Week 10 - Sodium Borohydride Reduction of 9-Fluorenone. IR...

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Sodium Borohydride Reduction of 9-Fluorenone. IR Analysis of Product Mark Gumapas November 29, 2007 Methods and Background The purpose of the lab is to produce a ketone, 9-fluorenone, and reduce it to an alcohol, 9-fluorenol, using sodium borohydride. The identity of the product was then supposed to be verified through the use of an IR spectroscopy and melting point determination experiment. 9-fluorenone 9-fluorenol In this lab, the process of reduction is observed. This process is a basic chemical reaction that can be defined as the gain of electrons. In organic chemistry, however, it does not involve a gain of electrons, but instead an increase in electron density at a carbon atom due to a replacement of bonds to more electronegative atoms, the gain of bonds to hydrogen, or a decrease in oxidation number. Organic functional groups that contain double and triple bonds go through a reduction process when there is a net addition of elements of one or two molecules of hydrogen across the π-bond, thus causing unsaturated compounds to become saturated because they can no longer accept any hydrogen. Reduction are effected by either catalytic or chemical methods. The first method, catalytic hydrogenation, involves the addition of a molecule of hydrogen across a carbon-carbon or carbon double or triple bond in the presence of a metal catalyst. The chemical reduction of many organic functional groups is effected by using a metal hydride as a reducing agent. Metal hydride reducing agents have different reactivities toward distinct functional groups. This is important because of the fact that these reducing agents react selectively with only one type of functional group. For example, lithium aluminum hydride is very reactive and unselective, that reduces aldehydes, ketones, carboxylic acids, esters, and amides. Sodium borohydride, on the other hand, is less reactive and more selective, reducing only aldehydes and ketones to primary and secondary alcohols, respectively. The experiment calls for the reduction a carbonyl group to alcohol by catalytic hydrogenation or with metal hydrides. In this lab, it involves the transfer of a hydride ion from a borohydride ion to the electrophilic carbonyl carbon of 9-fluorenone, while the boron atom transfers to the carbonyl oxygen. When this happens, all 4 hydrogen atoms attached to the boron get transferred along with it to produce the intermediate borate salt. When this undergoes hydrolysis in acidic conditions, it decomposes to form the wanted 9-fluorenol.
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The process used in the formation of the alcohol is that of recrystallization. This is one of the most common methods used to purify solids. With other techniques such as sublimation, extraction, and chromatography; recrystallization can still be applied to purify the solid even more. It involves dissolving the solid in an appropriate solvent at a higher temperature and allowing the crystals to re-form on cooling, so that any impurities
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Week 10 - Sodium Borohydride Reduction of 9-Fluorenone. IR...

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