Nitrogen diazonium salts

The diazonium salts usually decompose when warmed with water to give a phenol and nitrogen. When treated with CuCl, CuBr, KI, the diazo group is replaced by chlorine, bromine or iodine respectively (Sandmeyer reaction). A diazonium sulphate and hydroxyl-amine give an azoimide. The diazonium salt of anthranilic acid (2-aminobenzoic acid) decomposes to give benzyne. ... 

When potassium iodide or hydrogen iodide is added to an aqueous solution of a diazonium salt, nitrogen is readily evolved (no catalyst being necessary) and the corresponding iodo-compound is formed. lodo-compounds can thus... 

When a diazonium salt in aqueous solution is gently warmed, it reacts with the water, liberating nitrogen and forming the corresponding phenol ... 

When an aqueous solution of a diazonium salt is added to an alkaline solution of a phenol, coupling occurs with formation of an azo-compound (p. 188). If ho vc cr the ntiueous solution of the diazonium salt, t. . ., />-bromohenzene diazonium chloride, is mixed with an excess of an aromatic hydrocarbon, and aqueous sodium hydroxide then added to the vigorously stirred mixture, the diazotate which is formed, e.g., BrC,H N OH, dissolves in the hydrocarbon and there undergoes decomposition with the formation of nitrogen and two free radicals. The aryl free radical then reacts with the hydrocarbon to give a... 

When a solution of a diazonium salt is heated, the diazo group is replaced by hydroxyl and nitrogen is evolved ... 

The Lassaigne procedure for detecting nitrogen in organic compounds frequently gives unsatisfactory results with explosive compounds (diazonium salts, polynitro compounds and the like) and with certain volatile nitrogenous substances, such as bases, their acyl derivatives or their salts. These difficulties... 

Amino-5-methylthiazole does not react with diazotized p-nitroaniline in solutions acidified with acetic or hydrochloric acid (391). 2-Amino-4,5-dimethylthiazole with the diazonium salts of para-substituted anilines, however, gives product 193, involving reactivity of the exocyclic nitrogen (Scheme 122) (399). 

Primary arylamines like primary alkylammes form diazonium ion salts on nitro sation Aryl diazonium 10ns are considerably more stable than their alkyl counterparts Whereas alkyl diazonium 10ns decompose under the conditions of their formation aryl diazonium salts are stable enough to be stored m aqueous solution at 0-5°C for a rea sonable time Loss of nitrogen from an aryl diazonium ion generates an unstable aryl cation and is much slower than loss of nitrogen from an alkyl diazonium ion... 

A reaction of aryl diazonium salts that does not involve loss of nitrogen takes place when they react with phenols and arylamines Aryl diazonium ions are relatively weak elec trophiles but have sufficient reactivity to attack strongly activated aromatic rings The reaction is known as azo coupling two aryl groups are joined together by an azo (—N=N—) function... 

Oxidative Couplings of Heterocyclic Hydrazones. This method has opened the way to the preparation of azo derivatives of diazo compounds unobtainable by other means, ie, heterocycHc compounds ia which the diazotizable amino group is conjugated with the heterocycHc nitrogen atom as ia 2- and 4-amiQopyridine, compounds which do not normally yield stable diazonium salts (38). The reaction occurs as illustrated by equation 7 for the iateraction of (A/-methylcarbostyryl)hydrazone [28219-37-6] and dimethyl aniline the overall process is oxidation. 

Inductive and resonance stabilization of carbanions derived by proton abstraction from alkyl substituents a to the ring nitrogen in pyrazines and quinoxalines confers a degree of stability on these species comparable with that observed with enolate anions. The resultant carbanions undergo typical condensation reactions with a variety of electrophilic reagents such as aldehydes, ketones, nitriles, diazonium salts, etc., which makes them of considerable preparative importance. 

Aromatic diazonium salts are almost as important for reactions in which the diazonio group is lost as molecular nitrogen and in which aryl cations and radicals are the reagent proper (dediazoniation reactions, see Chs. 8 and 10). 

This diazotization is typical of many aminoazoles the diazonium ions formed are relatively strong acids. The pATa values of five di-, tri-, and tetrazolediazonium ions are reported to be between 3 and 4, i. e., about 10 units lower (more acidic) than those of the respective unsubstituted heterocycles (Vilarrasa et al., 1974). Therefore, deprotonation of the diazonium ion is easy and, depending on reaction conditions, yields either the diazonium salt or its conjugate base, the diazo compound. The electrophilic reactivity of the P nitrogen atom in the diazo group of the base is lower than the reactivity of the diazonio group of the cation (Diener and Zollinger, 1986 see Sec. 12.2). 

In all the diazotization reactions discussed in Sections 2.1-2.4 an equimolar amount of water is formed as byproduct. There are two general pathways for obtaining diazonium salts without formation of water. One is based on the rearrangement of 7V-nitroso-7V-arylacetamides, the other on the nitrosation of a monoarylated sp2-hybridized nitrogen compound by nitrosating reagents XNO in which X is a weak nucleophile. 

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. 

It has been suggested that the initial formation of iodine on addition of iodide to a diazonium salt solution is caused by oxidation of the iodide by excess nitrite from the preceding diazotization. Packer and Taylor (1985) demonstrated that, if urea was added as a nitrite scavenger (see Sec. 2.1) to a diazotization solution, that solution produced iodine much more rapidly than a portion of the same diazonium salt solution not containing urea, but eventually the latter reaction too appeared to follow the same course. This confirms the role of excess nitrite, and suggests that the iodo-de-diazoniation steps only occur in the presence of iodine or triiodide (I -). The same authors also found that iodo-de-diazoniation is much slower under nitrogen. All these observations are consistent with radical-chain processes, but not with a heterolytic iodo-de-diazoniation. 

In the scientific sector, the understanding of the generally higher reactivity of heteroaromatic diazo components relative to that of aromatic diazonium salts has increased. The number of heterocyclic nitrogen atoms in azolediazonium ions has a marked influence on the N-H acidity of these ions. The pvalues of a series of such ions in aqueous solution at 0 °C (Scheme 12-4) indicate that the electrophilicity of the diazonio group in these compounds increases with the number of nitrogen atoms in the ring. ... 

When primary aromatic amines are treated with nitrous acid, diazonium salts are formed. The reaction also occurs with aliphatic primary amines, but aliphatic diazonium ions are extremely unstable, even in solution (see p. 448). Aromatic diazonium ions are more stable, because of the resonance interaction between the nitrogens and the ring ... 

Other compounds with nitrogen-nitrogen bonds have been used instead of diazonium salts. Among these are N-nitroso amides [ArN(NO)COR], triazenes, and azo compounds. Still another method involves treatment of an aromatic primary amine directly with an alkyl nitrite in an aromatic substrate as solvent. ... 

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