Aqueous infrared carboxylate absorbances: Aliphatic di-acids

Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy
By: , and 

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Abstract

Aqueous attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectra of 18 aliphatic di-carboxylic acids are reported as a function of pH. The spectra show isosbestic points and intensity changes which indicate that Beer's law is obeyed, and peak frequencies lie within previously reported ranges for aqueous carboxylates and pure carboxylic acids. Intensity sharing from the symmetric carboxylate stretch is evident in many cases, so that bands which are nominally due to alkyl groups show increased intensity at higher pH. The asymmetric stretch of the HA species is linearly related to the microscopic acidity constantof the H2A species, with σpK<0.25 log units; this relationship falls on the same line as previously observed for mono-carboxylic acids. The linear relationship applies to the acidity constant of the HA species only when the two acid groups are well separated (>2 intervening atoms). The results suggest that aqueous ATR-FTIR may be able to estimate `intrinsic' pKa values of carboxylic acids, in addition to providing quantitative estimates of ionization.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Aqueous infrared carboxylate absorbances: Aliphatic di-acids
Series title Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy
DOI 10.1016/S1386-1425(97)00258-8
Volume 54
Issue 3
Year Published 1998
Language English
Publisher Elsevier
Contributing office(s) Toxic Substances Hydrology Program
Description 10 p.
First page 449
Last page 458