GB753218A - Process for the production of acetals - Google Patents

Abstract

A substantially water-white acetal is obtained by the condensation of an aldehyde (other than acrolein) with an alcohol containing at least 3 carbon atoms in the molecule in the presence of an entraining agent which forms an azeotropic mixture with water and which is substantially inert towards the reactants and the condensation product and in the presence of a quantity of a non-volatile organic acid condensation catalyst constituting less than 0.1 per cent by weight of the reaction mixture. The preferred acids are aromatic sulphonic acids, particularly p-toluene sulphonic acid or benzene sulphonic acid and the acid is preferably used in an amount of 0.01 to 0.05 per cent by weight of the reaction mixture. Specified entraining agents are hydrocarbons or mixtures of hydrocarbons, e.g. a hexane fraction. Particularly suitable aldehydes and/or alcohols are those obtained by the oxo synthesis or from the products obtained by catalytic hydrogenation of carbon monoxide according to the Fischer-Tropsch process in the presence of iron catalysts. The yield of oxygen-containing compositions in the latter process may be increased by converting the olefines present into aldehydes by the addition of water gas and if desired, converting the aldehydes into alcohols by hydrogenation. The aldehyde and alcohol products may be used in admixture or separately. Also, the alcohols obtained by hydrogenation of carbon monoxide may be converted into aldehyde by using copper, zinc, or other dehydrogenation catalysts and these aldehydes may be used together with the alcohols from the same source or with alcohols from a different source. It is preferred to use an excess of 20-50 per cent of the alcohol over the stoichiometric amount required. The acetals formed may be converted into unsaturated ethers by heating them in the presence of small amounts of an acid and the unsaturated ethers may be converted to saturated ethers by hydrogenation. In examples: (1) n-butanol and butyraldehyde are mixed with n-hexane and p-toluene sulphonic acid added to the mixture which is then heated to boiling point in a still provided with a column. The effluent from the top of the column is condensed to give a mixture of water, n-hexane and small amounts of butyraldehyde. The reaction water is continuously separated from the condensate and removed from the process whilst the hexane which contains the butyraldehyde is returned to the still. The acetal formed is fractionally distilled to remove hexane and excess butanol; (2) a gaseous mixture of hydrogen and nitrogen is passed at 310 DEG C. over a catalyst prepared by precipitating an aqueous solution of iron, copper, and calcium nitrates with hot sodium carbonate solution until 70 per cent of the iron has been reduced to the elementary state. Water gas is then passed over the reduced catalyst at elevated temperature and pressure to yield a liquid product containing oxygencontaining compounds (mainly alcohols). The non-aqueous phase of the synthesis product is treated to saponify the esters present and the product extracted with aqueous methanol to yield aliphatic alcohols of four or more carbon atoms; C3-C4 alcohols are recovered from the aqueous phase by distillation in the form of an azeotropic alcohol-water mixture which is then mixed with butyraldehyde and hexane and the mixture reacted in the presence of p-toluene sulphonic acid to form acetals using a procedure similar to that used in (1). Comparative examples are given to show that when sulphonic acid is used and the catalyst in (1) instead of the organic acid the product has a dark colour and is obtained in reduced yield and that when hydrochloric acid is used as the catalyst it distils off and the reaction ceases. Specification 716,541 is referred to.