A spectroscopic study of the reversible reactions of aromatic nitrocompounds with sulphur bases

Abstract

The reversible reactions of 1,3,5-trinitrobenzene with sodium thioethoxide and thiophenoxide have been investigated in methanol and in methanol–dimethyl sulphoxide mixtures. At low concentrations of base, 1:1 adducts are formed by covalent addition of base at a ring carbon carrying hydrogen. With sodium thioethoxide a 1:2 adduct is also formed at higher base concentrations. The equilibrium constants for formation of the adducts in methanol have been determined and are compared with the values for oxygen bases. These values, which give a measure of the thermodynamic affinities (carbon basicities) of the bases for aromatic carbon, decrease in the order SEt^– > OMe^– > SPh^– > OPh^–. The effect of changing the solvent to dimethyl sulphoxide on these equilibria is examined. Measurements with nitroanilines indicates that, relative to sodium methoxide, the sulphur bases have a greater tendency to form covalently bound addition products rather than abstract an amine proton.