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Unit 6

Unit 6. Alcohols and Ethers. Alcohols. Nomenclature Physical Properties Synthesis Reactions. Alcohols. contain at least one C-OH bond. are similar in structure to water (an alkyl group replaces one of the H’s in water). The C bonded to the -OH is called the carbinol C atom.

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Unit 6

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  1. Unit 6 Alcohols and Ethers

  2. Alcohols Nomenclature Physical Properties Synthesis Reactions

  3. Alcohols • contain at least one C-OH bond. • are similar in structure to water (an alkyl group replaces one of the H’s in water). • The C bonded to the -OH is called the carbinol C atom.

  4. Nomenclature of Alcohols methyl alcohol 2° alcohol phenol 1° alcohol 3° alcohol

  5. Nomenclature of Alcohols • Apply the same rules you learned for the alkanes. • Use the root name of the longest chain containing the hydroxyl group, but change -e to -ol. IUPAC: butan-1-ol1-butanol common: n-butyl alcohol IUPAC: methanol common: methyl alcohol

  6. Nomenclature of Alcohols • Number the longest C chain containing the -OH, starting at the end nearer the -OH, and use the appropriate number to indicate the position of the -OH. IUPAC: 6-bromoheptan-3-ol6-bromo-3-heptanol

  7. Nomenclature of Alcohols • With a cyclic alcohol, the -OH is assumed to be on the #1 C. IUPAC: 2-methylcyclohexanol

  8. Nomenclature of Alcohols • Priority: The alcohol is the highest priority functional group of the ones we have studied so far: • Alcohols • Amines • Alkenes • Alkynes • Alkanes • Ethers • Halides

  9. Nomenclature of Alcohols IUPAC: (E)-hept-5-en-3-oltrans-5-hepten-3-ol IUPAC: cyclohex-2-en-1-ol

  10. Nomenclature of Alcohols • An alcohol group that is a substituent is called “hydroxy”. IUPAC: 2-hydroxybutanoic acid

  11. Nomenclature of Alcohols • Alcohols with two -OH groups are diols. • Vicinal diols are called glycols. IUPAC: propane-1,2-diol common: propylene glycol IUPAC: 4-cyclopentylheptane-3,5-diol. Note the “e.”

  12. Nomenclature of Thiols • A thiol is an organic compound with an -SH group, the sulfur analog of an alcohol. • aka a mercaptan IUPAC: 4-cyclopentylheptane-3-thiol

  13. Nomenclature of Phenols IUPAC: 3-bromophenol common: meta-bromophenol IUPAC: 2-bromophenol common: ortho-bromophenol IUPAC: 4-bromophenol common: para-bromophenol

  14. Nomenclature of Phenols IUPAC: benzene-1,3-diol common: resorcinol IUPAC: benzene-1,4-diol common: hydroquinone IUPAC: benzene-1,2-diol common: catechol

  15. Nomenclature of Alcohols • Give IUPAC acceptable names. 3-(iodomethyl)-2-isopropylpentan-1-ol (1R,3R)-3-(2-hydroxyethyl)cyclopentanol (Z)-4-chlorobut-3-en-2-ol

  16. IR spectrum of alcohol with hydrogen bonding Cyclohexanol, neat SDBSWeb : http://riodb01.ibase.aist.go.jp/sdbs/ (National Institute of Advanced Industrial Science and Technology, 10/16/11)

  17. IR spectrum of alcohol with very little hydrogen bonding Cyclohexanol in CCl4 SDBSWeb : http://riodb01.ibase.aist.go.jp/sdbs/ (National Institute of Advanced Industrial Science and Technology, 9/3/11)

  18. Physical Properties of Alcohols • The -OH group is polar and forms a hydrogen bond. • The boiling points of alcohols are high: Most of the common alcohols up to C11 or C12 are liquids at room temperature. • The short-chain alcohols are miscible with water.

  19. Physical Properties of Alcohols • BP increases with the amount of H-bonding. • 1-propanol bp = 97°C • 1,2-propanediol bp = 188°C • propylene glycol • 1,2,3-propanetriol bp = 290° • glycerol

  20. Physical Properties of Alcohols • The alkyl part of the alcohol is nonpolar. • As the carbon chain gets longer, alcohols become more suitable for dissolving nonpolar compounds. • As the carbon chain gets longer, alcohols become less soluble in water. • Rule of thumb: One -OH can carry 4 carbon atoms into solution.

  21. Physical Properties of Alcohols • Like water, the -OH group in an alcohol can act as an acid and lose H+. Lower pKa, more acidic. Higher Ka, more acidic.

  22. Physical Properties of Alcohols

  23. Physical Properties of Alcohols • As the previous slide shows, alcohols are weak acids. • Only phenols react with NaOH to lose the H+. • Other alcohols require a much stronger base before they lose their acid H+.

  24. Physical Properties of Alcohols • Acidity increases with the ability to pull electrons away from C-O-. • e- withdrawing groups stabilize anions (e- donating groups stabilize carbocations) pKa=15.9 pKa=14.3 pKa=12.2 pKa=10.0

  25. Physical Properties of Alcohols • Phenols are the most acidic alcohols because resonance stabilizes the conjugate bases. • …can you draw the resonance-stabilized forms of the phenoxide ion?

