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CARBOHYDRATES AS RAW MATERIALSFOR CHEMICAL INDUSTRY

Frieder W. Lichtenthaler - Institute of Organic Chemistry - Darmstadt University of TechnologyDarmstadt, Germany

A raw material as feedstock should be renewable ther than depleting wherever tecnically and

economically practicable.”1

Introduction

Coal, oil and natural gas, the fossil resources built up over eons, are not only our main energy sup-pliers but they are also raw materials for a great variety of man-made products ranging from gasoline anddiesel oil to bulk, intermediate and fine chemicals. However, as our fossil raw materials are irrevocablydecreasing and as the pressure on our environment is building up, the progressive changeover of chemicalindustry to renewable feedstocks for their raw materials emerges as an inevitable necessity,2-5 i.e. it will haveto proceed increasingly to the raw materials basis that prevailed before natural gas and oil outpaced allother sources.

The present over-reliance of chemical industry on fossil raw materials has its foreseeable limits asthey are depleting and irreplaceable. The basic question today is not “When will affordable fossil fuels beexhausted?”, as fossil oil will be around for a long time, even if it has to be isolated eventually from olif-erous rocks or shale. The prevailing issue is: “When will be the end of cheap oil ?” or, stated more appro-priately: “When will fossil raw materials have become so expensive that biofeedstocks are an economi-cally competitive alternative ?” Experts realistically prognosticate this for 2040 at the latest.6

The transition to a more biobased production system is hampered by a variety of obstacles: Fossilraw materials are not only more economic at present, but the process technology for their conversion intoorganic chemicals is exceedingly well developed and basically different from that required for transform-ing bio-based raw materials into products with industrial application profiles. This situation originatesfrom the inherently different chemical structures of the two types of raw materials. Compared to coal, oiland natural gas, terrestrial biomass is considerably more complex, constituting a multifaceted array of lowand high molecular weight products: sugars, hydroxy and amino acids, lipids, and biopolymers such ascellulose, hemicelluloses, chitin, starch, lignin, and proteins. By far the most important class of organiccompounds in terms of volume produced are carbohydrates as they represent roughly 75 % of the annual-ly renewable biomass of about 200 bill. tons:

Of these, only a minor fraction (ca. 4 %) is used by man, the rest decays and recycles along nat-ural pathways Thus, carbohydrates, a single class of natural products - aside from their traditional uses

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for food, lumber, paper, and heat - are the major biofeedstocks from which to develop industrially andeconomically viable organic chemicals that are to replace those derived from petrochemical sources.The bulk of the annually renewable carbohydrate biomass are polysaccharides, yet their non-food utiliza-tion is confined to textile, paper, and coating industries, either as such or in the form of simple esters andethers. Organic commodity chemicals, however, are usually of low molecular weight, so they are moreexpediently obtained from low molecular weight carbohydrates than from polysaccharides. Accordingly,the constituent repeating units of these polysaccharides - glucose (cellulose, starch), fructose (inulin), xylose (xylan),or disaccharide versions thereof,most notably sucrose -,are the actual carbohydrate raw materials for organic chem-icals with tailor-made industrial applications: they are inexpensive, ton-scale accessible, and provide an ensuingchemistry better worked out and more variable than that of their polymers.

1. Availability of mono- and disaccharides

Table 1 lists the availability and bulk-quantity prices of the eight least expensive sugars - all wellbelow ¤ 10/kg - as compared to some sugar-derived, naturally occurring compounds and basic chemicalsfrom petrochemical sources. The result is stunning, since the five cheapest sugars, some sugar alcohols, andsugar-derived acids are not only cheaper than any other natural product, but they compare favorably withbasic organic bulk chemicals such as acetaldehyde or aniline. Actually, the first three of these sugars,sucrose, glucose, and lactose, are in the price range of some of the standard organic solvents.

