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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.

The energetics of the C-Cl bond in 2-chloropropionic acid was investigated by using a combination of experimental and theoretical methods. The standard molar enthalpy of formation of liquid (S)-(-)-2chloropropionic acid, at 298.15 K, was determined as ∆ f H°m(C 3 H 5 O 2 Cl, l) ) -( 534.6 ( 1.1) kJ‚mol -1 , by rotating-bomb combustion calorimetry. The corresponding enthalpy of vaporization, ∆ vap H°m(C 3 H 5 O 2 Cl) ) (64.9 ( 0.5) kJ‚mol -1 , was also obtained from vapor pressure versus temperature measurements by the transpiration method, leading to ∆ f H°m(C 3 H 5 O 2 Cl, g) ) -(469.7 ( 1.2) kJ‚mol -1 . This value, together with the enthalpy of the isodesmic and isogyric gas-phase reaction CH 3 CH(X)COOH(g) + C 2 H 5 (g) f CH 3 CHCOOH(g) + C 2 H 5 X(g) (X ) H, Cl) predicted by density functional theory calculations and other auxiliary data, was used to derive the enthalpy of formation of the gaseous 1-carboxyethyl radical as ∆ f H°m[CH(CH 3 )COOH, g] ) -( 293( 3) kJ‚mol -1 , from which DH°[H-CH(CH 3 )COOH] ) 380.7 ( 3.9 kJ‚mol -1 and DH°[Cl-CH(CH 3 )COOH] ) 298.0 ( 3.2 kJ‚mol -1 were obtained. These values are compared with the corresponding C-H and C-Cl bond dissociation enthalpies in XCH 2 COOH, XCH 3 , XC 2 H 5 , XCH 2 -Cl, XCH(CH 3 )Cl, XCHdCH 2 , and XC 6 H 5 (X ) H, Cl). The order DH°(C-H) > DH°(C-Cl) is observed for the carboxylic acids and all other RX compounds. Comparison of DH°[X-CH(CH 3 )COOH] and DH°[X-CH 2 COOH] (X ) H, Cl) indicates that the replacement of a hydrogen of the CH 2 group of XCH 2 COOH by a methyl group leads to a decrease of both the C-H and C-Cl bond dissociation enthalpy. It is finally concluded that the major qualitative trends exhibited by the C-Cl bond dissociation enthalpies for the series of compounds addressed in this work can be predicted based on Pauling's electrostatic-covalent model. † Part of the special issue "Jack Beauchamp Festschrift". ‡ This article is dedicated to Professor Jack L. Beauchamp on the occasion of his 60th birthday.

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In revision hip replacement surgery cortical strut grafts made of allograft bone are used to augment femoral bone stock and to fix periprosthetic femoral fractures. These struts are made from femoral bone as hemi-cylinders and are fixed to host bone with cerclage wires. We developed an artificial bone substitute for such strut grafts in order to overcome availability restrictions and potential infectious hazards with allograft bone. The partially biodegradable implant consists of a functionally-graded combination of titanium, polylactide, hydroxyapatite, and calcium carbonate. It is made by manual dip-coating of the metal (after chemical surface treatment) into solutions of polylactide with suspended calcium salts. In this way the titanium core is surrounded by an inner layer of slowly biodegradable poly(L-lactide) with calcium carbonate. The part of the implant that is in contact with the bone consists of rapidly biodegradable poly(D,L-lactide), hydroxyapatite and calcium carbonate. This method leads to an implant which is easily adaptable before the implantation to the geometry of the patient's bone when moderately heated (70 degrees C), but has a sufficient mechanical strength to serve as support under physiologic temperatures. The implant is mechanically stable, biocompatible, partially biodegradable, and provides a scaffold for growing bone.

Reaction-solution calorimetry was used to determine the standard molar enthalpies of formation of a series of lithium and sodium halogenoacetates in the crystalline state at 298.15 K. The obtained values were as follows: 740.9 ( 0.7) kJ‚mol -1 , ∆ f H°m(BrCH 2 COONa, cr) ) -(700.2 ( 1.2) kJ‚mol -1 , and ∆ f H°m(ICH 2 COONa, cr) ) -(642.0 ( 1.6) kJ‚mol -1 . Microcombustion calorimetric studies of a polyglycolide sample with the empirical formula C 2.000 H 2.160 O 2.032 Cl 0.009243 Na 0.004404 (PGA) led to ∆ f H°m(PGA, pol) ) -( 379.1 ( 1.1) kJ‚mol -1 . These results were used to discuss the energetics of the solid-state polymerization of alkali metal halogenoacetates leading to polyglycolide. In agreement with experimental observations, it is concluded that for a given metal, the reaction becomes less favorable when the halogen changes along the series Cl f Br f I. The reaction is also considerably less favorable for the lithium than for the homologue sodium salts. These differences in reactivity seem to be mainly determined by the lattice enthalpy of the alkali metal halide salt formed in each reaction.

The energetics of the reaction between Ca(NO3)2(aq) and (NH4)2HPO4(aq) leading to the formation of calcium phosphate nanoparticles was investigated by flow calorimetry. The relationship between the observed enthalpy change, the pH of the (NH4)2HPO4(aq) solution, and the elemental composition and morphology of the obtained compounds was studied. Results of elemental analysis, combined thermogravimetry−infrared spectroscopy, X-ray powder diffraction, and scanning electron microscopy showed that the change of the pH during the precipitation reaction through the addition of controlled amounts of NaOH(s) to the (NH4)2HPO4(aq) solution leads to significant and reproducible changes of the chemical composition, morphology, and amorphous character of the obtained materials. These changes are reflected by the corresponding enthalpy of reaction, which seems to be predominantly determined by the differences in chemical composition.

Poly(,-lactide) has been obtained by thermal elimination of alkali chloride from alkali 2-chloropropionates. Preparative studies and differential scanning calorimetry (DSC) have shown that while the sodium and potassium compounds undergo a clean polymerisation, the lithium analogues decompose on heating without polymerisation. The energetics of the polymerisation reaction have also been investigated by determining the enthalpies of formation of sodium and lithium (S )-2-chloropropionates (from reaction-solution calorimetry), and the enthalpies of formation of poly(-lactide) and poly(,-lactide) (from micro combustion calorimetry). The results suggest that the polymerisation process is thermodynamically favourable for the sodium compounds but not for the lithium compounds, in good agreement with the experimental observations. Copolyesters of glycolic acid (polyglycolide) and lactic acid (polylactide) have been prepared by thermal reaction of crystal mixtures of sodium or potassium chloroacetates and sodium or potassium 2-chloropropionates, which were obtained by co-precipitation of the precursor compounds from methanol solutions. The crystal mixtures and reaction products have been characterised by a number of techniques, including solid state NMR spectroscopy and X-ray powder diffraction. For high contents of glycolide, the reaction occurred entirely in the solid state, whereas for cases with more than 10 mol% lactide, a melt is formed which solidifies on cooling to room temperature. The products are lactide-terminated block copolymers with typical chain lengths of 40 monomer units. Due to the solvent-free nature of the synthesis, all polymers can be obtained with microporous morphology.