Dimerization of Carboxylic Acids and Salts:  An IR Study in Perfluoropolyether Media

Abstract

It was found that perfluoropolyethers (PFPE) with carboxylic acid end groups, PFPE-COOH, and their sodium salts, PFPE-COONa, afford an anhydrous fluid medium in which the direct pair-wise interaction of these end groups may be examined. An IR study (of the carbonyl band) of these materials revealed not only the dimerization of acid units, but also the formation of salt dimers, (salt)2, and mixed dimers, (acid)(salt). The carbonyl spectra of PFPE-acid/salt mixtures exhibit temperature-dependent broadening, shift, and, in some cases, coalescence of the bands which are attributed to the pseudocoalescence phenomenon stemming from the presence of relatively low energy cation exchange passages among the three possible dimers. Examination of the corresponding CH3COOH/CH3COONa system by ab initio calculations (6-31G) yielded the heat of dimerization of ∼20, ∼50, and ∼35 kcal/mol for the acid−acid, the salt−salt, and the acid−salt dimers, respectively. The calculated dimer structures are shown and discussed. The calculations also yielded the carbonyl stretching frequencies in good accord, and in support of the analyses/postulates made for the PFPE-acid/salt system.

Polyamide thin-film composite membranes based on carboxylated polysulfone microporous support membranes for forward osmosis

“…After PSF carboxylation, water uptake increases with increasing DS from 0.93% (DS=0) to 3% (DS=0.85). The acidity of carboxylic acid groups is lower than that of sulfonic acid groups, and carboxylic acids usually exist as dimeric pairs due to their tendency to "self-associate" via hydrogen bonding [37]. For these reasons, CPSF exhibits lower water uptake than sulfonated polymers at similar ion exchange capacity (IEC) [36,38].…”

Hierarchical Self‐Assembly of Amphiphilic Peptide Dendrons: Evolution of Diverse Chiral Nanostructures Through Hydrogel Formation Over a Wide pH Range

“…[16] When the pH value changed to 11 or 13, amide I and II bands showed obvious shifts to 1641 and 1551 cm À1 , respectively, which suggests that more of the b-sheet conformation existed in the gels formed at higher pH. In addition, the C= O vibration shifted to 1734 cm À1 and the typical vibration of COO À at 1600 cm À1 became more obvious.…”

Supramolecular self-assembly of linear oligosilsesquioxanes on mica – AFM surface imaging and hydrophilicity studies

“…Solvents ratio was selected to provide good solubility of LPSQ-COOH using the lowest amount of polar solvent. Two broad bands near 1550 cm -1 (anti-symmetrical) and 1400-1300 cm -1 (symmetrical 105 vibration) 59,60,66 should appear in the spectrum on formation of carboxylate groups, as in the proposed model of adsorption. The solutions are clear and transparent for at least 30 hours.…”