| 摘要 |
Aromatic isocyanates are prepared by feeding an aromatic primary monoamine into a mixture of an inert organic liquid diluent and excess phosgene. The temperature of the liquid is kept below that of the decomposition temperature of the aromatic carbamyl chloride, so formed, until all the amine has been added, when the temperature is gradually increased in order to decompose the carbamyl chloride. The reflux of phosgene is continued throughout the process. Preferably the aromatic primary amine is a phenyl primary monoamine such as aniline, p-chloroaniline, 3,4-dichloroaniline, m-chloroaniline, p - methylaniline, 3 - chloro - 4 - methylaniline, alpha - naphthylamine, beta - naphthylamine, 3,5-dichloro - 4 - methylaniline, p-bromoaniline, 3-chloro-4-isopropylaniline, 3-chloro-4-ethylaniline. The inert organic liquid used should preferably boil above 75 DEG C. and be a solvent for both the amine and the phosgene reactants. Examples are benzene, toluene, xylene, tetrahydronaphthalene, mono-chlorobenzene, ortho-dichlorobenzene, anisole, nitrobenzene and 1,4-dioxane. Preferably the proportions of phosgene and inert liquid diluent should be such that the phosgene boils between 20 DEG and 45 DEG C. A phosgene reflux is maintained either by gradually increasing the temperature or by adding additional phosgene, without letting the temperature rise above the decomposition point of the carbamyl chloride. During the amine addition the temperature may be kept between 20 DEG and 70 DEG C. The temperature is then slowly increased to that of the boiling-point of the organic diluent, but not above 150 DEG C. The mixed phosgene and hydrogen chloride vapours leaving the reaction zone are passed into a reflux condenser, the phosgene returning to the reaction zone and the hydrogen chloride passing through uncondensed. At least 1.05 mols. of phosgene per mol. of amine reactant should be used. Catalysts such as dimethylaniline, or tetramethylurea may be used. Examples are given for the preparation of p-chlorophenyl isocyanate, and 3,4-dichlorophenyl isocyanate. Specification 372,355, [Group IV], is referred to. |
