Patent GB-713088-A (GB)
Title: Process of producing acrolein acetals
Filed: 1951-08-13
Abstract: An acetal of acrolein is obtained by heating acrolein and a monohydric aliphatic alcohol containing from 1 to 8 carbon atoms inclusive in the presence of about 0.001 to 0.010 mol. per cent, based on the acrolein, of an acid containing the group -SO2OH as a catalyst and an inert water-immiscible organic liquid while continuously distilling the water formed, from the reaction mixture, in the form of an azeotropic mixture with the inert organic liquid, and subsequently recovering the acrolein acetal from the reaction mixture.  The process is conveniently carried out at between 25 DEG and 50 DEG  C. and preferably between 25 DEG  and 35 DEG  C. Specified acids which may be used as catalysts are sulphuric acid, sulphamic acid, the aliphatic sulphonic acids such as methane- and ethane-sulphonic acids and the aromatic sulphonic acids such as benzene-, toluene- and naphthalene sulphonic acids. Specified inert organic liquids are hydrocarbons and halogenated hydrocarbons such as benzene, toluene, xylenes, ethylene p  dichloride, methylene dichloride, carbon tetrachloride, pentanes, hexanes and heptanes.  It is preferred to use a liquid boiling below 50 DEG  C., e.g. a petroleum fraction containing a predominance of pentanes, boiling at 35 DEG  C. and distilling between 35 DEG  and 60 DEG  C.  As some alcohol and acrolein co-distil with the water and reaction solvent a preferred procedure is to separate the organic phase and return it to the reaction zone and since a little alcohol and acrolein are dissolved in the water separated from the organic phase it is preferred to continue the reaction until about 130 per cent of the theoretical volume of aqueous phase has been collected.  The acetal formed may be isolated by removing the catalyst, preferably by neutralization with a mild base such as sodium bicarbonate or copper carbonate, and fractionally distilling the liquid to recover the inert solvent, alcohol, and unreacted acrolein and the residue which consists essentially of acrolein acetal may be further purified by fractional distillation.  The monohydric alcohols that may be used include methanol, ethanol, n-propanol, isopropanol, n-butanol, n-octanol, isobutanol, isopentanol, iso-octanol and tertiary-butanol. In examples: (1) a mixture of commercial acrolein, ethanol, a pentane fraction, and p-toluenesulphonic acid monohydrate is refluxed in a still-pot equipped with a fractionating column and a continuous water or phase separator, the vapour temperature being maintained at 29 DEG C. for 24 hours and the solution then cooled, treated with copper carbonate, filtered and fractionally distilled to yield acrolein diethyl acetal; (2) as in (1) except that the fractionating column is provided with a tube containing silica gel to dry the distillate before it is returned to the reaction vessel the refluxing period being 39 hours; (3) following the procedure used in (1) the dimethyl-, di-isopropyl-, di-n-propyl, di-n-butyl-, and di-isobutyl-acetals of acrolein are obtained from acrolein and the corresponding alcohol using varying times of reflux; (4) as in (1) except that methylene chloride is used as the inert liquid and after 22 hours reflux an additional amount of p-toluene sulphonic acid monohydrate is added and heating continued for a total of 72 hours. A comparative example is also given to show that the yield is reduced when more than the specified amount of catalyst consisting of sulphamic acid or naphthalene b -sulphonic acid monohydrate is used in the production of the diethyl acetal.