Hydroxy azo compounds

The conversion of azoxy compounds, (144) on acid treatment, to p-hydroxy azo compounds (145, or sometimes the o-hydroxy isomers ) is called the Wallach rearrangement. When both para positions are occupied, the t -hydroxy product... 

A photochemical Wallach rearrangement is also known The product is the o-hydroxy azo compound, the OH group is found in the farther ring, and the rearrangement is intramolecular. ... 

Two important classes of derivatives of the azo compounds which include some very valuable dyes are the amino azo and hydroxy azo compounds. The latter which are also called oxy azo compounds are derivatives of the azo compounds resulting from the substitution of one or more hydroxyl groups in the rings. 

Constitution.— Both of these reactions of preparation establish the constitution of the amino azo compounds and also of the hydroxy azo compounds as we have represented them. While three isomers are possible in each case, depending on whether the azo group and the amino or hydroxyl group are in the ortho, meta or para positions in relation to each other, yet in fact only ortho and para compounds are known in most instances. The full constitution of the ortho and para amino azo benzene is then. 

This compound is very unstable and explosive and forms hydroxy azo compounds by coupling with hydroxy compounds. Furthermore, it gives sulphur dioxide when treated with dilute acids just as sulphite salts do. It appears, therefore, that this compound is a true diazonium compound, viz., a diazonium sulphite and the reaction should be... 

Thus the acceptance of the Bloomstrand-Strecker-Erlenmeyer formula for the diazonium base and salts, and of the Hantzsch modification of the Kekule formula for the isomeric diazotates and the acid diazo hydroxide, together with the tautomeric transformations which occur, makes possible the explanation of all the facts which we have considered in the preceding discussion. These may be stated again briefly for the sake of emphasis and review, (i) The reaction of diazotization (2) the diazonium base and salts, (3) the diazotates and acid diazo hydroxide, (4) the isomerism of the diazotates, (5) the diazonium sulphites and diazo sulphonic acidsj (6) the relationship of diazo compounds to nitroso amines (7) to hydrazines (8) the coupling with amino and hydroxy compounds to form amino azo and hydroxy azo compounds, (9) the reactions of decomposition. Most of these last reactions we have not considered, but will do so presently and we shall find that they all may be likewise satisfactorily explained. The tautomeric constitution of the diazo compounds, therefore, meets every test and is generally accepted. 

Under certain conditions aromatic ring hydroxy compounds yield analogous products though the usual reaction is the one already given (p. 569) by which hydroxy azo compounds are formed. 

Fluorescein.—It is an important compound in its reaction with phthalic anhydride, yielding beautiful dyes known as fluorescein and eosine. Hydroxy azo compounds formed from it, however, are not valuable as dyes. 

The reduction may be brought about either by means of tin and hydrochloric acid or electrolytically. Hydroxy azo compounds also yield amino phenols on reduction, the former being the product of the reaction between a diazonium salt and a phenol. This gives an indirect method of preparing amino phenols from the phenols. 

Azo phenols which are of course the same as hydroxy azo compounds (p. 576), azoxy phenolsy hydrazo phenolsy phenol hydrazines and di-azo phenols are all known either as phenols or as phenol ethers. The last group is interesting historically as the first diazo compound made by Griess was di-nitro phenol diazonium chloride,... 

The equilibrium of Schiff bases (48) has been studied in detail because of their interesting properties both in the solid state (Section II.N) and in biological reactions. This can be done as just described for o-hydroxy azo compounds ( 7(N,H) coupling constants and deuterium isotope effects on C and N chemical shifts)Based on /(N,H) it could be concluded that the Schiff bases form a conventional tautomeric equilibrium that can be described by two species. ... 

If o-hydroxy azo compounds (LXXVII) are used instead of o-amino phenols, then, under pressure at 200° C benzoxazoline-2-thiones (LXXVI) are formed along with 2-(phenylamino) benzoxazoles (LXXVIII (193) (see Table 12, method B). Azobenzene on the other hand yields only benzothiazoline-2-thione. 

Deuteriation at C 2) made it possible to observe an isotope effect, AN(CD), over three bonds, analogously to the large values of long-range isotope effects on nitrogen studied in the case of o-hydroxy azo compounds. ... 

The 3-amino-derivatives of 4,4-dimethyl-5a-cholestane (476) gave the mixture of deamination products depicted (Scheme 19), in proportions depending upon the original C-3 configuration and the reaction conditions (protic or aprotic). The various products are thought to be formed through three distinct intermediates a covalent hydroxy-azo-compound, a diazonium ion as part of an ion-pair, or a discrete carbonium ion. 

Conversion of azoxy compounds to p-hydroxy azo compounds upon treatment with acid. 

Azoxy-con unds (RN(0)NR ). Heat a very small quantity (ca 1 mg) of the substance with 1 ml of concentrated sulphuric add at 90 for 30 seconds. Azoxy-compoimds are converted to hydroxy-azo-compounds, which possess rich orange or red-brown colours. 

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