Experiment 5 (Part 1): Aldol

Transcription

1 1 By: Krishnaa Siva Date: November 28, 2012, Thursday 1:30-5:30 PM Lab Group TA: Mathieu Bedard Experiment 5 (Part 1): Aldol 1. Objective: 1 mark What is the purpose of this experiment? The objective of this lab is to produce a product through an aldol condensation reaction between a substituted benzaldehyde and a substituted acetophenone and then identify the product. Use the melting point analysis, IR, NMR and mass spectroscopy to identify the product that was formed. 2. Introduction: 1 marks Brief description of the concept/reaction studied aldol reaction The Aldol Condensation reaction is another useful way to make a carboncarbon bond. This reaction is generally used in organic chemistry to create bigger molecules as it involves two aldehydes or ketones reacting in the presence of a dilute base (McHale, 2007). In the case where two aldehydes are used, a molecule with both an aldehyde and alcohol functional groups and this is where this reaction gets its name. 3. Reaction Equation: 1 marks Include proper structures and data for reactants and products [molar mass, concentration, density, volume, mass, moles, etc including theoretical yield]

2 2 Molar mass (g/mol ) Melting Point ( C) Boilin g Point ( C) Densit y (g cm 3) Volume/ Mass Acetophenone (Unknown D) ml substituted benzaldehyde (4- Chlorobenzaldehyde)= Moles (Unknown 3) g NaOH g Ethanol Chlorochalcone Theoretical: Theoretic al: C C g Crude product: g 5 Experiment al: C C Pure product: 0.64 g Procedure: 1 marks Summary of lab procedure what YOU did, third person, past tense be concise! g (5 mmol) of Unknown 3 was mixed with 0.58 ml (5mmol) of Unknown D and 2 pellets ( g) of NaOH in a mortar and pestle. This mixture was ground for 5 minutes. Next, 10 ml of water was added to the mortar and pestle containing the mixture. After scraping the sides, the suspension was filtered using vacuum filtration. The melting point and weight of the crude product was taken. This crude product was then put in a beaker of hot ethanol (placed on a hot plate) and it was left for some time for the product to dissolve. The beaker was then put in an ice bath in order to get the product recrystallized and the product was vacuum filtrated. The IR and melting point of the pure product was taken. To take the NMR, a small amount of the product was added to the NMR tube along with deuterated chloroform (until half way of the tube). This tube was then placed in the NMR machine. 5. Results: 2 marks a. Table 1: Yield and Physical Properties

3 3 Crude Aldol Product Purified Aldol Product Yield (g) g Yield (%) 120% 53% Appearance Yellow, powdery, crystalized substance Yellow solid/crystals substance (Styrofoam like substance) Melting C C Point Recovery 44% (%) b. Figures: IR and NMR Spectra i. IR Spectrum of aldol product attach and label important stretching frequencies ii. NMR Spectra of aldol product attach and list data for all 1 H s (chemical shift, multiplicity, coupling constant, identity) 6. Discussion: 4 marks a. Discussion of Yield crude, purified, % recovery why less than 100%? The yield of the pure product in this lab was was only 53% due to some experimental errors. When the mixture of the substituted benzaldehyde and substituted acetophenone was transferred much of the product was lost. A lot of the product was stuck onto the mortar (the bowl) and this is where a huge portion of the lose comes from this step. Furthermore, during the filtration steps, some of the crystals went right through the filter paper into the flask and this resulted in the lost of some of the product. If there was more time to perform the experiment, some of that product would have been saved by taking the flask and repouring it over the filter paper. These are two reasons for the low yield. b. Determination Identity of both reactants and product i. Analysis of Melting Point, IR spectrum, NMR spectrum There is a melting point that is unique to each substance. The melting point of the product was experimentally measured to be C C and this is close to the actual melting point of C C. A slightly lower experimental melting point of the product could have been because the product was still somewhat wet or due to the presence of some impurities such as ethanol that was not fully evaporated from the recrystallization step. While taking into consideration some of the possible experimental and human errors, the melting point being very close to the actual melting point is a very good indication that indeed the correct product was formed.

4 4 With just IR Spectrum alone it would be tough to identify what product is exactly formed, but certain characteristics from it does support the fact that it is 4-Chlorochalcone that is formed. The stretch at 1656 cm -1 is indicative of the conjugation found in the molecule along with the C=O bond. The stretch at ~1600 cm -1 is indicative of the C=C alkene stretch. There is no stretch near the and this indicates that there is no O-H group in the molecule. (There are also some stretches such as the cm -1 stretch which indicates the trans-alkene, the 820 cm -1 stretch which indicates a disubstituted aromatic ring, and 687cm -1 stretch which indicates a mono substituted aromatic ring.) The 1H NMR spectrum also gives some valuable information regarding the product that was formed. The stretches from the pm region is indicative of the presence of aromatics. The pair of doublet in the aromatic region indicates that aceteophenone is para-substituted (with the chlorine). There are some stretch possibly resulted from the presence of impurities. The stretch at 2.17 ppm is a singlet and that is not something that is expected since every proton (hydrogen) attached to a carbon is attached to a carbon with atleast one hydrogen (it is possibly from one of the unreacted reactants). c. Mechanism detailed mechanism for the aldol reaction of your reactants

5 5 References McHale, Mary. "Aldol Condensation". Connexions. 4 Oct Web. 27 Nov Mehta, Akhul. " Aldol Condensation Base Catalyzed". PharmaXChange. 6 Jun Web. 27 Nov Solomons, T.W.G. Graham, Fryhle, Craig and Johnson, Robert. Organic Chemistry. 10 th ed. New York: John Wiley & Sons, Print.