Chapter 10 Structure and Synthesis of Alcohols

Chapter 10Structure and Synthesis

of Alcohols

Organic Chemistry, 6th EditionL. G. Wade, Jr.

Chapter 10 2

Structure of Alcohols

• Hydroxyl (-OH) functional group• Oxygen is sp3 hybridized.

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.

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.

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

Chapter 10 6

Naming Priority

• Acids• Esters• Aldehydes• Ketones• Alcohols• Amines

• Alkenes• Alkynes• Alkanes• Ethers• Halides

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

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

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

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-chlorophenol

meta-chlorophenol

4-methylphenolpara-cresol

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.

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.

Chapter 10 15

Methanol• “Wood alcohol”

• Industrial production from synthesis gas

• Common industrial solvent

• Fuel at Indianapolis 500Fire can be extinguished with waterHigh octane ratingLow emissionsBut, lower energy contentInvisible flame

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

Chapter 10 17

2-Propanol

• “Rubbing alcohol”

• Catalytic hydration of propene

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!

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.

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

Chapter 10 22

Synthesis (Review)

• Nucleophilic substitution of OH- on alkyl halide

• Hydration of alkeneswater in acid solution (not very effective)oxymercuration - demercurationhydroboration - oxidation

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.

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

Chapter 10 25

Some Grignard Reagents

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.

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.

Chapter 10 28

Synthesis of 1° Alcohols

Grignard + formaldehyde yields a primary alcohol with one additional carbon.

Chapter 10 29

Synthesis of 2º Alcohols

Grignard + aldehyde yields a secondary alcohol.

Chapter 10 30

Synthesis of 3º Alcohols

Grignard + ketone yields a tertiary alcohol.

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. =>

Chapter 10 32

Grignard + Acid Chloride (1)

• Grignard attacks the carbonyl.• Chloride ion leaves.

Chapter 10 33

Grignard and Ester

• Grignard attacks the carbonyl.

• Alkoxide ion leaves! ? !

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.

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.

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

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.

Chapter 10 38

Lithium Aluminum Hydride

• Stronger reducing agent than sodium borohydride, but dangerous to work with.

• Converts esters and acids to 1º alcohols.

Chapter 10 39

Comparison of Reducing Agents

• LiAlH4 is stronger.

• LiAlH4 reduces more stable compounds which are resistant to reduction. =>

Chapter 10 40

Catalytic Hydrogenation

• Add H2 with Raney nickel catalyst.

• Also reduces any C=C bonds.

Chapter 10 41

End of Chapter 10