Diazonium salts benzenediazonium

Diazonium salts couple readily with aromatic primary amines, giving diazoamino compounds. If for instance an aqueous solution of aniline sulphate is diazotised with a deficiency of nitrous acid, only part of it is converted into benzenediazonium sulphate and the latter then couples with the unchanged aniline to give diazoaminobenzene. The reaction is carried out at the opti-CeHsNHj.HjSO + HONO = CbHsNjHSO, + zHaO... 

A method for the generation of benzyne involves heating the diazonium salt from o aminobenzoic acid (benzenediazonium 2 carboxylate) Using curved arrows show how this sub stance forms benzyne What two inorganic compounds are formed in this reaction" ... 

Ultraviolet spectra of diazonium salt solutions were recorded for the first time by Hantzsch and Lifschitz as early as 1912. However, electron spectra did not provide significant information on the structure of diazonium ions, either at that time or later. For example, Anderson and coworkers (Anderson and Steedly, 1954 Anderson and Manning, 1955), compared spectra of 4-amino-benzenediazonium salts with those of diphenylquinomethane (4.18). Their conclusion that the structures of these compounds are analogous is basically correct, but the arguments given by Anderson can easily be refuted, as shown by Sorriso (1978, p. 102). 

This and related syntheses involving diazonium salts were reviewed by Biffin et al. (1971, p. 148). The hypothesis that the triazene occurs as intermediate in Scheme 6-14 has been corroborated by the experiments of Clusius and Hiirzeler (1954) using benzenediazonium salts labeled with 15N at the a- or Impositions. Ammonia adds exclusively at the p-nitrogen no rearrangements were observed. 

Table 10-9. Yields in homolytic dediazoniation reactions of 2-(2 -propenyl)benzenediazonium salts (10.55, Z = 0, 7i = l, R=H or CH3) and the related diazonium salt 10.59.

The first diazonium-salt-crown-ether adduct was isolated and identified as a 1 1 complex by Haymore et al. (1975). Unfortunately Haymore never published the X-ray structural analysis of benzenediazonium hexafluorophosphate with 18-crown-6 which he performed in 1980. ORTEP drawings with measured bond angles and lengths from Haymore s investigation can be found in a review chapter by Bartsch (1983, p. 893). A few data from Haymore s work (e.g., R = 0.064) were also mentioned by Cram and Doxsee (1986, footnote 7). Groth (1981) published the results of his X-ray investigation of 4-methoxybenzenediazonium tetrafluoroborate and 21-crown-7 (R = 0.042) and Xu et al. (1986) those of 4-methoxybenzenediazonium tetrafluoroborate and dibenzo-24-crown-8 (R = 0.086). 

More recently, Bagal and coworkers (Luchkevich et al., 1991) obtained similar results in a kinetic investigation of the coupling reactions of some substituted benzenediazonium ions with 1,4-naphtholsulfonic acid, and with 1,3,6-, 2,6,8-, and 2,3,6-naphtholdisulfonic acids. The kinetic results are consistent with the transient formation of an intermediate associative product. The maximum concentration of this product reaches up to 94% of the diazonium salt used in the case of the reaction of the 4-nitrobenzenediazonium ion with 1,4-naphtholsulfonic acid (pH 2-4, exact value not given). The authors assume that this intermediate is present in a side equilibrium, i. e., the mechanism of Scheme 12-77 mentioned above rather than that of Scheme 12-76, and that the intermediate is the O-azo ether. 

Incidentally, 31 contributes more to the hybrid than 32, as shown by bond-distance measurements. In benzenediazonium chloride, the C—N distance is 1.42 A, and the N—N distance 1.08 A, which values lit more closely to a single and a triple bond than to two double bonds (see Table 1.5). Even aromatic diazonium salts are stable only at low temperatures, usually only below 5°C, though more stable ones, such as the diazonium salt obtained from sulfanilic acid, are stable up to 10 or 15°C. Diazonium salts are usually prepared in aqueous solution and used without isolation, though it is possible to prepare solid diazonium salts if desired (see 13-20). The stability of aryl diazonium salts can be increased by crown ether complexion. ... 

Juri and Bartsch (1979) have studied the coupling of 4-t-butylbenzene-diazonium tetrafluoroborate with N,N-dimethylaniline in 1,2-dichloroethane solution. The addition of one equivalent (based on diazonium salt) of 18-crown-6 caused the rate constant to drop by a factor of 10, indicating that complexed diazonium is less reactive than the free cation. Benzenediazonium tetrafluoroborate complexes of crown ethers are photochemically more stable than the free salt. The decomposition into fluorobenzene and boron trifluoride is strongly inhibited but no explanation has been given (Bartsch et al., 1977). 

Several of these internal diazonium salts, prepared by diazotisation of anthranilic acids, are explosive in the solid state, or react violently with various materials. Individually indexed compounds (including analogous sulfonates) are Benzenediazonium-2-carboxylate, 2659 Benzenediazonium-3 or 4-carboxylate, 2661... 

