of < 5% household bleach (assumed to be about 5% concentration) were put into a 1 l beaker and stirred in an ice bath. 32 g of sodium hydroxide pellets were added in small portions, not allowing the temperature to rise beyond 14 °C. The solution was then left to cool to 7.5 °C. A solution of 22 g of urea (Honeywell, p. a.) in about 25 ml of water was prepared and heated in the microwave for about 30 seconds to dissolve everything. A solution of 0.75 g of gelatin powder in about 10 ml of water was made and warmed in the microwave for about 15 seconds. After cooling these two solutions were combined.
In the fume hood: The cooled alkaline sodium hypochlorite solution was strongly stirred on a hotplate. The gelatin/urea solution was added all at once and the beaker covered with plastic foil. After a short while strong bubbling occurred which gave the solution a turbid appearance. Foaming was not a problem. The bubbling gradually subsided after about one hour of stirring, so the hotplate was turned on and the solution (which was slightly yellow) was heated up to 85 °C. After a few minutes at this temperature the solution gradually lost its yellow hue. When no change in color could be observed any more the solution was taken off the hotplate and left to cool to room temperature. It was put into an ice bath and cooled to about 7 °C. About 120 ml of cold 50% sulfuric acid (-15 °C) was added carefully with stirring and the solution gradually warmed up to about 25 °C. No precipitate formed. The solution was again put into an ice bath. At about 10 °C white crystals began to form. More sulfuric acid was added but there was no additional precipitation. The solution was kept in a fridge for about an hour but no more crystals formed. The precipitate was vacuum filtered off. The yield when wet was 9.60 g. The mass was put into a vacuum desiccator and dried over calcium chloride for about two days. The final yield of white crystals was 9.05 g corresponding to about 21.4% of the theoretical.

Titration of the bleach:
To help explain the low yield the concentration of the bleach was determined as follows:
The sodium hypochlorite solution was titrated using sodium thiosulfate after mixing with a potassium iodide/starch indicator, according to the procedure specified in [2].
The volume of the samples was 5 ml. 40 ml of indicator solution were added to each sample.
The necessary volume of 0.1 mol/l Na2S2O3*5H2O solution was 31.5 ml in each run.
The concentration of active chlorine was determined to be (see [2]):
C(Cl2) = 31.5 ml * 0.1 mol/l * 35.4257 g/mol / 5 ml = 22.32 g/l = 2.23% [wt% available Cl2]
According to [3] this corresponds to a weight content of NaOCL of 1.05 * 2.23 [wt% NaOCl] = 2.34%.
The specific gravity of the bleach was found to be 1.04 g/ml which is off the chart in [3] but the value seems to work out.

It is therefore obvious that the sodium hypochlorite concentration was much lower than expected.
NileRed's yield in [1] was 20.25 g (48%) when using a bleach concentration of 4.9%. This corresponds to a gram yield per bleach concentration percent of 20.25 g / 4.9% = 4.13 g/%.
The value in this experiment was 9.05 g / 2.34% = 3.86 g/% which is a bit lower but quite close (6.5% difference).

Testing the result:
A small amount of the product was heated in a test tube. The mass began to foam and smoke emerged. In the upper portion of the test tube white and yellow precipitates began to form and there was a smell of sulfur dioxide. A little transparent, colorless residue remained that was soluble in water and gave no color with phenolphthalein.
As a comparison a sample of anhydrous sodium hydrogen sulfate was subjected to the same test. There was little white precipitate but no yellow could be seen. The salt melted in the bottom of the test tube and left a white residue that was soluble in water and gave no color with phenolphthalein.
A tiny amount of the hydrazine sulfate was burned in a bunsen flame which showed the typical color of sodium. The sample evaporated quickly without leaving any residue. It was concluded that there was at least some small amount of sodium contamination.
The Tollens test was done by adding about 2 ml of a weak ammonia solution to about 1 ml of silver nitrate solution, until the white precipitate of silver hydroxide had dissolved. To this was added a small spatula of the hydrazine sulfate. Immediately a silver mirror began to form in the test tube even in the cold. There was slight evolution of gas. It was concluded that the substance was indeed highly reducing and likely to be hydrazine sulfate of a reasonable purity.

