Chemistry of osazones

Eldebfibld, Robert C., The Carbohydrate Components of the Cardiac Glycosides, 1, 147-173 El Khadem, Hassan, Chemistry of Osazones, 20, 139-181 El Khadem, Hassan, Chemistry of Osotriazoles, 18, 99-121 Ellis, G. P., The MaiUard Reaction, 14, 63-134... 

Phenylhydrazine on exposure to light slowly darkens and eventually becomes deep red in colour salts of the base share this property but to a lesser degree, the sulphate and acetate (of the common salts) being most stable to light. Phenylhydrazine is largely used in organic chemistry to characterise aldehydes and ketones as their phenyl-hydrazones (pp. 342, 345), and carbohydrates as their osazones (pp. 136-140). It is readily reduced thus in the process of osazone formation some of the phenylhydrazine is reduced to aniline and ammonia. On the... 

Peat, Stanley, The Chemistry of An-hydro Sugars, 2, 37-77 Peat, Stanley. See also, Bourne, E. J. Percival, E. G. V., The Structure and Reactivity of the Hydrazone and Osazone Derivatives of the Sugars, 3, 23-44... 

The chemistry of carba sugars is quite similar to that of cyclitols both groups lack the latent carbonyl groups of their saccharide counterparts, and therefore fail to exhibit many of the characteristic properties of monosaccharides. Thus carba sugars and cyclitols do not form hydrazones or osazones, nor do they mutarotate, or reduce heavy-metal salts in base, in contrast to their oxidation products, the inososes. 

Historically, the discovery of osazone formation marked a significant advance in the practical aspects of sugar chemistry. Sugars are well known for their reluctance to crystallize from syrups. Their osazones, however, readily form yellow aystals with sharp melting points, thus simplifying the isolation and characterization of many sugars, particularly if they have been formed as mixtures or are impure. 

An outstanding contribution to osazone chemistry was made by Hann and Hudson"" who examined the effect of boiling osazones with... 

Osazone A molecule of the general formula RC(=N-NHPh)-C(=N-NHPh)R particularly important in carbohydrate chemistry. 

First of all, new (substituted) hydrazones and osazones will be described these have been characteristic derivatives in sugar chemistry for a long time, but are now, to a certain degree, replaced by the osotriazoles. The common substituted hydrazones have been reviewed, but during the past decade a great deal of work has been done in this field, not only to resolve the last remaining doubts about osazone formation, but especially in a study of the... 

A study of the scope of this reaction has been performed which shows that excess phenylhydrazine will convert the disubstituted quinoxalines 19 into the pyrazolo[3,4-h]quinoxaline 20. Analogously hydroxylamine gave the isoxazolo compound 21 from these starting materials. The compounds 19 (R = Me or Ph) did not undergo cyclization with phenylhydrazine. A reaction mechanism has been suggested (see Scheme 1) which is analogous to osazone formation in sugar chemistry. 

Nevertheless the disentangling of these closely related compounds offered practical stumbling blocks which even the finest experimental skill could hardly surmount. It was Fischer s discovery of phenylhydrazones and osazones that opened afresh the pathway toward complete understanding. The new tool supplied by phenylhydrazine was most powerful and produced a complete change in one aspect of the carbohydrate chemistry. In an almost incredibly short time, Fischer carried to a successful conclusion a vast research which ended with the deterrnination of the structures and spatial configurations of all the known pentoses and hexoses. 

Interesting in this context is the fact that Fischer had already included D-fruc-tose in his studies on the osazone formation [16,17] and, consequently, would have conducted the Heyns rearrangement quite early in the history of carbohydrate chemistry (see Sect. 1.1). 

In this arrangement, one glncose retains its unprotected hemiacetal unit with its distinctive chemistry. For example, maltose is a reducing sugar it forms osazones, and it nndergoes mntarotation. Maltose is hydrolyzed to two molecules of glucose by aqueous add or by the enzyme maltase. It is abont one-third as sweet as sucrose. 

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