From: Leslie J Harrison (chmhl$##$leonis.nus.edu.sg)
Date: Tue Apr 27 1999 - 22:14:49 EDT
The pKa of MeCN is approx. 25.
At 11:52 AM 4/28/99 +1000, you wrote:
>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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