PHYSICAL PROPERTIES OF ETHENE
1. It is a colourless gas with a faint sweetish smell.
2. It is slightly less dense than air.
3. It is sparingly soluble in water.
4. It is neutral to litmus paper.
CHEMICAL PROPERTIES OF ETHENE
A. COMBUSTION: C
2
H
4 burns readily in air or oxygen with a smoky luminous flame, because of its high carbon content, to form CO
2 and H
2
O.
C
2
H
4(g)
+ 3O
2(g)
CO
2(g)
+ H
2
0
(g)
B. ADDITION REACTION: All unsaturated compounds undergo addition reaction. It involves the direct addition of an attacking reagent across the double or triple bond of an unsaturated compound to yield a saturated product or one in which the degree of saturation is increased. Ethene undergoes addition reaction with hydrogen, halogens, hydrogen halides and many other compounds. E.g
1. Hydrogenation
2. Halogenation:
Similar reactions are possible with bromine and iodine.
3. With hydrogen halides:
CH
2
CH
2(g)
+ HI
(g)
CH
3
CH
2
I
(l)
Similar reactions occur with HCl and HB but at slower rate.
When hydrogen halides react with unsymmetric alkene, the addition reaction is according to
Markonikov’s rule. The rule states that the hydrogen atom of the added hydrogen halide goes to the carbon atom which has more hydrogen atoms, while the other carbon atoms receives the halogen or non- hydrogen atom e.g

4. With chlorine and bromine water: Chlorine water contains oxochlorate(I) acid, HOCl and bromine water contains oxobromate(I) acid, HOBr, when ethene combines with bromine water or chlorine water, 2-chloroethanol or 2-bromoethanol are produced.
5. With tetraoxosulphate(VI) acid : Conc. H
2
SO
4 readily absorbs ethene at room temperature to form ethylhydrogentetraoxosulphate(VI), which under goes hydrolysis when boiled with water to produce ethanol and H
2
SO
4.
6. With tetraoxomanganate(VII): When bubble into a dilute solution of KMnO
4
, ethene is oxidized rapidly to ethane-1,2-diol (also known as ethylene glycol). It is used in antifreeze mixture for car radiators and for making terylene, an important polyester.
If the solution is alkaline, the purple KMnO
4 is reduced to a green solution of potassium tetraoxomanganate(VI) but if acidic, a colourless solution of manganese(Ii) is obtained.
7. With oxygen: When ethene is mixed with air or oxygen and passed over a silver catalyst at about
250 0 C, epoxyethane is formed. Epoxyethane (or ethylene oxide) is used in making ethane-1,2-diol and some liquid detergent.

8. With ozone: Ethene combines with ozone to form ozonides, viscous liquid, often explosive, unstable to heat and used in confirming the position of double bond in carbon chains.
C. POLYMERIZATION REACTION: It is the combination of two or more simple molecules to form a complex molecule. The simple molecules are called monomers while the complex molecule is called polymer. The polymerization of ethene takes place at 200 0 C and 100atm.
Polyethene is used as packaging materials
USES OF ETHENE
1.
In the manufacturing of many important organic compounds such as ethane, ethanol etc.
2.
It is the raw material for many plastics e.g polyethene, polyvinylchloride (pvc) etc.
3.
It is used for the production of synthetic rubber such as styrene-butadiene rubber.
4.
It is used for hastening the ripening of fruits.
5.
1,2-dibromoethene is used as a petrol additive.
6.
Ethene is used in the manufacture of glycerol and detergent.
ASSIGNMENT
Draw and label the laboratory set ups for the preparation of methane and ethene.

