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 are readily available starting materials and are relatively non-reactive to many substrates. Our synthesis will be acid catalyzed, and will use a mercury salt. We will form the ketone from an enol, which will tautomerize from the double bond into the carbonyl. Here are a couple of generic examples of this chemistry:
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 in 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 the ketone which is our final product.
This reaction is pretty useful, insomuch as alkynes are 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. Here are a couple of more examples of it.
Dr. Michael Pa
Dr. Michael Pa got a bachelors degree in chemistry from Binghamton University, a masters degree in organic chemistry from the University of Arizona and a Ph.D. in organic chemistry from the University of Arizona. His research focus was on novel pain killers which were more potent than morphine but designed to have fewer side effects. There may even be a patent or two that came out of it. Prior to all of this, he was a chemist at Procter and Gamble. After all of that, he (briefly) worked as a post-doctoral assistant at Syracuse University, working on novel organic light-emitting diodes (OLEDs). In between, he did NOT compete at the 1996 Olympics, make the Atlanta Braves opening day roster, or become the head coach of the Indiana Pacers, as he had intended. #fail During this entire time, he always loved helping students, especially if they were struggling with organic chemistry. In 2006, Dr. Pa founded AceOrganicChem.com in order to make learning organic chemistry fast and easy. 14 years and about 60,000 students later we are still helping students to learn organic chemistry one reaction at a time at https://www.aceorganicchem.com
