Patent GB-634188-A (GB)
Title: Improvements in or relating to the production of fluoroacetic acids, and derivatives thereof
IPC: C07C51/16
Filed: 1947-02-17
Abstract: Fluoroacetic acids, esters and salts thereof are produced by a process which comprises the step of reacting a fluorethylenic compound of the type CF2XCY=CYZ, in which X is hydrogen, fluorine or chlorine, Y is hydrogen or chlorine and Z is hydrogen, chlorine or CF2X, with an aqueous permanganate solution in the presence of sufficient calcium oxide or hydroxide to combine with all the acids liberated by the reaction.  Specified starting materials are 3,3,3-trifluoro-1,1,2-trichloropropene-1; 3,3-difluoro-1,1,2,3 - tetrachloropropene - 1 and 1,1,1,4,4,4-hexafluoro - 2,3 - dichloro - butene - 2.  Specified permanganates are calcium permanganate and potassium permanganate, the latter being preferred.  Calcium hydroxide is preferred and any permanganate remaining in the reaction mixture may be destroyed by reaction with sulphur dioxide, hydrogen peroxide, sodium sulphite, sodium bisulphite or sodium hydrosulphite. The temperature range may be from 20 DEG  to 130 DEG  but is preferably 70 DEG  to 80 DEG  C.  Atmospheric or higher or lower pressures may be employed. After destroying any excess permanganate, the salt of the fluoroacetic acid may be isolated, admixed with calcium chloride (if lime is used), and potassium chloride (if potassium permanganate is used), by filtration to remove manganese dioxide, calcium sulphate, calcium carbonate and any unreacted lime, and evaporation to dryness or the reaction mixture may be treated with a water-soluble carbonate, e.g. sodium or potassium carbonate, and the solution of the crude salt, e.g. the sodium or potassium salt, filtered off from the precipitated calcium carbonate.  The fluoroacetic acid may be obtained by treating this filtered reaction mixture with sulphuric acid, distilling off the aqueous fluoroacetic acid, neutralizing with sodium carbonate, drying the sodium salt and then mixing the latter with sulphuric acid and distilling to recover the fluoroacetic acid.  Alternatively the acid may be obtained from the reaction mixture after neutralizing or from the mixture of salts obtained by evaporation as above, by extraction with an organic solvent such as methyl, ethyl, isopropyl or secondary butyl alcohol, diethyl ether, acetone, dioxane and ethyl acetate.  The salts and acids produced by the process may be esterified by the usual methods, e.g. by destroying any excess permanganate in the reaction mixture, filtering, evaporating the filtrate to dryness and adding sulphuric acid and the alcohol to be esterified and recovering the ester by distillation.  In examples: (1) 3,3,3-trifluoro-1,1,2-trichloropropene-1 is added to a solution of potassium permanganate and calcium hydroxide in water maintained at 65-70 DEG  C.  After the addition, the solution is heated to 95 DEG C., cooled, decolourized by adding sodium bisulphite and then filtered.  The filtrate is treated with potassium carbonate solution and after filtering to remove calcium carbonate the solution is evaporated to dryness and extracted with methanol yielding potassium trifluoroacetate; (2) trifluorotrichloropropene is oxidized as in (1) and the dry solid obtained on evaporation is treated with concentrated sulphuric acid, the trifluoroacetic acid is distilled off as it is formed and is finally redistilled; (3) 1,1,1,4,4,4-hexafluoro-2,3-dichlorobutene-2 is added to a mixture of potassium permanganate, calcium oxide and water and the mixture heated to 95 DEG  C.  The mixture is then treated as in (1) to obtain potassium trifluoroacetate.  Specification 577,481 is referred to.