The Influence of Different Solvents on 2-Ammonio-4-chloro-5-methylbenzenesulfonate, Including Its De- and Resulfonation

Abstract

The title compound (2-ammonio-4-chloro-5-methylbenzenesulfonate), C7H8ClNO3S, 1, is an intermediate in the synthesis of laked red and yellow azo pigments. Heating 1 in 2-picoline, quinoline and N,N′-dimethylacetamide (DMAc) [or N-methyl-2-pyrrolidone (NMP)] resulted in the formation of three different compounds: a 2-picolinium hydrate (2), a quinolinium quinoline solvate (3), and a sulfate of the desulfonated title compound (4). The three new compounds were structurally characterised using single-crystal diffraction data and chemically using thermal analysis (DTA/TGA), elemental analysis and spectroscopic methods (IR and NMR). By heating 2, 3 and 4 in the solid state, compound 1 is obtained again. In the case of 4, this corresponds to a desulfonation-resulfonation reaction in subsequent steps, which is rarely observed as such. The title compound 2-ammonio-4-chloro-5-methylbenzenesulfonate was heated in 2-picoline, quinoline and N,N′-dimethylacetamide (DMAc) resulting in the formation of three different compounds: a 2-picolinium hydrate (2), a quinolinium quinoline solvate (3), and a sulfate of the desulfonated title compound (4 see Figure). Heating 2, 3 and 4 in the solid state, compound 1 is obtained again. In the case of 4, this corresponds to a desulfonation-resulfonation reaction in subsequent steps, which is rarely observed as such.