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-C_n) where n= 6, 8, 10, 12, 14, 15 and 16, and with a series of highly branched alkanes (br-C_n), 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: V^E, dV^E/dT, dV^E/dP, Δ(γVT), C^E_p, Δ(αγVT) and ΔC_ν. Excess enthalpies, H^E, for 1-chloronaphthalene–br-C_n, C^E_p for p-xylene–n-C_n(n= 8, 10 and 14), 1-chloronaphthalene–cyclohexane and 1-methylnaphthalene–n-C₁₂ are also reported. V^E and dV^E/dT are strongly negative, and dV^E/dP are positive, for the lower n- and br-C_n, 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)=–H^E which is predicted by the Flory theory and other theories which assume van der Waals behaviour. Contrasting with cyclohexane–n-C_n and benzene–n-C_n, where –Δ(γVT) > H^E, 1-chloronaphthalene with n-C_n gives –Δ(γVT) < H^E for n > 8. The excess heat capacity C^E_p is anomalously positive for the n-C_n series and has higher values than for br-C_n. C^E_p equimolar values show a maximum against the carbon number n; similar behaviour was found for Δ(αγVT). ΔC_ν=C^E_p–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 dV^E/dT, Δ(γVT) and C^E_p, as in cyclohexane and benzene–n-C_n. For 1-chloronaphthalene–n-C_n(1–2) compensatory order formed in solution has the opposite effect, producing –Δ(γVT) < H^E and C^E_p > 0.