High-pressure differential thermal analysis study of the phase behaviour in sometert-butyl compounds: pivalic acid, 2-methylpropane-2-thiol and tert-butylamine

Abstract

Pressure–temperature phase diagrams of thetert-butyl compounds (Bu^tX) pivalic acid (X=CO₂H), 2-methylpropane-2-thiol (X=SH) and tert-butylamine (X=NH₂ ) have been determined at temperatures between 100 K and the melting curve and up to 300 MPa with the aid of differential thermal analysis (DTA) under pressure. New normal as well as high-pressure induced phases have been found for 2-methylpropane-2-thiol and tert-butylamine. The results for the studied compounds are compared to those previously obtained for compounds belonging to the same tert-butyl family (i.e. X=Cl, Br, CH₂OH, NO₂ , Me and CN) in order to establish similar trends in the phase behaviour as well as in the thermodynamic properties of the phase transitions. For the related tert-butyl compounds, with the exception of the X=CN compound, the average of the slopes (dT/dp) of the melting and the II to I transition curves have been determined to be (0.64±0.14) and (0.27±0.13) K MPa^-1 respectively.