Benzene and alkyl-substituted benzenes can be hydroxylated by reaction with H2 O2 in the presenc

Benzene and alkyl-substituted benzenes can be hydroxylated...

Key Concepts

Reactive Electrophile Structure

The reactive species in this type of hydroxylation reaction is typically a protonated form of the oxidant, such as protonated hydrogen peroxide. This protonated intermediate, often represented as HOOH2+, is highly electrophilic due to the positive charge, making it capable of attacking the electron-rich aromatic ring. Understanding the structure of this electrophile is crucial in mapping out the reaction mechanism.

Reaction Mechanism Steps

The overall transformation involves several clearly defined steps: first, acid protonates hydrogen peroxide to generate the electrophilic intermediate; second, the electrophile attacks the aromatic ring, forming a non-aromatic sigma-complex (arenium ion); finally, deprotonation occurs to restore the aromaticity of the ring. Each step is critical in ensuring the successful incorporation of a hydroxyl group onto the aromatic system.

Electrophilic Aromatic Substitution

This is a fundamental reaction mechanism in aromatic chemistry where an electrophile reacts with an aromatic ring to form a sigma-complex (arenium ion) intermediate. The process is followed by the loss of a proton to restore aromaticity. It is a common route for introducing substituents into aromatic systems and involves the balance between electrophilic strength and the stabilization of the intermediate species.

Acid-Catalyzed Electrophile Generation

In many reactions, an acid acts as a catalyst to activate a reagent, converting it into a more potent electrophile. The acid protonates the incoming reagent, increasing its electrophilicity, which is necessary for the subsequent attack on the aromatic ring. Protonation lowers the energy barrier for formation of the reactive electrophilic intermediate and is a key step in catalysis.

Transcript

00:01 All right.

00:01 This is actually one of my favorite questions in this chapter.

00:07 So you're essentially learning a new form of oxidation chemistry with benzene.

00:12 We're able to add a hydroxyl group to benzene in the presence of hydrogen peroxide and a strong acid.

00:18 So i want to give you an idea of how strong this acid actually is.

00:22 So this is triflic acid.

00:25 We call this triflic acid.

00:30 So it has a trifloromethyl group on a sulfonic acid group.

00:38 So you note sulfonic acid, if this was an oh, this would be sulfonic acid.

00:44 Forget that.

00:45 That's sulfonic acid.

00:47 That has a pca around.

00:49 I forget if it's negative two.

00:51 It's close to zero, right? it's a strong acid.

00:58 Anyway, it's a strong bronze -ded acid.

01:01 This is what triphylac acid looks like.

01:07 So you have an electron withdrawing group in the cf3 that is forcing electron density away from this proton, which makes this proton so much more partially positive than it is in sulfuric acid.

01:21 So if i can give you an idea on how acidic this is, this has a pca of estimated to be negative 15.

01:30 So we call this a super acid.

01:32 Super acid meaning it's probably going to protonate a majority it's going to react to the majority of organic compounds in some way it's so it's such a strong acid it's going to protonate it's going to cause addition chemistry so what is it going to do here um i just realized i can scroll on this document they changed this thing up here recently like the actual, like the stuff that i touch to do stuff to my thing.

02:07 I didn't realize i can scroll.

02:09 That's genius.

02:10 Anyway, sorry.

02:12 So, right.

02:14 So when you have an acid catalyst, what are you going to protonate? right.

02:18 So this probably is even strong enough to protonate benzene and form a carbocadion if you wanted to.

02:32 But in order to do that, you know how low energy? it would be, you know, how much energy you would need to break aromaticity.

02:41 This is probably possible...