6.1 Aldehyde and Ketone – Both aldehyde and ketone are carbonyl

compound (organic with C=O in it). Both has the same molecular

formula as CnH2nO

6.1.1 Nomenclature of aldehyde

� functioning group of aldehyde are and end with –al

butanal 3-methylpentanal 4-chloro-3-

methylbutanal

benzaldehyde m- chlorobenzaldehyde 2-phenylethanal

6.1.2 Ketone : functioning group of ketone are and end with –

one

propanone butanone Pentan-2-one

hexan-3-one 2,4-dimethyl

pentan-3-onecyclohexanone

� Explanation : Butane is a non-polar molecule, where molecules were

held by temporary dipole-induced dipole. Propanal and propanone are

polar molecule, which has a permanent dipole-permanent dipole

attraction forces. However, the dipole moment of ketone is greater

than aldehyde, so ketone usually have higher b.p than aldehyde.

Propan-1-ol has high boiling point due to strong hydrogen bond

between them, however, ethanoic acid has greater hydrogen bond than

propan-1-ol, since they form dimer between them

Molecule Butane (C4H10)Propanal

(C2H5COH)

Propanone;

CH3COCH3

Propan-1-ol

C3H7OH

Ethanoic acid

CH3COOH

RMM 58 58 58 60 60

Boiling point

(oC)1 48 56 97 118

δ+ δ- δ+ δ-

� Solubility : Lower aliphatic aldehydes such as methanal &

ethanal are soluble in water because they are able to form

hydrogen bond with water (as shown in diagram). Higher

member of aliphatic carbonyl compounds are insoluble as there

are presence of hydrophobic alkyl group

δ+ δ- δ+ δ-

� Isomerism of aldehyde and ketones : Given the molecular formula of

organic compound are C5H10O, out line all possible isomers of the

organic compound

6.2 Chemical preparation of aldehyde and ketone

6.2.1 Aldehyde

1. Oxidation of primary alcohol

� Controlled oxidation of alcohol by using acidified potassium

dichromate (VI)

� Prevention : Having excess alcohol over oxidant & distilled off

aldehyde.

+ H2O

propan-1-ol propanal

2. Using catalytic oxidation (Cu at 400oC) on a 10 alcohol

propan-1-ol propanal

� This process is also known as dehydrogenation as hydrogen is

produced.

6.2.2 Ketone

1. Oxidation of secondary alcohol

� Oxidation of alcohol by using acidified potassium dichromate (VI)

� Unlike oxidation on 1o alcohol, it does not need prevention as ketone

formed will not further oxidise to other substances.

+ H2O

Propan-2-ol propanone

2. Using catalytic oxidation (Cu at 400oC) on a 20 alcohol

propan-2-ol propanone

� This process is also known as dehydrogenation as hydrogen is

produced.

6.3 Chemical reaction of aldehyde and ketone

6.3.1 Reduction of aldehyde and ketone.

� Reagent : LiAlH4 (lithium aluminium hydride) in dry ether

propanal propan-1-ol

� From reaction above, we can tell that 10 alcohol is formed back using

reduction. Hence, we can summarised the reaction as

Propan-1-ol propanal

6.3.2 Oxidation of aldehyde

� Aldehyde can be further oxidised to form carboxylic acid.

� Reagent : KMnO4 / H+ (acidified potassium manganate (VII)

Propanal propanoic acid

� However, no further reaction for oxidation of ketone.

6.3.3 Addition reaction of aldehyde and ketone

� Reagent : HCN (hydrogen cyanide) + little KCN

� The nitrile compound formed is then further hydrolysed under acidic

condition, to form 2-hydroxybutanoic acid according to the equation

� The nitrile compound formed can also be reduced to form amine, where

� The mechanism can be describe as below.

� Reagent : R-MgBr (Grignard reagent)

� When aldehyde react with Grignard reagent (Chap 4.4.2), a secondary

alcohol is formed

KETONE

� Reagent : HCN (hydrogen cyanide) + little KCN

� The nitrile compound formed is then further hydrolysed under acidic

condition, to form butanoic acid according to the equation

� Reduction

� Reagent : R-MgBr (Grignard reagent)

� When ketone react with Grignard reagent (Chap 4.4.2), a tertiary alcohol is

formed.

6.3.4 Condensation reaction of aldehyde / ketone

For aldehyde :

� Reagent : (NO2)2C6H4NHNH2 (2,4-dinitrophenylhydrazine)

� An orange precipitate surfaced when 2,4-dinitrophenylhydrazine is

added to aldehyde or ketone

For ketone

� Reagent : (NO2)2C6H4NHNH2 (2,4-dinitrophenylhydrazine)

� Similar to aldehyde, an orange precipitate will surface after the

reaction

Test Aldehyde Ketone

Triiodof

orm

• Reagent : (I2 + NaOH) Iodine in

sodium hydroxide Only work for

ethanal as it has methyl-carbonyl

group

• Observation : a yellow crystal of

triiodomethane is observed

Equation :

CH3CH=O + 3 I2 + NaOH �

CHI3 + HCOO–Na+ + 3 HI

• Reagent : (I2 + NaOH) Iodine in

sodium hydroxide Only work for

those which has methyl-carbonyl

group

• Observation : a yellow crystal of

triiodomethane is observed

Equation : CH3COCH3 + 3 I2 + NaOH

� CHI3 + CH3COO–Na+ + 3 HIHI

Test Aldehyde Ketone

Fehling’s

solution

• Reagent : Fehling solution [solution of complex copper

(II) ion]

• Positive Test : only works for aldehyde

• Observation : blue solution turns to red precipitate of

Cu2O

Equation :

red ppt.

