Process for the preparation of low molecular weight polyhydroxyl compounds

In a process for the preparation of a mixture of low molecular weight polyhydroxyl compounds and optionally hydroxy aldehydes and hydroxy ketones by the condensation of formaldehyde hydrate, in the presence of from 0.01-10% by weight, based on formaldehyde, of metal compounds as catalyst, and from 0-10% by weight, based on formaldehyde, of co-catalysts which are based on compounds capable of enediol formation, the improvement which comprises condensing formaldehyde hydrate at a reaction temperature of from 10.degree.-150.degree. C. in the presence of

• I. a soluble or insoluble compound of a metal of the first to eighth sub-group or second to fourth main group of the Periodic System of Elements, optionally bound to a high molecular weight carrier, and
• II. more than 10% by weight, based on formaldehyde, of one or more dihydric or higher hydric low molecular weight alcohols and/or higher molecular weight polyhydroxyl compounds,
• maintaining the pH of the reaction solution between 5.5 and 9.0 by controlled addition of one or more inorganic and/or organic bases up to a conversion rate of 5-40% by weight, lowering the pH of from 0.5 to 3 units and thereafter maintaining the pH at from 4.0-8.5 until the termination of the condensation reaction;
• then stopping the reaction in known manner by inactivation of the catalyst when the residual formaldehyde content is from 0-10% by weight;
• removing the catalyst and, optionally, reducing the aldehyde and keto groups present in the reaction product to hydroxyl groups.