GB789388A - Improvements in or relating to diol perfluoro esters and diols therefrom - Google Patents

Abstract

The invention comprises esters having the general formula: <FORM:0789388/IV (b)/1> wherein R and R1 represent hydrogen or alkyl radicals having from 1 to 3 carbon atoms and n is an integer from 1 to 3, except that R and R1 do not both represent the methyl radical when n = 3, and a method for the preparation of these and other glycol di-esters of aliphatic perfluoro carboxylic acids comprising reacting a saturated epoxide with an anhydride of an aliphatic per-fluoro carboxylic acid at a temperature in the range 25 DEG to 200 DEG C. at which the epoxide ring opens. The reaction is preferably effected in the presence of an esterification catalyst such as zinc chloride, aluminium chloride, sulphuric acid, acetic acid or, desirably, a per-fluoro carboxylic acid corresponding to the acid anhydride reactant. Normally, at least one mol. of anhydride per mol. of epoxide is used. Inert solvents may be present and elevated pressure may be used. The epoxides preferably have a tetra- or pentamethylene ring and include those having the formula: <FORM:0789388/IV (b)/2> wherein n is 2 or 3 and wherein one or more of the hydrogen atoms may be replaced by C1-15 alkyl groups, chlorine, bromine or carboxylic acid or carbalkoxy radicals and numerous examples are given. There may also be used ethylene oxide, 1 : 2-epoxy butane, 2 : 3-epoxy butane, trimethylene oxide, 2-ethyl-1 : 3-epoxy propane, 2 : 4-epoxy octane and 2 : 4-epoxy pentane. The perfluoro acid anhydrides are preferably those from monobasic acids, e.g. perfluoro acetic, propionic and butyric acids; anhydrides of dibasic acids, e.g. tetrafluoro succinic acid anhydride, are said to tend to yield polymeric compounds. The glycol diesters may be treated to yield the corresponding glycols by saponification or preferably by alcoholysis with a C1-3 alkanol, if desired in the presence of a catalyst which may be an acid but is preferably an alkali metal alcoholate, a quaternary ammonium base or a basic ionexchange resin; in some cases, simple hydrolysis may be used. In examples: (1) trifluoro acetic anhydride, obtained by refluxing trifluoro acetic acid with P2O5, is heated with 2 : 5-dimethyl tetrahydrofuran and trifluoracetic acid as catalyst in a glass pressure flask at 95 DEG C. and the products are worked up to isolate the resulting hexane-2 : 5-diol di-trifluoro acetate and a small amount of hexene-5-ol trifluoroacetate; the di-ester is alcoholysed with methanol to give the free diol; (2) the catalyst used in (1) is replaced by zinc chloride; (3) the epoxide and anhydride of (1) are refluxed at atmospheric pressure in the presence of zinc chloride catalyst and then further heated in a closed vessel at 95 DEG C.; the resulting di-ester is then alcoholysed with methanol in aqueous hydrochloric acid; (4) the method of (2) is repeated and the di-ester containing product, without isolation, is alcoholysed as in (3) yielding the free diol and some hexenol.