Reactions of LiAlH4, NaBH4 and H2/Ni (Recap)

Let’s do a reactions recap of what we have learned so far.
We’re going to review reactions of lithium, aluminum hydride, sodium borohydride, and
we’re going to go back and review catalytic hydrogenations.
In this particular case, we’re only going to focus on hydrogen gas in the presence of
nickel as the catalyst.
So these reactions are specifically also when we do catalytic hydrogenations using nickel
only.
Take a look at what I have here on the right side.
We have our footnotes that are going to help us to memorize what is happening here.
So we have that lithium aluminum hydride can reduce aldehydes, ketones, acyl chlorides,
and carboxylic acids.
Basically lithium aluminum hydride can reduce anything that contains a carbonyl group,
but it cannot reduce double bonds or alkenes.
So the first reaction when we treat this starting material with lithium aluminum hydride,
we’re going to reduce anything that has a carbonyl group and we’re going to leave the
double bond intact.
That is the only thing that cannot be transformed.
This aldehyde, this ketone, and this carboxylic acid, all three of them will be converted
into alcohols.
Let’s take a look at the second reaction.
It calls for reduction with sodium borohydride.
Sodium borohydride can reduce aldehydes, ketones, anhydrides, and acyl chlorides, but it does
not reduce carboxylic acids, esters, or alkenes or double bonds for sodium borohydride.
We’ll be able to reduce the aldehyde and the ketone, but we will not be able to reduce
the carboxylic acid or the double bond.
Those will be untouched.
And so what we will get is that molecule where the new alcohol groups come from the aldehyde
and the ketone groups.
Let’s take a look at the third case.
In this case, we’re going to be using hydrogen gas in the presence of nickel as catalyst.
Hydrogen gas and nickel can reduce aldehydes, ketones, and alkenes or double bonds, but
they do not reduce carboxylic acids, esters, or amides.
This particular case, the carboxylic acid, will be untouched, and it will be able to
reduce the aldehyde to an alcohol, the double bond to a single bond, and the ketone to the
alcohol or secondary alcohol.
And so that will be the final product.
Let’s take a look at the last three reactions, and it’s similar to what we did on the top.
And so the first one is now catalytic hydrogenation with nickel as catalyst.
What we’ll see here is that the carboxylic acid will be untouched, and everything else
will be reduced.
This hydrogen gas in the presence of nickel can reduce the ketone, it can reduce the double
bond to a single bond, and it can reduce the aldehyde to form the following product.
And so the carboxylic acid, notice, was untouched, stays the same.
The next reaction calls for lithium aluminum hydride.
We know that lithium aluminum hydride can reduce anything that contains a carbonyl.
The only thing that will be untouched will be the double bond, and so we’ll get that
final product.
And lastly, sodium borohydride won’t be able to reduce the carboxylic acid or reduce the
double bond, but it will be able to reduce the ketone to a secondary alcohol and the
aldehyde to a primary alcohol to get that final molecule.