Priscilla L. Grellier

Determination of olive oil–gas and hexadecane–gas partition coefficients, and calculation of the corresponding olive oil–water and hexadecane–water partition coefficients

Olive oil–gas partition coefficients, Loil, have been determined for 80 solutes at 310 K using a gas chromatographic method in which olive oil is used as the stationary phase. Combination with other literature values has enabled a list of 140 log Loil values at 310 K to be constructed. Hexadecane–gas partition coefficients, Lhex, have similarly been determined for 140 solutes at 298 K. It is shown that olive oil–water partition coefficients, Poil, calculated indirectly from Loil and Lwater partition coefficients agree quite well with directly determined Poil values. Similarly, hexadecane–water partition coefficients, Phex, obtained from Lhex and Lwater agree with directly determined values. It is suggested that in the case of the two particular solvents, olive oil and hexadecane, mutual miscibility of the two phases is of little consequence, and that Poil and Phex values can conveniently be obtained by combining the respective solvent–gas and water–gas partition coefficients.

Hydrogen bonding. Part 7. A scale of solute hydrogen-bond acidity based on log K values for complexation in tetrachloromethane

A scale of solute hydrogen-bond acidity has been constructed using equilibrium constants (as log K values) for complexation of series of acids (i) against a given base in dilute solution in tetrachloromethane, equation (A). Forty-five such equations have been solved to yield LB and DB, log Ki=LB log KAHI+DB(A) values characterising the base, and log KAH values that characterise the acid. In this analysis, use has been made of the novel observation that all the lines in equation (A) intersect at a given point where log K= log KAH=–1.1 with K on the molar scale. Some 190 log KAH values that constitute a reasonably general scale of solute hydrogen-bond acidity have been obtained. It is shown that there is no general connection between log KAH; and any proton-transfer quantities, although certain family dependences are obtained. A number of acid-base combinations are excluded from equation (A), and alternative log KAHE values have been determined for such cases. The general log KAH values may be transformed into α2H values suitable for use in multiple linear-regression analysis through the equation α2H=(log KAH+ 1.1)/4.636.

Solubility properties in polymers and biological media. II. A new method for the characterisation of the adsorption of gases and vapours on solids.

Henrys constants at zero solute pressure have been determined by the gas chromatographic peak shape method for twenty-two solutes on four adsorbents (Rohm and Haas Ambersorb XE-348F carbonaceous adsorbent at 323 and 373 K, Sutcliffe Speakman 207A and 207C at 323 K, and Calgon Filtrasorb activated carbon at 323 K). The limiting values of log KH have been analysed in terms of solute dipolarity (pi 2*), solute hydrogen-bond acidity (alpha 2), and basicity (beta 2), and a new solute parameter (log L16), the solute Ostwald absorption coefficient on eta-hexadecane. The multiple linear regression equation, SP = SP0 + l.log L16 + s(pi 2* + d delta 2) + a alpha 2 + b beta 2 where in this instance SP = -log KH, can be used to identify the nature of the solute-adsorbent interactions, and to predict further values of log KH. For the solutes and solids we have studied, only the l.log L16 term is statistically significant, and hence--log KH is proportional to l.log L16. It is concluded that interactions between the gaseous solutes (that include alcohols and amines) and the four adsorbents involve just general dispersion forces.

Solvation of gaseous non-electrolytes

Linear free energy equations, log L=c+sπ*2+aαH2+bβH2+l log L16 log L=c+sµ22+aαH2+bβH2+l log L16 have been used to analyse the solvation of a series of gaseous non-electrolytes in a given bulk solvent as log L values where L is the Ostwald solubility coefficient. The parameters π*2, αH2, βH2, log L16 and µ2 characterise the solutes and the constants c, s, a, b and l are obtained by multiple linear-regression analysis. It is shown that for solvation in the bulk solvents ethyl acetate, acetonitrile, ethanol and methanol, the contribution of hydrogen-bonding terms to solvation is quite small, the main contributing terms being an endoergic cavity term and an exoergic solute–solvent dispersion interaction term. Even with bulk water as the solvent, hydrogen-bonding interactions of the type solute (base)–water (acid) and solute (acid)–water (base) are not more than ca. -15 or -11 kJ mol–1, respectively, for DMSO (base) and ethanol (acid). It is shown also that linear free energy equations can be used for the correlation and prediction of the solubility of gaseous solutes in a given liquid phase, even when the latter is polymeric in nature.

Solubility properties in polymers and biological media: 10. The solubility of gaseous solutes in polymers, in terms of solute-polymer interactions

Abstract A general equation SP=SP 0 +l log L 16 +s(π 2 ∗ + d δ 2 ) + aα 2 + bβ 2 has been used to describe solubility properties of a wide range of gaseous solutes in polymers. The property, SP, may be a log VG value, an enthalpy of solution, etc., and the explanatory variables are solute parameters: L16 is the Ostwald solubility coefficient of the solute on hexadecane at 25°C, π∗ 2 is the solute dipolarity, δ2 a polarizability correction term, α2 the solute hydrogen-bond acidity, and β2 the solute hydrogen-bond basicity. Solubilities may then be discussed in terms of the various solute-solvent interactions that are reflected by the coefficients of the various terms. These are cavity effects and dispersion forces (l), dipole-dipole and dipole-induced-dipole interactions (s), and hydrogen-bonding between solute acid and polymer base (a) or between solute base and polymer acid (b). For non-dipolar solutes in all non-aqueous solvent phases, and for weakly dipolar solutes in weakly dipolar phases, the general equation reduces to a more specific equation that includes only the term due to cavity effects and dispersion forces SP=SP 0 +l log L 16

