Solution-reaction Calorimetry Research Articles

Thermochemistry of alkaline-earth phenoxides

The standard molar enthalpies of formation of some alkaline-earth metal phenoxides were determined by reaction–solution calorimetry. The results obtained at T = 298.15 K were as follows: Δ f H m ∘ [ M ( OR ) 2 , cr ] / kJ · mol - 1 = - ( 837 . 9 ± 7 . 5 ) [ Mg ( OPh ) 2 ] ; − ( 837 . 4 ± 7 . 2 ) [ Ca ( OPh ) 2 ] ; - ( 888 . 1 ± 7 . 2 ) [ Ca ( O - 2 , 6 - Me 2 Ph ) 2 ] , - ( 828 . 8 ± 7 . 3 ) [ Sr ( OPh ) 2 ] ; - ( 808 . 6 ± 7 . 3 ) [ Ba ( OPh ) 2 ] ; - ( 880 . 7 ± 7 . 3 ) [ Ba ( O - 2 , 6 - Me 2 Ph ) 2 ] . Together with an appropriate Born–Haber cycle, these results allow the calculation of lattice energies for the [M(OR) 2] compounds. The thermochemical radii of the anions OR − were obtained using the Kapustinskii equation and the lattice energies previously determined. A set of lattice energies and standard molar enthalpies of formation for alkaline-earth metal phenoxides [M(OR) 2, M = Mg, Ca, Sr, Ba; R = OPh, 2,6-Me 2OPh], was presented. Estimates for these properties for unmeasured compounds were made based on a model first applied to aliphatic alkaline metal alkoxides.

Thermochemistry of Li, Na, K, Rb and Cs alkylated phenoxides

Lattice energies and thermochemical radii of the anions OR − (R = 2-Me; 2,6-Me 2; 2,4,6-Me 3; 2,6- t-Bu 2) in alkali metal phenoxides, MOR (M = Li, Na, K, Rb and Cs) were investigated based on the corresponding standard molar enthalpies of formation determined by reaction–solution calorimetry. The results obtained at 298.15 K were as follows: Δ f H m ∘ (MOR, cr)/kJ mol −1 = −398.4 ± 1.1 (LiO-2-MePh), −423.4 ± 1.6 (LiO-2,6-Me 2Ph), −457.3 ± 7.1 (LiO-2,4,6-Me 3Ph), −346.6 ± 1.4 (NaO-2-MePh), −399.1 ± 1.5 (NaO-2,6-Me 2Ph), −422.4 ± 7.1 (NaO-2,4,6-Me 3Ph), −496.6 ± 7.1(NaO-2,6- t-Bu 2Ph), −367.8 ± 1.2 (KO-2-MePh), −399.1 ± 1.4 (KO-2,6-Me 2Ph), −368.8 ± 1.2 (RbO-2-MePh), −403.6 ± 1.3 (RbO-2,6-Me 2Ph), −387.0 ± 1.6 (CsO-2-MePh) and −413.6 ± 1.3 (CsO-2,6-Me 2Ph). Estimates of thermochemical raddi, lattice energies and standard enthalpies of formation of not experimentally measured alkali metal phenoxides was successfully done with a model based on the Kapustinskii equation and the set of values experimentally determined.

Thermal decomposition of lanthanide complexes with sulfoxid ligand and study of volatile products liberated

The standard molar enthalpy of formation of crystalline bisdimethyldithiocarbamate zinc(II) complex, Zn[S 2 CN(CH 3 ) 2 ] 2 was determined through reaction-solution calorimetry in acetone, at 298 K. Using the standard molar enthalpy of formation of the gaseous chelate, the homolytic (-619.78±8.95 kJ mol -1 ) and heterolytic (-2747.71±8.95 kJ mol -1 ) mean enthalpies of zinc-sulphur bond dissociation were calculated. The investigation on the electronic structure involved the use of molecule orbital calculations.

