Transfer enthalpies of <em>tert-</em>butyl chloride in some aquo-organic solvents

Abstract

Transfer enthalpies, <img src='/image/spc_char/delta.gif' border=0><em>H</em><img src='http://www.niscair.res.in/jinfo/zerot.gif' border=0><em>, </em> of <em>tert-butyl </em>chloride (<em>t</em>-BuCl) from water to aqueous mixtures of various cosolvents viz., protic ethanol (EtOH), <em>tert-</em>butanol (<em>t</em>-BuOH)<em>, </em>ethanediol (EG) and methoxyethanol (ME), aprotic 1,2-dimethoxyethane (OME) and 1,4-dioxane (D) and dipolar aprotic N,N-dimethylformamide (DME) and dimethyl sulphoxide (DMSO), have been determined at 25°C by measuring the partial molal heats of solution at infinite dilution (<img src='/image/spc_char/delta.gif' border=0><img src='http://www.niscair.res.in/jinfo/hbar.gif' border=0><img src='http://www.niscair.res.in/jinfo/equation144.gif' border=0>) with a rapid response Tronac (model 458) recording titration calorimeter by avoiding the uncertainties from hydrolysis of <em>t-BuCI </em> in the solvents. These <img src='/image/spc_char/delta.gif' border=0><img src='http://www.niscair.res.in/jinfo/hbar.gif' border=0><img src='http://www.niscair.res.in/jinfo/equation144.gif' border=0> values on extrapolation to zero cosolvent composition in each of the aqueous cosolvent systems lead to a common value for that of water (_w<img src='/image/spc_char/delta.gif' border=0><img src='http://www.niscair.res.in/jinfo/hbar.gif' border=0><img src='http://www.niscair.res.in/jinfo/equation144.gif' border=0>)<em>, </em> which is equal to 6.27±0.25 kJ mol^-1. <img src='/image/spc_char/delta.gif' border=0><i>H</i><em><img src='http://www.niscair.res.in/jinfo/zerot.gif' border=0> </em> values of the initial state (IS) of <em>t</em>-BirCl ( = _s<img src='/image/spc_char/delta.gif' border=0><i>H</i>^≠ - _w<img src='/image/spc_char/delta.gif' border=0><i>H</i><img src='http://www.niscair.res.in/jinfo/equation144.gif' border=0>) on subtraction from the corresponding transfer activation energies <em>∂</em><img src='/image/spc_char/delta.gif' border=0><em>H</em>^≠ (=_s<img src='/image/spc_char/delta.gif' border=0><em>H</em>^≠<em> - </em>_w<img src='/image/spc_char/delta.gif' border=0><em>H</em><img src='http://www.niscair.res.in/jinfo/equation40.gif' border=0>) as obtained from parallel kinetic studies of the hydrolysis/solvolysis of <em>t-</em>BuCl in the solvents at different temperatures, and reported elsewhere, helped determine the transfer enthalpies <img src='/image/spc_char/delta.gif' border=0><i>H</i><img src='http://www.niscair.res.in/jinfo/zerot.gif' border=0> (TS) of the transition state (TS). A comparative view of the composition profiles of <img src='/image/spc_char/delta.gif' border=0><img src='http://www.niscair.res.in/jinfo/hbar.gif' border=0><img src='http://www.niscair.res.in/jinfo/equation144.gif' border=0><em>, </em>as well as of <em>∂</em><img src='/image/spc_char/delta.gif' border=0><em>H</em>^≠<em> </em> and <img src='/image/spc_char/delta.gif' border=0><i>H</i><img src='http://www.niscair.res.in/jinfo/zerot.gif' border=0> (TS) in the solvent systems reflects that while the variations in <img src='/image/spc_char/delta.gif' border=0><img src='http://www.niscair.res.in/jinfo/hbar.gif' border=0><img src='http://www.niscair.res.in/jinfo/equation144.gif' border=0> values are guided by complex structural and interaction effects in the respective solvents, <img src='/image/spc_char/delta.gif' border=0><i>H</i><img src='http://www.niscair.res.in/jinfo/zerot.gif' border=0> (IS) values are fairly small as compared to <em>∂</em><img src='/image/spc_char/delta.gif' border=0><em>H</em>^≠<em> </em> values. Evidently, <em>∂</em><img src='/image/spc_char/delta.gif' border=0><em>H</em>^≠ values are guided by the contributions of <img src='/image/spc_char/delta.gif' border=0><i>H</i><img src='http://www.niscair.res.in/jinfo/zerot.gif' border=0> of TS rather than that of IS, contrary to what has been concluded by Arnett <em>et al.</em> from the corresponding studies only in aqueous ethanol system.