Abstract: Technically pure 2,4-diisocyanatotoluene or an isomer mixture having an increased 2,4-diisocyanatotoluene content is obtained from an isomer mixture of 2,4- and 2,6-diisocyanatotoluene. The 2,4- and 2,6-diisocyanatotoluene mixture is first cooled to a temperature of from 4.degree. to 9.degree. C. and further cooled to between -2.degree. to -6.degree. C. at a rate of 0.5.degree. to 3.degree. C. per hour. The temperature of the mixture is maintained at that temperature for at least 30 minutes. Any liquid present is removed and the solid remaining is then melted. Melting is preferably carried out by heating the solid at a rate of 0.5.degree. to 3.degree. C. per hour until the remaining solid has a 2,4-diisocyanatotoluene content of at least 98%. The liquid melt is removed and the solid having the desired 2,4-diisocyanatotoluene content is then melted.

Abstract: A process for pre-phosgenating organic primary amines is provided wherein a phosgene solution and an amine solution are combined in the suction side of a multiple stage rotary pump.