Styrene, the simplest alkenylbenzene, is prepared commercially for use in plastics manufacture b

Styrene, the simplest alkenylbenzene, is prepared...

Key Concepts

Electrophilic Aromatic Substitution

This concept involves the aromatic ring of benzene reacting with an electrophile to replace one of its hydrogen atoms. Understanding this reaction mechanism is crucial because it explains how benzene can be transformed into substituted aromatic compounds—a foundational process in organic synthesis.

Friedel-Crafts Alkylation

Friedel-Crafts alkylation is a method to introduce an alkyl group into an aromatic ring by reacting benzene with an alkyl halide in the presence of a Lewis acid catalyst. This reaction is important in building the carbon framework of complex aromatic compounds, and in this context, it can be used to convert benzene into alkylbenzene derivatives.

Dehydrogenation Reaction

Dehydrogenation is the process of removing hydrogen atoms from a molecule, typically to form a more unsaturated compound. This reaction is key in converting an alkylbenzene, such as ethylbenzene, into an alkenylbenzene like styrene. Understanding dehydrogenation mechanisms is essential for designing synthetic pathways that require forming carbon–carbon double bonds in organic molecules.

Transcript

00:01 Okay, so using what we know from this chapter, we have to find a way to make styrene, which is allel benzene.

00:10 Right.

00:12 So what's interesting about these problems is that you don't necessarily have to have the, in some of these reactions, you're going to have a mixture of products.

00:23 And i'll say that, i'll show you what i mean as i'm doing this problem.

00:28 So you start with benzene and the only substituent that we're going to add is some alcohol group right so we haven't learned a way to directly add some kind of unsaturated alcohol group onto a chain a benzene ring directly so chances are we're going to have to add a regular alcohol chain or maybe even an aesel chain and then find some way to get those double bonds on there so the first thing i'm going to do is i'm going to add an ethel group so we could just directly add two carbons, right, by friedelcraft's acillation.

01:09 Make sure you have your reagents properly, right? so you need aluminum chloride.

01:12 So that's going to give us ethylbenzine.

01:16 But that's irritating because you also learned that these have a tendency to die substitute, right? so you know that you're going to get some degree of para -ephylbenzyne.

01:28 Right so just assume you can purify that away right so after that we have to find a way to pluck off some of those get rid of some of the hydrogens on that alcohol chain so we just learned about radical bromination something that you had already learned about when you were studying the alyl reactions with aline and owl chains right so you know that you could use nbs and nbromostis and nbromo cinnamon in the presence of benzoyal peroxide, which you can write or you can draw it.

02:09 It's an organic peroxide that looks like this.

02:16 And that's going to give you a bromine in the benzol position.

02:20 So now we have a benzene on here.

02:23 A bromine, sorry, it's going to give you bromine in the benzol position.

02:27 And then the final step is elimination, right? so in this case, we don't have to worry about some kind of, some kind of zyte -sev rule forming the most stable alkyne.

02:44 There's only one way we can push the electrons, and that's by deprotonating the h -adam there, and then kicking off the bromine and some kind of an e2 mechanism...

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