PROCESS FOR THE SEPARATION OF TECHNICALLY PURE 2,4-DIISOCYANOTOLUENE, OR OF MIXTURES OF ISOMERS HAVING AN INCREASED CONTENT OF 2,4-DIISOCYANOTOLUENE, FROM MIXTURES ESSENTIALLY CONSISTING OF 2,4- AND 2,6-DIISOCYANOTOLUENE

摘要

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 DEG to 9 DEG C. and further cooled to between -2 DEG to -6 DEG C. at a rate of 0.5 DEG to 3 DEG 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 DEG to 3 DEG 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.