Effect of β-cyclodextrin on the behaviour of thermophysical and spectroscopic properties of binary mixtures of (isomeric butanediol + pyrrolidin-2-one)

Thermophysical parameters viz. excess molar volume VE, speed of sound u, viscosity η and spectroscopic parameters viz. FT-IR, 1H and 13C NMR have been measured for the ternary liquid mixtures of {isomeric butanediol (butane-1,2-diol, butane-1,3-diol, butane-1,4-diol, butane-2,3-diol) + pyrrolidin-2-one} in β-cyclodextrin over the whole composition range at T = 308.15 K. The deviation in the isentropic compressibility ΔκS  , partial molar quantities QiE, deviation in viscosity Δη, deviation in Gibbs energy of activation for viscous flow g(x) and excess NMR chemical shift δE have been estimated and analysed. Results indicate that the position of hydroxyl groups of butanediol showed a noticeable effect on the thermophysical properties. Furthermore, the effect of addition of β-cyclodextrin caused significant changes, due to difference in the fitting of isomeric butanediol in the hydrophobic cavity of β-cyclodextrin. Particularly, visible changes in thermophysical properties of 1,4-BTD system have been observed in comparison to other isomers of BTD indicating that hydrogen bonding and affinity of fitting between (1,4-BTD and β-CD + PY) are greater than the other isomers. These results have been found to be in excellent concurrence with NMR and FT-IR studies. However, for 2,3-BTD and 1,3-BTD systems dispersion forces due to dissociation of self-associated PY and diols are predominant. The spectroscopic measurements (FT-IR, 1H and 13C NMR) confirm that the interaction between unlike molecules take place through hydroxyl groups of isomeric butanediol and carbonyl group of pyrrolidin-2-one.

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► Thermophysical and spectroscopic parameters have been studied for BTD + β-CD in PY.
► Placement of two –OH of BTD showed a noticeable effect on thermophysical properties.
► Results showed the fitting of 1,4-BTD in the hydrophobic cavity of β-CD in PY.
► 1,2-BTD is partially fitted and no complexation of 1,3-BTD and 2,3-BTD with β-CD.
► Excellent correlation between thermodynamic and spectroscopic studies is observed.