Chapter 17 (Lecture #17)

Chapter 17 (Lecture #17) - Nitriles One standard way of...

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Nitriles This synthesis is an alternative to the reaction of an alkyl halide with cyanide ion, which proceeds by an S N 2 mechanism. One standard way of preparing a nitrile is by the dehydration of the corresponding primary amide with reagents such as P 4 O 10 (called phosphorous pentoxide , P 2 O 5 ) or refluxing acetic anhydride . CH 3 CH 2 CNH 2 O = propionamide P 2 O 5 85 o C CH 3 CH 2 C N (-H 2 O) propanenitrile
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Hydrolysis of Nitriles Nitriles are considered derivatives of carboxylic acids because hydrolysis of a nitrile produces an acid. As with amides, the rate of hydrolysis is faster under either acidic or basic conditions than at neutral pH. R-C N H 3 O + H 2 O heat HO - H 2 O heat RCO 2 H + NH 4 + RCO 2 - + NH 3
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A Mechanism for the Acidic Hydrolysis of Nitriles The nitrile is a polar functional group similar to a carbonyl: R-C N: R-C=N: : + - R-C N: ! + !" polarization of charge in the nitrile function Stage 1: hydrolysis of nitrile to amide protonation of the nitrile R-C N: + H-O-H H + R-C=N-H + R-C N-H + protonated nitrile more reactive towards nucleophilic attack R-C N-H + + :O-H H nucleophile slow R-C=N-H H-O: H + nucleophilic addition deprotonation -H + +H + R-C=N-H H-O: amide tautomer
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Chapter 17 (Lecture #17) - Nitriles One standard way of...

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