Liquid structure and second-order mixing functions for 1-chloronaphthalene with linear and branched alkanes

Abstract

Expansion coefficients (α), thermal pressure coefficients (γ), isothermal compressibilities, densities and heat capacities have been measured at 25 °C for pure components and the following mixtures: 1-chloronaphthalene with the series of normal alkanes (n-Cn) where n= 6, 8, 10, 12, 14, 15 and 16, and with a series of highly branched alkanes (br-Cn), 2,2-dimethylbutane, 2,2,4-trimethylpentane, 2,2,4,6,6-pentamethylheptane and 2,2,4,4,6,8,8-heptamethylnonane. With these data the following first- and second-order mixing quantities are reported: VE, dVE/dT, dVE/dP, Δ(γVT), CEp, Δ(αγVT) and ΔCν. Excess enthalpies, HE, for 1-chloronaphthalene–br-Cn, CEp for p-xylene–n-Cn(n= 8, 10 and 14), 1-chloronaphthalene–cyclohexane and 1-methylnaphthalene–n-C12 are also reported. VE and dVE/dT are strongly negative, and dVE/dP are positive, for the lower n- and br-Cn, becoming smaller for higher alkanes. Flory theory gives excellent predictions for each quantity with both series. The mixing function, Δ(γVT), deviates from the equality Δ(γVT)=–HE which is predicted by the Flory theory and other theories which assume van der Waals behaviour. Contrasting with cyclohexane–n-Cn and benzene–n-Cn, where –Δ(γVT) > HE, 1-chloronaphthalene with n-Cn gives –Δ(γVT) 8. The excess heat capacity CEp is anomalously positive for the n-Cn series and has higher values than for br-Cn. CEp equimolar values show a maximum against the carbon number n; similar behaviour was found for Δ(αγVT). ΔCν=CEp–Δ(αγVT) values are strongly positive for both series of alkanes. The results are explained by temperature-sensitive ordering of (2–2) and (1–2) contacts. The (2–2) order between long-chain alkanes is destroyed on mixing, giving negative contributions to dVE/dT, Δ(γVT) and CEp, as in cyclohexane and benzene–n-Cn. For 1-chloronaphthalene–n-Cn(1–2) compensatory order formed in solution has the opposite effect, producing –Δ(γVT) 0.