n-Hexyl acetate n-hexyl alcohol water → 1-Hexanol

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One of the commercially important ways to manufacture n-hexyl acetate is by the catalytic esterification of n-hexyl alcohol wih acetic acid. n-Hexyl acetate (b.p.=171.5° C.), n-hexyl alcohol (b.p.=157.5° C.) and water (b.p.=100° C.) form a minimum ternary azeotrope boiling at 97.0° C. and containing 18.5 weight percent n-hexyl acetate, 52.9 wt.% n-hexyl alcohol and 28.6 wt.% water. n-Hexyl acetate forms a binary azeotrope with water boiling at 97.4° C. and containing 39 wt.% n-hexyl acetate. n-Hexyl alcohol also forms a binary minimum azeotrope with water which boils at 97.8° C. and contains 25 wt.% n-hexyl alcohol. Thus in the esterification of n-hexyl alcohol with acetic acid to form n-hexyl acetate and water, the rectification of this mixture has two binary and a ternary azeotrope to contend with, and yields the lowest boiling constituent, namely the n-hexyl acetate-n-hexyl alcohol-water ternary azeotrope. It is therefore impossible to produce n-hexyl acetate from n-hexyl alcohol and water mixtures by rectification because the lower boiling ternary azeotrope will always come off overhead as the initial product. Any mixture of n-hexyl acetate, n-hexyl alcohol and water subjected to rectification at one atmosphere pressure will produce an overhead product boiling at 97° C. and containing 18.5 wt.% n-hexyl acetate, 52.9 wt.% n-hexyl alcohol and 28.6 wt.% water. Extractive distillation would be an attractive method of effecting the separation of n-hexyl alcohol from n-hexyl acetate if agents can be found that (1) will break the n-hexyl acetate-n-hexyl alcohol-water azeotrope and (2) are easy to recover from the n-hexyl acetate, that is, form no azeotrope with n-hexyl acetate and boil sufficiently above n-hexyl acetate to make the separation by rectification possible with only a few theoretical plates.

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