Detection of Dyes possessing a p‐Phenylenediamine or a p‐Nitroaniline Structure by means of Spot Tests

Abstract

When Bandrowski's base and azo dyes containing a p‐phenylenediamine or a p‐nitroaniline structure are fused with a dry mixture of sodium formate and sodium hydroxide at 210–230°C. p‐phenylenediamine is formed by reductive cleavage. Under these conditions the diamine sublimes and the vapour reacts with an acetic‐acid solution of aniline and alkali‐metal persulphate to yield the indamine dye Phenylene Blue. This procedure may be conducted by the technique of spot test analysis and serves to detect such dyes. The detection limits are in the range 5–10 μg., as has been verified by testing thirteen pertinent compounds.