From: Richard Prankerd (richard.prankerd$##$pharmacy.uq.edu.au)
Date: Tue Apr 27 1999 - 21:52:44 EDT
To list:
I remember Merlin's previous query about deuterium exchange. I also accept
that exchange mediated by the acidity of acetonitrile could occur, but I
don't have a pKa value close to hand. However, the following are relevant:
Malononitrile (CH2(CN)2) has pKa 11.2 at 25 deg C
Cyanoform (CH(CN)3) has pKa < 1 at 25 deg C
Hence, pKa of acetonitrile could be expected to be quite high (certainly
>14) -- but only a trace of protium is needed to catalyze the exchange.
Regards
Richard
>----------------------------------------------------------------------
>Merlin wrote:
>>
>> I actually posted a similar query on a similar matter a little while
>> ago. To the best of my knowledge, the dielectric constant and
>> polarizability seem to indicate a possibility for CH3CN to perform such
>> a transformation, but I'm not going to say for 100% certainty that it
>> will occur.
>
>
>Acetonitrile is somewhat acidic due to to strong electron withdrawing
>effect of the cyano group stabilizing the anion. The pKs could be around
>12, couldn't find it exactly right now. So a deprotonation /
>reprotonation is likely.
>
>------------------------------
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$##$pharmacy.uq.edu.au
http://www.uq.edu.au/pharmacy/rprank.html
(including photo)
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