How would you prepare the following compounds from benzene? More than one step is required in ea

How would you prepare the following compounds from benzene?...

Key Concepts

Electrophilic Aromatic Substitution

This is a fundamental reaction mechanism in aromatic chemistry where an electrophile replaces one of the hydrogen atoms on a benzene ring. The reaction’s rate and the position at which the new substituent attaches are strongly influenced by the nature of any substituents already present on the ring. Mastery of EAS is essential for planning multistep syntheses from benzene, as it dictates the order of functional group introduction and the regioselectivity of subsequent reactions.

Directing Effects

Substituents already attached to an aromatic ring can activate or deactivate the ring towards further electrophilic attack and direct incoming substituents to ortho, meta, or para positions. Understanding the electron-withdrawing or electron-donating nature of groups like carboxyl, halogen, or alkyl is crucial for achieving the desired substitution pattern in complex syntheses, especially when different positions are required for different target compounds.

Friedel–Crafts Reactions

Friedel–Crafts alkylation and acylation are key methods for attaching carbon chains to aromatic rings. In acylation, a more controlled introduction of a carbonyl group occurs, which can later be manipulated (for example, oxidation) to yield carboxylic acids. However, these reactions also require an understanding of substrate limitations, as strongly deactivating groups can hamper the reaction, thus influencing the order in which reactions must be performed.

Side-Chain Oxidation Reactions

Side-chain oxidation is a process by which an alkyl side chain attached to an aromatic ring is oxidized to a carboxylic acid. This reaction, typically carried out using strong oxidants such as KMnO4, is particularly useful in aromatic synthesis where the only difference between a substituted benzene and a benzoic acid derivative is the oxidation state of a side chain. It allows for the transformation of precursors like toluene derivatives into the corresponding benzoic acids.

Nucleophilic Substitution at Benzylic Positions

The benzylic position, being adjacent to an aromatic ring, has enhanced reactivity in nucleophilic substitution reactions due to the stabilization provided by resonance. This concept is critical in syntheses where a benzyl halide is converted into other functional groups such as cyanides, which can then be hydrolyzed to yield carboxylic acid derivatives. The use of nucleophilic substitution at this position is a common strategy for building carbon chains attached to aromatic cores.

Chloromethylation Reaction

Chloromethylation is a reaction that introduces a CH2Cl group onto an aromatic ring, typically using formaldehyde and a chlorinating agent. This reaction is especially important for synthesizing benzylic compounds, serving as a gateway to further transformations such as nucleophilic substitutions. It is a versatile tool for elongating the carbon skeleton on aromatic rings without disturbing the aromaticity of the benzene core.

Transcript

0:00 Textbook.

00:02 In this problem, we're asked to prepare three compounds starting from benzene, and we are told that more than one step is going to be required in each of these cases.

00:12 So first, we are trying to prepare metaclorobenzioic acid.

00:17 So starting from benzene, there are not a lot of ways to introduce functionality to benzene.

00:26 So the first thing that we're going to do is going to be a friedel -crafts, alcohol.

00:30 Collation.

00:32 And so we will make tallyene by using chloromethane, so ch3cl.

00:43 And then for the fidel crafts, we need aluminum chloride, or aluminum trichloride is the typical strong lowest acid there.

00:55 And so that, as i said, is going to get us to tallyene.

01:05 So we've added a methyl group.

01:07 Now we can oxidize that benzolic carbon using potassium permanganate with some water here.

01:26 And so that is going to get us to benzolic acid.

01:41 And then now we can chlorinate the aromatic ring.

01:47 And that carboxylic acid there is going to direct this to a metaposition.

01:57 So we just do that with chlorine and iron trichloride.

02:13 Okay.

02:14 And so that is our product for part a, metaclorobenzioic acid.

02:22 Okay.

02:23 For part b, we are going to make parabromo benzoic acid.

02:29 And so again, starting from benzene, we need to start by doing a free of craft's alkalation to introduce a methyl group.

02:45 And so that's going to be exactly the same as part a.

03:03 Okay.

03:04 So now we have toluene.

03:07 And this time we are going to do the bromination on the aromatic ring before we oxidize that benzellic position.

03:22 So we'll use bromine and iron tribromine.

03:31 And so this is going to alcalate the aromatic ring at the para position this time...

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