Reduction of diazonium salts

There are also reports of improved yields in the hypophosphorous acid reduction of diazonium salts, particularly in the presence of a trace of cuprous oxide (Korzeniowski et al., 1977a see also Sec. 10.2), and in bromo-, and cyano-de-diazoniations if acetate ions are present (Korzeniowski and Gokel, 1977 see also Eustathopoulos et al., 1985). The positive effect of crown ethers on the yield in the... 

The trapping of hydroxyl radicals has also been of interest in connection with electrochemistry. Bard et al. (1974) initiated electrochemical applications of spin trapping and showed, for example, that the cathodic reduction of diazonium salts in the presence of PBN gives aryl-radical spin adducts. A route... 

The most feasible method consists in the reduction of diazonium salts with sodium sulfite. Although this method is given in several laboratory manuals, the results were not found entirely satisfactory. The present directions provide for a lengthy but essential heating of the diazonium-sulfite mixture, omit the useless zinc dust reduction, and supply exact details for preparation on a fairly large laboratory scale. 

Reduction of diazonium salts in aqueous solution under constant current conditions can give up to 30% yield of the phenylliydrazine [134] by interception of the... 

Photochemical arylation 4-24 Reduction of diazonium salts 4-29 Dimerization of diazonium salts 4-30 Methylation of diazonium salts 4-33 Coupling of Grignard reagents 4-34 Coupling of arylboranes 4-35 Coupling of other organometallic compounds... 

Sulfite reduction of diazonium salts leads to hydrazines. 

Metals, Metallic Oxides, and Salts. In an effort to facilitate the reduction of diazonium salts by ethanol, a number of metals, oxides, and salts are added to the reaction mixture. Finely divided cop-per, 2 - 37 68- 66- 67 cuprous oxide,6 -44- - f and cupric sulfate °-70 are often employed. 

Very often reduction of diazonium salts by ethanol requires tempera tures in the neighborhood of the boiling point of the alcohol. The reaction may take place with violence so that, once it is started, moderation by external cooling may be necessary.14 28 84... 

The reduction of diazonium salts by alkaline formaldehyde affords good yields of deaminated products in a number of instances.4 The method is simple in practice, and it is particularly effective where the ethyl alcohol procedure is of little or no value. Although there are comparatively few examples of deaminations employing alkaline formaldehyde, several generalizations can be made. 

Reduction of diazonium salts by sodium sulfite or stannous chloride usually produces hydrazines. These compounds may be oxidized to the hydrocarbons, thus providing a deamination sequence.7... 

A reaction that may seem rather pointless is the reduction of diazonium salts, that is, the replacement of N 2 by H. A good reagent is H3PO2. 

The substitution pattern of the first example is particularly important as the neurotransmitter hi serotonin is an indole with a hydroxyl group in the 5-position, and many important drugs follow that pattern. Sumatriptan (marketed as Imigran), is an example that we can also use to show that substituted phenylhydrazines are made by reduction of diazonium salts (Chapter 23). The first stage of the synthesis is nitrosation of the aniline and reduction with SnCl2 and HC1 to give the salt of the phenylhydrazine. 

Allongue P, Delamar M, Desbat B, Fagebaume O, Hitmi R, Pinson J, Saveant J-M. (1997) Convalent modification of carbon surfaces by aryl radicals generated from the electrochemical reduction of diazonium salts. / Am Chem Soc 119 210-207. 

Aryl hydrazines are formed by the reduction of diazonium salts with tin(II) chloride in hydrochloric acid (Scheme 8.24). The reduction can also be achieved by treatment with sodium sulfite solution. 

The reduction of diazonium salts by sodium sulfite forms monosub-stituted arylhydrazines. An improved procedure for the synthesis of phenylhydrazine in 84% yield is typical. Arylhydrazine salts substituted in the nucleus with halo," ether, carboxyl, or nitro groups have been prepared. The free bases are liberated from the salts by the action of aqueous sodium hydroxide or sodium acetate. 

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