Abstract: Aromatic polyisocyanates are prepared by reacting at least one compound (A), containing at least two primary amine functions and at least one aromatic nucleus, with a relatively modest quantity of phosgene, in the gaseous phase, the amount of phosgene ranging from the stoichiometric amount to a stoichiometric excess of 100% with respect to the number of moles of amine functions of compound (A), carried out in a mixed reactor which comprises a first, homogenizing zone constituting from 20% to 80% of the total volume thereof, and a second, essentially piston flow downstream zone constituting from 80% to 20% of the total volume thereof.

Abstract: Aromatic polyisocyanates, e.g., toluene diisocyanate, are prepared by reacting/contacting at least one aromatic compound (A) bearing at least two primary amine substituents, e.g., toluenediamine, xylylenediamine and/or phenylenediamine,, with phosgene, in gaseous phase and in a reactor/reaction zone devoid of active mechanical stirring.