1 / 14

Ester Hydrolysis in Base: Saponification

Ester Hydrolysis in Base: Saponification. O. O. +. RC O R'. HO –. RCO –. Ester Hydrolysis in Aqueous Base. is called saponification is irreversible, because of strong stabilization of carboxylate ion

norm
Download Presentation

Ester Hydrolysis in Base: Saponification

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Ester Hydrolysis in Base:Saponification

  2. O O + RCOR' HO– RCO– Ester Hydrolysis in Aqueous Base • is called saponification • is irreversible, because of strong stabilization of carboxylateion • if carboxylic acid is desired product, saponification is followedby a separate acidification step (simply a pH adjustment) + R'OH

  3. O CH2OCR1 O R2COCH CH2OCR3 O O O O Soap-Making • Basic hydrolysis of the glyceryl triesters (from fats and oils) gives salts of long-chain carboxylic acids. • These salts are soaps. NaOH , H2O, heat R1CONa R2CONa R3CONa

  4. •• •• O O •• •• – – •• •• •• •• RC OR' OH OR' RC OH •• •• •• •• •• •• Which bond is broken when esters arehydrolyzed in base? • nucleophilicacyl substitution. + +

  5. H O C6H5 CH3C C O CH3 H O C6H5 CH3CONa C HO CH3 Stereochemistry gives the same answer • alcohol has same configuration at chirality center as ester; therefore, nucleophilicacyl substitution NaOH, H2O +

  6. Mechanism of Ester Hydrolysisin Base • Involves two stages: • 1) formation of tetrahedral intermediate2) dissociation of tetrahedral intermediate

  7. O + RCOR' H2O OH OR' RC OH First stage: formation of tetrahedral intermediate • water adds to the carbonyl group of the ester • this stage is analogous to the base-catalyzed addition of water to a ketone HO–

  8. Mechanism of formationoftetrahedral intermediate

  9. •• O •• H RC O •• •• – •• OR' •• •• – •• O H •• •• RC O •• •• OR' •• •• Step 1

  10. •• O H H •• – •• O RC O •• •• •• •• H OR' •• •• – •• •• O H O •• H •• •• H RC O •• •• OR' •• •• Step 2

  11. Dissociation oftetrahedral intermediate

  12. •• O H H •• – •• O RC O •• •• •• •• H OR' •• •• •• •• O H O •• •• H RC – •• OR' O H •• •• •• •• Step 3

  13. •• O •• RC – O •• •• •• •• OR' H •• •• HO– O •• RC – •• OR' O H •• •• •• •• Step 4 H2O

  14. Key Features of Mechanism • Nucleophilic addition of hydroxide ion to carbonylgroup in first step • Tetrahedral intermediate formed in first stage • Hydroxide-induced dissociation of tetrahedralintermediate in second stage

More Related