Amide formation from Acyl Chloride - Carboxylic Acids and Derivatives - Chemistry Video Lecture - Class 12

Let's think about what might
happen if we had a molecule of
butanoyl chloride.
So one, two, three,
four carbons.
That's where the but-
comes in, and then
it's a butanoyl chloride.
So it's an acyl halide or
it's an acyl chloride.
Let me write this down
just to give us some
practice with namings.
This is butanoyl chloride.
We saw a couple of videos ago
that acyl halides, you just
count the main number
of carbons.
One, two, three, four carbons.
That's where butan-
comes from.
And then this is an acyl
chloride, so the acyl chloride
part, this part, gives
us the -oyl.
Or I guess you could look
at even the carbonyl.
We could even say this whole
part over here, we know it's a
carboxylic acid derivative.
It's in an acyl chloride.
So that's why we have the -oyl
here and the chloride.
So let's think about what would
happen if we have a
molecule of butanoyl chloride or
if we had a solution, even
better, of butanoyl chloride,
and for every molecule of
butanoyl chloride, we had two
molecules of dimethylamide, or
sorry, dimethylamine.
Let me draw that.
So dimethyl, so two
methyl groups.
One, two, and then we have one
hydrogen, and then we're going
to have two molecules of this
for every one molecule of our
butanoyl chloride.
So let me copy and paste this.
So edit, copy.
And edit, paste.
So let's think about what would
happen in a solution
with these reactants in
this ratio right here.
And just as a bit of review,
this right here is dimethyl.
We kind of have a tie for our
longest chain attached to the
nitrogen: dimethylamine.
You could pick one of these as
the longest chain and then it
would actually be
N-methylmethylamine.
Either one, this is the
one that you're
more likely to see.
But this video isn't about
naming, this video is to think
about what's likely to happen.
So what are we dealing with?
We have amine here and then
we have an acyl chloride.
And if we look at our hierarchy
of stability that we
looked at in the last video,
we saw that when an amine
reacts or a carboxylic
derivative from an amine,
which is an amide, is
much more stable
than an acyl chloride.
This is the least stable.
So if we're starting with an
acyl chloride and we have the
ingredients for an amide, this
reaction will probably end up
with amide.
So let's see how we
can get there.
What we know from previous
videos when we studied amines,
that they are pretty good
nucleophiles, so they could
have a nucleophile attack
on this carbonyl
carbon right over here.
So you can imagine this amine
right here, this nitrogen,
gives an electron to this
carbonyl carbon.
This carbonyl carbon can then
let go of this electron to
this top oxygen over here.
It was already hogging
it to begin with.
And so the next step of our
reaction would look like this.
What was the butanoyl chloride
will now look like one, two,
three, four carbons.
Now you only have
a single bond.
This oxygen up here now
has a negative charge.
Since it took an electron from
this central carbon right over
here, you are still bonded
to this chlorine.
And actually let me do that in
a different color so we can
keep track of it.
You are still bonded to this
chlorine atom and then the
nitrogen has been bonded.
So this bond I'll drawn green
because we're giving this
green electron to form the bond,
and then the rest of the
dimethylamine is still
over there.
Let me do it in that
same color.
The rest of the dimethylamine,
so you have CH3, CH3 and then
you just have your hydrogen.
And then this nitrogen gave away
an electron, so it has a
positive charge.
Now, the next step, and this
is chlorine, it's fairly
electronegative.
It's a not-so-bad
leaving group.
It will want to hog this
electron that is on the
central carbon.
So you can imagine in the next
step that this oxygen gives
back an electron to reform the
carbonyl group at the exact
same time that this chlorine
takes an electron and forms a
chloride anion.
So the next step in this will
look like-- so the molecules
will now look like--
you have there one,
two, three, four carbons.
That's one of the bonds to that
oxygen, but now you've
now formed another bond.
That electron was given back to
that central atom and now
you have the bond to the
nitrogen, this bond right
here, and then the nitrogen is
bound to one methyl group, two
methyl groups, and a hydrogen.
And it had given away an
electron so it has a positive
charge, and the chloride anion
has been bumped off.
The chloride anion, it took an
electron from that central
carbon, so now it has
a negative charge.
Now, we still have that other
dimethylamine molecule, or for
every one of these, we should
have two of these.
We've only use one of them, so
let me bring the other one
into the mix, and this one could
just be in the mix to
make this other molecule neutral
now, and this could go
in either direction.
This part right here could
go in either direction.
This guy's not so weak or it's
not a bad base, so this guy
could give an electron to this
hydrogen proton, and then the
hydrogen proton's electron, or
that hydrogen atom's electron,
can be taken back by this
nitrogen to make it neutral.
And I'll make this go
in both directions.
So this could go in
both directions.
So then this molecule over here
will look like one, two,
three, four carbonyl group.
And let me color code it the
same way just so we know what
parts are which parts.
We have this green bond to this
nitrogen, which has now
lost a proton.
It was able to take
back an electron,
so it is now neutral.
It is bonded to one,
two methyl groups.
This dimethylamine
took a hydrogen.
So let me draw it over here.
So it's nitrogen one, two, and
then it already had one
hydrogen and now it's gaining
another hydrogen.
It's gaining this hydrogen
right over here.
So now it's bound to
that hydrogen.
It gave an electron to get that
hydrogen nucleus so it
now has a positive charge.
And, of course, we can't forget
about that chloride
anion that's floating around.
And these might be attracted
to each other.
One's positive, one's negative,
form a salt.
So what are we left with?
And then once again, this
is a little bit
of practice of naming.
We started with an acyl chloride
and we ended with an
amide because we now have this
nitrogen group attached.
So what is this?
This has one, two, three, four
carbons so it's butan-, but
it's an amide.
So this part tells us that we're
dealing with an amide.
It's butanamide, but to specify
what type of amide, we
see that we have two methyl
groups attached to the
nitrogen there, so we would call
this-- let me put another
color here.
We have one, two methyl groups
attached to the nitrogen, so
we would call this N comma
N-dimethylbutanamide.
This N comma N let's us know
that the methyl groups are
attached here as opposed to on
the butyl group, I guess we
could view it this way.
So we end up with
N,N-dimethylbutanamide, which
is an amide, one of the most
stable carboxylic acid
derivatives.
And then this right here,
this salt, what is this?
This right here is dimethyl,
and this is now no longer
dimethylamine.
We now are a positively charged
cation, so this is
dimethylammonium.
We get that from the fact
that we have four bonds.
We have a positive charge.
This dimethylammonium, and then
we have this negative
anion, dimethylammonium
chloride.
I'll just go to the next line.
Dimethylammonium chloride.
But I really just wanted to show
you a mechanism here of
how you could go from a less
stable or one of the least
stable carboxylic acid
derivatives to one of the most
stable, going from an acyl
chloride, which butanoyl
chloride was, to an amide.