[chrisr789]

Hello,

I want to make a 2 molar ethanolic solution of HCl. 2 moles of acetyl chloride in a litre of ethanol should do the business I think, with the 2 moles EtOAc floating about as well. Can anyone see any problems with this plan? For example, is the HCl likely to escape as a gas?

Cheers,

Chris

[Honclbrif]

You're ignoring the volume of acetyl chloride which on your scale will not be inconsiderable.

Are you planning on doing this for real, or is it an exercise?

[Dan]

It will be fine, I've done this many times with methanol.

If you want it to be accurately 2 M, then add the AcCl (slowly) to, say 750 mL EtOH. Make sure it's cold, and cool constantly with stirring, it will get hot. Once that's done you will have to allow it to reach room temp, the total volume should be less than 1 L, so you can then top it up to 1 L with EtOH.

[OC pro]

You can also use TMSCl. For really dry HCl in EtOH you can develop HCl (g) by dropping conc. H2SO4 to NaCl (covered with conc. HCl) and passing it through conc. H2SO4. This HCl is transferred via tube into a flask with dry EtOH. 

[the.khemist.ds]

If you've got the choice then I'd definately recommend TMS-Cl or acetyl choride for generating your ethanolic HCl solution. If you need to avoid having anything apart from ethanol and HCl in the solution then HCl gas is the way forwards. But it does require a great deal more work.

At the simplest level of explanation you just need to place a known volume of dried ethanol into a Schlenk (or other sealable container) weigh the filled container, then pass HCl gas through the ethanol. By weighing the Schlenk again after you've passed some HCl through it, you can see the mass difference and work out how much HCl is dissolved in you ethanol and hence work out the concentration. You can then alter the concentration by adding more HCl or more ethanol (though in many cases it is sufficient just to know the concentration of your solution)

At a practical level there are several considerations that require a careful choice of apparatus. I always used a cylinder of HCl gas as the source of my HCl. This can present challenges with controlling the flow of HCl - primarily because: if the flow of HCl is slow or you stop it, the HCl in the tubing (between the cylinder and where you introduce the gas into the ethanol) continues to dissolve in the ethanol, as this is taken out of the tubing you develop a vacuum which can draw the ethanol back towards the cylinder (this process can be remarkably quick). For this reason, you need a dry trap between your cylinder and the solvent (just in-case) and I always set up my apparatus so that I blended the HCl gas with a flow of nitrogen so that when I stopped the flow of HCl, I could compensate with more N2.
You are now trying to maintain a slight positive pressure of HCl/N2 in the system (too much and you are wasting HCl, too little and you get suck back). In this situation it is worthwhile having some sort of exit flow from the system (to avoid too much pressure in the system) this generally needs some sort of scrubber on the exit. Again, you need to be very careful about the possibility of 'suck back' on any traps that you place between your ethanolic HCl and the exit and set up your system accordingly.
I'd also note that the process of dissolving HCl in ethanol is exothermic - I never had serious problems but it is worthwhile considering.

It's about 4 years since I last had to do this prep and so I might have forgotten some aspects of this process/apparatus and would encourage anyone thinking of trying this to think through all of the possibilities themselves (obviously, as always you need to ensure that you take responsibility for your own safety assessment etc.). But I hope I've supplied useful information on some of the things that can cause problems when trying to do this procedure to be helpful.