Standard molar enthalpies of formation of two crystalline bis[ N-(diethylaminothiocarbonyl)benzamidinato]nickel(II) complexes

The standard ( p ∘=0.1 MPa) molar enthalpies of formation of the crystalline complexes bis[ N-( N″, N″-diethylaminothiocarbonyl)benzamidinato]nickel(II), {Ni(datb) 2}, and bis[ N-( N″, N″-diethylaminothiocarbonyl)- N ′-phenylbenzamidinato]nickel(II), {Ni(datpb) 2}, were determined, at T=298.15 K, by high precision solution-reaction calorimetry. Δ f H m ∘ (cr)/(kJ · mol −1) Ni(datb) 2 6.5 ± 7.9 Ni(datpb) 2 285.1 ± 11.3 From the obtained results, the metal–ligand exchange enthalpies in the crystalline phase were derived. The enthalpy of a hypothetical metal–ligand exchange reaction in the crystalline phase was derived, thus allowing a discussion of the energetics of complexation in comparison with known crystal-structural parameters.

Energetics of the interaction of the antitumour agent titanocene dichloride with glycine: enthalpy of formation of [Ti(η 5-C 5H 5) 2(OOCCH 2NH 3) 2]Cl 2

The standard molar enthalpy of formation of [Ti(η 5-C 5H 5) 2 (OOCCH 2NH 3) 2]Cl 2 in the crystalline state, at T=298.15 K, was determined as Δ f H m ∘{[Ti(η 5-C 5H 5) 2(OOCCH 2NH 3) 2]Cl 2, cr}=−(1447.6 ± 8.1) kJ · mol −1, by reaction-solution calorimetry. A discussion of the energetics of the direct interaction of the antitumour agent Ti(η 5-C 5H 5) 2Cl 2 with glycine is also presented.

Thermochemical parameters of dimethyl and di-iso-propyl dithiocarbamate complexes of palladium(II)

The standard molar enthalpy of formation of crystalline dialkyldithiocarbamate chelates, [Pd(S2CNR2)2], with R=CH3 and i-C3H7, was determined through reaction-solution calorimetry in 1,2-dichloroethane, at 298 K. Using the standard molar enthalpies of formation of the gaseous chelates, the homolytic (526±18 and 666±10) and heterolytic (2693±18 and 2957±10 kJ mol-1) mean enthalpies of palladium-sulphur bond dissociation were calculated.

Thermogravimetric and calorimetric study of cadmium iodide adducts with cyclic ureas

Adducts of general formula CdI2·nL [n=1 and 2; L: ethyleneurea (eu) and propyleneurea (pu)] were synthesized by a solid state route and characterized by elemental analysis, infrared spectroscopy, thermogravimetry and reaction solution calorimetry. The infrared results shown that eu and pu coordinate through oxygen atom. All adducts release the ligand molecules in a single mass loss step, suggesting that, in the bisadducts, both ligand molecules are in equivalent coordination sites, exhibiting similar bond enthalpies. For all thermogravimetric curves, the first mass loss step is associated with the release of ligand molecules and the second one with the sublimation of cadmium iodide: CdI2·nL(s)→CdI2(s)+nL(g); CdI2(s)→CdI2(g). The observed thermal stability trend is: CdI2·eu (228°C) > CdI2·pu (213°C) > CdI2·2pu (200) > CdI2·2eu (186°C). The standard molar reaction enthalpy in condensed phase: CdI2(cr)+nL(cr)=CdI2·nL(cr); ΔrHmθ, were obtained from reaction-solution calorimetry, to give the following values for mono and bisadducts: −7.16 and −27.61, −4.99 and −9.07kJmol−1 for eu and pu adducts, respectively. Decomposition (ΔDHmθ) and lattice (ΔMHmθ) enthalpies, as well as the mean cadmium–oxygen bond dissociation enthalpy, D(CdO), were calculated for all adducts.

Solvent Effects on the Energetics of the Phenol O−H Bond: Differential Solvation of Phenol and Phenoxy Radical in Benzene and Acetonitrile

