Process for the preparation of .beta.-halogeno-tert.-alkyl isocyanates

#The invention relates to a new process for the preparation of known .beta.-halogeno-tert.-alkyl isocyanates, which can be used as intermediates for the synthesis of rubber additives or of biologically active compounds, such as for example herbicides (cf. e.g. EP-A 294 666).

#It is already known that .beta.-monochloro-tert.-alkyl isocyanates are obtained when .beta.-hydroxy-tert.-alkylamines are first hydrochlorinated using thionyl chloride and then the corresponding chloro-amine-hydrochloride is converted to the isocyanate using phosgene (cf. DE-OS (German Published Specification) 2 045 906).

#The poor yields of the chlorinated tert.-alkyl isocyanates are a disadvantage of this process.

#812 g of tert.-butyl isocyanate are initially introduced, and are chlorinated with stirring by direct introduction of undiluted chlorine at 85.degree. to 100.degree. C. under irradiation by a (water-cooled) high-pressure Hg vapour immersion lamp. Samples are taken and the course of chlorination is followed by gas chromatography (GC). After a conversion of 95%, the reaction is terminated. 1225 g of crude product are obtained, which is fractionated on a 20 cm packed column (containing 3 mm glass Raschig rings).

#The composition of the chlorination mixture immediately after the end of chlorination is as follows (in % by area): ##STR7## The following are obtained: ##STR8##

#desired product