Waste-Free Chemistry of Diazonium Salts and Benign Separation of Coupling Products in Solid Salt Reactions

Abstract

Gas–solid and solid–solid techniques allow for waste‐free and quantitative syntheses in the chemistry of diazonium salts. Five techniques for diazotations with the reactive gases NO2, NO and NOCl are studied. Two types are mechanistically investigated with atomic force microscopy (AFM) and are interpreted on the basis of known crystal packings. The same principles apply to the cascade reactions that had been derived from one‐step reactions. Solid diazonium salts couple quantitatively with solid diphenylamine and anilines to give the triazenes. Azo couplings are achieved with quantitative yields by cautious co‐grinding of solid diazonium salts with β‐naphthol and C–H acidic heterocycles, such as barbituric acids or pyrazolinones. Solid diazonium salts may be more easily applied in a stoichiometric ratio for couplings in solution. Co‐grinding of solid diazonium salts with KI gives quantitative yields of various solid aryl iodides. The unavoidable coupling products in salt reactions are completely separated from the insoluble products in a highly benign manner. The solid‐state reactions compare favourably with similar solution reactions that produce much waste. The structures of the products are elucidated with IR and NMR spectroscopy and mass spectrometry, while the tautomeric properties of the compounds are studied with density functional calculations at the B3LYP/6–31G* and BLYP/6–31G** levels.

Organic Solid-State Reactions

“…Alternatively, the powders of both components can be cautiously mixed, let for 24 h, and ultrasounded for completion of the reaction. Numerous combinations with solid phenols or 1,3-dicarbonyl compounds have been reported [31,68,198,199]. Only two typical examples with preferred hydrazo structure are shown in Scheme 25.…”

“…After the safe grinding and 1 day rest, the IR spectrum lacks the characteristic diazonium band. Water washings leave a quantitative yield of the aromatic iodide after drying [198].…”

“…The zwitterionic (R = SO 3 H) diazonium salts can be freed from HNO 3 and H 2 O in a good vacuum. Special cases are biphenyl-bis-diazonium salt, the technical anthraquinone diazonium salt from 1-aminoanthraquinone [198], and the tautomeric heterocyclic diazonium nitrate with very minor energy difference between the two tautomers. This diazonium salt is quantitatively formed despite the additional NH bond [200].…”

“…Water-free solid diazonium chlorides are directly obtained by reaction of solid aromatic amines with (highly corrosive) NOCl. Furthermore, solid nitrosobenzenes (their dimers) or benzanilides give quantitatively water-free diazonium nitrates by reaction with nitrogen monoxide [198]. Another water-free diazonium nitrate is quantitatively synthesized by the reaction of 4-nitro-acetanilide with liquid nitrogen dioxide (not shown in Scheme 34).…”

Spectrophotometric studies on some arylazo diamino pyrimidinol in organic solvents and in buffer solutions

“…Various reports had appeared recently discussing the electronic spectral properties of pyrimidine bases and their derivatives [12][13][14][15][16][17][18][19][20][21][22][23]. Pyrimidine is an active component of antibiotics and antineoplastics (e.g.…”