Re: ORGLIST - orglist Digest - V01 #193

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From: Richard Prankerd (richard.prankerd$##$pharmacy.uq.edu.au)
Date: Thu Oct 01 1998 - 21:22:06 EDT


In reply to the following:
>
>
>Dear pals,
>Could any one suggest me why the following reaction does not work.
>1. I have reacted piperazine (2 mole) with n-propyl bromide (1 mole) to
>give n-propyl piperazine. The reaction was carried out in ethanol (under
>reflux)with 1 mole of NaOH for 7 hrs. Unfortunately, what i obtained
>was the disubstituted product and unreacted piperazine.
>
>I could be much greatly if you'll could offer me other procedure to
>synthesize the above mentioned compound. I would also like to know on
>the commercial availability of theis compound. Any other suggestion is
>welcome.
>

Unfortunately, this is a classic problem -- how to react only one of two
functional groups which have similar or the same reactivity. I've had to
deal with a similar type of nucleophilic substitution problem and found
that a mixture of monosubstituted and disubstituted was always obtained, so
a chromatographic separation was essential. It appears in your case that
substitution of one of the piperazine nitrogens with the alkyl group has
increased the reactivity of the other group on the same molecule. You
should be able to change the ratio of products (disubstituted to
monosubstituted) by manipulating: (i) the order and speed of addition of
each of the 3 reactants; and (ii) the molar ratio of the reactants. The

Possibly the desired product could be obtained by performing the reaction
on piperazine that has been covalently, but reversibly, immobilised on a
solid support such as is used for peptide synthesis.

I would be interested to hear what others can offer in the way of suggestions
Best regards
Richard

Richard J. Prankerd, PhD
Senior Lecturer
School of Pharmacy
University of Queensland Phone: INT + (617) 3365-3179
St Lucia QLD 4072 Fax: INT + (617) 3365-1688
AUSTRALIA richard$##$uqpharmacy.pharmacy.uq.edu.au
                        http://www.uq.edu.au/pharmacy/academic.html


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