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Amide Formation from Acyl Chloride
相關課程
- 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.
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