Organic Lab 2
February 14, 2009
Experiment 4: Borohydride Reduction of 2-Methylcyclohexanone Introduction:
When learning about reduction reactions, we know that the addition of nucleophilic hydride anion (H-) to the carbonyl group will in turn result in the reduction of aldehydes to primary alcohols. Borohydride, and Lithuim aluminum hydride are commonly used as reducing agents. We can note that both of these reagents have a (H-) anion, hence it will be a powerful base and also take the role of being the nucleophile. For the experiment sodium borohydride was used since its properties make it easier to be handled. In this experiment both the trans and the cis isomers of the 2-methylcyclohexanone were to be formed. This is due to the chiralty of the compound itself. The product will either be thermodynamically controlled or controlled by the kinetics itself. IR spectroscopy can then be used to determine the conversion of the ketone to alcohols in the experiment. This procedure is very frequently used in the laboratory setting to obtain as accurate of a result as possible. Experimental:
-Weight of cis and trans-2-methylcyclohexanol= 34.39 g
-Weight of empty flask used= 33.3 g
Synthesis of 2-methylcyclohexanol (mechanism):
-Percentage yield of cis and trans-2-methylcyclohexanol=
*We observed an OH peak at 3350. No carbonyl peak.
Rf (methanol with 2-methylcyclohexane) = 2.5cm/4cm= .62cm
Rf (mixture) = 1.8cm/3.1cm= .58cm
Discussion and conclusion:
Our experiment was successful since we managed to get an extra gram of product and hence got rid of the double bond (carbonyl peak) when observing the 1HNMR spectrum. We had a clear formation of alcohol after observing our data; hence our experiment was a success. There was no side reactions observed within our experimental calculations. It was very evident that borohydride did in fact reduce our initial mixture to an alcohol (2-methylcyclohexanol). In the beginning of the experiment...
References: 1. Wade Jr., L.G. Organic Chemistry. 6th Edition. New Jersey: Pearson Prentice Hall, 2006.
2. Weldegirma, Solomon. Experimental Organic Chemistry. Ohio: Cengage Learning, 2008
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