Alcohol reactions

Alcohols – reactions

• Addition of alkene to form alcohol.• Elimination of alcohol to form

alkene.• Halogenation (substitution) of

alcohol to form haloalkane.• Oxidation of alcohol to form

aldehyde/ketone and carboxylic acid.

Alkene to alcohol• Addition – Adding water to alkene gives an alcohol.• this occurs when we heat the alcohol with 50% sulfuric

acid.• The hydrogen and the OH of the water is added to the

alkene around the double bond.

Alcohol to alkene• Elimination – removing water from an alcohol

produces an alkene (by conc H2SO4)

• The removal of 2 atoms or groups is known as an elimination reaction

• The –OH and hydrogen from the neighbouring atom are removed.

Alcohol and oxygen• Combustion: Alcohol of low molar mass burn easily in

the presence of oxygen, to form carbon dioxide and water.

Alcohols - Elimination

• Or dehydration –removal of the hydroxyl group and hydrogen atom of the neighbouring carbon

• conc H2SO4/heat

CH3CH(OH)CH3 CH3CH=CH2 + H2O

propan-2-ol propene

Alcohols – Halogenation (substitution)

Alcohols - substitution• Or halogenation: –OH replaced by halogen atom

forms a haloalkane– PCl5 – phosphorus pentachloride– SOCl2 – thionyl chloride(These things put chloride on and kick off –OH group)

• Performed under reflux – increases the rate of substitution

• These can be used to substitute the –OH group in an alcohol with a –Cl:

CH3OH + PCl5 CH3Cl + POCl3 + HCl

CH3OH + SOCl2 CH3Cl + SO2 + HCl

Lucas reagent• Lucas reagent – anhydrous Zinc chloride (ZnCl2)

and conc HCl.• The Lucas reagent is used to primary, secondary

and tertiary alcohols• The zinc chloride is a catalyst for the substitution

reaction between the alcohol and HCl.• The chloroalkane (haloalkane) formed is a cloudy

suspension in water as they are insoluble. • The rates at which different alcohols react make it

possible to classify them.

Alcohols - Substitution

Alcohols - Oxidation• Back in Level 2 organic chemistry we learnt that alcohols come in

three main forms:– Primary– Secondary – Tertiary

• We also found out that primary alcohols can be oxidised to form carboxylic acids

• Later we will discover that primary alcohols can be partially oxidised to form a group called aldehydes. Then the aldehydes can be oxidised further to form carboxylic acids:

• This year we will also discover that secondary alcohols can be oxidised to form ketones:

OH

CH3 CH CH3

O

CH3 C CH3

OHCH3 C

O

OHCH3 CH2

O

CH3 CH

Alcohols - Oxidation

Alcohols - Oxidation