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Author Topic: Nah vs NaH + KOtBu(cat)  (Read 697 times)

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cultlife

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Nah vs NaH + KOtBu(cat)
« on: March 13, 2018, 06:25:54 AM »

I have a question.
i am running a reaction with indanone, NaH, Diethylcarbonate in THF solution and it needs reflux condition.

Besides i found some reaction can be done in room temperature , adding KOt-Bu catalytic amount.
I’m curious what might be the role of KOt-Bu in this reaction. What makes this reaction work in room temperature.

I am trying to find some information but not easy for me to find the exact reason.

Thanks
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pgk

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Re: Nah vs NaH + KOtBu(cat)
« Reply #1 on: March 14, 2018, 08:30:07 AM »

Both reactions occur via preliminary formation of the indanone-enol salt, which reacts with diethyl carbonate, through conjugation and leads to C-substitution. But both reactions are highly exothermic and therefore, reactants are slowly added, in order to prevent any uncontrolled, exothermic heat. After the end of the reactants addition, the reaction mixture is gradually heated, in order to offer an amount of heat that is equal to the activation energy (minus the exothermic heat) and thus, the reaction is completed.
Theoretically, both reactions can effectively occur at room temperatures in high dilution but NaH is not compatible with diethyl carbonate; in contrast to t-BuOK, which is.
« Last Edit: March 14, 2018, 09:07:09 AM by pgk »
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cultlife

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Re: Nah vs NaH + KOtBu(cat)
« Reply #2 on: March 21, 2018, 11:14:36 AM »

So, why is NaH not compatitable with diethyl carbonate? but potassium t-butoxide is compatible?

My friend is talking about the solubility of the Nah vs KOtBu in THF.  He is saying that KOtBu is more soluble in
THF, that makes the reaction faster.?
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pgk

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Re: Nah vs NaH + KOtBu(cat)
« Reply #3 on: March 22, 2018, 06:44:49 AM »

Although solubility of reactants plays an important role, this is not a question of solubility because both NaH and t-BuOK react with the enol form of indanone. In other words, indanone behaves as a reactive co-solvent for NaH, hereby.
However, NaH is a weak reducing agent that can partially reduce diethyl carbonate and therefore, NaH is incompatible and unsuitable for addition in a mixture of ketone and diethyl carbonate.
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