WEEK 9
TOPIC: ALKYNES
Alkynes are homologous series of unsaturated hydrocarbons with a general formula of C n
H
2n-2
. Alkynes show a higher degree of unsaturation than the alkenes and are therefore more reactive than the corresponding alkenes and alkanes.
The following are some common alkynes:
Molecular Formula
C
C
3
2
H
H
2
CH
4
4
H
C
4
H
6
C
5
H
8
6
Structural formula
CH CH
IUPAC name
Ethyne
Propyne
But-1-yne
But-2-yne
Pent-1-yne
Common Name
Acetylene
Methylacety
Ethylacety
Dimethylace
Propylacety
ETHYNE:
It is the first member of the alkyne series. It has a molecular formula C
2
H
2
.
LAB PREPARATION OF ETHYNE
C
2
H
2 is prepared in the laboratory by the action of cold water on calcium carbide. The gas evolved is passed through an acidified CuSO
4 solution to remove phosphine, PH
3 present as an impurity. The reaction evolves great amount of heat. This is carried out in a heap of sand inside the flask to prevent the flask from cracking.
PHYSICAL PROPERTIES OF ETHYNE
1.
It is a colorless gas with a characteristic sweet smell when pure.
2. It is sparingly soluble in water.
3. It is slightly less dense than air.
4. It is unstable and may explode on compression to a liquid. For storage purposes, it is usually dissolved in acetone (propanone) and kept in steel cylinders at about 12 atmospheric pressure.
CHEMICAL PROPERTIES OF ETHYNE
1.
COMBUSTION: In air, ethyne burns with a very smoky and luminous flame due to high carbon content. However, in pure oxygen, ethyne undergoes complete combustion with a non luminous and very hot flame of about 3000 0 C. This flame is used in the oxy-ethyne (oxyacetylyne) torch used in welding and cutting metal scarps.
2C
2
H
2(g)
+ 5O
2(g)
2H
2
O
(g)
+ 4CO
2(g)
2.
ADDITION REACTION: Ethyne contains electron-rich triple carbon-carbon bond in its structure.
Hence it forms addition reaction which takes place in two stages. The first stage produces a double a.
carbon-carbon bond product while the second stage converts it to a fully saturated compound.
With Hydrogen: in the presence of nickel catalyst and 200 0 C, C
2
H
2 reacts with twice its volume of hydrogen gas (H
2
) to first form ethene and then ethane.

b.
With halogens: In the presence of metallic halide catalyst, ethyne reacts with Cl
2 or Br
2 temperature to yield halogenated compounds. However, in the absence of catalyst Cl
2 at room and pure ethyne reacts to form carbon and hydrogen chloride gas with a violent explosion.
c.
With hydrogen halides: At room temperature and 100 0 C, ethyne combines with hydrogen iodide and hydrogen bromide respectively. However, with hydrogen chloride, the reaction is very slow.
d.
With water: Ethyne reacts additively with water, if passed into dilute H
2
SO
4 mercury(ii)tetraoxosulphate(vi) as catalyst. The product is ethanol.
at 800 0 C* with
Ethanol and ethanal are isomers. Ethanol is too unstable to be isolated but exist in dynamic equilibrium with ethanal.
e.
With Tetraoxomanganate(vii): C
2
H
2 rapidly decolourizes acidified KMnO4 solution while it turns an alkaline solution green at room temperature. In the process ethyne is converted (i .e oxidized) into ethanedioc acid.
3.
SUBSTITUTION REACTION : a.
With copper(i) chloride: If C
2
H
2 is passed at room temperature into ammoniacal solution of copper(i)chloride, a reddish brown precipitate of copper(i)cabide is formed.
b.
With silver trioxonitrate(v): If ethyne is passed through a solution of AgNO
3 temperature, a whitish yellow precipitate of silver dicarbide is formed.
in ammonia at room
A solution of silver(i)oxide in ammonia will give similar reaction

