(to give a final concentration of Trp. of 0.75 M)
What is Trp.?
This is an odd reaction for you to be using 3 eq of acetyl chloride, unless this is only part of the sequence. When I've seen this reaction in use, it has been for preparing an anhydrous solution of HCl in methanol, usually for making an HCl salt. I don't know of any particular use for methyl acetate. The way you presented your question, it appears that you are supposed to be adding three equivalents of acetyl chloride to one equivalent of methanol, which would give a final solution of 1 equivalent of methyl acetate in two equivalents of acetyl chloride? Are you using any solvent, or is this the total reaction?
My guess, based on the ways I have used this reaction, is that you have already prepared some basic compound, such as an amine, and are now going to prepare an HCl salt. To do so, you are preparing three equivalents of HCl in a methanol solution, where the equivalents of HCl are measured against the basic compound rather than against the methanol (which being the solvent is present in large excess). After you have prepared your HCl solution, you will add it to a solution of the basic compound and either precipitate the salt or strip the solvents down. Excess HCl and the largely inert methyl acetate will disappear either way. Is this anywhere close to what you are doing, or am I completely off?