Bromination of (E)-Stilbene

Bromination of (E)-StilbeneKaisha ButzAbstractThe purpose of this experiment was to synthesize the second intermediate (meso-stilbene di bromide) in the E-Stilbene reaction by Bromination. It was hypothesized that if the reaction was heated at 120C for five minutes the reaction between E-stilbene and the pyridium bromide perbromide would occur, and meso-stilbene would be created. After the reaction occurred the results were analyzed by IR and by an ignition test. The hypothesis was supported by the employed methods.IntroductionThis experiment was performed to show how bromination of alkenes reacts, and to be able to successfully synthesize meso-stilbene dibromide. The reaction of bromine with alkenes is an summation reaction where the nucleophilic double bond attacks the electrophilic bromine (Mayo, et. al, 2013). Bromine only becomes electrophilic because of induction due to its ability to be polarizable (Mayo, et. al, 2013). Induction occurs when there is a transmission of point (Bruice, 2014). Bromine as it approaches the (E)-stilbenes double bond becomes polarized and takes on a slightly positive charge (Mayo, et. al, 2013). This allows it to form a cyclic bond (cyclic bromonium ion) with both(prenominal) sp2, now sp3, carbons. The cyclic bromonium ion takes on a positive charge and by anti-addition the second bromine (negatively charged) attacks from the back of the cyclic compound and bonds to either carbon on the opposite side of the other bromine. This creates a meso-stilbene which is 100% formed. There are no stereoisomers formed (Mayo, et. al, 2013).It was hypothesized that (E)-stilbene, in a solution of glacial acetic acrid reacted with pyridium bromide perbromide heated to 120C and cooled in an ice bath, would result in the formation of meso-stilbene. It was expected that only meso-stilbene dibromide would be formed, and that its formation could be tested by using IR. The Bromination reaction was also tested by an ignition test.Structures/Mechan ismsMaterial and MethodsPlease refer to pgs. 444-449 of Microscale Organic Laboratory with Multistep and Multiscale Synthesis by Mayo, Pike, and Forbes.DeviationsProcedure was done in microscale230mg of (E)-stilbene was used quite of 600mg.2.2ml of glacial acetic unpleasant was used instead of 6ml.A 10ml round-bottom flask was used instead of a 50ml flask.The magnetic spin bar was a baby magnetic spin bar.450mg of pyridium bromide perbromide was used instead of 1.2g.2ml of glacial acetic blistering was used to wash down the perbromide instead of 6ml.4.5 ml of distilled water was used instead of 12ml.Acetone and distilled water were added drop-wise to the crystals instead of three 2ml of distilled water and two 2ml of acetone.ResultsIR spectrographic analysis (E)-Stilbene attached to backIR spectroscopy meso-stilbene attached to backTable 1Table 2Table 3Table 4CalculationsCrystals .2451g .1045g = .1406gLimiting Reagent (E)-Stilbene.230g (E)-Stilbene * (1 mole / 180.25g MW) = 0.0 013 moles.450g Pyridium Bromide Perbromide * (1 mole / 319.83g MW) = 0.0014 molesTheoretical Yield0.0013 moles * 340.05g MW = .4421gPercent Yield(.1406g/.4421g) * 100 = 31.8%DiscussionIt was found that after bromination of (E)-stilbene into meso-stilbene dibromide that the IR spectroscopy of both were relatively similar in the fingerprint region ( 500-1000cm-1). This should be the case. The only difference in the spectroscopy was the lack of the carbon-carbon double bond in the meso-stilbene dibromide. The IR spectroscopy in the lab does not substantiate the ability to measure the wavelength of carbon-bromine bonds because it is not within the range of the machine. Therefore, the two IR spectroscopies of the two substances were really similar because they both contained aromatic rings with similar wave numbers (cm-1) (Table 1, Table 2).It was expected that (E)-stilbene after undergoing bromination in a solution of acetic acid would produce crystals of meso-stilbene. That was the c ase Success Although the part yield was low the experiment did produce meso-stilbene dibromide. This was supported by an ignition test. A part of the product was burned, and the flames were green. verdancy flames were indicative of bromide. Because carbon-bromide bonds were not seen in the IR spectroscopy, the flame test was necessary to show that the (E)-stilbene had, in fact, reacted with the pyridium bromide dibromide and created meso-stilbene dibromide.The percent yield could have been better. nonpareil mistake was that the (E)-stilbene was heated and turn at 85C instead of 120C. The experiment continued regardless, and the pyridium bromide dibromide was also heated and dissolved at 85C. Once the temperature was noted to be too low the solution was placed back into the heat until the temperature reached 120C. The improper temperatures were most liable(predicate) the main cause for the low percent yield. The temperature was too low for the reaction to occur completely and ef fectively.According to Table 1 the aboriginal peaks were all in the fingerprinting zone and were as follows at wave number 961.39cm-1 (indicated a C=C bond), 762.29cm-1 and 690.00cm-1 (indicated aromatic ring structures). According to Table 2 the primary peaks were also all in the fingerprinting region and were as follows 761.88cm-1, 688.59cm-1, and 626.87cm-1 (all of which indicated aromatic ring structures).The hypothesis was proven because meso-stilbene was synthesized even with the incorrect temperature at first. The (E)-stilbene reacted with the pyridium bromide dibromide to create meso-stilbene.ConclusionIt was found that (E)-stilbene could be brominated in order to synthesize the second intermediate in a line of reactions so that meso-stilbene could be obtained. The percent yield was poor yet present. The experiment could have gone more smoothly if the temperature had been monitored better, and the mixture not placed on the heat until it was sufficiently hot. That would have allowed for a higher percent yield then previously achieved.BibliographyBruice, Paula. Organic Chemistry. 7th ed. Pearson, 2014. 1337. Print.Mayo, Dana, Ranold Pike, and David Forbes. Microscale Organic Laboratory with Multistep and Multiscale Synthesis. 5th ed. John Wiley and Sons, 2011. 751. Print.