Silicon Tetraisocyanate

Finely powdered silver isocyanate (660 g. 4.4 mols 10% theoretical excess) is mixed with 800 ml. of anhydrous sodium-dried benzene contained in a 3-1. three-necked standard-taper flask fitted with a motor-driven stirrer, a thermometer, a 125-ml. dropping funnel, and a 300-mm. Allihn condenser topped by a Drierite-filled tube. Silicon-(IV) chloride (170 g. 1.0 mol) is added dropwise to the suspension over a 30- to 45-minute period with rapid stirring. The reaction is strongly exothermic, and the temperature of the mixture must be maintained below 45° by cooling the bottom of the flask, as necessary, in an ice-water bath. After the silicon (IV) chloride has been added, the mixture is heated at gentle reflux for 3 hours, with con- 

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Michael reaction, A1<9) octalone, 45, 82 N Mono- and N,N disubstitdted UREAS AND THIOUREAS 45, 69 N Monosubstituted thioureas from primary amines and silicon tetra-lsothiocyanate, 45, 69 N Monosubstituted ureas from primary amines and silicon tetraisocyan-ate, 46, 69... 

N-Monosubstituted ureas from primary amines and silicon tetraisocyan-ate, 45, 69... 

Silicon tetraisocyanate is prepared from silicon tetrachloride and silver cyanate or lead cyanate. ... 

Reaction of amines with silicon tetraisocyanate and silicon tetraiso-thiocyanate to give ureas and thioureas, respectively [101a, b]. 

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

Silicon tetraisocyanate and methylsilicon isocyanates, of the type (CH3) Si(NCO)4 (n = 1, 2, or 3), were first prepared in 75 to 90% yields by treating silicon(IV) chloride or the appropriate methylchlorosilane with silver isocyanate in anhydrous 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. 

A 10% excess of silver isocyanate or lead cyanate has repeatedly been found to give the highest yields of product. A 25% excess produces no greater yield. Stoichiometric amounts produce slightly lower yields. On the other hand, a 10% excess of silicon(lV) chloride results in only a 40% yield of silicon tetraisocyanate. ... 

When freshly prepared lead cyanate (642 g. 2.2 mols 10% theoretical excess) is employed in the above procedure instead of silver isocyanate, the reaction is only slightly exothermic. The silicon(IV) chloride can therefore be added at a fairly rapid rate after the reaction has been initiated by heating to 35 to 40". The mixture is then refluxed with vigorous stirring for 3 hours. After the benzene is distilled, the 3ueld of silicon tetraisocyanate is 121 g. [61.8% based on silicon(IV) chloride]. 

The preparation of silicon tetraisocyanate from finely powdered potassium cyanate gives only a 2% yield, in agreement with the observation of Forbes and Anderson. ... 

Methylsilicon triisocyanate and dimethysilicon diisocyanate can be prepared from the appropriate methyl-chlorosilane and a 10% theoretical excess of the inorganic cyanate with the same equipment and procedure as employed in the synthesis of silicon tetraisocyanate. With... 

Silicon tetraisocyanate is a stable white crystalline solid which melts at 26.0 0.5° and boils at 185.6 0.3°. It is soluble in benzene, chloroform, carbon tetrachloride, acetone, and petroleum naphtha. On exposure to moist air or water, it is rapidly hydrolyzed to gelatinous silica and cyanic acid. It reacts vigorously with most primary and secondary aliphatic and aromatic amines to produce, respectively, W-mono- or W,W-disubstituted ureas - and thus is useful in the synthesis of these classes of compounds. 

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°. 

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