Relative Molar Heat Research Articles

Study on the thermodynamic properties for ionic liquid [C6mim][OAc](1-hexyl-3-methylimidazolium acetate)

Using the solution-reaction isoperibol calorimeter, molar enthalpies of solution in water, ΔsolHm, for ionic liquid [C6mim][OAc] with different molalities were measured in the temperature range from (288.15 to 308.15±0.01) K with an interval of 5K. According to Archer's method, the values of the standard molar enthalpies of solution, ΔsolHmθ, were obtained for [C6mim][OAc], respectively. According to Glasser's theory of lattice energy, the hydration enthalpy of cation and anion in infinite dilution aqueous [C6mim][OAc] was calculated, (ΔH++ΔH−)=−598kJmol−1, at 298.15K. The hydration enthalpy of the cation, ΔH+ ([C6mim]+)=−173kJmol−1, was determined. In comparison with hydration enthalpy of [C2mim]+, the hydration enthalpy of [C6mim]+ is a little bit weaker. A linear relationship was found by plotting the experimental values of ΔsolHmθ against (T—298.15) K. The standard molar heat capacity of solution, ΔCp,mθ = 313JK−1mol−1, was obtained from the slope of the regression line, the specific heat capacity of solution, ΔCpθ = 1.38Jg−1K−1, and the apparent relative molar heat capacity, ΦCp, were also calculated for [C6mim][OAc].

Gas chromatographic separation and identification of linear and branched-chain alkyl chlorides

Polar and non-polar liquid stationary phases (Apiezon L, tricresyl phosphate and Carbowax 20M) were used for the analysis of C 5–C 8 linear and branched-chain alkyl chlorides. Specific retention volumes, retention index and relative molar heats of solution of alkyl chlorides with respect to the homomorphous alkanes were measured and correlated with molecular structure, in order to permit the identification of isomeric compounds in a mixture. The behaviour of alkyl chlorides was compared with that of the corresponding bromo- and iodoalkanes, on the basis of previously published data.

Gas chromatographic separation and identification of linear and branched-chain alkyl bromides

Polar and non-polar liquid phases (Apiezon L, tricrescyl phosphate and Carbowax 20M) were used for the analysis of linear and branched-chain alkyl bromides having four to eight carbn atoms. Specific retention volumes, retention index and relative molar heats of solution of alkyl bromides with respect to the homomorphous alkanes were measured and correlated with molecular structure, in order to permit the identification of isomeric compounds in a mixture. Mixed columns that ensure the best resolution of closely eluting isomeric alkyl bromides were tested.

Gas chromatographic identification of alkyl radicals formed in plasma radiofrequency discharges by using iodine as a scavenger

Alkyl radicals formed in low-pressure radiofrequency plasmas were identified by gas chromatography using iodine as a scavenger compound. Iodine vapours, injected into the glowing plasma discharge, reacted with active radicals in the gas phase, yielding various saturated alkyl iodides, that were trapped by freezing in an organic solvent and analyzed on Apiezon L and Carbowax 20M columns. Analyses carried out at different temperatures permitted the retention times and indices to be measured and the relative molar heats of solution to be calculated.

Selectivity of stationary phases for the resolution of polycyclic aromatic hydrocarbons

Relative retentions, heats and entropies of solution for 16 PAH in seven different stationary phases were measured under standard isobaric conditions using GC. The experimental conditions to obtain reproducible retention data at non-linear adsorption isotherms are discussed and standard conditions are recommended using the linear relationship between retention time and 1/log h (where h is the peak height). A linear relationship was established between the relative molar heats of solution and the number of carbon atoms in the PAH-molecule. This relationship is valid only for non-polar stationary phases. Certain effects of the isomeric structures of PAH are studied using the relative molar heats and entropies of solution. The latter function is very sensitive to the spherical form of a molecule. Different aspects of isomeric selectivity are discussed and it is concluded that the better way for resolving complex PAH-mixtures is rather an improvement in column efficiency than searching for new stationary phases.

Selectivity of stationary phases for the resolution of some simple substances

The relative molar heats and entropies of solution for methylbenzenes, chlorotoluenes, chlorobenzenes and chloroxylenes have been determined using the relative retentions on Apiezon L, poly(ethyleneglycoladipate), poly(phenyl ether) and methylphenylsilicone; the corresponding values for C 5-C 6 olefins were calculated on pentadecane and dinitriloadipate. It was shown that the semi-empirical theory of selectivity of the stationary phases being applied to such systems permits one to obtain reasonable results, within the limit of experimental error. The relative molar heats of solution give information about the number and nature of the substituents in the benzene ring. The difference between the relative molar heats of solution in polar and non-polar stationary phases is proposed as an analytical parameter for identification that is sensitive to the polarity of the solute. It was shown that the orientation forces in a polar stationary phase do not affect the selectivity for methyl and chlorobenzenes strongly. A “hyperconjugation” effect is discussed for the solutes under study in non-polar stationary phases and some semi-empirical equations are derived for calculating the relative molar heats of solution of methylbenzenes and olefins using this effect. The calculated values of the relative entropies of solution permit one to estimate the positions of substituents in the benzene ring. The possibility of calculating the relative molar entropy of solution of light olefins is discussed. Some semi-empirical equations are derived for calculating the enthalpic and entropic selectivities of non-polar stationary phases.