Patent GB-627992-A (GB)
Title: Reaction of enol esters with anhydrides
IPC: C07C69/145
Filed: 1946-09-14
Abstract: An enol-ester which is a monocarboxylic acid ester of the enol form of a ketone is converted into an ester of another and different monocarboxylic acid by heating said enol-ester to a reacting temperature in the presence of an acidic esterification catalyst with the anhydride of said other monocarboxylic acid, said anhydride containing at least three carbon atoms in each acyl group thereof, and said enol-ester containing an acyl group having fewer carbon atoms than each acyl group of said anhydride. The monocarboxylic acids whose anhydrides may be used as starting materials may be open chain or cyclic, saturated or unsaturated, aromatic or aliphatic, including cycloaliphatic and preferably containing not more than twenty carbon atoms to the molecule, e.g. propionic, butyric, pentanoic, hexanoic, heptanoic, octanoic, nonanoic, decanoic, lauric, myristic, palmitic, margaric, stearic, acrylic, crotonic, angelic, pentenoic, hexenoic, oleic, linoleic, linolenic, benzoic, toluic, cyclohexane-carboxylic acid and sorbic acid.  Specified enol esters are those of the enolic form of acetone, methyl ethyl ketone, methyl propyl ketones, methyl butyl ketones, methyl pentyl ketones, methyl hexyl ketones, methyl heptyl (octyl, nonyl and decyl) ketones, diethyl ketone, ethyl propyl (butyl, pentyl, hexyl or heptyl) ketones, dipropyl ketones, propyl butyl (pentyl or hexyl) ketones, dibutyl ketones, butyl pentyl ketones, dipentyl ketones, methyl cyclohexyl ketone, ethyl (or propyl) cyclohexyl ketone, cyclohexyl acetone, cyclohexanone, methyl cyclohexanones, ethyl (propyl or butyl) cyclohexanones, acetophenone, tolyl methyl ketones, benzyl methyl ketone, acetyl acetone.  The reaction temperature may be from about 40 DEG  to 275 DEG  C. and preferably from 80 DEG  to 175 DEG C. and atmospheric or higher or lower pressures may be employed.  The reaction may be conducted in the liquid phase or in the vapour phase. Specified esterification catalysts are sulphuric acid, p-toluene sulphonic acid, phosphoric acid, zinc chloride, aluminium chloride or boron trifluoride.  If the products are separated by fractional distillation the acidic catalyst may be first neutralised with a tertiary amine or with sodium acetate.  The reaction products consist of the enol-ester product and a mixed anhydride, thus when isopropenyl acetate and butyric anhydride are reacted the products are isopropenyl butyrate and the mixed acetic butyric anhydride.  The latter may be converted to acetic anhydride and butyric anhydride and the latter returned to the process whilst the acetic anhydride may be reacted with butyric acid to produce butyric anhydride for use in the process.  In examples: (1) 2-ethyl hexoic anhydride, isopropenyl acetate and concentrated sulphuric acid are heated, the catalyst then neutralized with sodium acetate and the mixture fractionally distilled under reduced pressure yielding isopropenyl 2-ethyl hexoate, acetic anhydride and 2-ethyl hexoic anhydride; (2) a mixture of butyric anhydride, isopropenyl acetate and concentrated sulphuric acid is refluxed and isopropenyl butyrate recovered from the mixture as in (1); (3) isopropenyl propionate is obtained by heating propionic anhydride and isopropenyl acetate in the presence of sulphuric acid, as in (1); (4) a mixture of the enol acetates of methyl ethyl ketone, 2-ethylhexoic anhydride and sulphuric acid is heated under reflux, buten-2-yl-2-2-ethylhexoate being recovered as in (1); (5) a mixture containing benzoic anhydride, isopropenyl acetate and sulphuric acid is heated under reflux and the reaction mixture distilled yielding isopropenyl benzoate; (6) a mixture of sorbic anhydride, isopropenyl acetate and concentrated sulphuric acid is refluxed and the reaction mixture treated as in (1) to yield isopropenyl sorbate.  Sorbic anhydride is prepared by reacting sorbic acid with acetic anhydride and removing the acetic acid and excess anhydride.  The Specification as open to inspection under Sect. 91 is not restricted to the use of monocarboxylic acid anhydrides containing at least three carbon atoms in each acyl group and the anhydrides of acetic, succinic, adipic, maleic and benzilic acids are also specified.  It is also stated that the carboxylic acid may be used instead of the anhydride, thus when isopropenyl acetate is heated with 2-ethylhexoic acid in the presence of sulphuric acid, acetone and the mixed anhydride of acetic acid and 2-ethyl hexoic acid are formed, the mixed anhydride then reacting with excess isopropenyl acetate to give isopropenyl 2-ethyl hexoate and acetic anhydride.  This subject-matter does not appear in the Specification as accepted.