As long as the compound has an amino group on can use tha A/B to go from a free base to a acid......so read Mad Max's excellent write up on the subject.....java
cathinone is madly unstable outside of the plant matter. Khat is consumed fresh and there is a good reason for it. the plant matter has some stabilizing material in it, which helps keep the cathinone. once the leaves are cut fromt he plant they do not stay "active" for a very long time. although ive seen several khat drinks made by y emens, and that remained active for the whole day or even 2 days, mostly it is prepared ande aten fresh.
what u need for it is to do a quick a/b with some good acid, onl problem is that too strong acid wil destroy the cathinone, personal experimentation will yield eventaully a good tekniq, but expect low to no yields at the begning...