Stereochemistry: Addition of Bromine to Trans-Cinnamic Acid

STEREOCHEMISTRY ADDITION OF BROMINE TO trans-CINNAMIC ACID Required Prelab ReadingsMcMurry Chapter 5, Sections 8. 2 & 21. 2 Morhig, Sections 7. 1 and 7. 3. Previous techniques that you must know and be able to perpetrate Suction Filtration and warming Point This experiment is designed to demonstrate 2 concepts. First, it will provide a demonstration of how chemists faeces use chemical replys to understand reaction mechanisms. Second, is the concept of multi- footstep synthesis. You will be performing the followers reaction Isomer IIsomer II + Enantiomer+ EnantiomerBrominetrans-Cinnamic Acid2,3-Dibromo-3-phenylpropanoic sharp MW 160 g/molMW 148 g/molMW 308 g/mol bp 60 Cmp 133-134 Cmp 93-95 Cmp 202-204 C When an electrophile, such as bromine, jibes to an alkene, the access can be d matchless in a syn fashion, in which the devil groups add to the same side of the molecule, or in an anti fashion, in which the groups add to opposite sides of the molecule. Depending on the m ode of assenting, syn or anti, and the stereochemistry of the starting time alkene, variant stereoisomers will topic. In some cases, a racemic mixture of crops is formed, other times a meso compound is produced.Feature Article Free-Radical BrominationThe Fischer projections deputen above are dickens possible stereoisomers that could form in the bromination reaction that you will perform. One is the result of a syn assenting, the other is the result of an anti addition mode. Note that from from each one one would form as a racemic mixture, (+). You are to determine, based on the thawing point of your harvest-time, which pair of enantiomers is produced. By knowing which enantiomeric pair is formed one can guess a plausible mechanism. Hint you can predict the stereochemical outcome of a syn vs. anti addition of bromine to alkenes before you step foot into the laboratory.The simplest example of a multi-step synthesis is to examine virtually each commercial medicine. Al app roximately without exception that medicine was prepared by a series of reactions rather than in a single step. A multi-step synthesis generally requires a chemist to perform a chemical reaction, isolate, cast and characterize the product and then use that product as the starting solid for the next reaction. You will be using the product of this reaction as your starting material next week. It will be all important(predicate) for you to have the product from this week properly identified so you can readyly predict the product of next weeks reaction. The most time-consuming part of this experiment is setting up the glassware. Be sure enough all fittings are tight, well-greased, and clamped so as to prevent any get off of bromine vapors into the laboratory environment. An actual set-up is provided for you in the lab for you to get word at. ? You will request to set up the apparatus as shown in figure 7. 4 a on page 63 of Mohrig. dis curtainYou are responsible for calculating t he fall of trans-cinnamic acid (in grams) equivalent to 4mmol. You must have this done before you enter the lab. HazardsMolecular bromine is super toxic and corrosive its vapors are damaging to the skin marrow and respiratory tract. Wear gloves and UNDER NO CIRCUMSTANCES ARE YOU TO postulate THE BROMINE STOCK SOLUTION FROM THE HOOD. Only remove your bromine response in the stoppered funnel. Sodium thiosulfate reduces Br2 to Br-1. When working with Br2, always keep a bottle of 5% sodium thiosulfate handy for rinsing the skin in case of contact. Experimental ? Assemble a 50 mL bottomed flask with a Claisen head, reflux condenser, and addition funnel. Into the round-bottom flask, add trans-cinnamic acid (4 mmol) and 10 mL of methylene chloride.Add a stir bar. ? Obtain 4. 0 mL of a 1. 0 M solution of bromine in methylene chloride in the addition funnel. Attach a heating mantle and variac and heat the mixture to a gentle reflux. The variac setting should initially be 25-30. Adjust this setting as necessary until the solution is refluxing . ? While it is refluxing, add the bromine solution at a rate of two drops per second. You need not loosen the stopper on the funnel for the bromine addition due to the high density of methylene chloride. The red-orange color in of the bromine should horse around as it reacts with the mixture.Continue to reflux for an additional 10 minutes after the withstand of the bromine has been added. ? The color of your final solution should be a precise pale yellow. If the red-orange color persists after the 10 min, add cyclohexene dropwise (1-2 mL) until the red color disappears. ? Remove the reaction flask and cool it in an ice clean for 10 minutes with a greased stopper on top. reserve the product, 2,3-dibromo-3-phenylpropanoic acid, to crystallize. ? Meanwhile, disassemble the rest of the reflux apparatus and sit it in the stomach of your hood to allow the fumes to dissipate.Rinse the glassware with a small amount of sodium thiosulfate to destroy any remaining bromine. ? Collect the crystalline product by suction-filtration, and rinse with a minimal amount of ice-cold methylene chloride. Allow it to air-dry and record the mass and melting range of the product. cod your instructor check the weight of your product and initial this value in your lab notebook. Save all of your product as it is the starting material for next week. STEREOCHEMISTRY Addition Of Bromine To trans-Cinnamic Acid DATA SHEET hang Section Number Overall Reaction (including stereochemistry, Symyx Draw) plug of acid Theo mmol product mmol of acidTheo mass product Volume of Br2 soln Mass recovered product mmol of Br2 mmol recovered product % yield of product Melting point of recovered product Literature melting point Calculations (notebook) mark Lab Questions 1. What is the stereochemical relationship between Isomer I and Isomer II? 2. Use perspective drawings, Fischer Projections and words, to demonstrate whether syn addition of bromine to trans-cinnamic acid results in Isomer I or Isomer II. Repeat the process for anti addition. NOTE CAREFULLYThe question is astir(predicate) mode of addition (syn vs. anti), not mechanisms do not use curving arrows to explain your answer.3.Based on your results, did the addition occur by a syn or anti mode? Explain your reasoning. 4. Provide the electron-pushing mechanism for this reaction and show how both enantiomers are produced. Use perspective representations to draw structures. Assign the R / S configuration to each stereocenter in the products. 5. Using perspective drawings with the correct stereochemistry, redraw the pair of enantiomers you drew in question 4 and show how each can be redrawn as the Fischer projection of Isomer I, Isomer II, or the enantiomer. Clearly mark off all stereocenters as R or S. 6. Show the products of the following electrophilic addition reactions (symyxdraw)