Can anyone point me to where the rules are for non-spell based touch attacks? I'm specifically referring to using something like contact poison (while immune like an alchemist) or acid or some other alchemical attack that is delivered by contact?
Is it delivered by the touch attack mechanic? If not, what mechanic is it?
If you have the alchemical attack, and it is delivered by touch attack, do you threaten squares around you similar to a spell?
There's no special rules for non spell touch attacks. A touch attack is a touch attack. If a particular ability uses a touch attack, it will say so.
The things you're asking about, I don't believe that are any written rules for them so you would have to work it out with your group.
I would say that if you applied a contact poison to something that wouldn't immediately absorb it you would still need to hit regular AC as things that impact regular AC like armor and shields would reasonably protect against poison. If you tried to apply it directly to your hand you would be affected by the dose of poison and there's nothing left over to affect anyone else. If you're immune the poison just doesn't do anything to you. It doesn't mean that it will still be active.
Trying to apply acid and then attack with it... I just don't see how that would work. Whatever you apply the acid to would be affected by the acid.
Either way, it would not make you threaten if you wouldn't threaten anyway.