Oxidation of alcohols and aldehydes

L.O.:Recognise and name aldehydes and ketones.Describe the oxidation of alcohols (primary, secondary)

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• Test on Friday.

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

RCO

H or RCHO

Aldehydes are named using the suffix –al.

HCO

Hor HCHO is methanal

O

H Or C6H5CHO. Benzenecarbaldehyde

Name this Aldehydes

COHC

HHH

COHC

H

HCH

HH

COHC

HCH

HH CH3

Ethanal

Propanal

2-Methylpropanal

Ketones are named using the suffix –one.

CO

CH

HCHH

HH Propanone (acetone)

Name the following ketones

CO

CH

HCH

HH

CHC

H H

HCH

HH

CO

CH

HCH

HH

CH

HH

CO

CH

HCH

HH

CH

HCHH

H

CO

CH

CHH

CHC

H H

HCH

HH

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