Monte Carlo statistical mechanics simulations, density-functional theory calculations, time-resolved photoacoustic calorimetry, and isoperibol reaction-solution calorimetry experiments were carried out to investigate the solvation enthalpies and solvent effects on the energetics of the phenol O−H bond in benzene and acetonitrile. A good agreement between theoretical and experimental results is obtained for the solvation enthalpies of phenol in benzene and acetonitrile. The theoretical calculations also indicate that the differences between the solvation enthalpies of phenol (PhOH) and phenoxy radical (PhO•) in both benzene and acetonitrile are significantly smaller than previous estimations based on the ECW model. The results for the solvation enthalpies are used to obtain the O−H bond dissociation enthalpies in benzene and acetonitrile. For benzene and acetonitrile, the theoretical results of 89.4 ± 1.2 and 90.5 ± 1.7 kcal mol-1, respectively, are in good agreement with the experimental values (90.9 ± 1.3 and 92.9 ± 0.9 kcal mol-1), obtained by photoacoustic calorimetry. The solute−solvent interaction energies of phenol and phenoxy radical with both acetonitrile and benzene differ by less than 2 kcal mol-1. A detailed analysis of the solvent contributions to the differential solvation enthalpy is made in terms of the hydrogen bonds and the solute−solvent interactions. Both PhOH and PhO• induce a significant, although equivalent, solvent reorganization enthalpy. Finally, the convergence of the solute−solvent interaction is analyzed as a function of the distance to the solute and illustrates the advantages and limitations of local models such as microsolvation and hydrogen-bond-only models.

Bonding energetics in alkaline metal alkoxides and phenoxides.

The bonding energetics in a variety of alkaline metal, alkoxides and phenoxides, MOR, was investigated based on the corresponding enthalpies of formation in the crystalline state determined by reaction-solution calorimetry. The results obtained at 298.15 K were as follows: Delta(f)H(m)(o)(MOR, cr)/kJ mol(-1) = 382.7+/-1.4 (LiOC(6)H(5)), 513.6+/-2.5 (NaO-nC(6)H(13)), 326.4+/-1.4 (NaOC(6)H(5)), 375.2+/-3.4 (KOCH(3)), 434.5+/-2.7 (KOC(2)H(5)), 467.1+/-5.2 (KO-nC(3)H(7)), 459.3+/-2.1 (KO-nC(4)H(9)), 464.6+/-5.7 (KO-tC(4)H(9)), 464.3+/-2.5 (KO-nC(6)H(13)), 333.3+/-3.1 (KOC(6)H(5)), 380.6+/-2.9 (RbOCH(3)), 434.1+/-2.9 (RbOC(2)H(5)), 345.3+/-2.9 (LiOC(6)H(5)), 379.1+/-3.0 (CsOCH(3)), 432.3+/-3.1 (CsOC(2)H(5)), 466.9+/-5.0 (CsO-nC(3)H(7)), 461.3+/-3.5 (CsO-nC(4)H(9)), 461.9+/-2.5 (CsO-tC(4)H(9)), 349.2+/-1.4 (CsOC(6)H(5)). These results together with revised Delta(f)H(m)(o)(MOR, cr) values from the literature, were used to derive a consistent set of lattice energies for the MOR compounds and discuss general trends in the structure-energetics relationship based on the Kapustinskii equation.

Driving Force for the Thermally Induced Solid State Polymerization of Alkali Metal Halogenoacetates: A Thermochemical Analysis

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: (ClCH2COOLi, cr) = −(763.6 ± 1.3) kJ·mol-1, (BrCH2COOLi, cr) = −(723.7 ± 1.7) kJ·mol-1, (ICH2COOLi, cr) = −(671.1 ± 2.0) kJ·mol-1, (ClCH2COONa, cr) = −(740.9 ± 0.7) kJ·mol-1, (BrCH2COONa, cr) = −(700.2 ± 1.2) kJ·mol-1, and (ICH2COONa, cr) = −(642.0 ± 1.6) kJ·mol-1. Microcombustion calorimetric studies of a polyglycolide sample with the empirical formula C2.000H2.160O2.032Cl0.009243Na0.004404 (PGA) led to (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 → Br → 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.

Calorimetric study of the adducts CdBr 2· nL ( n = 1 and 2; L = ethyleneurea and propyleneurea)

A calorimetric study was performed for adducts of general formula CdBr 2· nL ( n=1 and 2; L=ethyleneurea (eu) and propyleneurea (pu)). The standard molar reaction enthalpy in condensed phase: CdBr 2(c)+ nL(c)=CdBr 2· nL(c); Δ r H m θ , were obtained by reaction–solution calorimetry, to give the following values for mono- and bis-adducts: −19.54 and −34.59; −7.77 and −19.05 kJ mol −1 for eu and pu adducts, respectively. Decomposition (Δ D H m θ ) and lattice (Δ M H m θ ) enthalpies, as well as the mean cadmiumoxygen bond dissociation enthalpy, D〈CdO〉, were calculated for all adducts.

