In the Lucas reagent for alcohol tests, what is the effect of replacing concentrated HCl with dilute HCl?

Question

The Lucas reagent consists of ZnCl2 in concentrated HCl. Its reaction with alcohols goes: R-OH + HCl ---> R-Cl + H2O. Now, what will happen if we use dilute HCl instead of the concentrated one?

Answer 1

Lancenigo di Villorba (TV), Italy

You wrote chemical equation.
It is right!
Who preceeds me whole highlighted that the greater reactant's concentrations, the greater reaction' rate.
In effect, time processes follows significatively HCl's concentrations, that is you could have timing's change like greatness's orders!!
This reaction denotes great "activation's energy" (see A. S. Arrhenius, equation of kinetic's constant).
Precisely, it exist an intermediate known "carbocation" or an poli-atomic carbon-based aggregate who has one or more positive charge carbon-hosted. Carbocation is involved for more reactives alcohols like tertiary, allylic- or benzylic-types. Carbocations are very reactive intermediates, so they accumulate not and convert readily ; here, they become alkyl chlorides. Carbocation's formation need very reactive alcohols and high hydro-halogenic acid's concentrations, since the latter send off one water molecule (see chemical equation).
Least reactive alcohols, those are primary alcohols, fail the test since give not "carbocation" ; they prefer react with other acidic reactives, e.g. sulphuric acid for ethers/alkenes producing.
High HCl's concentration is common request for Lucas conversion of alcohols.

I hope this helps you.

Answer 2

I think you have to have concentrated HCl in order to allow the reaction to happen at a significant rate. The presence of water will either slow or even completely prevent the reaction from occurring.