NOTE: The two reactions above are used to distinguish between ethyne (alkynes) and ethene (alkane).
Ethene does not undergo these reactions.
Both Cu
2
C
2 and Ag
2
C
2 are explosive when dry and heated although the silver salt is more violent. Also, the two carbides give off ethyne if warmed with dilute acid.
4.
POLYMERIZATION REACTIONS: Ethyne polymerizes to form the aromatic hydrocarbons (benzene) when passed through a hot tube containing a complex organic nickel catalyst.
TEST FOR UNSATURATION
Unsaturated hydrocarbons undergo addition reactions with bromine water and KMnO
4
. The reddish – brown bromine water turns colourless while the purple solution of KMnO
4 also becomes colourless in the presence of unsaturated hydrocarbons
USES OF ETHYNE
1. It is used as fuel in lamps e.g
2. It is used to produce oxy-acetylene flame used for cutting and welding metals.
3. It is the source of ethanol, 1, 1, 2-trichloroethene and 1,1,2,2-tetrachloroethane used in industry and dry cleaning
4. It is a good starting material for the production of other important organic compounds e.g
ethanoic acid.
5. It is used in making vinylchloride which polymerize to the plastic(polyvinyl chloride), P.V.C.
6. It polymerizes to form synthetic fibres and artificial rubber.
AROMATIC HYDROCARBONS (BENZENE)
Aromatic hydrocarbons are benzene and compounds that resemble benzene in chemical behavior. They have the general formals C n
H
2n-6 where n =6. Benzene is obtained from the destructive distillation of coal.
STRUCTURE OF BENZENE
As suggested by August Kekule in 1865, benzene’s structure is represented as a regular hexagon with alternate single and double lines which indicate single and double bonds.
The molecule is considered to be resonance hybrid i.e the two equivalent forms are in equilibrium.
NOTE: Resonance occurs when two equivalent forms of a compound are in equilibrium.
The Kekule structure of benzene accounts for the stability but could not account for the reasons why benzene fails to undergo many of the addition reactions being undergone by alkenes. For examples benzene does not immediately decoulourize bromine water, it does not reduce KMnO
4
, it doesn’t react additionally with hydrogen halides nor with conc.H
2
SO
4
.
Most reactions of benzene are substitution reactions. Because of these points mentioned, the bonds in benzene molecule are considered as a delocalized electron-bond spread out over the whole ring of benzene. Hence, the modern structure of benzene is a plane hexagonal with an inscribed circle. The inscribed circle represents the electron cloud* spread out over the whole benzene ring.

NOTE: all the compounds containing benzene ring in their structures are called aromatic compounds.
PHYSICAL PROPERTIES OF BENZENE
1. It is a colourless, volatile liquid with a sweet smell.
2. Benzene vapour is highly toxic and carcinogenic*
3. It boils at 80 0 C and freezes at 5 0 C .
4. It is highly inflammable.
5. It is insoluble in water, but mixes in all proportions with ethane, ethoxy ethane and methylbenzene.
6. It is a good organic solvent for oils, fats, iodine* and sulphur.
CHEMICAL PROPERTIES OF BENZENE
1. Combustion – Because of its high carbon content, benzene burns in air with a smoky, luminous flame.
2. Substitution reaction- As a saturated hydrocarbons, benzene undergoes substitution reactions with ethene, chlorine, bromine, conc. HNO
3
.
a. With ethene: In the presence of heat, pressure and anhydrous aluminium(iii) chloride catalyst, benzene reacts with ethane to form ethylbenzene.
C
6
H
6
+ C
2
H
4
C
6
H
5
C
2
H
5 ethylbenene b. With halogens –In presence of catalysts …….. iron, iron (iii) or aluminium (iii) chloride, generally known as halogen carries, benzene reacts with chlorine or bromine to form halogenobenzene e.g
C
6
H
6
+ Cl
2
C
6
H
5
Cl + HCl.
c. Nitration reaction –if benzene is treated with a mixture of conc. Solution of HNO
3 and H
2
SO
4
(i.e
nitrating mixture) at room temperature, a nitrobenzene is rapidly formed with evolution of heat.
d. Sulphonation- when benzene is treated with conc. H substituted for by hydrogen trioxosulphate (iv). (HSO
2
3
-
SO
4 for several hours, one hydrogen atom is
). The reaction is faster with oleum.
3. ADDITION REACTION a. Hydrogenation: When a mixture of hydrogen and benzene vapour is passed over a nickel catalyst at about 150 0 C, cyclohexane is formed.

