Grignard Synthesis 3 - 1 Grignard Synthesis Sam Keath CHEM...

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Grignard Synthesis Sam Keath CHEM 2642L-265 Instructor: Dr. David Jeffrey November 7, 2010
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2 INTRODUCTION The purpose of this experiment was to synthesize an alcohol, triphenylmethanol, using the Grignard synthesis method. Since our Grignard reagent, phenylmagnesium bromide, was reacted with methyl benzoate, we expect our product to be triphenylmethanol. One of the most important considerations of this experiment was the absence of water. According to theory, the Grignard reagent has the formula RMgX where X is a halogen such as Br or Cl and is highly reactive. The Grignard reagent is considered to be the magnesium salt of a weak acid R-H. It will be displaced from its salt in the presence of a stronger acid such as H2O. If the aldehyde is not dry, then H2O with react with it and eliminate the Grignard reagent. Therefore, it was very important to make sure that all reagents and equipment were absolutely dry as possible. The product of the Grignard synthesis reaction would be an alcohol which is formed from the reaction of an alkyl halide and a carbonyl compound. According to Williamson, one of the by products of this reaction is biphenyl which has an odor. However, the alcohol should not have an odor according to Williamson. Br BrMg COOMe e t h e r OH H 3 O + 2 2 2 M g d i e t h y l e t h e r a m b i e n t T D R Y !
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3 METHODS Table 1: Reaction Table Reactants /products formula MW (g/ mol) Dens ity (“d”;g /cm 3 ) d source mL g mol LR 1 T. yiel d (g) Lit. m.p./b .p. ( o C) Bromobenzene C6H5Br 157.02 1.491 William son 4.5 6.71 0.042 99 no n/a b.p. 156 Mg Mg 24.305 n/a William son n/a 1.02 66 0.042 282 no n/a n/a Diethyl ether Et2O b.p. 34 o C Methyl benzoate C6H5C OOCH3 136.15 1.083 7 William son 2.5 2.72 5 0.020 013 yes n/a b.p. 199.6 o C Ligroin 15 b.p. 60-80 o C Sulfuric Acid H2SO4 30 Triphenylmetha nol C19H15 OH 260.34 n/a n/a n/a n/a n/a n/a 5.18 08 m.p. 164.2 o C Calculations: Determination of Limiting Reactant
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4 4.5 mL bromobenzene x 1.491 g/mL = 6.75 g 6.75 g x 1 mol /157.02 g = 0.04299 mol bromobenzene 1.0266 g magnesium x 1 mol / 24.3050 g = 0.42282 mol magnesium 2.5 mL methyl benzoate x 1.09 g/mL = 2.725 g 2.725 g x 1 mol / 136.16 g = 0.020013 mol methyl benzoate (limiting reactant) Theoretical yield 0.020013 mol x 260.34 g/mol = 5.1808 g Procedure: PREPARATION OF THE PHENYLMAGNESIUM BROMIDE (PHENYL GRIGNARD REAGENT) The mixture of diethyl ether and bromobenzene was added to the reaction vessel containing Mg. The pieces of Mg were then pressed with a glass stir rod. The flask was then placed into a beaker of warm water. After a few minutes, the solution began to reflux and became cloudy as the Mg began to dissolve. After fifteen minutes, the solution began to turn orange. The water was changed occasionally as it cooled down.
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This note was uploaded on 11/06/2010 for the course CHEM 10258 taught by Professor Dr.doodoohead during the Spring '10 term at Gwinnett Technical College.

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Grignard Synthesis 3 - 1 Grignard Synthesis Sam Keath CHEM...

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