A practical phosgenation procedure has been devised for the preparation of isocyanates labeled with 14C, Three such isocyanates : I-tolyl isocyanaie, 4-tolyl isocyanate, and 2,4-tolylene diisocyanate (TDI) were prepared. The 14C distribution in the latter was determined by scintillation counting of some o j its derivatives, one of which was 3-amino-4,2',6'-trimethylcarbanilide, from which the ,fraction of IgC in the 4-isocyanate group of T D I was obtained.
INTRODUCTION.
Poly(urethanes) prepared from poly(propy1ene oxide) and 2,440lylene diisocyanate [I] labeled with 14C in the isocyanate groups have been used in the study of polymer degradation mechanisms'l). Because of the high sensitivity of radioactivity measurements, very small extents of bond scission can be detected, and specific reactions can easily be followed during the course of the degradative process. The labeled diisocyanate [l] can be readily prebared from 2,Ctolylene diamine or its dihydrochloride and 14C enriched phosgene. However, the distribution of I4C in the 2-and 4 . positions depends upon the kinetics and mechanism of diisocyanate formation including accompanying isotope effects. It also depends to a large extent on the particular set of experimental conditions employed for the preparation. Procedures for the syntheses of labeled 2,4-tolylene diisocyanate, 2-tolyl isocyanate, and 4-tolyl isocyanate *