|
Element Index
Cadmium
Calcium
Carbon
Cerium
Chlorine
Chromium
Cobalt
Copper
Hydrogen
Chemical's truth
|
In December 1984, methyl isocyanate was accidentally released in a chemical plant at Bhopal, India, killing around 6000 people. |
|
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
X
Y
Z
|
Chlorine dioxide
(chlorine peroxide)
CAS no: 10049-04-4 Formula: ClO2 Molecular weight: 67.452
Physical Data
Appearance: Orange-yellow gas with pungent smell
|
Melting point: -59°C
Boiling point: 11°C
|
Density: 2.757 g/L
Solubility: -
|
|
|
Thermodynamic Data (gas)
Enthalpy of formation: 102.5 kJ/mol
Gibbs energy of formation: 120.5 kJ/mol
|
Entropy: 256.8 J/mol K
Heat capacity: 42.0 J/mol K
|
|
|
Production and preparation
Chlorine dioxide was first made by the reaction of concentrated sulfuric acid on potassium chlorate (KClO3). The reaction occurs
via disproportionation of chloric acid (HClO3):
This is a violent, and explosive reaction since chlorine dioxide is an endothermic compound and decomposes readily into its constituents.
A better method of the preparation is to heat gently moist crystals of ethanedioic (oxalic) acid and potassium chlorate:
On an industrial scale, an aqueous solution of chlorine dioxide is made by passing nitrogen dioxide up a tower, packed with
alundum (a refractory material made by fusing aluminium oxide with clay), down with a solution
of sodium chlorate flows:
|
|
|
Behavior and Chemical Properties
The structure of chlorine dioxide is similar to that of nitrogen dioxide, there being an unpaired electron in the molecule, making it paramagnetic. Chlorine dioxide is
soluble in water, of which the aqueous solution is safer to handle than that in gaseous state. The crystalline hydrate, ClO2.8H2O, can be obtained.
On standing in the presence of light, the solution slowly forms a mixture of acids: hydrochloric (HCl), hypochlorous (HClO), chlorous (HClO2), chloric (HClO3) and perchloric (HClO4).
Passing chlorine dioxide into alkali gives a mixture of chlorite and chlorate ions:
However, with metals such as magnesium, nickel and zinc, it gives only the chlorite:
Chlorine dioxide is also a good oxidizing agent. For instance, the aqueous solution can oxidize sulfur to sulfuric acid:
An acidified iodide solution can also be oxidized to iodine when chlorine dioxide is added:
Chlorine dioxide also reacts with fluorine, by adding one atom of fluorine to the molecule to give chloryl fluoride (ClO2F), an unstable gas.
|
|
|
History and Uses
In the early days, chlorine dioxide was used indirectly as a match. Invented by Jean Chancel in 1805, he placed some amount of potassium chlorate (available to
treat sore throats at that time) and sugar on a splinter of wood. When a little concentrated sulfuric acid is added, the chemical reaction turns violent (as mentioned in the Preparation Section above) and ignite the
sugar, which burns long enough for the wooden stick to catch fire and, as a result, the match lights.
Chlorine dioxide is a good bleaching agent and is used to bleach wood-pulp for paper making, de-tanning of leather and to bleach flour.
It is also used in water sterilization. Unlike chlorine, it does not produce an unpleasant taste.
Since early 1900's it is also used as antimicrobial pesticides to kill harmful microorganisms including bacteria, viruses or fungi on inanimate objects and surfaces.
|
|
|
Hazard, Storage and Handling
Exposure to chlorine dioxide can cause irritation to the nose and throat, causing coughing and chest pain;
eye irritation with watery eyes and seeing halos around lights.
Breathing chlorine dioxide can irritate the lungs causing coughing and/or shortness of breath. Higher exposures can cause a build-up of fluid
in the lungs (pulmonary oedema), a medical emergency but which might not occur for 24 hours, with severe shortness of breath and possibly death.
|
|
|
(Last update: March 2007) |
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
X
Y
Z
|
|
