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

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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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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

  50. POWER POINT IMAGES FROM “ORGANIC CHEMISTRY, 5TH EDITION”L.G. WADEALL MATERIALS USED WITH PERMISSION OF AUTHORPRESENTATION ADAPTED FOR BURLINGTON COUNTY COLLEGEORGANIC CHEMISTRY COURSEBY:ANNALICIA POEHLER STEFANIE LAYMAN CALY MARTIN Chapter 21