THE MECHANISM OF THE ISOMERIZATION OF ORGANOSILICON CYANATES TO ISOCYANATES

Isomerization of the cyanate (Me(3)Si)(3)CSi(CD3)(2)OCN in the molten state at 150 degrees C gives the unrearranged isocyanate (Me(3)Si)(3)C Si(CD3)(2)NCO and the rearranged isocyanate (Me(3)Si)(2)[(CD3)(2)MeSi] CSiMe(2)NCO in a ratio of ca. 75/25, and isomerization in solution in Ph(2)O at 220 degrees C gives the same products in a ratio of ca. 85/1 5. The occurrence of a significant amount of rearrangement is consiste nt with a mechanism involving initial ionization of the cyanate. In co ntrast, no rearrangement accompanies the isomerization in CCl4 catalyz ed by ICI, indicating that ionization is not involved; this conclusion is supported by the observation that the isomerization of (Me(3)Si)(2 )(PhMe(2)Si)CSiMe(2)OCN, in which the Ph group would provide anchimeri c assistance to ionization, proceeds at a similar rate to that of (Me( 3)Si)(3)CSiMe(2)OCN.