Dolbier HW Solutions 425

Dolbier HW Solutions 425 - 519 CARBOXYLIC ACIDS (c) Cyanide...

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( c ) Cyanide ion is a good nucleophile and will displace bromide from bromoacetic acid. ( d ) Cyanoacetic acid, prepared as in part ( c ), serves as a convenient precursor to malonic acid. Hydrolysis of the nitrile substituent converts it to a carboxyl group. ( e ) Iodoacetic acid is not prepared directly from acetic acid but is derived by nucleophilic substi- tution of iodide in bromoacetic acid. ( f ) Two transformations need to be accomplished, a bromination and esteri f cation. The correct sequence is bromination followed by esteri f cation. Reversing the order of steps is not appropriate. It must be the carboxylic acid that is subjected to halogenation because the Hell Volhard Zelinsky reaction is a reaction of carboxylic acids, not esters. ( g ) The compound shown is an ylide. It can be prepared from ethyl bromoacetate as shown The f rst step is a nucleophilic substitution of bromide by triphenylphosphine. Treatment of the derived triphenylphosphonium salt with base removes the relatively acidic a proton, form- ing the ylide. (For a review of ylide formation, refer to Section 17.12.)
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