Could you give some hints on how to prepare toluene diisocyanate?
The large-scale industrial process starts out from the phosgenisation of amines. First of all, carbamic acid chlorides are formed via various intermideate stages, together with substituted urea derivatives. The amine component must be protected through salt formation. To carry out the reaction it is necessary to have exces phosgene.
Phosgenisation of the amine hydrochlorides occurs by passing in phosgene at elevated temperatures, accompanied by vigorous stirring. During this process, the amine salt goes into solution,hydrogen chloride being liberated. Fractional distillation then produces isocyanate mixtures which are then separated and purified by fairly complicated methods.
Preparation of Toluene Diisocyanate
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