No abstract

under contract No. F33615-78-C-2075, and by the Division of Chemical Sciences, Office of Basic Energy Sciences, U.S. Department of Energy, under contract W-7405-eng-26 with the Union Carbide Corp. M.S. is grateful for financial assistance from Norges Teknisk-Naturvitenskapelige Forskningsrád. We note with thanks the technical assistance of J. Cobb and D. Goff, and helpful advice from J. Brynestad and C. A. Angelí.

Applications of gas chromatography have been enhanced through conversion of many chemical compounds to derivatives with suitable reagents. This study measured retention volumes of a number of hydroxylic derivatives in polymeric stationary phases. A number of alkanes and aromatics were included in the study for comparison with the derivatives. The stationary phases include a poly(dimethylsiloxane), a poly(methylphenylsiloxane), a poly[methyl(trifluoropropyl)siloxane], and a methoxy poly(ethylene oxide). The selected derivatives were acetates, trimethylsilyl ethers, trifluroroacetates, and pentafluoropropionates. The hydroxylic compounds included butyl alcohol, cyclohexanol, and m- and p-methylphenols; n-butyl tert-butyl ether was included for comparison with n-butyl trimethylsilyl ether. The effects of derivatizing groups on the interaction parameter were considered as a summation of hydrocarbon core and derivative groups. Linear free energy relationships were identified for n-alkanes, aromatics, and n-butyl derivatives. Some thermodynamic results could be interpreted in terms of molecular structure of molecules and specific solute−solvent interactions. Results here support an approach to selecting derivatives for separations matched to column liquid phases.

Careful gas chromatographic studies provide thermodynamic data for insights into solution processes in nonvolatile solvents. Using 24 solutes and five stationary phases, several entropy-enthalpy compensation effects in the thermodynamics of solution were identified. Despite solute structure differences, when excess enthalpy and entropy of solutions were examined, entropy-enthalpy compensation effects were found in solvents dominated by single types of interaction: squalane and, to some extent, methoxy poly(ethylene oxide) (PEO). The main reason for the absence of linearity in other solvents is pure solute state interactions in the reference state and the multicharacter nature of solvents. In this study, consideration of solute state interactions was removed through examination of the thermodynamics of transfer between solvent pairs. It was found that solute transfers from squalane to poly[methyl(trifluoropropyl)siloxane] (QF-1) and to poly(methylphenyl) (DC-550) also gave linear relationships. The former system contains a second correlation for ester type solutes. The transfer data for squalane to poly(methylsiloxane) (DC-200) had smaller ranges and were more scattered. The effects of derivatizing groups on the transfer enthalpy and entropy were treated as a summation of hydrocarbon cores with the derivative groups. The group properties of transfer then also show entropy-enthalpy compensation effects. Many solution effects could be explained on the basis of solvent composition and local interactions with solutes.

There are 11 benzenepolycarboxylic acids, some of which are sold as the anhydride or the methyl ester. Two of these substances, terephthalic acid and phthalic anhydride, are principal chemical products. Two others, isophthalic acid and trimellitic anhydride, have substantial commercial sales. The rest have low volume specialized applications or are not available commercially. This is a review of the basic physical properties, manufacturing methods, production volumes and prices, toxicological aspects, and uses of these compounds. Terephthalic acid and its dimethyl ester rank about tenth in tonnage for all organic chemicals, and production is expanding substantially. They are used to make poly(ethylene terephthalate) for fibers, film, and containers. The principle mode of commercial manufacture is direct liquid‐phase oxidation of p ‐xylene using a homogeneous heavy metal–bromine catalyst system. Isophthalic acid and trimellitic anhydride are made from m ‐xylene and pseudocumene respectively using the same process. Phthalic anhydride is made primarily by gas‐phase oxidation of o ‐xylene over a fixed catalyst containing vanadium and titanium oxides. It is used as a raw material for plasticizers, unsaturated polyesters, and other resins.