Chapter 10 Alcohols 1 - San Diego Miramar Collegefaculty.sdmiramar.edu/choeger/Chapter 10 Alcohols...
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Chapter 10Structure and Synthesis
of Alcohols
Chemistry 231MiramarFall 2007
Chapter 10: Alcohols Slide 10-2
Structure of Alcohols
• Hydroxyl (-OH) functional group• Oxygen is sp3 hybridized.
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Chapter 10: Alcohols Slide 10-3
Classification• Primary: carbon with –OH is bonded to one other carbon.• Secondary: carbon with –OH is bonded to two other carbons.• Tertiary: carbon with –OH is bonded to three other carbons.• Aromatic (phenol): –OH is bonded to a benzene ring
(technically, not an alcohol!).
NOTE: An alcohol does NOT have an OH bound to an sp2carbon!
Chapter 10: Alcohols Slide 10-4
IUPAC Nomenclature• Find the longest carbon chain containing the carbon with the -
OH group.• Drop the -e from the alkane name, add -ol.• Number the chain, starting from the end closest to the -OH
group.• Number and name all substituents.• Unsaturated alcohols: -OH takes priority
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Chapter 10: Alcohols Slide 10-5
Naming Priority
• Acids• Esters and Amides• Aldehydes• Ketones• Alcohols• Amines
• Alkenes• Alkynes• Alkanes• Ethers• Halides
Chapter 10: Alcohols Slide 10-6
Hydroxy Substituent• When -OH is part of a higher priority class of compound, it is
named as hydroxy.• Example:
also known as GHB
O
OH
HO
4-hydroxybutanoic acid!
"
#
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Chapter 10: Alcohols Slide 10-7
Common Names• Alcohol can be named as alkyl alcohol.• Useful only for small alkyl groups.• Examples:
isobutyl alcoholIsopropyl alcoholEthyl alcoholTert-butyl alcohol
Chapter 10: Alcohols Slide 10-8
Naming Diols• Two numbers are needed to locate the two
-OH groups.• Use -diol as suffix instead of -ol.
hexane-1,6- diol
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Chapter 10: Alcohols Slide 10-9
Glycols• 1, 2 diols (vicinal diols) are called glycols.• Common names for glycols use the name of the alkene from
which they were made.
ethane-1,2- diol
ethylene glycol
propane-1,2- diolpropylene glycol =>
Chapter 10: Alcohols Slide 10-10
Physical Properties• Unusually high boiling points due to hydrogen bonding
between molecules.• Small alcohols are miscible in water, but solubility decreases
as the size of the alkyl group increases.
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Chapter 10: Alcohols Slide 10-11
Boiling Points
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Chapter 10: Alcohols Slide 10-12
Solubility in Water
Solubility decreases as the size of the alkyl group increases.
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Chapter 10: Alcohols Slide 10-13
Methanol• “Wood alcohol”• Industrial production from synthesis gas• Common industrial solvent• Fuel at Indianapolis 500
Fire can be extinguished with waterHigh octane ratingLow emissionsBut, lower energy content Invisible flame =>
Chapter 10: Alcohols Slide 10-14
Ethanol
• Fermentation of sugar and starches in grains• 12-15% alcohol, then yeast cells die• Distillation produces “hard” liquors• Azeotrope: 95% ethanol, constant boiling• Denatured alcohol used as solvent• Gasahol: 10% ethanol in gasoline• Toxic dose: 200 mL ethanol, 100 mL methanol
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Chapter 10: Alcohols Slide 10-15
Acidity of Alcohols• pKa range: 15.5-18.0 (water: 15.7)• Acidity decreases as alkyl group increases.• Halogens increase the acidity.• Phenol is 100 million times more acidic than cyclohexanol!
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Chapter 10: Alcohols Slide 10-16
Table of Ka Values
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Chapter 10: Alcohols Slide 10-17
Formation of Alkoxide Ions
React methanol and ethanol with sodium metal or NaH (redoxreaction).
React less acidic alcohols with more reactive potassium or KH.
CH3CH2 OH + Na (s) CH3CH2 ONa + H2 (g)
(CH3)3C OH + K (s) (CH3)3C OK + H2 (g)
Chapter 10: Alcohols Slide 10-18
Formation of Phenoxide IonPhenol reacts with hydroxide ions to form phenoxide ions - no
redox is necessary.
O H+ OH
O
+ HOH
pKa = 10.0pKa = 15.7
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Chapter 10: Alcohols Slide 10-19
Synthesis (Review)• Nucleophilic substitution of OH- on alkyl halide• Hydration of alkenes
water in acid solution (not very effective)oxymercuration - demercurationhydroboration - oxidation
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Chapter 10: Alcohols Slide 10-20
Glycols (Review)• Syn hydroxylation of alkenes
osmium tetroxide, hydrogen peroxide cold, dilute, basic potassium permanganate
• Anti hydroxylation of alkenesperoxyacids, hydrolysis
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Chapter 10: Alcohols Slide 10-21
Organometallic Reagents• Carbon is bonded to a metal (Mg or Li).• Carbon is nucleophilic (partially negative).• It will attack a partially positive carbon.
