Download Ketones - WordPress.com

KETONES
William, Nanda, Hafiz & Mio
Introduction

Alcohols are found in two forms:
 Primary:
-OH group attached at the end of the chain.
 Secondary:
-OH group attached to a carbon atom not
located at the end of the chain.
Formation of ketones

When a secondary alcohol is heated with the
oxidising agent potassium dichromate (VI), it
oxidises into a ketone.
CH3CH(OH)CH3 + [O]  CH3COCH3 + H2O
propan-2-ol

potassium dichromate
propanone
Ketones cannot be oxidised any further.
water
So what is a ketone?

A ketone is a carbonyl compound where one of the
carbon atoms along the chain (not at the ends) is
double-bonded to an oxygen atom.
Naming convention
Carbon atoms Name
3
propanone
4
butanone
5
6
7
pentanone
hexanone
heptanone
8
9
10
octanone
nonanone
decanone
Applications




Polymer precursor
Pharmaceuticals
Solvents
e.g.:
 acetone
 methylethyl
ketone
 cyclohexanone
Reduction of ketones

When a ketone is warmed with the reducing agent
NaBH4 (sodium tetrahydridoborate), it reverts into a
secondary alcohol.
CH3COCH3 + 2[H]  CH3CH(OH)CH3
propanone

reducing agent
propan-2-ol
We can think of it as a nucleophilic addition,
where H- ions from the reducing agent act as the
nucleophile.
Testing for ketones



Testing for ketones and aldehydes
in a solution may be done with
2,4-dinitrophenylhydrazine (2,4DNPH).
If the solution contains either, an
orange precipitate will be
formed.
This is an example of
condensation reaction between
2,4-DNPH and the ketone.
Testing with Tollens’ reagent




Both aldehydes and ketones form an
orange precipitate with 2,4-DNPH.
To differentiate, we may react the
solution with Tollens’ reagent – a
solution of silver nitrate in excess
ammonia.
When it is warmed with an aldehyde, a
silver precipitate builds up.
Ketones, however, will remain colourless.
Fehling’s solution



is an alkaline solution
containing copper (II)
ions.
It oxidises and turns from
clear blue to an opaque
red/orange when heated
with an aldehyde.
Ketones cannot be
oxidised any further, so
the solution remains blue.
Nucleophilic addition with HCN


The carbonyl group C=O is highly polarised, as the
oxygen atom has more electron pairs (and
therefore more negative).
The carbon atom, being more positive, is open to
addition reactions* from nucleophilic ions (i.e.
negative ones).
- O - C
- -
*”nucleophilic attack” is a proper term and sounds cooler.
Mechanism


Addition, as you’ll recall, involves the breakdown of a double
bond into a single bond.
An example of a nucleophile is the CN- ion in HCN, hydrogen
cyanide.
- -
- -
O
C
-
- -
H
O-
C
- -
CN
H+
CN
- -
H
O
C
- -
CN-
-
CN
Thank You