Alcohols

2

Structure of Water and Methanol

• Oxygen is sp3 hybridized and tetrahedral.• The H—O—H angle in water is 104.5°. • The C—O—H angle in methyl alcohol is 108.9°.

3

Classification of Alcohols• 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.

4

Examples of Classifications

CH3 C

CH3

CH3

OH*

CH3 CH

OH

CH2CH3*CH3 CH

CH3

CH2OH*

Primary alcohol Secondary alcohol

Tertiary alcohol

5

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 giving the —OH group the

lowest number possible.• Number and name all substituents and write

them in alphabetical order.

6

Examples of Nomenclature

2-methyl-1-propanol2-methylpropan-1-ol

2-methyl-2-propanol2-methylpropan-2-ol

2-butanolbutan-2-ol

CH3 C

CH3

CH3

OH

CH3 CH

CH3

CH2OH CH3 CH

OH

CH2CH33 2 1 1 2 3 4

2 1

7

Alkenols (Enols)• Hydroxyl group takes precedence. Assign the carbon

with the —OH the lowest number.• End the name in –ol, but also specify that there is a

double bond by using the ending –ene before -ol

4-penten-2-ol pent-4-ene-2-ol

CH2 CHCH2CHCH3

OH

5 4 3 2 1

8

Naming Priority1. Acids2. Esters3. Aldehydes4. Ketones5. Alcohols6. Amines 7. Alkenes8. Alkynes9. Alkanes10. Ethers11. Halides

Highest ranking

Lowest ranking

9

Hydroxy Substituent• When —OH is part of a higher priority class of

compound, it is named as hydroxy.

4-hydroxybutanoic acidalso known as -hydroxybutyric acid (GHB)

C H2C H2C H2C OOH

OHcarboxylic acid

4 3 2 1

10

Common Names• Alcohol can be named as alkyl alcohol.• Useful only for small alkyl groups.

isobutyl alcohol sec-butyl alcohol

CH3 CH

CH3

CH2OH CH3 CH

OH

CH2CH3

11

Naming Diols• Two numbers are needed to locate the two

—OH groups.• Use -diol as suffix instead of -ol.

hexane-1,6- diol 1 2 3 4 5 6

OHOH

12

Glycols• 1, 2-diols (vicinal diols) are called glycols.• Common names for glycols use the name of the alkene

from which they were made.

OHOH

ethane-1,2- diolethylene glycol propane-1,2- diol

propylene glycol

OHOH

13

Phenol Nomenclature• —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-chlorophenol(meta-chlorophenol)

4-methylphenol(para-cresol)

OH

Cl

OH

H3C

14

Give the systematic (IUPAC) name for the following alcohol.

The longest chain contains six carbon atoms, but it does not contain the carbon bonded to the hydroxyl group. The longest chain containing the carbon bonded to the —OH group is the one outlined by the green box, containing five carbon atoms. This chain is numbered from right to left in order to give the hydroxyl-bearing carbon atom the lowest possible number.

The correct name for this compound is 3-(iodomethyl)-2-isopropylpentan-1-ol.

Solved Problem 1

Solution

15

Physical Properties• Alcohols have 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.

16

Boiling Points of alcohols

• Alcohols have higher boiling points than ethers and alkanes because alcohols can form hydrogen bonds.

• The stronger interaction between alcohol molecules will require more energy to break them resulting in a higher boiling point.

17

Solubility in Water

Small alcohols are miscible in water, but solubility decreases as the size of the alkyl group increases.

18

Methanol

• “Wood alcohol”• Industrial production from synthesis gas• Common industrial solvent• Toxic Dose: 100 mL methanol• Used as fuel at Indianapolis 500

– Fire can be extinguished with water– High octane rating– Low emissions– Lower energy content– Invisible flame

19

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

20

Formation of Alkoxide Ions

• Ethanol reacts with sodium metal to form sodium ethoxide (NaOCH2CH3), a strong base commonly used for elimination reactions.

• More hindered alcohols like 2-propanol or tert-butanol react faster with potassium than with sodium.

21

Formation of Phenoxide Ion

The aromatic alcohol phenol is more acidic than aliphatic alcohols due to the ability of aromatic rings to delocalize the negative charge of the oxygen within the carbons of the ring.

