From Big Medical Encyclopedia

DIAZO COMPOUNDS — a class of organic compounds with the general formula Ar — N = N — X, where Ar — the aryl rest, and X — a hydroxyl or an acid residue. In the latter case these connections are called diazonium salts and play a large role in production of dyes and pharm, drugs, and also in a histochemistry. Use of diazonium salts in a histochemistry opened essentially new way of definition of a number of enzymes based on use of reaction of azocoupling. During the replacement of an acid residue in a molecule D. on a hydroxyl the fragile bases are formed [ArN + = N] OH - , having sharply expressed alkaline properties. D.'s receiving carries the name of reaction of diazotization and happens at action nitrogenous to - you on arylamine:

Ar • NH 2 + HNO 2 + HCl -> [ArN + = N] Cl + 2H 2 O.

Practically to the water solution of salt of amine containing surplus to - you, flow solution of sodium nitrite; about completeness of reaction judge by a posineniye of a potassium iodide piece of paper. Diazotization is carried out during the cooling. One of the reasons of broad use of D. in organic sinteza is their property to exchange diazogroup for other groups or atoms. So, during the heating of water solutions of diazoniyevy salts phenols are formed:

Ar • N 2 • Cl + H 2 >O-Ar • OH + N 2 + HCl;

during the heating with alcohol group — N = N — is replaced with the spirit rest:

Ar • N 2 • Cl + HO • With 2 H 5 -> Ar • O • With 2 H 5 + Na + HCl

or hydrogen atom therefore

Ar hydrocarbon • Is formed by N 2 • Cl + HO • With 2 H 5 -> ArH + N 2 + HCl + C 2 H 4 O;

at interaction of diazoniyevy salt with solution of cuprous or cupric bromide in concentrated salt to - those it turns out aromatic halide-derivative:

Ar • N 2 • Cl -> ArCl + N 2 .

Under the influence of protosalts of copper also exchange of group for cyan is possible:

Ar • N 2 • Cl + KCN -> Ar • CN + N 2 + KCl.

At interaction of diazoniyevy salts with amines or phenols as a result of so-called coupling reaction are formed azo compounds (see).

Soft recovery of diazonium salts leads to receiving aromatic derivatives hydrazine (see). Reaction is carried out by two ways:

1) according to Fischer when products of interaction of diazonium salts with sulfites of alkali metals, so-called diazosulphonates, recover sulphurous to - that or zinc dust and to - that is acetic

2) according to Meyer when solution of diazonium salt is mixed with solution of stannous chloride at a low temperature.

Arylhydrazines and diarylhydrazines are good reactants on carbonyl group, they react with aldehydes (see) and ketones (see) with formation of hydrazones or osazones (see) are also often used in laboratory and gistokhy. to practice. Especially often as such reagent phenylhydrazine is applied (see. Fenilgidrazinovaya test ).

When D. receive action in the cold nitrogenous to - you on sulphanilic to - that (sulphanilic acid), as a result of diazotization receive benzene-azo-sulphonic acid:

Benzene-azo-sulphonic acid in alkaline condition reacts with phenolic group tyrosine (see), with indole group tryptophane (see) and with imidazolny group histidine (see) with formation of the painted reaction products.

This reaction in J. F. Danielli's modification is applied for gistokhy, definitions of protein in cuts of fabrics.

Reaction of diazotization in Morel's modification — Sisley is applied for gistokhy, definitions of tyrosine: diazonitrates in alkaline solution enter coupling reaction and give the painted reaction products.

See also Diazo test , Endrashika-Klegkhorna-Grofa method .

Bibliography: Fizer L. and Fizer M. Organic chemistry, the lane with English, t. 1 — 2, M., 1969 — 1970; Chichibabin A. E. Main beginnings of organic chemistry, t. 1, M., 1963.

S. Medvedev.