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Chapter 17

Chapter 17. Carboxylic Acids, Anhydrides, Esters, and Amides. Introduction. Carboxylic acids, another carbonyl containing functional group also anhydrides, esters, and amides loss of H 2 O is commonality here. Carboxylic Acids.

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Chapter 17

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  1. Chapter 17 Carboxylic Acids, Anhydrides, Esters, and Amides

  2. Introduction • Carboxylic acids, another carbonyl containing functional group • also anhydrides, esters, and amides • loss of H2O is commonality here

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

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

  5. Nomenclature • in these examples, the common name is given in parentheses • an -OH substituent is indicated by the prefix hydroxy-; an -NH2 substituent by the prefix amino-

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

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

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

  9. Physical Properties • carboxylic acids have high boiling points • 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

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

  11. Acidity of RCOOH • The hydrogen on the oxygen is acidic • substituents of high electronegativity, especially -OH, -Cl, and -NH3+, near the carboxyl group increase the acidity

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

  13. Ionization versus pH • The form in which a carboxylic acid exist in an aqueous solution depends on the solution’s pH

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

  15. Esters • The ester is a carbonyl group bonded to an -OR group • 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 -icacid by -ate • a cyclic ester is called a lactone

  16. 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 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-

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

  18. Amides • the cephalosporins are also b-lactam antibiotics

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

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

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

  22. Hydrolysis of Anhydrides • carboxylic anhydrides, particularly the low-molecular- weight ones, react readily with water to give two carboxylic acids

  23. Hydrolysis of Esters • 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

  24. Hydrolysis of Esters • hydrolysis of an ester using a hot aqueous base can also work – but not a catalyst here! • this reaction is often called 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

  25. Hydrolysis of Amides • 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

  26. 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 requires one mole of base

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

  28. Phosphoric Esters • 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 phospho- • dihydroxyacetone phosphate and pyridoxal phosphate are shown as they are ionized at pH 7.4, the pH of blood plasma

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

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

  31. Polyamides • the polyaromatic amide known as Kevlar is also made from aa aromatic dicarboxylic acid and an aromatic diamine

  32. Polyesters • the first polyester involved polymerization of this diacid and ethylene glycol

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

  34. Chapter 18 End Chapter 18

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