Although the Seigfried method is all over the place, I think the theory is roughly right. His method using CH3CN solvent and K2CO3 to mop up the HCl & HBr formed looks right, but the product will not be 100% pure, having KBr & unreacted PEB & piperidone in it as well as the PTC catalyst. So, how to clean? Well, PEB is insolvent in water but the salts of PEP & piperidone are, so addition of hydrochloric adic & washing in toluene removes your PEB. If you use excess PEB, you SHOULD end up with virtually no piperidone left so your aqueous solution contains PEP & the PTC. Now, here is the question: will a bisulfite (or NaI) addition complex form allowing the PEP to be crashed out? If so, THEN you would have a pure product...
Oh, I did consider vacuum distillation but PEB boils at 200C so even under vacuum it would be a lengthy process.
Maybe if you can find an ebook on PTC then this will give some useful information. It is a rather specialised technique so there is a certain amount of expertise involved.
I've done PTC before now. I'm sure PTC IS used to produce fentanyls as a DEA report specified benzyl fentanyl as an impurity which they described as 'a logical side product from synthesis'. Well, I know from experience that TEBA will tend to benzylate & seigfried does specify that as one of the options for catalyst. here is a link to that remark http://www.cnoa.org/N-05.pdf though I have seen the same point mentioned in several DEA articles.
Thinking on...
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