Benzenediazonium chloride, reaction with

C,H5N,NHC,Hs+HC1 = C,H 5N C1+H,NC,H5- C H5N NC H NH +HC1 gen atom of the aniline molecule, giving aminoazobenzene. Since this reaction is irreversible, whilst the former is freely reversible, the final result is the complete conversion of the diazoaminobenzene into the aminoazobenzene. (The intermediate formation of the benzenediazonium chloride can be demonstrated by adding dimethylaniline, with which the diazonium chloride couples preferentially, giving dimethylaminoazobenzene, C6HsN NC6HiN(CH3)i.)... 

Aromatic compounds that are sufftciendy nucleophilic to condense with benzenediazonium chloride and form azo compounds generally condense with TCNE, eg, the reaction of /V, /V- dim ethyl a n i1 in e proceeds stepwise (21,22). 

Diphenylbutadiene has been obtained from phenylacetic acid and cinnamaldehyde with lead oxide, by the dehydrogenation of l,4-diphenyl-2-butene with butyllithium, and by the coupling reaction of benzenediazonium chloride and cinnamyl-ideneacetic acid." The present method gives better yields than those previously reported, is adaptable to the preparation of a variety of substituted bistyryls, and is relatively easy to carry out. 

Reaction offluoroolefins with fluoride ion and benzenediazonium chloride... 

Pyridine has been phenylated with the following free-radical sources benzenediazonium chloride with aluminum trichloride the Gomberg reaction " phenylhydrazine and metal oxides A -nitroso-acetanilide dibenzoyl peroxide phenylazotriphenylmethane di-phenyliodonium hydroxide and electrolysis of benzoic acid. ° Although 2-phenylpyridine usually accounts for over 50% of the total phenylated product, each of the three phenyl derivatives can be obtained from the reaction by fractional recrystallization of the... 

There is an early report that thiophene reacts at the 3-position in phenylation with benzenediazonium chloride and aluminum trichloride, but in the Gomberg reaction thiophene has been found to substitute mainly at the 2-position both with p-tolyl and with p-chloro-phenyl radicals.Bcnzothiazole is phenylated at the 2-position in low yield by dibenzoyl peroxide a small quantity of the 4-isomcr is also obtained. ... 

Ionization. The pKa at 25° in w is 3.60, 50% aq et ale 4.11, et ale 7.5, and me ale 7.2 (Ref 17) Reactions. It reacts with benzenediazonium chloride to give yellow crysts, mp 75° with gas evolution, whose structure was first thought to be (PhN N)2C(N02)2 (Ref 3). More recently the reaction with p-nitro benzenediazonium fluoroborate was examined in greater detail (Ref 11). The first prod isolated was the hydrazone p-02NC6H4NHN C(N02)2, orange-red crysts, mp 120—25° with decompn. It deflagrates when heated on a spatula, and its solns decomp slowly in the cold and more rapidly on heating, with evolution of oxides of N. From the mother-liquor was obtained another compd, mp 164°, which was considered to be a meso-ionic compd ... 

Based on observations by Bamberger, Bucherer, and Wolff at the turn of the century, Matrka et al. (1967) described experiments which show that alkaline solutions (pH 8.5-9.2) of substituted benzenediazonium chlorides form nitrite ions and triazenes. The latter is obviously the reaction product of the amine formed in a retro-diazotization with the diazonium ion that is still present. The yield of nitrite formed was between 0.5% (benzenediazonium ion) and 50.2% (2-nitrobenzenediazonium ion). 

A different synthesis of arylmercuric chlorides (10.67) was described recently by Hu and Yu (1989). They showed that chloromercuryacetaldehyde (10.66) reacts with arenediazonium salts in aqueous acetone as shown in Scheme 10-89. The reaction is catalyzed by cupric chloride (yield 66-88% twelve substituted benzenediazonium chlorides were investigated). 

Barbituric acid can be considered as a cyclized malonic acid diamide (malonyl-urea). It is therefore a cyclic diketone that may be classified, in the sense of the compounds discussed in Section 12.6, as a coupling component with a methylene group activated by two carbonyl groups in the a- and a -positions. The reaction with arenediazonium salts was studied by Nesynov and Besprozvannaya (1971). These authors obtained coupling products (in good yield) that they considered to be arylhydrazones. Coupling with 4-(phenylazo)benzenediazonium chloride was studied by Chandra and Thosh (1991). The lH NMR spectra of these compounds are consistent with the arylhydrazone structure 12.68. 

When Wiberg and Pracht (1972b) synthesized 3,3-di-(trimethylsilyl)-l-phenyltri-azene by reacting benzenediazonium chloride with sodium di-(trimethylsilyl)amide they found a faintly yellow compound if the reaction was carried out at -78 °C and an orange form at — 20 °C. NMR spectra were consistent with (Z)/( )-stereoiso-merism. Measurement of the isomerization rates at various temperatures in ether and in pentane indicates that the mechanism involves an inversion transition state (13.5) and not a rotation, because the free reaction enthalpies are independent of the polarity of the solvent. 

The CgHs-N Cl- (benzenediazonium chloride) enthalpy of decomposition was calculated. Comparing its value (AH j = -1.5 kJ/g) with the CHETAH criterion C, makes it moderately stable. Accidents have been observed during reactions that are schematised below and these illustrate what has been stated. They are all due to the explosive character of the diazonium sulphides formed. Here is one example ... 

