669-78-3Relevant articles and documents
Hydrogen-bond symmetry in difluoromaleate monoanion
Perrin, Charles L.,Karri, Phaneendrasai,Moore, Curtis,Rheingold, Arnold L.
supporting information; experimental part, p. 7766 - 7772 (2012/07/02)
The symmetry of the hydrogen bond in hydrogen difluoromaleate monoanion is probed by X-ray crystallography and by the NMR method of isotopic perturbation in water, in two aprotic organic solvents, and in an isotropic liquid crystal. The X-ray crystal structure of potassium hydrogen difluoromaleate shows a remarkably short O-O distance of 2.41 A and equal O-H distances of 1.206 A, consistent with a strong and symmetric hydrogen bond. Incorporation of 18O into one carboxyl group allows investigation of the symmetry of the H-bond in solution by the method of isotopic perturbation. The 19F NMR spectra of the mono-18O-substituted monoanion in water, CD2Cl2, and CD3CN show an AB spin system, corresponding to fluorines in different environments. The difference is attributed to the perturbation of the acidity of a carboxylic acid by 18O, not to the mere presence of the 18O, because the mono-18O dianion shows equivalent fluorines. Therefore, it is concluded that the monoanion exists as an equilibrating pair of interconverting tautomers and not as a single symmetric structure not only in water but also in organic solvents. However, in the isotropic liquid crystal phase of 4-cyanophenyl 4-heptylbenzoate, tetrabutylammonium hydrogen difluoromaleate- 18O shows equivalent fluorines, consistent with a single symmetric structure. These results support earlier studies, which suggested that the symmetry of hydrogen bonds can be determined by the local environment.
PROCESS FOR THE PREPARATION OF DIFLUOROMALEIC ANHYDRIDE AND INTERMEDIATE COMPOUNDS PRODUCED THEREBY
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, (2008/06/13)
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AN ABBREVIATED ROUTE TO DIFLUOROMALEIC ANHYDRIDE
Krespan, Carl G.
, p. 339 - 343 (2007/10/02)
Difluoromaleic anhydride is obtained in good yield by reaction of either hexafluoro-2,5-dihydrofuran or hexafluoro-2,5-dihydrothiophene with sulfur trioxide.Hexafluoro-2,5-dihydrothioyphene is prepared from sulfur and commercially available hexafluorocyclobutene, so its conversion to difluoromaleic anhydride in one step makes the latter readily available as well.