Waste-free solid-state organic syntheses: Solvent-free alkylation, heterocyclization, and azo-coupling reactions

Solid-state techniques allow for waste-free quantitative syntheses. The solid-solid reactions of alpha-haloketones with several pyrazolones and with thiosemicarbazones were shown to afford the corresponding pyrazolyl ethers and 4-substituted 2-(arylidenehydrazino)thiazoles. The product yields are quantitative in all cases and the products do not require purifying workup. Therefore, these reactions are truly solvent-free, sustainable, and no wastes are produced. A diazonium nitrate is quantitatively accessible by gas-solid reaction of the corresponding amine with NO2 gas. It is a useful material for environmental synthesis of azo dyes through solid-state coupling with a variety of coupling compounds, as e.g. beta-naphthol, acetoacetanilide, pyrazolones, and barbituric acid.