The aromaticity of pyracylene: an experimental and computational study of the energetics of the hydrogenation of acenaphthylene and pyracylene.

In this work, the aromaticity of pyracylene (2) was investigated from an energetic point of view. The standard enthalpy of hydrogenation of acenaphthylene (1) to acenaphthene (3) at 298.15 K was determined to be minus sign(114.5 +/- 4.2) kJ x mol(-1) in toluene solution and minus sign(107.9 +/- 4.2) kJ x mol(-1) in the gas phase, by combining results of combustion and reaction-solution calorimetry. A direct calorimetric measurement of the standard enthalpy of hydrogenation of pyracylene (2) to pyracene (4) in toluene at 298.15 K gave -(249.9 plus minus 4.6) kJ x mol(-1). The corresponding enthalpy of hydrogenation in the gas phase, computed from the Delta(f)H(o)m(cr) and DeltaH(o)m(sub) values obtained in this work for 2 and 4, was -(236.0 +/- 7.0) kJ x mol(-1). Molecular mechanics calculations (MM3) led to Delta(hyd)H(o)m(1,g) = -110.9 kJ x mol(-1) and Delta(hyd)H(o)m(2,g) = -249.3 kJ x mol(-1) at 298.15 K. Density functional theory calculations [B3LYP/6-311+G(3d,2p)//B3LYP/6-31G(d)] provided Delta(hyd)H(o)m(2,g) = -(244.6 +/- 8.9) kJ x mol(-1) at 298.15 K. The results are put in perspective with discussions concerning the "aromaticity" of pyracylene. It is concluded that, on energetic grounds, pyracylene is a borderline case in terms of aromaticity/antiaromaticity character.

Thermochemical Properties of Palladium(II) Chelates Involving Dialkyldithiocarbamates

The standard molar enthalpies of formation of crystalline dialkyldithiocarbamates chelates, [Pd(S2CNR2)2], with R=C2H5, n-C3H7, n-C4H9 and i-C4H9, were determined through reaction-solution calorimetry in acetone, at 298.15 K. From the standard molar enthalpies of formation of the gaseous chelates, the homolytic (172.4±3.8, 182.5±3.2,150.9±3.1 and 162.6±3.1 kJ mol−1) and heterolytic (745.0±3.8, 803.7±3.3,834.3±3.1 and 735.2±3.0 kJ mol−1) mean palladium-sulphur bond-dissociation enthalpies were calculated.

Synthesis, characterization and thermodynamics of the reaction of calcium methylphosphonate with n-alkylmonoamines

Lamellar crystalline calcium methylphosphonate, Ca[(HO)O2PCH3]2.H2O reacted with a series of n-monoalkylamines to yield the compounds Ca[(HO)O2PCH3]2·xH2N(CH2)nCH3·(1−x)H2O (n=0–4). Intense bands of the phosphonate group in the 1095–995 cm−1 region in the infrared spectrum were detected. X-ray diffraction patterns showed a sharp and intense peak with an interlamellar distance of 907 pm. 31P NMR spectrum gave a peak at 27.38 ppm for phosphonate groups. On heating methylphosphonate water molecules, organic moiety and P2O5 were released to yield a residue of pyrophosphate. The aminated compound presented the same sequence of mass loss, with amine being lost in the first stage. 3C NMR spectrum presented peaks at 15 and 17 ppm for methylphosphonate groups. The original crystallinity of the compound is disturbed by the reaction with the n-alkylmonoamine, giving constant interlamellar distance. The energetic effect caused by amine was determined through reaction-solution calorimetry in the solid–liquid interface from aqueous solution. The thermodynamic data showed that the system is favored by enthalpy, Gibbs free energy, and entropy values.

Porous poly(D,L-lactide) and poly(D,L-lactide-co-glycolide) produced by thermal salt elimination from halogenocarboxylatesElectronic supplementary information (ESI) available: detailed results of the combustion calorimetric experiments. See http://www.rsc.org/suppdata/dt/b1/b104979h/

Poly(D,L-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(L-lactide) and poly(D,L-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.