To determine the purity of the hydrazine sulfate the following iodometric titration was performed using the solutions made for titration of the bleach:
5 ml of bleach were put into an Erlenmeyer flask and about 30 ml of the potassium iodide/starch solution were added. The solution took on a dark color. Some more solid potassium iodide was added to ensure that all iodine was fully liberated (KI/starch solution had run out). With strong stirring sodium hydrogen carbonate was added until the foaming stopped, plus an additional spatula for a slight excess of NaHCO3[4]. The approximate amount of hydrazine sulfate necessary for reduction of the formed iodine was calculated as follows:
Titration with sodium thiosulfate:
2 S2O3(2-) + I2 => S4O6(2-) + 2I-
Therefore two moles of sodium thiosulfate reduce one iodine molecule.
The amount of I2 in the solution can be reduced by 31.5 ml * 0.1 mol/l Na2S2O3*5H2O = 31.5 * 0.1/1000 mol/ml = 0.00315 mol. Therefore, 0.001575 mol of I2 were released by the bleach.

Hydrazine reduces iodine to iodide according to the following equation:
N2H5+ + 2 I2 => N2 + 4 HI
One mole of hydrazinium ion is required to reduce two moles of iodine. Therefore, 0.0007875 mol of hydrazine sulfate (130.12 g/mol) are required which is about 0.102 g. To account for possible impurities the amount was chosen to be 0.20 g.
0.20 g of hydrazine sulfate were dissolved in 50 ml of distilled water. The iodine solution was titrated. Though the endpoint was kind of hard to determine because the solution remained slightly pink titration was stopped when 22.2 ml had been added. After this point no color change could be noticed any more.
This result was a bit surprising because this amount was less than the theoretical minimum amount (about 25 ml). The solution might have contained less than the theoretical amount of iodine, possible due to the reaction with the alkaline solution. Perhaps the excess of sodium hydrogen carbonate had been too great, and pH had not been checked (according to [4] the pH should be 7.4 for optimum results). It is also possible that the sodium thiosulfate titration (which is said to be unreliable, see [4]) was not very accurate.
In any case the hydrazine sulfate was assumed to be pure enough to further work.
Some of the hydrazine sulfate was further used in the synthesis of 2,4-dinitrophenylhydrazine with satisfactory results.

Conclusions:
- It is better to know the concentration of your starting solutions beforehand.
- Even though urea was present in large excess this didn't seem to influence the yield very much.
- The excess of sulfuric acid might have been helping with purifying the hydrazine sulfate by converting the sodium sulfate into sodium hydrogen sulfate which has more than six times greater solubility in water. Also, there was about twice the volume of water in the solution. Together, this might have reduced the sodium sulfate impurities even though the solution had been cooled in the fridge (contrary to original recipe recommendations).

Next time:
- Use twice the amount of this bleach or half of the other reagents.
- Use EDTA instead of gelatin to avoid foaming.
- Use battery acid instead of making 50% sulfuric acid from concentrated acid.

References:
[1] NileRed (Youtube): Making Hydrazine Sulfate from Urea and Bleach
[2] Titration Of Active Chlorine, Antenna Foundation; https://www.antenna.ch/wp-content/uploads/2017/03/Titration-...
[3] OxyChem Sodium Hypochlorite Handbook; https://www.oxy.com/OurBusinesses/Chemicals/Products/Documen...
[4] K. S. Panwar, N. K. Mathur, S. P. Rao, Hydrazine As A Titrimetric Reagent in Iodometry Part 1, Jodhpur, 1960 (doi:10.1016/0003-2670(61)80114-1)

[Edited on 10-10-2018 by RadicallyStabilized]




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