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entropy51
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When I smell vinegar, I think "acetic acid". Ac2O has a different smell, to me at least. This was discussed, possibly upthread.
All of my organic texts and some of the literature I looked at say that hydrolysis of an ester yields the carboxylic acid. Normally you don't make an
anhydride in an aqueous environment, since anhydrides react with water to yield the acid.
Hydrolysis of esters has been extensively studied and something as odd as you speculate had happened it might have been reported. I can't find it.
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not_important
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Quote: Originally posted by pHzero  | I just heated some dry ASA (acetylsalicylic acid, aka aspirin) with a tiny bit of water and it smelt strongly of vinegar. I'm guessing that smell came
from acetic anhydride since i only added a tiny bit of water.
This formula seemss to suggest so (note only 1 mole of water for every 2 moles of aspirin):
2C6H4COOHOAc (aspirin) + H2O --> 2C6H5COOH (salicylic acid) + Ac2O
... |
Nope. ASA is the acetic acid ester of 2-hydroxy-benzoic acid (salicylic acid). You can not easily remove the HO- from the benzine ring, as you show
in your proposed reaction - getting C6H5COOH instead of the actual C6H4(OH)COOH; hydrolysis of the ester linkage is what you will obseve.
C6H4COOHOAc + H2O --> C6H4(OH)COOH + AcOH
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pHzero
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| Quote: Originally posted by not_important | | Quote: Originally posted by pHzero | I just heated some dry ASA (acetylsalicylic acid, aka aspirin) with a tiny bit of water and it smelt strongly of vinegar. I'm guessing that smell came
from acetic anhydride since i only added a tiny bit of water.
This formula seemss to suggest so (note only 1 mole of water for every 2 moles of aspirin):
2C6H4COOHOAc (aspirin) + H2O --> 2C6H5COOH (salicylic acid) + Ac2O
... |
Nope. ASA is the acetic acid ester of 2-hydroxy-benzoic acid (salicylic acid). You can not easily remove the HO- from the benzine ring, as you show
in your proposed reaction - getting C6H5COOH instead of the actual C6H4(OH)COOH; hydrolysis of the ester linkage is what you will obseve.
C6H4COOHOAc + H2O --> C6H4(OH)COOH + AcOH
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Hmm, do you think that'd even happen if you used an excess of ASA?
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not_important
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Yes, it happens all the time within a bottle of ASA; the acetic acid smell in an old bottle is a result of hydrolysis by moisture in the air -
certainly a case of excess ASA.
A phenolic OH group is difficult to remove, particularly for rings with only a few bland substitutes. The old school way to do so was distillation
with zinc dust, giving low yields of the vase aromatic hydrocarbon. A little warm water isn't going to touch the OH on the ring.
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Lambda-Eyde
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pHzero: How would a hydrolysis reaction proceed without water? If you're using an excess of ASA, then the water will be the limiting reactant. The
reaction will just stop when the water is consumed, and you will have some acetic acid along with the excess ASA.
[Edited on 16-6-2009 by Lambda-Eyde]
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4-Aminophenol
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Hi,
a very easy way to synthesise Acetic anhydrid ist out of acetyl chloride. The problem that its hard to buy acetyl chloride. But there is an easy way
to make acetyl chloride out of benzoyl chloride. First you have to chlorinate benzaldehyd (oil of bitter almonds). The benzaldehyde reacts with the
Chlorine to benzoylchloride. For the next step you need anhydrous acetic acid and zinc chloride as catalyst. Heat up the benzoylchlorid with the zinc
chloride. Now you add the acetic acid slowly with a dropping funnel. When all the acetic acid is added you have to distill it with a column. In the
receiver you get nearly pure acetyl chloride.
greeting
[Edited on 17-6-2009 by 4-Aminophenol]
[Edited on 17-6-2009 by 4-Aminophenol]
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Magpie
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Greetings 4-Aminophenol!
Thank you for a most interesting route to acetyl chloride. Can you provide references to any of the procedures? I'm especially interested in the
conversion of benzaldehyde to benzoyl chloride.
Is any of this described already on versuchschemie.de, or elsewhere?
(My apologies to Sauron if he has already suggested such a route.)
The single most important condition for a successful synthesis is good mixing - Nicodem
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entropy51
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Magpie, the chlorination of benzaldehyde to yield benzoyl chloride is in one of the BzCl threads. The thread is
http://www.sciencemadness.org/talk/viewthread.php?tid=9121#p...
The reference is British Patent 310909, posted by garage chemist:
http://v3.espacenet.com/publicationDetails/originalDocument?...
Catalysis by UV, peroxides, or sulfur with preps is give in US 3,894,923
http://www.google.com/patents/about?id=Z4EyAAAAEBAJ&dq=3...
There may also be a prep in Systematic Organic Chemistry in the forum library.
