GB740398A - Process for condensing formaldehyde - Google Patents

Abstract

Carbohydrates are produced by the catalytic condensation of formaldehyde by a process comprising forming a body of aqueous reaction liquor containing the carbohydrates and unchanged formaldehyde, continuously supplying to it an aqueous mixture containing between 5 and 20 per cent by weight of formaldehyde, continuously withdrawing a portion of the reaction liquor, stopping the condensation reaction within that portion, and maintaining the concentration of formaldehyde in the liquor in the reaction zone at between 1/2 and 1/100 of that of the said aqueous mixture. By this means a high proportion of C2-C4 compounds is obtained. The catalyst used is preferably a lead salt soluble in the reaction mixture, for example lead nitrate, lead acetate or basic lead acetate or it may be lead oxide. Other known catalysts, for example, magnesium, calcium or barium hydroxide, and tin formate, may be used. An activator, e.g. benzoin, hydroxy acetone, glucose or glycollic aldehyde may be used. The reaction can be carried out at a pH of about 4 to 9 and to control the pH of the mixture an inorganic base, e.g. lime or sodium hydroxide or an organic base, e.g. triethyl amine, may be added to the feed. In the examples: (a) aqueous formaldehyde is condensed in the presence of lead acetate according to the process of the invention to give a mixture of carbohydrates which on hydrogenation in the presence of Raney nickel gave a mixture of ethylene glycol, glycerol and erythritol.