Acidity of new exhaustively substituted p-nitrosophenols

Abstract

SHORT COMMUNICATIONSA number of exhaustively substituted p-nitrosophenols I having ester groups in the ortho positions with respect to the hydroxy group were reported in [1].Ia, 5.33 ± 0.01; Ib, 5.35 ± 0.04; Ic, 5.35 ± 0.03; Id, 5.38 ± 0.04; Ie, 5.58 ± 0.03; If, 5.42 ± 0.03; Ig, 5.64 ± 0.06.These data show that the acidity constant almost does not depend on the alkyl group in the ester fragments of exhaustively substituted p-nitrosophenols. We can only note some tendency of pK a to increase with increase in the size of the alkyl group. REFERENCES 1. Belyaev, E.Yu., Tovbis, M.S., and El'tsov, A.V., Zh. Org. Khim., 1978Khim., , vol. 14, p. 2375 ISSN 1070-4280, Russian Journal of Organic Chemistry, 2011, Vol. 47, No. 9, p. 1432. © Pleiades Publishing, Ltd., 2011. Original Russian Text © D.G. Slashchinin, A.A. Kukushkin, M.S. Tovbis, 2011, published in Zhurnal Organicheskoi Khimii, 2011, Vol. 47, No. 9, p. 1406 DOI: 10.1134/S1070428011090296We recently showed by the X-ray powder diffraction method that these compounds, unlike all known nitrosophenols, exist as dimers like azodioxides [2]. Hydrogenation of such polysubstituted nitrosophenols makes it possible to readily obtain the corresponding exhaustively substituted aminophenols [3] which are used in the synthesis of modern antiarrhythmic agents [4]. On the other hand, the acidity of compounds I was not studied. Only the acidity constant of diethyl 2-hydroxy-4,6-dimethyl-5-nitrosobenzene-1,3-dicarboxylate (Ib) was reported (pK a 5.35 ± 0.04) [5].We now report on the acidity of a series nitrosophenols Ia-Ig and its relation to the nature of alkyl group in the ester moieties. The acidity constants were determined by spectrophotometry [6] at 25.0 ± 0.1°C using citrate buffer [7]. The pK a values are as follows: