Question

Introduction Three aromatic compounds that have ortho-para directing and activating substituents will be brominated. The extent of activation will be judged by the number of bromine atoms that add to the benzene ring in each case. For each of the compounds shown below you will work out if a mono- di- or tri- brominated derivative formed following treatment with acetic acid and bromine in hydrobromic acid. This will be determined by measuring the melting point and interpreting the H NMR spectrum of each product CH NH CH aminobenzene methoxybenzene N-phenylacetamide Experimental Electrophilic bromination of three substituted benzenes In this experiment you will brominate three different substituted benzenes (aminobenzene, methoxybenzene and N-phenylacetamide), using three large test tubes as the reaction vessels. Label each test tube with the structure of one reactant substituted benzene and your initials. Place a magnetic stirrer bar in each test tube. Carry out the initial set up of the test tubes in the fume hood. Add aminobenzene (370 HL, 0.37 g, 4 mmol), methoxybenzene (430 HL, 0.43 g, 4 mmol) and N-phenylacetamide (0.54 g, 4 mmol) to the appropriately labelled test tube, and then add glacial acetic acid (5.0 mL) to each test tube. The three test tubes can be bound together with a rubber band and the test tubes can now be removed from the fume hood. Set up a beaker containing warm tap water (23 -27 °C) on a magnetic stirrer. Stand the test tubes in the beaker and secure with a clamp Stagger the starting time for each reaction by 5 minutes. Bromine in hydrobromic acid (6.0 mL, 16 mmol Br2) must be added to each test tube all at once with vigorous stirring. Stir each reaction mixture for 20 minutes, and then stagger the quenching of each reaction by 5 minutes. Quench each reaction by adding water (30 mL) and saturated aqueous sodium hydrogen sulfite (3.0 mL) with stirring. Continue stirring until the red colour disappears After all three reactions have been quenched cool the test tubes in an ice bath for 15 minutes. If the product from bromination of methoxybenzene does not solidify, scratch the side of the test tube with a glass rod Isolate the solid products using vacuum filtration, wash with cold water and air dry. The products can be dried further by pressing between filter papers. Products can be dried in the oven, but be sure to check the expected melting points of your products and the oven temperature setting before doing this. Each solid product wil be analysed without purification by 'H NMR. Weigh out approximately 20 mg of each solid product into a vial to prepare the sample. The demonstrator will show you how to prepare the samples for NMR using CDCl3 as the solvent. Determine the yield and melting point of each solid product You will interpret the H NMR data to answer questions for the report on this experiment.

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