Henry A. Skinner

Thermochemistry of arene chromium tricarbonyls and the strenghts of arene-chromium bonds

Abstract From microcalorimetric measurements at elevated temperatures of the heats of thermal decomposition and of iodination, values of the standard enthalpies of formation of the following arene chromium tricarbonyl compounds were determined: Δ H ° f [η-C 6 H 5 Me)Cr(CO) 3 ,c] = − ± 1.5 kcal mol -1 (−476 ± 6 kJ mol -1 , Δ H ° f [(η-1,3,5-C 6 H 3 Me 3 )Cr(CO) 3 ,c] = −136.5 ± 2 kcal mol -1 (−571 ± 8 kJ mol -1 ), Δ H o f [(η-C 6 H 5 Cl)Cr(CO) 3 ,c] = −111.5 ± 5 kcal mol -1 (−467 ± 21 kJ mol -1 . A microcalorimetric vacuum sublimation technique is described, from which enthalpies of sublimation, Δ H sub (298°K), were obtained for benzoic acid, 2-, 3- and 4-chlorobenzoic acids, anthracene, Cr(CO) 6 , W(CO) 6 , W(CO) 6 [C 6 H 6 Cr(CO) 3 ], [(C 6 H 5 Me)Cr(CO) 3 ], [(1,3,5-C 6 H 3 Me 3 )Cr(CO) 3 ], [C 6 Me 6 Cr(CO) 3 ], [(C 6 H 5 Cl)Cr(CO) 3 ], and [(cyclo-C 7 H 8 )Cr(CO) 3 ]. Values are derived for areneCr bond enthalpy contributions in a series of [(arene)Cr(CO) 3 ] molecules in the gas phase: these decrease along the series (C 6 Me 6 Cr) ⋟ (C 6 H 3 Me 3 Cr) > (C 6 H 5 MeCr) ≈ (C 6 H 6 Cr) > (C 6 H 5 Cr) > [(cyclo-C 7 H 8 )Cr].

Enthalpy of micellization I. Sodium n-dodecylsulphate☆

Abstract The enthalpy of micellization of sodium n -dodecylsulphate in aqueous and in 0.023 mol dm −3 sodium chloride solution, as a function of concentration of surfactant and of temperature has been measured using a Beckman 190B microcalorimeter. The dilution of the micellar solutions from a concentration 150 times the critical micelle concentration was found to be endothermic. The micellization process becomes more exothermic with increasing concentration of surfactant, with increasing temperature, and on addition of salt.

The enthalpies of formation of CH3Mn(CO)5 and of CH3Re(CO)5, and the strengths of the CH3Mn and CH3Re bonds

Abstract From measurements of the heats of iodination of CH 3 Mn(CO) 5 and CH 3 Re(CO) 5 at elevated temperatures using the ‘drop’ microcalorimeter method, values were determined for the standard enthalpies of formation at 25° of the crystalline compounds: Δ H o f [CH 3 Mn(CO) 5 , c] = −189.0 ± 2 kcal mol −1 (−790.8 ± 8 kJ mol −1 ), Δ H o f [Ch 3 Re(CO) 5 ,c] = −198.0 ± kcal mol −1 (−828.4 ± 8 kJ mo −1 ). In conjunction with available enthalpies of sublimation, and with literature values for the dissociation energies of MnMn and ReRe bonds in Mn 2 (CO) 10 and Re 2 (CO) 10 , values are derived for the dissociation energies: D (CH 3 Mn(CO) 5 ) = 27.9 ± 2.3 or 30.9 ± 2.3 kcal mol −1 and D (CH 3 Re(CO) 5 ) = 53.2 ± 2.5 kcal mol −1 . In general, irrespective of the value accepted for D (MM) in M 2 (CO) 10 , the present results require that, D (CH 3 Mn) = 1 2 D (MnMn) + 18.5 kcal mol −1 and D (CH 3 Re) = 1 2 D (ReRe) + 30.8 kcal mol −1 .

