D 1967 (OTTO) p-Dimethylaminocinnamaldehyde, GR 99%+ Cas 6203-18-5 - used in an acidic solution to detect indoles. D 1967 (OTTO) p-Dimethylaminocinnamaldehyde, GR 99%+ Cas 6203-18-5 - used as a reagent for detection of indole derivatives particularly the assay of tryptophanase and apotryptophanase.