The spectrophotometric determination of indole-3-methanol in small samples with p-dimethylaminocinnamaldehyde on the basis of the formation of an azafulvenium salt.

Indole-3-methanol is coupled, at acidic pH, with p-dimethylaminocinnamaldehyde to give a highly colored azafulvenium salt. IR, 1H NMR, and mass spectroscopic evidence indicates that this azafulvenium salt is the 2-[3'-(p-dimethylaminophenyl)-2'-propenyliden]-3-hydroxymethyl-2H- indolenine hydrochloride. This reaction led us to elaborate a rapid colorimetric assay for quantitative determination of indole-3-methanol formed by peroxidases as the product of oxidation of the plant growth regulator indole-3-acetic acid.