Diazonium compounds, reduction with

Some of the examples where a diazo or a diazonium compound reacts with activated double bonds, specifically with enamines and with 1,2-dimethoxy-ethene have been mentioned in sections 2.1.2 and 2.1.4, respectively (12, 29). A similar reaction is the azo coupling of arenediazonium salts with tropolones (34) The diazonio group reacts at the C-5 atom, so the reaction is used as a diagnostic tool for the presence of substituents at C-5, as well as for the synthesis of 5-amino tropolones by reduction of the azo compound. 

Toluene from Toluidine.—It is often desirable to obtain tbe hydiocarbon from the base. The process of diazotisntion offers the only convenient method. The diazonium salt may be reduced by alcohol (Reaction 1, p. 162) or, as in the piesent instance, by sodium stannite. Less direct methods are the con-veision of the diazonium compound into (i) the hydrazine (see p. 174), (2) the acid and distillation with lime (p. 200), (3) the halogen derivative and reduction with sodium amalgam, 01, finally (4) the phenol and distillation with zinc dust. 

Figure 19.22 Phenolic compounds may be derivatized to contain reactive diazonium groups by nitration with tetranitromethane followed by reduction with sodium dithionite and diazotization with sodium nitrite in dilute HCI.

More abundant are reductions with sodium sulfite which is applied in aqueous solutions (solubility 24%). Its specialties are reduction of peroxides to alcohols [257], of sulfonyl chlorides to sulfinic acids [252], of aromatic diazonium compounds to hydrazines [253], and partial reduction of geminal polyhalides [254] Procedure 43, p. 216). 

Aromatic diazonium compounds which are prepared readily by diazotization of primary amines can be converted either to their parent compounds by replacement of the diazonium group with hydrogen, or to hydrazines by reduction of the diazonium group. Both reactions are carried out at room temperature or below using reagents soluble in aqueous solutions, and usually give high yields. 

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. 

Diazonium compounds have been treated with a great variety of reducing agents, some of which have become incorporated into procedures for replacing the diazo group by hydrogen. The more important of these processes involve reduction by ... 

The present, straightforward, two-step synthesis of 5.6-dimethoxyindazole from 3,5-dimethoxyacetophenone illustrates the usefulness of this amination reaction. With standard chemistry the introduction of a hydrazine group into the acetophenone molecule would have required four steps 1) nitration, 2) reduction of the nitro group to the aniline, 3) diazotization and 4) reduction of the diazonium compound to the hydrazine. 

Oxycellulose and phenylhydrazine gave a yellow compound, which formed a diphenylformazan, showing that the oxycellulose had reacted in one of the two possible hemiacetal forms. Aminophenols and oxycellulose gave derivatives which coupled with diazonium compounds, enabling chemically colored fibers to be prepared. Reduction of oxycellulose oxime with lithium aluminum hydride, sodium borohydride, or sodium amalgam gave an amino-oxycellulose (109) in which up to 25 % of the oxime groups had been reduced. ... 

The synthesis of 2(2-hydroxy-5-methy lphenyl)2H-4 -vinyl-benzo-triazole was accomplished (31) by a sequence of reactions similar to those which gave 2H5V. The starting material for this synthesis was, however, not o-nitroaniline but 4-ethyl-o-nitroaniline. After diazo-tiation, the diazonium compounds were allowed to react with p-cresol the condensation product gave 2(2-hydroxy-5-methylphenyl)2H-4-ethyl-benzotriazole after reductive cyclization. This compound was acetyl-ated, brominated, dehydrobrominated, and hydrolyzed to 2(2-hydroxy-5-methylphenyl)2H-4 —viny1-benzotriazole. 

The chemical properties of nitroestrones are much the same as those of simpler aromatic compounds. The nitro group in 19-1 can, for instance, be converted to the aniline 21-1 for example by reduction with tin and acid treatment of the resulting aniline with nitrous acid then gives the diazonium salt 21-2 (Scheme 3.21). Photolysis of that salt in methanol leads to formation of 2-methoxyestrone, (21-3), in this case confirming the structure of one of the metabolites of estradiol. 

Diazoninm and Azo Compounds. - Aryl diazonium compounds undergo reductive metabolism to aryl radicals, which react with DNA. Studies on the p-hydroxybenzenediazonium ion have shown that such compounds can also undergo conversion to radicals through reactions catalysed by the hydroxyl ion. 

Oxidative cleavage of 280 by copper(ll) acetate generates a peroxy radical, which oxidizes the substrate to form an alcohol function and an oxy radical. Further reaction with the substrate affords again the corresponding alcohol in addition to a carbon radical. Thus, two equivalents of alcohol and only one equivalent of the carbon radical are formed. Since the reaction products originate from the carbon radical (see Fig. 112), the maximum yield could be 33%. The combined yields of 274 on one hand and 275-279 on the other hand are actually higher, hence further reduction of the alcohol must have occurred. It is very iikely that the copper(l) ion, which behaves as a moderately strong reductant (99), converts the alcohol, at least partially, to the reactive carbon radical. This mechanism explains the catalytic activity of copper(ll) acetate and resembles the reaction of arene diazonium compounds with copper(l) salts (100). 

Electrochemical reduction of the trithiapentalenes (804 R = H, Me, or Ph) yields the corresponding radical anions, which are converted into the thiapyran-thiones (807)/" ° 1-Phenyl-6,6a-dithia-l,2-diazapentalene (808) is nitrated mainly in position 3, but the 3,4-dimethyl derivative undergoes nitro-dediazoniation to the dithiole (809). Treatment of compound (808) with nitrous acid yields the phenylazo-oxadithiazapentalene (810) a similar reaction is the transformation of dioxathiapentalene (805) into the oxathiadiazapentalene (811) by the action of nitrobenzene-p-diazonium fluoroborate. ... 

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