Lab 8 CHEM233

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University of Illinois, Chicago *

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233

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Chemistry

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Apr 3, 2024

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Introduction: The goal of this experiment is to successfully reduce 9-fluorenone to 9-fluorenol through the process of reduction utilizing sodium borohydride and methanol as reducing agents. The product was purified using recrystallization and the melting point was measured. Thin layer chromatography was used during the experiment to monitor the process of the experiment in order to recognize when the reaction was complete. Lastly, the Lucas test was conducted on the products in order to verify the formation of an alcohol and compare the product with other alcohol samples. The measured melting point, the IR and NMR spectroscopy data, and the results of the Lucas test were analyzed and used to characterize the molecular structure of the product. Percent yield of the product is calculated, as well as the Rf value from the TLC process. Figure 1: Illustrates the reduction of 9-fluorenone to 9-fluorenol The reaction illustrated in Figure 1 is considered a Redox reaction, or a reduction and oxidation reaction. This means that the reaction will involve the transfer of a hydride ion to the electrophilic carbonyl atom. Within Redox reactions, a reducing agent is necessary in order to provide a source of hydride ion to catalyze the reaction. There are 3 different reduction agents used in redox reactions: Molecular Hydrogen, Lithium Aluminum Hydride, and Sodium Borohydride. In this experiment, we used sodium borohydride as a reducing agent because of the fact that is is more selective than both H2 and LAH, as well as being less potent, along with the ability for NaBH4 to reduce ketones, present in our starting product, fluorenol. The reduction of a molecule involves the swapping of a carbon bound to a more electronegative atom with a carbone bound to a less electronegative atom. With reduction reactions, the electron density around the carbon atom increases. On the other hand, oxidation reactions involve the swapping of a carbon bound to a less electronegative atom with a carbon bound to a more electronegative atom. With oxidation reactions, the electron density around the carbon atom decreases. In order to determine which of these states a particular reaction may be in, one must first identify the oxidation state of the carbon. The oxidation state is a way of counting electrons in order to understand what the charge on an atom might be if all bonds were to be ionic. In simple terms, if the oxidation state of carbon increases during the reaction, that means that the reaction is an oxidation reaction. Transversely, if the oxidation state of the carbon decreases, that means that the reaction is a reduction reaction. To figure out whether the oxidation state of a carbon is increasing or decreasing, you must follow this guide: every bond carbon creates to a more electronegative atom, you will add 1, every bond carbon creates to a less electronegative atom, you will subtract 1, and for every bond carbon creates with another carbon, you will add 0. In

this case, the oxidation state of our carbon within the reaction from 9-fluorenone to 9-fluorenol (Figure 1) is in reduction since the conds changed from +2 to 0. The use of thin layer chromatography helps oversee the progress of the reaction in order to recognize when the reaction has reached success. As usual for TLC, a solvent was prepared for the process, as well as a slide. The slide was then eluted to monitor the reactions progress. Below, an illustration (Figure 2) shows the difference between a slide showing the competition of the reaction versus a slide that exhibits an incomplete reaction. When the reaction is complete, the 9-fluorenone within the reaction mixture will disappear from the slides. Rf values were then recorded and analyzed. The spots cannot be visualized by the human eye, and must be seen under UV light. Figure 2: illustrates the difference between a complete and incomplete TLC slide, with a completed slide missing the Rxn spot . The Lucas tests allowed us to distinguish the product as a secondary alcohol amongst primary and tertiary alcohol samples, as well as allowed us to recognize alcohol functional groups present within the obtained sample we were testing. This test incorporates the addition of the Lucas Reagent (ZnCl2) to an alcohol sample in order to observe the reaction that follows. The fact reaction from clear to cloudy solution indicates the presence of a tertiary alcohol. The slow reaction from a clear to a cloudy solution indicates the presence of a secondary alcohol. Lastly, no reaction at all indicates the presence of a primary alcohol. Figure 3: illustrates the reactions of the Lucas test and what each reaction means.

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