Basf Aktiengesellschaft

Eckhardt Brandt

Franz Merger

Wolfgang Schwarz

Peter Magnussen

Andreas Otterbach

Otto Mattner

Roland Minges

Karl Gerhard Baur

Hans Volkmar Schwarz

Erwin Brunner

Hans V Schwarz

A process for preparing essentially pure 3-chlorophthalic anhydride from a mixture in which 3-chlorophthalic anhydride is present in addition to 4,5-dichlorophthalic anhydride, which involves first distilling off a mixture of 3-chlorophthalic anhydride and 4,5-dichlorophthalic anhydride, so that the obtained bottoms is essentially free of 4,5-dichlorophthalic anhydride, and then by distillation of the obtained bottoms, recovering 3-chlorophthalic anhydride in a second distillation step. The starting mixture is preferably prepared without solvent in a melt by incomplete chlorination of phthalic anhydride using FeCl.sub.3 as a catalyst.

Preparation of 3-chlorophthalic anhydride

In a reactor for the thermal cleavage of mono- and polyfunctional carbamic esters into the corresponding isocyanates and the hydroxyl component in the liquid phase, the geometry of the reactor, defined by the degassing area in relation to the volume and the arrangement of the heating surfaces, permits cleavage in a two-phase mixture which has a volumetric gas content of more than 50%.

Thermal cleavage of carbamic esters

A multistep process for the continuous preparation of organic polyisocyanates, preferably aliphatic or cycloaliphatic diisocyanates, by reacting the corresponding organic polyamines with carbonic acid derivatives and alcohols to give monomeric polyurethanes and pyrolyzing the latter involves separating the resultant polyisocyanates and worthless residues in certain reaction steps and recycling the reusable by-products into earlier steps.

Multistep, continuous preparation of organic polyisocyanates

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Schifferstadt, Germany

Eckhardt Brandt