| Abstract |
The standard molar enthalpy of the base catalysed hydrolysis of methyl paraben, Delta H-r(m)o, was obtained at 298.02 K, 303.04 K and 310.01 K. The determination relied on isothermal microcalorimetry measurements and on a thermochemical scheme that, in contrast with previous strategies, does not require kinetic information. The results obtained were Delta H-r(m)o = -(50.99 +/- 0.61) kJ . mol (1) at 298.02 K, Delta H-r(m)o = -(50.60 +/- 0.82) kJ . mol (1) at 303.04 K, and Delta H-r(m)o = -(49.64 +/- 0.90) kJ . mol (1) at 310.01 K. The Delta H-r(m)o value at 298 K is in very good agreement with the previously recommended benchmark at this temperature. The current procedure allowed, however, a similar to 7-fold improvement in precision. It was also found that the Delta H-r(m)o values show a linear variation with temperature. The fact that this variation is small lends support to the previous assumption of a negligible temperature dependency of Delta H-r(m)o around 298 K. The present work resolves some important discrepancies in the reported standard molar enthalpies of the base catalysed hydrolysis of methyl paraben. Such inconsistencies can have a considerable impact on the determination of the effective volume of flow-through calorimetric apparatus. This parameter is essential to obtain kinetic and thermodynamic information on the growth, metabolism, and adaptation of living cells from flow calorimetry experiments. (C) 2016 Elsevier Ltd. |
