12 Grignard.docx - Lab#11 Dehydration of...

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Lab #11: Dehydration of 2-methylcyclohexanol Yook Teng (Tiffany) Lam April 30, 2015 TA: Lukas Klees CHEM 335, Section B74 Department of Chemistry, Binghamton University, Binghamton, NY 11362
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Introduction The Grignard reagent is an organomagnesium compound that is synthesized from solid magnesium (Mg) and alkyl or aryl halides. Solvents commonly used to carry out the reaction are diethyl ether or tetrahydrofuran because they are anhydrous and unreactive. Otherwise water or alcohol components would react with the reagents and form insoluble hydroxides or alkoxides. Halogens also cannot be part of solvent. The nucleophilic carbon in the Grignard reagent attacks the carbon in carbon dioxide thus creating a magnesium carboxylate complex intermediate. A simple acid-base reaction would protonate the oxygen and lead to the acid product. The purpose of the lab is to prepare a Grignard reagent that is then used to make benzoic acid. The product will be analyzed by measuring its melting point. Bromobenzene and Mg turnings will be reacted to create the Grignard addition product in ether. Then it is reacted with carbon dioxide that produces the magnesium carboxylate complex. It will be protonated with concentrate hydrochloric acid to give the benzoic acid, which is then extracted by using sodium hydroxide and more hydrochloric acid. Experimental Procedure A 100ml round bottom flask, Claisen arm, condenser, addition funnel, and drying tubes were obtained from the oven. The apparatus was assembled like Figure 1 in page 71 of manual without connecting the water supply. 1.32g of Mg turnings, 1mL dry bromobenzene, and 8mL anhydrous ethyl ether was added into round bottom flask. 4.5mL bromobenzene and 14mL diethyl ether was added into the addition funnel. Mixture was swirled to ensure complete mixing.
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  • Spring '12
  • Dr.Kematick
  • Diethyl ether, Grignard reaction

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