Enthalpies of transfer of alkane solutes from the vapor state to organic solvents

Abstract

. Heats of solution of 5-8 Cs-C,, alkane liquids have been determined in each of 19 organic solvents covering the Taft-Kamlert T* (dipolarity-polarizability) range -0.08 to 1.00. Enthalpies of alkane transfer from vapor to solvents have been calculated (AH(v + S) = AH, -AH,). The methylene increments in AH(v + S) in the 19 solvents and water (-1.18 to -0.67 kcal/mol) are not well correlated with the Hildebrand solubility parameter 6, but an empirical correlation exists with solvent T* and polarizability:( n = 20, r = 0.977, see = 0.032). By this criterion the small methylenc increment in water appears to be associated with the high dipolarity and low polarizability of water.RICHARD FUCHS et W. KIRK STEPHENSON. Can. J. Chem. 63, 349 (1985). On a determine les chaleurs de solution de 5-8 alcanes liquides en C5-Clb dans 19 solvants organiques couvrant des valeurs de polaritC/polarisabilite (T* de Taft-Kamlet) allant de -0,08 a 1,OO. On a calculC les enthalpies de transfert (AH(v + S) = AH, -AH,). I1 n'y a pas de bonne correlation entre, d'une part, les valeurs des increments par methylhe pour le AH(v + S) dans les 19 solvants et I'eau (-1,18 2 -0,67 kcal/mol) et, d'autre part, le paramktre de solubilitb, 6, de Hildebrand; toutefois, il existe une correlation empirique entre la valeur T* du solvant et la polarisabilitC:(ou n = 20, r = 0,977, erreur st. = 0,032). En se basant sur ce critere, il semble que le faible increment par methylhe dans I'eau soit associe a la polarit6 6levCe et la faible polarisabiliti de I'eau.[Traduit par le journal] IThe free energy of transfer (AG(v -+ S)) of nonpolar solutes from the gas to liquid water is highly unfavorable (endogenic), and this is particularly true of alkane solutes (1). However, for the rare gases, several inorganic gases (H?, N?, CO, 0 2 ) , and C,-C, alkanes, the enthalpy contribution (AH(v + S)) is actually more favorable for transfers to water than for transfers to organic solvents (1). Entropies of transfer (TAS(v + S)) of I these species to water are particularly unfavorable (negative), leading to the observed endogenic values of AG(v + S), and low solute solubility. Alkane AG(v + w) values reach a minimum at ethane, and become increasingly endogenic with alkane molecular weight (1) (C1-C7 methylene increment, 0.16 kcal/mol). The corresponding methylene increment in AH(v + w) is -0.67 kcal/mol, which Abraham ( I ) regarded as the net result of a "normal" solvent effect (-0.97 kcal/mol), and an unfavorable hydrophobic effect. He concluded that the hydrophobic contribution to the free energy, 0.54 kcal/mol, is more an enthalpic effect (0.30-0.44 kcal/mol) than an entropic effect (0.10-0.24 kcal/mol). The rare gases and inorganic gases were regarded as "normal" solutes in water, and this behavior was used (1, 2) to predict the "normal" solvent effect of alkanes in water. Differences between the "normal" and experimental values of AH(v + w) were attributed to a special (hydrophobic) effect. Calculations of solvent-solute interaction terms and scaled particle theory...

Thermodynamics of solvation of some linear and branched aliphatic aldehydes in water and heptane

“…This value is practically the same as that obtained for the methylene increment ðDtrH 1 m Þ w h ½CH2 in alkanes [36]. Lower values were obtained for the transfer of both ketones (1.3 kJ Á mol À1 ) and alkanes (1.9 kJ Á mol À1 ) from cyclohexane to water [15,36] since the methylene contribution in different apolar solvents may display slightly different values due to different CH 2 solvent interactions.…”

Structure and Stability of Carbohydrate–Lipid Interactions. Methylmannose Polysaccharide–Fatty Acid Complexes

“…However, further studies are needed to establish the generality of this finding. These values, which are also similar to the contribution of methylene groups to the heats of transfer of n ‐alkanes from the gas phase to polar solvents, such as acetone (0.88 kcal mol −1 ) and dimethylformamide (0.89 kcal mol −1 ), suggest that solvation of FAs by MMP is primarily through dipole‐induced dipole interactions…”

“…However, furthers tudies are needed to establish the generality of this finding. These values, which are also similar to the contribution of methylene groups to the heats of transfer of n-alkanes from the gas phase to polar solvents, such as acetone (0.88 kcal mol À1 )a nd dimethylformamide (0.89 kcal mol À1 ), [54,55] suggest that solvation of FAsb yM MP is primarilyt hrough dipole-induced dipole interactions. [31][32] The E a value determined forL Ad eviates considerably from the linear trend found for the longer FAs, with E a (21.5 kcal mol À1 )b eing much lower than expected (~24.5 kcal mol À1 ).…”

Solution calorimetry of organic nonelectrolytes as a tool for investigation of intermolecular interactions

“…[62,[78][79][80][81] It was ascertained that solvation enthalpy of alkyl derivatives of various substances is the additive function of the number of methylene groups in solute molecule. [62,80] Besides, it was shown in References [78,82] that solution enthalpy for alkanes of various structure is proportional to the volume of alkane molecule. Molar volume and molar refraction (Lorenz-Lorentz equation) were used as the measure of alkane molecule volume.…”