- Electrophilic Aromatic Substitution. Part 25. The Nitration in Aqueous Sulphuric Acid of Some Cinnamic Acids and Other Styrene Derivatives
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The rates of nitration of ethyl cinnamate, cinnamic acid, β-nitrostyrene, and trimethyl(styryl)ammonium ion in sulphuric acid of a range of concentrations have been determined.The nitrovinyl and the trimethyl(vinyl)-ammonium groups deactivate the aromatic nucleus by factors of ca. 330 and 60, respectively.The yields of products from ethyl cinnamate and β-nitrostyrene, nitrated over a range of sulphuric acid concentrations, are reported.With ethyl cinnamate the o:p ratio falls with increasing acidity.The acidity dependences of the rates of reaction of ethyl-4-nitrocinnamate, 4-nitrocinnamic acid, ethyl 3-nitrocinnamate, and 3-nitrocinnamic acid with nitric acid in sulphuric acid show the primary reaction in each case to be attack by the nitronium ion (at the β-carbon atom).The reactions are completed by addition, giving nitroalcohols.A similar but much slower reaction occurs with β,4-dinitrostyrene.In every case the nitroalcohol decomposes in concentrated sulphuric acid to give the nitrobenzaldehyde.With absolute nitric acid, ethyl 4-nitrocinnamate gives the side-chain nitro-nitrate by formal syn-addition.Addition of nitromethane to the reaction solution leads to addition in both stereochemical modes.The nitro-nitrate gives the nitro-alcohol in sulphuric acid, but in aqueous media gives ethyl α-nitro-β-(4-nitrophenyl)acrylates.These apparent side-chain nitrations are thus addition-elimination reactions, as suggested by van der Lee.Similar processes have been detected in the cases of 4-nitrocinnamic acid and β,4-dinitrostyrene.
- Moodie, Roy B.,Schofield, Kenneth,Taylor, Peter G.,Baillie, Philip J.
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p. 842 - 847
(2007/10/02)
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