Problem in Diastereoselectivity

Purpose The spirit of this experiment is to determine the stereo chemic break throughcome of a reaction. A second chiral center is existence formed in this experiment and deuce diastereomeric compounds are created. Table of Reagents Safety Precautions or Hazards Do non place pipettes in paper trash. Must be impel away in the broken wish-wash container Take caution when adding HCl. CO2 maturation whitethorn be vigorous so be sure to vent displace. never directly heat ethanol everyplace hot plate, use water bath. Conc. H2SO4 is passing corrosive Equations for all Reactions Mechanism(s)Experimental originate Part A 1. Add a magnetic resurrect bar, 2g of benzoin, and 20 ml of absolute ethanol in a 125ml Erlenmeyer flaskful. 2. While citering, (do not turn on the heater) here and nowly add 0. 4 g (10. 6 mmol) of sodium borohydride portion-wise to the medley over 5 legal proceeding. After the step-up is complete, stir the mixture for another 15 minutes at room tempera ture. A tweed precipitate result form. 3. Cool the flask in an ice-water bath and decompose the unornamented sodium borohydride by first adding 30 mL of water followed by the careful and dropwise addendum of 2 mL of 3M HCl.The HCl addition should be done quite slowly, no more than ab tabu 3 drops per minute (whitethornbe 10-15 minutes total time). The mixture may foam uncontrollably if the savage is added in addition quickly. If the foam reaches the 100 mL chink on the flask, stop adding HCl until the foaming subsides. 4. When the HCl addition is complete, add another 10 mL of water and stir the mixture for 15 minutes. 5. Collect the white precipitate by suction filtration. Wash the product glycol with water on the suction displace (about 150 mL) and allow the product to form prohibitionist on a pick up paper. Safely store the product in your drawer until next week. . The filtrate should be located in the aqueous acerb exorbitance container. It contains water, B(OH) 3, HCl, and ethanol. 7. Then, record the mp when the stress is completely run dry out (mp 136-137 ? C). Discard filtrate in the organic waste container. 8. shew the IR spectrum and compare it to the spectrum of the starting benzoin, noting the absence seizure of the carbonyl-stretching band. Your product should be completely dry before going on next week to the next reaction. Part B 1. Dissolve 1 g (4. 67 mmol) of the diol in 15 mL of anhydrous reagent grade propanone in a 50 mL rhythm method bottomed flask fitted with a stir bar. . Add 2 mL of acetone dimethyl acetal (2,2-dimethoxypropane). Immediately conversation quid the flask and assuredness it in an ice bath. 3. Remove the stopper and add 12 drops of concentrated sulfuric acid. (Caution conc. H2SO4 is highly corrosive). 4. Carefully replace the stopper and continue to stir the cooled flask for 20 minutes. 5. Then, transfer the cold reaction mixture to a separatory displace. Rinse the reaction flask with two 25 mL por tions of diethyl ethyl ether and add the rinses to the separatory funnel. Carefully add 30 mL of Na2CO3 solution to the separatory funnel.Swirl the funnel piano before inserting its stopper. (Caution CO2 evolution may be vigorous. ) Insert the stopper and at a time invert the funnel and vent it by opening the stopcock. With the stopcock open, swirl the funnel again to complete the neutralization of the acid and evolution of CO2. Close the stopcock. Position the funnel upright and remove the stopper. 6. Drain glum the lower aqueous layer and straighten up the remaining organic layer with two-30 mL portions of water and then one 30 mL portion of saturated sodium chloride solution. 7.Transfer the organic layer to an Erlenmeyer flask and dry the solution over Na2SO4. DECANT the dry solution into a round-bottomed flask and evaporate the solvent on a rotary evaporator (rotovap). Your TA will explicate to you how the rotovap works. 8. The aqueous layer should be placed in the aqueous basic waste container. 9. Scrape your crystalline product out of the round-bottomed flask. Dry. If your crystals are sticky, your TA will assist you by washing with cold pentane. Record the mp and IR of your product. Be sure to calculate a cede for steps 1 and 2 and an overall mother.Results and Observations I noticed that it was very tall(prenominal) to get the solid substance out of the erlinmeyer flask without rinsing several times. I do not believe this gave me brachydactylous results or is a cause for reorient yield. In part A I got a run record of 122*C and collected 1. 427g of product. In part B I got . 4857g of product. My melt point was 49*C and there was no IR taken because the machine was down. Product information The product in part A is officially called erythro-1,2-diphenyl-1,2-ethanediol. It has a melting point of 136*C. It has the chemical formula of C14H14O2 and molecular sens of 214. 64 g/mol. The product in part be is officially called meso-2,2-dimeth yl-4,5-diphenyl-1,3-dioxolane. The melting point for this is 57*C and has a molecular weight of 254. 329 g/mol. Its chemical formula is C17H18O2 . Discussion of Results My yield was courteous but because of the lower than normal melting points Ive determined that my product is not as pure as Id like it to be. Also, I am without an IR spectrum of my product in part B so I cannot canvas my own chemicals stereochemistry. Percent yield and mp MP part A 122*C MP part B 49*C % yield A % yield B % yield Overall