I may have explained it incorrectly, I'm a bit rusty.
I did a lot of work in pharmaceutical route development, where some patent does "ABCD123" and we'd do "ABCD456". My point is more that, patents are usually laid out like:
1. A method for crystallization of a pharmaceutical in an organic solvent with some counterion.
2. (1), where the solvent is ethanol, or methanol
3. (1), where the counterion is Cl, SO4, or NO3
4. (1), where the pharmaceutical is a COX2 inhibitor
So that patent doesn't allow you to claim any crystallization route with ethanol. If I crystalize from ethanol but use mesylate as the counterion, I'm not infringing.
Considering the doctrine of claim differentiation, your hypothetical could still be infringing Claim 1. You’d have to consider the spec, among other things, to persuasively argue one way or the other.
I did a lot of work in pharmaceutical route development, where some patent does "ABCD123" and we'd do "ABCD456". My point is more that, patents are usually laid out like:
1. A method for crystallization of a pharmaceutical in an organic solvent with some counterion.
2. (1), where the solvent is ethanol, or methanol
3. (1), where the counterion is Cl, SO4, or NO3
4. (1), where the pharmaceutical is a COX2 inhibitor
So that patent doesn't allow you to claim any crystallization route with ethanol. If I crystalize from ethanol but use mesylate as the counterion, I'm not infringing.