215F07-notes-10-8-07 - Chem 215 F07 Notes Dr Masato Koreeda...

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Chem 215 F07 Notes – Dr. Masato Koreeda - Page 1 of 4. Date: October 8, 2007 Chapter 15: Carboxylic Acids and Their Derivatives. III Synthesis of Carboxylic Acids (cont’d) Hydrolysis of nitriles under basic conditions: Under milder basic conditions, an amide is obtained. Mechanism for the base-catalyzed hydrolysis of nitriles: C N R H O R C O O H R C N H O H amide H O H H O H O H R C N H H H O H O H O R C N H H H O O H O H H O R C N H O H H O R C N H O R C N H O H O H R C O O nitrile carboxylate Alternatively, R C NH 2 O * * * This is to avoid the generation of highly unfavorable R-NH species. The pKa of R-NH 2 is at ~35. ** ** This N is stabilized by resonance with C=O, thus allowable! The pKa of an amide H is at ~12. IV. Synthesis of Acid Chlorides and Acid Anhydrides (1) Acid Chlorides: highly electrophilic C=O carbons; react with even weak nucleophiles such as ROH; need to be prepared under anhydrous conditions. Prepared from carboxylic acids. a. With SOCl 2 : H 3 C OH O + SOCl 2 H 3 C Cl O + SO 2 + HCl (gas) (gas) ! mechanism: R OH O Cl S Cl O R OH O Cl S Cl O R OH O Cl S O Cl R OH Cl O S Cl O R Cl O H Cl R Cl O -SO 2 -Cl -HCl b . With PCl 3 : (more common) H 3 C OH O + PCl 3 H 3 C Cl O ! 3 3 + H 3 PO 3 H 3 C OH O 2 ! high temperatures (800 °C) H 3 C O CH 3 O O + H 2 O removed by heating at ~100 °C bp higher than H 2 O OH O (H 2 C) 10 H 3 C 2 O O (H 2 C) 10 H 3 C (H 2 C) 10 H 3 C H 3 C O CH 3 O O O mp 42 °C (decanoic anhydride) H 3 C OH O 2 + + !
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