Alditols complex-formation

Decarbonylation of aldoses.2 Although this rhodium complex has been known since 1968 to effect decarbonylation of aldehydes, it has been used for decarbonylation of sugars only recently, probably for lack of a compatible solvent. Actually, this reaction when carried out in N-methyl-2-pyrrolidinone (NMP) at 110-130° is extremely useful in the case of simple aldoses, which are converted to the lower alditol with formation of carbonylchlorobis(triphenylphosphine)rhodium(I). The yields are 75-95%. This method of degradation has the further advantage that protecting groups are not necessary. Deoxyaldoses, particularly 2-deoxyaldoses, are decar-bonylated in 75-99% yield. A disadvantage of this reaction is that a full equivalent of the complex is required. 

Bourne and coworkers studied the electrophoretic behavior of many polyols in copper acetate and basic copper acetate solutions as electrolytes. Although the sugars were found to be rather unresponsive, all alditols tested showed considerable mobility, which was interpreted as being due to complex-formation with Cu " ions. Actually, the preponderant ionic species in those solutions are [Cu2(OH)2] " and CuOAc" " the behavior of copper acetate with carbohydrates will be discussed in Section III,2. 

All of the alditols form complexes with cations, but the extent of complex-formation varies considerably, the Af, values of hexitols ranging from 0.24... 

Ing retention of "free" water in the resin. While the Ca -form resin retained even less "free" water, polyols and ribose were strongly retained due to complex formation. It was confirmed that the best separation of hexoses and pentoses is obtained with the Ca -form resin, while for sugar alcohols and polyols, the -form was best. Specific applications of cation-exchange resin columns include the determination of low levels of monosaccharides, alditols, and cyclltols in sheep plasma on a Ca -form column with u.v. detection at 190 nm, an extension of this involving collection... 

Angyal et al. (1974) and Kieboom et al. (1975) have investigated the interaction of alditols with the nitrate salts of Eu and Pr, respectively. They have found that the extent of complex formation depends upon the arrangement and configuration of the hydroxyl groups. The threo-threo... 

Although many analyses are performed on alditol acetates (see Section VII, p. 56), in order to avoid the formation of multiple peaks, such a reduction is not practical when the mixture contains ketoses, notably fructose. Such analyses are mainly encountered with medical samples and in the examination of sugars occurring free in Nature. Furthermore, the peak-area ratios may be used as a means of identification, to check on the completeness of trimethylsilylation,67,89 and, despite the complex chromatograms obtained from trimethyl-silyl derivatives, they have the merit of being rapidly formed.89 For all of these reasons, improvements in the separation of monosaccharides as their trimethylsilyl derivatives continue to be of considerable importance. 

The fact that each monosaccharide may give more than one peak owing to the formation of anomeric derivatives has led to a search for means to eliminate this complication. The anomeric center may be removed either by conversion into the oxime5 or the nitrile,394,3943 by oxidation followed by formation of the lactone (see Section IX, p. 71), or by reduction to the alditol. The last method is simpler than oxidation, and the separation of alditols and of aldononitriles will be discussed here additional examples are given in Table V (see p. 119). The early work on the separation of alditols has been discussed by Bishop.4 The necessity of decomposing borate complexes... 

From these findings with triols, it follows that, apart from the expectation that formation of five- and six-membered rings would be favored (see, however, the exceptional compound 19), no general conclusions can be drawn regarding the structures of boronates derived from more-complex polyhydric alcohols. In Table V, alditol boronates are listed with structures when these can be concluded either from the method of synthesis, from physical studies, or by deduction (as with the 1,2 5,6-diesters formed from 3,4-di-O-substi-tuted mannitols). 

The relative stereochemistry of alditols can be deduced by formation of borate complexes, acetylation, partial hydrolysis to the polyol acetates, and then n.m.r. analysis. Borate complexes form preferentially in the sequence l,2-syn> 1,3-syn > 1,2-anti, 1,3-anti, and terminal diols (in staggered conformation). ... 

Thionyl chloride, as well as other inorganic acid chlorides, reacts with polyols to form mixed esters (see under Sulfate esters. Chapter III). In the presence of pyridine, partial chlorohydrin formation may occur (95), Selenium oxychloride forms a selenite ester upon reaction with mannitol (96), Phosphorus pentachloride yields unsaturated chlorohydrins of mannitol and galactitol which have the composition CeHeCU (97), Extremely interesting are the so-called complexes of alditols with various inorganic polybasic acids, their salts, or anhydrides in aqueous solutions. Complexes with boric, molybdic, tungstic, and other acids, as well as the oxides of antimony and arsenic, have been reported. It is believed that these complexes are true esters with one or more moles of alditol, a chelate type of structure being involved at some point. For the hexitols a compound with boric acid such as the following is postulated (98),... 

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