Are there any rules for combining prepositions/adjectives with -che to make a new conjunction?

Question

I've seen on this site, a few times, words like benché, finché, fintantoché, etc. and while all of these are words that I know -- they seem to be contractions of a word and -che.

A few examples:

benché =      bene + che
finché =      fino + che
fintantoché = fintanto + che
perché =      per + che
talché =      tal + che
tantoché =    tanto + che

Is there a pattern or formula I can follow for creating new words like this? It doesn't seem like Treccani or other sources I use talk about this topic specifically.

It seems like, in that list, some of the words are adjectives, some are prepositions -- is there a particular rule on which are allowed and which aren't? For example, I can't do con + che = conché can I?

Answer 1

While there may be some etymological history as to the origin of the compound words (derived from the meanings of their separate parts) it seems like the answer to the second part of the question is no; you can't just do this on the fly to make new words.

For a larger list of these compound conjunctions/adverbs, than the one I provided, see the links in @mle's comments.