Chemistry of Sodium Chlorite Bleaching

Chemistry of Sodium Chlorite Bleaching

Sodium Chlorite ((NaClO2) is known as anhydrous salt. Anhydrous sodium chlorite is a colourless hygroscopic substance. It is stable and when heated sodium chlorite decomposes according to the following reaction:
NaClO2 = NaCl + O2

Sodium chlorite may explode under impact only in the presence of traces of organic substances. It is readily dissolved in water. As an oxidizing agent, sodium chlorite occupies the place somewhere between hypochlorite and chlorite. Thus, for instance, the oxidation-reduction potential of the reaction.
Cl+4O2 + 4H+ + 4e- = Cl0 + 2H2O

In a strong alkaline medium (pH-11) hypochlorite quickly oxidizes to chlorate as
NaClO2 + NaOCl = NaClO3 + NaCl

However, oxidation proceeds only to chlorine dioxide:
2NaClO2 + NaOCl + H2O = ClO2 + NaCl + 2 NaOH
Chlorine reacts with chlorite in the same way
2NaOClO2 + Cl2 = 2 NaCl + 2 ClO2
By simple acidifying of chlorite solution chlorine dioxide is obtained.
5NaClO2 + 4HCl = 2ClO2 + 5 NaCl + 2H2O
Acidic Sodium chlorite bleaching solution have a pH 4.
Hefti gives the following schemes of sodium Chlorite decomposition in an acid medium.
i) 5ClO-2 + 2H+ = 4ClO2 + Cl- + 2OH-
ii) 3ClO-2 = 2 ClO3 + Cl-
iii) ClO2 = Cl + 2O
Sugar oxidation was taken as an example to study the effect of sodium chlorite on fibrous material and particularly on cellulose. The sugar oxidation are shown by the following reaction:
R—CH2OH + 3ClO2 = R—CHO + Cl +2OH
Sodium chlorite oxidation potential is insufficient for breaking the link between the carbon atoms in the chain of the main valencies of cellulose.