b. Chlorination: In the presence of UV light chlorine reacts with hot benzene to form hexachlorocyclohexane.
Type of bond
% of C by mass
Addition reactions
DIFFERENCES BETWEEN ALKENE AND BENZENE
Alkene Benzene
-carbon-carbon double bond
-localised electrons
-Resonance hybrid structure
-delocalised electrons
85.7% 92.3%
Yes e.g it decolorizes bromine water
Only under very vigorous conditions
Substitution reaction
Polymerization
NO Yes it undergo polymerization addition
TEST FOR AROMATIC HYDROCARBON.
does not polymerization undergo
Nitration and sulphonation reactions (earlier discussed) are used to distinguish liquid benzene and members of its homologous series from liquid alkanes.
*To distinguish benzene from liquid alkenes, benzene can neither decolorize bromine water nor reduce
KMnO
4
–unlike alkenes.
USES OF BENZENE
1. It is used as fuel.
2. It is used as organic solvent for fats and oil.
3. It is the raw material for the production of styrene, nitrobenzene, phenol, which are used in the manufacture of plastic, dyes, drugs and insecticides.

WEEK: 10
TOPIC: ALKANOLS
Alkanols are organic compounds with one or more hydroxyl (-OH) functional groups. Linked to a carbon atom. Their general molecular formular is C n
H
2n+1
OH. They are named by replacing the ‘- e -‘ at the end of the corresponding alkane with ‘- ol -’. The following are the first members of the family.
Molecular formula Structural formula IUPAC names
CH
3
OH or CH
4
O Methanol (wood spirit)
C
2
H
5
C
3
H
7
OH or C
2
H
6
OH or C
2
H
8
O
O
Ethanol
Propan – 1- ol
C
4
H
9
OH or C
4
H
10
O Butan -1-ol
CLASSIFICATION OF ALKANOLS
A. Classification base on the number of –OH group per molecule.
Monohydric alkanol – they have only one –OH group per molecule e.g ethanol
dihydric alkanols – they have two –OH groups per molecule e.g. ethan-1,2-diol
trihydric alkanol – they possess three –OH groups per molecule e.g. propan-1,2,3-triol (glycerol)
B. Classification base on the number of alkyl group per molecule.
The general formula for alkanol is R-OH where R is an alkyl group. There are three types of alkanol base on this classification.
Primary alkanol – it has only one alkyl group attached to the carbon atom carrying the –OH group i.e.
Secondary alkanols – they have 2 alkyl groups attached to the carbon atom that carries the –oH group i.e.

