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lab 10 - Sodium Borohydride Reduction of 9-Fluorenone/IR...

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Sodium Borohydride Reduction of 9-Fluorenone/IR Analysis of Product Mayank Kumar April 27, 2007 Methods and Background The purpose of the experiment was to reduce 9-fluorenone, a ketone, to 9-fluorenol, an alcohol, using sodium borohydride and identify the product by means of melting point determination and infrared spectroscopy analysis. Reduction is a basic type of chemical reaction that can be defined as the gain of electrons, loss of bonds to oxygen, gain of bonds to hydrogen, or decrease in oxidation number. Organic functional groups containing double bonds undergo reduction by the net addition of the elements of one molecule of hydrogen across the π-bond, causing unsaturated compounds to become saturated. Metal hydride reducing agents cause reduction reactions and they have different reactivities toward specific functional groups. For instance, lithium aluminum hydride is a very reactive, and thus unselective, hydride donor that rapidly reduces aldehydes, ketones, carboxylic acids, esters, and amides (even though the latter carbonyl compounds, especially amides, are not particularly reactive due to resonance), while sodium borohydride is less reactive, and thus more selective, reducing only aldehydes and ketones into primary and secondary alcohols, respectively. Sodium borohydride may be used in alcoholic and aqueous solutions because it reacts much more rapidly with the carbonyl group than with the solvent, while lithium aluminum hydride reacts rapidly with protic solvents, so it must be used in anhydrous ethereal solvents. The experimental reaction involves the transfer of hydride ion from borohydride ion to the electrophilic carbonyl carbon of 9-fluorenone (the carbonyl bond is polarized because of the electronegativity difference between oxygen and carbon, rendering the carbonyl carbon electrophilic) with simultaneous transfer of the electron-deficient boron atom to the carbonyl oxygen. All four of the hydrogen atoms attached to boron may be transferred in this way to produce an intermediate borate salt, which upon addition of water and acid (hydrolysis conditions) decomposes through cleavage of the boron-oxygen bond to yield 9-fluorenol. Thus, 1 mmol of sodium borohydride can reduce 4 mmol of ketone. Filtration is used to separate solids from liquids. A specific type of filtration, vacuum filtration, is used to collect crystalline solids from solvents after recrystallization or precipitation. In this technique, flowing water is used to create a vacuum, which is utilized in filtering liquid from solid through a Büchner funnel.
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Solution recrystallization involves dissolving a solid in an appropriate solvent at a high temperature and allowing the crystals to re-form upon cooling, so that impurities remain in solution. To be successful in this process, there must be a large difference in the solubility of the solute in a hot solvent and its solubility in the same solvent when it is cold.
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