Diazonium compounds stability

In some cases the use of nitrosylsulfuric acid may be avoided if 1-naphthalenesul-fonic acid is added to moderately concentrated sulfuric acid (20-60%). This greatly reduces the evolution of nitrous fumes compared with a solution of pure sulfuric acid of the same hydrogen ion concentration. It has not yet been investigated whether the phenomenon is due to the formation of an ion pair, [C10H7 —SO NO+], or whether it is simply a solubility effect. In any case, the total acidity range of 4-12 m has thereby become available for diazotization technically crude sulfonation mixtures are used after dilution with water, for example, a solution of total acidity 4 m, of which 2.7 m is due to sulfuric acid. A further advantage of the method lies in the stabilizing effect of the naphthalenesulfonic acid on the diazonium compounds formed (see Sec. 2.3). 

A deamination procedure for which general application is claimed has been described by Hodgson and Madden.6 An aqueous solution of the diazotized amine is treated with the molar quantity of naphthalene-1,5-, disulfonic acid or 2-naphthol-l-sulfonic acid, whereupon the stabilized diazonium compound is precipitated. In most cases the stabilized diazo salts require slight variations in technique for their preparation in optimum yield. "The dry salt is reduced at room temperature in ethanol containing zinc or copper. Overall yields of the order of 90% are reported however, the purity of the product is not specified. 

It is to be noted that diazo compounds are much more strongly basic than the amines from which they are derived. A solution of diazotized p-nitroaniline, for example, can be diluted with water to any desired extent, or even neutralized with acetate, without setting the diazonium base free. The stability of the diazonium compound is much less under these conditions, however, than in strongly acid solution. 

The triazole (346) can be used to stabilize plastics (73JAP7308667). The reaction of tributyl lead hydroxide and aminotriazole affords (347) which has been recommended as an antiwear component of lubricating oils (68FRP1525268). Diazonium compounds detonate, although they are safer to handle than comparable derivatives of tetrazole. Polyfluorotriazolines (67USP3326889) are oxidants their suitability as bleaching agents, for rocket fuels and constituents of pyrotechnic compositions has been claimed. 

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... 

Diazonium salts are formed by the diazotization reaction, the action of nitrous acid on primary aromatic amines in the presence of a mineral acid. As salts, these compounds are able to stabilize the reactive azo group in preparation for making dyes and other products. Nitrates of diazonium compounds are diazonium nitrate salts. 

In normal laboratory practice, diazonium salts are used as intermediates in the preparation of a variety of aromatic compounds. Since many diazonium salts may detonate when warmed or when dry, they are usually used in solution without isolation. Obviously, since diazonium compounds are used widely in the dye industry, dry diazonium salts of considerable stability can be prepared. Particularly those diazonium salts which contain electron-withdrawing groups may be converted to relatively stable salts. Even in those cases, it would be well if materials were handled with considerable care. In particular, the compounds should be stored in a cool dark place. Furthermore, since many diazonium salts are quite sensitive to ultraviolet... 

Many fluoroborate salts of aromatic diazonium compounds have a high degree of stability. 

The diazotization of amino derivatives of six-membered heteroaromatic ring systems, particularly that of aminopyridines and aminopyridine oxides, was studied in detail by Kalatzis and coworkers. Diazotization of 3-aminopyridine and its derivatives is similar to that of aromatic amines because of the formation of rather stable diazonium ions. 2- and 4-aminopyridines were considered to resist diazotization or to form mainly the corresponding hydroxy compounds. However, Kalatzis (1967 a) showed that true diazotization of these compounds proceeds in a similar way to that of the aromatic amines in 0,5-4.0 m hydrochloric, sulfuric, or perchloric acid, by mixing the solutions with aqueous sodium nitrite at 0 °C. However, the rapidly formed diazonium ion is hydrolyzed very easily within a few minutes (hydroxy-de-diazonia-tion). The diazonium ion must be used immediately after formation, e. g., for a diazo coupling reaction, or must be stabilized as the diazoate by prompt neutralization (after 45 s) to pH 10-11 with sodium hydroxide-borax buffer. All isomeric aminopyridine-1-oxides can be diazotized in the usual way (Kalatzis and Mastrokalos, 1977). The diazotization of 5-aminopyrimidines results in a complex ring opening and conversion into other heterocyclic systems (see Nemeryuk et al., 1985). 

Salts of diazonium ions with certain arenesulfonate ions also have a relatively high stability in the solid state. They are also used for inhibiting the decomposition of diazonium ions in solution. The most recent experimental data (Roller and Zollinger, 1970 Kampar et al., 1977) point to the formation of molecular complexes of the diazonium ions with the arenesulfonates rather than to diazosulfonates (ArN2 —0S02Ar ) as previously thought. For a diazonium ion in acetic acid/water (4 1) solutions of naphthalene derivatives, the complex equilibrium constants are found to increase in the order naphthalene < 1-methylnaphthalene < naphthalene-1-sulfonic acid < 1-naphthylmethanesulfonic acid. The sequence reflects the combined effects of the electron donor properties of these compounds and the Coulomb attraction between the diazonium cation and the sulfonate anions (where present). Arenediazonium salt solutions are also stabilized by crown ethers (see Sec. 11.2). 

The reversibility of aromatic diazotization in methanol may indicate that the intermediate corresponding to the diazohydroxide (3.9 in Scheme 3-36), i. e., the (Z)-or (is)-diazomethyl ether (Ar — N2 — OCH3), may be the cause of the reversibility. In contrast to the diazohydroxide this compound cannot be stabilized by deprotonation. It can be protonated and then dissociates into a diazonium ion and a methanol molecule. This reaction is relatively slow (Masoud and Ishak, 1988) and therefore the reverse reaction of the diazomethyl ether to the amine may be competitive. Similarly the reversibility of heteroaromatic amine diazotizations with a ring nitrogen in the a-position may be due to the stabilization of the intermediate (Z)-diazohydroxide, hydrogen-bonded to that ring nitrogen (Butler, 1975). However, this explanation is not yet supported by experimental data. 

However, an evaluation of the observed (overall) rate constants as a function of the water concentration (5 to 25 % in acetonitrile) does not yield constant values for ki and k2/k i. This result can be tentatively explained as due to changes in the water structure. Arnett et al. (1977) have found that bulk water has an H-bond acceptor capacity towards pyridinium ions about twice that of monomeric water and twice as strong an H-bond donor property towards pyridines. In the present case this should lead to an increase in the N — H stretching frequency in the o-complex (H-acceptor effect) and possibly to increased stabilization of the incipient triazene compound (H-donor effect). Water reduces the ion pairing of the diazonium salt and therefore increases its reactivity (Penton and Zollinger, 1971 Hashida et al., 1974 Juri and Bartsch, 1980), resulting in an increase in the rate of formation of the o-complex (ik ). 

See THERMAL STABILITY OL REACTION MIXTURES AND SYSTEMS See Other CYANO COMPOUNDS, DIAZONIUM SULFATES, INDUCTION PERIOD INCIDENTS, NITROARYL COMPOUNDS... 

As mentioned above, the conventional diazonium salts have good optical properties as CEL dyes and negative working sensitizers for the two-layer resist system. However, almost all diazonium salts are stabilized with metal-containing compounds such as zinc chloride, tetrafluoroborate, hexafluoro-antimonate, hexafluoroarsenate, or hexafluorophosphate, which may not be desirable in semiconductor fabrication because of potential device contamination. To alleviate the potential problem, new metal-free materials have been sought for. 

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