-1
$\begingroup$

Let's take for example a reaction that would benefit from having less water in it, ester formation from alcohol and acid. We know that the equilibrium can be shifted to the right (ester formation) if water is constantly removed through distillation. My question is: would adding an excess of NaCl affect the reaction and push the reaction to the right?

The water would solvate the NaCl and theoretically be "preoccupied." I would like to think that water adding back to the ester to form an alcohol and acid would be more energetically favourable, but I don't really have enough knowledge to answer that on my own. Any thoughts?

$\endgroup$
3
$\begingroup$

Esterification

$\ce{R_1-COOH + HO-R_2 <=> R1-COO-R2 + H2O}$

has the equilibrium constant, expressed in compound activities:

$$K = \frac{a_\mathrm{ester} \cdot a_\mathrm{\ce{H2O}} }{ a_\mathrm{acid} \cdot a_\mathrm{alkohol}}$$

The water activity is decreased by dissolved salts by 2 ways:

  1. decreasing the molar fraction of water by dissolved salt
  2. decreasing its activity coefficient by bounding it by ion hydration.

As the result, dissolved salts decrease the numerator of the equilibrium expression and shift the equilibrium toward production of ester.

Present dissolved salts will partially affect activities of the acid and the alcohol as well, but in lesser extend.

$\endgroup$
3
  • $\begingroup$ A limited search yielded a work by Huang et al. (2016RSCAdv2106) cites chlorides of Cr, Sn, Zn, Al as previously used «used in the conversion of carbohydrates (e.g. cellulose, glucose and fructose) into platform molecules (e.g. HMF) through their Lewis acidity and Brønsted acidity.» then sticks (1 mmol scale, microwave heating; 400 W, 110 C and 10 min heating) to 20mol% of $\ce{Al2(SO4)3}$ ». Question @Poutnik Are you aware of examples (no microwave heating) of greater scale than, e.g. 0.2 mol you could include as reference? $\endgroup$ – Buttonwood Feb 12 at 15:06
  • $\begingroup$ @Buttonwood I am not aware of any particular references ( nor have I currently time resources to find any ), applying just general principles on high level. $\endgroup$ – Poutnik Feb 12 at 15:15
  • $\begingroup$ Thank you very much! $\endgroup$ – DemoralizedOS Feb 15 at 10:50

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.