Tertiary alkanols – they have three alkyl groups attached to the carbon atom that carries the –OH group i.e.
LABORATORY PREPARATION OF ALKANOLS
There are several ways to synthesize alkanols in the laboratory e.g.
- By hydrolysis of haloalkanes – for example by boiling chloroethane with aqueous sodium hydroxide.
CH
3
CH
2
Cl
(l)
+ NaOH
(aq)
CH
- By hydrolysis of ethyl esters with a hot alkali e.g
3
CH
2
OH
(l)
+ NaCl
(aq)
CH
3
COOC
2
H
5(aq)
+ KOH
(aq)
C
2
H
5
OH
(l)
Note: ethanol is seldom prepared in the laboratory because it is so readily available commercially.
INDUSTRIAL PREPARATION OF ALKANOLS
Alkanols are produced commercially by;
+ CH
3
COOK
(aq)
- Hydration of alkenes
- Fermentation
Manufacture of ethanol from ethane
The process involves passing a mixture of ethane and steam over tetraoxophosphate (V) acid, the catalyst, at 500 0 C – 600 0 C and a pressure of 80 to 100 atm. Most of the ethanols required for industrial use are prepare by this method.
C
2
H
4(g)
+ H
2
O
(g)
Fermentation
C
2
H
5
OH
(l)
Fermentation is the slow decomposition by micro-organisms of large organic molecules (such as starch) into smaller molecules (such as ethanol).
Yeast is the common micro-organism used in fermentation because it contains a variety of enzymes that bring about decomposition of starches and sugars to ethanol.
(a) From starchy foodstuff: starchy foodstuff like cassava, potato and cereals (e.g. rice, maize, guinea corn, millet and barley) are good sources of ethanol. The starchy food is crushed and treated with steam to extract the starch granules. Malt is then added at about 55 0 C – 60 0 C for an hour. (malt is a partially germinated barley which contains enzyme diastase). The enzyme converts starch to maltose.
2(C
6
H
10
O
5
)n
(s)
+ nH
2
O
(l) diastase nC
12
H
22
O11
(aq)
Starch maltose
Yeast is then added at room temperature. The yeast contains two enzymes; maltase which converts maltose to glucose and zymase which converts glucose to ethanol and carbon(IV) oxide.
C
12
H
22
O
11(aq)
+ H
2
O
(l) maltase 2C
6
H
12
O
6(aq)

Maltase
C
6
H
12
O
6(aq)
Glucose zymase glucose
2C
2
H
5
OH
(aq) ethanol
+ 2CO
2(g)
(b) From molasses – molasses is a syrupy liquid that remains after the crystallization of sugar from sugar cane. Molasses contains sucrose (a disaccharide). The enzyme invertase in yeast acts on sucrose and converts it to glucose and fructose which are later fermented into ethanol by the enzyme zymase.
C
C
12
6
H
H
22
12
O
O
11(aq)
6(aq)
+ H
2
O
(l) zymase invertase
2C
2
H
5
C
OH
6
H
(aq)
12
O
6(aq)
+ 2CO
+ C
2(g)
6
H
12
O
6(aq)
(c) From other sources – the other sources of ethanol are fruits (like grapes, plantains, pineapples and apples), sugar cane and honey. Palm wine can be fermented to produce local gin.
Concentration of ethanol
The ethanol obtained by fermentation has a maximum concentration of 18% because yeast cannot survive any concentration above that. Fractional distillation is used for further concentration and purification of ethanol.
The generally sold ethanol is 95% ethanol and is called rectified spirit. When rectified spirit is distilled over quicklime, it produces absolute ethanol which is 99.5% ethanol. It is very hygroscopic and must be kept away from atmospheric moisture.
The following are examples of alcoholic drinks and the percentage ethanol contents.
Raw material Alcoholic drink % ethanol content Method of preparation
Barley
Grape/rice
Beer
Wines
3 – 8
8 – 18
Fermentation
Fermentation
Barley
Grapes
Whisky
Brandy
30 – 60
30 – 60
Fermentation and distillation
Fermentation and distillation
Physical properties of ethanol
- It is a colourless, volatile liquid with a characteristic taste and smell.
- It is readily soluble in water in all proportion (due to the presence of the hydroxyl group).
- It has a boiling point of 78 0 C.
- It is neutral to litmus paper.
Note:
By comparism, alkanols have much higher boiling points than hydrocarbons of similar relative molecular mass due to the presence of hydrogen bond occasioned by the hydroxyl gropu e.g. the boiling point of npentane is 36 0 C while that of butan-1-ol is 118 0 C.
Also, hydrocarbons are not soluble in water but alkanols are soluble due to the presence of the hydroxyl groups. The solubility decreases with increasing number of carbon atoms. Primary alkanols with more than 5 carbon atoms are insoluble in water.
R O - - - - H
H
O
H- - - - - O
H
R Hydrogen bonds

