卤代乙酸中C-Cl、C-Br和C-I键的能量学：XCH2COOH（X = Cl、Br、I）化合物及羧甲基自由基的生成焓

Energetics of C-Cl, C-Br, and C-I bonds in haloacetic acids: enthalpies of formation of XCH2COOH (X=CI, Br, I) compounds and the carboxymethyl radical.

作者信息

Lagoa A L, Diogo H P, Dias M P, Minas da Piedade M E, Amaral L M, Ribeiro da Silva M A, Martinho Simões J A, Guedes R C, Costa Cabral B J, Schwarz K, Epple M

机构信息

Centro de Química Estrutural, Complexo Interdisciplinar Instituto Superior Técnico, Lisboa, Portugal.

出版信息

Chemistry. 2001 Jan 19;7(2):483-9. doi: 10.1002/1521-3765(20010119)7:2<483::aid-chem483>3.0.co;2-a.

DOI:10.1002/1521-3765(20010119)7:2<483::aid-chem483>3.0.co;2-a

PMID:11271535

Abstract

The standard molar enthalpies of formation of chloro-, bromo-, and iodoacetic acids in the crystalline state, at 298.15 K, were determined as deltafH(o)m(C2H3O2Cl, cr alpha)=-(509.74+/- 0.49) kJ x mol(-1), deltafH(o)m(C2H3O2Br, cr I)-(466.98 +/- 1.08) kJ x mol(-1), and deltafH(o)m (C2H3O2I, cr)=-(415.44 +/- 1.53) kJ x mol(-1), respectively, by rotating-bomb combustion calorimetry. Vapor pressure versus temperature measurements by the Knudsen effusion method led to deltasubH(o)m(C2H3O2Cl)=(82.19 +/- 0.92) kJ x mol(-1), deltasubH(o)m(C2H3O2Br)=(83.50 +/- 2.95) kJ x mol(-1), and deltasubH(o)m-(C2H3O2I) = (86.47 +/- 1.02) kJ x mol(-1), at 298.15 K. From the obtained deltafH(o)m(cr) and deltasubH(o)m values it was possible to derive deltafH(o)m(C2H3O2Cl, g)=-(427.55 +/- 1.04) kJ x mol(-1), deltafH(o)m (C2H3O2Br, g)=-(383.48 +/- 3.14) kJ x mol(-1), and deltafH(o)m(C2H3O2I, g)=-(328.97 +/- 1.84) kJ x 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, deltafH(o)m(CH2COOH, g)=-(238 +/- 2) kJ x mol(-1), obtained from density functional theory calculations, led to DHo(H-CH2COOH)=(412.8 +/- 3.2) kJ x mol(-1), DHo(Cl-CH2COOH)=(310.9 +/- 2.2) kJ x mol(-1), DHo(Br-CH2COOH)=(257.4 +/- 3.7) kJ x mol(-1), and DHo(I-CH2COOH)=(197.8 +/- 2.7) kJ x mol(-1). A discussion of the C-X bonding energetics in XCH2COOH, CH3X, C2H5X, C2H3X, and C6H5X (X=H, Cl, Br, I) compounds is presented.

摘要

通过转动弹式燃烧量热法测定了在298.15K下晶体状态的氯乙酸、溴乙酸和碘乙酸的标准摩尔生成焓，分别为ΔfHmθ(C2H3O2Cl, cr α)=-(509.74±0.49) kJ·mol-1、ΔfHmθ(C2H3O2Br, cr I)=-(466.98±1.08) kJ·mol-1和ΔfHmθ (C2H3O2I, cr)=-(415.44±1.53) kJ·mol-1。用努森 effusion 法测量蒸气压与温度的关系，得到在298.15K时，ΔsubHmθ(C2H3O2Cl)=(82.19±0.92) kJ·mol-1、ΔsubHmθ(C2H3O2Br)=(83.50±2.95) kJ·mol-1和ΔsubHmθ-(C2H3O2I) = (86.47±1.02) kJ·mol-1。根据得到的ΔfHmθ(cr)和ΔsubHmθ值，可以推导出ΔfHmθ(C2H3O2Cl, g)=-(427.55±1.04) kJ·mol-1、ΔfHmθ (C2H3O2Br, g)=-(383.48±3.14) kJ·mol-1和ΔfHmθ(C2H3O2I, g)=-(328.97±1.84) kJ·mol-1。这些数据，结合已发表的乙酸生成焓值，以及通过密度泛函理论计算得到的羧甲基自由基的生成焓ΔfHmθ(CH2COOH, g)=-(238±2) kJ·mol-1，得出DHo(H-CH2COOH)=(412.8±3.2) kJ·mol-1、DHo(Cl-CH2COOH)=(310.9±2.2) kJ·mol-1、DHo(Br-CH2COOH)=(257.4±3.7) kJ·mol-1和DHo(I-CH2COOH)=(197.8±2.7) kJ·mol-1。本文还讨论了XCH2COOH、CH3X、C2H5X、C2H3X和C6H5X（X = H、Cl、Br、I）化合物中C-X键的能量学。