Heterocyclic diazonium compounds

The relatively infrequent availability of stable heterocyclic diazonium compounds explains the paucity of information on this group. In diazotizing 5-amino-2,4-dichlorop3nimidine, the chlorines are displaced by hydroxy groups. A related type of activation is also indicated by the very ready decarboxylation of 5-aminopyrimidine-... 

Heterocyclic diazonium compounds undergo cycloaddition with compounds containing reactive CH bonds, as shown, for example, in reaction 31 . See also reaction 24. 

Non-aromatic diazonium cations decompose in the presence of nucleophiles with nitrogen elimination, and do not effect coupling reactions. However, some heterocyclic diazonium compounds were found to have reactivity similar to that of arenediazonium compounds, including production of coupling derivatives. Such is the case of 1,3,4-thiadiazolinediazonium cations (reaction 32) and diazonium betaines (reaction 33). ... 

Hammett equation, applied to azines, 217 Hetarynes, 121-143 contrasted with arynes, 125 Heteroaromatic compounds, covalent hydration of, 1-41 "pKa generalizations for, 48-61 Heterocyclic acids, pH-rate profile for, 67 Heterocyclic diazonium compounds, 241 Heptaazanaphthalenes, 393 Hexaazanaphthalenes, 393 Hippuroflavin, 80 Hydrated salts, isolation of, 16 Hydrates, alcoholates from, 16 isolation of, 16... 

The aza-transfer reaction between 3-hydrazinopyridazines and aromatic diazonium salts or heterocyclic diazo compounds affords the corresponding tetrazolo[l,5-6]pyridazines, while 3-hydrazinopyridazine 1-oxide gives 3-azidopyridazine 1-oxide (76TL3193, 76X725). 

A quantitative study of the azo coupling reactions of heterocyclic diazo compounds was made by Sawaguchi et al. (1971), who measured the coupling rates of seventeen heterocyclic diazonium ions with R-acid (2-naphthol-3,6-disulfonic acid) and compared them with those of the benzenediazonium ion with the same coupling component. All the heterocyclic diazonium ions investigated react faster with R-acid than does the benzenediazonium salt. More recently, Diener and Zollinger (1986) confirmed Sawaguchi s results and interpreted them in more detail. 

As mentioned previously (see p. 237), the 1,2,3-benzotriazinones function as masked diazonium compounds, and the so-called Pologenowe dyes developed in Poland are operated on this principle and have been in use there since 1959. There are three major advantages associated with the use of 1,2,3-benzotriazinones as azo-dye equivalents (1) The equilibrium that theoretically exists between the heterocyclic system and the diazonium compound normally lies completely to the side of the cyclic compound. Opening of the heterocyclic ring can be easily accomplished thermally, and hence dye formation can be induced by heat treatment processes. (2) Many 1,2,3-benzotriazinones are reasonably water soluble and the sodium salts even more so consequently, complete permeation of fabric fibres by the dye precursors immediately prior to generation of the dye can be ensured. (3) The colors produced are fast, and some of them can be made highly water insoluble. ... 

Hydrolysis of condensed 1,2,3-triazines results in cleavage of the heterocyclic ring and is in many respects an unexceptional and fully predictable type of reaction. The relative ease with which ring fission takes place, and the products formed, depend almost entirely on the nature of the substituents at the 3- and 4-positions and on the reaction conditions employed. Moreover, hydrolysis under basic conditions normally leads to fission of the N,—C4 bond whereas under acidic conditions most 1,2,3-benzotriazine derivatives behave as masked diazonium compounds, and hydrolysis proceeds with fission of the N2— N3 bond and transient formation of a diazonium compound, from which the observed products are ultimately derived. Hydrolysis of certain derivatives probably also involves covalent hydration as the key step. 

Azo dyes, characterized by the presence of one or more azo groups (-N=N-), are the most commercially important class of dyes. These compounds are synthesized using a diazoti-zation reaction in which a primary aromatic amine reacts with nitrous acid to form a diaz-onium salt. The diazonium compound then typically is coupled with phenols, napthols, aromatic amines, heterocycles, or a variety of other compounds containing active methylene groups. Azo dyes are used in acid, direct, disperse, fiber reactive, and mordant applications. 

Heterocycles as Coupling Components. If heterocyclic polyamine coupling components, e g., 2,4-diamino-6-hydroxypyrimidine, are used as coupling components with aromatic diazonium compounds, dyes are obtained that color polyacrylonitrile in lightfast yellow shades and are characterized by excellent leveling properties [5], An example is 1 [6979-64-2],... 