Calorimetric study of ethyleneurea, ethylenethiourea and propyleneurea cadmium chloride adducts

Adducts of the general formula CdCl 2· nL [ n=1 and 2; L=ethyleneurea (eu), ethylenethiourea (etu) and propyleneurea (pu)] were synthesized by a solid state route and characterized by elemental analysis, infrared spectroscopy, and reaction solution calorimetry. The infrared results showed that eu and pu coordinate through carbonylic oxygen atoms, whereas etu uses the nitrogen as coordinating site. The standard molar reaction enthalpy in condensed phase: CdCl 2(c)+ nL(c)=CdCl 2· nL(c); Δ r H m θ , were obtained from reaction–solution calorimetry, to give the following values for mono and bisadducts: −20.0±0.1; −19.9±0.1; −13.3±0.1 and −38.6±0.1; −56.9±0.1; −17.0±0.1 kJ mol −1 for eu, etu and pu, respectively. The values of decomposition (Δ D H m θ ) and lattice enthalpy (Δ M H m θ ) as well as the mean cadmiumligand bond dissociation enthalpy, D(CdL), were calculated for all adducts.

Thermochemical data on adducts of cyclic ureas and copper chloride: the resemblance to biological systems

Adducts of the general formula CuCl 2·4L (L: ethyleneurea (eu), ethylenethiourea (etu) and propyleneurea (pu)) were synthesized and characterized by elemental analysis, infrared spectroscopy, thermogravimetry and calorimetry. The infrared results showed that eu and pu coordinate through carboxylic oxygen atoms, whereas etu uses the nitrogen atom to bond the cation. Thermal degradation of adducts starts at 130, 160 and 140°C, respectively, and is reflected by a one stage mass loss. Decomposition temperatures correlate, to some extent, with metal–ligand bond strength. The standard enthalpies of the reaction: CuCl 2(c)+4L(c)=CuCl 2·4L(c) in the condensed phase ( Δ r H m θ ) were determined by reaction–solution calorimetry. The following values were obtained: −42.50±0.92; −48.76±0.66 and −43.64±0.51 kJ mol −1 for eu, etu and pu adducts, respectively. Using Δ r H m θ values and auxiliary enthalpies of sublimation of copper chloride and adducts, the enthalpies of decomposition ( Δ D H m θ ), lattice enthalpies ( Δ M H m θ ), enthalpies of reaction in the gaseous phase ( Δ g H m θ ) and the mean metal–ligand bond enthalpies (D〈M–L〉) were calculated to be: Δ D H m θ =377.3±7.7;518.0±8.4;400.8±10.0; Δ M H m θ =552.0±7.7;692.7±8.5;575.5±10.1; Δ g H m θ =468.3±8.0;575.4±8.8;486.2±10.4 and D〈M–L〉=117.1±2.0;143.8±2.2;121.6±2.6, for eu, etu and pu adducts, respectively.

Standard Enthalpies of Formation of Li, Na, K and Tl Cyclopentadienyls

The enthalpies of formation of lithium, sodium, potassium and thallium cyclopentadienyls were determined by reaction-solution calorimetry as ΔfH° [LiCp] = −76.5 ± 2.9 kJ/mol, ΔfH° [NaCp] = −39.7 ± 2.5 kJ/mol, ΔfH° [KCp] = −83.2 ± 3.2 kJ/mol, and ΔfH° [TlCp] = +117.7 ± 1.9 kJ/mol. Using a previously developed model, the enthalpies of formation of RbCp and CsCp were estimated.

Standard Enthalpies of Formation of Li, Na, K and Tl Cyclopentadienyls

The enthalpies of formation of lithium, sodium, potassium and thallium cyclopentadienyls were determined by reaction-solution calorimetry as ΔfH° [LiCp] = −76.5 ± 2.9 kJ/mol, ΔfH° [NaCp] = −39.7 ± 2.5 kJ/mol, ΔfH° [KCp] = −83.2 ± 3.2 kJ/mol, and ΔfH° [TlCp] = +117.7 ± 1.9 kJ/mol. Using a previously developed model, the enthalpies of formation of RbCp and CsCp were estimated.

Enthalpies of formation of crystalline dimethyldithiocarbamate complexes of chromium(III) and iron(III): the estimation of the mean M–S bond-dissociation enthalpies

The standard (po= 0.1 MPa) molar enthalpies of formation of crystalline dimethyldithiocarbamate complexes of Cr(III) and Fe(III) were determined, at the temperature 298.15 K, by solution–reaction calorimetry. From these values, and estimated values for the standard enthalpies of sublimation of the complexes, the mean molar bond-dissociation enthalpies 〈Dm〉(M–S) were estimated.