Yes, I would not add AcCl to TEA, that is asking for side reactions. The normal prep for these reactions is to mix the TEA and alcohol, then add the
AcCl dropwise or very slowly. Since Ac2O is less reactive, it can often be added much faster. Since AcCl can react with amines, even teriary ones,
it is often not used for complex acylations, like morphine, which might react at the nitrogen as well as the phenol. There are even some reactions
that utilize a harsh reagent like AcCl to remove a methyl group from a dimethylamino group.
So for many simple reactions, they are interchangable, but in general anhydrides are less reactive, but milder, which often can give better yields.
But for some cases, the chloride is able to react when the anhydride is not reactive enough.
Also, I would rarely reflux a reaction like these, and the solvent would typically be what controls the boiling point. I would never run a reaction
in anhydride at 140 C, its just too harsh. If the AcCl contains HCl, you could just distille it, which would remove some, or just add some TEA or
pyridine to the substrate, before adding the AcCl, it will eventually soak up the HCl. |