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. 

Ring transformation involving the intramolecular reaction of a hydrazone or in situ formed hydrazone also appeared. The transformation of 6-methyl-2//-pyran-2,3,4-trione 3-arylhydrazones 332 into l-aryl-6-methyl-4-oxo-l,4-dihydropyridazine-3-carboxylic acids 333 is an example of the former (Scheme 82). Compound 332 are formed via reaction of 4-hydroxy-6-methyl-27/-pyran-2-one 331 with substituted benzenediazonium chlorides. These are normally not isolated and immediately used further <2005EJM1325>. An example where a hydrazone is formed in situ is the reaction of 2-amino-5-aryldiazenyl-4-oxo-6-phenyl-4//-pyran-3-carbonitriles 334 with H2SO4 in glacial acetic acid, yielding 2-aryl-6-benzoyl-3-hydroxy-5-oxo-2,5-dihydropyridazine -carbonitriles 335 (Scheme 83) <2001T6787>. 

Thiazolyl)pyrimido[4,5-i/]pyridazines have been prepared by utilizing the reaction of the active methylene compound 46 with benzenediazonium chloride (Scheme 24) to give a hydrazone, which cyclizes spontaneously <1999JPR147>. A further approach described recently <2002HAC108> involves reaction of the malononitrile derivative 47 with a further equivalent of malononitrile, forming a pyrimidine with a suitably disposed hydrazine, which cyclizes on exposure to strong base (Scheme 25). 

In a mechanistically similar process, the neutral palladium(II) dipyridylamine complex (24), obtained by deprotonation of complex (23), underwent reaction with benzoyl chloride to give the substituted complex (25) together with some free ligand (Scheme 8).33 This particular reaction sequence could not be generalized because of the relative instability of other metal complexes related to compound (24). However, a more extensive series of electrophilic substitutions could be carried out on the neutral complex (26), which displayed ambident nucleophilic behaviour by reaction with benzyl chloride and benzoyl chloride at nitrogen and reaction with benzenediazonium fluoroborate at carbon (Scheme 9). 

Reaction offluoroolefins with fluoride ion and benzenediazonium chloride affords perfluoroalkylazobenzenes [200] (equation 37)... 

Show how these observations support an SN1 reaction of benzenediazonium chloride, and can be used to argue against a benzyne-type elimination-addition with water acting as the E2 base (Section 14-6C) or an SN2 reaction with water as the nucleophile (Section 8-4, Mechanism B, and Section 14-6). 

Reactions of benzenediazonium chloride with 3-bromomethylbenzo-[sodium acetate afforded the hydrazonoyl bromides 35 [90ZN(B)1067]. 

Similarly, the reaction of benzenediazonium chloride with sodium diphen-ylarsenite, (C6H5)2AsONa, leads to triphenylarsine oxide, (C6H5)3As0.4... 

Sodium carbonate is often employed as a buffering agent in the ordinary Bart reaction. In this way phenylarsonic acid has been prepared in yields ranging from 50-60% 7 to as high as 86% 8 as compared with yields of 40-50% by the original process. The yield from benzenediazonium chloride and sodium arsenite is greatly influenced by the concentration of the arsenite, the speed of reaction, and especially by the pH of the solution (which should remain constant). All compounds, like sodium carbonate, which play the role of buffer, tend to increase the yield.9... 

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). 

As already mentioned, hydroxypyrazines exist in tautomeric equilibria with the corresponding pyrazinones which are normally the predominant species in the equilibria. Some of the reactions of hydroxypyrazines are reminiscent of those of phenols they can, for example, be coupled with diazonium salts and brominated and nitrated in either the ortho or para position to the hydroxyl group. Coupling with diazonium salts occurs in neutral or weakly alkaline solution, but if the reaction is carried out in 1 M sodium hydroxide solution, arylation of the pyrazine ring takes place. From hydroxy-pyrazine and benzenediazonium chloride 47% 2-hydroxy-3-phenyl-and 4% 2-hydroxy-3,6-diphenylpyrazine are obtained. 

The benzenediazonium chloride solution is then added with stirring during a period of one hour to the suspension of sodium arsenite, cooled in an ice and salt bath to o°. The temperature during the reaction is held below 50 (Note 1). Frothing takes place owing to the escape of nitrogen, but this is easily controlled... 

The Mannich reaction occurred at C-6 of ethyl 2-phenyl-4//-furo[3,2-6]pyrrole-5-carboxylate (94) giving the amine (106). 2-Aryl-4//-furo[3,2-6]pyrroles <83CCC772> easily undergo reaction with benzenediazonium chloride at C-5 forming the azo compounds (107) and (108). 

The most common synthetic approach by a Hofmann-type reaction of pyridazine-4,5-dicarboxamide or the cyclization of a / -enamino ester with guanidine or formamide have been reported in CHEC-I. Some new strategies have been developed. A novel and simple way to pyrimido[4,5-c/]pyridazines is the coupling of a functionalized pyrimidine (e.g. (60)) with benzenediazonium chloride to the arylhydrazone derivative (e.g. (61)) which cyclizes to the pyrimidopyridazine (62) (Scheme 11) <82JCS(P1)2667>. 

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