Lab 8 - Gaurav Singh Brooke Leslie/ Gaurav Singh April 8,...

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Gaurav Singh Brooke Leslie/ Gaurav Singh April 8, 2009 Lab Eight : Hydration of a Terminal Alkyne, Preparation of 3-Methyl-3-hydroxy-2- butanone. Introduction and Background Figure 1.1: Synthesis of 3-hydroxy-3-methyl-2-butanone The objective of this lab was to prepare 3-hydroxy-3-methyl-2-butanone by hydration of 2-methyl-3-butyn-2-ol, as is displayed in figure 1.1 above. Then, to ensure the accuracy of the reaction and the purity of the isolated sample the sample was subjected to and I.R. analysis and a semicarbazone was also derived. After such characterization, the final product is then recrystallized. The above synthesis undergoes a hydration reaction to form 3–methyl-3-hydroxy- 2-butanone. This process is regeoselective , which means that the reaction chooses to take place at one site of the functional group over the other sites that undergo the same kind of reaction, as shown in figure 1.2 below.
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Figure 1.2: Mechanishm of synthesis of 3-hydroxy-3-methyl-2-butanone by hydration of 2- methyl-3-butyn-2-ol The melting point of a semicarbazone is useful in order to determine the purity of a compound. Pure solids melt over a narrow range of temperature which is usually 1º C or less. If the isolated sample is impure it will exhibit a broad melting point range as well as a depression of the melting point. Conversely, the boiling point analysis of a liquid sample is far less accurate and relatively less precise than that of the melting point. Nearly all compounds that contain an aldehyde or a ketone functional group can be transformed to their respective semicarazones via a condensation reaction with either aldehyde or ketone, and semicarbazide. 2-methyl-3-butyn-2-ol is an alkyne which undergoes an electrophilic addition to the carbon carbon triple bond. As shown in Fig 1.2 above, it is hypothesized that mercuric ion forms a vinyl cation which is stabilized by formation of a cyclic mercurinium ion. Next, attack occurs at the cyclic ion then most substituted carbon gets attacked in accordance with markovnikov's rule. This is why compound seven in the lab, which is the anti-markovnikov product, does not form because of the way the mercury ion attacks the substituents. Next, a few proton transfers occur in which the mercuric ion is lost which then yields a substituted vinyl alcohol which tautomerizes to yield the carbonyl group of the ketone functional group in the final product.
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This note was uploaded on 04/14/2010 for the course ENGL 104 taught by Professor Osbourne during the Spring '08 term at A.T. Still University.

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Lab 8 - Gaurav Singh Brooke Leslie/ Gaurav Singh April 8,...

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