Reactivity, of sucrose

Pivalates. The selective pivaloylation of sucrose with pivaloyl (2,2-dimethylpropionyl) chloride has been thoroughly investigated (56). The reactivity of sucrose toward pivaloylation was shown to be significantly different from other sulfonic or carboxyflc acid chlorides. For example, reaction of sucrose with four molar equivalent of toluene-/)-sulfonyl chloride in pyridine revealed, based on product isolation, the reactivity order ofO-6 0-6 > 0-1 > 0-2 (57). In contrast, a reactivity order for the pivaloylation reaction, under similar reaction conditions, was observed to be 0-6 0-6 > 0-1 > 0-4. 

The purpose of this chapter is to provide an update on our understanding of the reactivity of sucrose and the selectivity of its transformations into functionalized derivatives that have become industrial realities because of their biodegradability or biocompatibility. It follows historical accounts on the topic books on sucrose and its chemistry,1 4 a series of books dealing with the use of carbohydrates (in general) as organic raw materials,5 8 and also chapters and review articles.9 24... 

Besides the special reactivity of the OH-2, OH-1, and OH-3 groups lies also the classical relative reactivity between the primary and secondary hydroxyl groups. Depending on the reaction conditions and the nature of the electrophilic species, it may be seen that these two types of possible reactivity can direct the reactivity of sucrose. Of course, the product distribution also depends on whether the transformations are kinetically or thermodynamically controlled. For those reactions under kinetic control, if there is enough difference in the rate of the first substitution at the most reactive hydroxyl group and the second one, then the regioselectivity also monitors the degree of substitution. 

Mixed carbonates and alkyl carbamates having long alkyl chains were prepared in aqueous alcoholic medium by reaction with chloroformates and isocyanates, respectively, demonstrating that water-sensitive reagents can be used in aqueous media on account of the significantly higher reactivity of sucrose as compared to water and simple alcohols.130,132 The higher stability towards basic conditions of the carbamates as compared to esters or carbonates is such that these materials can be used in basic pH formulations. 

Sucrochemistry is already more than 50 years old, and has become a field of carbohydrate chemistry on its own. Indeed, considerable progress has been achieved in the monitoring of the chemical reactivity of sucrose, with the efforts of many research teams who have built on the steps of a few pioneers. Many sucrose derivatives can now be prepared, and sophisticated synthons as well as simple substituted compounds have been reported. However, only a few examples have yet reached the level of the industrial development, and these are mainly in the field of food and cosmetic additives and surfactants. Various polymers, additives for materials, and some chemical intermediates have also been produced. Bioconversions are certainly a major avenue for using sucrose as a starting material, and ethanol production will increase as a consequence of high oil prices. Current awareness of the shortage of fossil resources emphasizes the potential for chemical transformations of sucrose in providing new uses of this abundant natural resource. 

Introductory Remarks on the Chemical Reactivity of Sucrose, E. L. Hirst, C. R. Assemblee Comm. Intern. Tech. Sucrerie, 10e, Londres, 12 (1957). 

Sulfonate Esters. Sucrose sulfonates are valuable intermediates for the synthesis of epoxides and derivatives containing halogens, nitrogen, and sulfur. In addition, the sulfonation reaction has been used to determine the relative reactivity of the hydroxyl groups in sucrose. The general order of reactivity in sucrose toward the esterification reaction is OH-6 OH-6 > OH-1 > HO-2. 

The apphcation of bimolecular, nucleophilic substitution (S ) reactions to sucrose sulfonates has led to a number of deoxhalogeno derivatives. Selective displacement reactions of tosyl (79,85), mesyl (86), and tripsyl (84,87) derivatives of sucrose with different nucleophiles have been reported. The order of reactivity of the sulfonate groups in sucrose toward reaction has been found to be 6 > 6 > 4 > 1. ... 

Direct halogenation of sucrose has also been achieved using a combination of DMF—methanesulfonyl chloride (88), sulfuryl chloride—pyridine (89), carbon tetrachloride—triphenylphosphine—pyridine (90), and thionyl chloride—pyridine—1,1,2-trichloroethane (91). Treatment of sucrose with carbon tetrachloride—triphenylphosphine—pyridine at 70°C for 2 h gave 6,6 -dichloro-6,6 -dideoxysucrose in 92% yield. The greater reactivity of the 6 and 6 primary hydroxyl groups has been associated with a bulky halogenating complex formed from triphenylphosphine dihaUde ((CgH )2P=CX2) and pyridine (90). 

The reactive intermediate, (C2H3)2NCH2CH2C1 HCl, which is used to produce cationic starch, is made by the reaction of (C2H3)2NCH2CH20H with thionyl chloride. A synthetic sweetener (qv), sucralose [56038-13-2] is made by the reaction of sucrose or an acetate thereof with thionyl chloride to replace three hydroxy groups by chlorines (187,188). 

Sugg and Hehre43 also obtained precipitin reactions with dextran or with sterile filtrates of sucrose broth cultures of L. mesenteroides (designated for convenience strain A) and not only anti-Leuconostoc sera, but also pneumococcus Types II, XII and XX antisera. Leuconostoc organisms cultured on D-glucose broth neither stimulated the production of dextran-reactive antibodies in rabbits, nor absorbed dextran-reactive antibodies from sera, as did organisms cultured on sucrose. Absorption with the homologous bacteria (Leuconostoc, pneumococcus Types II,... 

The Sn2 reaction of octa-0-(methylsulfonyl)sucrose with sodium bromide revealed further the comparative reactivities of the sulfonyloxy substituent at C-6, C-6, and other carbon atoms.97 On treatment with sodium bromide in butanone, octa-0-(methylsul-fonyl)sucrose gave 6,6 -dibromo-6,6 -dideoxy-2,3,4,l, 3, 4 -hexa-O-(methylsulfonyl)sucrose and an equimolar mixture of 6- and 6 -bromodeoxysucrose heptakis(methanesulfonates) in 21 and 61% yield, respectively. Unlike the conclusion from previous observations,29,96 presence of the latter product suggested that the reactivities of the 6- and 6 -sulfonyloxy substituents in octa-O-(methylsulfonyl)-sucrose are comparable. The evidence was based only on the results of measurement of the intensity peaks of the H n.m.r. spectra of the... 

These results support the earlier observation (see Section VII, 1) that the reactivity of sulfonyloxy groups in sucrose sulfonates for Sn2 reaction is in the order C-6 > C-6 > C-4 > C-l. ... 

T,6,-tri-0-/t77 -butyldimethylsilyl ethers in yields of 10.5, 36.4, and 33.5%, respectively. Monosubstitution at C-6 and C-T under the conditions employed was not observed. When sucrose was treated with one molar equivalent of the more sterically hindered / -butyldiphenylsilyl chloride in pyridine, 6,-0-/t77 -butyldiphenylsilylsucrose was isolated in 49% yield (28). 6,6,-Di-0-/ -butyldiphenylsilylsucrose (78%) is obtained as the principal product when three molar equivalents of the silyl ating reagent are used. The 6,l,6,-tri-0-/ -butyldiphenylsilylsucrose is the principal product on treatment of sucrose with 4.6 molar equivalents of the silyl ating reagent. These results clearly show that HO-6 is the most reactive site toward silylation. 

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