Diisobutylaluminium hydrideDIBAL is a strong, bulky reducing agent. Unlike lithium aluminum hydrideit will not reduce the dibal hexane further if only dibal hexane equivalent is added. It will also reduce other carbonyl compounds such hexanne amides, aldehydes, ketones, and nitriles. So long as the temperature is kept here for the duration of the experiment and only one equivalent of DIBAL hxane added, the aldehyde is obtained. The imines are then hydrolyzed to aldehydes upon addition of water.
Diisobutylaluminum Hydride (DIBAL-H)
DIBAL is a strong, bulky reducing agent. Unlike lithium aluminum hydride , it will not reduce the aldehyde further if only one equivalent is added. It will also reduce other carbonyl compounds such as amides, aldehydes, ketones, and nitriles. So long as the temperature is kept here for the duration of the experiment and only one equivalent of DIBAL is added, the aldehyde is obtained.
The imines are then hydrolyzed to aldehydes upon addition of water. That is, the first step in the reaction is coordination of a lone pair from the carbonyl oxygen a nucleophile to the aluminum electrophile. It is only after coordinating to its carbonyl host that DIBAL delivers its hydride to the carbonyl carbon, resulting in formation of a neutral hemiacetal intermediate that is stable at low temperatures. Quenching of the reaction then breaks down the hemiacetal, resulting in isolation of the aldehyde.
The same mechanism is in effect in the reduction of nitriles to imines and then on to aldehydes. Coordination of the nitrile nitrogen to aluminum is followed by delivery of hydride, and from there, addition of water leads to hydrolysis of the imine and subsequent isolation of the aldehyde.
The good news about this reaction for me are twofold. Then quench the reaction with saturated aq. The bad news is you had to let this biphasic mixture stir vigorously for at least 90 min-2hr before separating the layers.
As long as enough Et2O was added, the emulsion broke down and separation became very manageable if stirred long enough. Somebody recommended to me that the Fieser work up followed by a filtration over Celite should remove the Al salts emulsion just as well. I am probably going to use this method as a first choice from now on, because trying to extract my product from Rochelle salts solution caused me a lot of grief! I mistakenly used methanol earlier on and looking at the mechanism of imine hydrolysis above, that might explain why I got a nasty mixture of crap when I quenched the imine with Methanol!
Guess I can just pour the reaction on to water at 0 Celsius, rather than quenching direct at So I just re-oxidized the alcohol with DMP and was done with it. Aluminum salts are notorious for their bitching emulsions. For LiAlH4 I always use the Fieser workup and filter off the solid… no extraction required, thank goodness.
It was an OH-protected aldol adduct utilizing a thiazolidinethione as a chiral auxiliary. We developed the conditions for the aldol addition in our laboratory. Suffice it to say we did the diastereoselective aldol addition a lot. Partial reduction of the thioimide to the aldehyde was a common next transformation, so we always had a fresh bottle of DIBAL in the fridge. I reduced 5 different thioimides this way who knows how many times as I ran through the synthetic scheme who knows how many times.
The one time I did reduce an actual ester, it was on 0. Usually when discussing it amongst themselves, organic chemists call it DIBAL because it rolls more easily off the tongue than either of the other two. Any reference you have? Under the acidic conditions, convert the aluminum salt to the hemiacetal. When we grade quizzes, students freak out when they see the hemiacetal under acid conditions and they are unable to figure out what to do next. Then the students proceed to use OH- because remember in student parlance, OH- is always available in acidic solution.
I use 2,,5 eq to reduce my esters to alcohols. You usually use a couple of eqivs of dibal to reduce ester to aldehyde not 1 eq as stated above. Just using 1eq would not help anyway as the aldehyde is more facile to reduce than the ester. Love the site and have learnt a lot from it so far: Dibal has another trick up its sleeve. If you have an a,b-unsat.
Actualy, I have just used 2 eq. Then should I use toluene instead of DCM? And should I add the ester to the dibal or the opposite? Follow this, for instance: If you want the aldehyde, you MUST keep it at A non polar solvent is ideal. Avoid ethereal solvents they tend to coordinate to the aluminum and this can affect reactivity , DCM should be fine.
Toluene can present solubility problems, but might be OK for you at If you are aiming for the alcohol, then warming is fine. In the mechanism of Dibal reduction, from ester to aldehyde, we know that OCH3 is a bad leving group but it still goes out.
I have to explain this dibal mechanism in my seminar. The formation of the C-O double bond along with expulsion of CH3O - is therefore not accompanied by a huge energy barrier. CH3O - is not a great leaving group, but still a much better one than H - or most carbon-based leaving groups. All rights reserved Organic Chemistry Is Awesome.
Does this also reduce carboxylic acids? It would come in the workup step when water is added. Hi, I want to reduce an ester to an aldehyde. Thanks a lot Reply. I have to explain this dibal mechanism in my seminar Reply.
Yes, it should give an aldehyde. Cancel reply Leave a Comment. Mar 23, Disubstituted Benzenes: Mar 19, Why are halogens ortho- para- directors? Mar 05, Amides: Properties, Synthesis, and Nomenclature Posted on: What Makes A Good Nucleophile? A Dean-Stark trap is a good way to do it.
Excess acid or ex So I decided to teach organic chemistry anyway! Deprotonation and SN2 Amines Aromaticity: Walkthrough of A Sample Problem Synthesis: Exercise 1 Bond Rotations: Exercise 2 Bond Rotations: Exercise 3 Bond Rotations: Exercise 4 Bond Rotations: Exercise 5 Bond Rotations: Condensed Formula 1 Exercise: Allyl Carbocation Formal Charge Exercise: CN Formal Charge Exercise: CO3 Formal Charge Exercise: Hidden Hydrogens Formal Charge Exercise: N3 Formal Charge Exercise: NH4 Formal Charge Exercise: O3 Formal Charge Exercise: Experiments Introduction to the SN2: Leaving Groups SN2 Exercise: