In this work, five protic ionic liquids (PILs) have been synthesized through atom economic neutralization reaction between N-butyl hydroxyethyl amine and bronsted acid RCOOH, where R is H, CH3, C2H5, and C4H9. Thermophysical properties such as density, speed of sound and viscosity were measured in the temperature range from 293.15 to 343.15 K at 0.1 MPa pressure. The density data have been fitted to second order polynomial equation as well as correlated with group contribution method developed by Gardas and Coutinho. From the density correlation, molecular volume data for cation and anion constituents of studied ionic liquids have been proposed. Further, the coefficient of thermal expansion, isentropic compressibility, standard entropy, intermolecular free length and potential energy have been calculated by using experimental density and speed of sound data. Viscosity data were correlated with the Vogle-Tamman-Fulcher equation. The relationship between the standard entropy of ionic liquid and the carbon atom number in alkyl chain of the carboxylate anions studied at 298.15 K. Furthermore, the effect of alkyl chain length and temperature has been analyzed for the studied properties. (C) 2016 Elsevier B.V. All rights reserved.