9
$\begingroup$

Diisobutylaluminium hydride(DIBAL-H) reduces only carboxylic acid, ester or both?

The answer given was that it only reduces ester.

Is it correct that under any condition carboxylic acids are not reduced by DIBAL-H?

$\endgroup$
3
  • 1
    $\begingroup$ Bulky groups are there for selectivity, so while it might do that, it's not supposed to. $\endgroup$
    – Mithoron
    Commented Dec 26, 2017 at 15:35
  • $\begingroup$ Yes I think it does. Like BH3, DIBAL-H is an electrophilic reducing agent. In other words, it is best able to reduce electron-rich compounds like amides, acids and esters. I have seen various sources saying that too. However, it is best known for its reduction of the ester to the aldehyde and not the alcohol. $\endgroup$ Commented Nov 6, 2018 at 6:16
  • 2
    $\begingroup$ Conditions matter a lot in this question. Are you using a full equivalent or two equivalents? Your answer might be very different with 10 equivalents... $\endgroup$
    – Zhe
    Commented Jan 5, 2019 at 2:49

2 Answers 2

8
$\begingroup$

Does diisobutylaluminium hydride (DIBAL-H) reduce only carboxylic acids? Or only carboxylic acid esters? Or reduce both both types of compounds?

The answer is yes, it does reduce both. Not only them, it also reduces nitriles to aldehydes, and is a more selective reagent than lithium aluminum hydride (LAH) in the reduction of nitriles (Ref.1). About reduction of carboxylic acid, Miller et al. (Ref.1) found that DIBAL-H can be used to reduce benzoic acid to give 72% yields of benzyl alcohol in 1959. In same publication, they have also shown that esters can be reduced to corresponding alcohols as well.

In reduction of nitriles to aldehydes, following results were achieved and compared with the result obtained by Amundsen and Nelson (Ref.2) using $\ce{LiAlH4}$:

Benzonitrile Reduction

The summery of reduction of carboxylic acids and their esters are illustrated in following scheme, where two different groups (Ref.1 & Ref.3) achieved two different results for ester reduction under different conditions:

Acid&Ester Reduction


References:

  1. A. E. G. Miller, J. W. Biss, and L. H. Schwartzman, “Reductions with Dialkylaluminum Hydrides,” J. Org. Chem. 1959, 24(5), 627–630 (DOI: 10.1021/jo01087a013).
  2. L. H. Amundsen, L. S. Nelson, “Reduction of Nitriles to Primary Amines with Lithium Aluminum Hydride,” J. Am. Chem. Soc. 1951, 73(1), 242–244 (DOI: 10.1021/ja01145a082).
  3. L. I. Zakharkin, I. M. Khorlina, “Reduction of esters of carboxylic acids directly into aldehydes with diisobutylaluminum hydride,” Tetrahedron Letters 1962, (14), 619-620 (https://doi.org/10.1016/S0040-4039(00)70918-X).
$\endgroup$
2
  • $\begingroup$ Sir, please tell that does DIBAL-H reduce aldehydes and ketones to alcohols? If it does, then why aldehyde formed in reduction of esters is not reduced further to alcohols ? $\endgroup$ Commented Sep 29, 2022 at 16:38
  • 1
    $\begingroup$ @An_Elephant: Look here the mechanism for ester to aldehyde reaction and description given. $\endgroup$ Commented Sep 29, 2022 at 21:13
4
$\begingroup$

enter image description here

My book (Cengage for JEE Adv) doesn't mention anything about carb acids, but I was able to find this website that says DiBAL-H reduces carb acids to aldehydes and alcohols, but requires 2-3 equivalents, at a high temperature.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.