Chemistry Forums for Students > Organic Chemistry Forum

aldehyde + tert-butoxide,exercise

(1/3) > >>

xshadow:
HI, I  have to write the products of these two reactions:





Are these  written products right?
In the first  "question", I think that no  reaction can occour....because I haven't any  C-H in alpha position; tert-butoxide con acts only as a strong base..I think it can't act as nucleohile (C=O attack)  ---> so I suppose no reaction .

Is it right?

rolnor:
This could be useful;

https://en.m.wikipedia.org/wiki/Tishchenko_reaction

spirochete:
If this is basic sophomore organic, the original poster may have been taught it is simply "no reaction" under any circumstances for an aldehyde with no alpha hydrogens + base. Professors sometimes don't think very hard about questions like this, and in that case they also don't expect the student to.

If they are indeed responsible for something like benzaldehyde + alkoxide or hydroxide, OP should also read up on "Cannizaro reaction" to understand the result: https://en.wikipedia.org/wiki/Cannizzaro_reaction . The metal also seems to be important as a Lewis acid, but you could imagine a simplified mechanism that does not involve the metal.

For the second aldol, that looks correct. You might also consider aldol condensation, but your professor may have taught you that this requires "heat."

xshadow:
Thanks ... but We haven't done the Tishchenko reaction...only Cannizzaro one.

Is benzaldehyde +  potassium tert-butoxide  campatible with Cannizzaro reaction?

Because usually we need NaOH....here we have tert -butoxide: a very weak nucleophilic (steric hindrance)  but strong base.. but in the first step of Cannizzaro reaction we have the OH-  nucleophilic attack towards the C of   C=O : tert-butoxide is a weak nucleophilic

spirochete:
If you have studied cannizarro, then it would be reasonable to think Tischenko might be fair game. Draw a cannizarro mechanism first, and then below it try to draw a similar mechanism for Tischenko.

Disclaimer: I don't specifically know if it works with t-butoxide. But t-butoxide is occasionally a nucleophile, mainly in situations where it has no possible way for it to act like base. For example, you can do Williamson ether synthesis (Sn2) with t-butoxide to make tert-butyl methyl ether. In this case the electrophile is a methyl halide.

Navigation

[0] Message Index

[#] Next page