Download Oxidation of alcohols and aldehydes

Oxidation of alcohols and
aldehydes
L.O.:
Recognise and name aldehydes and ketones.
Describe the oxidation of alcohols (primary,
secondary)
• http://drbravochemistry.wikispaces.com/
• Test on Friday.
CARBONYL COMPOUNDS - STRUCTURE
Structure
carbonyl groups consists of
a carbon-oxygen double bond
the bond is polar due to the
difference in electronegativity
Difference
ALDEHYDES - at least one H attached to the carbonyl group
H
CH3
C=O
H
C=O
H
CARBONYL COMPOUNDS - STRUCTURE
Structure
carbonyl groups consists of
a carbon-oxygen double bond
the bond is polar due to the
difference in electronegativity
Difference
ALDEHYDES - at least one H attached to the carbonyl group
H
CH3
C=O
C=O
H
H
KETONES - two carbons attached to the carbonyl group
CH3
C2H5
C=O
CH3
C=O
CH3
R
O
C
H
or RCHO
Aldehydes are named using the suffix –al.
H
O
C
or HCHO is methanal
H
O
H
Or C6H5CHO.
Benzenecarbaldehyde
Name this Aldehydes
H O
H C C H
H
H H O
H C C C H
H H
H H O
H C C C H
H CH3
Ethanal
Propanal
2-Methylpropanal
Ketones are named using the suffix –one.
H O H
H C C C H
H
H
Propanone (acetone)
Name the following ketones
H H O H
H C C C C H
H H
H
Butanone
H H O H H
H C C C C C H
H H
H H
3-Pentanone
H H O H H H
H C C C C C C H
H H
H H H
3-Hexanone
H H O H H H
H C C C C C C H
H CH3 H H H
2-methyl-3-hexanone
Oxidising alcohols
Reaction conditions:
1. The oxidising agent is always acidified
potassium dichromate written above the
arrow like this:
K2Cr2O7/H2SO4
2. The reactants are the alcohol and “[O]”
symbolising the oxidation agent
3. Heat is always needed
Potassium dichromate
In its oxidised state it is a
bright orange liquid
Problem.
CH3CH2OH reacts with potassium dichromate.
1) What are the organic products?
2) Which product has a higher boiling point?
3) How could you isolate the aldehyde?
Reflux apparatus
Clamp stand
Cooling tube (tap water
goes in at the top and out
at the bottom
continuously)
Reaction container
Heat source
Further oxidation of a primary alcohol
• Using a process known as REFLUX, the
reaction contents are continually heated at
their boiling point temperature, so HOTTER
and LONGER heating then alcohol conversion
to an aldehyde
• Still uses acidified potassium dichromate
Primary + Oxidising  Carboxylic + water
alcohol
agent
acid
Draw out the conversation of ethanol
to ethanoic acid using the displayed
formula
Oxidation of secondary alcohols
• Like primary alcohols, also require acidified
potassium dichromate and heat (but not
reflux)
• Converts the alcohol into a ketone
Write out, using displayed formula, the
oxidation of hexan-2-ol to hexa-2-one
Oxidation of tertiary alcohols
• The carbon attaching to the OH doesn’t have
any hydrogens attached to it, so these can’t
be oxidised.
Potassium dichromate colour changes