The Photochemistry of Aromatic Azo Compounds in Organic Solvents

Qualitative observations have been made on the photochemistry of azobenzene and 4–amino–4–nitroazobenzene solutions in isopropyl alcohol and isooctane in the presence of various amounts of oxygen. The fading reaction consists in the addition of hydrogen, extracted from the solvent, to the azo linkage to form a substituted hydrazine and later substituted anilines. In the presence of oxygen there is a photosensitised oxidation of the solvent. In iaopropyl alcohol as solvent the fading of the dye is completely inhibited by one atmosphere of oxygen, but after exhaustion of the oxygen the dye fades very rapidly. In the presence of a large excess of oxygen the dye eventually fades slowly. The rate of oxygen consumption increases during the exposure and continues to increase after complete destruction of the dye. In this case the oxidation products contain aliphatic acids and carbon dioxide in addition to acetone. The number of carbonyl groups produced is in excess of equivalence to the molecular oxygen consumed.