BaseCatalyzedOxidation-ReductionofAldehydesbytheCannizzaroReaction

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Base-Catalyzed Oxidation-Reduction of Aldehydes by the Cannizzaro Reaction Prepared by Mike Tran THEORY The purpose of this experiment is to oxidize and reduce an aromatic aldehyde, 4-chlorobenzaldehyde, and isolated to form benzoic acid and benzyl alcohol. MAIN REACTION(S) AND MECHANISMS The Cannizzaro reaction consists of an oxidation-reduction reaction between a hydroxide ion and aldehydes without α-hydrogen atoms. With the presence of a strong base, the first aldehyde molecule reduces to a
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  Base-Catalyzed Oxidation-Reductionof Aldehydes by the CannizzaroReaction Prepared by Mike Tran THEORY   The purpose of this experiment is to oxidize and reduce an aromaticaldehyde, 4-chlorobenzaldehyde, and isolated to form benzoic acid andbenzyl alcohol. MAIN REACTION(S) AND MECHANISMS  The Cannizzaro reaction consists of an oxidation-reduction reactionbetween a hydroxide ion and aldehydes without α-hydrogen atoms.With the presence of a strong base, the first aldehyde moleculereduces to a second aldehyde molecule and then becomes a primaryalcohol. Within this process the molecule oxidizes itself to thecarboxylate anion and will result in a carboxylic acid and an alcohol.  PROCESS  The course of this experiment was broken up into multiple scenarios:setting up and preparing the reagents for the reaction, the reactionitself, and then the isolation and purification process of the products. To prepare the reagents, potassium hydroxide (5.0 g) was dissolved indistilled water (5 mL) inside an Erlenmeyer flask. 4-chlorobenzaldehyde (1.0 g) and methanol (2.5 mL) was added to to a25 mL round bottom flask with a stir bar and set to dissolve as well. An  apparatus was also set up for heating under reflux and simpledistillation. Then, potassium hydroxide (50% aqueous, 1.5 mL) wasadded to the round bottom flask reaction vessel and set to heat underreflux so that none of the reactants were able to escape during theexperiment.A water bath was prepared so that temperature was more easilyregulated rather than using sand. This temperature was set to 75degrees C and the reaction vessel underwent the heating process for1.5 hours with automatic stirring from the magnetic stir bar. Once theheating under reflux stage was complete, the solution was transferredto a separatory funnel for separation of the two products. Althoughboth solutions were transparent, it was easy to distinguish that thereaction formed two layers of compounds. The lower layer was theorganic layer and the upper was the aqueous layer. Each layer wasthen extracted to separate beakers as the Cannizzaro reaction was notcomplete. The carboxylic acid was in the aqueous layer and thealcohol was in the methylene chloride (organic) layer. To recover the p-chlorobenzyl alcohol, the methylene chloride layerwas wash it with two portions saturated aqueous sodium chloride (2x5mL) as this will neutralize the solution of residual acid. Once the layerhas been extracted, it was dried with several spatula tips of anhydroussodium sulfate until the solution turned clear. The solution underwentsimple distillation to remove the dichloromethane, resulting in 4-chlorobenzyl alcohol leftover. To recover the p-chlorobenzoic acid, it was cooled by placement insidean ice-water bath and acidified by adding concentrated hydrochloricacid (2.5 mL) until it was acidic (approximately pH = 3). It was thenfiltrated with a Hirsh funnel and allowed for collection of the whiteprecipitate product, p-chlorobenzoic acid. This was set out to dry priorto gathering the product’s weight and melting point. DATA AND OBSERVATIONS After the chemical components were added to recover the acid and thealcohol layer, I had completely mixed up which was the organic layerand which was the aqueous layer. Hydrochloric acid was added to the  alcohol layer so to make the solution acidic. Litmus paper was usedperiodically to check the acidity of the solution to make sure it wasapproximately at the pH level of 3. The acid layer had 5 mL of anhydrous sodium sulfates and 2.5mL of hydrochloric acid added to itbefore the product was filtrated out of the solution. The product of thealcohol layer was a cloudy white color when extracted and yieldedwhite crystals when weight and melting point were measured. RESULTS  Product Data for Alcohol Layer ProductTheoretical Actual% YieldActualLiteratureYieldYield m.pm.pp-chlorobenzyl alcohol4.03 g1.25 g31%68-6970-72Product Data for Acid Layer ProductTheoretical Actual% YieldActualLiteratureYieldYield m.pm.pp-chlorobenzoic acid0.215 g0.11 g51%166-172149-150 Percent YieldAqueous Layer(0.09g / 0.289g) x 100 = 31% recovered Organic Layer(0.1464g / 0.285g) x 100 = 51% recoveredCONCLUSION  The p-chlorobenzyl alcohol from the alcohol layer was pure within a 1degree C melting point range and a 3.5% error, however only 31% of the product was retrieved. Such a low percent yield could have beencaused by the acid and the other chemicals added to acidify thesolution after mistaking the two different layers. The results foundwith the p-chlorobenzoic acid from the acid layer however did not show  such promising results. The melting point range was 6 degree C, whichindicates that the product was not pure and something went wrong inthe experiment. Again, this and the 51% product retrieved may beexplained by the mix up of the two different layers.
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