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stygian
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wrt acetonitrile, http://nopr.niscair.res.in/bitstream/123456789/30881/1/IJCT%...
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Mush
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Quote: Originally posted by Formatik  | | Quote: | Originally posted by Taoiseach
urea with acetic acid
Is acetic anhydride necessary for this reaction to work? |
No, I don't think so. Gmelin says heating urea with AcOH to 110 deg.C. forms acetamide, pitty nothing further like reaction time, extraction, etc. but
they reference: M.T. Dangyan (Bull. Armenian Branch Acad. USSR 1942 No. 9/10 (23/4), pg. 53/72), C.A. 1946 3399, and
J.M. Das-Gupta (J. Indian Chem. Soc. 10 [1933] 117/23). These references, especially the first should have more details about this
process. |
Studies on the Decompositions and Reactions of Urea.Part II. Reactions of Urea with Acids , Anhydrides, etc.
By Jnanendra Mohon Das-Gupta.
J. Indian Chem. Soc. 10 [1933] 117
Attachment: 10_1933-113-119.pdf (194kB)
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BAV Chem
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Acetonitrile prep without P2O5
I've been looking into this for a while now and weirdly enough everyone just talks about using phosphorus pentoxide or other fancy dehydrating agents
for this. Seems strange because acetonitrile was first synthesized by French chemist Jean-Baptiste Dumas in 1847 by dehydrating acetamide with water
free phosphoric acid. No unobtainium pentoxide involved. I don't know any french so sadly I can't read his original article. However i also found
another article from 1856 by Buckton and Hofmann (see below) on the reaction of oleum with amides and nitriles and they gave a pretty good procedure for the preparation of
acetonitrile. It's written in German so i shall translate:
Preparation of Acetonitrile. - When trying to prepare this substance by the action of potassium methylsulfonate on potassium
cyanide only small amounts of a highly impure product are obtained. The presence of even small amounts of moisture present in these salts leads to
formation of a variety of secondary products which mainly consist of ammonium carbonate, ammonium cyanide and a gas that lends an unbearable odor to
the distillate. The most advantageous method for producing acetonitrile consists of the action of water free phosphoric acid on acetamide, which has
previously been suggested by Dumas.
The ethyl acetate doesn't immediately dissolve in an adequate volume of ammonia solution; only after 5 to 6 hours of contact time do the layers that
were originally formed unite to give a homogenous liquid. If the distillation is carried out soon after almost no acetamide is obtained. The
conversion can however be completed by digestion at 120 to 130°C lasting two or three hours. For this operation we have used forged iron cylinders,
similar to the ones Frankland used in his experiments. [...] The safety valves on these pressure cylinders are usually manufactured from brass. When
working with ammonia solutions the brass valve has to be replaced by a steel screw and a lead washer to achieve a good seal. Preferrably equal volumes
of ethyl acetate and concentrated aqueous ammonia are used. After six hours of digestion the conversion is complete and the generated acetamide may be
separeated from the regenerated alcohol by distillation. Everything that passes over above 260°C is rather pure Acetamide. When this substance is
mixed with a roughly equal volume of water free phosphoric acid a violent reaction takes place. Subsequently the colorless nitrile contaminated with
hydrocyanic acid and acetic acid distills over. At the end of the distillation rather high temperatures are needed to make the last volatile matter
pass over. The aqueous distillate is shaken with enough potassium hydroxide solution to neutralize the acids. Upon standing the nitrile quickly forms
a clear layer on the surface. This is collected using a pipette and rectified again over water free phosphoric acid to obtain the pure acetonitrile.
The substance obtained in this manner has an ethereal odor reminescent of that of cyanide. Its aromatic smell is pungent but not unpleasant.
[...]
I haven't yet tried the preparation of acetamide from ammonia and ethyl acetate but their description implies that merely ammonium acetate is formed
which needs some additional persuasion to convert it to acetamide.
I made my acetamide from acetic acid and ammonia and i tried the reaction with phosphoric acid.
Attempt 1:
The phosphoric acid was concentrated by boiling it down as far as possible. Then 12ml each of melted acetamide and concentrated phosphoric acid were
mixed and things got quite warm but no obvious reaction was observed. Distillation in an (overheated) oil bath gave a clear distillate with a strong
smell of acetic acid. Quite a lot of potassium hydroxide solution was necessary to neutralize all acid but no upper layer formed. Salting out with
potassium carbonate and later even more KOH also didn't afford anything. The residue in the reaction flask was extremely viscous but seemed to be
mostly unchanged phosphoric acid.
I decided to reuse it for Attempt 2:
Another 12ml of Acetamide was added to this residue and distilled as before. The reaction took longer and foamed more this time. The distillate was
redistilled and i collected everything that came over below 90°C. Mixing this with a solution of sodium carbonate gave quite a lot of CO2 and finally
an organic layer separated. I pipetted this off and dried it over CaCl2. In the end i got 4,9ml of crude acetonitrile which is a 46% yield.
Chemplayer only got something like a 65% yield using P2O5 so it's not too bad. Perhaps this could also get there if done right. In an act of late
night craziness i also tried this with sodium pyrosulfate. I dehydrated sodium bisulfate in the oven as far as it would go and then finished it off by
heating it in a test tube. When white fumes of SO3 (supposedly) came off I figured it was done.
Attempt 3:
6ml of acetamide and 26g of finely powdered sodium pyrosulfate were mixed to give a thick paste. This was also distilled in an oil bath and a clear
distillate was obtained. Redistilling this gave a fraction that was mostly acetonitrile but no yield was determined.
Looks all very promising so I'm gonna scale up the phosphoric acid run and see where that gets me.
Attachment: php1wvIEK (1.6MB)
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clearly_not_atara
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I'm impressed and of course mildly surprised that you seem to be the first amateur to even attempt this. Everyone talks about using fancy reagents and
I have always known the literature says it isn't necessary but this might be the first "proof" we have.
Nice work.
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BAV Chem
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Thank you but I'm afraid I have to bring some disappointing news. As it turns out I screwed up my yield calculation real bad and only got a 23% yield
in the previous run, not 46% (oops, I swear I'm normally better at this). Also I ran the same procedure with 25ml each of acetamide and phosphoric
acid and got practically the same amount so roughly half of my previous yield (12% to be exact) so that sucks .
It seems like the more depleted acid did better because there's less side reactions happening. The main one is probably hydrolysis of acetamide to
ammonium acetate which reacts with the phosphoric acid to give acetic acid and ammonium phosphate. The latter is likely what is turning the residue so
viscous. Perhaps ammonium dihydrogen phospate or another dihydrogen phospate salt could still work as a dehydration catalyst of sorts.
The "water free" phosphoric acid those chemists used in the 1850s appears to be mostly polyphosphoric acids with quite a high degree of
polymerization/dehydration. It makes sense that "water free" would mean thoroughly dehydrated as in boiled at red heat in a
quartz beaker for an entire day (maybe not quite) because it was written by Germans.
Pyrosulfate might still be worth looking at but I doubt it could be practical because quite a large amount of it is needed for a small amount of
acetamide and the residue is a really hard mass adhered to the flask. I've shattered RBFs like that before and I don't wanna do it again.
Really I think instead of a single use dehydrating agent (e.g. P2O5) some sort of catalyst like the stuff mentioned on Page 2
would be the way to go but more experiments are needed.
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clearly_not_atara
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I think the hydrolysis theory makes sense, ammonium phosphate is stable to 300 C ish. Bronsted acids may not be the way.
Alumina was the best catalyst but carbon black (a pigment) and pumice are notable for being much more accessible. Don't get carbon black on your
clothes.
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