Silicon tetraisothiocyanate

Finely powdered ammonium thiocyanate (190 g. 2.5 mols 25% theoretical excess) is mixed with 800 ml. of anhydrous sodium-dried benzene contained in a 2-1. threenecked standard-taper flask fitted with a motor-driven stirrer, a thermometer, a 125-ml. dropping funnel, and a 

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Silicon tetraisothiocyanate reaction with 2,6-dimethylamhne to yield 2,6 dimethylphenyl thiourea, 46, 70... 

Silicon tetraisothiocyanate (26.0 g., 0.10 mole) (Note 10) is finely ground under 100 ml. of anhydrous benzene, and the mixture is quickly transferred to a 1-1. round-bottomed flask. The mortar and pestle are washed with two 25-ml. portions of anhydrous benzene, and the washings are added to the flask. A solution of 2,6-dimethylaniline (48.5 g., 0.4 mole) (Note 1) in 100 ml. of anhydrous benzene is added to the well-stirred mixture. The reaction is mildly exothermic. The mixture is heated at the reflux temperature for 30 minutes, and the benzene is then removed using a rotary evaporator. Dilute isopropyl alcohol (200 ml.) (Note 5) is added to the residue, and the resulting mixture is heated at the reflux temperature for 30 minutes. The mixture is then processed in exactly the same manner as described above for the preparation of cyclohexylurea. The crude 2,6-dimethylphenylthiourea (m.p. 193-197°, 71.3 g., 99% yield) is recrystallized from 280 ml. of isopropyl alcohol (Note 8) to give 50 g. (72%) of product, m.p. 201-202°. Concentration of the mother liquor affords 11 g. (15%) of less pure product, m.p, 197-199° (Note 11). 

Dipolar cycloadditions with 3-phenylsydnone, 46, 98 N,N-Disubstituted thioureas from secondary amines and silicon tetraisothiocyanate, 46, 69 N,N-Disubstituted ureas from secondary amines and silicon tetraiso-cyanate, 45, 69... 

Silicon tetraisothiocyanate is prepared from silicon tetrachloride and silver thiocyanate or, preferably, ammonium thiocyanate. The silicon tetraisothiocyanate used by the checkers was slightly yellow however, this did not affect the yield of product. 

Dimethylaniline, reaction with silicon tetraisothiocyanate to yield... 

Silicon tetraisothiocyanate and methylsilicon isothiocyanates (includes silver thiocyanate), synthesis 7... 

Silicon tetraisothiocyanate was first prepared by Miquel and Reynolds by treating silicon(IV) chloride with lead thiocyanate. Later, Forbes and Anderson prepared many substituted silicon isothiocyanates by metathetical reaction of the corresponding chlorosilanes with silver thiocyanate. On the bases of molecular refraction studies, the latter workers concluded that the silane derivatives are isothiocyanates rather than the isomeric thiocyanates. Conclusive proof that these compounds are isothiocyanates is their formation in good yield from isocyanosilanes and sulfur ... 

When silver thiocyanate is employed in the above preparation, the resulting silicon tetraisothiocyanate is yellow. Silicon tetraisothiocyanate freshly prepared from ammonium thiocyanate is colorless, although on standing for several days the product assumes a pale yellow color. 

When freshly prepared from ammonium thiocyanate, silicon tetraisothiocyanate is a stable colorless crystalline solid which melts at 143.8° and boils at 313°. It is soluble in chloroform, carbon tetrachloride, acetone, benzene, and petroleum naphtha. 

Silicon tetraisothiocyanate is rapidly hydrolyzed to gelatinous silica and thiocyanic acid on exposure to moist air or water. With primary or secondary aliphatic or aromatic amines, silicon tetraisothiocyanate reacts to produce N-mono- or iV,iV-disubstituted thioureas, respectively, in essentially 100% yields. ... 

In chemical reactions and physical properties the methylsilicon isothiocyanates are very similar to silicon tetraisothiocyanate. Methylsilicon triisothiocyanate and dimethylsilicon diisothiocyanate are colorless solids at room temperature, whereas trimethylsilicon isothiocyanate is a colorless liquid. All possess pungent odors and are lacrimators. The melting and boiling points are respectively methylsilicon triisothiocyanate, 72.4°, 266.8° dimethylsilicon diisothiocyanate, 18.0°, 217.3° trimethylsilicon isothiocyanate, — 32.8°, 143.1°. 

Like silicon tetraisothiocyanate, methylsilicon triisothiocyanate turns pale yellow on standing. 

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