Table 1: Annual production volume and prices of simple sugars, sugar-derived alcohols and acids as compared to some petrochemically derived basic chemicals and solvents

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Despite their large-scale accessibility, chemical industry, at present, utilizes these mono- and disac-charides only to a minor extent as feedstock for organic chemicals, which is amply documented by thefact that of the 100 major organic chemicals manufactured in the US in 1995,7 seven were derived frombiofeedstocks, and of these only five - ethanol, sorbitol, citric acid, lysine, and glutamic acid - used sug-ars as the raw materials source. The reasons, already alluded to, lie in the inherently different structureof carbohydrates and fossil raw materials, of which the essence is manifested in their structure-basednames (figure 1): Our fossil resources are hydrocarbons, distinctly hydrophobic, oxygen-free, and lack-ing functional groups; annually renewables are carbohydrates, overfunctionalized with hydroxylgroups and pronouncedly hydrophilic. Needless to say, that methods required for converting carbohy-drates into viable industrial chemicals - reduction of oxygen content with introduction of C=C andC=O unsaturation - are diametrically opposed to those prevalent in the petrochemical industry.

Figure 1: Hydrocarbons vs carbohydrates: more than a play on words, as their names, taken lite-rally, reveal the basic differences in their utilization as organic raw materials

Intense efforts within the last decade8-11 to boost the acquisition of organic chemicals from thesugars listed in Table 1 have, so far, not been able to bridge the conceptional, technological, and eco-nomic gap between hydrocarbons and carbohydrates as organic raw materials.

2. Current non-food industrial uses of carbohydrates

The present utilization of carbohydrates as a chemical feedstock - be it for bulk, intermediate, finechemicals, pharmaceuticals, agrochemicals, or high-value-added speciality chemicals - is modest.The few examples presently realized on an industrial scale are outlined briefly.

Ethanol. The manufacturing costs of petrochemical ethanol from ethene or, bio-based by fermenta-tion from glucose e.g. in sucrose molasses are said to be roughly the same at a comparable plant size.Its major non-food use is as a fuel additive, which requires hefty government subsidy to remain com-petitive. Another disadvantage is in the fact, that fermentation generates two moles of CO2 per moleof sugar. Thus, the process does not contribute to the reduction of CO2 in the environment.

Lactic Acid. Large-scale production is based on fermentation processes starting from glucose-con-taining materials (sucrose, whey, starch). Whilst its major use is in food industry, recent non-food

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applications have made it a large-scale organic commodity chemical, of which most is subsequentlypolymerised via its cyclic dimer (lactide) to a high molecular weight polyester, polylactic acid(“PLA”).12 Due to its high strength it can be fabricated into fibers, films, and rods that are fullybiodegradable and compostable, having degraded within 45-60 days. Accordingly, PLA and copoly-mers of lactic and glycolic acid are of particular significance for food packaging and for agriculturalor gardening applications.

Figure 2: Non-food applications of lactic acid

Another encouraging “green” development based on lactic acid is its ethyl ester (“VertecTM”),that has recently been marketed for applications in specialty coatings, inks, and straight use cleaningbecause of its high performance and versatility.13 As a most benign solvent – green, readily biodegrad-able, and with excellent toxicology records – it has the potential to displace various petrochemicallybased solvents such as acetone, DMF, toluene or N-methylpyrrolidone in industrial processes.

Furfural. With an annual production of about 250 000 tons, furfural (2-furfuraldehyde)appears to be the major large-volume organic prepared from carbohydrate sources. Indeed, its priceof about 250 ¤/t lies in the range of the basic petrochemicals mentioned, benzene and toluene beingin the ¤ 225 – 250 region. The technical process involves exposure of agricultural or forestry wastesto aqueous acid and fairly high temperatures (figure 3), the pentosans first being hydrolyzed to pen-toses and then undergoing cyclodehydration.14

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Figure 3: Generation of furfural from pentosans in agricultural wastes (corn cobs, oat hulls,wood chips, bagasse) and furanic commodity chemicals derived therefrom.

