Oxidation of alcohols and aldehydes L.O.: Recognise and name aldehydes and ketones. Describe the...
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Transcript of Oxidation of alcohols and aldehydes L.O.: Recognise and name aldehydes and ketones. Describe the...
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Oxidation of alcohols and aldehydes
L.O.:Recognise and name aldehydes and ketones.Describe the oxidation of alcohols (primary, secondary)
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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
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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
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RC
O
H or RCHO
Aldehydes are named using the suffix –al.
HC
O
Hor HCHO is methanal
O
H Or C6H5CHO. Benzenecarbaldehyde
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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
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Ketones are named using the suffix –one.
C
O
C
H
H
C
H
H
H
H Propanone (acetone)
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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
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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
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Potassium dichromate
In its oxidised state it is a bright orange liquid
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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?
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Reflux apparatus
Clamp standCooling tube (tap water goes in at the top and out at the bottom continuously)Reaction containerHeat source
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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
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Draw out the conversation of ethanol to ethanoic acid using the displayed
formula
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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
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Oxidation of tertiary alcohols
• The carbon attaching to the OH doesn’t have any hydrogens attached to it, so these can’t be oxidised.
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Potassium dichromate colour changes
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