Aldaric acid preparation

Aldaric acid (Section 25 19) Carbohydrate in which car boxyhc acid functions are present at both ends of the chain Aldanc acids are typically prepared by oxidation of aldoses with nitnc acid... 

Unprotected and 0-protected aldaric acids such as 22-36 have been extensively used in polycondensation reactions, mainly in the preparation of polyamides and... 

Aldaric acids may be prepared from aldoses or aldonic acids by oxidation in aqueous solution with oxygen over platinum-charcoal255 or platinum-on-alumina.256 The effect of such promoters as bismuth or gold has also been studied.257 Hydrogen peroxide in the presence of iron salts has been used for the oxidation of uronic acids to aldaric acids.258... 

Bromine (hypobromite) and hypoiodite oxidations are particularly useful for the preparation of aldonic acids from aldoses and of aldaric acids from glycuronic acids. Primary alcohol groups also undergo oxidation by these reagents, although this conversion is of less value glycosides can thus be converted into glycosiduronic acids, and alditols into aldoses and aldonic acids. 

Given that D-glucose, produced on a massive scale worldwide by starch hydrolysis, is by far the most available and inexpensive aldose, the corresponding aldaric acid, D-glucaric acid, would appear to be the most attractive aldaric acid for commercial development. This report will focus on several potentially important aldaric acids, consider some of their applications as standalone chemicals, and describe how diey can be used as diacid monomers for the preparation of assorted polyamides, labeled polyhydroxypolyamides (PHPAs) or Hy oxylated Nylons. 

The term carbohydrate diacids as used in this report represents that class of compoimds know as aldaric acids, i.e., simple diacids derived from oxidation of the terminal carbons of aldoses. As a class of compounds aldaric acids have been known for more than a century and some of these diacids played an important role in Emil Fischer s assignment of the relative configurations of naturally occurring D-aldoses (1). Surprisingly, these molecules have seen very little chemical application over the past century but their time may have arrived to be considered as valuable and versatile synthons for preparation of specialty chemicals and polyamides. The material in this report presents an overview of... 

Our current major interest in aldaric acids is as monomers for polycondensation reactions with diamines to yield a broad class of polymers called polyhydroxypolyamides (PHPAs) or Hydroxylated Nylons (10). The original reports of examples of this class of polyamides were from the laboratory of N. Ogata and coworkers in Japan, beginning in the 1970s (11). More recent reports on these polymers have come from the laboratories of Hashimoto and coworkers (12) and those of author (13). Our general preparation of these polyamides, exemplified with a generic hexaric acid, is outlined in Figure 2. 

Several aspects of this research are particularly exciting. The condensation polymerization method allows for preparation of a broad spectrum of polymers with different primary structures based simply on using different diacid and diamine monomers. As a result, by choice of the acid and diamine monomers, one can alter, in somewhat predictive fashion, such polymer properties as melting point, solvent solubility, crystallinity, film and adhesive characteristics and undoubtedly other polymer properties that remain to be studied. Furthermore, the condensations require no aldaric acid hydroxyl group protection/deprotection, a very important cost consideration in the potential production of any of these materials. 

Aliphatic polyesters may be classified into two groups, depending on the bond constitution of the monomCTs poly(hydroxy acid)s i.e. polyhydroxyalkanoates (PHAs)) and polyfalkylene dicarboxylate)s [68]. The former are polymers of hydroxy acids (a, p,...(i)-hydroxy acids), obtained by ring-opening polymerization or polycondensation reactions. The latter are S3uithesized by the polycondensation reaction of diols with dicarboxylic acids. Aldonic and aldaric acids can be used to prepare both groups of polyesters. 

Garcfa-Martfn et al. reported [98] on the AABB polyamides based on these pentaric acids. Two different types of polycondensate were prepared fully sugar-based polyamides (PA-ArAr and PA-XyXy), and polyamides derived from aldaric acids and aliphatic diamines (PA- Ar and PA- Xy, = 6, 8, 12). In all these cases, aregic polymers were formed, since both sugar configurations lack the C2 axis. 

The formation of D-glucaric acid by platinum-catalysed oxidation of D-gluconic acid has been noted in the previous section. Mono- and per-allyl ether derivatives of xylaric and galactaric acids have been prepared by treating the aldaric acid with allyl alcohol in the presence of an appropriate acid catalyst. Diallyl 3-0-allyl-2,4-0-methylenexylarate was obtained in good yield when 2,4-0-methylenexylaric acid reacted with allyl bromide in the presence of alkali. The reaction of 2,3,4-tri-O-acetylxylaryl dichloride with diazomethane has been mentioned in Chapter 7. 

Aldaric acids are prepared in the laboratory by oxidation of aldoses with nitric acid. Like aldonic acids, aldaric acids exist mainly as lactones when the rings are five-membered or six-membered. 

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