The use of BzCl to prepare AcCl from AcOH is given in this article by H.C. Brown, posted by Solo in the propionyl chloride thread, but it doesn't use
zinc chloride:
http://www.sciencemadness.org/talk/files.php?pid=87977&a...
[Edited on 17-6-2009 by entropy51]
[Edited on 17-6-2009 by entropy51]
[Edited on 17-6-2009 by entropy51]
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Magpie
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Thank you entropy51.
My apologies also to garage chemist.
Looks like I have some interesting lab work ahead of me. 
The single most important condition for a successful synthesis is good mixing - Nicodem
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benzylchloride1
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Magpie, Organic Syntheses Collective volume 1 gives a procedure for the preparation of o-chlorobenzoyl chloride from o-chlorobenzaldehyde. This
procedure can be adapted to benzaldehyde. The chlorination takes a very long time for 1 mole of the benzaldehyde, 15 hours.
Amateur NMR spectroscopist
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entropy51
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But US patent 3,894,923 that I posted above converted 1 mole of benzaldehyde in 1.5 hours with a sulfur catalyst.
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Nicodem
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pHzero, the hydrolysis of aspirin can not give acetic anhydride, but its pyrolysis might give acetic anhydride and acetic acid as the main volatile
products. The only mention I could find of aspirin pyrolysis in Aspirin and related drugs by K. D. Rainsford is a single paragraph on page 53
which discusses only solid products of the pyrolysis and does not mention any volatiles, but gives this reference:
J. C. Reepmeyer. Thermal decomposition of aspirin: formation of linear oligomeric salicylate esters. Journal of Pharmaceutical Sciences, 72
(1983) 322-323.
I suggest you to check this paper as it might have some information about acetic anhydride formation. Making acetic anhydride from aspirin would
surely be an incredibly retarded method, but as an experiment it is actually interesting.
Benzaldehyde oxidation to benzoyl chloride can be done with trichloroisocyanuric acid as well (FR2633616). No need to use Cl2. This route to acetic anhydride was actually already discussed on the page 20 of this thread.
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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hissingnoise
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Since may 'O2 every possible route to Ac2O has been discussed in this thread and all are equally difficult. . .
When all social drugs are legalised the nightmare will end!
Until then, fuck politics *and* politicians!
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birdman
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Acetic Anhydride preparation
Hello,
I haven't read all the dialogue in this thread, so perhaps somebody has already offerred this, but the acyl chloride of acetic acid and sodium salt
of the same acid should give acetic anhydride in very good yield. were the salt and chloride of different carboxylic acids used, one would get three
products, those being the mixed acid anhydride, and the two respective symmetrical anhydrides.
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manimal
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No shit. That is the classical synthesis of AA.
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hissingnoise
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Yeah, if we could get acetyl chloride OTC or if its synth was easy this thread wouldn't exist (frustrations section!). . .
Anyway, welcome to SciMad (yep, I'm heavily sedated?) birdman.
Just give us your source of that damn acid chloride, or we'll send the boys round.
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birdman
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Sorry guys,
I'm just a dumb-dumb who's read too many books. I spent five years reading all the chem texts I could get when I had nothing else to do and no
opportunity to try any of it. Now that I am able to get some practical lab experience, I am playing around. But I only just got done examining the
boiling point elevation of sucrose and NaCl soloutions and ended up getting molar mass determinationsPISSED and insecure all at the same time. I
should probably keep my mouth shut to lessen the risk of getting my foot stuck in it.
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birdman
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Hey again,
For some reason my recent reply posted with text missing. I was writing that I just attempted molar mass calculations based on boiling point
elevation of some lousy sucrose and NaCl solutions and they didn't even come out CLOSE to right. Very confidence inspiring for a wishfully aspiring
chemist. That, however, is the the extent of my intimidating expertese.
Regarding Acyl chlorides however,... are they really THAT hard to get? Even Ac2O itself,... I mean, I understand it is a List II chem, but can't
somebody purchase it in amounts below the threshhold quantities w/o serious scrutiny? I recently ordered some HgCl2, which I am given to understand is
a watched chem in California but it's sold by hobbiest chem outlets and I have perfectly legal experiments planned for it. Should I expect a visit
from Men In Black or parole agents in HAZMAT suits?
[Edited on 23-7-2009 by birdman]
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Magpie
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| Quote: |
I just attempted molar mass calculations based on boiling point elevation of some lousy sucrose and NaCl solutions and they didn't even come out CLOSE
to right.
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Give us all the details of these failed experiments and we will be glad to help you troubleshoot. Preferably do this in another thread under
Beginnings.
There is often a world of separation between literature syntheses and home lab capability. A requirement for extreme temperature and/or pressure
conditions is one reason. Availability of reagents to the private citizen is another.