C - XC = O
• A new carbon-carbon bond forms. =>
Chapter 10: Alcohols Slide 10-22
Grignard Reagents• Formula R-Mg-X (reacts like R:- +MgX)• Stabilized by anhydrous ether• Iodides most reactive• May be formed from any halide
primary secondary tertiaryvinyl aryl =>
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Chapter 10: Alcohols Slide 10-23
Some Grignard Reagents
Chapter 10: Alcohols Slide 10-24
Organolithium Reagents• Formula R-Li (reacts like R:- +Li)• Can be produced from alkyl, vinyl, or aryl halides, just like
Grignard reagents.• Ether not necessary, wide variety of solvents can be used.
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Chapter 10: Alcohols Slide 10-25
Reaction with Carbonyl• R:- attacks the partially positive carbon in the carbonyl.• The intermediate is an alkoxide ion.• Addition of water or dilute acid protonates the alkoxide to
produce an alcohol.
Chapter 10: Alcohols Slide 10-26
Synthesis of 1° AlcoholsGrignard + formaldehyde yields a primary alcohol with one
additional carbon. Reaction with ethylene oxide yields aprimary alcohol with TWO additional carbons:
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Chapter 10: Alcohols Slide 10-27
Synthesis of 2º AlcoholsGrignard + aldehyde yields a secondary alcohol.
Chapter 10: Alcohols Slide 10-28
Synthesis of 3º AlcoholsGrignard + ketone yields a tertiary alcohol.
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Chapter 10: Alcohols Slide 10-29
Grignard Reactions with Acid Chlorides and Esters
• Use two moles of Grignard reagent.• The product is a tertiary alcohol with
two identical alkyl groups.• Reaction with one mole of Grignard reagent produces a ketone
intermediate, which reacts with the second mole of Grignardreagent.
Chapter 10: Alcohols Slide 10-30
Grignard + Acid Chloride (1)
• Grignard attacks the carbonyl.• Chloride ion leaves.• Ketone intermediate
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Chapter 10: Alcohols Slide 10-31
Grignard and Ester (1)• Grignard attacks the carbonyl.• Alkoxide ion leaves! ? !
Chapter 10: Alcohols Slide 10-32
Second step of reaction• Second mole of Grignard reacts with the ketone intermediate
to form an alkoxide ion.• Alkoxide ion is protonated with dilute acid.
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Chapter 10: Alcohols Slide 10-33
Grignard Reagent + Ethylene Oxide
• Epoxides are unusually reactive ethers.• Product is a 1º alcohol with 2 additional carbons.
Chapter 10: Alcohols Slide 10-34
Limitations of Grignard• No water or other acidic protons like
O-H, N-H, S-H, or -C—C-H. Grignard reagent is destroyed,becomes an alkane.
• No other electrophilic multiple bonds, like C=N, C≡N, S=O,or N=O.
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Chapter 10: Alcohols Slide 10-35
Reduction of Carbonyl• Reduction of aldehyde yields 1º alcohol.• Reduction of ketone yields 2º alcohol.• Reagents:
Sodium borohydride, NaBH4
Lithium aluminum hydride, LiAlH4
Raney nickel
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Chapter 10: Alcohols Slide 10-36
Sodium Borohydride
• Hydride ion, H-, attacks the carbonyl carbon, forming analkoxide ion.
• Then the alkoxide ion is protonated by dilute acid.• Only reacts with carbonyl of aldehyde or ketone, not with
carbonyls of esters or carboxylic acids.
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Chapter 10: Alcohols Slide 10-37
Lithium Aluminum Hydride
• Stronger reducing agent than sodium borohydride, butdangerous to work with.
• Converts esters and acids to 1º alcohols.
Chapter 10: Alcohols Slide 10-38
Comparison ofReducing Agents
• LiAlH4 is stronger.• LiAlH4 reduces more stable
compounds which are resistantto reduction. =>
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Chapter 10: Alcohols Slide 10-39
Catalytic Hydrogenation• Add H2 with Raney nickel catalyst.• Also reduces any C=C bonds.
Chapter 10: Alcohols Slide 10-40
Thiols (Mercaptans)• Sulfur analogues of alcohols, -SH.• Named by adding -thiol to alkane name.• The -SH group is called mercapto.• Complex with heavy metals: Hg, As, Au.• More acidic than alcohols, react with NaOH to form thiolate
ion.• Stinks! =>
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Chapter 10: Alcohols Slide 10-41
Thiol SynthesisUse a large excess of sodium hydrosulfide with unhindered alkyl
halide to prevent dialkylation to R-S-R.
Chapter 10: Alcohols Slide 10-42
Thiol Oxidation• Easily oxidized to disulfides, an important feature of protein
structure.
• Vigorous oxidation with KMnO4, HNO3, or NaOClproduces sulfonic acids.
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Chapter 10: Alcohols Slide 10-43
End of Chapter 10