Noncovalent Derivatization: A Laboratory Experiment for Understanding the Principles of Molecular Recognition and Self-Assembly through Phase Behavior

Abstract

An experiment focusing on the creation of phase diagrams involving nonconvalent derivatives of hydroquinone and bis[N,N-diethyl]terephthalamide (HQ-DETPA) is presented. A phase diagram was assembled by taking samples of different compositions (i.e., 40% hydroquinone and 60% bis[N,N-diethyl]terephthalamide, 70%/30%, etc.) and determining the melting points of each sample. This experiment is suitable for students enrolled in a physical chemistry class or materials science course and was effectively accomplished by three pairs of students. The experiment requires two 3-h lab sessions. Background information, experimental procedure and hazards, and results of the research are detailed. Results indicate that the noncovalent derivatization successfully provides a co-crystal that assembles into a 50:50 molar ratio. The eutectic points are shown to take place at the 25:75 and 75:25 molar ratios, respectively. Because entropy was the driving force behind the assembly of the co-crystals, the presence of a maximum point on the phase diagram, which represents the highest value of enthalpy and lowest point of entropy, was also witnessed and occurred at the 50:50 molar ratio of HQ to DETPA.