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Organic Lab Reactions 108


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MONOSUBSTITUTED BENZALDEHYDES 103 the aldol condensation, followed by the condensation of formaldehyde with the acetaldehyde so formed (p. 101). OH" HCHO CH 3 CH=CHCHO + H 2 O ^—^ 2CH3CHO > C(CH 2 OH) 4 Aldehydes containing the grouping —C=C CHO do not undergo dis- mutation when treated with alkali but are cleaved readily to yield the corresponding acetylene and formic acid. Propiolaldehyde and phenyl- and methyl-propiolaldehydes are cleaved smoothly in the following way. 68 NaOH -> RO^CH + HCO 2 Na (R=H, CH 3 , C 6 H S ) Aromatic Aldehydes The formation of benzoic acid when benzaldehyde is treated with aqueous alkali was first observed by Liebig and Wohler. 69 Some years later Cannizzaro 60 recognized that benzyl alcohol is formed also. Later studies have shown that aromatic aldehydes which are not diortho- substituted generally react smoothly to give the corresponding snyl carbinols and aromatic acids in good yields. The usefulness of the reac- tion, which in the past has been employed largely as a route to the
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