Phenylacetonitriles -> Phenylacetones

[Rhodium]

alpha-(3,4-Dimethoxyphenyl)-acetoacetonitrile

A solution of sodium ethylate was prepared from 389 g (17 moles) of sodium and 4530 cc. of absolute ethanol. To this hot solution was added a solution of 1000g (5.65 moles) of 3,4-dimethoxyphenylacetonitrile in 1710 g (19.4 moles) of dry ethyl acetate. After refluxing for 4 hours the mixture, containing a light precipitate, was allowed to stand at room temperature overnight. The white crystalline mass was filtered off after cooling in ice for 2 hours. Washing with ethyl acetate and then ether gave 1403g of the sodium salt, mp 296-300°C dec. Solution of the salt in 5400 ml of water, cooling to 10°C and acidifying with 1420 ml of glacial acetic acid gave a nearly solid mass. The product was collected and washed with water; weight 1244g (97.7%), mp 77.5-78°C. Recrystallization from methanol gave analytically pure material, mp 98-100°C.

3,4-Dimethoxyphenylacetone

Crude nitrile from above (1212 g) was added over one hour to a stirred and cooled (0-5°C) solution of 3008 ml of concentrated sulfuric acid in 727 ml of water. The brown solution resulting on heating to 80°C for 10 minutes was cooled to 0°C and diluted (stirring) with 10.75 L of cold water. During heating on the steam-bath for 3 hours, an oily layer separated. After cooling, ether extraction, washing of the extract with dilute bicarbonate solution, and drying, the ether extract was concentrated to give 610.8g (56.5%) of orange oil which was purified by vacuum distillation; weight 549.3g (51%), bp 142°C/2.6mmHg (bp 118°C/0.4mmHg).

alpha-(3-Methoxyphenyl)-acetoacetonitrile

Treatment of 3-methoxyphenylacetonitrile essentially as described above for 3,4-dimethoxyphenylacetorlitrile was followed by addition of petroleum ether to precipitate 275g of the sodium salt of alpha-(3-methoxyphenyl)-acetoacetonitrile, mp 280-290°C (dec). After acidification with acetic acid the yield was 206g (83.6%), mp 83-85°C. Two recrystallizations from methanol gave analytically pure material, mp 90-91°C.

3-Methoxyphenylacetone

The crude nitrile was hydrolyzed as described for 3,4-dimethoxyphenylacetonitrile  but at 90-95°C. The yield of ketone was rather poor (46.5%), and considerable unreacted nitrile was recovered. After redistillation the ketone was analytically pure, bp 95-97°C/0.7 mmHg.

Ref: JACS 77, 700 (1955)

[Nemo_Tenetur]

The yield could be improved by using H₃PO₄ instead of H₂SO₄ for hydrolysis. I saw this in a short CA reference some years ago for plain, unsubstituted alpha-acetylbenzylcycanide, it should work also for substituted derivatives.

[Osmium]

This reaction sequence sucks, it's long, tedious and doesn't work nearly as well as it seems. I've done it before with straight benzyl cyanide, I can still smell that shit when I think back.

An alternative would be hydrolysing the benzylcyanide to PAA, and reacting with Ac2O and NaOAc. Much easier to do and yields won't be any worse.


I'm not fat just horizontally disproportionate.

[raffike]

Acetic anhydride could be hard to get chemical cuz it's listed.I'd not go to supplier and ask for some.Lead acetate method seems little more practical.
For those about to synth,we salute you

[Rhodium]

Calcium acetate works just as well, and at the same time being cheaper and environmentally friendly:

https://www.thevespiary.org/rhodium/Rhodium/chemistry/p2p.paa-ca.html

[Osmium]

The Vogel procedure for ketene production which will produce 1kg of acetic anhydride per day from cheap acetone and some electricity.

Post 247901 (missing)

(Osmium: "Re: Acetic Anhydride", Chemicals & Equipment)

Post 200045 (missing)

(Osmium: "Re: Relativly simply Acetic Anhydride Synth.", Chemistry Discourse)

Since most of the anhydride can be reused, it doesn't matter when a big excess is used. Yields will definitely be better than the carboxylic salt pyrolysis. I tried that one too, with the barium salt, and I think the flask I used is still dirty many years later. Yield was horrible of course, a few percent of an ugly stinking mixture of all kinds of crap.
I'm not fat just horizontally disproportionate.