Hi guys,
I want to synthesize the compound in the below picture.
(Ref from Chem. Commun., 2017,53, 3189-3192 )
Its synthetic procedure seems gabriel synthesis using phthalimide
So, I used same starting materials and then I get final product. However its yield is too low than that of paper yield.
The yield of first step, attatching phthalimide to R-X, was very high almost 90% after vacuum drying but final product is not.
What can I do for increasing yield?
Also I have questions about this procedure. First, most gabriel synthesis schemes note OH- maybe using base. Then, is it helpful for my synthsis? And why the pH is adjusted from acidic condition to basic condition? I don't know exact meaning about pH.
Please help me!
Thanks
Your product is probably in the aqueous layer. You need to add excess base such that all the acid is neutralised, i.e. pH > 7. You can calculate based on the amount of acid added, or measure by pH paper.
Even then I am doubtful you can extract out from water a compound with 2 primary amines and a pyridine ring....
Are you sure that using Gabriel synthesis is a good idea for this? It's way too complex for a simple product and usually used for more exotic substrates. On the top of my head I can think of several ways to do it simpler.
1) Ammonia solutions. Slow addition of halogen derivative solution to a large excess of 5M ammonia in methanol. should do the trick. Dilute solution is important because it prevents oligomerisation with monoamine derivative.
2) Azide intermediate. You can convert halogen derivatives to azides and then reduce them (Staudinger or zinc or several other ways). Care needs to be taken with this as azides should never be heated over 40 degrees centigrade and are somewhat toxic, but otherwise it's a really simple approach to primary amines.
You can increase the yield by using ultrasound bath (sonication) instead of refluxing and heating for such long time.By which decrease the time and increase the yield.
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