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Aldehydes & Ketones

Aldehydes & Ketones. In General. Fragrant odors Basic building block of housing materials Hormones Digestion Vision. In General. Carbonyl group C=O Aldehydes RCH=O Formyl Ketones RC=OR’. Nomenclature. Aldehydes IUPAC end in “al” Common end in “ aldeyde ”

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Aldehydes & Ketones

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  1. Aldehydes & Ketones

  2. In General • Fragrant odors • Basic building block of housing materials • Hormones • Digestion • Vision

  3. In General • Carbonyl group • C=O • Aldehydes • RCH=O • Formyl • Ketones • RC=OR’

  4. Nomenclature • Aldehydes • IUPAC end in “al” • Common end in “aldeyde” • Carbonyl C is always #1 • Cyclic cpds • Carbaldehyde is ending for most

  5. Nomenclature • Aldehydes methanal (formaldehyde) ethanal (acetaldehyde) propanal (propionaldehyde) butanal (n-butyraldehyde)

  6. Nomenclature • Aldehydes 3-methylbutanal 3-butenal 2,3-dihydropropanal (glyceraldehyde)

  7. Nomenclature • Aldehydes cyclopentanecarbaldehyde (formylcyclopentane) benzenecarbaldehyde (benzaldehyde) 2-hydroxybenzenecarbaldehyde (salicylaldehyde)

  8. Nomenclature • Ketones • IUPAC end in “one” • Common end in “ketone” • Carbonyl C is never #1, but always gets low number preference • Cyclic cpds • Carbaldehyde is ending for most

  9. Nomenclature • Ketones propanone (acetone) 2-butanone (ethyl methyl ketone) 3-pentanone (diethylketone)

  10. Nomenclature • Ketones cyclohexanone 2-methylcyclopentanone 3- buten-2-one (methyl vinyl ketone)

  11. Nomenclature • Ketones acetaphenone (methyl phenyl ketone) benzophenone (diphenyl ketone) dicyclopropylketone

  12. Common Aldehydes & Ketones • Formaldehyde • Simplest aldehyde • Manufactured on large scale (8 billion lbs per annum) from catalyzed oxidation of methanol CH3OH CH2=O + H2 • Gas at RT (bp = -21˚C) but cannot be stored in free state due to polymerization • Normally 37% soln called formalin (preservative) • Most used in making of plastics, insulation, particle board, and plywood

  13. Common Aldehydes & Ketones • Acetaldehyde • Boils close to RT (bp = 20˚C) • Made by catalyzed oxidation of ethylene 2 CH2=CH2 + O2 2 CH3CH=O • ~1/2 is oxidized to acetic acid • Remainder used for production of 1- butanol and others.

  14. Common Aldehydes & Ketones • Acetone • Simplest ketone • Large scale production like formaldehyde • Produced from oxidation of propene, isopropyl alcohol, or isopropylbenzene • ~30% used directly, great solvent, H2O miscible • Rest used to make stuff like epoxy resins

  15. Common Aldehydes & Ketones • Quinones • Cyclic conjugate diketones • Simplest is 1,4-benzoquinone • All are colored and are thus used often as dyes • Alizarin…used to dye the red coats of the British Army during American Revolution • Vitamin K is required for normal clotting of blood

  16. Common Aldehydes & Ketones 1,4-benzoquinone alizarin Vitamin K vitamin K

  17. Synthesis of Aldehydes & Ketones • Oxidation • 1˚ ROH gives aldehyde • 2˚ ROH gives ketone • Cr reagents (PCC) are common

  18. Synthesis of Aldehydes & Ketones • Friedel-Crafts Acylation • Recall the rxn? • Makes aromatic ketones benzyl chloride benzophenone

  19. Synthesis of Aldehydes & Ketones • Hydration of terminal alkynes • Gives methyl ketones • Catalyzed by acid and mercuric ion

  20. Aldehydes & Ketones in Nature • Many have pleasant odors • Used in the perfume industry • Extremely expensive to gather from natural producers • Chanel No. 5 (my mom’s fave perfume) was first perfume to use synthetic organic chemicals in 1921

  21. Aldehydes & Ketones in Nature benzaldehyde cinnamaldehyde vanillin

  22. The Carbonyl Group • C atom is sp2 hybridized • Bond angles? • C=O bond length is 1.24Å (compared to 1.43Å for C-O in ROH and ROR • O is more EN than C • Makes a polar bond

  23. The Carbonyl Group • Most carbonyl reactions are nucleophilic attacks on the carbonyl C • C=C usually is attacked by an electrophile • Due to polarization, physical properties differ from HC’s and ROH’s • bp’s are higher than HC’s, lower than ROH’s

  24. The Carbonyl Group • C=O is permanently polarized • Positive part of one molecule is attracted to negative part of another molecule • Dipole-dipole forces, weaker than H-bonds, stronger than LDF

