chapter 10 structure and synthesis of alcohols
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Organic Chemistry , 6 th Edition L. G. Wade, Jr. Chapter 10 Structure and Synthesis of Alcohols. Structure of Alcohols. Hydroxyl (-OH) functional group Oxygen is sp 3 hybridized. Classification. Primary: carbon with –OH is bonded to one other carbon. - PowerPoint PPT PresentationTRANSCRIPT
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Chapter 10Structure and Synthesis
of Alcohols
Organic Chemistry, 6th EditionL. G. Wade, Jr.
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Chapter 10 2
Structure of Alcohols
• Hydroxyl (-OH) functional group• Oxygen is sp3 hybridized.
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Chapter 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.
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Chapter 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.
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Chapter 10 5
Unsaturated Alcohols
• Hydroxyl group takes precedence. Assign that carbon the lowest number.
• Use alkene or alkyne name.
4-penten-2-ol pent-4-ene-2-ol
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Chapter 10 6
Naming Priority
• Acids• Esters• Aldehydes• Ketones• Alcohols• Amines
• Alkenes• Alkynes• Alkanes• Ethers• Halides
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Chapter 10 7
Hydroxy Substituent
• When -OH is part of a higher priority class of compound, it is named as hydroxy.
• Example:
4-hydroxybutanoic acid
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Chapter 10 8
Common Names
• Alcohol can be named as alkyl alcohol.• Useful only for small alkyl groups.• Examples:
isobutyl alcohol sec-butyl alcohol
=>
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Chapter 10 9
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 10
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 glycolpropane-1,2- diol
propylene glycol
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Chapter 10 11
Naming Phenols
• -OH group is assumed to be on carbon 1.• For common names of disubstituted phenols,
use ortho- for 1,2; meta- for 1,3; and para- for 1,4.
• Methyl phenols are cresols.
3-chlorophenolmeta-chlorophenol
4-methylphenolpara-cresol
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Chapter 10 12
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 13
Boiling Points
=>
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Chapter 10 14
Solubility in Water
Solubility decreases as the size of the alkyl group increases.
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Chapter 10 15
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 contentInvisible flame
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Chapter 10 16
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 17
2-Propanol
• “Rubbing alcohol”• Catalytic hydration of propene
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Chapter 10 18
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 19
Table of Ka Values
=>
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Chapter 10 20
Formation of Alkoxide Ions
React methanol and ethanol with sodium metal (redox reaction).
React less acidic alcohols with more reactive potassium.
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Chapter 10 21
Formation of Phenoxide Ion
Phenol reacts with hydroxide ions to form phenoxide ions - no redox is necessary.
O H+ OH
O
+ HOH
pK a = 10.0pK a = 15.7
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Chapter 10 22
Synthesis (Review)
• Nucleophilic substitution of OH- on alkyl halide
• Hydration of alkeneswater in acid solution (not very effective)oxymercuration - demercurationhydroboration - oxidation
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Chapter 10 23
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.
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Chapter 10 24
Grignard Reagents
• Formula R-Mg-X (reacts like R:- +MgX)• Stabilized by anhydrous ether• Iodides most reactive• May be formed from any halide
primarysecondarytertiaryvinylaryl
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Chapter 10 25
Some Grignard Reagents
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Chapter 10 26
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 27
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.
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Chapter 10 28
Synthesis of 1° Alcohols
Grignard + formaldehyde yields a primary alcohol with one additional carbon.
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Chapter 10 29
Synthesis of 2º AlcoholsGrignard + aldehyde yields a secondary
alcohol.
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Chapter 10 30
Synthesis of 3º Alcohols
Grignard + ketone yields a tertiary alcohol.
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Chapter 10 31
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 Grignard reagent. =>
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Chapter 10 32
Grignard + Acid Chloride (1)
• Grignard attacks the carbonyl.• Chloride ion leaves.
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Chapter 10 33
Grignard and Ester• Grignard attacks the carbonyl.• Alkoxide ion leaves! ? !
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Chapter 10 34
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 35
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, CN, S=O, or N=O.
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Chapter 10 36
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 37
Sodium Borohydride• Hydride ion, H-, attacks the carbonyl
carbon, forming an alkoxide 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 38
Lithium Aluminum Hydride
• Stronger reducing agent than sodium borohydride, but dangerous to work with.
• Converts esters and acids to 1º alcohols.
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Chapter 10 39
Comparison of Reducing Agents
• LiAlH4 is stronger.
• LiAlH4 reduces more stable compounds which are resistant to reduction. =>
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Chapter 10 40
Catalytic Hydrogenation
• Add H2 with Raney nickel catalyst.• Also reduces any C=C bonds.
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Chapter 10 41
End of Chapter 10