Pyruvaldehyde phenylosazone

A dehydration of this type has actually been observed as a side reaction of a Lobry de Bruyn-Alberda van Ekenstein transformation in a very simple system. Thus, in experiments with the DL-glycerose-l,3-dihy-droxy-2-propanone isomerization in acetate, formate, and trimethylacetate buffers, pyruvaldehyde appeared in the reaction mixtures. (The formation of pyruvaldehyde from l,3-dihydroxy-2-propanone- and dl-glycerose-mineral acid mixtures had been observed much earlier.) Since these experiments in acidic buffers established that this reaction is subject to general acid and base catalysis, pyruvaldehyde must be formed in alkaline mixtures also. The results of Wohl s and Evans and Hass s experiments with DL-glycerose in alkaline solutions containing phenyl-hydrazine, in which pyruvaldehyde phenylosazone was isolated, support this view. 

The name phenylosazone formazan is suggested for this group of compounds, of which a few simple representatives have been known for some time, such as those where R = CH3 or R = CO2H however, these were not made from osazones, but by treatment of the corresponding a-keto-formazans with phenylhydrazine (as shown in the lower left of the above equation). For example, pyruvaldehyde phenylosazone formazan (C-acetyl-A, A -diphenylformazan phenylhydrazone) was prepared by Bamberger and Lorenzen as early as 1892 by condensation of acetyl-formazan with phenylhydrazine. The violet or brownish-black color characteristic of all known compounds of this group can be attributed to the three chromophoric groups present in the structure. 

Fig. 12.—Ultraviolet Spectra in Ethanol. 1. n-Glucose Phenylosazone Formazan 2. n-Glucose Phenylosazone Formazan Tetraacetate 3. Pyruvaldehyde Phenylosazone Formazan 4. n-Glucose Diphenylformazan.

The fact that the formazan is formed ehminates structures XVII, XVIII, and XXI, which do not meet the conditions for this reaction. This fimiishes dired evidence in place of the indirect evidence on which Hardegger and Schreier had discarded structures XVIII and XXI. The bicyclic structure XIX, and XX, proposed by Percival" can be dismissed on comparison of the ultraviolet spectra. This compound, after coupling, should contain the two chromophoric groups of the simple formazans, whereas osazone formazans contain three of them. Anhydro- D-glucose phenylosazone formazan and its diacetate display practically the same maxima (maxima at 335 and 405 ran and 340 and 405 m/x, respectively) as does the indisputably-acyclic pyruvaldehyde phenylosazone formazan (maxima at 335 and 410 m/t), and these peaks differ substantially from the values for the simple sugar for-... 

The isolation of D-aroWno-hexulose phenylosazone from both 1,4-anhydro-D-mannitol and 1,5-anhydro-D-glucitol indicates that o-aroMno-hexosulose is among the reaction products. - Crude methyl D-glucofurano-sides in dilute sulfuric acid yield pyruvaldehyde, and 2-amino-2-deoxy-D-glucose hydrochloride suffers oxidative deamination. ... 

Because of the chelated structure of sugar osazones, the osazone formazan 181, obtained by coupling diazotized [14C]aniline to a saccharide phenylosazone (180) loses 42%) of the label (as aniline) upon conversion to an osolriazole (182), whereas the formazan of an unchelated osazone, such as pyruvaldehyde osazone loses exactly half of the radioactivity as aniline during osolriazole formation (Scheme 40).168... 

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