GB810461A - Production of trichloroacetic acid and its functional derivatives - Google Patents

Abstract

Trichloroacetic acid and functional derivatives thereof which are hydrolysable to the acid by reaction with water are prepared by passing gaseous chlorine into a heated mixture of 15 to 75 per cent by weight of glacial acetic acid and 85 to 25 per cent by weight of acetic anhydride until substantially the whole of the reaction mixture has been converted to trichloroacetic acid and said functional derivatives, at least the latter part of the chlorination being carried out in the presence of 0.01 to 2 per cent by weight, calculated on the sum of the weights of glacial acetic acid and acetic anhydride, of an acid of phosphorus. This acid is preferably orthophosphoric acid used in an amount of from 0.01 to 1 per cent, although other phosphorus oxyacids, a list of which is given, can also be used. In a preferred embodiment the acid is present throughout the chlorination but it may equally well be added when about 80 per cent of the reaction mixture has been converted to trichloroacetic acid and derivatives thereof or at the stage when formation of monochloroacetic acid is substantially complete. The process of the invention may be combined with the additional step of adding water to the reaction product at a temperature above the melting point thereof to convert the functional derivatives to trichloroacetic acid, or with the additional step of treating the product with an alkali or with a salt of a weak or easily displaced acid to form a salt of trichloroacetic acid, or with the additional step of esterifying the product. In examples: (1) chlorine is introduced into a mixture of 25 parts of acetic anhydride and 75 parts of glacial acetic acid at 70 DEG to 110 DEG C. until the monochloroacetic acid stage has been reached, the temperature is raised to 150 DEG C. and 85 per cent phosphoric acid is added periodically until the product has a trichloroacetic acid content of 97 to 98 per cent, a figure which may be changed to approximately 100 per cent by addition of water at 100 DEG C. to hydrolyse the functional derivatives (mainly trichloroacetyl chloride); (2) a process similar to (1) is performed, except that the phosphoric acid is present throughout; (3) a mixture of 42 parts of acetic anhydride and 58 parts of glacial acetic acid is converted to trichloroacetic acid by a process similar to (1); (4) a mixture of 60 parts of acetic anhydride and 40 parts of glacial acetic acid is converted to trichloroacetic acid by a process similar to (1), phosphoric acid being added after 90 per cent conversion; (5) a mixture of 85 parts of acetic anhydride and 15 parts of glacial acetic acid is converted to trichloroacetic acid by a procedure similar to (1); (6) the reaction product, prior to hydrolysis, of (2) is heated with soda ash at 60 DEG C. to give sodium trichloroacetate containing a small amount of sodium dichloroacetate, and the preparation of other alkali metal, alkaline earth metal and ammonium salts is also referred to; and (7) the reaction product, prior to hydrolysis, of (2) is heated with isopropyl alcohol to give isopropyl trichloroacetate, and reference is also made to the formation of esters with other saturated or unsaturated, primary, secondary or tertiary, substituted or unsubstituted aliphatic, aromatic or heterocyclic alcohols. Specification 706,440 and U.S.A. Specification 2,674,620 are are referred to.