A quantitative measure of solvent solvophobic effect

Gibbs energies of transfer of argon, alkanes, and alkane-like compounds from water to numerous aqueous–organic mixtures and to pure solvents are tabulated. It is shown that these ΔGt° values can be correlated through a set of equations, where ΔGt° refers to transfer of a series of solutes from water to a ΔGt°(to solvent)=MRT+D given solvent, RT is a solute parameter, and M and D characterise the solvent. For 20 solutes in 51 solvent systems, 375 ΔGt° values are thus correlated with a standard deviation of 0.078 kcal mol–1. The M values in the above equation are then used to define a solvent solvophobic effect so that Sp values are scaled Sp= 1 –M/M(hexadecane) from unity (water) to zero (hexadecane). The Sp values so obtained agree with the qualitative series reported by Sinanoglu and Abdulnur for pure solvents, and are shown to be quantitatively related to h.p.l.c. capacity factors.

Limiting activity coefficients of triethylamine in 30 solvents by a simple gas-liquid chromatographic method

Abstract Limiting values of the Raoults-law activity coefficients of triethylamine in 30 solvents at 298.15 K have been obtained by a simple procedure based on the use of gas-liquid chromatography to determine the mole fraction of triethylamine in the vapour above dilute solutions. Where comparisons can be made, there is good agreement with literature values and with values derived from liquid-liquid distribution coefficients measured in this work.

Substitution at saturated carbon. Part 26. A complete analysis of solvent effects on initial states and transition states for the solvolysis of the t-butyl halides in terms of G, H, and S using the unified method

The influence of 20–30 solvents on ΔG‡, ΔH‡, and ΔS‡ for the solvolysis of t-butyl chloride and t-butyl bromide has been dissected into initial-state and transition-state contributions. Using the unified method in which the general equation (i) is applied to both these contributions, it is shown that the decrease in ΔG‡ due to solvent dipolarity (π1*) and to solvent hydrogen-bond acidity (α1) is primarily a transition-state effect, that there is little effect of solvent hydrogen-bond basicity (β1) on either initial-state or transition-state, and that large effects of solvent Hildebrand solubility parameter (δH) on initial-state and transition-state partly cancel out. XYZ = XYZ0+s(π1*+dδ)+aα1+bβ1+hδ2H/100 (i)A similar analysis carried out on the transition-state transfer quantities, ΔHt0 and ΔSt0, yields the surprising results that the influence of solvent π1* and α1 values on the transition-state is primarily an entropic effect and that there is a very large influence of solvent hydrogen-bond basicity in increasing both ΔHt0 and ΔSt0 for the transition-state in an almost exactly compensatory way. It is suggested that this latter effect, previously unsuspected, may arise through solute/solvent lone pair/lone pair repulsions.

Substitution at saturated carbon. Part XIX. The effect of alcohols and water on the free energy of solutes and on the free energy of transition states in SN and SE reactions

Standard free energies of transfer from methanol to other alcohols and to water are reported for nearly 40 solutes, ranging from hydrocarbons to amino-acids. These transfer free energies from methanol to alcohols are negative for nonpolar inert solutes, but quite positive for amino-acids and ion pairs; from the assembled data it is predicted that linear free energy relationships between ΔG‡ values for substitution reactions in alcohols will in general be approximate only. By combination of initial-state effects with values of ΔG‡ previously determined, free energies of transfer from 20 different substitution reactions involving electrically neutral reactants. The various values of ΔGot(Tr) are by no means linearly related, but by comparison with values for polar species such as amino-acids and ion pairs it is shown that the polarity of transition states increases in the order [R4Pb–I2]‡ < [R3N–RI]‡⩽[R4Sn–I2]‡ < [R4Sn–HgX2]‡ < [ButX]‡⩽[phCHMeCl]‡⩽[ph2CHCl]‡. The α-amino-acids are shown to be suitable model solutes for highly polar transition states, especially when any differences in molar volume between solute and transition states, especially when any differences in molar volume between solute and transition are taken into account.

Calculations of steric effects. Part I. Uncatalysed SE2 substitution of alkylmercury(II) salts by mercury(II) salts in ethanol

Steric effects of alkyl groups in reaction (1) have been calculated by setting up nonbonded potential functions, RHgX + HgX2 [graphic ommitted] RHgX + HgX2(1) and obtaining the various nonbonded interaction energies in both initial states and transition states. These interactions lead to restricted rotation of methyl groups both in the initial state (β-rotation) and transition state (α- and β-rotation), and a treatment is given that allows the effect of restricted rotation on the relative rate constants to be determined. Calculations carried out on an open transition state model lead to close agreement between observed and calculated relative rate constants for R = Me, Et, and ButCH2(X = Br at 100°) and for R = Me and Bus(X = OAc at 60°), viz. observed (Me : Et : ButCH2 : Bus), 1 : 0·42 : 0·33 : 0·06 and calculated, 1 : 0·50 : 0·38 : 0·05, and it is shown that the above sequence is mainly due to the effect of restricted rotation of groups in the transition state. Similar calculations carried out using a cyclic transition state model do not yield relative rate constants that are at all compatible with the observed relative rates.