Will you be questioned if you order Ac2O? I don't know. Will you be questioned if you order KCN? Probably. There's no hard and fast rules out
there. You have to use your own judgement. It's your neck and you are on your own. If you stay with this forum long enough and read enough of the
existing threads you will develop your own sense about this.
The single most important condition for a successful synthesis is good mixing - Nicodem
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birdman
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Thanks Magpie,
I prepared my solns all over again last night, paying closer attention to masses and volume measurements. this morning I noticed that the
thermometer I had used has the word 'total' on it. I'm assuming that means it's a total immersion thermometer. My ground glass adapter, stillhead
thermometer is 75 mm immersion, but I don't have 75 mm of fluid in my samples. I have a cheap, alcohol candy thermometer. I'm going to measure ambient
temperature with them all, then the boiling point of distilled water and see how they compare. I'll probably go with the candy therm of it shows
reasonable linearity in that range.
I love setting up my ground glass and watching condensate spin down the coils of my graham condenser and yelling in my garage about having
perfected the flux capaciter, so I'm having fun, no matter what. I'm going to go check out the Beginings forum.
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S.C. Wack
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It seemed odd that the oldest literature on the S2Cl2/carboxylic acid reaction in this language, 100 year old JCS articles by Denham, haven't been
posted anywhere; so I thought that I'd post some excerpts, even though this is not something that you may be interested in, has been touched on
before, and in fact barely mentions acetic anhydride. It seems better to dump all this related crap here than to put it in any one of 50 threads by
Sauron about the same thing over and over again. So:
The author has found that the sodium, or better, the silver, salts of many monobasic organic acids react smoothly with sulphur monochloride in
presence of such solvents as light petroleum, ether, or benzene to give the chloride of the metal and unstable derivatives of the acids, in which,
apparently, sulphur replaces the hydrogen of ths hydroxyl group. These compounds decompose even when kept in sealed tubes, and the products of
decomposition are found to be the anhydride of the acid, sulphur dioxide, and free sulphur. The following equations may perhaps be taken as
representing respectively the formation and decomposition of the benzoic acid derivative:
2C6H5COONa + Cl2S2 -> (C6H5COOS)2 + 2NaCl
2(C6H5COOS)2 -> 2(C6H5CO)2O + SO2 + 3S
Action of Sulphur Monochloride on Sodium Benzoate. - This reaction has been carried out repeatedly in slightly varying ways, using different solvents;
the following may be taken as typical. 2.9 g. of dry, powdered sodium benzoate were mixed with about 20 ml. of light petroleum, and the calculated
quantity (1.4 g.) of sulphur chloride dissolved in a few ml. of the same solvent was added all at once. The mixture was then boiled on the water-bath
for an hour and a-half under a reflux condenser provided with a calcium chloride tube; a slight odour of sulphur dioxide was noticed during this
operation. About one gram of freshly reduced copper powder* was then added, and the boiling was continued for half-an-hour longer. The copper became
black, and the solution green, but, on filtering, a clear, colourless liquid was obtained, from which crystals separated on cooling. In this way a
good yield is obtained of the substance, (PhCOOS)2, in well-defined, colourless crystals, which, however, soon turn yellow and evolve sulphur dioxide,
leaving sulphur and benzoic anhydride. This decomposition takes place even in an atmosphere of carbon dioxide, and in warm weather may occur
instantaneously with the formation of a liquid mass consisting of a mixture of sulphur and benzoic anhydride. The compound is easily soluble in
alcohol, ether, benzene, carbon disulphide, or glacial acetic acid, more sparingly so in light petroleum. The solution in benzene may be kept for a
day or two without evidence of decomposition, whilst that in glacial acetic acid soon decomposes.
* The copper is not essential. It was added in one experiment to see if it would remove the sulphur and leave benzoyl peroxide, but this did not
happen. The use of it was continued in after experiments, since it appeared to destroy final traces of sulphur chloride and to be better for this
purpose than excess of sodium benzoate.
This compound, (PhCOOS)2, may be prepared more readily by shaking together dry silver benzoate and a solution of sulphur chloride in ether in the
manner described below for other silver salts.
Action of Sulphur Monochloride on Silver Acetate. - Since sulphur chloride does not react readily with sodium acetate, the silver salt was employed,
and after a number of preliminary experiments, the following simple method was found to give satisfactory results.
To 2.5 g. of dry silver acetate, about 20 ml. of dry ether were added, and then 0.4 ml. (rather less than the calculated quantity) of sulphur
chloride, dissolved in a few ml. of dry ether. The containing vessel was closed and shaken for a minute, when the mixture became warm and the yellow
colour of the sulphur chloride disappeared.
After filtering, the ether was distilled off, the last traces being removed by means of a current of dry hydrogen. The compound, (CH3COOS)2, was thus
obtained as a clear, faintly yellow, viscous liquid with a faintly pungent odour. Some of it, after being kept for three days in a closed flask in the
ice-chest, was found to be completely decomposed into sulphur dioxide, sulphur, and acetic anhydride.
