Aromatic nitrodesilylation.

Reviews are given of the cleavage of the aryl-silicon bond by electrophilic reagents and of aromatic nitration by reagents other than nitric acid or nitric acid - sulphuric acid mixtures. The mechanism of nitrodesilylation has been studied, using p-tolyltrimethylsilane as the representative compound. With nitric acid - acetic anhydride - acetic acid the ratio of nitrodesilylation to nitration is decreased by increasing the concentration of nitric acid, is increased by the addition of a small quantity of sulphuric acid (the rate of the reaction is increased), and is not altered by the addition of nitrate ion (the rate of the reaction is decreased markedly). Similar alterations of reaction rate and ratio of desilylation to nitration occur when dinitrogen pentoxide - acetic anhydride - acetic acid is used as the nitrating mixture, except that the addition of sulphuric acid does not alter the ratio. It is suggested that with these reagents the nitronium ion and to some extent the dinitrogen pentoxide molecule are the effective agents in the nitration process, and that desilylation proceeds via a multi-centre mechanism in which dinitrogen pentoxide is the attacking entity. No cleavage of the aryl-silicon bond occurs when nitronium tetrafluoroborate is used as the nitrating agent. Limits to the use of nitrodesilylation as a preparative technigue are discussed. The preparation of forty three new organic and organo- silicon compounds is described. It has been shown that the addition of C13SIH to m- or p-C1:C6H4.(CH2)2CH=CH2 gives m- or p-Cl.C6h4. (CH2)4SiCl2 and m- or p-Cl.C6H4.CH(SiC13)CH2- CH2CH3. The mechanism of these addition reactions is discussed. A study has been made of the protodesilylation of the compounds o-, m-, and p-Me2Si.C6H4. (CH2)nSiMe3 (where n = 1 to 4). The rates of cleavage for the ortho and para compounds fall in the order (n =) 1> 2> 4> 3, whereas for the meta compounds the order is (n=) 1> 3> 2> 4. These results are discussed, together with those of Chernyshev et al. for the competitive nitration of the compounds C6H5. (CH2)nSiMe3 (where n = 1 to 4)