The chemistry of furfural is well-developed, providing a host of versatile industrial chemicalsby simple, straightforward operations (figure 3): furfuryl alcohol and its tetrahydro derivative (hydro-genation), furfurylamine (reductive amination), furoic acid (oxidation) and furanacrylic acid (Perkinreaction), or furylidene ketones (aldol condensations). Furfural is also the key chemical for the com-mercial production of furan (through catalytic decarbonylation) and tetrahydrofuran (hydrogenation),thereby providing a biomass-based alternative to its petrochemical production via dehydration of1,4-butanediol.14

Alkyl Polyglucosides (“APG’s”) combine high performance as non-ionic surfactants with non-toxicity, low-skin irritation, and biodegradability. They are technically produced - presently on an esti-mated 60 000 t/a scale worldwide - either through acid-induced glycosidation of glucose with a longchain fat alcohol or by transglycosylation of a short-chain alkyl glucoside with the appropriate long-chain alkanol.15 The resulting mixtures contain the a-D-glucosides majorily, as designated by the for-mula (figure 4), and are marketed as dishwashing detergents and in formulations of shampoos, hairconditioners, and other personal care products.

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Figure 4: Alkyl polyglucosides (APG’s) from D-glucose and fat alcohols (n = 4-7, x = 0.3-0.7).

These few examples of multi-ton scale use of sugar-based non-food products represent a mod-est, yet encouraging beginning in the endeavour to unlock the huge potential lying in carbohydratesas a chemical feedstock chemical industry. Thus, a fundamental research objective of the near future- hopefully incorporated into the next EU Framework Program - must be, to improve existing meth-ods and to develop new ones for the conversion of carbohydrates into industrially viable chemicals.Major veins, along which broad-scale exploratory research towards carbohydrate-based non-foodproducts is to be pursued, are outlined in the sequel for three of the most abundant low-molecular-weight carbohydrates: D-glucose, D-fructose, and sucrose.

3. Non-food valorization of glucose: Development lines

Although D-glucose is the component sugar of cellulose and starch, only the latter is the rawmaterial for its commercial production.16 As a reducing sugar, D-glucose can form pyranoid, furanoidand acyclic tautomers, so for straightforward ensuing reactions, the tautomeric form has to be fixedfirst (figure 5): isopropylidenation leads to the furanoid diacetonide, mercaptalization to an acyclicdithio-acetal, pyranoid structures may be effectively generated in the form of glucosides, and estersof glucal, and hydroxyglucal.17

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Figure 5: Well accessible, tautomerically fixed D-glucose derivatives with which to embark towardsversatile building blocks.17

Another simple, one-step entry from D-glucose to highly substituted furans involves theirZnCl2-mediated reaction with acetylacetone.18 As only the first two sugar carbons of D-glucose con-tribute to the formation of the furan, a distinctly hydrophilic tetrahydroxybutyl side chain is elaborat-ed which can be shortened oxidatively to the dicarboxylic acid or a variety of other furanic buildingblocks (figure 6). By contrast, under mildly basic conditions D-glucose reacts with pentane-2,4-dionein an entirely different way, elaborating the 2-C-glucosyl-propanone via C-addition and subsequentretroaldol type elimination of acetate.19 As this conversion can be performed with the unprotectedsugar and with simple reagents in aqueous solution, it fully complies with green and sustainable prin-ciples.1 The procedure is equally well feasible with other monosaccharides, and, thus, one of thecleanest and most efficient preparative entry into the area of C-glycosides, which as stable “mimics”to the usual O-glycosides command major interest as glycosidase inhibitors.20

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Figure 6: One-pot conversions of D-glucose into hydrophilic furans18 or, alternatively, into C-gluco-sides by reaction with acetylacetone.19

Despite the ready accessibility of these “entry products”, and their fairly well developed ensu-ing chemistry, their exploitation towards industrial intermediates is exceedingly modest. To neverthe-less emphasize their potential towards industrial intermediates, be it as enantiopure building blocksfor the synthesis of non-carbohydrate natural products21 or for agrochemicals and/or high-value addedpharmaceuticals, a highly versatile array of six-carbon dihydropyrans is represented in figure 7, allbeing accessible from D-glucose (via the glucal and hydroxyglucal esters) in no more than three tofive straightforward steps.