  25. The Carbonyl Group • C=O’s with low MW are soluble in water • Can form H-bonds with water or ammonia

  26. An Overview of Nucleophilic Addition to Carbonyl Groups • Why does the attack occur? • If rxn occurs in hyroxylic solvent (water or ROH), a proton is usually added to the O

  27. An Overview of Nucleophilic Addition to Carbonyl Groups • Carbonyl cpds are weak Lewis bases due to lone pairs on O • Acids can catalyze the addition of weak nucleophiles to carbonyl cpds through protonation

  28. An Overview of Nucleophilic Addition to Carbonyl Groups • Nucleophiles add reversibly • Good leaving groups, CB of SA • Nucleophiles add irreversibly • Poor LG, CB of WA • In general, ketones are less reactive than aldehydes • Steric…sp2 v. sp3, R v. H • Electronic…alkyl groups are electron-donating…ketones have two

  29. Addition of Alcohols: Formation of Hemiacetals and Acetals • Alcohols are oxygen nucleophiles • OR goes to C, and H goes to O • Because ROH’s are weak nucleophiles, acid catalyst must be used • Product is a hemiacetal • Contains both alcohol and ether on same C • Addition is reversible

  30. Addition of Alcohols: Formation of Hemiacetals and Acetals • Mechanism of hemiacetal formation has 3 steps • Carbonyl O is protonated by acid catalyst • ROH’s O then attacks carbonyl C • Proton is then lost from resulting +O • Each step is reversible

  31. Do You Get It? • Write an equation for the formation of a hemiacetal from acetaldehyde, ethanol, and an acid catalyst. Show each step in the rxn mechanism.

  32. Addition of Alchols: Formation of Hemiacetals and Acetals • Excess ROH means hemiacetals react further to produce acetals • Hydroxyl group of hemiacetal is replaced by an alkoxyl group. • Acetals have two ether groups on same C

  33. Addition of Alchols: Formation of Hemiacetals and Acetals • Mechanism of acetal formation

  34. Addition of Alchols: Formation of Hemiacetals and Acetals • Mechanism of acetal formation

  35. Addition of Alchols: Formation of Hemiacetals and Acetals • Aldehydes that have appropriately located hydroxyl group can exist in equilibrium with a cyclic hemiacetal…5-hydroxypetanal

  36. Addition of Alchols: Formation of Hemiacetals and Acetals • Aldehydes that have appropriately located hydroxyl group can exist in equilibrium with a cyclic hemiacetal…5-hydroxypetanal

  37. Addition of Alchols: Formation of Hemiacetals and Acetals • Cpds with hydroxyl group 4 or 5 C’s from the aldehyde group tend to form cyclic hemiacetals and acetals due to lack of strain • Carbohydrates

  38. Addition of Alchols: Formation of Hemiacetals and Acetals • Ketones also form acetals • If a glycol is used, product is cyclic

  39. Addition of Alchols: Formation of Hemiacetals and Acetals • Summary • Aldehyde or ketone reacts with ROH • Hemiacetal is formed • Further ROH makes acetal

  40. Addition of Water: Hydration of Aldehydes and Ketones • Water is an oxygen nucleophile, like ROH’s • Can add reversibly

  41. Addition of Water: Hydration of Aldehydes and Ketones • Aside from formaldehyde hydrate most other hydrates cannot by isolated because they lost water…Keq<1 • One exception is trichloroacetaldehyde (chloral) • Forms a stable crystalline hydrate, chloral hydrate, CCl3CH(OH)2 • Used as a sedative

  42. Addition of Grignard Reagents and Acetylides • Grignard reagents act as carbon nucleophiles toward carbonyl cpds • Grignard reagent adds irreversibly to the carbonyl carbon, forming a new C-C bond • Favorable because product (an alkoxide) is a much weaker base than the starting carbanion • The alkoxide can be protonated to give an ROH

  43. Addition of Grignard Reagents and Acetylides • Useful route to alcohols • Type of carbonyl determines class of ROH • Formaldehyde gives 1˚ ROH’s

  44. Addition of Grignard Reagents and Acetylides • Other aldehydes give 2˚ ROH’s

  45. Addition of Grignard Reagents and Acetylides • Ketones give 3˚ ROH’s

  46. Addition of Grignard Reagents and Acetylides • Other organometallic cpds like organolithiumcpds and aceylides react with carbonyl cpds similarly to Grignard reagents

  47. Addition of Hydrogen Cyanide: Cyanohydrins • HCN adds reversibly to carbonyl group of aldehydes and ketones to make cyanohydrins • Hydroxyl and cyano group attached to same C • Basic catalyst is needed

  48. Addition of Hydrogen Cyanide: Cyanohydrins • Acetone reacts as follows:

  49. Addition of Hydrogen Cyanide: Cyanohydrins • Cyanohydrins play important role in the defense system of the millipede • Two-chambered gland like the bombadier beetle • Benzaldehyde cyanohydrin is stored and then converted to a mixture of benzadehyde and hydrogen cyanide and secreted

  50. Addition of Hydrogen Cyanide: Cyanohydrins • Write an equation for the addition of HCN to benzaldehyde.

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