Abstract: The subject of the invention is a process for the preparation of polyisocyanates containing isocyanurate groups which comprises trimerizing a proportion of the isocyanate groups of organic polyisocyanates or mixtures of di- and monoisocyanates in the presence of basic alkali metal compounds as catalysts and terminating the trimerization reaction by the addition of a catalyst poison, characterized in that the trimerization catalysts are complexes of(i) basic alkalimetal compounds and(ii) acyclic organic compounds which(a) have at least 6 alkylene oxide units of the formula --R--O--, wherein R represents C.sub.1 -C.sub.

Abstract: The instant invention relates to an improved process for the production of formose from formaldehyde. The improvement resides in using relatively small quanities of basic lead compounds as catalysts for the condensation reaction of the formaldehyde and, at the same time, for controlling the pH-value. By following this technique, organic or inorganic bases which, hitherto, have normally been used for this purpose are no longer needed.

Abstract: Waste polyurethane materials are made re-usable by converting them to liquid mixtures. Such liquid mixtures are made by reacting up to 70 parts by weight of polyurethane with a low-melting polyisocyanate at 100.degree. to 250.degree. C. in the presence of a catalyst. Suitable catalysts include the acid and neutral salts, phenolates, enolates and alcoholates of a metal of the 3rd, 4th or 5th Main Group or 1st, 2nd, 4th, 7th or 8th subgroup of the Periodic System of elements. The thus-produced mixtures contain isocyanates and are suitable as an isocyanate component in the production of polyurethane plastic materials.