Continuing now to discuss how you can make a ketone, we will look at the synthesis of ketones from alkynes. The hydration of an alkyne is an easy way to form the ketone that we want. Alkynes\u00a0are readily available starting materials and are relatively non-reactive to\u00a0many substrates. Our synthesis will be acid catalyzed, and will use a mercury salt. We will form the ketone from an enol, which will tautomerize\u00a0from the double bond into the carbonyl. Here are a couple of generic examples of this chemistry:<\/p>\n
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The mechanism of the reaction is shown below. The first step is addition of a proton to the triple bond. The proton adds on the less substituted side\u00a0in a Markovnikov fashion (BTW, Markovikov was a crap chemist who has a crummy rule….my rant, or should i say rationale, on that can be found at Markovnikov is a fat liar). This forms a carbocation at the more substituted end, which is then attacked by water. After a couple of proton transfers, we now see an enol. This tautomerizes to give\u00a0the ketone which is \u00a0our final product.<\/p>\n
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This reaction is pretty useful, insomuch as alkynes\u00a0are relatively easy to form or obtain. We think this is a good reaction for you to stick in your toolbox for a time when you might need it. \u00a0Here are a couple of more examples of it.