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Hydrogen bonding phase-transfer catalysis
offers a convenient solution
to activate safe and economical metal alkali fluorides for enantioselective
nucleophilic fluorination. Herein, we demonstrate the scalability
of this protocol with the fluorination of 200 g of racemic trans-N,N-dibenzyl-2-bromocyclohexan-1-amine
in a mechanically stirred 1 L glass reactor using 0.5 mol % of a bis-urea
organocatalyst. In these experiments, full conversions were obtained
for high mixing intensities (impeller average shear rate >10 000
s–1; maximum energy dissipation per unit of mass
>300
W/kg). The thermal safety of the reaction was assessed by differential
scanning calorimetry and reaction calorimetry, assigning the reaction
to Stoessel’s critical class 3.
A method using statistical design is proposed to determine the measurement error of specific heat capacities (Cp) of liquids in any reaction calorimeter. This method only takes into account the experimental specific heat of the liquid, its volume and the reactors stirring rate. With the RC1e calorimeter used in this study, the Cp measured by its QuickCal mode was overestimated by up to 0.4 J 3 g À1 3 K À1 , whereas with its RTCal mode, more accurate values of Cp (( 0.2 J 3 g À1 3 K À1 ) were obtained. The statistical model obtained based on the QuickCal mode predicts experimental conditions which improve the accuracy of Cp, and could also be used to correct the value of Cp in the rest of the experimental domain. The corrected values of Cp for test solvents using this model were close to those cited in literature (e5%). As an application, the specific heat capacities at 25 °C of less well documented solvents were determined: anisole, ethyltertiobutylether, methyl-tetrahydrofurane, diethoxymethane, dimethyl-ethyleneurea and dimethylpropyleneurea.
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