Recently I was solving carbonyl compounds and I came across this. Is there some priority order, or logic behind why alcohol reacts first with Grignard reagent and then ketone. Whereas ester could've reacted with 2 moles of RMgX but didn't.
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1$\begingroup$ What is the difference between Grignard reagent reacts with either $\ce{R-OH}$ or $\ce{R-CO-R'}$? There is a pretty good reason for that. $\endgroup$– Mathew MahindaratneCommented Jul 10, 2020 at 1:05
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3$\begingroup$ so the first one seems like a base so acid-base reaction? And the second one will undergo nucleophilic addition ? so acid-base before substitution . is that it?(●'◡'●) $\endgroup$– shreyaCommented Jul 10, 2020 at 1:10
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$\begingroup$ Looks good but is the structure of R shown? $\endgroup$– user55119Commented Jul 10, 2020 at 1:13
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1$\begingroup$ @shreya: You are correct, when acidic hydrogen is present it react first such as tin the case of given 1st reaction to give $a$. $\endgroup$– Mathew MahindaratneCommented Jul 10, 2020 at 6:00
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1 Answer
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For the compound given in the question, the priority order of Grignard reagent attack follows,
$\ce{R-OH > R-CO-R' > R-COOR'}$
Reason:
Acid-base neutralisation are very fast.
Carbonyl carbon is more nucleophilic than carboxylic carbon, as the latter one is stabilized by resonance.
Therefore, first alcohol is attacked and hence P is (a), then the carbonyl part is attacked and hence Q is (b).
Finally, one more mole of RMgX gets used up on the carboxyl part, hence R is not (d).
answered Jul 10, 2020 at 5:59