Chapter 17 Carboxylic Acids Anhydrides Esters and Amides

Chapter 17 Carboxylic Acids, Anhydrides, Esters, and Amides

Introduction l Carboxylic acids, another carbonyl containing functional group l also anhydrides, esters, and amides l loss of H 2 O is commonality here

Carboxylic Acids l The functional group of a carboxylic acid is a carboxyl group, group which can be represented in any one of three ways

Nomenclature l IUPAC names Find the longest carbon chain that contains the carboxyl group as the parent alkane l drop the final -e and replace it by -oic acid l carboxyl group is carbon 1 l because the carboxyl carbon is understood to be carbon 1, there is no need to give it a number l

Nomenclature l in these examples, the common name is given in parentheses l an -OH substituent is indicated by the prefix hydroxy-; an -NH 2 substituent by the prefix amino-

Nomenclature dicarboxylic acids have the suffix -dioic acid and the parent contains both carboxyl groups l the numbers of the carboxyl carbons are not indicated l

Nomenclature l for common names, use, the Greek letters alpha (a), beta (b), gamma (g), and so forth to locate substituents

Physical Properties l The carboxyl group contains three polar covalent bonds; C=O, C-O, and O-H l the polarity of these bonds determines the major physical properties of carboxylic acids

Physical Properties carboxylic acids have high boiling points l these are a result of their polarity and the fact that hydrogen bonding between two carboxyl groups creates a dimer that behaves as a higher-molecular-weight compound l

Physical Properties l carboxylic acids are more soluble in water than are alcohols, ethers, aldehydes, and ketones of comparable molecular weight

Acidity of RCOOH The hydrogen on the oxygen is acidic l substituents of high electronegativity, especially -OH, -Cl, and -NH 3+, near the carboxyl group increase the acidity l

Reaction With Bases l All carboxylic acids react with Na. OH, KOH, and other strong bases to form water-soluble salts l they also form water-soluble salts with ammonia and amines

Ionization versus p. H l The form in which a carboxylic acid exist in an aqueous solution depends on the solution’s p. H

Anhydrides l The anhydride is two carbonyl groups bonded to the same oxygen The most common are symmetrical but the mixed anhydride may be made. l to name an anhydride, drop the word "acid" acid and add the word "anhydride" anhydride l

Esters l The ester is a carbonyl group bonded to an -OR group l l l esters names are derived from the names of the parent carboxylic acids name the “R” first, followed by the name of the acid; replace the suffix -ic acid by -ate a cyclic ester is called a lactone

Amides l The functional group of an amide is a carbonyl group bonded to a nitrogen atom l l 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 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-

Amides l l a cyclic amide is called a lactam the penicillins are referred to as b-lactam antibiotics

Amides l the cephalosporins are also b-lactam antibiotics

Fischer Esterification l one of the most commonly used preparations of esters l carboxylic acid reacted with an alcohol in the presence of an acid catalyst l reversible

Preparation of Amides l If a carboxylic acid an amine are mixed, an acid-base reaction to form an ammonium salt results l if this salt is heated to a high enough temperature, water is eliminated an amide forms

Preparation of Amides l it is much more common to prepare amides by treating an amine with an anhydride

Hydrolysis of Anhydrides l carboxylic anhydrides, particularly the lowmolecular- weight ones, react readily with water to give two carboxylic acids

Hydrolysis of Esters l l l esters hydrolyze 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

Hydrolysis of Esters l l hydrolysis of an ester using a hot aqueous base can also work – but not a catalyst here! this reaction is often called saponification, saponification a reference to its use in the manufacture of soaps the carboxylic acid formed reacts with hydroxide ion each mole of ester hydrolyzed requires one mole of base

Hydrolysis of Amides l l amides require more vigorous conditions hydrolysis in hot aqueous acid is not catalytic 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 requires one mole of acid

Hydrolysis of Amides l l l 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 requires one mole of base

Phosphoric Anhydrides l the functional group of a phosphoric anhydride is two phosphoryl (P=O) groups bonded to the same oxygen atom

Phosphoric Esters l l l phosphoric acid forms mono-, di-, and triphosphoric esters it is common to name the organic molecule and then indicate the presence of the phosphoric ester by either the word "phosphate" or the prefix phosphodihydroxyacetone phosphate and pyridoxal phosphate are shown as they are ionized at p. H 7. 4, the p. H of blood plasma

Step-Growth Polymers l Step-growth polymers are formed by reaction between molecules containing two functional groups, with each new bond created in a separate step l in this section, we discuss three types of step-growth polymers; polyamides, polyesters, and polycarbonates

Polyamides l Nylon-66 was the first purely synthetic fiber l it is synthesized from two six-carbon monomers

Polyamides l the polyaromatic amide known as Kevlar is also made from aa aromatic dicarboxylic acid an aromatic diamine

Polyesters l the first polyester involved polymerization of this diacid and ethylene glycol

Polycarbonates l Lexan, the most familiar polycarbonate, polycarbonate is formed by reaction between the disodium salt of bisphenol A and phosgene

Chapter 18 End Chapter 18