Infrared spectroscopy of aqueous carboxylic acids: Comparison between different acids and their salts

被引:467
作者
Max, JJ [1 ]
Chapados, C [1 ]
机构
[1] Univ Quebec, Dept Chim Biol, Trois Rivieres, PQ G9A 5H7, Canada
关键词
D O I
10.1021/jp036401t
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
The attenuated total reflection-infrared (ATR-IR) spectra in the 4800-700 cm(-1) range of nine carboxylic acids and their sodium salts in aqueous solutions are obtained and analyzed. Overall, 22 species are studied. Six IR titrations are made with five different acids: acetic acid, malic acid, betaine, glycine, and N,N-((butyloxy)propyl) amino diacetic acid (BOPA). From the spectra of these titrations, the spectra Of four types of water (acidic, basic, saline, and pure water) are Subtracted, giving spectra with flat baselines without any artificial adjustment. Factor analysis (FA) made on the water-subtracted spectra yield the spectra of the principal species, and their abundances. Titration curves obtained from these precisely fit the theoretical curves and the pK(a) values in the literature. The remaining water bands that are not subtracted are assigned to water solute close-bound situations. The hydration number varied from 5 to 1, with an average of almost 2 per carboxyl carbonyl group. The IR CO band positions ( +/-16 cm(-1)) are assigned to the different species: 1723 and 1257 cm(-1) for the un-ionized acid double and single bonds 1579 cm(-1) for CO2 (-) asymmetric stretch; 1406 cm-1 for CO,- symmetric stretch; and 1094 cm(-1) for noncarboxylic ethoxy groups. The OH absorption I wide. The near-3400 cm(-1) covers the full re-ion, from 3700 to 1700 cm(-1). in four bands that are similar to220 cm(-1) band is assigned to solvated water, alcoholic OH, and NH groups, because these are hydrogen-bonded groups. The 3000 and 2600 cm(-1) bands are assigned to the carboxyl OH groups that are hydrogen-bonded to other carboxyl groups in the pure acrylic species or to water in the aqueous solutions cases. The 2100 cm(-1) band is assigned to a combination band that involves the far IR absorption. The absorption from 3700 to 1700 cm-1. which is sometimes called the "continuous absorption", cannot be attributed to the hydronium ion (H3O+), because the acids are not ionized; rather, it results from the strong hydrogen bonds between water and the carboxylic acids.
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页码:3324 / 3337
页数:14
相关论文
共 45 条
[1]  
Alpert N. L., 1970, IR THEORY PRACTICE I, V2nd
[2]   Infrared titration of phosphoric acid [J].
Baril, J ;
Max, JJ ;
Chapados, C .
CANADIAN JOURNAL OF CHEMISTRY-REVUE CANADIENNE DE CHIMIE, 2000, 78 (04) :490-507
[3]   Infrared intensities of liquids .20. The intensity of the OH stretching band of liquid water revisited, and the best current values of the optical constants of H2O(1) at 25 degrees C between 15,000 and 1 cm(-1) [J].
Bertie, JE ;
Lan, ZD .
APPLIED SPECTROSCOPY, 1996, 50 (08) :1047-1057
[4]  
Brzezinski B, 1996, J MOL STRUCT, V380, P195, DOI 10.1016/0022-2860(96)09221-6
[5]   Aqueous infrared carboxylate absorbances: aliphatic di-acids [J].
Cabaniss, SE ;
Leenheer, JA ;
McVey, IF .
SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY, 1998, 54 (03) :449-458
[6]   Aqueous infrared carboxylate absorbances: Aliphatic monocarboxylates [J].
Cabaniss, SE ;
McVey, IF .
SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY, 1995, 51 (13) :2385-2395
[7]   SEPARATION OF OVERLAPPING SPECTRA FROM EVOLVING SYSTEMS USING FACTOR-ANALYSIS .1. THEORY TO OBTAIN REAL SPECTRA [J].
CHAPADOS, C ;
TRUDEL, M .
BIOPHYSICAL CHEMISTRY, 1993, 47 (03) :267-276
[8]  
KISLINA IS, 1985, B RUSS ACAD SC, V11, P2274
[9]  
KISLINA IS, 1976, RUSS J PHYS CHEM, V50, P1676
[10]   FTIR INVESTIGATION OF POLARIZABLE HYDROGEN-BONDS IN CARBOXYLIC ACID-PYRIDINE COMPLEXES IN THE MID-IR AND FAR-IR REGION [J].
LANGNER, R ;
ZUNDEL, G .
JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS, 1995, 91 (21) :3831-3838