The synthesis characterization of historical novel azo pigments: implications for conservation science

Abstract

A series of synthetic organic pigments (SOP’s) with azo-containing linkages have been synthesized and characterized by Fourier transform infrared (FTIR) and Raman spectroscopies and laser desorption ionization mass spectrometry (LDI-MS). These pigments include representatives of the chemical classes arylide (Hansa) yellow, diarylide yellow and oranges, and Naphthol AS. Certain of these (PR7, PR10, PR11, PR18, PR19, PO14, PO15, PO16, PY49, PY98, PY106, PY113, PY124, PY203) are historical pigments, that is they were manufactured but subsequently were removed from production. Of these, some have been brought back into limited production. In addition to the above-mentioned pigments, 18 products of azo-linkage reactions formed between N,N′-bis(acetoacetyl)-o-toluidine and substituted anilines have been synthesized and characterized by the methods listed above as well as by visible reflectance spectroscopy. While not commercially available azo pigments, these colorants will serve as model systems to study substituent effects on pigment color.