Hydrogen fluoride dianhydrides

Variations in the proportions of the different components of product mixtures are observed in reactions that involve anhydrous HF31-80-82-84-85 and in pyridinium poly(hydrogen fluoride).86 These variations can also be explained in terms of kinetic and thermodynamic control. Thus, less stable, but more rapidly formed, dianhydrides isomerize under thermodynamic conditions to give more-stable products. It has also been noted that the starting isomeric forms of the ketose influence the kinetic outcome of the reaction.119... 

In 1993, the di-D-fructose dianhydrides were summarized as being of little, if any, commercial importance. 73 However, a search of the literature reveals an appreciable number of patents issued since 1989 for the manufacture of these compounds. These include enzymic methods for the production of individual dianhydrides (Ref. 130) or methods of production of mixtures using anhydrous HF or pyridinium poly(hydrogen fluoride) (see Ref. 131). Most cite the di-D-fructose dianhydrides as low-calorie sweetening agents (Ref. 132), and some claim anti-cariogenic properties (Refs. 132 and 133). 

Depending on the process (acid- or base-catalyzed, leading to aromatic or color caramel) and on the particular sugar substrate (sucrose, fructose), different proportions and types of these molecules can be found.291 Some of the caramel components are similar to those observed when fructose and sucrose react in hydrogen fluoride, notably bisglycosylated difructose dianhydrides.287 341... 

A number of carboxylic anhydrides have been converted into trifluoromethyl compounds by treatment with sulfur tetrafluoride, usually in the presence of hydrogen fluoride. As in the case of carboxylic esters, vigorous conditions are needed. Some examples have been presented in Houbcn-Weyl, Vol. 5/3, pp 92, 93. Depending on the reaction conditions, different compounds can be isolated. In some, cyclic di- or tetrafluorinated ethers predominate. 1.253.254 Upon reaction with sulfur tetrafluoride/hydrogen fluoride, pyromellitic dianhydride, as well as pyromellitic acid (benzcnc-l,2,4,5-tetracarboxylic acid), gives a mixture of 1,2,4,5-tet-rakis(trifluoromethyl)bcnzcne, 1,1,3,3-tetrafluoro-5,6-bis( trifluoromethyl)- ,3-dihydroisoben-zofuran, and the fully fluorinated tetrahydrobenzodifuran in an 85-88 10-13.5 1-2 ratio (see formation of compounds 13-15, vide supra)d ... 

Anthonsen, and P. Sandford (Eds.), Chitin and Chitosan, Elsevier, London, 1990, pp. 415 29. K. Bock, C. Pedersen, I. Defaye, and A. Gadelle, Steric and electronic effects in the formation of dihexulose dianhydrides. Reaction of racemic sorbose in anhydrous hydrogen fluoride and a facile synthesis of D-sorbose, Carbohydr. Res., 216 (1991) 141-148. 

L-Sorbose has been converted into a mixture of six disorbose dianhydrides (two of which were previously known) by treatment with anhydrous hydrogen fluoride, L-sorbofuranosyl fluoride being the intermediate. Five of the dianhydrides were 1,2 2,1 -Isomers [e.g., compound (19)] differing in ring size and anomeric configuration, while the sixth was the 2,1 3,2 -dianhydrlde (20). 

Treatment of l-0-(a-D-glucopyranosyl)-D-fructose with hydrogen fluoride in pyridine has afforded a l,T 2,2 dianhydride mixture with the fructose moiety in either the pyranose or furanose fonn. Some novel 1,6-anhydro-lactose derivatives for the synthesis of oligosaccharides containing N-acetyl-lactosamine residues are mentioned in Chapter 4, and a 3,6-anhydroglucofuranose derivative resulting from an unusual molecular rearrangement of a xanthate is described in Chapter 7. 

When D- and L-sorbose were mixed with hydrogen fluoride in liquid sulfur dioxide CC-D-sorbopyranose-a-L-sorbopyranose l,2 2,r-dianhydridc was formed preferentially, and similar treatment of D-sorbose and D-fructose afforded p-D-fructopyianose-a-D-sorbopyianose l,2 2,r-dianhydride. Some 1,3-anhydro-P-D-mannopyranose derivatives have been prepared by conventional means. and the NMR spectra of some 1,3-anhydro-P-L-rhamnopyranose and -P-D-mannopyranose ethers are covered in Chapter 21. 

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