US 6,486,346 B1Granted

Process for the preparation of durene diisocyanate

AssigneeBayer Aktiengesellschaft

InventorsPeter Heitkämper, Klaus Jost, Stefan Penninger

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Abstract

Durene diisocyanate is prepared by reacting durene with nitric acid in sulfuric acid, catalytic hydrogenation of the dinitrodurene that is formed, and phosgenation of the resultant durene diamine in a conventional manner. The intermediate products dinitrodurene and durene diamine do not have to be worked up in a complicated manner as solid products, but can be worked up in dissolved form. The intermediate products dinitrodurene and durene diamine do not have to be isolated and purified in a complicated manner. but can be processed directly after preparation. Another advantage of this process is that only a single organic solvent need be used for the overall preparation process. Separation and re-use of spent acid in the conversion of durene with nitric acid also renders the process of the present invention significantly less environmentally harmful than the known processes of the prior art.

Claims13

Dependent claims

A process for the production of 2,3,5,6-tetramethyl-1,4-diisocyanatobenzene comprising:

a) reacting 1,2,4,5-tetramethylbenzene with nitric acid in the presence of sulfuric acid to form 2,3,5,6-tetramethyl-1,4-dinitrobenzene,
b) diluting liquid reaction mixture from a) with water to form a suspension,
c) intensively mixing the suspension from b) with an aprotic organic solvent that is substantially immiscible with water and inert with respect to hydrogen to dissolve 2,3,5,6-tetramethyl dinitrobenzene present in the suspension and to form two liquid phases,
d) separating the liquid phases from c) to recover a solution of 2,3,5,6-tetramethyl dinitrobenzene in organic solvent,
e) hydrogenating the 2,3,5,6-tetramethyl-1,4-dinitrobenzene in the presence of a Raney catalyst, a palladium catalyst or a platinum catalyst to form 2,3,5,6-tetramethyl-1,4-diaminobenzene,
f) removing water and the Raney catalyst, palladium catalyst or platinum catalyst from the hydrogenated mixture to obtain a solution of 2,3,5,6-tetramethyl-1,4-diaminobenzene, and
g) phosgenating the 2,3,5,6-tetramethyl-1,4-diaminobenzene solution from f) to form 2,3,5,6-tetramethyl-1,4-diisocyanatobenzene.

4 more elements

Dependencies are inferred from the claim text.