Multistep process for the preparation of diisocyanates

Abstract

Provided is a process for preparing an organic diisocyanate of the formula: OCN—R—NCO (1), wherein R represents a bivalent hydrocarbon radical containing 3 to 20 carbon atoms, the carbon atoms being arranged in a way that the two nitrogen atoms are separated from each other by at least 3 carbon atoms, the process comprising, Step (I) preparing a diurethane of the formula wherein R is the same as in formula (1), R' and R″ independently represent organic radicals selected from the group consisting of 4 to 36 carbon atoms, 4 to 74 hydrogen atoms, 0 to 12 oxygen atoms that have the oxidation state −2, and 0 to 1 halogen atoms from a diarylurethane of the formula, wherein R is the same as in formula (1), Ar and Ar′ independently represent a substituted or unsubstituted aryl or heteroaryl radical selected from the group containing a total of 4 to 20 carbon atoms by transesterification, Step (II) subjecting the diurethane of the formula (2) to a cleavage reaction to form the hydroxy compounds R′—OH and R″—OH and the organic diisocyanate of the formula (1), Step (III) separating the diisocyanate of the formula (1) from the hydroxy compounds R′—OH and R″—OH by distillation, wherein the hydroxy compounds R′—OH and R″—OH have higher standard boiling points than the standard boiling point of the diisocyanate OCN—R—NCO and the sum of the molecular weights of the radicals Ar and Ar′ is lower than the sum of the molecular weights of the radicals R′ and R″.