Post on 24-Dec-2015
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Oxidation of alcohols and aldehydes
L.O.:Recognise and name aldehydes and ketones.Describe the oxidation of alcohols (primary, secondary)
CARBONYL COMPOUNDS - STRUCTURE
Structure carbonyl groups consists ofa carbon-oxygen double bond
the bond is polar due to thedifference in electronegativity
Difference ALDEHYDES - at least one H attached to the carbonyl group
C = O
H
CH3
C = O
H
H
CARBONYL COMPOUNDS - STRUCTURE
Structure carbonyl groups consists ofa carbon-oxygen double bond
the bond is polar due to thedifference in electronegativity
Difference ALDEHYDES - at least one H attached to the carbonyl group
KETONES - two carbons attached to the carbonyl group
C = O
H
CH3
C = O
H
H
C = O
CH3
CH3
C = O
C2H5
CH3
RC
O
H or RCHO
Aldehydes are named using the suffix –al.
HC
O
Hor HCHO is methanal
O
H Or C6H5CHO. Benzenecarbaldehyde
Name this Aldehydes
C
O
HC
H
H
H
C
O
HC
H
H
C
H
H
H
C
O
HC
H
C
H
H
H CH3
Ethanal
Propanal
2-Methylpropanal
Ketones are named using the suffix –one.
C
O
C
H
H
C
H
H
H
H Propanone (acetone)
Name the following ketones
C
O
C
H
H
C
H
H
H
C
H
C
H H
H
C
H
H
H
C
O
C
H
H
C
H
H
H
C
H
H
H
C
O
C
H
H
C
H
H
H
C
H
H
C
H
H
H
C
O
C
H
CH
H
C
H
C
H H
H
C
H
H
H
H
CH3
Butanone
3-Pentanone
3-Hexanone
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 standCooling tube (tap water goes in at the top and out at the bottom continuously)Reaction containerHeat 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 + wateralcohol 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