Reactions of Diazonium Compounds

Solid diazonium salts are very sensitive to shock when perfectly dry and detonate violently upon gentle heating they are, therefore, of little value for preparative work. Happily, most of the useful reactions of diazonium compounds can be carried out with the readily-acoeasible aqueous solutions, so that the solid (explosive) diazonium salts are rarely requir. ... 

The preparation of A4-l,2,3-triazoIines (Scheme 7, where n = 1 or 2)2,2a involves the reaction of diazonium compounds of primary aromatic or... 

Howard, AN, Wild, F. Reactions of diazonium compounds with 50. amino acids and proteins. Biochem. J. 1957 65 651-659. 

B. Reaction of Diazonium Compounds with Nucleophiles I. Ammonia and its derivatives... 

Reaction of diazonium compounds with primary and secondary aliphatic amines usually results in the formation of substituted tri-azenes (equation 120). However, an interesting exception with... 

Carbon-carbon bonds can be formed in very varied ways in reactions of diazonium compounds. For example, l-chloro-4-(/ -nitrophenyl)-2-butene (88% yield) is formed from diazotized / -nitroaniline and butadiene in aqueous acetone containing copper chloride and sodium acetate,787 whereas in the same conditions 5-phenyl-2,4-pentadienoic acid gives l-(/ -nitrophenyl)-4-phenyl-1,3-butadiene.788 The latter reaction is a special case of Meerwein arylation, by which stilbenes are formed in good yields from diazonium salts and cinnamic acids 789... 

Coupling reactions of diazonium compounds methanol, ethanol, glacial acetic acid, pyridine... 

The student is recommended to carry out the preparation of iodo-benzene in order to gain experience in the preparation of aqueous solutions of diazonium compounds, and then to prepare a solution of benzenediazonium hydrogen sulphate with which to carry out the chief reactions that diazonium compounds undergo. 

The most noteworthy reaction of azo-compounds is their behaviour on reduction. Prolonged reduction first saturates the azo group, giving the hydrazo derivative (C NH-NH C), and then breaks the NH NH linkage, with the formation of two primary amine molecules. If method (1) has been employed to prepare the azo-compound, these two primary amines will therefore be respectively (a) the original amine from which the diazonium salt was prepared, and (6) the amino derivative of the amine or phenol with which the diazonium salt was coupled. For example, amino-azobenzene on complete reduction gives one equivalent of aniline, and one of p-phenylene diamine, NHaCeH NH benzene-azo-2-naphthoI similarly gives one equivalent of aniline and one of... 

Aromatic diazonium compounds became industrially very important after Griess (1866a) discovered in 1861/62 the azo coupling reaction, by which the first azo dye was made by C. A. Martius in 1865 (see review by Smith, 1907). This is still the most important industrial reaction of diazo compounds. Hantzsch and Traumann (1888) discovered that a heteroaromatic amine, namely 2-aminothiazole, can also be diazotized. Heteroaromatic diazonium compounds were, however, only used for azo dyes much later, to a small extent in the 1930 s, but intensively since the 1950 s (see Zollinger, 1991, Ch. 7). 

Superior passive stabilised diazo compounds are afforded by the diazoamino compounds (triazenes) that arise by reaction of diazonium salts with a variety of secondary amines [114]. Typically, sarcosine (CH3NHCH2COOH), which gives products based on structure 4.114, as well as N-methyltaurine (CH3NHCH2CH2SO3H) and N methylaniline-4 Sulphonic acid,... 

Coupling reaction of diazonium ions with electron-rich aromatic compounds... 

Not all reactions of diazonium ions involve cleavage of the C-N bond. An important group of reactions of arenediazonium ions involves aromatic substitution by the diazonium ion acting as an electrophilic agent to yield azo compounds, Ar—N=N—Ar ... 

Reactions on or close to solid surfaces maybe inhibited by deposition ofinsoluble or poorly soluble products on the reactant surface, a phenomenon referred to as overgrowth. Examples include the reaction of amines with chloranil [7], the diazotisation of poorly soluble aromatic amines in which the product diazonium salt is also insoluble and halogen exchange reactions of chloroaromatic compounds using potassium fluoride in dipolar aprotic solvents where the potassium chloride product may coat the potassium fluoride [8]. 

The stabilities of pyridine-2- and -4-diazonium ions resemble those of aliphatic rather than benzenoid diazonium cations. Benzenediazonium ions are stabilized by mesomerism which involves electron donation from the ring, but such electron donation is unfavorable in 2- and 4-substituted pyridines. On formation, pyridine diazonium cations normally immediately react with the aqueous solvent to form pyridones. However, by carrying out the diazotization in concentrated HC1 or HBr, useful yields of chloro- and bromopyridines 752 can be obtained. Iodinated pyridines can be obtained in good yield using the Sandmeyer reaction. Aminopyridazines and -pyrazines, 2- and 4-aminopyrimidines, and amino-1,2,4-triazines behave similarly. Nucleophilic fluorination via the BalzSchiemann reaction of diazonium fluoroborates yields fluoropyridines, including 2-fluoropyridines. Fluoroborates can also be converted into fluoro compounds by ultraviolet irradiation. 

A number of reactions of organomagnesium compounds with compounds containing nitrogen-nitrogen multiple bonds give products containing new carbon-nitrogen bonds [A, E], but few of them are useful in synthesis. The main exceptions are reactions with azides, and some reactions of diazonium salts. 

Compared to diazonium salts, diazo compounds are generally much less reactive towards nucleophiles than towards electrophiles. As a result of this azo coupling reactions of diazo compounds are the exception rather than the rule. Electron withdrawing substituents on the diazo carbon increase the reactivity towards nucleophiles. Consequently the ability to undergo azo coupling reactions increases from diazomethane to diazocarbonyl- and 2-diazo-l, 3-dicarbonyl compounds. Among the earliest reactions known were those with cyanide and sulfite ions Tertiary phosphines, as opposed to amines, can form stable addition complexes with diazoalkanes probably due to the ability of phosphorus to stabilize the betaine with its empty d orbitals (6). 

A slightly different situation was found by Hashida et al. when investigating the reaction of diazonium ions with l-dialkylamino-3-acylaminobenzenes 123). It is well known that dialkylanilines react with diazonium ions (at the 4-ix)sition), but that N-acylated anilines do not. For compounds of type 123, however, evaluation of the rates of azo coupling as a function Of pH demonstrates that the anion 124 has a reactivity which is 8 powers of ten higher than that of 123. 

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