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Figure 7: Pyranoid six-carbon building blocks accessible from D-glucose via glucal (upper half) orhydroxyglucal esters (lower entries) as key intermediates. All products require no more than 3 to 5straightforward steps from D-glucose.22-31

Levoglucosenone, a bicyclic dihydropyranone, is accessible even more directly by vacuumpyrolysis of waste paper.32 Although the yield attainable is relatively low - levoglucosan is alsoformed, their proportions depending on the exact conditions (figure 8) - relatively large amounts canbe amassed quickly; levoglucosenone has been used for the synthesis of a diverse variety of naturalproducts in enantiopure form.33

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Figure 8: High vacuum pyrolysis of cellulose.32

Kojic acid, a g-pyrone, is readily obtained from D-glucose either enzymatically by Aspergillusoxyzae growing on steamed rice 34 or chemically via pyranoid 3,2-enolones.21,35 A structurally corre-sponding a-pyrone can be effectively generated by oxidation of glucose to D-gluconic acid and acety-lation.36 Both, at present, are of little significance as six-carbon building blocks, despite a surprising-ly effective route to cyclopentanoid products37 which is surmised to have industrial potential:

4. D-Fructose: Potentials for Non-Food Uses

The substantial amounts of this ketohexose are mainly prepared by base-catalyzed isomeriza-tion of starch-derived glucose,38 yet may also be generated by hydrolysis of inulin, a fructooligosac-charide.39 As fructose – de facto only the b-D-fructopyranose tautomer – is about 1.5 times sweeterthan sucrose, it is widely used as a sweetener for beverages (“high fructose syrup”). Its non-food uti-lization is modest - not surprising since its basic chemistry is more capricious and considerably lessdeveloped than that of glucose. Nevertheless, there are various “entry reactions” into simple pyranoidderivatives (Figure 9) with which to exploit their industrial application potential.

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Figure 9: Readily accessible pyranoid derivatives of d-fructose.40-46

Equally simple entries - in fact one-pot reactions each - lead from D-fructose to N-heterocyclesof the pyrrole and imidazol type as well as C-fructosides (figure 10), all of which due to theirhydrophilic substitution patterns are considered to be useful building blocks towards pharmaceuticals.

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Figure 10: Versatile building blocks from D-fructose: a C-fructoside47 and hydrophilically substituted pyrroles48 and imidazoles.49,50

By far the highest industrial potential is to be attributed to 5-hydroxymethylfurfural (HMF),which has been termed “a key substance between carbohydrate chemistry and mineral oil-basedindustrial organic chemistry”.51 It is readily accessible from fructose or inulin hydrolysates by acid-induced elimination of 3 moles of water52 (figure 11), and even a pilot plant size process has been elab-orated.51

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Figure 11: Furanoid intermediate chemicals from d-fructose.42,53-56

Of the products readily generated from HMF in simple, large scale adaptable transformations(figure 11), the 5-hydroxymethyl-furoic acid, the 2,5-dicarboxylic acid, the respective 1,6-diol and1,6-diamine are most versatile intermediate chemicals of high industrial potential. De facto, they rep-resent six-carbon monomers that could replace adipic acid, terephthalic acid, hexamethylenediamineor alkyldiols in the production of polyesters and polyamides. Indeed, an impressive series of suchpolymers have been prepared57 (figure 12) either with furanic components, exclusively, or via theircopolymerization with lactic acid, hexamethylenediamine or phenylenediamine, the latter being ananalog of the commerical polyamide Kevlar“. Despite of promising properties of these polymers, theall-furanic and mixed polyamides in particular, none has proved competitive to existing products.Thus, HMF is, as of now, not produced on an industrial scale. An assessment of its economics as com-pared to petrochemical raw materials58 clearly unfolds the reasons: ton prices of naphtha and ethyleneare in the 150-400 ¤ range, distinctly above of that of inulin (500 ¤/t) or fructose (~1000 ¤/t), entail-ing a market price of HMF of about 2500 ¤/t, much too expensive at present for a bulk-scale indus-trial product. Accordingly, as long as the economic situation favors fossil raw materials, and as longas HMF is not subsidized to the extent Biodiesel is presently, its applications lie in high value-addedproducts, such as pharmaceuticals or special niche materials.

