Acta Pharm. 55 (2005) 195-205

Thermodynamic study of the transfer of acetanilide and phenacetin from water to different organic solvents

YOLIMA BAENA,¹ JORGE A. PINZÓN², HELBER J. BARBOSA¹ and FLEMING MARTÍNEZ^1*

fmartinezr@unal.edu.co

¹Universidad Nacional de Colombia, Departamento de Farmacia, A.A. 14490, Bogotá D.C., Colombia
²Universidad Nacional de Colombia, Departamento de Química, A.A. 14490, Bogotá D.C., Colombia

The molar (K^Co/w) and rational (K^Xo/w) partition coefficients in the octanol/buffer, i-propyl myristate/buffer, chloroform/buffer, and cyclohexane/buffer systems were determined for acetanilide and phenacetin at 25.0, 30.0, 35.0, and 40.0 °C. In all cases except for cyclohexane, the K^Co/w and K^Xo/w values were greater than unity. This demonstrates that these two drugs have predominantly lipophilic behavior. Gibbs and van't Hoff thermodynamic analyses have revealed that the transfer of these drugs from water to organic solvents is spontaneous and that it is mainly driven enthalpically for i-propyl myristate and chloroform, and entropy-driven for octanol and cyclohexane.

Keywords: acetanilide, phenacetin, partition coefficient, thermodynamics