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CHE 242 Unit VIII The Structure, Properties, Reactions and Mechanisms of Carboxylic Acids and Their Derivatives CHAPTER

CHE 242 Unit VIII The Structure, Properties, Reactions and Mechanisms of Carboxylic Acids and Their Derivatives CHAPTER TWENTY-ONE. Terrence P. Sherlock Burlington County College 2004. =>. Acid Derivatives. All can be converted to the carboxylic acid by acidic or basic hydrolysis.

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CHE 242 Unit VIII The Structure, Properties, Reactions and Mechanisms of Carboxylic Acids and Their Derivatives CHAPTER

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  1. CHE 242Unit VIIIThe Structure, Properties, Reactions and Mechanisms of Carboxylic Acids and Their DerivativesCHAPTER TWENTY-ONE Terrence P. Sherlock Burlington County College 2004

  2. => Acid Derivatives • All can be converted to the carboxylic acid by acidic or basic hydrolysis. • Esters and amides common in nature. Chapter 21

  3. benzyl formate benzyl methanoate => Naming Esters • Esters are named as alkyl carboxylates. • Alkyl from the alcohol, carboxylate from the carboxylic acid precursor. isobutyl acetate 2-methylpropyl ethanoate Chapter 21

  4. 4-hydroxy-2-methylpentanoic acid lactone -methyl--valerolactone => Cyclic Esters • Reaction of -OH and -COOH on same molecule produces a cyclic ester, lactone. • To name, add word lactone to the IUPAC acid name or replace the -ic acid of common name with -olactone. Chapter 21

  5. Bond angles around N are close to 120. => Amides • Product of the reaction of a carboxylic acid and ammonia or an amine. • Not basic because the lone pair on nitrogen is delocalized by resonance. Chapter 21

  6. Classes of Amides • 1 amide has one C-N bond (two N-H). • 2 amide or N-substituted amide has two C-N bonds (one N-H). • 3 amide or N,N-disubstituted amide has three C-N bonds (no N-H). => Chapter 21

  7. N-ethyl-N,2-dimethylpropanamide N-ethyl-N-methylisobutyramide => Naming Amides • For 1 amide, drop -ic or -oic acid from the carboxylic acid name, add -amide. • For 2 and 3 amides, the alkyl groups bonded to nitrogen are named with N- to indicate their position. Chapter 21

  8. 4-aminopentanoic acid lactam -valerolactam => Cyclic Amides • Reaction of -NH2 and -COOH on same molecule produces a cyclic amide, lactam. • To name, add word lactam to the IUPAC acid name or replace the -ic acid of common name with -olactam. Chapter 21

  9. => Nitriles • -CN can be hydrolyzed to carboxylic acid, so nitriles are acid derivatives. • Nitrogen is sp hybridized, lone pair tightly held, so not very basic. (pKb about 24). Chapter 21

  10. Naming Nitriles • For IUPAC names, add -nitrile to the alkane name. • Common names come from the carboxylic acid. Replace -ic acid with -onitrile. 5-bromohexanenitrile -bromocapronitrile Cyclohexanecarbonitrile => Chapter 21

  11. Acid Halides • More reactive than acids; the halogen withdraws e- density from carbonyl. • Named by replacing -ic acid with -yl halide. 3-bromobutanoyl bromide -bromobutyryl bromide => benzoyl chloride Chapter 21

  12. => Acid Anhydrides • Two molecules of acid combine with the loss of water to form the anhydride. • Anhydrides are more reactive than acids, but less reactive than acid chlorides. • A carboxylate ion is the leaving group in nucleophilic acyl substitution reactions. Chapter 21

  13. 1,2-benzenedicarboxylic anhydride phthalic anhydride => Naming Anhydrides • The word acid is replaced with anhydride. • For a mixed anhydride, name both acids. • Diacids may form anhydrides if a 5- or 6-membered ring is the product. ethanoic anhydride acetic anhydride Chapter 21

  14. ethyl o-cyanobenzoate => Multifunctional Compounds • The functional group with the highest priority determines the parent name. • Acid > ester > amide > nitrile > aldehyde > ketone > alcohol > amine > alkene > alkyne. Chapter 21

  15. m.p. 79C => Melting Points • Amides have very high melting points. • Melting points increase with increasing number of N-H bonds. m.p. -61C m.p. 28C Chapter 21

  16. Solubility • Acid chlorides and anhydrides are too reactive to be used with water or alcohol. • Esters, 3 amides, and nitriles are good polar aprotic solvents. • Solvents commonly used in organic reactions: • Ethyl acetate • Dimethylformamide (DMF) • Acetonitrile => Chapter 21

