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Kieren Reeves

Synthesis of benzophenone

Cyril Gamage  Follow

Your basic strategy to involve a Friedel-Crafts acylation is correct, but your route is a bit circuitous. You could acylate benzene directly to produce benzaldehyde in one step using carbon monoxide and hydrochloric acid to generate formyl chloride in situ.

enter image description here

While it is "just another" Friedel-Crafts acylation, it has it's own name, the Gatterman-Koch reaction, after its discoverers. Once in hand, you could oxidize benzaldehyde to benzoic acid.

An alternate approach would be to 1) brominate benzene to form bromobenzene, 2) form the Grignard reagent with magnesium and 3) react it with carbon dioxide to produce benzoic acid.

In either case, with benzoic acid in hand, you can procede as you've indicated, on to benzophenone.

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Angel Lacret  Follow

I disagree with Ron on this one. First off, he got the Gatterman reaction wrong. The reaction he showed does not work, since the formyl chloride $\ce{(HC=OCl)}$ breaks down under the conditions required for Friedel–Crafts to occur, giving you $\ce{HCl}$ and $\ce{CO}$.The actual Gatterman reaction would work, since it uses a $\ce{C=N}$ instead of a $\ce{C=O}$ for the reaction.enter image description here

Simply oxidize this compound (benzaldehyde) with something like LiAlH4 (edit: this is a reducing agent, use KMnO4 in aqueous base or Chromic Acid) to get to benzoic acid, then continue with your thionyl chloride and then the second Friedel–Crafts reaction with another benzene.

Ron's second suggestion of using a Grignard to synthesize benzoic acid is also good, just note that you need to add an acid (even just water is a strong enough acid) to remove the Grignard reagent afterwards. Here's an image of the reaction he is referring to, except they used $\ce{HCl}$ to remove the Grignard.

enter image description here

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Eugene Stavitskiy  Follow
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Francois Leyvraz  Follow
The Gattermann-Koch reaction is not the same as the Gattermann reaction, they are two distinct reactions, see the link in my answer for clarification. The G-K reaction was specifically designed to generate formyl chloride More
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Hannah Madden  Follow
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John Crooks  Follow
over the Gatterman is that the latter route involves the use of $\ce{HCN}$. Also, Im not sure what you mean by "oxidize this compound (Benzaldehyde) with something like $\ce{LiAlH4}$." $\ce{LiAlH4}$ is a reducing agent.More
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JJM  Follow
Oh yeah, thanks Ron, I messed that up with LiAlH4, its quite obviously a reducing agent. KMnO4 in aqueous base or Chromic Acid would do the trickMore
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