Derivatives osazones

In view of the indefinite melting-points of many sugars and of their readily obtainable derivatives e.g., osazones, cf. p. 139), their identification should be based primarily on their chemical properties. Their rotatory power can often be used for identification purposes, but is not considered in this book. 

Simple sugars undergo reaction with phenylhydrazine, PhNHNH2, to yield crystalline derivatives called osazones. The reaction is a bit complex, however, as shown by the fact that glucose and fructose yield the same osazone. 

However, in some cases azines can be converted to hydrazones by treatment with excess hydrazine and NaOH. Arylhydrazines, especially phenyl, p-nitrophenyl, and 2,4-dinitrophenyl, are used much more often and give the corresponding hydrazones with most aldehydes and ketones.Since these are usually solids, they make excellent derivatives and are commonly employed for this purpose. Cyclic hydrazones are also known, ° as are conjugated hydrazones. a-Hydroxy aldehydes and ketones and ot-dicarbonyl compounds give osazones, in which two adjacent carbons have carbon-nitrogen double bonds ... 

The 2-keto acids such as 2-keto-D-galactonic acid (XXIV) can be derived from the corresponding osone (XXIII) by oxidation with bromine.10 Oxidation of L-gulosone by the same method has provided 2-keto-L-gulonic acid. The success of this oxidation depends to a large extent upon the purity of the osone subjected to oxidation and this, as previously stated, is controlled by the purity of the osazone. 

The reaction of these aldehydes, derived from periodate oxidation, with carbonyl reagents has also been investigated. Studies 147 148 were made on oxidized laminarin, a (1 —> 3)-linked polysaccharide, in which only the terminal residues had been oxidized. The addition of phenylhydrazine acetate detached the remainder of the terminal residue as glyoxal phenyl-osazone. When the aldehydic compounds derived from the periodate oxidation of raffinose and trehalose818a were reacted with p-nitrophenylhydrazine, the authors were surprised to find that one molecule of oxidized raffinose, containing six aldehydic functions, reacts with only three molecules of the reagent, and that the four aldehydic functions of the oxidized trehalose molecule react with only two. The reactions of periodate-oxidized carbo-... 

LaForge and Hudson194 prepared an osone from the phenylosazone obtained from sedoheptulose (D-aZ(ro-heptulose). The osone reduced Fehling solution strongly, formed the original osazone with phenylhydrazine, and gave a crystalline derivative with o-phenylenediamine. 

As early as 1917, it was known that C2 and C3 in this trimethyl sugar each carried a methoxyl group, since (a) it failed to yield an osazone, and (b) the trimethyl-D-glucoheptonic acid derived from it by a cyanohydrin synthesis gave a lactone only with the concomitant loss of one of the methyl radicals.135 The production of a dimethyl- and not a trimethyl-... 

Historically, techniques such as the formation of osazones and the demonstration of fermentation have contributed significantly to the separation and identification of carbohydrates. Observation of the characteristic crystalline structure and melting point of the osazone derivative, prepared by reaction of the monosaccharide with phenylhydrazine, was used in identification. This method is not completely specific, however, because the reaction involves both carbon atoms 1 and 2 with the result that the three hexoses, glucose, fructose and mannose (Figure 9.19), will yield identical osazones owing to their common enediol form. 

Hydrolysis of the diacetamides is effected by acids. Dilute hydrochloric, sulfuric and nitric acid have been used. An aldose with one carbon atom less than the original nitrile is then liberated from the combination. Only exceptionally can this aldose be isolated in pure condition without transforming it into an insoluble derivative in these instances, the method has been employed for preparative work. In most cases the sugar has been characterized as an osazone. The aldose, without great purification, has been employed successfully for reduction - or oxidation experiments. ... 

The saccharide derivatives best suited for cyclization to pyrazolines and pyrazoles are the hydrazones and osazones, which possess the two adjacent nitrogen atoms required. 

The trihydroxypropyl derivative 63 was prepared from dehydro-L-ascorbic acid phenylosazone (62) by opening the lactone ring with warm alkali and acidifying the mixture after a few minutes, whereupon the pyrazolinone 63 separated immediately.63 The structure of this compound was established by degradation,63 and confirmed by a study of its n.m.r. spectrum.64 The p-tolyl-, p-(bromophenyl)-, and p-(iodophenyl)-osazones of dehydro-L-ascorbic acid were also converted into the corresponding l-aryl-4-phenylazo-3-(trihydroxy-propyl)-5-pyrazolinone, and their acetylation and benzoylation products were prepared.64... 

The fourth student in this group, Stanford Moore, began his doctoral thesis research with Link in 1935. His work involved the development of a new, and still useful, procedure for oxidizing aldoses to the aldonic acids by potassium hypoiodite in methanol solution the resulting aldonic acids were then converted into nicely crystalline benzimidazole derivatives that proved more suitable for the characterization of carbohydrates than the classical osazones. This method, developed by Moore and Link (1940), was extended to the characterization of hexuronic acids, as their bis(benzimidazole)s, after oxidation to the glycaric acid (R. Lohmar, Dimler, Moore, and Link, 1942), of lactic acid (Moore, Dimler, and Link, 1941 Dimler and Link, 1942), and of ribose, fucose, and digitoxose (Dimler and Link, 1943). During these... 

Melting Points of Monosaccharide Osazone Derivatives Many carbohydrates react with phenylhydrazine (C6H5NHNH2) to form bright yellow crystalline derivatives known as osazones ... 

The melting temperatures of these derivatives are easily determined and are characteristic for each osazone. This information was used to help identify monosaccharides before the development of HPLC or gas-liquid chromatography. Listed below are the melting points (MPs) of some aldose-osazone derivatives ... 

As the table shows, certain pairs of derivatives have the same melting points, although the underivatized monosaccharides do not. Why do glucose and mannose, and galactose and talose, form osazone derivatives with the same melting points ... 

Carbohydrate M.P. 20°. [Pg.457]

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