if you want anhydrous organic/HCl mix, you will need to create the HCl and have it bubble through into the solvent. A common technique for esterifying with methanol is to create the HCl in situ and have it bubble into the methanol solvent.

Yep, it will be a mess. You have to use gaseous HCL and bubble it.

Even if you find an agent that can 'dry' your mixture, then with a lack of water HCL will start boiling under the normal pressure conditions, unless your organic phase is such a good media for HCL that it will manage to drop the equilibrium pressure of HCL above the solution below the atmospheric pressure, which I kinda doubt (if we are talking about real high proportions of HCL)

why not try some solid acids? there are so many available

Thanks for all the answers!

By the way, what I was doing until recently (following a published protocol...) is to "dry" methanol with MgSO4 and then add Acetyl-chloride to it, since Acetyl-chloride is supposed to react with the Methanol and produce HCl.

This method, however, has (at least) two problems that I know of (and perhaps that's why the final reagent was not so effective in what it was supposed to do):

First, MgSO4 dissolves to some extent in Methanol: I needed, for the protocol to procduce, in addition to the methnolic HCl, a methanolic base, for neutrilzation of the reaction. When I added to KOH, or NaOH to the "anhydrous" methanol, I gol Mg(OH)2 precipitation, so the basicity was always much lower than intended.

Second, after reading Philipp's answer, I realize that when adding the Acetyl chloride to the anhydrous Methanol, perhaps most of the HCl immediately escaped as a gas, and instead of staying in solution (so that the acidity of the mix was also lower than intended).

If anyone has any advice for better controlling the reagent preparation (in addition to check the acidity/basicity by titration) I'll be happy to hear!

Thanks!

To dry THF, you'd need molecular sieves or alumina, per the attached paper.  Sieves are mildly basic and can soak up HCl, so I'd go with neutral (or acidic) alumina.

THF will readily cleave to give 4-chloro-1-butanol, so don't plan on storing the solution for any length of time.  You're better off with 1.4-dioxane or dibutyl ether.

Thanks again!