Alcohols

Recap: Acidity of ethanol and water

Video

Acidity of ethanol and 2-chloroethanol

Preparation of Alcohols Method 1 – Electrophilic Addition

followed by Hydrolysis (laboratory method)

CH3CH=CHCH3

Preparation of Alcohols Method 2 (industrial method)

Preparation of Alcohols NUCLEOPHILIC SUBSTITUTION OF

HALOGENOALKANES

CH3CHBrCH2CH3

Preparation of Alcohols REDUCTION OF CARBOXYLIC ACIDS,

ALDEHYDES OR KETONES

LiAlH4 in dry ether

Reactions of Alcohols

• with Na· with RCOOH

• with HX / PX3

• with conc. H2SO4

COMBUSTION  With a good supply of air, alcohols burn

with a pale blue (non-luminous) flame to give carbon dioxide and water.

C2H5OH(l) + 3O2(g) 2CO2(g) + 3H2O(l)

FISSION OF RO–H BOND

• with Na· with RCOOH

REACTIONS INVOLVING FISSION OF RO–H BOND Reaction with sodium (Redox reaction or

Acid–metal reaction)

Na(s) or K(s)R O H R O Na+ + H2

Effervescence observed. Gas extinguished a lighted splint with a ‘pop’ sound.

C 3CH2O NaCH3CH2OH + Na + ½ H2

Esterification (Condensation reaction

Try…catalytic amount of

conc. H2SO4heat under reflux

CH3CH2CH2 CHO

O

CH3

+CH3CH2CH2

ethanoic acidPropanol Propyl ethanoate

O HO

CCH3

O

catalytic amount of

conc. H2SO4heat under reflux

CH3CH2 CHO

O

CH2CH2CH3

+CH3CH2

butanoic acidEthanol ethyl butanoate

O HO

CCH2CH2CH3

O

Fission of R-OH bond• with HX / PX3

• with conc. H2SO4

REACTIONS INVOLVING FISSION OF R–OH BOND

R OHdry HX(g)

R Xheat

To produce RCl: HCl, anhydrous ZnCl2

To produce RBr: NaBr, conc. H2SO4 To produce RI: NaI, conc. H3PO4

R OH R Xroom temperature

PX3

To produce RCl: PCl3

To produce RBr: PBr3 To produce RI: red P4, I2

R OHPCl5 or SOCl2

R Clroom temperature

Note: VIDEOCH3CH2Cl + POCl3 + HClCH3CH2OH + PCl5

Observations: Steamy white fumes of HCl produced.This is often used as a distinguishing test for the presence of the –OH group in alcohols and carboxylic acids.

Anhydrous condition must be used as PX3, PX5 and SOCl2 reacts readily in water

DEHYDRATION (ELIMINATION REACTION)

C C

excess conc. H2SO4, 170oCOR Al2O3, 350oC

C C

H OH

excess conc. H2SO4

170 oCCH3CHCH2CH3

OHC C

H

CH3 CH3

H

H C C

H

CH2CH3

H

+

major minor

OxidationK2Cr2O7, H2SO4R C OH

H

HR C O

H

heat with immediate distillationK2Cr2O7, H2SO4

R C O

OH

heat under reflux

1o alcohol aldehyde carboxylic acid

KMnO4, H2SO4

heat under reflux

R C OH

R'

HR C O

R'K2Cr2O7, H2SO4 OR KMnO4, H2SO4

heat under reflux

2o alcohol ketone

OxidationObservations: Orange K2Cr2O7 turns green

Purple KMnO4 decolourises

Tertiary alcohols are resistant to oxidation.

Oxidation can be used as a test to distinguish tertiary alcohols from primary and secondary alcohols.

VIDEO

HCH3CH2OH + [O]K2Cr2O7, H2SO4(aq)

distilCH3C

O

H2O+

OHCH3CH2OH + 2[O]K2Cr2O7, H2SO4(aq)

refluxCH3C

O

H2O+

CH3CHCH3

OH

+ [O] K2Cr2O7, H2SO4(aq)

refluxCH3CCH3

O

H2O+

K2Cr2O7, H2SO4

heat under reflux

2o alcohol

OH O+ [O] + H2O

K2Cr2O7, H2SO4

heat under reflux1o alcohol

(CH3)3CCH2OH + 2[O] (CH3)3CCO2H + H2O

K2Cr2O7, H2SO4

heat under reflux

3o alcohol

No oxidation

OH

TRI–IODOMETHANE (IODOFORM) TEST (OXIDATION)

R C OH

CH3

H

R C OI2, NaOH(aq)warm O-Na+

+ CHI3

CH3CHCH3

OH

+ 4I2 + 6OH- CH3 C

O

+ CHI3 + 5I- + 5H2OO-

Yellow ppt of tri-iodomethane (iodoform) are formed.