Chemical properties of ethanol
1.
Combustion: ethanol burns readily in air or oxygen with a pale blue flame yielding water and carbon
(IV) oxide.
C
2
H
5
OH
(aq)
+ 3O
2(g)
3H
2
O
(l)
+ 2CO
2(g)
2. Reaction with sodium and potassium – at room temperature, ethanol reacts with sodium to produce hydrogen and sodium ethoxide. On heating the solution, a white deliquescent solid; sodium ethoxide is left behind. It is rapidly hydrolyzed by cold water to give an alkaline solution. Potassium undergoes similar reaction with ethanol.
2C
2
H
5
OH
(aq)
C
2
H
5
ONa
(s)
+ 2Na
(s)
+ H
2
O
(l)
2C
2
H
5
ONa
C
2
(aq)
H
5
+ H
2(g)
OH
(aq)
+ NaOH
(aq)
3. Oxidation – under favourable condition, ethanol is readily oxidized to ethanol by warming it with potassium heptaoxodichromate (VI) solution which has been acidified with H2SO4.
C
2
H
5
OH
(aq)
+ [O]
From K
2
Cr
2
O
7
CH
3
CHO
(g)
+ H
2
O
(l)
On further oxidation in the presence of excess H
2
SO
4
, the ethanal is converted to ethanoic acid.
CH
3
CHO
(g)
+ [O] CH
3
COOH
(aq)
The oxidation reaction can also be carried out catalytically by passing the ethanol vapour over finely divided copper at 300 0 C and the ethanol vapour over manganese (II) ethanoate respectively.
Note: wine sometimes becomes sour on prolonged exposure to air because of the bacterial oxidation of ethanol to ethanoic acid.
Generally, primary alkanols are oxidized to alkanals and carboxylic acid. Secondary alkanols to alkanones but tertiary alkanols are not oxidized.
CH
3
CHOHCH
3
+ [O] CH
3
CH
3
CO + H
2
Propan-2-ol propanone
4. Esterification – in this process, alkanols react reversibly with carboxylic acids in the presence of mineral acid to form alkanoates (ester). E.g.
CH
3
COOH
(aq)
+ C
2
H
5
OH
(aq)
CH
3
COOC
2
H
5(l)
+ H
2
O
(l)
5 . Dehydration
Ethylethanoate
– ethanol reacts with excess H
2
SO
4 at about 170 0 C to form ethylhydrogen tetraoxosulphate(VI), which then decompose to yield ethane.
C
2
H
5
OH
(aq)
+ H
2
SO
4(aq)
C
2
H
5
HSO
4(aq)
+ H
2
O
(l)
C
2
H
5
HSO
4(aq)
C
2
H
4(g)
+ H
2
SO
4(aq)
If the alkanol is in excess and the temperature is lower, the product of the reaction is ethoxyethane
(diethylether).
C
2
H
5
OH
(aq)
C
2
H
5
HSO
+ H
2
SO
4(aq)
4(aq)
+ C
2
H
5
OH
(aq)
C
2
H
5
HSO
4(aq)
+ H
C
2
H
5
OC
2
O
(l)
2
H
5(g)
+ H
2
SO
4(aq)
Ethoxyethane
Note: both the formation of ethene and ethoxyethane from ethanol are dehydration reactions.
C
2
2C
H
2
5
H
OH
5
OH
-H2O
-H2O
C
2
C
2
H
4
H
5
OC
2
H
5
6. Reactions with chlorides of phosphorus – ethanol reacts with phosphorus (V) chloride vigorously in the cold liberating steamy fumes of hydrogen chloride and chloroethane vapour.

C
2
H
5
OH
(aq)
+ PCl
5(l)
C
2
H
5
Cl
(g)
+ POCl
3(l)
+ HCl
(g)
With phosphorus (III) chloride, similar but less vigorous reaction occurs.
3C
2
H
5
OH
(aq)
+ PCl
3(l)
Assignment
State the various uses of alkanols
3C
2
H
5
Cl
(g)
+ H
3
PO
3(aq)