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I would like to know how to make 1-phenylprop-1-ene ($\ce{C6H5-CH=CH-CH3}$) from propiophenone ($\ce{C6H5-CO-CH2-CH3}$)?

I think carbonyl group ($\ce{C=O}$) of propiophenone is electron-withdrawing group because of Oxygen of carbonyl group. So the carbonyl group of propiophenone will be attacked by nucleophile. And this will be oxidized to make double bonds.

But I don’t know the detail reaction mechanism to make phenylprop-1-ene from propiophenone.
Can anyone help me understand this reaction mechanism?

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  • $\begingroup$ A detailed reaction mechanism is an orthogonal question to a synthetic route. At the very least, you are confused about what kind of answer you need for this problem. (It's probably not a mechanism, though that may be helpful.) $\endgroup$
    – Zhe
    Jul 27, 2019 at 17:32
  • $\begingroup$ Your suggested synthetic rought is not going to happen. Thus, can't suggest a mechanism. Yet, the best way to do this is given in Waylander's answer. I think you should accept that answer because it is best way to do this transformation. $\endgroup$ Jul 28, 2019 at 3:13
  • $\begingroup$ I think I should ask a synthetic route, too as you teach me. I didn't understand the exact meaning of reaction mechanism. $\endgroup$
    – Jan
    Jul 28, 2019 at 15:15

1 Answer 1

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This can be done it 2 simple steps. You are not adding to the carbon count so all you need to do is operate on propiophenone.

Step 1 - reduce the carbonyl group to a secondary alcohol. Sodium borohydride in $\ce{MeOH}$ or $\ce{EtOH}$ will do this in high yield and the workup is straightforward.

Step 2 - dehydrate the secondary alcohol to give the double bond. As it is a benzylic alcohol, protonation of the $\ce{-OH}$ group and formation of the benzylic cation is strongly favoured and will give you the alkene you want. Catalytic para-toluenesulfonic acid in refluxing toluene (with water removal by Dean-Stark apparatus) will do this easily.

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  • $\begingroup$ I can understand it is necessary to make alcohol from carbonyl group with the help of hydride reduction and to make alkene with dehydration reaction. Thank you so much for your great answer! $\endgroup$
    – Jan
    Jul 28, 2019 at 17:42

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