Nitrative Cleavage of 2, 2'-Dihydroxy-3, 3'-dimethyl 5, 5'-methylenedibenzoic Acid

Abstract

Reactions of the title compound [1] with nitric acid (d=1.38) have been investigated in chloroform, carbon tetrachloride, nitromethane, methanol, and acetic acid. In every case, [1] underwent facile nitrative cleavage and nitrodecarboxylation to yield 2-hydroxy-3-methy1-5- nitrobenzoic acid [2] as the major isolable product. Other products obtained include 4, 4'- dihydroxy-3, 3'-dimethyl-5, 5'-dinitrodiphenylmethane [3], 4-hydroxy-3-methyl-5-nitrobenzyl nitrate [4], and 4, 6-dinitro-o-cresol [5].
Substantial amounts of [3] were formed in the reactions in acetic acid. In addition to these, 4-hydroxy-3-methy1-5-nitrobenzyl methyl ether [7] and 4-hydroxy-3-methyl-5-nitrobenzyl acetate [8] were obtained from the reactions in methanol and acetic acid, respectively. These benzylic compounds probably arose from the solvolysis of the initial product [4].
With increase in the amount of nitric acid, formation of [5] and unidentified carbonyl compounds became prominent. Further addition of nitiric acid upon C 3 3 in chloroform led to similar cleavage, giving [4], [5], and 4-hydroxy-3-methyl-5-nitrobenzaldehyde [9]. By heating in acetic acid under, gentle reflux, [4] was readily converted into a mixture of [5] and [8]. Possible pathway from [1] to [2] has been suggested.