HERE I HAVE MENTIONED THE TECHNIQUES TO PREPARE ALKANES FROM OTHER HYDROCARBONS

1. 11th grade
Preparation of
ALKANES

2. Whoa
COMMMMME OOOOONNNNNN!!!!!!!!!

3. —William Crookes
“Chemists do not usually stutter. It
would be very awkward if they did,
seeing that they have at times to
get out such words as
methylethylamylophenylium.”

4. Table of contents
INTRODUCTION
IT’S ALL ABOUT THE
ALKANES!!
PREPARATION OF ALKANES
THERE IS SOMETHING TO
KNOW...
FROM CARBOXYLIC
ACID
TWO METHOD TO DESCRIBE
FROM ALKYL
HALIDES
WHAT IS INSIDE?!
WURTZ REACTION
WHAT DID WURTZ SAY??
01 02 03
04 05

5. Introduction
ALKANES ARE SATURATED HYDROCARBON CONTAINS ONLY
SINGLE BOND CARBON BONDS IN THEIR MOLECULES. THEY ARE
ALSO CALLED PARAFFINS. AT HIGH TEMPERATURES AND
PRESSURE UNDERGO SOME REACTION. THE ALKANES MAY BE
DIVIDED AS:
❖ OPEN CHAIN OR ACYCLIC ALKANES
❖ CYCLOALKANES OR CYCLIC ALKANES

6. PREPARATION
OF ALKANES
01

7. PREPARATION OF ALKANES
F
R
O
M
A
L
K
Y
L
H
A
L
I
D
E
S
FROM
UNSATURATED
HYDROCARBONS
F
R
O
M
C
A
R
B
O
X
Y
L
I
C
A
C
I
D

8. FROM UNSATURATED HYDROCARBONS
❖ The Unsaturated Hydrocarbons (Alkenes and Alkynes) are converted
into alkanes by catalytic hydrogenation. In this process dihydrogen is
passed through alkenes or alkynes in the presence of finely divided
catalysts such as Raney Ni, Pt or Pd.
❖ These metals absorbs dihydrogen gas on their surfaces and activate the
hydrogen-hydrogen bond. Platinum and Palladium catalyse the
reaction at room temperature. However, higer temperature
(523k-573k) and pressure are required with nickel catalysts.
❖ Methane cannot be prepared by this method because starting of alkenes
are allowed only from the ethene..

9. Sabatier reaction
The hydrogenation reaction of unsaturated
hydrocarbon using nickel at a temperature of
523-573k is commonly called as sebatier or sender’s
reaction or reduction.

10. Mr.Paul Sebatier

11. WURTZ
REACTION
03

12. Alkyl halides on treatment with sodium metal in
dry ethereal (free from moisture) solution give
higher alkanes.
This reaction is known as Wurtz reaction and is
used for the preparation of higher alkanes
containing even number of carbon atoms.
WURTZ REACTION

13. From Carboxylic acid
Decarboxylation reaction
From carboxylic acid
Kolbe’s electrolytic method

14. Decarboxylation reaction
❖ Sodium salts of carboxylic acids on heating with
soda lime (mixture of sodium hydroxide and
calcium oxide) gives alkanes containing one carbon
atom less than the carboxylic acid.
❖ The process of elimination of carbon dioxide from a
carboxylic acid is known as decarboxylation
reaction.

15. Kolbe’s electrolytic method
❖ This Method is used for the reduction of CO2+
❖ An Aqueous solution of sodium or potassium salt of a carboxylic acid on
electrolysis gives alkane containing even number of carbon atoms at the
anode.
❖ At the cathode there is reduction of water into hydrogen free radicals and
that is converted into hydrogen and given off

16. Hermann Kolbe

17. Reaction mechanism of Kolbe’s electrolytic method
❖ In a mechanism there are three steps
➢ Initiation
➢ Propagation
➢ Termination
❖ Initiation:
➢ Here sodium acetate is converted into acetate and sodium ion

18. Reaction mechanism of Kolbe’s electrolytic method
❖ Propagation:
➢ At Anode:
❖ Termination:
➢ At Cathode:

19. FROM ALKYL
HALIDES
04

20. FROM ALKYL HALIDES
❖ Alkanes can be produced from alkyl halides predominantly by two ways:
➢ Alkanes can be prepared from alkyl halides (except fluorides)
through reduction with zinc and dilute hydrochloric acid.
➢ Example: CH3-Cl +H2 → CH4+HCl
➢ Wurtz reaction: In dry ethereal solution, on treating alkyl halides
with sodium metal, production of alkanes is higher. By this
reaction, we can achieve higher alkanes with an even number of
carbon atoms
➢ Example: CH3-Br+2Na+BrCH3 → CH3-CH3+2NaBr

21. AN PRESENTATION BY
S.AJAY ADITHYA