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Energetics of C−Cl, C−Br, and C−I Bonds in Haloacetic Acids: Enthalpies of Formation of XCH 2 COOH (X=Cl, Br, I) Compounds and the Carboxymethyl Radical
Author(s) -
Lagoa Ana L. C.,
Diogo Hermínio P.,
Dias M. Pilar,
Minas da Piedade Manuel E.,
Amaral Luísa M. P. F.,
Ribeiro da Silva Manuel A. V.,
Martinho Simões José A.,
Guedes Rita C.,
Costa Cabral Benedito J.,
Schwarz Karsten,
Epple Matthias
Publication year - 2001
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20010119)7:2<483::aid-chem483>3.0.co;2-a
Subject(s) - chemistry , standard enthalpy of formation , enthalpy , calorimetry , haloacetic acids , thermochemistry , analytical chemistry (journal) , chlorine , thermodynamics , organic chemistry , physics
The standard molar enthalpies of formation of chloro‐, bromo‐, and iodoacetic acids in the crystalline state, at 298.15 K, were determined as Δ f H $\rm{_{m}^{\,o}}$ (C 2 H 3 O 2 Cl, cr α )=−(509.74±0.49) kJ mol −1 , Δ f H $\rm{_{m}^{\,o}}$ (C 2 H 3 O 2 Br, cr I)=−(466.98±1.08) kJ mol −1 , and Δ f H $\rm{_{m}^{\,o}}$ (C 2 H 3 O 2 I, cr)=−(415.44±1.53) kJ mol −1 , respectively, by rotating‐bomb combustion calorimetry. Vapor pressure versus temperature measurements by the Knudsen effusion method led to Δ sub H $\rm{_{m}^{\,o}}$ (C 2 H 3 O 2 Cl)=(82.19±0.92) kJ mol −1 , Δ sub H $\rm{_{m}^{\,o}}$ (C 2 H 3 O 2 Br)=(83.50±2.95) kJ mol −1 , and Δ sub H $\rm{_{m}^{\,o}}$ (C 2 H 3 O 2 I)=(86.47±1.02) kJ mol −1 , at 298.15 K. From the obtained Δ f H $\rm{_{m}^{\,o}}$ (cr) and Δ sub H $\rm{_{m}^{\,o}}$ values it was possible to derive Δ f H $\rm{_{m}^{\,o}}$ (C 2 H 3 O 2 Cl, g)=−(427.55±1.04) kJ mol −1 , Δ f H $\rm{_{m}^{\,o}}$ (C 2 H 3 O 2 Br, g)=−(383.48±3.14) kJ mol −1 , and Δ f H $\rm{_{m}^{\,o}}$ (C 2 H 3 O 2 I, g)=−(328.97±1.84) kJ mol −1 . These data, taken with a published value of the enthalpy of formation of acetic acid, and the enthalpy of formation of the carboxymethyl radical, Δ f H $\rm{_{m}^{\,o}}$ (CH 2 COOH, g)=−(238±2) kJ mol −1 , obtained from density functional theory calculations, led to DH $\rm{_{}^{\,o}}$ (H−CH 2 COOH)=(412.8±3.2) kJ mol −1 , DH $\rm{_{}^{\,o}}$ (Cl−CH 2 COOH)=(310.9±2.2) kJ mol −1 , DH $\rm{_{}^{\,o}}$ (Br−CH 2 COOH)=(257.4±3.7) kJ mol −1 , and DH $\rm{_{}^{\,o}}$ (I−CH 2 COOH)=(197.8±2.7) kJ mol −1 . A discussion of the C−X bonding energetics in XCH 2 COOH, CH 3 X, C 2 H 5 X, C 2 H 3 X, and C 6 H 5 X (X=H, Cl, Br, I) compounds is presented.