Silicon Tetraisocyanate and Methylsilicon Isocyanates

Submitted bt Roy G. NEVii,i,B t and John J. McGee Checked by Constance WRioHTt and Earl L. McETTERTiEst 

Silicon tetraisocyanate and methylsilicon isocyanates, of the type (CH3) Si(NCO)4 n ( = 1, 2, or 3), were st prepared in 75 to 90% yields by treating silicon(IV) chloride or the appropriate methylchlorosilane with silver isocyanate in anhydirous benzene. Forbes and Anderson report that much smaller yields are obtained when lead cyanate is used instead of silver isocyanate. The following procedure, however, when performed with lead cyanate, produces 52 to 71% yields of the silicon isocyanates. Comments on the use of less expensive lead cyanate are therefore included along with the silver isocyanate method of preparation. 

Procedures for the corresponding thiocyanate compounds are described in synthesis 7. 

---

See also Silicon tetraisocyanate and methylsilicon isocyanates (includes silver isocyanate), synthesis 6... 

The methylsilicon isocyanates are very similar in chemical and physical properties to silicon tetraisocyanate. They are colorless liquids at room temperature, possess pungent odors, and are strong lacrimators. The melting and boiling points, respectively, are as follows trimethylsilicon isocyanate, —49.0 + 3°, 91.0 0.3° dimethylsilicon diisocyanate, —31.2 3°, 139.2 + 0.3° methylsilicon triisocyanate, —2.7 0.5°, 170.8 0.3°. 

---