Acetic acid and cyclohexane are two very different substances that are nevertheless miscible above 3.9℃ (their UCST). In a cooled reactor, these will form two separate liquid layers allowing for liquid-liquid partitioning of any solutes therein. More easily than in the laboratory, in the plant the reactor can be kept closed and inerted; consequently, more easily water-free. The acetic acid in the lower layer will be glacial acetic acid so long as water is neither introduced into nor produced in the procedure. More polar components of a reaction conducted therein might be removed by simple phase separation. Glacial acetic acid will be much better at dissolving some substances than a mixture with water present to any extent.
After a cut, there will still be some acetic acid residue in the cyclohexane layer, but acetic acid and cyclohexane give an azeotrope bp. 79.6 ℃ that contains 2% acetic acid. Thus, the predominantly cyclohexane layer can be freed of even traces of acetic acid by distilling out from the reaction vessel a small first fraction. A work-up is possible, still without adding any water!
Where Could Such a Solvent System Be Useful?
This cyclohexane/glacial acetic acid solvent mixture, above 3.9℃ when it is a single-phase, might be a good candidate for conducting acetylations with either acetic anhydride or acetyl chloride reagents. The excess reagent might be removed without decomposing it by cooling to <0℃ and cutting the two phases.
This mixture of fluids might also serve for dehydrations or acid-catalyzed rearrangements. Adding anhydrous hydrogen halides would protonate acetic acid, giving rise to a very strong acid in situ. Excess hydrogen halide would be removed with the acetic acid-rich layer when the reactor was cooled. The system would protonate olefins perhaps inducing rearrangement but hydrogen halide would be unlikely to add across the unsaturation since the halide anion would be strongly solvated and deactivated by hydrogen bonds with the acetic acid.
Acetic acid might catalyze enol formation from ketones. Enols could react internally with a terminal double bone to give a cyclic product or they could be condensed, dehydrated, and so dimerized.
This post is speculative. It does not report experimental evidence.
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