  17. IR Spectroscopy => => Chapter 21

  18. 1H NMR Spectroscopy => Chapter 21

  19. => Interconversion ofAcid Derivatives • Nucleophile adds to the carbonyl to form a tetrahedral intermediate. • Leaving group leaves and C=O regenerates. Chapter 21

  20. Reactivity Reactivity decreases as leaving group becomes more basic. => Chapter 21

  21. Interconversion of Derivatives More reactive derivatives can be converted to less reactive derivatives. => Chapter 21

  22. => Hydrolysis of Acid Chlorides and Anhydrides • Hydrolysis occurs quickly, even in moist air with no acid or base catalyst. • Reagents must be protected from moisture. Chapter 21

  23. => Acid Hydrolysis of Esters • Reverse of Fischer esterification. • Reaches equilibrium. • Use a large excess of water. Chapter 21

  24. Saponification • Base-catalyzed hydrolysis of ester. • “Saponification” means “soap-making.” • Soaps are made by heating NaOH with a fat (triester of glycerol) to produce the sodium salt of a fatty acid - a soap. • One example of a soap is sodium stearate, Na+ -OOC(CH2)16CH3. => Chapter 21

  25. => Hydrolysis of Amides Prolonged heating in 6 M HCl or 40% aqueous NaOH is required. Chapter 21

  26. => Hydrolysis of Nitriles • Under mild conditions, nitriles hydrolyze to an amide. • Heating with aqueous acid or base will hydrolyze a nitrile to an acid. Chapter 21

  27. => Reduction to Alcohols Lithium aluminum hydride reduces acids, acid chlorides, and esters to primary alcohols. Chapter 21

  28. => Reduction to Aldehydes Acid chlorides will react with a weaker reducing agent to yield an aldehyde. Chapter 21

  29. => Reduction to Amines • Lithium aluminum hydride reduces amides and nitriles to amines. • Nitriles and 1 amides reduce to 1 amines. • A 2 amide reduces to a 2 amine. • A 3 amide reduces to a 3 amine. Chapter 21

  30. Organometallic Reagents Grignard reagents and organolithium reagents add twice to acid chlorides and esters to give alcohols after protonation. => Chapter 21

  31. Grignard Reagentsand Nitriles A Grignard reagent or organolithium reagent attacks the cyano group to yield an imine which is hydrolyzed to a ketone. => Chapter 21

  32. => Acid Chloride Synthesis • Use thionyl chloride, SOCl2, or oxalyl chloride, (COCl)2. • Other products are gases. Chapter 21

  33. acid anhydride => Acid Chloride Reactions (1) acid ester amide Chapter 21

  34. acylbenzene => Acid Chloride Reactions (2) 3° alcohol ketone 1° alcohol aldehyde Chapter 21

  35. acylbenzene => Anhydride Reactions acid ester amide Chapter 21

  36. => Anhydride vs. Acid Chloride • Acetic anhydride is cheaper, gives a better yield than acetyl chloride. • Use acetic formic anhydride to produce formate esters and formamides. • Use cyclic anhydrides to produce a difunctional molecule. Chapter 21

  37. acid acid chloride acid anhydride => methyl ester Synthesis of Esters Chapter 21

  38. 3° alcohol => Reactions of Esters acid ester amide 1° alcohol Chapter 21

  39. => Lactones • Formation favored for five- and six-membered rings. • For larger rings, remove water to shift equilibrium toward products Chapter 21

  40. acid acid chloride acid anhydride ester => nitrile Synthesis of Amides Chapter 21

  41. nitrile => Reactions of Amides acid and amine amine 1° amine Chapter 21

  42. Lactam Formation • Five- and six-membered rings can be formed by heating - and -amino acids. • Smaller or larger rings do not form readily. => Chapter 21

  43. Amide  ester !! => -Lactams • Highly reactive, 4-membered ring. • Found in antibiotics isolated from fungi. Chapter 21

  44. 1° amide alkyl halide diazonium salt aldehyde or ketone cyanohydrin => Synthesis of Nitriles Chapter 21

  45. acid amide ketone => Reactions of Nitriles 1° amine Chapter 21

  46. => Thioesters More reactive than esters because: • -S-R is a better leaving group than -O-R • Resonance overlap is not as effective. Chapter 21

  47. => Carbonic Acid Esters • CO2 in water contains some H2CO3. • Diesters are stable. • Synthesized from phosgene. Chapter 21

  48. => Urea and Urethanes • Urea is the diamide of carbonic acid. • Urethanes are esters of a monoamide of carbonic acid. Chapter 21

  49. => Polymers • Polycarbonates are long-chain esters of carbonic acid. • Polyurethanes are formed when a diol reacts with a diisocyanate. Chapter 21


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