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.In investigation of the lrinetics of the protodeboronation of benzeileboronic acid in water in the pH range 2.0 to 6.7 is described. In addition to the acid-catalyzed reaction studied earlier a reaction whose rate is independent of pH and one whose rate increases linearly with hydroxide ion concentration have been observed. The effect of malonate buffer concentration a t low pH confirms the earlier observations of general acid catalysis. Changes in buffer concentration a t pH 6.70 have no effect on rate indicating specific hydroxide ion catalysis. Effect of substituents in the ortho, meta, and para position of the benzene ring on the rate of protodeboronation have been examined. Ortho-para ratios for this reaction are high; possible reasons for this are discussed. The Hainmett equation using u correlates the rates for meta and para substituents.Among the reactions of areneboronic acids in which the dihydroxyboron group is subjected to electrophilic displacement the simple hydrolysis or protodeboronation (eq. [I]) is particularly interesting. Ainley and Challenger (1)showed that the hydrolysis of boronic acid proceeds in water a t 150°, and is catalyzed by concentrated sodium hydroxide, concentrated hydrochloric acid, as well as zinc and cadinium bromides. An~moniacal silver nitrate has been shown t o be an effective catalyst for the protodeboronation of benzeneboronic acid and others of the arene series (2, 3, 4). An understanding of the mechanisms by which these catalysts function would be desirable, and we have embarked upon a series of kinetic investigations toward this end.A fairly extensive and detailed study of the kinetics of acid-catalyzed protodeboronation has been described (5,6,7). Observation of the variation of rate constants in several acidic media, and in deuterium, as well as protium, solvents, along with determination of substituent effects led to the conclusion that the reaction is an electrophilic displacement in which the rate-determining step is the transfer of a proton from an acid t o the boronic acid. In view of this an examination of the same reaction catalyzed by base was in order, especially because the strongest electrophile which might be present in significant concentration in aqueous base might well be water. The possibility that a SE1 type of reaction (eqs. 12-41) might be involved also provided some attraction.

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Organotin hydrides are useful intermediates for reduction of organic compounds such as halides, aldehydes, ketones, isocyanates, and isothiocyanates. They also find use for synthesis of other organotin compounds because they add to carbon-carbon double and triple bonds. Certain of these reactions can proceed by free-radical mechanisms in which organic radicals are intermediates. Hydrogen atom transfer from organotin hydrides to these radicals is a very fast process (k N 104-10G M-' sec-l). As a result, it has been possible to trap initially formed radicals before they undergo secondary reactions. Examples discussed involve cyclooct-4-enyl, w-alkenyl, bicycloheptenyl, tritylmethyl, and 0-haloalkoxy radicals, as well as l-naphthaldehyde triplet states.