Absolute rate constants for addition reactions of arylthiyl radicals (YC,H,S' ) to arylacetylenes (XC6H4C&H) have been determined by a flash-photolysis method. The rate constants (in dm3 mol-' s-')from 1 .O x lo5 (X = m-NO, and Y = p-MeO) t o 1 .O x lo7 (X = p -M e 0 and Y = p-Br). For all arylthiyl radicals, a Hammett plot of the (T+ -constants for the X-substituents yields negative p + (Y) values. The p'(Y) values depend also on the Y-substituents on the arylthiyl radicals [p'(Y) = -0.22 for Y = p -M e 0 and p'(Y) = -0.53 for Y = p-Br]. These p'(Y) values are slightly smaller than the p'(Y) values reported for the corresponding arenesulphonyl radicals, reflecting the low electrophilicity of the arylthiyl radicals. On the other hand, for each arylacetylene a Hammett plot of the rate constants for YC6H4S' vs. o'(Y) yields positive p'(X) values which increase with the increasing electron density on the triple bond.
The radical chain addition of tosyl iodide to some alkenes has been studied. The reaction was carried out at room temperature under visible light, giving the usual high yields of P-iodo sulfones. These adducts were transformed into the corresponding unsaturated sulfones. Relative reactivities of the addition of the tosyl radical to alkenes were measured in acetonitrile, dichloromethane and carbon tetrachloride, the effect of the solvent being important only with polarized alkenes, such as vinyl and allyl cyanides, which are stabilized in solvents with greater n* and AN parameters. The delocalization of the unpaired electron in the adduct radicals over the carbonyl and cyano groups is not important; the phenyl group is the only group that is able to affect the reactivity, increasing it notably. Polar and steric effects are dominant in all the other cases.
The addition of arenesulfonyl iodides (I), especially tosyl iodide (Ia), to phenylacetylenes (II) and styrenes (V) in MeOH, EtOH, or benzene is studied.
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