Quaternary ammonium carboxylate salts are produced and isolated to be used directly in applications or to diagnose factors for successful phase-transfer catalysis reactions.
In US Patent 11,636,986 (25-Apr-2023), the carboxylate salts of L-proline were formed with tetrabutylammonium and tetraethylammonium as electrolytes in “supercondensers” that have the capacity to store high content of electrical charge.
The procedure described is a neutralization of L-proline (a carboxylic acid) with a molar equivalent amount of either tetrabutylammonium hydroxide or tetraethylammonium hydroxide. The quat hydroxides were used as 40% aqueous solution and the proline was also prepared as an aqueous solution. The two aqueous solutions were combined.
We find it surprising that the aqueous mixture of quat hydroxide and proline was heated to 60 deg C for 2 hours before isolating the quat-prolinate salt. Since this is a simple neutralization of a carboxylic acid with hydroxide in water, the energy of activation should be as trivial as adding sodium hydroxide to acetic acid to form sodium acetate. We would expect the neutralization to be nearly instantaneous at room temperature.
In this case, the quat-prolinate salt required drying. After the neutralization, the water from the solution evaporated under reduced pressure to maintain the temperature no higher than 80 deg C (presumably to avoid decomposition of the quat), then the residue dissolved in acetonitrile, dried with magnesium sulfate and the acetonitrile was evaporated to produce the dry quat-prolinate salt.
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