Preparation and Structure of Sugar Formazans

When allowed to react in pyridine solution with cold solutions of dia-zonium compounds, aldose phenylhydrazones yield brilliant-red, readily 

Acetylation of hexose formazans with a mixture of pyridine and acetic anhydride affords readily crystallized, red pentaacetates. - 

Acetylation of the formazan of n-galacturonic acid leads to a lactone acetate which has three acetyl groups and is an appropriate starting material for the preparation of the corresponding tetrazolimn compound. 

These sugar compounds show all the characteristic properties of the formazans a brilliant red color, complexing with salts of heavy metals, and ready oxidation to colorless compounds. Nevertheless, further evidence was sought, in order to prove that they really belong to the formazan group. According to all current views on the mechanism of formazan formation, secondary phenylhydrazones, such as a 2-methyl-2-phenyl- 

As has been pointed out in Section I, 2, when R and R differ, the two isomers (A and B) permitted by the classical formulation cannot be isolated (because of the chelated structure of the formazans). This phenomenon, so very characteristic of the formazans, is also encountered in the formazans of sugars. The mono-p-bromo derivative of n-galactose diphenylformazan was prepared by two routes one was by causing n-galactose p-bromo-phenylhydrazone to react with diazotized aniline the other, by coupling D-galactose phenylhydrazone with diazotized p-bromoaniline as follows. 

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