Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
19 General, Organic, and Biochemistry, 8e Bettelheim, Brown, Campbell, & Farrell © 2006 Thomson Learning, Inc. All rights reserved 19-1 19 Introduction • In this chapter, we study three classes of compounds derived from carboxylic acids; anhydrides, esters, and amides • Each is related to a carboxyl group by loss of H2O. O RCOH A carboxylic acid O O RCOCR' An anhydride -H2 O O O RC- OH H- OCR' © 2006 Thomson Learning, Inc. All rights reserved O RCOR' An ester -H2 O O RCN H2 An amide -H2 O O O RC- OH H- OR' RC- OH H- NH 2 19-2 19 Anhydrides • The functional group of an anhydride is two carbonyl groups bonded to the same oxygen. • The anhydride may be symmetrical (from two identical acyl groups), or mixed (from two different acyl groups). Your book does not discuss how to name the mixed anhydrides so you will not be responsible for being able to name a mixed anhydride. • To name an anhydride, drop the word "acid" from the name of the carboxylic acid from which the anhydride is derived and add the word "anhydride”. © 2006 Thomson Learning, Inc. All rights reserved O O CH3 C-O-CCH3 Acetic anhydride 19-3 19 Esters • The functional group of an ester is a carbonyl group bonded to an -OR group. • Both IUPAC and common names of esters are derived from the names of the parent carboxylic acids. • Name the alkyl or aryl group bonded to oxygen first, followed by the name of the acid; replace the suffix -ic acid by -oate. • A cyclic ester is called a lactone. O CH3 COCH2 CH3 Ethyl ethanoate (Ethyl acetate) © 2006 Thomson Learning, Inc. All rights reserved O O O O Diethyl pentanedioate (Diethyl glutarate) O O A five-membered lactone 19-4 19 Amides • The functional group of an amide is a carbonyl group bonded to a nitrogen atom. • To name an amide, drop the suffix -oic acid from the IUPAC name of the parent acid, or -ic acid from its common name, and add -amide. • If the amide nitrogen is also bonded to an alkyl or aryl group, name the group and show its location on nitrogen by N- ; two alkyl or aryl groups by N,N-di-. O O CH3 CNH2 CH3 CNHCH3 Acetamide N -Methylacetamide (a 1° amide) (a 2° amide) © 2006 Thomson Learning, Inc. All rights reserved O HCN(CH3 ) 2 N ,N-D imethylformamide (a 3° amide) 19-5 19 Amides • A cyclic amide is called a lactam. O O b NH A four-memb ered lactam (a b-lactam) NH A seven-memb ered lactam • The penicillins are referred to as b-lactam antibiotics. HO The p enicillins differ in th e group bond ed to th e carbonyl carbon © 2006 Thomson Learning, Inc. All rights reserved Theb-lactam rin g O N NH2 H O S N CH3 CH3 COOH A moxicillin 19-6 19 Amides • The cephalosporins are also b-lactam antibiotics. O The cephalosporins differ in the group bonded to the carbonyl carbon... © 2006 Thomson Learning, Inc. All rights reserved N H N H2 O S ...and the group bonded to this carbon of the six-membered ring N CH3 COOH Cephalexin (Keflex) (a b-lactam antibiotic) 19-7 19 Fischer Esterification • Fischer esterification is the most commonly used preparation of esters (Chapter 18). • In Fischer esterification, a carboxylic acid is reacted with an alcohol in the presence of an acid catalyst, such as concentrated sulfuric acid O H2 SO4 CH3 C-OH + H-OCH2 CH3 Ethanoic acid Ethanol (Acetic acid) (Ethyl alcohol) © 2006 Thomson Learning, Inc. All rights reserved O CH3 COCH2 CH3 + H2 O Ethyl ethanoate (Ethyl acetate) 19-8 19 Preparation of Amides • In principle, we can form an amide by treating a carboxylic acid with an amine and removing -OH from the acid and an -H from the amine. • In practice what occurs if the two are mixed is an acidbase reaction to form an ammonium salt. • If this salt is heated to a high enough temperature, water is eliminated and an amide forms. O CH3 C-OH + H2 NCH2 CH3 Acetic Ethanamine acid (Ethylamine) © 2006 Thomson Learning, Inc. All rights reserved O + CH3 C-O H3 NCH2 CH3 An ammonium s alt O h eat CH3 C-NHCH2 CH3 + H2 O An amid e 19-9 19 Preparation of Amides • It is much more common, however, to prepare amides by treating an anhydride with an amine. O O CH3 C-O-CCH3 + H2 NCH2 CH3 Acetic anhdyride © 2006 Thomson Learning, Inc. All rights reserved O O CH3 C-NHCH2 CH3 + CH3 COH A n amide 19-10 19 Hydrolysis of Anhydrides • Hydrolysis is a chemical decomposition involving breaking a bond and the addition of the elements of water. • Carboxylic anhydrides, particularly the low-molecularweight ones, react readily with water (hydrolyze) to give two carboxylic acids. O O CH3 COCCH3 + H2 O Acetic anhydride © 2006 Thomson Learning, Inc. All rights reserved O O CH3 COH + HOCCH3 Acetic acid Acetic acid 19-11 19 Hydrolysis of Esters • Esters hydrolyze only very slowly, even in boiling water. • Hydrolysis becomes considerably more rapid, however, when the ester is heated in aqueous acid or base. • Hydrolysis of esters in aqueous acid is the reverse of Fischer esterification. • A large excess of water drives the equilibrium to the right to form the carboxylic acid and alcohol (Le Chatelier's principle). O CH3 COCH2 CH3 Ethyl acetate © 2006 Thomson Learning, Inc. All rights reserved + H2 O H + O CH3 COH + CH3 CH2 OH Acetic acid Ethanol 19-12 19 Hydrolysis of Esters • We can also hydrolyze an ester using a hot aqueous base, such as aqueous NaOH. • This reaction is often called saponification, a reference to its use in the manufacture of soaps. • The carboxylic acid formed in the hydrolysis reacts with hydroxide ion to form a carboxylic acid anion. • Each mole of ester hydrolyzed requires one mole of base. O H2 O CH3 COCH2 CH3+ N aOH heat Ethyl acetate Sodium hydroxide © 2006 Thomson Learning, Inc. All rights reserved O CH3 CO - N a++ CH3 CH2 OH Sodium Ethanol acetate 19-13 19 Hydrolysis of Amides • Amides require more vigorous conditions for hydrolysis in both acid and base than do esters. • Hydrolysis in hot aqueous acid gives a carboxylic acid and an ammonium ion. • Hydrolysis is driven to completion by the acid-base reaction between ammonia or the amine and the acid to form an ammonium ion. • Each mole of amide hydrolyzed requires one mole of acid. O CH3 CH2 CH2 CNH2 + H2 O + HCl Butanamide © 2006 Thomson Learning, Inc. All rights reserved H2 O heat O + CH3 CH2 CH2 COH + NH4 Cl Butanoic acid 19-14 19 Hydrolysis of Amides • Hydrolysis of an amide in aqueous base gives a carboxylic acid salt and ammonia or an amine. • Hydrolysis is driven to completion by the acid-base reaction between the carboxylic acid and base to form a salt. • Each mole of amide hydrolyzed requires one mole of base. O CH3 CNH Acetanilide © 2006 Thomson Learning, Inc. All rights reserved + NaOH H2 O heat O CH3 CO-Na+ + H2 N Sodium acetate Aniline 19-15 19 Reaction with Alcohols • Anhydrides react with alcohols and phenols to give an ester and a carboxylic acid. O O CH3 COCCH3 + HOCH2 CH3 Acetic anhydride Ethanol O O CH3 COCH 2 CH 3 + HOCCH3 Ethyl acetate Acetic acid • Aspirin is prepared by the reaction of salicylic acid with acetic anhydride. COOH OH Salicylic acid © 2006 Thomson Learning, Inc. All rights reserved + O O CH3 C- O-CCH3 Acetic anhydride COOH OCCH 3 O Acetyls alicylic acid (Aspirin) + O CH3 C- OH Acetic acid 19-16 19 Reaction with Amines • Anhydrides react with ammonia and with 1° and 2° amines to form amides. • Two moles of amine are required; one to form the amide and one to neutralize the carboxylic acid by-product. O O CH3 C- O-CCH3 + N H3 O CH3 C- OH + N H3 O O CH3 C- O-CCH3 + 2 N H3 Acetic anhydride © 2006 Thomson Learning, Inc. All rights reserved O O CH3 CN H2 + CH3 C- OH O CH3 CO - N H4 + O O CH3 CN H2 + CH3 CO - N H4 + Acetamide Ammonium acetate 19-17 19 Reaction with Amines • Esters react with ammonia and with 1° and 2° amines to form amides. O O OCH2 CH3 + N H3 Ethyl 2-phenyl acetate N H2 + CH3 CH2 OH 2-Phenylacetamide • Thus, an amide can be prepared from a carboxylic acid by first converting the carboxylic acid to an ester by Fischer esterification and then reaction of the ester with an amine. © 2006 Thomson Learning, Inc. All rights reserved 19-18 19 Reaction with Amines • Amides do not react with ammonia or with amines. • You have a quiz next class on amines. It is a very small amount of information with only two reactions, so be prepared to complete the reactions and be able to name the products. © 2006 Thomson Learning, Inc. All rights reserved 19-19 19 March Science Night • For the remaining portion of class I want you to discuss what you will be doing for the March Science Night. • Seniors: I need to know if you will be presenting on your senior project, doing a new project or being an assistant (helper) on the actual night. • Juniors: I need to know what your project, talk or activity will be. You may work in groups of up to four students. If you are already doing a project for Mr. Isel you don’t have to do one for me. Next class I will be putting up a sign up sheet and a list from 1B to see if you want to join two projects. © 2006 Thomson Learning, Inc. All rights reserved 19-20 19 Chapter 19 End Chapter 19 © 2006 Thomson Learning, Inc. All rights reserved 19-21