Enthalpies of combustion of the three hydroxy-pyridines and the four hydroxy-2-methylpyridines

Abstract The enthalpies of combustion in oxygen at 298.15 K were measured in a static-bomb calorimeter and the enthalpies of sublimation at 298.15 K were measured by microcalorimetry for the following crystalline compounds: −ΔH c o (c)/(kJ·mol −1 ) ΔH o (sub.)/(kJ·mol −1 ) 2-Hydroxypyridine (2515.8 ± 0.4) (86.6 ± 1.3) 3-Hydroxypyridine (2550.1 ± 0.9) (88.3 ± 1.3) 4-Hydroxypyridine (2537.5 ± 1.1) (103.8 ± 1.7) 2-Methyl-3-hydroxypyridine (3187.9 ± 0.9) (89.1 ± 1.3) 2-Methyl-4-hydroxypyridine (3176.8 ± 0.7) (113.0 ± 1.3) 2-Methyl-5-hydroxypyridine (3195.5 ± 1.3) (96.2 ± 2.1) 2-Methyl-6-hydroxypyridine (3149.2 ± 1.9) (92.0 ± 1.3) The derived enthalpies of formation of the gaseous compounds are compared with theoretically predicted values for certain of these compounds.

The thermochemistry of carbonyl complexes of Cr, Mo, Wand Co with arenes, cycloheptatriene, and norbornadiene

Microcalorimetric measurements at elevated temperatures of the heats of thermal decomposition and of iodination of a number of arenemetal carbonyls have led to values for the standard enthalpies of formation of the following crystalline compounds (values given in kJ mol−1) at 25°C: (C6H6)Co4(CO)9 = −(1313 ± 13); (C6H3Me3)Co4(CO)9 = −(1444 ± 13); (C6Me6)Co4(CO)9 = −(1555 ± 17); (C6H3Me3)Mo(CO)3 = −(533 ± 13); (C6H3Me3)W(CO)3 = −(477 ± 13); (C6Me6)Cr(CO)3 = −(671 ± 13); (C6Me6)Mo(CO)3 = −(631 ± 8); (cyclo-C7H8)Mo(CO)3 = −(297 ± 8); (cyclo-C7H8)W(CO)3 = −(236 ± 8); (nor-C7H8)Cr-(CO)4 ∼ −(400 ± 13); (nor-C7H8)Mo(CO)4 = −(428 ± 10). Separate measurements by the vacuum-sublimation microcalorimetric technique gave the following values for ΔHsub298 (kJ mol−1): (cyclo-C7H8)Cr(CO)3 = (87.9 ± 4); (cyclo-C7H8)Mo(CO)3 = (87.9 ± 4); (cyclo-C7H8)W(CO)3 = (92.0 ± 4); (nor-C7H8)Cr(CO)4 = (88.7 ± 4) and (nor-C7H8)Mo(CO)4 = (91.6 ± 4). From these (and other) data, the bond-enthalpy contributions of the various ligand—metal bonds (D(LM)) in the gaseous metal complexes were evaluated as follows (values in kJ mol−1): (C6H6)−Co = 270; (C6Me3H3)−Co = 285; (C6Me6)−Co = 310; (C6Me3H3)−Cr = 191; (C6Me3H3)−Mo = 279; (C6Me3H3)−W = 334; (C6Me6)−Cr = 205; (C6Me6)−Mo = 292; (cyclo-C7H8)−Cr = 150; (cyclo-C7H8)−Mo = 264; (cyclo-C7H8)−W = 311; (nor-C7H8)−Cr ∼ (80); (nor-C7H8)−Mo, ∼ 187. The bond-enthalpy contribution, D(ML), for a given ligand increases on ascending the series M = Cr → Mo → W, and for a given metal, D(ML) increases on changing L along the series L = benzene → mesitylene → hexamethylbenzene. Thermal stability, however, is not generally determined by the magnitude of the bond-enthalpy contributions, D(ML) and D(MCO), and complexes of Mo and W are frequently less stable to heat than the corresponding complexes of Cr. It is suggested that the thermal decomposition of some complexes may take place in the condensed state, and involve the initial formation of poly-nuclear metal carbonyl products, and of the metal hexacarbonyls.

Enthalpy of interaction between some globular proteins and sodium n-dodecyl sulphate in aqueous solution

The enthalpy of binding of sodium n-dodecyl sulphate (SDS) to serum albumin, ovalbumin and ribonuclease A has been measured by microcalorimetry over the temperature range 18.5 to 32.0°C. The amount of SDS bound to the proteins has been measured over a wide range of SDS concentration by equilibrium dialysis. Changes in protein conformation have been monitored by viscometry. The results are consistent with a mechanism in which SDS binds initially to ionic sites on the protein molecules and initiates chain unfolding. At high binding levels the interaction is predominantly of a hydrophobic nature.