Coupling Components With Condensed Cyclic Ammo nium Residues. Heterocyclic compounds in which the condensed benzene ring is substituted by a hydroxyl or an amino group can be coupled with diazonium compounds and may also be quatemized, either prior or subsequent to the coupling reaction, to yield cationic azo dyes. l,2-Dialkyl-6-nitroindazolium salts are reduced to the 6-amino compounds and then coupled with diazonium salts of aromatic amines. These dyes (e g., 21) color polyacrylonitrile in bright yellow to orange shades [64],... 

These and other methods of introducing halogen into heterocycles, such as the transformation of a- and y-hydroxypyridinoid bases with inorganic acid halides, the treatment of pyridinoid A-oxides with sulfur or phosphorus halides, and the decomposition of diazonium compounds, are treated adequately in existing references. 

The heterocyclic diazo compounds such as diazopyrroles bear the same relation to diazocyclopentadiene that pyridine does to benzene. Just as pyridine is a base and forms a pyridinium ion, in acid solution, so diazopyrroles (5) form pyrrole diazonium salts (6). 

Diazoindazole (11) was first prepared by the diazotization of 3-aminoindazole (9) followed by the treatment of the resulting diazonium salt (10) with base,1,5 This remains the most important method of synthesis for the whole class of heterocyclic diazo compounds. (See p. 4.)... 

Pyrrole and indole diazonium salts are acidic and lose a proton even in dilute acid to yield the diazo compound. Pyrazole diazonium salts, on the other hand, are only feebly acidic and the diazo compound is liberated only in quite strong alkali. In many cases the difficulty in obtaining the heterocyclic diazo compound has mainly centered round the preparation of the preceding amino compound. Nitration... 

By far the most important azo coupling reaction, i.e. the reaction of arenediazonium ions with aromatic coupling components, has been known for many decades and has been extensively reviewed Therefore, in this section we shall concentrate on reactions of aliphatic diazonium ions, diazoalkanes and diazocarbonyl compounds which have not been known previously as well as on coupling reactions which have gained in importance more recently, specifically those of heterocyclic diazonium ions. 

The high reactivity of heterocyclic diazonium ions in azo coupling reactions is the reason why in some cases the primary diazotization products cannot be isolated. 2-Methyl-5-aminotetrazole 38, for example, yields directly the diazoamino compound 39 on diazotization, the intermediate diazonium ion being reactive enough to give the N-coupling product with the parent amine, even under strongly acidic conditions (22)60.61)... 

Reactions of potentially high synthetic utility are intramolecular azo coupling reactions of heterocyclic diazonium ions to give new fused-ring heterocycles. Some examples are given in (25-27) . The use of heterocyclic diazo compounds in organic synthesis has recently been reviewed by Ti ler and Stanovink ,... 

The synthesis of azidocycloimonium fluoborates, compounds which possess a quasi-aromatic heterocyclic nucleus, has been reported by BalU and Kersting . Halogen atoms adjacent to quaternary nitrogens in heteroaromatic salts such as 154 157 undergo replacement by azide ion at low temperatures to produce the resonance stabilized azidinium salts (158). On the basis of infrared studies and reactivity towards nucleophiles, Balli has suggested that these salts are best considered as iV-diazonium compounds... 

When a diazonium fluoroborate gives only a poor yield of the corresponding fluorinated aromatic compound on thermal decomposition in the dry state, it may be added in portions to an anhydrous hydrocarbon that is heated a few degrees above the decomposition temperature of the fluoroborate m- and o-fluoropropiophenone, for instance, have been obtained in this way in boiling toluene or heptane 1245 the procedure has also been applied, in particular, to decomposition of heterocyclic diazonium fluoroborates, e.g., for the preparation of 3-fluoropyridine,1246 3-fluoroquinoline,1247 and 4-fluoroisoquino-line.1248... 

In many cases amino groups attached to pseudoaromatic heterocyclic systems can also be replaced by hydroxy groups by way of the diazonium compounds. E.g., xanthine was obtained from guanine in this way.564... 

Iminium Inflates can also react with diazonium compounds to form new C-C bonds.Condensation with nitriles or hydrazides will lead to the formation of various heterocycles, such as substituted pyridines, pyrimidines,triazoles, and substituted indazoles. ... 

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