Spectra, of osazones

Acetylation.— Acetylation of n-arabino- and n-li/xo-hexulose phenyl-osazones results in the formation of crystalline tetraacetates. Wolfrom and coworkers have established an analytical technique that differentiates between iV-acetyl and 0-acetyl groups the latter were determined by the procedure of Kunz and Hudson. They were thus able to show that all four acetyl groups are 0-acetyl groups. This discovery eliminated the possibility of cyclic structures, which would have required three 0-acetyl groups and one A-acetyl group. The infrared spectra of osazone acetates also support the acyclic structure, as these compounds show only one carbonyl band, namely, that of the 0-acetyl groups. 

The nuclear magnetic resonance spectra of osazones and then-acetates (see Figs. 1 and 2) afford additional proof of the acyclic structure of the osazones. Both the acyclic osazone acetates and the free osazone, such as (43), show two imino protons in their nuclear magnetic resonance spectra which disappear on deuteration, and, as cyclization as in (48) would result in the formation of a third imino proton, it may be concluded that the free osazone exists mainly in the acyclic form (43). 

Chapman and co-workers followed the nuclear magnetic resonance spectra of osazones in methyl sulfoxide during the process of mutarotation, and observed that the spectra become constant when the optical rotation reaches the equilibrium values. They found that, during the course of mutarotation, new NH resonances appear in the region of the unchelated... 

The ultraviolet spectra of osazones have been intensively studied, and, as shown earlier (see p. 154), the characteristics favor assigning of an acyclic structure to osazones. The spectra of osazones are characterized by three maxima, at about X256, 308-314, and 395-399 m/jt, which aid in their recognition. ... 

The nuclear magnetic resonance spectra of osazones show, besides... 

Figure 2. Electron spin resonance spectra of sugar phenylhydrazones and osazones (2.5 mM to 3.5 mM, in Me2SO-l% K-tert-BuO)...

C-NMR spectra 65b,c and those of glucose osazone support a possible nonclassical aromatic system (80T2955). Closely related shifts for the C-2, C-3, and C-4 carbon atoms provide additional evidence for the 1,4-lactone structure of ascorbic acid osazone. The structural change of ZZ to an EE-configuration in DMSO for 65a and 65b is more rapid than for 65c. However, the spectra of 74a,b and 72a,b revealed marked differences. Unlike the case of compounds 65, they do exist in the solid state or in chloroform in the unique ZZ-configuration, which can be estimated to be about 50%. In contrast, compound 71 in chloroform showed only an EE-... 

It was found that the mutarotation of the sugar phenylosazones indicates a reaction of the first order, as shown in Fig. 14. With the solvent carefully evaporated in vacuo, the osazone is recovered unchanged. Repeated mutarotation takes practically the same course. As regards the ultraviolet spectra of the phenylosazones during mutarotation, a slight shift of the characteristic maximum at about 395 ma toward shorter wavelengths and a gradual disappearance of the minimum around 345 m/x are distinctly noticeable (see Fig. 15) the same holds true in respect to the recovered material. 

The infrared spectra of phenylosazones have also been studied in detail, and have been suggested as a means of identification of the different saccharide osazones. Saccharide osazones show the characteristic hydroxyl bands at 3 n, the C=N band of the hydrazone residues at 6.3 n, and three bands attributed to the phenyl ring. In the case of acetylated osazones, the 0-acetyl band appears at 1735 cm. and JV-acetylated derivatives show the A-acetyl band at " about 1640 cm.. These characteristics have greatly simplified the differentiation of 0-acetyl from iV-acetyl groups in acetylated osazones. Also, for benzoylated osazones, the differentiation offers no difficulty the 0-benzoyl band appears at 1725 cm. and the A-benzoyl band at 1685 cm.. ... 

Picric acid and the picrate salts of amines absorb at 380 nm with a molar absorptivity of 13,400. An accuracy of +2% was obtained for the spectrophotometric determination of molecular weights of amines [30]. Molecular-weight determinations have been reported of sugars from the absorption spectra of their osazones... 

Emission and excitation spectra of D-arablno-hexulose phenyl-osazone have been measured to determine the singlet and triplet... 

The solutions were examined in a Varian model V-4548 aqueous solution sample cell. All experiments in solution required a trace of oxygen. Freshly prepared solutions of phenylhydrazones or osazones (0.1 to 3.5 mM) in methyl sulfoxide were mixed with base [1 to 3% (90 mM to 270 mM) potassium terf-butoxide in methyl sulfoxide] and exposed to air for about 30 sec. Initial ESR spectra were recorded in about 30 sec after mixing. 

Roberts, who pointed out the difference in the chemical behavior of ascorbic acid and sugar osazones, preferred a 3-phenylhydrazino-4-phenylazo-5//-furan-2-one structure, which he supported by its remarkably high UV absorption [79JCS(P1)6O3]. However, this type of structure was ruled out by the C-NMR spectra. 

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-... 

Formazan formation, the presence of two 0-acetyl groups in the acetylation product of the osazone formazan obtained, and the comparative study of the ultraviolet spectra, are all in harmony with formula XXII proposed by Hardegger and Schreier i and afford evidence of its correctness. 

The sugars are occasionally identified by conversion to the crystalline hydrazones or osazones which are characterized in turn by their melting points and infrared spectra. Chromatography on columns of calcium carbonate [61] and alumina [62] resolves mixtures of the osazones and some success has attended paper chromatographic methods [62]. 

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