Title: THE ADDITION OF THIOLS TO ACETYLENIC COMPOUNDS III. THE ADDITION OF THIOPHENOL TO β-ALKYLPHENYLACETYLENES
Abstract: Under the initiation of benzoyl peroxide or ultraviolet light, thiophenol added smoothly to 1-phenylpropyne-1 and to 1-phenylbutyne-1. When equimolecular ratio of the reactants was used, the addition products were 1-phenyl-2-phenylthiopropene-1(Ⅰ)and 1-phenyl-2-phenylthiobutene-1 (Ⅱ), respectively. When the amount of thiophenol used was doubled, there were obtained, besides the one-to-one adducts named, two-to-one adducts; 1-phenyl-2,2-di-(phenylthio)-propane (Ⅴ) and l-phenyl-2,2-di-(phenylthio)-butane (Ⅵ), respectively. The structure of these adducts was proved through the reaction with 2,4-dinitrophenylhydrazine in acidic medium, yielding the 2,4-dinitrophenyl-hydrazone of the corresponding ketone. The addition reaction takes place by a free radical mechanism; the fact that phenylthiyl radical is linked to the carbon adjacent to the alkyl group indicates that the stability of the intermediate radical is the determining factor in the direction of addition, since the conjugative effect of the phenyl group is greater than that of the alkyl groups.Results of competitive experiments showed that phenylacetylene exhibited a greater reactivity towards the phenylthiyl radical than 1-phenylpropyne-1. This can be ascribed to the steric effect of the β-methyl group. When competitive experiment was conducted with 1-phenylpropyne-1 and styrene, only the adduct of the former was obtained. This indicates that the reactivity of an acetylene towards the phenylthiyl radical is much greater than that of the corresponding olefin. The results can be explained by the fact that the energy required to break one π-bond in an acetylene is less than that required to break the π-bond in an olefin.
Publication Year: 1964
Publication Date: 1964-01-01
Language: en
Type: article
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