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Figure 12: Furanoic polyesters and polyamides of potential industrial significance.

5. Non-Food Valorization of Sucrose

Sucrose, affectionately called “the royal carbohydrate”,59 is a non-reducing disaccharidebecause its component sugars, D-glucose and D-fructose, are glycosidically linked through theiranomeric carbon atoms. Hence, it constitutes a b-D-fructofuranosyl a-D-glucopyranoside (figure 13).It is widely distributed throughout the plant kingdom, is the main carbohydrate reserve and energysource and an indispensable dietary material for humans. For centuries, sucrose has been the world’smost plentiful produced organic compound of low molecular mass (cf. Table1). Due to the usual over-production, and the potential to be producable on a even higher scale if required, it is, together withstarch-derived glucose, the major carbohydrate feedstock of low molecular weight, from which toelaborate organic chemicals.

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Figure 13: Common structural representations of sucrose (top entries). The molecular geometry reali-zed in the crystal is characterized by two intramolecular hydrogen bonds between the glucose and fruc-tose portion60 (center left). In aqueous solution, the two sugar units are similarly disposed towards eachother, caused by insertion of a water molecule between the glucosyl-2-OH and fructosyl-1-OH,61,62 a“water-bridge”, so to say, fixed by hydrogen bonding (center right). The bottom entries show the sol-vent-accessible surfaces (dotted areas) of the crystal form (left) and the form adopted in water63 (right).

The ensuing chemistry of sucrose is capricious. The pronounced acid sensivity of the intersac-charidic linkage excludes any reaction that requires acidic conditions, and, featuring eight hydroxylgroups with only subtle reactivity differences, reactions with high regioselectivities for one or two ofthe OH-groups are few, in fact mostly enzymatic.

Oxidation. Prototype of an “entry reaction” into modified sucroses is the essentially regiospe-cific oxidation by Agrobacterium tumefaciens, whose dehydrogenase exclusively generates 3g-keto-sucrose.64 This ready access opened the way to manifold modifications at the 3g-carbonyl function65

(Figure 14). Chemical oxidation proceeds less uniformly, e. g. agitation of an aqueous solution of pH6.5-7.0 at 35 °C with air in the presence of 0.5 % Pt/C gave a 9:9:1 ratio of the 6g-, 6f- and 1f-saccha-

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ronic acids.66 On further oxidation, particularly when using large amounts of the Pt catalyst and high-er temperature (80-100 °C), the preferred formation of the 6g,6f-dicarboxylic acid has been observed,67

which may be isolated in up to 70 % yield by continuous electrodialytic removal.68

Figure 14: Useful oxidation products of sucrose.

