OCHEM Sodium Borohydride Reduction 9

OCHEM Sodium Borohydride Reduction 9 - Sodium Borohydride...

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Sodium Borohydride Reduction: The Conversion of Benzophenone to Diphenylmethanol Lindy Hilpert Brad Hutnick Organic Chemistry 330 November 14, 2007
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Introduction : This experiment was done to convert benzophenone to diphenylmethanol using sodium borohydride as a reducing agent and then characterize the product through melting point and IR spectroscopy. Theory, Reactions, and Mechanisms: Reduction is the reaction in which there is a gain of electrons, and the oxidation number decreases. This can be achieved though the loss of oxygen across a bond, the addition of a hydrogen to a bond, or the replacement of a more electronegative atom with a carbon or hydrogen. Some reducing agents include catalytic hydrogen (H2/Pt) and hydride transfer reagents (NaBH4, LiAlH4). Catalytic hydrogen must be used at high temperature and pressure. It is not selective; it will interact with any pi-bond. NaBH4 on the other hand, is selective. It reacts only with a pi-bond between a carbon and oxygen. This is because it is a polar substance, so it reacts with polar bonds. LiAlH4 is selective for the same reason. It also reacts with a pi-bond between a carbon and oxygen; however, it is stronger than NaBH4. LiAlH4 is a stronger because the bond between aluminum and hydrogen is weak making it easier to break. The bond between the boron and the hydrogen is stronger making it harder to break. Both lithium aluminum hydride and sodium borohydride produce four moles of hydride per mole. They also both reduce aldehydes to primary alcohols and ketones to secondary alcohols. LiAlH4, however, can also reduce carboxylic acid to primary alcohols, esters, and amides. A dry reflux apparatus was used to heat the solution without gaining any water from the atmosphere. Reflux is the cycle of a liquid going through vaporization and condensation. There are many benefits to using a reflux apparatus. Molecules dissolve faster in heated liquids because the molecules are moving faster and thus collide harder and more often. Second, the heat needed to cause the solution to reflux is energy that can assist molecules in acquiring enough energy to overcome the activation energy barrier. The liquid in the flask boiling, vaporizes, then hits the cool condenser and condenses back into the flask. A dry reflux is one that uses a drying tube. The drying tube contains CaCl2 which absorbs any water that enters the reflux system from the atmosphere. Extraction is a way of separating two insoluble compounds through their differences in polarity. In this experiment, chemical extraction was needed which involves chemically changing the polarity of one of the substances. The two insoluble substances are mixed together. When the solution settles, two layers form, one contains the polar molecules, and one contains the non-polar molecules. They do not combine however, because polar substances cannot dissolve non-polar substances. One of the layers can then be drained off, separating the polar and non-polar components. Washing
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OCHEM Sodium Borohydride Reduction 9 - Sodium Borohydride...

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