Schiff test

In the currently accepted mechanism, the pararosaniline and bisulfite combine to yield the "decolorized" adduct with sulfonation at the central carbon as described and shown.

Such an imine-mediated mechanism was first proposed by Paul Rumpf (1908–1999) in 1935,[5] and experimental evidence was provided by Hardonk and van Duijn in 1964.

[6] In 1980, Robins, Abrams and Pincock provided substantial NMR evidence for the mechanism, leading to its general acceptance.

[9] The mechanism was proposed in 1921 by the eminent German organic chemist Heinrich Wieland and his student Georg Scheuing (1895–1949).

[10][11] Bisulphite was believed to react with the available aromatic amine functional groups to form N-sulfinic acid groups, Ar-NH-SO2H, followed by reaction with aldehyde to form sulfonamides, Ar-NH-SO2CH(OH)-R. The 1980 NMR data that allowed visualization of intermediates does not support this mechanism or the sulfonamides as the chromogenic product.