| Summary: | Reviews are given of the literature on the cleavage of aryl-silicon end -germanium bonds; of the reactions of organosilicon compounds with aluminium chloride, with sulphuric acid, and with sulphur trioxide; of sulphonation of aromatic compounds; of the Friedel-Crafts reaction; and of the reaction of triphenylmethyl chloride, and of phosphorus trichloride, with aromatic systems. Sulphur trioxide has been found to react rapidly with aryl-silicon and -germanium compounds to give silyl (germyl) esters of the arylsulphonic acids, which are easily hydrolysed to the sulphonic acids. Where two silyl (germyl) groups are present in the original compound only one is replaced in this sulpho-desilylation (-germylation) reaction to give the first examples of compounds having "both a sulpho and a silyl (germyl) group bonded directly to the nucleus. Acyl halides react readily with arylsilicon compounds in the presence of aluminium chloride, replacing the silyl group by the acyl group. Friedel-Crafts acylation (with retention of the silyl group) can occur if a position in the ring, other than that carrying the silyl group, is strongly activated. If two silyl groups are present one, or both, may be replaced by varying the reaction conditione. With an alkyl halide In place of the acyl chloride both of the silyl groups are replaced. Triphenylmethyl chloride will not react with arylsilicon compounds, unless the aryl-silicon bond is very strongly activated. The silyl group can be replaced by a dichlorophosphino group by the reaction of an arylsilicon compound with phosphorus trichloride and aluminium chloride. If, however, two silyl groups are present a polymeric material is obtained. These desilylation reactions provide means of introducing sulpho, acyl, alkyl, or phosphino groups at known positions in aromatic systems. By these means a number of compounds have been synthesized, including fifty-four new organo-silicon and -germanium compounds. Possible mechanisms are suggested for these reactions after a brief discussion of the mechanisms of proto-, bromo-, and nitro-desilylation.
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