  26. Synthesis of Alcohols - Review • from SN2 of -OH with alkyl halides • from alkenes • acid-catalyzed hydration • oxymercuration-demercuration • hydroboration-oxidation • hydroxylation (1,2-diols) • from addition of acetylides to carbonyl compounds

  27. Synthesis of Alcohols - New • industrial preparation of methanol and ethanol • from addition of organometallic reagents to carbonyl compounds • from reduction of carbonyl compounds

  28. Synthesis of Alcohols - Review • from SN2 of -OH with alkyl halides (e.g., NaOH in acetone)   inversion of configuration

  29. Synthesis of Alcohols - Review • from alkenes • acid-catalyzed hydration Markovnikov product

  30. Synthesis of Alcohols - Review • from alkenes • oxymercuration-demercuration Markovnikov product anti addition

  31. Synthesis of Alcohols - Review • from alkenes • hydroboration-oxidation syn addition

  32. Synthesis of Alcohols - Review • from alkenes - syn hydroxylation to make vicinal diols • cold, dilute KMnO4 in base or OsO4/H2O2

  33. Synthesis of Alcohols - Review • from alkenes - anti hydroxylation to make vicinal diols • step 1: make the epoxide • CH3CO3H (goes straight to diol) • MCPBA • step 2: acidify

  34. Synthesis of Alcohols - Review • from addition of acetylides to carbonyl compounds

  35. Industrial Synthesis of Methanol • widely used solvent and fuel • Prepared from synthesis gas • 3C(coal) + 4H2O  CO2 + 2CO + 4H2 • Preparation requires a temperature of 300-400°C, H2 pressure of 200-300 atm, and a CuO-ZnO/Al2O3 catalyst: • CO(g) + 2H2 (g) CH3OH Δ

  36. Industrial Synthesis of Ethanol • Solvent and fuel - The pure form is subject to expensive taxes. • Denatured alcohol contains impurities that render it undrinkable. • Prepared from ethylene: • H2C=CH2(g)+ H2O CH3CH2OH • Preparation requires a temperature of 300°C, an H2O pressure of 100-300 atm, and a catalyst (phosphoric acid adsorbed onto diatomaceous earth).

  37. Synthesis of Alcohols - New • from addition of organometallic reagents to carbonyl compounds • formaldehyde • aldehydes • ketones • esters and acid chlorides • epoxides • In every case, the C chain is lengthened.

  38. Organometallic Compounds • contain a covalent bond between C and a metal atom. • Grignard reagents (R-MgX) • organolithium reagents (R-Li) • contain a nucleophilicC. • Grignard reagents act like R:-+MgX • organolithium reagents act like R:-Li+

  39. Organometallic Compounds • contain a nucleophilicC. • We’ve already encountered a nucleophilic C…in the acetylides. • Sodium amide can deprotonate a terminal alkyne, but not an alkene or an alkane. • To make an alkane or an alkene act as a nucleophile, convert it into an organometallic compound.

  40. Organometallic Compounds • Grignard reagents are made from an alkyl halide and Mg in ether. • Ether is needed to dissolve the Grignard reagent. CH3I + Mg CH3MgI Careful: Water destroys the Grignard reagent! diethyl ether methylmagnesium iodide

  41. Organometallic Compounds • Organolithium reagents are made from an alkyl halide and Li in an ether or an alkane. CH3CH2Br + 2Li CH3CH2Li + LiBr Careful: Water destroys the organolithium reagent! ether or alkane ethyllithium

  42. Organometallic Compounds CH3CH2Li + H2O CH3CH3 + LiOH Careful: Water destroys the organolithium reagent! ethyllithium

  43. Synthesis of Alcohols - New • from addition of organometallic reagents to formaldehyde Step 1: Why can’t step 2 be combined with step 1? Step 2:

  44. Synthesis of Alcohols - New • from addition of organometallic reagents to aldehydes

  45. Synthesis of Alcohols - New • from addition of organometallic reagents to ketones

  46. Synthesis of Alcohols - New • from addition of organometallic reagents to esters and acid chlorides to make 3° alcohols with two identical groups. • Two (2) moles of the reagent are needed.

  47. Synthesis of Alcohols - New • Two (2) moles of the reagent are needed. Why? • Acid chlorides: Cl- is a good LG, and so, with one mole of the Grignard, a ketone forms. The ketone can be attacked by a second mole of the Grignard reagent. • Esters: Now the LG is RO-, not usually considered “good,” but the reaction takes place in ether, not water. RO- is a weaker base than R:-.

  48. Synthesis of Alcohols - New • from addition of organometallic reagents to epoxides • Grignard reagents will NOT react with ethers, which is why ether is the solvent. • The reagent attacks the less hindered (less substituted) C of the epoxide.

  49. Side Reactions of Organometallic Reagents • Grignard reagents and organolithium compounds are strong bases and strong nucleophiles. • They react immediately and irreversibly with water… and any other compound that can protonate a strong base. • O-H, N-H, S-H, -C≡C-H • Grignard reagents cannot contain the following unprotected groups, as they will be attacked: • C=O, C=N, C≡N, N=O.

  50. Side Reactions of Organometallic Reagents • Water is a poison to these reagents: CH3CH2MgBr + H-O-H  CH3CH3(g) + BrMgOH • HOCH2CH2CH2CH2Br + 2Li do NOT produceHOCH2CH2CH2CH2Li. The H from the –OH reacts immediately: HOCH2CH2CH2CH2Br + 2Li  Li+ -OCH2CH2CH2CH3 + LiBr

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