Hydrazones mutarotation

Die Mutarotation wird durch Substituenten am a-Stickstoff des an C-2 sitzenden Hydrazon-Rests und durch Acetyherung der OH-Gruppe an C-3 von Hexosen verhindert n ). Dies wird durch den nicht moglichen 0-Chelat-Ring 144 erklart. Nach Chapman et al. zeigt 0-Acetyl-trioseosazon jedoch Mutarotation. 

Fischer represented the hydrazones and osazones as open chain structures one sees at once, however, other structural possibilities since mutarotation occurs in solution in many cases. Unless this is due to decomposition, some form of tautomeric equilibrium must be postulated, and Haworth pointed out that cyclic structures must be considered Behrend and Lohr recognized the possibility of the existence of syn and anti forms, and it has also been suggested that there may be an equilibrium between hydrazone and azo structures in the osazones. 

Another controversial aspect of the bishydrazone structure concerns the hydrazone residues. The bishydrazone was proposed to have the structure 46, which mutarotates in solution to 47 (47). More recently, on the basis of a comparative study of the spectroscopic properties of the bis(phenylhydrazone) with some related compounds, the bishydrazone was assigned the structure 2,3-dideoxy-3-phenylazo-2-phenylhydrazino-L-threo-hex-2-enone-l,4-lactone (48) (48). However, this latter structure was inconsistent with its NMR spectra (49). 

D-Glucose phenylhydrazone [3713-25-5] M 358.4, m three forms. Crystallise the hydrazone from 70% aqueous EtOH or EtOH/Et20. Three forms have been described a form m 159°, 160° which mutarotates from [a] -87° to -50° (H2O) [Fischer Bcr 20 821 1887, Behrends Justus Liebigs Ann Chem 353 106 1907], p form m 140-141°, 142° which mutarotates from [a] -2° to -50° (H2O) [Behrends LohrLiebigs Ann Chem 362 78 790S], and Skraup s form m 115-116° which mutarotates from [a] -70° to -47° (H2O) [Skraup Monatsh Chem 10 406 1889, Butler Crechter J Am Chem Soc 51 3161 1921]. These mutarotate to the formazan. [Beilstein 1 IV 4322, Mester Major 7 A/n Chem Soc 77 4297 7955, Stanek et al. The Monosaccharides, Academic Press 1963, pp 539-541,543.]... 

Deoxy-D-x2/Zo-hexos-5-ulose reduced cold Fehling solution and readily formed a bis[(p-nitrophenyl)hydrazone] at room temperature and was rather alkali-labile. It showed mutarotation. The structure was deduced from elemental analysis of the compound and its derivative, and from the mode of preparation. 

The original purpose was to cyclize this compound to a cyclitol derivative by treatment with potassium in xylene. However, a crystalline diene derivative (115) was formed which, after hydrolysis of the methylene groups, gave crystalline l,6-dideoxy-D-(/ireo-2,5-hexodiulose (116). It showed no indications of the presence of a double bond and reduced Fehling solution in the cold. The location of the two keto groups at C-2 and C-5 in this compound and in the diulose (118), obtained later, was proved by ozonization of their parent diene compound (115) to yield D-threaric acid. The compound (116) showed no mutarotation and was converted into a crystalline bis[(p-nitrophenyl)hydrazone] and di-(p-nitrobenzoate). 

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. 

The hydrazones of sugars are capable of existing in various cyclic forms, whose presence is apparent from their nuclear magnetic resonance (NMR) spectra and from the complex mutarotation curves they exhibit110,111117118 (which seldom follow first-order kinetics). The principal structures encountered in saccharide hydrazones are the acyclic, Schiff base-type true hydrazones and the cyclic hydrazino forms, namely glycopyranosyl- and gly-cofuranosylhydrazines. For example, three isomeric forms of D-glucose phenylhydrazone have been isolated.119 The Schiff base derivatives can be... 

D-Glucose phenylhydrazone [3713-25-5] M 358.4, m three forms. Crystallise the hydrazone from 70% aqueous EtOH or Et0H/Et20. Three forms have been described a form m 159°, 160° which mutarotates from [a]g> -87° to -50° (H2O) [Fischer 20 821 1887, Justus Liebigs Ann Chem 353 106 1907],... 

Although the acetylated galactose hydrazones probably have acyclic structures, the hydrazones with free hydroxyls may exist in the ring forms. In solution, the sugar hydrazones show complex mutarotations which pass through a maximum or minimum 208 210, 211). The failure of the muta-rotation equation to follow the first-order equation indicates that three or more substances take part in the equilibrium. Three isomeric glucose eiO. H. Jacobi, Ann. 272, 170 (1892). 

The hydrazones and osazones rarely have sharp melting points, and disparities in reported values are often encountered. Moreover, optical rotations are frequently difficult to determine because of slow, complex mutarotations. Confirmation of the identity through a comparison of X-ray patterns or through other derivatives is desirable. The osotriazoles (Chapter VIII) prepared from the osazones by the reaction of copper sulfate generally have properties quite suitable for qualitative analyses. Isolation of the more-soluble osotriazoles is facilitated by adsorption on and elution from activated carbon (29a),... 

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