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20.18 Preparation of Nitriles

20.18 Preparation of Nitriles. Preparation of Nitriles. Nitriles are prepared by:. nucleophilic substitution by cyanide on alkyl halides (Sections 8.1 and 8.13) cyanohydrin formation (Section 17.7) dehydration of amides. CH 3 (CH 2 ) 8 CH 2 C. N. Example. K CN. S N 2.

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20.18 Preparation of Nitriles

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  1. 20.18Preparation of Nitriles

  2. Preparation of Nitriles Nitriles are prepared by: • nucleophilic substitution by cyanide onalkyl halides (Sections 8.1 and 8.13) • cyanohydrin formation (Section 17.7) • dehydration of amides

  3. CH3(CH2)8CH2C N Example KCN • SN2 CH3(CH2)8CH2Cl ethanol-water (95%)

  4. O OH CH3CH2CCH2CH3 CH3CH2CCH2CH3 C N Example KCN H+ (75%)

  5. O P4O10 N (CH3)2CHCNH2 (CH3)2CHC 200°C Preparation of Nitriles By dehydration of amides • uses the reagent P4O10 (often written as P2O5) (69-86%)

  6. 20.19Hydrolysis of Nitriles

  7. O + NH4 RCOH Hydrolysis of Nitriles Hydrolysis of nitriles resembles the hydrolysisof amides. The reaction is irreversible. Ammonia is produced and is protonated to ammonium ion in acid solution. + + + + 2H2O H RCN

  8. O RCO Hydrolysis of Nitriles In basic solution the carboxylic acid product is deprotonated to give a carboxylate ion. – – + + + H2O HO RCN NH3

  9. O CH2CN CH2COH H2O H2SO4heat NO2 NO2 Example: Acid Hydrolysis (92-95%)

  10. O 1. KOH, H2O, heat CH3(CH2)9COH 2. H+ Example: Basic Hydrolysis CH3(CH2)9CN (80%)

  11. O O N RC RCNH2 RCOH Mechanism of Hydrolysis of Nitriles • Hydrolysis of nitriles proceeds via thecorresponding amide. • We already know the mechanism of amidehydrolysis. • Therefore, all we need to do is to see how amides are formed from nitriles under the conditions of hydrolysis. H2O H2O

  12. O N RC RCNH2 Mechanism of Hydrolysis of Nitriles OH • The mechanism of amide formation is analogousto that of conversion of alkynes to ketones. • It begins with the addition of water across thecarbon-nitrogen triple bond. • The product of this addition is the nitrogen analog of an enol. It is transformed to an amideunder the reaction conditions. H2O NH RC

  13. H – O •• •• •• N RC •• Step 1

  14. H H – O O •• •• •• •• •• RC N RC •• N •• •• – Step 1

  15. H O •• •• RC H N H O •• •• •• – •• Step 2

  16. H O •• •• RC H N H O H •• •• •• – •• O •• •• RC H N H O •• •• •• – •• Step 2

  17. H O •• •• – •• H O •• •• RC N H •• Step 3

  18. H O •• •• H H O •• •• •• O – •• •• H RC – O N •• H •• •• •• RC N H •• Step 3

  19. •• O •• RC – N H •• •• Step 4 •• O H •• H

  20. •• O •• RC – N H •• – •• •• O •• •• H Step 4 •• O •• RC N H •• •• O H H •• H

  21. 20.20Addition of Grignard Reagentsto Nitriles

  22. NMgX NH N RC RCR' RCR' Addition of Grignard Reagents to Nitriles • Grignard reagents add to carbon-nitrogen triplebonds in the same way that they add to carbon-oxygen double bonds. • The product of the reaction is an imine. R'MgX H2O diethylether

  23. NMgX NH N RC RCR' RCR' O RCR' Addition of Grignard Reagents to Nitriles R'MgX H2O diethylether H3O+ Imines are readily hydrolyzed to ketones.Therefore, the reaction of Grignard reagents with nitriles can be used as a synthesis of ketones.

  24. N C F3C O CCH3 F3C Example + CH3MgI 1. diethyl ether 2. H3O+, heat (79%)

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