AGMF

Scheme 2.17 Generation of isomaltulose from sucrose, and the follow-up products with industrial potential.

however, affording the potassium salt of the next lower aldonic acid, that is, glucosyl-a-(l!5)-d-arabinonic acid ('GPA') (Scheme 2.17), isolable as such, or upon neutralization, as the GPA-lactone in high yields each.131

Another, industrially relevant follow-up reaction of isomaltulose comprises its ready conversion into 5-(a-d-glucosyloxymethyl)-furfural ("a-GMF") by acidic dehydration of its fructose portion under conditions (acidic resin in DMSO, 120°C132) that retain the intersaccharidic linkage (Scheme 2.17). As this process can also be performed in a continuous-flow reactor,132a a most versatile building block is available from sucrose in two steps, of which the first is already industrially realized, and the second simple enough to be performed on a large scale.

HO HC

HO HC

Acyl chloride H0

Fat alcohol H(

Scheme 2.18 Isomaltulose-derived products with surfactant and liquid crystalline properties.

GPA-Lactone

Fat amines

GMF-Amine

Acyl chloride H0

GMF-Acid

Fat alcohol H(

Scheme 2.18 Isomaltulose-derived products with surfactant and liquid crystalline properties.

Various products with industrial application profiles have been prepared from GPA and a-GMF (Scheme 2.18): Amidation of GPA-lactone with the C8- and C12-"fat amines," provided the GPA-amides,131 which not only exhibit promising detergent profiles but also surprising liquid crystalline properties, such as SAd— phases over a broad temperature range.133 As a glucosylated HMF, a-GMF provides a particularly rich chemistry:132,134 aldol-type condensations provide derivatives with polymerizable double bonds that are expected to yield novel, hydrophilic polymers; oxidation and reductive amination generate the a-GMF-carboxylate and a-GMF-amine, respectively, which on esterification with long-chain alcohols or N-acylation with fatty acids afford a novel type of liquid crystals,133 as the hydrophilic glucose part and the hydrophobic fat-alkyl residue are separated by an quasi-aromatic spacer; and they combine high surface activity with biocompatibility, making them promising candidates for biomedical applications.

2.3.4.5 Linear C—C-Polymers with Pendant Sucrose Residues. The synthesis of sugars carrying O-linked residues with polymerizable double bonds ("vinyl-saccharides") and their radical or cationic copolymerization has been extensively pursued over the last 70 years,135 with major emphasis on suitable derivatives of glucose and sucrose—the first example, the polymerization of 1,2:5,6-di-O-isopropylidene-3-O-vinyl-d-glucofuranose dating back to Reppe and Hecht in the 1930s.136 Thus, a large series of mono-O- and di-O-substituted derivatives of sucrose—with polymerizable C=C double bonds in ester or ether moieties

137138

attached—have been prepared, usually as mixtures with average degrees of substitution: esters of acrylic or methacrylic acid, or vinylbenzyl ethers mostly. Their polymerization as such, or copolymerization with the standard petroleum-based monomers (methyl methacryalate, methyl acrylate, acrylonitril, styrene, etc.), have led to a variety of interesting linear and cross-linked polymers with "sucrose

Figure 2.9 Idealized representation of a linear polymer resulting from radical polimerization of a mono-O-methacroyl-sucrose (left) and a 1:1 copolymerization product with styrene. Di-O-substituted vinyl-sucroses are deemed to lead to cross-linked polymers (right).

137 138

anchors" attached to the polymeric carbon chain(s), ' as schematically represented in Figure 2.9. Various surface modifications of polymers by graft polymerizations with vinyl-sucroses have also been reported, for example, grafting of sucrose acrylate on polyvinyl chloride (PVC) films.139

Despite the highly versatile application profiles of polymers with adjunct sucrose (or other sugar) residues—their major asset is enhanced hydrophilicity as compared to their hydrophobic petroleum-derived counterparts—interest appears to be restricted to biomedical uses. Currently none is produced commercially, as the generation of vinyl-sucroses and their often capricious polymerization have made their use as commodity plastics uneconomical. Another reason is their limited biodegradability: only the sugar portion is biodegradable, with a polymeric carbon chain left over. Because biodegradability is a major issue today,140 these polyvinylsaccharides are unlikely to become petrochemical substitution options in the near future.

2.4 CONCLUSION

The utilization in nonfoods of inexpensive, bulk-scale-accessible, low-molecular-weight carbohydrates—sucrose, glucose, xylose, and fructose being the most readily accessible—is at a rather modest level in terms of large-scale manufactured commodities currently on the market. The unusually diverse stock of readily accessible products described in this chapter, which covers a wide range of industrial application profiles, is mostly unexploited in its potentialities. The reasons are mostly economic as equivalent products based on petrochemical raw materials are simply cheaper. Nevertheless, a basic change in this scenario is clearly foreseeable. As depletion of our fossil raw materials is progressing, petrochemicals will inevitably increase in price, such that biobased products will eventually become competitive. Realistic prognoses5 expect this to occur by the middle of this century at the latest.

In the meantime, it is imperative that carbohydrates be used systematically to achieve efficient, environmentally benign, and economical processes for their

large-scale conversion into industrially viable products, be it bulk or intermediate chemicals, pharmaceuticals, or polymeric organic materials. In this endeavor, national and supranational funding institutions—in Europe, the corresponding EU bodies (in the European Commission's seventh framework program, hopefully) and/or the European Renewable Raw Materials Association141—will have to play a much more dynamic role than heretofore. One decisive action, of course, is the generous funding not only of applied but of basic research activities in this area, and this over a considerably longer time frame—5-10 years for promising projects, rather than expecting that marketable products be delivered within 3-5 years. Impatience with the development of renewable resources for high-value-added products (Figure 2.10) is futile if they are harvested too early.

Another key issue is the development of a concise, long-term strategy that takes hold in academia and chemical industry. This strategy should not to be directed toward generating the very same basic chemicals from carbohydrates that are easily accessible from petrochemical sources, but toward the development of products with analogous industrial application profiles, with as little alteration of the carbohydrate structural framework as possible. Only then will economically sound biobased alternatives to petrochemicals—various potential examples are contained in this chapter—become available.

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