Thermochemistry of bis-arene- and arenetricarbonyl-chromium compounds containing hexamethylbenzene, 1,3,5-trimethylbenzene and naphthalene.

Abstract Microcalorimetric measurements at elevated temperatures of the heats of thermal decomposition and iodination have led to values of the standard enthalpies of formation of the following crystalline compounds (values given in kJ mol−1) at 298K: [Cr(η6-1,3,5-C6H3(CH3)3)2] = (63±12); [Cr(η6-C6(CH3)6)2] : -(88±12); [Cr(1,2,3,4,4a,8a-η-C10H8)2] = (407±11); [Cr(CO)3(1,2,3,4,4a,8a-η-C10H8)] = -(258±8). Separate measurements by the vacuum sublimation microcalorimetric technique gave the following values for the enthalpy of sublimation at 298K (kJ mol−1) : [Cr(η6-1,3,5-C6H3(CH3)3)2] = (104±1); [Cr(η6-C6(CH3)6)2] = (119±4); [Cr(CO)3(1,2,3,4,4a,8a-η-C10H8)] = (107±3). From these and other data, the bond enthalpy contributions of the metal-ligand bonds in the gaseous metal complexes were evaluated as follows: [(η6-C6(CH3)6)-Cr] (155±7); [(η6-C6H3(CH3)3)-Cr] (151±6); [(1,2,3,4,4a, 8a-η-C10H8)-Cr](145±6) kJ mol−1] The question of the transferability of the enthalpy contributions of chromium—ligand bonds between organochronium complexes is discussed with aid of information from structural and spectroscopic investigation. The limitations of the procedure are defined. The thermodynamic data are used to discuss various substitution, redistribution and exchange reaction of Cr(η-arene)2 and [Cr(CO)3(η-arene)] compounds.

The enthalpies of thermal decomposition of ironolefin complexes, and the strengthens of ironolefin bonds

Abstract From microcalorimetric studies at elevated tempertures, values were obtained for the enthalpies of thermal decomposition f [(ethylene)Fe(CO) 4 ] and of selected [(diene)Fe(CO) 3 ] and [(diene) 2 Fe(CO)] compounds.. Dibutadieneirone carbonyl was found to decompose thermally on melting, and to give dimers and trimers of butadiene as products of decomposition. Dicyclohexadieneiron carbonyl gave dimeric cyclohexadiene as a product of decomposition. [(Butadiene)Fe(CO) 3 ] appeard to be thermally more stable than the [(butadiene) 2 Fe(CO)] complex. Measurements were also made of the enthalpies of sublimation (or of vaporization) of the complexes studied. The thermal decomposition data yield values for th C 2 Fe bond enthalpy contribution in [(C 2 H 4 )Fe(CO) 4 ] (23.1 kcal mol −1 , 96.7 kJ mol −1 ), and for the average dieneFe bond enthalpy contribution in selected [(diene)Fe(CO) 3 ] and [(diene) 2 Fe(CO)] compounds (ca. 44 kcal mol −1 , 184 kJ mol −1 ).

Enthalpies of combustion of four methyl-substituted heptane-3,5-diones and benzoylacetone

Abstract The standard enthalpies of combustion in oxygen at 298.15 K of the following β-diketones were measured in a static-bomb calorimeter: The standard enthalpies of formation of these β-diketones were derived for the keto-enol equilibrium mixtures in the condensed state and for the liquid and gaseous enol forms.

The thermochemistry of organometallic compounds

Organometallic chemistry is one of the growth areas of chemical investigation at the present time, and has been so for the past two decades. Due mainly to the intensive efforts of inorganic preparative chemists, numerous new compounds, in particular of the transition metals, have been isolated and investigated in respect of their molecular structures and characteristic spectra. The thermochemist is now presented with an area for investigation almost unexplored, challenging his technical skills, and beginning to be met. Readers of the Bulletin of Chemical Thermodynamics will certainly have noticed the increasing size of the Index in recent years, no small part of which has been due to the number of entries classified as “organometallic compounds”. It is pertinent to recall that the very thorough compilation of thermochemical data, published by Bichowsky and Rossini’r) in 1936, made reference to five compounds only which might be classified as “organometallic” in character.