Organic Chemistry 333L, section 03M LaboratoryPre-LabReactions of CarbocationsBy: Cameron Kahn22 October 2013TA: James CollieObjectives:In this lab, one will synthesize triphenylmethyl bromide from triphenylmethanol through a tritylcarbocation intermediate. This experiment will also teach one how to find the mass, melting point, and percent yield of triphenylmethyl bromide.Theory:In 1912, Victor Grignard received the Nobel Prize in chemistry for his work on the reaction that bears his name, a carbon-carbon bond-forming reaction by which almost any alcohol may be formed from appropriate alkyl halides and carbonyl compounds (University of Missouri). In this experiment, it is very similar to what Victor Grignard tested.Carbocations are reactive intermediates in many organic reactions. Triphenylmethanol is a tertiary alcohol and is the reason why it undergoes an SN1 reaction. It is important to note that tertiary alcohols undergo Sn1 reactions and in order for the alcohol to react, it must first form a carbocation and then the covalent bond can form (Handy). It is because of this that a 3o alcohol isneeded in the reaction. The following table shows the criteria for an Sn1 and Sn2 reactions.1 | P a g eCriteria Sn1 Sn2Solvent Choice Polar, protic solvents:Methanol, ethanol, water, acetic acid, etc.Paolar, aprotic solvents:DMSO, Acetone, dichloromethane, diethyl etherLeaving Group 3o, 2oMethyl, 1o,2oNucleophile Moderate to weakNucleophiles: H2O, CH3OH, NH3, CH3CO-, RSHModerate to strong: CN-, N3-, CH3S-, HO-, Br-, I-Rearrangement of StereocenterFinal product is a racemic mixtureFinal product is an inversion of stereochemistryForms Carbocation Yes; Rate Limiting Step No; concentrated reaction*the table is courtesy of the Chemistry 333 Lab Manual with copyrights to George Handy and Salman AliAnother thing to mention is that in general, carbocations have a center carbon atom that is sp2 hybridized and has an order of stability that goes like this: Allylic> 3o>2o>1o>methyl. The more alkyl groups attached to the carbocation, the more stable it will be (Handy). Triphenylmethyl carbocation is extremely stable and believed to be a super allylic carbocation with 10 resonance structures.In this experiment, triphenylmethanol dissolves in acetic aid. It will then react with hydrobromic acid. The intermediate carbocation will react with the bromide ion immmediately (Handy). This is seen in the following mechanism.Mechanism:2 | P a g eProcedure:Start by placing 100 mg of triphenylmethanol into a small test tube. Next, add 2 mL of acetic acid and then heat the test tube in a hot water bath until all the solids have dissolved. Take great care and insure to stir the contents of the test tube with a glass rod. The TA will now need to add 0.2 mL (~7 to 8 drops) of concentrated HBr to your test tube. This will need to take place under the fume hood. Now heat the solutions for 5 – 10 minutes on a steam bath. Take the test tube out of the bath and let the test tube cool to room temperature. Next, place the test tube in an ice bath to allow crystallization to occur. The compound crystallizes slowly, so allow adequate time for crystals to form (~10 – 15 minutes). Use suction filtration with a Buchner funnel to collect the cooled crystalline product and then wash the solids with 3 to 4 drops of water followed by 3 to 4 drops of ice cold hexane. Drain and air dry the product for a few minutes before one transfers thecrystalline product onto a piece of filter paper. Invert a beaker over the transferred product and 3 | P a g elet air dry. Weigh the product and record the measurement. Calculate percent yield and melting point and record the findings. An important reminder is that he/she will be expected to calculate the theoretical yield of triphenylmethyl bromide in the results.Apparatus:Apparatus pictures are copyright of George Handy and Salman Ali from the Chemistry 333 Lab manual.4 | P a g eMore zoomed in version on the Steam bathReagent Table:Name StructureMolecular weight (g/mol)Melting Point (oC)Boiling Point (oC)Density (g/ml)Acetic AcidCH3COOH60.0524 16.6 117.9 1.05Hydrobromic Acid HBr 80.9119 -87 -66.38 1.49TriphenylmethanolC19H16O260.3348 163 360 -HexaneC6H14-86.1766 -95 69 .659Triphenylmethyl bomideC19H15Br323.2315 152-154230 at 15mm Hg-Disposal:Dispose of all products in their proper container. Liquids go in liquids container. Gloves go in glove bucket. Glass goes in glass bucket. Organic solids and organic waste go in the organic waste containers. Place all paper towels in the trash can. If unsure about any disposal procedure,consult the TA.5 | P a g eReferences:1. Ali, George Handy and Salman. Essentials of Organic Chemistry. Montgomery, AL 36117: QDE Press, 2012. 2. Missouri, University of. Experiment 8 (part 1)-Grignard Synthesis of Triphenylmethanol. 28 Feb 2013. 02 03 2013 <http://www.chem.missouri.edu/chem2140/Chem333LGrignard.pdf>.6 | P a g