Major product of Crossed-Cannizzaro Reaction between benzaldehyde and formaldehyde

Asked Sep 24 '20 at 12:55

Active Sep 24 '20 at 22:05

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I came across a question:

Predict the major product when conc. $\ce{NaOH}$ is added to a mixture of $\ce{PhCHO}$ and $\ce{HCHO}$.

According to me, as $\ce{HCHO}$ is less hindered and $\ce{>C=O}$ of $\ce{HCHO}$ is more reactive, so the major products must be $\ce{CH3ONa}$ and $\ce{HCOONa}$. The hydride transfer should be from one Formaldehyde molecule to the other.

However, the answer was given as $\ce{HCOONa}$ and $\ce{PhCH2ONa}$. Is there a mistake on my part?

edited Sep 24 '20 at 22:05

user55119

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asked Sep 24 '20 at 12:55

Soumyadwip Chanda

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Rate determining step of Cannizaro is the hydride transfer and not nucleophilic attack – Safdar Faisal Sep 24 '20 at 12:59
Why would the hydride prefer transferring to the PHCHO? – Soumyadwip Chanda Sep 24 '20 at 13:06
Exactly... Thats how I get HCOONa... But I am concerned about the Alcohol product... HCOONa matches with my answer... PhCH2ONa does not – Soumyadwip Chanda Sep 24 '20 at 13:14
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So what happens to the benzaldehyde> – Safdar Faisal Sep 24 '20 at 13:18
It might also form some PHCH2ONa... But the major product must be CH2ONa according to me... And that isn't the question what happens to benzaldehyde. What is the major product is what the question demands – Soumyadwip Chanda Sep 24 '20 at 13:22
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See this earlier Q&A. – ron Sep 24 '20 at 13:39
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Ok but I still dont understand why the cross reaction is favored over one formaldehyde molecule reacting to the other – Soumyadwip Chanda Sep 24 '20 at 13:46
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Effectiively there is no free formaldehyde to accept hydride. – user55119 Sep 24 '20 at 14:45

Major product of Crossed-Cannizzaro Reaction between benzaldehyde and formaldehyde

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