In the Gatterman-Koch reaction, a formyl group (-CHO) is introduced directly onto a benzene ring

step 1 Okay, this is an interesting mechanism in this chapter. It's fairly inorganic, actually. It's in

In the Gatterman-Koch reaction, a formyl group (-CHO) is...

Key Concepts

Electrophilic Aromatic Substitution

A fundamental reaction mechanism in aromatic chemistry where an electrophile replaces a hydrogen atom on an aromatic ring. The process typically involves the formation of a non-aromatic sigma complex intermediate, followed by deprotonation to regenerate aromaticity.

Acylium Ion Formation

The generation of an acylium ion (R–C?O?) is a key step in acylation reactions. In the context of the Gatterman-Koch reaction, CO and HCl in the presence of a Lewis acid catalyst combine to form this electrophilic species, which is stabilized by resonance with the oxygen atom.

Friedel-Crafts Acylation

This is a substitution reaction where an acyl group is introduced into an aromatic ring using a Lewis acid catalyst. The mechanism involves the formation of an acylium ion, which reacts with the aromatic ring to yield a ketone product after deprotonation.

Substituent Directing Effects

Substituents already present on an aromatic ring can influence the regioselectivity of further electrophilic substitution reactions by donating or withdrawing electron density. Activating groups typically direct incoming electrophiles to the ortho and para positions, thereby determining the major product distribution in reactions like the Gatterman-Koch process.

Transcript

00:01 Okay, this is an interesting mechanism in this chapter.

00:04 It's fairly inorganic, actually.

00:07 It's interesting that it's in, it's pretty difficult.

00:11 I would say this might be one of the more difficult problems in the chapter, especially if, let's say this was on an exam, if a professor required you to use in your mechanism all of the reagents.

00:23 So for example, at first i didn't necessarily understand the role of the copper, the copper chloride.

00:32 So i don't necessarily know how an organic student would understand how to include that in a mechanism, especially without having taken inorganic chemistry.

00:43 So i'm going to be saying some things that you might not necessarily understand in order to walk through this mechanism.

00:51 And that's okay.

00:51 I hope i'm clear anyway.

00:53 So we're making benzaldehyde at the paraposition from ptoleene.

00:59 So in the presence of carbon monoxide and acid.

01:03 So i think to break it down as simple as possible, right, essentially the way you want to think about this is you know how to do fidelcrafts with like an acid chloride, right? so you could use formal chloride, for example, as a source of carbon.

01:28 All right.

01:29 So as a source of one carbon atom.

01:31 So upon activation with aluminum chloride, you know that you can arrive at a nucleophile that looks like this.

01:40 Sorry, that should be a positive charge.

01:41 And then through resonance, you can push those down to help stabilize you arrive at positive charge and oxygen carbon.

01:50 Right.

01:51 So you've seen this in the chapter.

01:54 So let's try to find a place where we could.

01:58 Get to this electrophile, which will then by the orthoparid directing nature of tullulene will direct that to the paraprovision.

02:08 So i got that far.

02:10 So that's the role of the aluminum chloride.

02:12 Somehow we have to make this electrophile, sorry, that's my eraser.

02:17 We have to make this electrophile from carbon monoxide and hcl.

02:27 Right? so maybe this is the h from hcl.

02:32 And then what's the role of the chloride? well, you know that aluminum chloride needs a chloride to activate the electrophile.

02:44 So then it would leave as alcl4.

02:48 So maybe some of these pieces are starting to come together.

02:50 And if that didn't make sense at first, try listening to it a few times.

02:56 Rewind.

02:56 I'm sure i'm going to talk through it again as i'm going through.

02:59 But that is that is kind of what i had to write out on paper to figure this out.

03:05 So really in that sense, the copper doesn't really play a role in the actual electrophile generation.

03:14 You can't really find a place to fit that in.

03:17 So what i think the copper does and what i verified through i have access to scientific literature, right? so what the copper does is the copper is a co -catalyst that doesn't really, react with aluminum chloride, right? so you would think that maybe the chloride, you would get something like, it's also copper one chloride.

03:37 So the oxidation state is copper one.

03:38 You might get something that looks like this.

03:42 And that might help activate the electrophile.

03:46 Not necessarily.

03:47 So what copper does, so copper one, when copper has an oxidation state of one, as an inorganic chemist, we call this a d10 metal.

03:55 And what that means is copper's de -electrons are completely, completely filled.

04:01 So copper being in the late period three, one of the later transition metals, it's a more electron rich metal, which means that it's going to be, you could think about it as an electron donating group if you want in this case.

04:19 So what copper one is actually going to do is copper is going to form a bond with carbon monoxide.

04:27 Right so you can just take the loan pair from carbon monoxide and you can push it to carbon to copper so that's what it does and what this does is i said you can treat it as an electron donating group what this does is it activates carbon monoxide for protonation from hcl so um the electron density is actually going to flow towards carbon monoxide um so you can think of electron density this is a if you think of this is a partially negative even though it has a formal positive charge, it's a more electron -rich positive charge.

05:03 So you would think of electron density flowing towards the carbon, which would eventually make the carbon more negative in terms of its electron density.

05:14 So that's what the role of copper does.

05:17 So because of that, now what you can do is you can have a plausible mechanism where you can think about if you through resonance you can push this bond.

05:32 Sorry, that should be a positive charge on carbon monoxide.

05:36 Not really, actually.

05:38 Forget that.

05:40 For reasons you don't understand, the oxygen won't be positive.

05:44 But anyway, so you can think about if you want to use one of the pie bonds in the carbon monoxide to take the electrons to attack the proton, you will arrive at c double bond to o, which is still on the copper, still has the h.

06:13 Right? so it may look weird the way that i drew carbon monoxide.

06:21 I actually drew it as the resident structure...

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