[Babcock_Hall]

I don't have any personal experience; can you elaborate a bit on the side reaction you mentioned?

I found this from the link you supplied, "Cool your finished reduction down to 0 degrees C, or lower depending on the situation (For my large scale reduction I cooled it with acetone/dry ice) and quench excess reducing agent with something non-protic. For example ethyl acetate or acetone works well. Just remember to use something you can easily evaporate off when things are done. Don't be impatient and add it dropwise with vigorous stirring. Use a addition funnel for larger scale reactions. When the quench is complete remove the cooling bath."

The site below recommends methanol as a quenching reagent:
"2) Why do we quench the reaction mixture with methanol after reduction with Lithium aluminium hydride?

Answer:

LiAlH4 can react with methanol in the same way as it reacts with water but less violently since the O-H bond in methanol is less polar.

LiAlH4 + 4MeOH -------> LiOMe + Al(OMe)3 + 4H2

Hence methyl alcohol is used in the quenching of LAH during workup. It is better to quench in cold conditions."

Elsewhere it suggests ethyl acetate followed by methanol:  "During the workup, the reaction mixture is initially chilled in an ice bath and then the Lithium aluminium hydride is quenched by careful and very slow addition of ethyl acetate followed by the addition of methanol and then cold water."  http://www.adichemistry.com/organic/organicreagents/lah/lithium-aluminium-hydride-1.html

Here is another quench:
"After reaction, destroy excess LAH by slow careful addition of ethyl acetate (diluted with an inert solvent such as dry THF), under nitrogen, keeping the temperature below 50°C. All LAH reactions should be carried out behind protective screens."  http://www.ch.ic.ac.uk/local/organic/0405Expt5.pdf

A site at Virginia Tech recommends isopropanol:  http://www.chem.vt.edu/facilities/resources/safety-quenching-pdf.pdf

[magician4]

just take a look at the mechanism for Meerwein-Pondorff-Verley reaction, and it should be obvious why I was a little reluctant to expose the aluminiumalcoholate of the very compound I took great efforts in to reduce it in the first place to a ketone like acetone - just for quenching purposes at that.


with respect to your further suggestions: I think we agree that any C-H acide (or N-H and so on) substance will react with the hydride supplied by LAH, thus "quenching" it.
some people wish to avoid the development of hydrogen along this line, and hence offer additional reduction equivalents in huge excess, like for example acetone and / or one ester or another

others don't like it hot, and instead of hydrolysis will have a stepwise solvolysis "methanol, water"

as we use to say here: many ways will lead to Rome...

regards

Ingo