An improved preparation of phenylacetoneKizlink, Juraj Chemicke Listy (1990), 84(9), 993-4.
(
http://hyperlab.0catch.com/ChemickeListy_1990_84_993.djvu) Journal written in Czech.
AbstractPhCH2COMe is prepd. in 52-67% yield from PhCH2COOH, AcONa or AcOK, and Ac2O in the presence of anhyd. CuSO4 at reflux for 24 h.
Here is translation of Slovak article from Chemicke Listy:
Phenylacetone - benzylmethylketone, 1-phenyl-2-propanone, C9H10O, is important intermediate in chemical, pharmaceutical industry and cosmetics. It is prepared by various methods; one branch of them are they using Grignard reagents [1,2], chloroacetone [3] or by saponification of phenylacetonitrile [4,5]. The second branch is based on decarboxylation of phenylacetic acid (or its salts) and reaction with acetic anhydride. For those methods the most determining factor is velocity and completeness of its decarboxylation, which can be improved by various catalysts. Reaction can be conducted by dry distillation of calcium salts of phenylacetic and acetic acid [6,7], boiling of mixture of these acids with alkali acetates [8-10], pyridine or quinoline [11], or methyllithium [12]. Advantageous are also the methods based on passing of phenylacetic-acetic acid mixture over various catalysts as ThO2 [5,13] or MnCO3 [14] at 350-400 C. Crude product is usually purified by fractionation or bisulfite method. Pure phenylacetone has m.p. -15 C, b.p. 215 C, d = 1.0018, nD = 1.5164; its
semicarbazone [8,11] has m.p. 188-198 C, thiosemicarbazone [15] m.p. 155 C, phenylhydrazone [9] m.p. 85 C, 4-nitrophenylhydrazone [16] m.p. 143 C and 2,4-dinitrophenylhydrazone [17] m.p 156 C.
Disadvantageous is long reaction time 24-72 h for liquid-phase methods and workup of the reaction mixture by neutralization with hydroxide, extraction or fractionation of its large volume for all methods. Yields are 30-50 % for liquid-phase methods and 40-65 % for gas-phase methods. The improved method provides yields min. 50 % with shorter reaction time, removing of the neutralization step, and replacement of extraction by easier decantation.
Experimental
To a mixture of 136 g (1.0 mol) phenylacetic acid, 70 g sodium or potassium acetate, and 16 g (0.1 mol) anhydrous cupric sulphate is introduced 2000 ml anhydrous acetic anhydride* in 4000 ml flask. The mixture is refluxed 24 h. After cooling 500 ml of solvent (CCl4, CHCl3, CH2Cl2) is added and the mixture is poured to a flask containing 2000 ml ice-water. After separation of layers upper layer is removed and lower layer is three times decanted with water, separated, dried (Na2SO4, CaCl2), and distilled. The solvent is distilled off and fractionation column is placed on the top of the flask. Remaining acetic acid and acetic anhydride is then removed, pure product is collected at 100 C (15 torr). Yield 70-90 g (52-67 %).
* Technical product, which contains water, can be dried by adding 10 g thionyl chloride.
