Diazonium compounds, production

When a solution of a diazonium compound in absolute methanol is boiled, the chief product is the corresponding methyl ether, henzenediiizonium hydrogen sulphate thus giying methyl phenyl etlier or anisole ... 

Dediazoniation refers to all those reactions of diazo and diazonium compounds in which an N2 molecule is one of the products. The designation of the entering group precedes the term dediazoniation, e. g., azido-de-diazoniation for the substitution of the diazonio group by an azido group, or aryl-de-diazoniation for a Gomberg-Bachmann reaction. The IUPAC system says nothing about the mechanism of a reaction (see Sec. 1.2). For example, the first of the two dediazoniations mentioned is a heterolytic substitution, whereas the second is a homolytic substitution. 

In this context two observations reported by Rondestvedt (1960, p. 214) should be mentioned (i) Meerwein reactions proceed faster in the presence of small amounts of nitrite ion. Meerwein reactions in which N2 evolution ceased before completion of the reaction can be reinitiated by addition of some NaN02. (ii) Optimal acidity for Meerwein reactions is usually between pH 3 and 4, but lower (pH — 1) with very active diazonium compounds such as the 4-nitrobenzenediazonium ion or the diphenyl-4,4 -bisdiazonium ion. At higher acidities more chloro-de-diazoniation products are formed (Sandmeyer reaction) and in less acidic solutions (pH 6) more diazo tars are formed. 

On heating, phenyl azide decomposes partially to give nonvolatile products which form colors with diazonium compounds. To minimize the presence of these impurities, the quantity of phenyl azide is limited to 2 drops in the triazole formation step. 

Crosslinking using diazonium compounds usually creates deeply colored products characteristic of the diazo bonds. Occasionally, the conjugated molecules may turn dark brown or even black. The diazo linkages are reversible by addition of 0.1 M sodium dithionite in 0.2 M sodium borate, pH 9.0. Upon cleavage, the color of the complex is lost. 

The production of azo pigments relies almost exclusively on the azo coupling reaction [1,2] to afford the azo group. Diazotization of an aromatic amine yields a diazonium compound, which subsequently reacts with a coupling component ( coupling ). 

In most cases, diazonium salts are unstable in the dry state and are sensitive to heat and impact. Since isolation is not necessary for azo pigment production, the diazonium compound is coupled with the coupling component as it is formed in solution or suspension. 

The most important side reaction during diazotization may lead to the formation of the diazoamino compound (Sec. 2.2.1). The diazonium compound may combine with unreacted amine to form the side product (Sec. 2.2.1). This effect is particularly prominent if it arises from a change of concentration. Insufficient nitrite pre-... 

Structurally, there are two basic types of disazo pigments, depending on whether the bifunctional element is introduced through the diazonium compound or through the coupling component. A bifunctional diazo component results in products of the type... 

The development of azo pigment lakes was initiated by the discovery of Lithol Red by Julius (BASF) in 1899. Lithol Red, which is synthesized by an indirect diazotization procedure using 2-naphthylamine-l-sulfonic acid as a diazonium compound, was initially employed in the form of its calcium and barium salts, which were precipitated onto inorganic carrier materials. The pigment was used in its pure form after it became apparent that the carriers contribute very little to the application properties of the product. Lithol Red is one of the earliest colorant developed specifically for application as pigment. 

In 1924 the German company Kalle Co. in Wiesbaden began production of blueprint paper, i.e. a diazo reprographic paper. In that process a sheet coated with a diazonium compound was exposed to an optical image and developed by diazo coupling using a mono-... 

Hydrolysis of condensed 1,2,3-triazines results in cleavage of the heterocycUc 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 Nj— 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. 

