2Objectives:To synthesize an a,b unsaturated ketone from an aldehyde and a ketone using solvent-free conditions.To purify the product through a recrystallization.To identify and analyze purity through TLC and melting point analysis.To analyze the product using IR spectra.
3Before coming to lab… Review these techniques: Recrystallization TLC AnalysisMelting Point Analysis
4ALDOL CONDENSATIONSAldol condensations are nucleophilic additions of an enolate ion, which are strong nucleophiles, to another C=O group under basic conditions.Protonation gives the aldol product.Once formed, the aldol product undergoes dehydration in base.Abstraction of an a proton gives an enolate that can expel an –OH ion to give a conjugated product.Dehydration is usually exothermic because it leads to a very stable conjugated product.
6MECHANISM Base removes a proton to form enolate ion. Resonance stabilized enolate forms carbanion, which attacks C=O of aldehydeOxygen anion removes proton from water, releasing–OH.When new C-C bond forms, C=O p bond breaks, electrons stay with oxygen.Acidic a proton is removed by –OH. Electrons form new p bond.
7TYPICAL ALDOL CONDENSATION A typical aldol condensation reaction is carried out in an organic solvent, such as ethanol, requiring eventual waste disposal.Isolation of the product requires a much more involved work up, not to mention the hazards to the experimenter and the environment due to waste disposal.Another challenge is that solution phase reaction is reversible, so low product yields may result.
8GREEN CHEMISTRY CONCERNS One of the main themes of greener chemistry is to cut down on the use of solvent, and hence cut down on solvent waste. The best way to do this is simply not to use any solvent at all.Workup is generally easier since as the reaction proceeds, the product separates from the melt as a solid, making work up much less complicated.Another benefit is that unlike a solution phase reaction, the solid-state reaction is irreversible, resulting in higher chemical yields.
9OVERVIEW Synthesize aldol product in test tube. Recrystallize solid in propanol/water to purify.Suction filter to isolate solid.Dry product in oven.Obtain product mass, calculate % yield, do melting point analysis.
10EXPERIMENTAL PROCEDURE (Synthesis) Place aldehyde and ketone in large test tube.Crush solids with glass rod until liquefied.Add NaOH. Mix and scrape sides of test tube until pale green solid forms.Continue to react for 15 minutes at room temperature.
11EXPERIMENTAL PROCEDURE (Purification and Product Isolation) Place test tube in a 90oC water bath.Add 90:10 PROPANOL/WATER and heat until solid dissolves.Suction filter.Transfer solid to PREWEIGHED WATCH GLASS AND PLACE IN OVEN 15 MINUTES to dry.Obtain final product mass and calculate % yield.Proceed to PRODUCT ANALYSIS (TLC, mp, IR).
12Table 22.1 Theoretical yield (g) Determine limiting reagent first, then calculate theoretical yield.HINT: Don’t round too soon!Actual yield (g)% yieldMelting range (oC)Start temperature dial on setting of 5. Back down one tic mark ~ 150oC and watch closely. Record Ti-Tf range.Compare to literature value to determine purity of product.Product AppearanceRecord the physical state and color of product.
13Experimental Atom Economy (%) Table 22.4Atom Economy (%)Calculate based on reactants ONLY!Review Experiment 13 for calculation.Experimental Atom Economy (%)“Eproduct”Cost Per Synthesis ($)Costs of stock bottles of compounds on p. 192.Remember to use reactants and catalyst in this calculation!Cost per Gram ($/g)CPS/actual yield (g)
143,4-dimethoxybenzaldehyde Table 22.2CompoundTLC Rf valuesStandardSample1-indanoneRf values are UNITLESS!Rf values are 2 decimal places ONLY!3,4-dimethoxybenzaldehydeAldol Product
17SAFETY CONCERNSSolid NaOH is very corrosive! Immediately flush skin with water if any gets on your skin!Propanol is very flammable! Use extreme caution during purification!
18WASTE MANAGEMENTPlace all liquid waste in container labeled “LIQUID ORGANIC WASTE”.Place all solid waste in container labeled “SOLID WASTE”.Place all used TLC capillaries and melting point capillaries in broken glass container, NOT TRASHCAN!Leave TLC chambers with lids off in your lab drawer.
19CLEANINGClean all glassware with soap, water, and brush, followed by a rinse with wash acetone before returning to lab drawer.DO NOT return any glassware to lab drawer dirty or wet!
20LABORATORY NOTEBOOK (Pre-lab) OBJECTIVE (Must clearly state…)What compounds will be made and howHow the compounds will be purifiedHow the purity of the product will be determinedCHEMICAL EQUATIONInclude the chemical equation from the top of page 185.TABLE OF PHYSICAL DATA (Complete the following table using a site listed on WWW Links ONLY. Wikipedia is unacceptable!)REFERENCE TO PROCEDURE (Must include…)full title including edition and author namespage numbers where actual procedure can be foundCompoundMW (g/mol)mp(oC)bp(oC)d (g/mL)HAZARDS3,4-dimethoxybenzaldehydeX1-indanoneSodium hydroxide1-propanolDiethyl etherhexane
21LABORATORY NOTEBOOK (In-lab) DATA/CALCULATIONSInitial weights of 1-indanone and 3,4-dimethoxybenzaldehyde usedWeights of filter paper and watch glassWeight of watch glass + filter + productFinal weight of dry productPhysical state and color of productTheoretical yield calculation% yield calculationTLC diagram including all cm measurementsAtom economy calculationExperimental atom economy calculation“Eproduct” calculationCost per synthesis and cost per gram calculationsEXPERIMENTAL PROCEDUREIn paragraph form, BRIEFLY describe the procedure that you actually followed during the lab.Paragraph must be written in PAST TENSE, PASSIVE VOICE.Include any volumes or weights of chemicals used during the experiment.Include any mistakes, accidents or observations if applicable.