Preparation of Propionic Anhydride from Silver Propionate. - To 18.1 g. of dry silver propionate in about 50 ml. of dry ether, 4 ml. of sulphur
chloride in 20 ml. of dry ether were added; this addition must be made gradually, as otherwise the reaction may become too vigorous. The mixture was
then shaken for a minute, and after filtering off the silver chloride and removing the ether by distillation, the syrup obtained was heated on the
water-bath for an hour or two until decomposition was complete. The clear liquid was then decanted and distilled, the distillation being stopped as
soon as the distillate appeared yellow; 5.5 g. of the crude anhydride distilled between 160° and 170°, the greater portion above 165°. The boiling
point of propionic anhydride is 168°, and the calculated yield from 18.1 g. of silver propionate is 6.5 grams.
Preparation of Propionic Anhydride from Sodium Propionate. - 9.6 g. of dry sodium propionate were boiled for an hour under reflux with 4 ml. of
sulphur chloride in presence of 40 ml. of light petroleum, a little copper powder being added towards the end. The solution was then filtered from
sodium chloride and treated as just described in the preparation from the silver salt; 4.5 g. of the crude anhydride distilled over at a little below
170°. The theoretical yield is 6.5 grams.
---
Similarly, although less readily and less smoothly, sodium benzoate when heated with sulphur chloride in equimolecular proportions gives essentially
benzoyl chloride, sodium chloride, sulphur dioxide, and free sulphur (Carius, Annalen, 1858, 106, 291). Benzoyl chloride is formed also when benzoic
anhydride is heated with sulphur chloride...The two stages represented by the equations:
2C6H5COONa + 2S2Cl2 -> (C6H5CO)2S + 2SOCl2 + Na2S -> 2C6H5COCl + 2NaCl + SO2 + 3S
Sulphur Chloride and Silver Benzoate. - 12.5 g. (instead of 11.5 g.) of silver benzoate suspended in 50 ml. of dry ether were treated with 3.4 g. of
sulphur chloride, and the mixture was shaken vigorously. After filtration from the silver chloride and removal of the ether, 7.5 g. of benzoyl
thiosulphite were obtained as a colourless syrup, which soon crystallised with marked evolution of heat, and afterwards decomposed. From the products
of decomposition 5.6 g. of the crude anhydride were extracted by means of ether, and 0.96 g. of sulphur was left. The calculated quantities (reckoning
on the amount of sulphur chloride used) are 7.6 g. of benzoyl thiosulphite, 5.65 g. of benzoic anhydride, and 0.95 g. of sulphur, if the reactions
which occur are represented by the equations:
2C6H5COOAg + Cl2S2 -> (C6H5COO)2S2 + 2AgCl
(C6H5COO)2S2 -> 2(C6H5CO)2O SO2 + 3S
The crude anhydride was now mixed with 3.4 g. of sulphur chloride and heated under reflux for four hours. On extraction of the product with ether, 1
g. of sulphur was left, and the ethereal extract contained 6 g. of dissolved matter, which consisted chiefly of benzoyl chloride. The calculated
amounts are 1.2 g. of sulphur and 7.1 g. of benzoyl chloride on the assumption that the reaction is represented by the equation:
2(C6H5CO)2O + 2S2Cl2 -> 4C6H5COCl + SO2 + 3S
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S.C. Wack
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Well I was thinking that there must be a variant in the literature of this preparation of acetyl chloride, changed in the obvious way for the production of acetic anhydride. And I seem to remember some stuff at the
Hive or here close to that, perhaps using solvent, but really I was looking for GB190825433, and it was found. Thought I'd mention it since I'm going on about sulfur.
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ammonium isocyanate
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I know that the rhodium archives has a chemically similar prep that is archived on erowid using bromine as a solvent and reactant as well as a small
amount of sulfur to produce Ac2O from AcONa in pretty good yields through the same intermediate. NaBr is of course generated as a byproduct and thus
using chlorine gas one could regenerate the bromine, which being a liquid is more convenient for a one-pot synthesis than chlorine, though with an
additional solvent I imagine a chlorine based synthesis might be workable.
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Saber
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Has anybody tried the Sodium acetate + S2Cl2 route to acetic anhydride?
This seems the most simple as the S2Cl2 is REALY easy to make and anhydrous Sodium acetate is cheap! I agree with Sauron, but the anhydrous salt
instead of trying to dry the trihydrate, its more trouble than its worth and its hard to get a fully dry solid without burning the solid.
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entropy51
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NaOAc trihydrate is easily dried. It will lose about 2 moles of H2O in a vacuum dessicator. Then heating while stirring constantly until it melts
and then solidifies again works every time for me. It's just a pain to keep stirring, but otherwise no problem.
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