Transhydrazonation, osazones

The choice between Weygand s Schemes A and B proved difficult, with authors at one time favoring one Scheme and then the other. An early attempt to test the validity of the respective Schemes was made by Ruggli and Zeller, using diphenylacetoin (p-bromophenyl)hydrazone and di-phenylacetoin (p-nitrophenyl)hydrazone, which they treated with phenylhydrazine they obtained the bis(phenylhydrazone) in both cases. This result was taken by them to exclude Scheme B, which, under similar conditions, should yield a mixed osazone, but this conclusion is now invalidated by our knowledge of transhydrazonation, that is, the exchange of hydrazone residues, as in (20) (21), a possibility, which has caused... 

Hexosulose hydrazones and the mixed osazones react with diazotized aniline to give formazans, and with hydrogen peroxide to give pentonic acids. Unlike the mixed osazones obtained by transhydrazonation, the derivatives obtained from the glycosulose hydrazones are pure, uncontaminated compounds, and the positions of their hydrazone residues are well established. Thus, they afford remarkable possibilities, not only in the preparation of new types of compound, but also in enabling the reaction of osazones to be followed more closely, as in the case of triazole formation," and in studying the structure of anhydro-osazones. ... 

The exchange of the hydrazone residues in osazones has been termed transhydrazonation and, sometimes, transosazonation. The phenomenon... 

Furthermore, he used the reaction to obtain a number of mixed osazones these compounds are, however, best prepared from the glycosulose hydra-zones. A detailed study of transhydrazonation was made by Mandel, who confirmed VotoCek s finding that the reaction proceeds best when the products have low solubilities, as with the (nitro- and dinitro-phenyl)-osazones. 

Ethers.—Methylation of D-arabino-hexulose phenylosazone (174) under mild conditions yields preferentially the 6-methyl ether.430431 Vigorous methylation leads to a mixture of methylated products. Mixed 1-Ar-methyl-A-phenyl-2-phenylosazones are obtained either by direct methylation of the unchelated nitrogen432,433 or by transhydrazonation of bis(yV-melhyl-jV-phenyl)osazones with phenylhydrazine.434 Two mono-iV-methyl derivatives of D-arabino-hexulose phenylosazone, designated mixed osazones A and B, have been described in the literature. Mixed osazone A was later identified as l-(A-methyl-A-phenyl)-2-phenylosazone, whereas mixed osazone B proved to be a mixture of compound A and d-arubino-hexulose phenylosazone.157,317,320... 

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