Figure 13-35 illustrates the mechanism for the formation of p-hydroxyazoben-zene beginning with the reaction of benzenediazonium chloride with an aromatic system activated by an -OH. The mechanism for the reaction with an amine is similar. Figure 13-36 illustrates the reaction of a diazonium salt with an amine. The product of the reaction in Figure 13-36 is p-(dimethylamino) azobenzene. 

Salicylic acid couples with diazonium salts in the expected manner. With diazotized aniline, ie, benzenediazonium chloride, the primary product is 5-phenylazosalicylic acid [3147-53-3] (eq. 7). 

Pyridine-2- and -4-diazonium ions are far less stable than benzenediazonium cations. Azole-diazonium salts generally show intermediate stability provided diazotization is carried out in concentrated acid, many of the usual diazonium reactions succeed. Indeed, azolediazonium salts are often very reactive in coupling reactions. 

To prepare the solid benzenediazonium chloride or sulphate, the reaction is conducted in the absence of water as far as possible. The source of nitrous acid is one of its organic esters (e.g. pentyl nitrite) and a solution of hydrogen chloride gas in absolute ethanol upon the addition of ether only the diazonium salt is precipitated as a crystalline solid. 

Dissolve 46.5 g (45.5 ml, 0.5 ml) of aniline in a mixture of 126 ml of concentrated hydrochloric acid and 126 ml of water contained in a 1-litre beaker. Cool to 0-5 °C in a bath of ice and salt, and add a solution of 36.5 g (0.53 mol) of sodium nitrite in 75 ml of water in small portions stir vigorously with a thermometer and maintain the temperature below 10 °C, but preferably at about 5 °C by the addition of a little crushed ice if necessary. The diazotisation is complete when a drop of the solution diluted with 3-4 drops of water gives an immediate blue coloration with potassium iodide-starch paper the test should be performed 3-4 minutes after the last addition of the nitrite solution. Prepare a solution of 76 g (0.69 mol) of sodium fluoroborate (1) in 150 ml of water, cool and add the chilled solution slowly to the diazonium salt solution the latter must be kept well stirred and the temperature controlled so that it is below 10 °C. Allow to stand for 10 minutes with frequent stirring. Filter the precipitated benzenediazonium fluoroborate with suction on a Buchner funnel, drain well and wash the yellow solid with about 30 ml of ice-water, 15 ml of methanol and 30-40 ml of ether suck the solid as free as possible from liquid after each washing (2). Spread the salt upon absorbent filter paper and allow to dry overnight, if possible in a current of air. The yield of benzenediazonium fluoroborate is 60—65 g the pure salt melts with decomposition at 119-120 °C. 

Attention has previously been drawn (Section 6.7.1, p. 922) to the fact that unless an excess of hydrochloric (or mineral) acid is used in the diazotisation process, coupling occurs between the diazonium salt and the amino group in the amine to give diazoamino compounds. Thus benzenediazonium chloride and aniline yield diazoaminobenzene. This substance may be conveniently prepared by dissolving two equivalents of aniline in three equivalents of hydrochloric acid, and adding one equivalent of sodium nitrite in aqueous solution followed by two equivalents of sodium acetate (Expt 6.86). 

The dry salt was more or less explosive, depending on the method of preparation [1]. DTA examination of a 15% solution of the diazonium salt in hydrochloric acid showed an exothermic decomposition reaction with the exotherm peak at 65°C. Adiabatic decompositon of the solution at 20°C took 80 min to attain the maximum temperature of 80°C [2]. The heat of decomposition Q was determined as 1.5 kJ/g [3], See Benzenediazonium tetrachlorozincate... 

See Hydrogen trisulfide Benzenediazonium chloride 4-Chloro-2-methylbenzenediazonium salts, 2715 Hydrogen trisulfide Benzenediazonium chloride, 4479 3-Quinolinethiol preparation from the diazonium salt, 3116 3-Toluenediazonium salts, Ammonium sulfide, or Hydrogen sulfide, 2770 3-Toluenediazonium salts, Potassium O-ethyl dithiocarbonate, 2770... 

Later it was found that the decomposition of benzenediazonium salts with ethanol actually yields phenyl ethyl ether contaminated with a little benzene. This, coupled with the fact that a number of instances of ether formation had been recorded, led to the suggestion that the normal products of reaction between diazonium salts and ethanol are the ethers. 

Careful studies of the action of absolute ethyl alcohol on various diazonium salts obtained from aniline have proved that phenetole is the main product, along with a very small quantity of benzene.10 The decomposition of benzenediazonium chloride, for example, results in a 61% yield of phenetole and a 5% yield of benzene.11 The remainder of... 

Reactions of enamines with diazonium salts have also been reported. Treatment of benzenediazonium chloride with l,3,3-trimethyl-2-methyleneindoline gave an azo compound,283 whereas with aliphatic enamines the final products were hydrazines of a-ketoaldehydes 284 or a-diketones (Scheme 10). 

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