Benzenediazonium, reaction

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. 

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... 

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.)... 

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" ... 

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). 

Diazo coupling occurs very readily between pyrroles and indoles and benzenediazonium salts. Reaction is much more rapid in alkaline solution when the species undergoing reaction... 

Hydroxythiophene also exists mainly in ketonic forms. Electrophilic reagents react either at oxygen or at C-5. O-Methyl and O-acetyl derivatives are obtained in alkaline solution, probably through intermediacy of the anion. In acidic solution, coupling with benzenediazonium ion, a characteristic phenolic reaction, is found to take place (Scheme 72). 

Pyridine-2- and -4-diazonium ions are far less stable than benzenediazonium ions. Azolediazonium 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. 

Benzenediazonium fluoroborate, 2-carboxy-xanthone synthesis from, 3, 838 Benzenediazonium ions phenyl azide formation from, 5, 839 Benzenediazonium salts, o-(imidazol-l-yl)-intramolecular diazo coupling, 5, 404 Benzene-1,2-disulfonimides N-substituted reactions, 6, 930 Benzene episulfide formation, 7, 577 Benzeneimine... 

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... 

The Reaction between Azide and Benzenediazonium-lP-N ] Ions a. The Distribution of the N -Lahel in the End Products. Clusius and Hiirzeler observed that phenyl azide-[a-A ] (16) and unlabeled nitrogen are formed by the union of unlabeled azide and isotopically unrearranged benzenediazonium-[a-A ] ions (15). They concluded... 

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. ... 

The preparation of an aryl fluoride—e.g. fluorobenzene 3—starting from an aryl amine—e.g. aniline 1—via an intermediate arenediazonium tetrafluoroborate 2, is called the Schiemann reaction (also called the Balz-Schiemann reaction) The diazotization of aniline 1 in the presence of tetrafluoroborate leads to formation of a benzenediazonium tetrafluoroborate 2 that can be converted into fluorobenzene 3 by thermolysis. 

Benzenediazonium carboxylate decomposes when heated to yield N2, C02. and a reactive substance that can t be isolated. When benzenediazonium carboxylate is heated in the presence of furan, the following reaction is observed ... 

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 ... 

More recently Gorelik s group determined the structure of 1-phenylsulfonyl-2-pyrazoline-3-diazonium tetrafluoroborate by X-ray crystallography (Gorelik et al., 1989) and calculated (Glukhovtsev et al. 1990) the heats of the dediazoniation reaction of seven cyclic five-membered diazonium ions (including 2.13, R=H) relative to that of the benzenediazonium ion by the MNDO method (see Sec. 8.4). 

The general applicability of this type of synthesis of quinone diazides is nevertheless limited since, depending on the type and number of substituents in the 2-, 4-, and 6-positions of benzenediazonium ions, either hydroxy-de-diazoniation (reaction A in Scheme 2-20) or nucleophilic substitution of one of the groups in the 2-, 4-, or 6-position (reaction B) will predominate. It is difficult to predict the ratio of the two reactions in a specific case. This is exemplified by two investigations carried... 

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). 

Luchkevich et al. (1986, Table 6) demonstrated that for the three isomeric nitro-benzenediazonium ions and their (Z)-diazohxydroxides the acidity constants can be determined by ultraviolet spectrophotometry, by potentiometry, from the kinetics of reaction with hydroxide ions, from the (Z) (E) isomerization kinetics, and from the kinetics of azo coupling reactions. These independent methods gave surprisingly consistent results. ... 

The rapid formation of the (Z)-diazoate is followed by the slower (Z/J )-isomeri-zation of the diazoate (see Scheme 5-14, reaction 5). Some representative examples are given in Table 5-2. Both reactions are first-order with regard to the diazonium ion, and the first reaction is also first-order in [OH-], i.e., second-order overall. So as to make the rate constants k and k5 directly comparable, we calculated half-lives for reactions with [ArNj ]0 = 0.01 m carried out at pH = 9.00 and 25 °C. The isomerization rate of the unsubstituted benzenediazonium ion cannot be measured at room temperature due to the predominance of decomposition (homolytic dediazoniations) even at low temperature. Nevertheless, it can be concluded that the half-lives for (Z/ )-isomerizations are at least five powers of ten greater than those for the formation of the (Z)-diazohydroxide (reaction 1) for unsubstituted and most substituted benzenediazonium ions (see bottom row of Table 5-2). Only for diazonium ions with strong -M type substituents (e.g., N02, CN) in the 2- or 4-position is the ratio r1/2 (5)/t1/2 (1) in the range 6 x 104 to 250 x 104 (Table 5-2). 

Table 5-2. Selected rate constants and half-livese) for some reactions of substituted benzenediazonium ions with buffer solutions (pH 9.00) at 25 °C (rate constants from Virtanen and Kuok-kanen, 1977 half-lives calculated by the present author).

Griess (1866 b) found that benzenediazonium tribromide (QHsN Br ) in the presence of ammonia is converted into phenyl azide in high yield. The reaction probably proceeds through phenyltriazene, as an intermediate which is subsequently oxidized to the azide by the tribromide ion (Scheme 6-14). 

The fundamental understanding of the diazonio group in arenediazonium salts, and of its reactivity, electronic structure, and influence on the reactivity of other substituents attached to the arenediazonium system depends mainly on the application of quantitative structure-reactivity relationships to kinetic and equilibrium measurements. These were made with a series of 3- and 4-substituted benzenediazonium salts on the basis of the Hammett equation (Scheme 7-1). We need to discuss the mechanism of addition of a nucleophile to the P-nitrogen atom of an arenediazonium ion, and to answer the question, raised several times in Chapters 5 and 6, why the ratio of (Z)- to ( -additions is so different — from almost 100 1 to 1 100 — depending on the type of nucleophile involved and on the reaction conditions. However, before we do that in Section 7.4, it is necessary to give a short general review of the Hammett equation and to discuss the substituent constants of the diazonio group. 

---