22

Synthesis of Alcohols (Review)• Alcohols can be synthesized by nucleophilic

substitution of alkyl halide.• Hydration of alkenes also produce alcohols:

– Water in acid solution (suffers from rearragements)

– Oxymercuration–demercuration– Hydroboration–oxidation

Chapter 10 23

Synthesis of Alcohols (Review)

• Alcohols can be synthesized by nucleophilic substitution of alkyl halide.

• Hydration of alkenes also produce alcohols:

Chapter 10 24

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

Chapter 10 25

Sodium Borohydride

• NaBH4 is a source of hydrides (H-)• Hydride 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.

Chapter 10 26

Lithium Aluminum Hydride

• LiAlH4 is source of hydrides (H-)• Stronger reducing agent than sodium

borohydride, but dangerous to work with.• Reduces ketones and aldehydes into the

corresponding alcohol.• Converts esters and carboxylic acids to 1º

alcohols.

Chapter 10 27

Reducing Agents• NaBH4 can reduce

aldehydes and ketones but not esters and carboxylic acids.

• LiAlH4 is a stronger reducing agent and will reduce all carbonyls.

Chapter 10 28

Catalytic Hydrogenation

• Raney nickel is a hydrogen rich nickel powder that is more reactive than Pd or Pt catalysts.

• This reaction is not commonly used because it will also reduce double and triple bonds that may be present in the molecule.

• Hydride reagents are more selective so they are used more frequently for carbonyl reductions.

Chapter 11 29

Alcohol Reactions

• Dehydration to alkene• Oxidation to aldehyde, ketone• Substitution to form alkyl halide• Reduction to alkane• Esterification• Williamson synthesis of ether

Chapter 11 30

Summary Table

Chapter 11 31

Oxidation States

• Easy for inorganic salts (reduced, organic oxidized)– CrO4

2- reduced to Cr2O3

– KMnO4 reduced to MnO2

• Oxidation: loss of H2, gain of O, O2, or X2

• Reduction: gain of H2 or H-, loss of O, O2, or X2

• Neither: gain or loss of H+, H2O, HX

Chapter 11 32

1º, 2º, 3º Carbons

Chapter 11 33

Oxidation of 2° Alcohols• 2° alcohol becomes a ketone• Reagent is Na2Cr2O7/H2SO4 = H2CrO4

• Active reagent probably H2CrO4

• Color change: orange to greenish-blue

CH3CHCH2CH3

OHNa2Cr2O7 / H2SO4

CH3CCH2CH3

O

=>

Chapter 11 34

Oxidation of 1° Alcohols• 1° alcohol to aldehyde to carboxylic acid• Difficult to stop at aldehyde• Use pyridinium chlorochromate (PCC) to

limit the oxidation.• PCC can also be used to oxidize 2° alcohols

to ketones.

CH3CH2CH2CH2

OH N H CrO3Cl

CH3CH2CH2CH

O

Chapter 11 35

3° Alcohols Don’t Oxidize• Cannot lose 2 H’s• Basis for chromic acid test

Chapter 11 36

Reduction of Alcohols

• Dehydrate with conc. H2SO4, then add H2

CH3CHCH3

OHH2SO4

CH2 CHCH3H2

PtCH3CH2CH3

alcohol alkene alkane

Chapter 11 37

Reaction with HBr• -OH of alcohol is protonated• -OH2

+ is good leaving group

• 3° and 2° alcohols react with Br- via SN1

• 1° alcohols react via SN2

H3O+

Br-

R O H R O H

H

R Br

Chapter 11 38

Reaction with HCl• Chloride is a weaker nucleophile than

bromide.• Add ZnCl2, which bonds strongly with

-OH, to promote the reaction.• The chloride product is insoluble.• Lucas test: ZnCl2 in conc. HCl

– 1° alcohols react slowly or not at all.– 2 alcohols react in 1-5 minutes.– 3 alcohols react in less than 1 minute.

Chapter 11 39

Dehydration Reactions• Conc. H2SO4 (or H3PO4) produces alkene

• Carbocation intermediate• Zaitsev product• Bimolecular dehydration produces ether• Low temp, 140°C and below, favors ether• High temp, 180°C and above, favors alkene

Chapter 11 40

Esterification• Fischer: alcohol + carboxylic acid• Nitrate esters• Phosphate esters

Chapter 11 41

Fischer Esterification

• Acid + Alcohol yields Ester + Water• Sulfuric acid is a catalyst.• Each step is reversible.

CH3 C OH

O

+ CH2CH2CHCH3

CH3

OHH

+

CH3C

O

OCH2CH2CHCH3

CH3

+ HOH

End Alcohols