Hydrolytic cleavage of condensed 1,2,3-triazine derivatives is normally a straightforward, high-jneld process which results in production of one or other of several distinct types of product. 3-Alkyl- and 3-aryl-3,4-dihydro-l,2,3-benzotriazines, for example, undergo facile hydrolysis in concentrated hydrochloric acid to give, via the diazonium compound, A(-alkyl- and W-aryl-substituted o-chlorobenzylamines (100, R = Cl). If the reaction is carried out in water or in dilute mineral acid, the corresponding -alkyl and iV-aryl-substituted o-hydroxybenzylamines (100, R = OH) are obtained. 

At low acid concentrations, nitric oxide tends to form. This evidently may attack nitrosophenol to form diazonium compounds directly. The diazonium salts, in turn, may couple with unreacted phenol to give colored products. Nitrous acid may also produce nitrophenols from phenols. The mechanism of this reaction may involve oxidation of initially formed nitrosophenols, homolytic attack by nitrogen dioxide, or nucleophilic attack by nitrite ions [1]. 

Diazotise 223 g. of 2-naphtliylamine-l-sulphonic acid as detailed under fi-Bromonaphthalene in Section IV,62. Prepare cuprous cyanide from 125 g. of cupric sulphate pentahydrate (Section IV,66) and dissolve it in a solution of 65 g. of potassium cyanide in 500 ml. of water contained in a 1-litre three-necked flask. Cool the potassium cuprocyanide solution in ice, stir mechanically, and add the damp cake of the diazonium compound in small portions whilst maintaining the temperature at 5-8°. Nitrogen is soon evolved and a red precipitate forms gradually. Continue the stirring for about 10 hours in the cold, heat slowly to the boiling point, add 250 g. of potassium chloride, stir, and allow to stand. Collect the orange crystals which separate by suction filtration recrystallise first from water and then from alcohol dry at 100°. The product is almost pure potassium 2-cyanonaphthalene-l-sulphonate. Transfer the product to a 2-litre round-bottomed flask, add a solution prepared from 400 ml. of concentrated sulphuric acid and 400 g. of crushed ice, and heat the mixture under reflux for 12 hours. Collect the -naphthoic acid formed (some of which sublimes from the reaction mixture) by suction filtration... 

JV-Nitraminopyridines are reducible both in acid and alkali. In hydrochloric acid the main product from 2-nitraminopyridine was the hydrazino-pyridine, formed in a six-electron reduction, but 2-aminopyridine and 2-chloropyridine were side products, the latter possibly through reaction by an intermediate diazonium compound with chloride. Contrary to nitramines of most primary amines, 2-nitraminopyridine431 is reducible in alkaline solution uptake of the first two electrons forms the 2-pyridyl-N-nitrosamine, which is further reduced to 2-aminopyridine. 

Benzotriazinium betaines (13) and (26) are stable toward acids. They are slightly basic compounds and form salts with acids which are easily hydrolyzed. The corresponding 1-oxides (33) behave similarly, being, for instance, souble in concentrated hydrochloric acid from which they are reprecipitated on dilution with water (27JCS323). 4-Amino-l,2,3-benzotriazines (38) and 4-imino-1,2,3-benzotriazines (39) behave as masked diazonium compounds (40) and the products of acidic treatment of these compounds are best explained as reaction products of the diazonium salts (78HC(33)78>. Treatment of 1,2,3-benzotriazine... 

As usual in Sandmeyer reactions, the product, if volatile, is separated by distillation in steam if non-volatile, extraction or filtration is used. The manner in which the cuprous salt reacts is not exactly known it certainly unites at first with the diazonium compound to form a double salt (c/. Reaction CLXVI.). The method is widely applicable, and as the yields are usually good, it is a standard method for the preparation of aromatic nitriles. 

Reaction LII. (b) Action of Cuprous Chloride on Nitro-diazonium Compounds. (B., 34, 3802 38, 725.)—Ordinarily when cuprous chloride acts on a diazonium salt in acid solution, a chloro-compound is the chief product (Sandmeyer s reaction, p. 345), and only a small quantity of the corresponding diphenyl compound is formed. But if a nitro-diazonium... 

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