Extended catalytic oxidation finally yields the 1f, 6f, 6g-tricarboxylic acid, i. e. all primaryhydroxyl groups have yielded to oxidation.69 An alternate useful oxidant to the tricarboxylate is theNaOCl/TEMPO system, which on applying high-frquency ultrasound, produces the tricarboxylate inup to 70 % yield.70

Esterification. Monoesters of sucrose with long chain fatty acids such as lauric, palmitic and/orstearic acid have HLB (hydrophilic-lipophilic balance) values of 12-15 which renders them usefulnon-ionic surfactants; they have also various applications in detergents, cosmetics, and pharmaceuti-cal formulations.71 Various routes have been elaborated for their chemical or enzymatic preparation.The original Hass-Snell process72 involves transesterification of a triglyceride fat or oil with sucroseusing a base catalyst at 90 °C in DMF or DMSO. The products contains > 50 % monoesters and somedi- and higher-esters (> 10 %), unreacted sucrose and triglyceride. A relatively safer process involvedreacting a microemulsion of sucrose in propylene glycol with the fatty acid methyl ester in the pres-ence of potassium carbonate, the product containing 85 % of sucrose monoester and 15 % of diesterafter purification.73 This process was later made more sustainable by development of solvent-freeesterification comprising the reaction between molten sucrose and fatty acid methyl esters in the pres-ence of potassium or sodium soaps,74 and, alternatively, by reacting a slurry or melt of sucrose, withtriglycerides and base catalyst at 130 °C.75

In either case, the resulting sucrose fatty acid monoesters are not defined products exclusive-ly acylated at one site, but mixtures with a mono-O-substitition pattern in preference for the 2g-OH(cf. figure 15) and the three primary sites (indicated by arrows), containing also some proportion ofthe respective diesters. There are various ways to effect the esterification of sucrose more regioselec-tively, yet non is economically competitive to the chemical process mentioned, by which sucrosemonoesters are presently produced at an estimated 5000 t/a level, mainly in Japan.76 Despite

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favourable surfactant properties - the lower the proportion of dister in the product, the better - andcombining low toxicity, skin compatibility, and biodegradability, these sucrose-monoesters are gain-ing only gradual acceptance as viable alternatives to the APG’s and the harder surface active agents.

Figure 15: Sucrose mono-esters and mono-ethers with useful surfactant properties.74,75,78

Etherifiaction. Due to the being next to the anomeric center and intramolecularly hydrogen-bonded, the 2g-OH of sucrose is the most acidic, hence is deprotonated first under alkaline conditions,and, thus, preferentially etherified. Benzylation with NaH/benzylbromide in DMF, for example,results in an 11:2: mixture of 2g-O-benzyl-sucrose (Figure 15) and its 1-O- and 3f-O-isomers.77 Theformer being thus readily accessible, it proved to be a versatile intermediate for the generation of 2g-modified sucroses, e. g. the 2g-keto and 2g-deoxy derivatives as well as sucrosamine (2g-amino-2g-deoxy-sucrose),77 whose application profiles remain to be investigated.

Of higher interest industrially is the etherification of sucrose with long-chain epoxides such as1,2-epoxydodecane78 or 1,2-epoxydodecan-3-ol79 which are performable as one-pot reactions inDMSO and the presence of a base to provide sucrose mono-ethers with regioselevtivities in prefer-ence of the 2g-O- and 1f-O-positions. Unlike sucrose esters, they are resistant to alkaline conditionswhich considerably extend their potential applications as non-ionic surfactants. They also have prom-ising liquid crystalline properties, their mesophases depending on the point of attachement of the fattychain to the sucrose.74

Sucrose Conversion to Isomaltulose. As a 6-O-a-D-glucosyl-D-fructose, isomaltulose is iso-meric with sucrose, from which it is produced at an approximate 60000 t/a scale (cf. Table 1). Theindustrial process involves a glucosyl shift from the 2f-O of sucrose to the 6f-OH, effected by actionof an immobilized Protaminobacter rubrum-derived a(1Æ6)-glucosyltransferase.80,81 The isomaltuloseproduced is subsequently hydrogenated to isomalt, an approximate 1:1-mixture of the terminallya-glucosylated glucitol and sorbitol (Figure 16), which is on the market as a low-caloric sweetener

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with essentially the same taste profile as sucrose.81

Figure 16: Generation of isomaltulose from sucrose, and ensuing products of industrial potential

