PHOTODECARBOXYLATION OF NITROPHENYLACETATE IONS

These studies characterize the primary process and products in the photodecarboxylation of nitrophenylacetate ions in aqueous solutions. 3-Nitrophenylacetate, 4-nitrophenylacetate, and 4-nitrohomophthalate ions decarboxylate with a quantum yield of about 0.6 at 367 nm, while that of o-nitro structures (2-nitrophenylacetate and 2,4-dinitrophenylacetate ions) is only 0.04. aci-Nitro intermediates are identified spectrally by flash photolyses from the o- and p-nitro structures, but not from the m-nitro structure. Results are consistent with a mechanism of photodecomposition into carbon dioxide and a nitrobenzyl anion which is stabilized as an aci-nitro anion in o- and p-nitro structures. The nitrophenylacetic acids are more stable photochemically than their ions; neither CO2 nor aci-nitro intermediates are observed from photolysis of the undissociated acids. The aci-nitro yield varies with pH according to the pK- of the acid being photolyzed; thus a pA of 4.8 is calculated for the α-carboxyl gr up of 4-nitrohomophthalic acid. Three of the aci-nitro anions occur via photochemical hydrogen-transfer reactions from other compounds so that by comparison with the photodecarboxylations the quantum yields of H-transfer photochromism in 2-nitrotoluene, 2,4-dinitrotoluene, and 5-nitro-o-toluate ions are estimated to be about 0.01, 0.003, and 0.07, respectively. © 1969, American Chemical Society. All rights reserved.