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.

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Chapter 10 Structure and Synthesis of Alcohols

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Chapter 10 structure and synthesis of alcohols

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

Chapter 10Structure and Synthesis of Alcohols


Structure of alcohols

Structure of Alcohols

  • Hydroxyl (-OH) functional group

  • Oxygen is sp3 hybridized.

Chapter 10


Classification

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


Iupac nomenclature

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


Unsaturated alcohols

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


Naming priority

Acids

Esters

Aldehydes

Ketones

Alcohols

Amines

Alkenes

Alkynes

Alkanes

Ethers

Halides

Naming Priority

Chapter 10


Hydroxy substituent

Hydroxy Substituent

  • When -OH is part of a higher priority class of compound, it is named as hydroxy.

  • Example:

4-hydroxybutanoic acid

Chapter 10


Common names

Common Names

  • Alcohol can be named as alkyl alcohol.

  • Useful only for small alkyl groups.

  • Examples:

sec-butyl alcohol

=>

isobutyl alcohol

Chapter 10


Naming diols

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


Glycols

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

propane-1,2- diol

ethylene glycol

propylene glycol

Chapter 10


Naming phenols

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.

4-methylphenol

3-chlorophenol

para-cresol

meta-chlorophenol

Chapter 10


Physical properties

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


Boiling points

=>

Boiling Points

Chapter 10


Solubility in water

Solubility decreases as the size of the alkyl group increases.

Solubility in Water

Chapter 10


Methanol

Methanol

  • “Wood alcohol”

  • Industrial production from synthesis gas

  • Common industrial solvent

  • Fuel at Indianapolis 500

    • Fire can be extinguished with water

    • High octane rating

    • Low emissions

    • But, lower energy content

    • Invisible flame

Chapter 10


Ethanol

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


2 propanol

2-Propanol

  • “Rubbing alcohol”

  • Catalytic hydration of propene

Chapter 10


Acidity of alcohols

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


Table of k a values

Table of Ka Values

=>

Chapter 10


Formation of alkoxide ions

Formation of Alkoxide Ions

React methanol and ethanol with sodium metal (redox reaction).

React less acidic alcohols with more

reactive potassium.

Chapter 10


Formation of phenoxide ion

Formation of Phenoxide Ion

Phenol reacts with hydroxide ions to form phenoxide ions - no redox is necessary.

O

O

H

O

H

+

+

H

O

H

p

K

=

1

5

.

7

a

p

K

=

1

0.0

a

Chapter 10


Synthesis review

Synthesis (Review)

  • Nucleophilic substitution of OH- on alkyl halide

  • Hydration of alkenes

    • water in acid solution (not very effective)

    • oxymercuration - demercuration

    • hydroboration - oxidation

Chapter 10


Organometallic reagents

Organometallic Reagents

  • Carbon is bonded to a metal (Mg or Li).

  • Carbon is nucleophilic (partially negative).

  • It will attack a partially positive carbon.

    • C - X

    • C = O

  • A new carbon-carbon bond forms.

Chapter 10


Grignard reagents

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

    • tertiary

    • vinyl

    • aryl

Chapter 10


Some grignard reagents

Some Grignard Reagents

Chapter 10


Organolithium reagents

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


Reaction with carbonyl

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


Synthesis of 1 alcohols

Synthesis of 1° Alcohols

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

Chapter 10


Synthesis of 2 alcohols

Synthesis of 2º Alcohols

Grignard + aldehyde yields a secondary alcohol.

Chapter 10


Synthesis of 3 alcohols

Synthesis of 3º Alcohols

Grignard + ketone yields a tertiary alcohol.

Chapter 10


Grignard reactions with acid chlorides and esters

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


Grignard acid chloride 1

Grignard + Acid Chloride (1)

  • Grignard attacks the carbonyl.

  • Chloride ion leaves.

Chapter 10


Grignard and ester

Grignard and Ester

  • Grignard attacks the carbonyl.

  • Alkoxide ion leaves! ? !

Chapter 10


Second step of reaction

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


Limitations of grignard

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.

Chapter 10


Reduction of carbonyl

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


Sodium borohydride

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


Lithium aluminum hydride

Lithium Aluminum Hydride

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

  • Converts esters and acids to 1º alcohols.

Chapter 10


Comparison of reducing agents

Comparison of Reducing Agents

  • LiAlH4 is stronger.

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

Chapter 10


Catalytic hydrogenation

Catalytic Hydrogenation

  • Add H2 with Raney nickel catalyst.

  • Also reduces any C=C bonds.

Chapter 10


Chapter 10 structure and synthesis of alcohols

End of Chapter 10

Chapter 10


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