Fluoride hydrogen bonding with carboxylic acids

Ions released into the matrix as the cement sets may interact with the organic part of the matrix. Metal ions, such as Ca + and AP+, may be chelated by car-boxylate groups, either on the polymer or on the tartaric acid additive. These have been considered in reasonable detail in the literature [230]. What has received far less attention is the possibility that fluoride ions might interact with carboxylic acid groups, either to modify the setting reaction or to become relatively securely anchored within the set cement. This possibility was raised in a review published in 1998 [230], but has not been followed up subsequently. It is based on the well-established observation that fluoride ion will form extremely strong hydrogen bonds with carboxylic acids in aqueous solution. They are of the type ... 

During electrochemical fluorination retention of important functional groups or atoms in molecules is essential. Acyl fluorides and chlorides, but not carboxylic acids and anhydrides (which decarboxylate), survive perfluorination to the perfluorinated acid fluorides, albeit with some cyclization in longer chain (>C4) species [73]. Electrochemical fluorination of acetyl fluoride produces perfluoro-acetyl fluoride in 36-45% yields [85]. Electrochemical fluorination of octanoyl chloride results in perfluorinated cyclic ethers as well as perfluorinated octanoyl fluonde. Cyclization decreases as initial substrate concentration increases and has been linked to hydrogen-bonded onium polycations [73]. Cyclization is a common phenomenon involving longer (>C4) and branched chains. a-Alkyl-substituted carboxylic acid chlorides, fluorides, and methyl esters produce both the perfluorinated cyclic five- and six-membered ring ethers as well as the perfluorinated acid... 

The only measured enthalpy of vaporization is for n-butyl lithium, 107.1 2.9 kJmoU, from which the constant b(Li) in equation 4 is derived as 85 kJmoU. This is a hefty value compared to fc(OH) = 29, b(—S(0)2—) = 53 and b(CY) = 11 kJmoU. However, the oligomeric states of the organolithium liquid and gas phases are not known with certainty. This is reminiscent of problems for hydrogen-bonded species such as carboxylic acids and hydrogen fluoride. 

Esters of carboxylic acids are resistant toward sulfur tetrafluoride up to 300 °C. However, in the presence of an excess of hydrogen fluoride, they react like the acids to give trifluoromethyl compounds [187,235] In contrast, esters of highly fluorinated acids or alcohols react with sulfur tetrafluonde in a hydrogen fluoride solution under mild conditions without cleavage of the ester bond and give products of the replacement of carbonyl oxygen by fluorine a,a-difluoroethers [235, 236, 237, 238] (equations 124 and 125). 

Structures and properties of other strongly associated liquids like hydrogen fluoride or carboxylic acids share many features with liquid water. Therefore, a separate discussion of other pure liquids is not needed here. Spectroscopic techniques can also be applied to solutions of hydrogen-bonded species in solvents that do not form hydrogen bonds. This method is particularly usefiil for investigations of solutions, with two solutes forming a strong... 

The use of NO and sulphur tetrafluoride (SF4) gas treatments allows more precise identification and quantification of hydroxyl (OH) and hydroperoxy (OOH) groups (as nitrites and nitrates, respectively, after NO reaction) and carboxylic acids (after SF4 treatment to produce acid fluorides) (cf. section 10.17.1.5) and ketones (after removal of the overlapping acid absorptions and hydrogen-bonding effects with —OH groups by SF4 reactions) [362]. The NO reaction products are particularly informative because of their intense absorptions (up to 4-7 times stronger than those of the original OH species) and because primary, secondary and tertiary products have different IR absorptions [362]. 

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