No reaction

occur for

ketone

Tollen’s

reagent

• Reagent : Tollen solution [solution of complex Ag(NH3)2]+]

• Positive test : only work for aldehyde

• Observation : colourless solution turn grey solid (silver

mirror)

Equation :

silver mirror

No reaction

occur for

ketone

� propanone � 2-bromopropane

� propanal � 2-hydroxybutanoic acid

� propene � propanone

� 2-butenal � butanoic acid

� Ethanal � Ethanamine

2. Outline a chemical test to distinguish between

a) propanal and propanone

b) ethanal and propanal

c) pentan-2-one and pentan-3-one

Reagent : Fehling / Tollen reagent (for aldehyde) ; Iodine in NaOH (for ketone)

Observation : Red brick precipitate formed when added propanal while no changes for

propanone

Equation : CH3CH2CHO + 2 Cu2+ + 5 OH- � CH3CH2COO

- + Cu2O + 3 H2O

Reagent : Iodine in NaOH

Observation : Yellow precipitate formed when added to ethanal but no changes for

propanal

Equation : CH3CHO + 3 I2 + OH- � HCOO- + CHI3 + 3 HI

Reagent : Iodine in NaOH

Observation : Yellow precipitate formed when added to pentan-2-one but no changes

for pentan-3-one

Equation : CH3CH2CH2COCH3 + 3 I2 + OH- �

CH3CH2CH2COO- + CHI3 + 3 H2O + HI

6.5 Natural Compound with Carbonyl Group – Carbohydrates

6.5.1 Monosaccharide

� Simplest form of carbohydrates that cannot be hydrolysed to simple sugar

� Examples : glucose and fructose

Glucose Fructose

Also known as aldose (functioning group

of CO–H)

Also known as ketose (functioning group

CO–CH3)

Open ring close ring open ring close ring

Adding glucose to Fehling solution will turn

the blue solution into a red precipitate

(positive test : aldehyde)

Adding fructose to Fehling will show no

changes to Fehling solution

6.5.2 Disaccharide

� Disaccharides are 2 monosaccharide joined together by glycosidic link.

� The process of joining 2 monosaccharides are condensation process as water

molecule is given off as side product. Molecular formula of disaccharide is

C12H22O11.Example

� 3 most common disaccharides

� => sucrose (sugar cane) => maltose (barley) => lactose (milk)

� Disaccharide can be break-up and formed back 2 monosaccharides by

hydrolysis of water

� Most disaccharides are non-reducing sugar.

6.5.3 Polysaccharides

� Polysaccharide ~ polymer containing long chains of

monosaccharide units. Example : starch and cellulose. They have

the empirical formula C6H10O5.

� All saccharides are bond using glycosidic ring and they can be

hydrolysed by heating with diluted acid where

(C6H10O5)n + n H2O n C6H12O6.

� Cellulose are mainly found in cell wall of plants. Cotton is almost

pure cellulose. It can be use to manufacture synthetic fiber

known as rayon.

→+boil;H

A , B , C

C , E

C , D , E

C

C , D

E

Chiral carbon atom is formed since C1 can rotate freely in different position

Element Carbon, C Hydrogen, H Oxygen, O

Mass 66.7 11.1 22.2

Mol = mass / mol 5.51 mol 11.1 mol 1.39 mol

Ratio 5.51 / 1.39 = 4 11.1 / 1.39 = 8 1.39 / 1.39 = 1

Orange precipitate is observed

Carbonyl compound

Butanone / CH3CH2COCH3

LiAlH4 in dry ether

Alcohol / hydroxyl group

CH3CH2CH(OH)CH3

Cl2 under UV

Cl2 under AlCl3

Iodine in NaOH

C gives yellow precipitate / crystal while F will not

C6H5COCH3 + I2 + OH- � C6H5COO- + CHI3 + HI

mass of CN needed = 0.03 x 60 = 1.8 g [1]

Mr = 154.5, amount = 1.8/154.5 = 0.012 mol [1]

H < D < G

� chlorine on the aryl ring is very inert /strong C-Cl bond / overlap between

unhybridise Cl with C in benzene ring1]

� chlorine on C=O is reactive because of highly δ+ carbon atom bonded to

electronegative O and Cl/ due to inductive effect [1]

CH3CHO + HCN CH3CH(OH)CN →KCN

Nucleophilic Additional reaction

CH3CH(OH)CN + 2 H2O + H+ � CH3CH(OH)COOH + NH4

+

hydrolysis

CH3CHO → CH3CH(OH)COOH

44 90 or

4.40 g → 9.00 g

% yield = 5.40 ×100 / 9.00

= 60%

E will give yellow precipitate when react with alkaline iodine solution

Product formed are CH3CH2CH2COO– + CHI3

D reduced to form pentan-3-ol [1] while E is reduced to pentan-2-ol, which is optical

active / chiral carbon atom