Azo- and Azoxy Compounds

Treatment of aromatic amines with sodium nitrite and hydrochloric 

The reaction of nitrosobenzene with alkylamines has been examined as a potential source of (phenylazo)alkanes, with moderate 

Studies concerning the activating effect of arylazo groups on olefins have been recorded and these have afforded a convenient synthesis of 2,2-diamino- from 2,2-dichloro-enazo compounds and amines,Addition and cyclisation reactions of 3-chloro-azo 

Traditional nomenclature for azo compounds nses the mnltiplicative prefix azo -N=N- e.g., Ph-N=N-Ph = azobenzene, Ph-N=N-CioH7 = 2-benzeneazonaphthalene or 2-phenylazonaphthalene. This is difficnlt to apply for more complex nnsymmetrical componnds, but remains in use. Another form fonnd in the older literature, especially for azo dyes, is naphthalene-2-azobenzene. 

More recently, the parent name diazene -N=N- (has also been called diimide not recommended) was introduced, e.g., Ph-N=N-Ph = diphenyldiazene. The 2006 CAS nomenclature changes have included the following  

In naming unsymmetrical azoxy compounds, the prefixes NNO- or ONN- are used to indicate the position of the oxygen atom, e.g., Ph-N(0)=N-CioH7 = phenyl-OAW-azoxynaphthalene. However, post-2006, such azoxy compounds are named in CAS as (1-oxidodiazenyl) or (2-oxidodiazenyl). 

Although a thoroughly consistent, systematic approach to the naming of virtually all azo and azoxy compounds - compounds which have traditionally been treated very disparately on the basis of the highly versatile parent hydride name diazene has existed for some time, several customary older naming modes are still perpetuated in pretty confusing ways (even by Chem. Abstr. ). These demand a more detailed discussion. 

Undisputed are diazene names for derivatives containing hydrocarbon, alkoxy, and comparable substituent groups or directly attached senior functionalities. 

Diazenedisulfonic acid dimethyl ester or Dimethyl diazenedisulfonate (Azodisulfonic acid dimethyl ester or Dimethyl azodisulfonate) 

First discrepencies are then already discernible for the covalent isomers of arenediazonium salts, which are properly named as aryldiazenols by lUPAC but, contrary to the rules, as arylhydroxydiazanes by Chem. Abstr. 

Systematic name Phenyldiazenol Chem. Abstr. Hydroxy(phenyl)diazene Traditional name Benzenediazo-hydroxide 

By using the malonic ester variation of the Japp-Klingemann 

Tritylhydrazone anions, when treated with electrophiles followed by 

6 -Tetramethylazobenzene has been prepared by the sodium tungstate-catalysed oxidation of 2,6-dimethylaniline with hydrogen 

Arylazo-methoxy-diphenylmethanes have been isolated as stable yellow crystals by reaction of benzophenone arylhydrazones with bromine, followed by methanolysis of the resulting 

1- arylcyclopropanediazonium cations have been generated by alkaline cleavage of the analogous nitrosocarbamates in methanol. Several brilliant blue azo dyes have been prepared by the 

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These radical anions have been detected by ESR. This mechanism is consistent with the following result when nitrosobenzene and phenylhydroxylamine are coupled, and N labeling show that the two nitrogens and the two oxygens become equivalent. Unsymmetrical azoxy compounds can be prepared by combination of a nitroso compound with an N,N-dibromoamine. Symmetrical and unsymmetrical azo and azoxy compounds are produced when aromatic nitro compounds react with aryliminodimagnesium reagents, ArN(MgBr>2. ... 

A large number of single-crystal X-ray studies were carried out on mesogenic azo and azoxy compounds [3, 5, 121-131]. The general chemical structure of... 

Table 14. Crystal data and phase sequences of mesogenic azo and azoxy compounds (see Fig. 23)... 

From photoreduction (> 280 nm) in diethylamine, low yields of 1-naphthyl-amine and the corresponding azo- and azoxy compounds have been obtained Photolysis (366 nm) in acidified 50% aqueous 2-propanol at varied HCl-concentrations results in remarkable enhancement of photoreduction compared to neutral 2-propanol. The highest disappearance quantum yield measured was 1.28 X 10 2 for 6 M HCl 4-chloro-l-naphthylamine is formed as main product 74.75). 

Hydrogen telluride reduces hydroxylamines to anilines, and nitroso, azo and azoxy compounds to the corresponding hydrazo compounds. - ... 

Azo and azoxy compounds are potential by-products of peroxyacetic acid oxidations, particularly when the rate of oxidation is slow. Competitive condensation reactions are usually avoided by using an excess of oxidant and also avoiding the presence of excess acid which retards amine oxidation. The latter is sometimes suppressed by using a sodium bicarbonate buffer.i i i ... 

