Organic 2 Review Problem 296

Organic 2 Review Problem 296 - small quantity of cold water...

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2 8o PRACTICAL ORGANIC CHEMISTRY (i) CH 2 (COOH) 1 + 38 -» £H(COOH,B) a + BH O H (ii) R-C=O f -CH(COOH^B) 2 -^- R-C-C(COOH,B) 2 H H H O H -^ R C-C(COOH,B) 2 + R-CHrC(COOH) 2 -V R CH:CH COOH H The reaction is readily illustrated by the formation of crystalline sorbic acid by the condensation of crotonaldehyde and malonic acid in hot pyridine solution: CH 3 -CHiCH-CHO + H 2 C(COOH) 2 -* CH S -CH:CH-CH:CH-COOH + H 8 O + CO 1 Required: Malonic acid, 4 g.; pyridine, 4 ml. (4 g.); croton- aldehyde, 3-1 ml. (2-7 g.). Add 4 g. of malonic acid to 4 ml. of pyridine, and then add 3-1 ml. of crotonaldehyde. Boil the mixture gently under reflux over an asbestos-covered gauze, using a small Bunsen flame, for 40 minutes and then cool it in ice-water. Meanwhile add 2 ml. of concentrated sulphuric acid carefully with shaking to 4 ml. of water, cool the diluted acid, and add it with shaking to the chilled reaction-mixture. Sorbic acid readily crystallises from the solution. Filter the sorbic acid at the pump, wash it with a
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Unformatted text preview: small quantity of cold water and then recrystallise it from water ( ca . 25 ml.). The colourless crystals, m.p. 132-133°, weigh i-o-i-2g. Sorbic acid could theoretically, by virtue of the two olefine linkages, exist in four geometrically-isomeric forms. The above synthesis gives only one form, which is undoubtedly the trans-trans form, analogous to the aoi-diphenylpolyenes (p. 238) which are also normally produced solely in one form. The Grignard Reagent. Grignard reagents are prepared by the interaction of alkyl or aryl halides (of general formula RX) with magnesium in the presence of ether, or (much more rarely) certain other solvents. Although the ether certainly takes part both in the formation and the composition of the Grignard reagent, the formation of the latter can, for the purpose of interpreting its reactions, be represented as a simple addition: RX + Mg = RMgX....
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This note was uploaded on 09/19/2011 for the course CHM 2211 taught by Professor Castalleano during the Fall '06 term at University of Florida.

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