(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, abromination and esterifcation. The correctsequence is bromination followed by esterifcation.Reversing the order of steps is not appropriate. It must be the carboxylic acid that is subjectedto 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 shownThe frst step is a nucleophilic substitution of bromide by triphenylphosphine. Treatment ofthe derived triphenylphosphonium salt with base removes the relatively acidic aproton, form-ing the ylide. (For a review of ylide formation, refer to Section 17.12.)
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