Reduction of substituted nitrobenzenes under alkaline conditions, usually with aqueous sodium acetate as electrolyte and a nickel cathode, is the classical method due to Elbs [45] for the formation of azo- and azoxy-compounds. Protons are used in the electrochemical reaction so that the catholyte becomes alkaline and under these conditions, phenylhydroxylamine reacts rapidly with nitrosobenzene to form azoxybenzene. Finely divided copper has long been known to catalyse the reduction of nitrobenzene to aniline in alkaline solution at the expense of azoxybenzene production [46]. Modem work confirms that whereas reduction of nitrobenzene at polycrystalline copper in alkaline solution gives mainly azoxybenzene, if the electrode is pre-oxidised in alkaline solution and then reduced just prior to the addition of nitrobenzene, high yields of aniline are obtained with good current efficiency... 

Electron-transfer initiation from other radical-anions, such as those formed by reaction of sodium with nonenolizable ketones, azomthines, nitriles, azo and azoxy compounds, has also been studied. In addition to radical-anions, initiation by electron transfer has been observed when one uses certain alkali metals in liquid ammonia. Polymerizations initiated by alkali metals in liquid ammonia proceed by two different mechanisms. In some systems, such as the polymerizations of styrene and methacrylonitrile by potassium, the initiation is due to amide ion formed in the system [Overberger et al., I960]. Such polymerizations are analogous to those initiated by alkali amides. Polymerization in other systems cannot be due to amide ion. Thus, polymerization of methacrylonitrile by lithium in liquid ammonia proceeds at a much faster rate than that initiated by lithium amide in liquid ammonia [Overberger et al., 1959]. The mechanism of polymerization is considered to involve the formation of a solvated electron ... 

Oxidation of organonitrogen compounds is an important process from both industrial and synthetic viewpoints . N-oxides are obtained by oxidation of tertiary amines (equation 52), which in some cases may undergo further reactions like Cope elimination and Meisenheimer rearrangement . The oxygenation products of secondary amines are generally hydroxylamines, nitroxides and nitrones (equation 53), while oxidation of primary amines usually afforded oxime, nitro, nitroso derivatives and azo and azoxy compounds through coupling, as shown in Scheme 17. Product composition depends on the oxidant, catalyst and reaction conditions employed. 

J. W. Timberlake u. J. C. Stowell in S. Patai, Preparation of azoxy compounds, B. T. Newbold. Oxidation and synthetic uses of hydrazo, azo and azoxy compounds, in Chemistry of the hydrazo, azo, and azoxy groups, edited by part 1, J. Wiley Sons, London New York Sidney Toronto 1975. 

Since azo compounds may be prepared by the oxidation of hydrazo compounds via procedures similar to those used in oxidizing azo compounds to azoxy compounds, better definition of reaction conditions is required to control the formation of either type of compound. The existing literature rarely, if ever, indicates that the oxidation of a 1,2-disubstituted hydrazine could conceivably produce a mixture of azo and azoxy compounds. 

Figure 14.10 Hydrazo, aliphatic azo and azoxy compounds, and aryldialkyltriazenes.

Nitroaromatic compounds (NACs) are one of the widespread contaminants in the environments. Sources of NACs are numerous they originate from insecticides, herbicides, explosives, pharmaceuticals, feedstock, and chemicals for dyes (Agrawal and Tratnyek, 1996). Under anaerobic conditions, the dominant action is nitro reduction by zero-valent iron to the amine. Other pathways do exist, such as the formation of azo and azoxy compounds, which is followed by the reduction of azo compounds to form amines. Also, in addition to the possibility of azo and azoxy compounds, phenylhydrox-ylamine may be an additional intermediate (Agrawal and Tratnyek, 1996). Nitrobenzene reduction forms the amine aniline. Known for its corrosion inhibition properties, aniline cannot be further reduced by iron. Additionally, it interferes with the mass transport of the contaminant to the surface of the iron. The overall reaction is as follows ... 

Nitration of azo compounds leads to mixtures of nitro derivatives of azo and azoxy compounds (Werner and Stiasny [1]). Thus, by nitrating azobenzene with 98% nitric acid at a temperature not exceeding +6°C, these authors obtained a mixture ofp- nitroazobenzene.p,p - dinitroazobenzene andp- nitroazoxybenzene. With 98% nitric acid without cooling, mainly a mixture of the trinitroazoxybenzene isomers was obtained. 

The reaction of nitroalkanes and dinitroalkanes with sodium hydrogen telluride gives nitrosoalkane dimers and olefins, respectively.96 The reduction of other nitrogenated species such as hydroxylamines, azides, nitroso, azo, and azoxy compounds can also be performed by using tellurium reagents.6,11,12... 

Keefer LK, Lunn G. 1985. Reductive destruction of nitrosamines, hydrazines, nitramines, azo- and azoxy-compounds. National Institute of Health, U.S. patent no. 4534154. 

Catalytic hydrogenation is a heterogeneous reaction which occurs at the surface of the catalyst. The mechanism is complex and proceeds through the nitroso and hydroxylamine derivatives minor by-products such as the azo and azoxy compounds occasionally appear. 

Aromatic azo and azoxy compounds may be prepared by chemical or electrolytic reduction of nitro compounds, the degree of reduction depending upon the experimental conditions. 

TABLE 108. AZO AND AZOXY COMPOUNDS TABLE 108. AZO AND AZOXY COMPOUNDS... 

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