Action of Alkali on Some-Substituted P-Nitrobenzyl Thioethers.

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Helmi Ishag, Nassim
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The following series of-substituted p-nitrobenzyl thioethers of the general formula: Z = CH2CO2H, –CH2-CH2-CO2H or –C(Me)2CO2H Series I: X = Me or Et and X' = H Series II: X = Me and X' = SZ Series III: X = X = Me The action of 5% NaOH solution on these compounds was investigated. I. When X =Me or Et and X=H : These compounds underwent carbanioon-sulphenium fission and the carbanion formed, rearranged to the azoxy carbonyl system.The sulphur atom in these compounds has become deficient in electrons due to the electromeric displacement,through the conjugated system,towards the powerful electron attractive nitro groub,thus leading to nucleophilic attack by OH¯ on the sulphur atom, with subsequent C–S fission. In all cases where X = Et, the p-azoxypropiophenone was obtained, except when Z = CH2–CO2H, When the azoxy compound originally formed was partly redused by the sulphide ion resulting from the decomposition of sulphenoacetic acid formed, giving a mixture of p-azo and p-azoxyacetophenone. All the thioethers in this series contain only one hydrogen atom in the benzyl -position and it seems that the presence of this –hydrogen atom is important for the formation of the azoxy carbonyl system. This view is supported by the fact that no azoxy compound was obtained as a result of action of alkali, when both X and X' are either phenyl or methyl. II. when X = Me and X' = SZ: Here no hydrogen atom in the –benzyl position is present . When Z = –CH2–CO2H: The relay of electromeric displacement towards the nitro group under the influence of alkali was one C–SZ fission and the resulting (–methyl–p–nitrobenzylthio) acetic acid, which now contains an -hydrogen atom gave as before p-azoxyacetophenone,which was partly reduced by sulphide ion giving as a final product a mixture of p-azo and p–azoxyacetophenone. However, when Z = –CH2–CH2–CO2H, only a red brown acid was obtained indicating that no C-S fission has taken place probably due to the retarding influence of the increased length of the acid chain of Z. III . When X = X' = Me: When Z = –CH2–CH2–CO2H or -C(Me)2CO2H, the acid was almost completely recovered unchanged. The + I of the two Me groups together with the retarding factors in the acid chain Z, counterbalanced the labilising influence of NO2 group on the C-S bond and the sulphur atom remained rich with it`s electrons, thus preventing the approach of the OH¯ ion. But when Z = –CH2–CO2H, 25% of the acid was recovered unchanged and a product containing N and S was formed in a side reaction. The non-nitro thioethers corresponding to series I and III were recovered unchanged under the same conditions. p-Azoxyacetophenone and p-azoacetophenone which are not clearly described in the literature , have been prepared in pure state and identified for the first time
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Action of Alkali on Some-Substituted P-Nitrobenzyl Thioethers. Author: Helmi Ishag Nassim, Action of Alkali, Some-Substituted, P-Nitrobenzyl Thioethers