thats one of the reasons i contimplated dmso, is its high dielectric constant.
but i understand it does not solvate anions well, so the rate at which iodine leaves might be slowed.
the problem with most protic solvents that i can think of is that they are apt to participate in side reactions with the carbocation and create for example a ether or alcohol rather then the desired benzoate-ester.
so what would be a good compromise of "proticity", polarity, and low reactivity?