Triesters of the general formula <FORM:0655040/IV (b)/1> are obtained by reacting a diester of general formula <FORM:0655040/IV (b)/2> with a carboxylic acid of general formula R3COOH, in the presence of a catalytically effective amount of an acid-reacting substance wherein in the formul R1, R2 and R3 are alkyl radicles, particularly those containing up to 8 carbon atoms, and R1, R11 and R111 are hydrogen or alkyl radicles, preferably lower alkyl radicles. The triesters thus obtained may be hydrogenated in the presence of a hydrogenation catalyst to yield 1 : 3-alkane diol esters. Particularly convenient starting esters for the first stage are those with a terminal methylene group, e.g. 1,1-diacetoxy-2-propene which with acetic acid yields 1,1,3-triacetoxypropane and 1,1 - diacetoxy - 2 - methyl - 2 - propene which in a similar fashion gives 1,1,3-triacetoxy-2-methyl propane. The diesters may be prepared by reacting an alpha, beta-unsaturated aldehyde with a carboxylic acid anhydride, optionally in the presence of an acid reacting substance such as sulphuric acid which is preferred, phosphoric and oxalic acid, stannous, zinc and ferric chlorides in amounts of 0.1-0.5 per cent at 0-20 DEG C., and with an inert diluent if required, or by reacting a metal salt, e.g. silver, lead or sodium salt, of a carboxylic acid with an alkylidene halide. Acrolein, crotonaldehyde, and alpha-beta-diethyl acrolein are typical of unsaturated aldehydes specified and acetic, acetic-propionic and butyric anhydrides typical of the anhydrides. Catalysts for the first stage desirably are substantially stronger than acetic acid, e.g. strong mineral acids and acidic substances specified are sulphuric, hydrochloric and phosphoric acids, acid reacting salts, e.g. sodium acid sulphate, sodium and potassium dihydrogen phosphate, organic acids, e.g. mono-, di- and tri-chloroacetic acid, oxalic acid and p-toluene sulphonic acid. With strong mineral acids 0.001 to 5 per cent by weight of the two reactants is used as catalyst although in general the amount of catalyst to be used is dependent on the reaction conditions, the reactants and the catalyst used. An inert diluent, e.g. ether, hydrocarbon, or chlorinated hydrocarbon, may be present and the catalyst may be contained on a support of conventional type. Either reactant may be in excess although it is generally preferred that at least an equimolar quantity of acid is used. Temperatures indicated are 30-150 DEG C., 30-90 DEG C. being preferred. Reaction may be effected in vapour or liquid phase, batchwise or continuously, under reduced pressure or at atmospheric pressure. Catalysts for the hydrogenation phase specified are the oxides and sulphides of nickel, tungsten, molybdenum, cerium, thorium, chromium or zirconium or mixtures thereof, alloys, e.g. of copper and silver, copper and chromium, copper and zinc and nickel and zinc, and the metals gold, silver, platinum, palladium, osmium, rhodium, iridium, chromium, thallium, nickel, iron or cobalt, optionally on conventional supports. Pyrophoric nickel, iron and cobalt are particularly advantageous. Promoters of conventional type may be present, those comprising soluble phosphates, molybdates, tungstates and selenates of the rare and alkaline earth metals, beryllium, magnesium, aluminium, copper, thorium, manganese, vanadium, chromium, boron and zinc or their oxygen-containing reduction products, e.g. selenites, being particularly suitable. With Raney nickel as catalyst amounts between 2 and 20 per cent by weight of 1,1,3-triacyloxyalkane may be used. Temperatures are preferably above room temperature, e.g. 50-350 DEG C., conveniently 75-200 DEG C., with hydrogen pressures of 500-5000 pounds per square inch, generally 500-2500 pounds per square inch. The reaction may be conducted in the liquid or vapour phase, liquid phase reactions being preferred. Reaction times of 1-6 hours are instanced and agitation is desirable. The diesters thus obtained may be saponified to the glycol. In examples: (1) 1,1-diacetoxy-2-propene is reacted with glacial acetic acid in the presence of sulphuric acid in diethyl ether at 50 DEG C. for 18 hours, the mixture cooled, catalyst neutralized with sodium acetate and 1,1,3-triacetoxypropane obtained by fractional distillation; (2) 1,1-diacetoxy-2-methyl-2-propene and acetic acid are reacted in the presence of phosphoric acid at 80 DEG C. for 12 hours, 2-methyl-1,1,3 - triacetoxypropane being removed by the method of (1); (3) 1,1,3-triacetoxypropane, prepared as in (1), is hydrogenated at 1000 pounds per square inch, and 100 DEG C., in the presence of Raney nickel catalyst and after 90 minutes at 1500 pounds per square inch and 150 DEG C. for a further 3 hours, the reaction mixture is filtered and fractionally distilled to recover the diacetate of 1,3-propanediol; (4) acrolein and acetic anhydride are reacted in the presence of sulphuric acid at 40 DEG C. for 4 hours, glacial acetic acid is added to the mixture which is held at 50 DEG C. for 18 hours, when 1,1,3-triacetoxypropane is recovered and hydrogenated at 1500 pounds per square inch and 150 DEG C. in the presence of Raney nickel catalyst to yield the diacetate of 1,3-propanediol which is recovered; and in (5) 2-methyl-1,1,3-triacetoxy-propane, prepared by reaction of methacrolein with acetic anhydride and of the product thus obtained with acetic acid in the presence of phosphoric acid, is hydrogenated by the process of (3) to yield the diacetate of 2-methyl-1,3-propanediol which is recovered. The R's of the Specification as open to inspection under Sect. 91 are not limited to alkyl group or H but comprise organic radicles in general, e.g. alkyl, alicyclic, alkynyl, aryl and heterocyclic, and may contain substituents with, e.g. oxygen, sulphur, nitrogen, phosphorus and halogen atoms. This subject-matter does not appear in the Specification as accepted.