The Aldol Condensation Reaction.docx

Preparation of Benzalacetophenones
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  TITLE The Aldol Condensation Reaction: Preparation of Benzalacetophenones (Chalcones) INTRODUCTION An aldol condensation is an organic reaction in which an enol or an enolate ion reacts with a carbonyl compound to form a β - hydroxyaldehyde or β -hydroxyketone, followed by a dehydration to give a conjugated enone. Benzaldehyde reacts with a ketone in the presence of base to give α,β -unsaturated ketones. This reaction is an example of a crossed aldol condensation where the intermediate dehydrates to produce the resonance-stabilized unsaturated ketone. As illustrated for the reaction of benzaldehyde with a general ketone, the ketone looses a proton from an α -carbon to form an enolate ion, which attacks the carbonyl carbon of the aldehyde to yield, after protonation, a β -hydroxy ketone. This intermediate is, for aromatic aldehydes at least, instable and undergoes base-catalyzed dehydration to yield the unsaturated product. OBJECTIVE:    To synthesis benzalacetophenones (chalcones) by aldol condensation reaction.    To determine the percentage yield of the crude product.    To identify the melting point of the purified product.    To characterize benzalacetophenones (chalcones) from the H1 NMR spectrum PROCEDURE 1.   0.75g of 3-nitrobenzaldehyde was weigh and was placed in 50ml Erlenmayer flask 2.   0.60ml of acetophenone and 4.0ml of 95% ethanol was added to the flask containing the aldehyde 3.   The flask was swirled to mix the reagent and any solids was dissolved. The solution was cooled at room temperature. 4.   0.5 ml of NaOH solution was added. The mixture was stirred until it solidified. 5.   10ml of ice water was added to the flask. 6.   The mixture was transferred to a beaker with 15ml of water. 7.   The solid was collected by vacuum filtration on a bunchner funnel. The solid was washed with cold water and was allowed it to dry for 30 minutes. 8.   The solid was weighed and the crude percent yield was determined. 9.   0.5 g of solid from 20ml of hot methanol was recrystallized. The solid was collected by vacuum filtration and was dry it in the oven. 10.   The dry pure product was weight and the percent yield was determined 11.   The melting point was measured and a proton NMR spectrum of the product obtained.   RESULT Mass of 3-nitrobenzaldehyde Mass of crude product Melting point CALCULATION Mass of 3-nitrobenzaldehyde = 0.7489g No. mol of 3-nitrobenzaldehyde = Mass of 3-nitrobenzaldehyde MW = 0.7489 g 151.12 g/mol = 0.005 mol H O H H O │   ║   │   │   ║  - C = O + CH3- C - - C = C  –  C - + H2O NO NO 3-nitrobenzaldehyde 3-nitrochalcone From the above reaction equation, 1 mol 3- nitrobenzaldehyde ≡ 1 mol 3 -nitrochalcone Therefore, no.mol of 3-nitrochalcone is 0.005 mol. Mass of 3-nitrochalcone (theoretical) = No.mol of 3-nitrochalcone x MW = 0.005 mol x 253.26 g/mol = 1.2663 g (theoretical)  Mass of 3-nitrochalcone (actual) = 0.5104 g Percentage yield = Actual yield x 100% Theoretical yield = 0.5104 x 100% 1.2663 = 40.31% Percentage error = Theoretical yield  –  Actual yield x 100% Theoretical yield = 1.2663  –  0.5104 x 100% 1.2663 = 59.69 % DISCUSSION CONCLUSION REFFERENCE ã  T.W. Graham Solomons & Craig B. Fry Organic Chemistry, 9th Edition (2007) ã  Donald L. Pavia, Gary M. Lampman, George S. Kriz, & Randall G. Enge Introduction of Organic Laboratory Techniques, 2nd Edition (2005) ã ã ã
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