Benzoylpseudotropine, Tropacocaine HCL and solubility

Discussion in 'Drug Chemistry' started by mannichone, Jul 30, 2013.

  1. mannichone

    mannichone Guest

    We have acquired pseudotropine from our licensed chemical supplier in my country. I do not reside in Europe or North America , nor any English speaking country so please note where we are this is legal and it is intended to be used as an anesthetic.The Benzoic Anhydride was acquired from Sigma and all that is required for this reaction is a simple benzoylation using reflux for 4 hours and benzoylpseudotropine results (plus some unreacted pseudotropine). According to Blount 1933 one then mixes in ether and hydrochloric acid to acquire the hydrochloride salt. The aqueous layer is separated out and if necessary further HCL is added to precipitate the benzoylpseudotropine HCL salt. (a similar benzoylation is in a patent by Wolfe and Maeder 1925 in which it is described in great detail).

    The benzoylation was accomplished without difficulty and a white HCL salt was crystallized with a tested pH of 4. So far so good. Here is where the rub comes. This benzoylpseudotropine HCL salt also is called Tropacocaine HCL which is soluble in water. Subsequently, benzoylpseudotropine freebase which is a viscous oil is not expected to be soluble in water (according the Lit.). However, on testing the benzoylpseudotropine HCL salt is NOT water soluble but the freebase is. The benzoylpseudotropine HCL (tropacocaine HCL) is soluble in the various solvents the literature describes but with the exception of water. We have recrystallized to increase purity but without change. This has been repeated several times and we can find no errors in such a simple process. A mystery. Seems the laws of chemistry and physics function differently here.

    Any ideas, comments or input regards solubility would be appreciated.
     

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