Excess molar heat capacities and excess molar volumes of (an n-alkylalkanoate+2,2,4-trimethylpentane, or 2,2,4,4,6,8,8-heptamethylnonane) at T=298.15K

Excess molar heat capacities C-p,m(E) at constant pressure have been measur ed, as a function of mole fraction x at the temperature T = 298.15 K and at mospheric pressure, for eight liquid mixtures consisting of an n-alkylalkan oate and a highly branched alkane (i.e. 2,2,4-trimethylpentane (isooctane) and 2,2,4,4,6,8,8-heptamethylnonane): [xHCOO(CH2)(3) CH3 + (1 - x)((CH3)(3) CCH2CH(CH3)(2) C(CH3),CH2CH(CH3)CH2C(CH3)(3))], (xCH(3)COOCH(2)CH(3) + CH( CH3)(2))], (xCH(3)COO(CH2)(3)CH3 + (1 - x)(CH3)(3)CCH2CH(CH3)(2)), [xCH(3)C H(2) COOCH3 + (1 - x)(CH3)(3)CCH2CH(CH3)(2)) [xCH(3)CH(2)COOCH(2)CH(3) + (1 - x) ((CH3)(3) CCH2CH(CH3)(2), or (CH3)(3)CCH2C(CH3)(2)CH2CH(CH3)CH2C(CH3) (3))] (xCH(3)CH(2)COO(CH2)(2)CH3 + (1 - x) (CH3)(3)CCH2CH(CH3)(2)) Excess m olar Volumes V-m(E) have been determined, as a function of mole fraction x at the same temperature and pressure, for the same eight mixtures. The inst ruments used were a Picker flow microcalorimeter and a vibrating-tube densi meter, respectively. All the mixtures show positive excess volumes with a m ore or less parabolic composition dependence, with the maximum values of V- m(E), ranging between c. 0.3 cm(3) mol(-1) and 0.9 cm(3) mol(-1) Most of th e C-p,m(E), against x curves show a pronounced W-shape. However, for xCH(3) CH2COO(CH2)(2)CH3 + (1 - x) (CH3)(3)CCH2CH(CH3)(2)) the C-p,m(E), curve ha s de generated to one with a virtually flat portion extending from about x = 0.2 to x = 0.8, and C-p,m(E) of (xHCOO(CH2)(3)CH3 + (1 - x)(CH3)(3)CCH2CH (CH3)(2)) is S-shaped with the negative part situated at small mole fractio ns of n-butylmethanoate, (C) 1999 Academic Press.