Its large scale availability made isomaltulose an attractive target for developing non-food appli-cations. Particularly relevant in this context are oxidative conversions, hydrogen peroxide as oxidantleading to shortening of the fructose chain by four carbons to provide the glucoside of glycolic acid(“GGA”) in 40 % yield.83 Air oxidation in strongly alkaline solution (KOH), however, is less rigor-ous, affording the potassium salt of the next lower aldonic acid, i. e. glucosyl-?-(1Æ5)-D-arabinonicacid ( GPA ) (Figure 16), isolable as such, or upon neutralization, as the GPA-lactone in high yieldseach.84

Another, industrially relevant ensuing reaction of isomaltulose comprises its ready conversioninto 5-(a-D-glucosyloxymethyl)-furfural (“a-GMF”) by acidic dehydration of its fructose portionunder conditions (acidic resin in DMSO, 120 °C) that retain the intersaccharidic linkage. As thisprocess can also be performed in a continuous flow reactor,85a a most versatile building block is avail-able in two steps from sucrose, of which the first is already industrially realized, and the second sim-ple enough to be performed on a large scale.

Various products with industrial application profiles have been prepared from GPA and ?-GMF(figure 17): Amidation of GPA-lactone with long-chain amines, e. g. the C8- and C12-“fat amines”,provided the GPA-amides86 which not only exhibit promising detergent profiles, but also surprisingliquid crystalline properties, such as SAd-phases over a broad temperature rang.87 As a glucosylatedHMF, ?-GFM provides a particularly rich ensuing chemistry:85b aldol-type condensations providederivatives 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,

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which on esterification with long-chain alcohols or N-acylation with fatty acids afford a novel type ofnon-ionic surfactants, and, notable, liquid crystals87, as the hydrophilic glucose part and the hydropho-bic fat-alkyl residue are separated by an quasi-aromatic spacer.

Figure 17: Isomaltulose-derived products with surfactant and liquid crystalline properties86,87

Conclusion

Despite of the various new “entry reactions” and “reaction channels” advanced here for the threemajor bulk-accessible, inexpensive sugars (cf. Table 1) - others exist for D-xylose,88 yet a scarcely few formaltose and lactose - their potential as an organic raw material for the elaboration of industrially usefulchemicals is far from being fully explored. The unusually diverse stock of readily accessible sugar-basedproducts described in this account, which cover a wide range of industrial application profiles, lies essen-tially unexploited in its potentialities. The reasons are majorily economic as equivalent products based onpetrochemical raw materials are simply cheaper. Notwithstanding, a basic change in this scenario isclearly foreseeable. As depletion of our fossil raw materials is progressing, petrochemicals will inevitablyincrease in price, such that biobased products will eventually become competitive. Realistic prognosesexpect this for the middle of this century at the latest.In the meantime, it is imperative that carbohydrates are systematically further exploited towards effi-cient, environmentally benign, and economical processes for their large-scale conversion into indus-trially viable products, be it bulk or intermediate chemicals, pharmaceuticals, or polymeric organicmaterials. In its endeavour, national and supranational funding institutions – in Europe the corre-sponding EU bodies and/or ERRMA89 will have to play a considerably more dynamic role thanheretofore. One decisive action, of course, is the generous funding not only of applied but of basicresearch activities in this area, and this over a considerably broader time frame – 5-10 years forpromising projects rather than an expectational horizon to deliver marketable products within 3-5years. Impatience with the exploitation of renewable resources towards high value-added products(cf. figure 18) is futile if harvested too early.

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Figure 18: Impatience with renewable resources90

Another key issue is the elaboration of a concise, long-term strategy that takes hold in academia andchemical industry. This strategy, thereby, is not to be directed towards generating from carbohydratesthe very same basic chemicals that are well accessible from petrochemical sources, but towards thedevelopment of products with analogous industrial application profiles, with as little alteration of thecarbohydrate structural framework as possible. Only then, economically sound biobased alternatives topetrochemicals – various potential examples are contained in this account – will become available.

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