Chlorine dioxide is a neutral chlorine compound with the formula ClO2. Although similar in name to chlorine, chlorine dioxide is very different from elemental chlorine, both in its chemical structure and in its behavior (think carbon v. carbon dioxide). One of the most important qualities of chlorine dioxide is its high solubility in water, especially in cold water. Chlorine dioxide does not hydrolyze (or undergo a chemical breakdown reaction) when it enters water. Instead, chlorine dioxide remains intact as a dissolved gas in water. In comparison, chlorine dioxide is approximately 10 times more soluble in water than chlorine.
The molecule ClO2 has an odd number of valence electrons, and therefore, it is a paramagnetic radical. Its electronic structure has long baffled chemists because none of the possible Lewis structures is very satisfactory. In 1933, L. O. Brockway proposed a structure that involved a three-electron bond. Chemist Linus Pauling further developed this idea and arrived at two resonance structures involving a double bond on one side and a single bond plus three-electron bond on the other. In Pauling’s view the latter combination should represent a bond that is slightly weaker than the double bond. In molecular orbital theory this idea is commonplace if the third electron is placed in an anti-bonding orbital. Later work has confirmed that the highest occupied molecular orbital is indeed an incompletely-filled antibonding orbital.
Acidification of Chlorite
5 ClO2 + 4H+ → 4 ClO2 + 2 H2O + Cl-
Oxidation of Chlorite by Chlorine
2 NaClO2 + Cl2 → 2 NaCl + ClO2
Oxidation of Chlorite by Persulfate
2 NaClO2 + Na2S2O8 → 2 ClO2 + 2 Na2SO4
Action of Acetic Anhydride on Chlorite
2 NaClO2 + (CH3CO)2O + H2O → ClO2 + NaCl + CH3COOH + CH3COONa + H2
Reduction of Chlorates by Acidification in the Presences of Oxalic Acid
2 HClO3 + H2C2O4 + H2O → 2 ClO2 + 2 CO2 + 2 H2O
Reduction of Chlorates by Sulfurous Anhydride
2 NaClO3 + H2SO4 + SO2 → 2 ClO2 + 2 CO2 + 2 NaHSO4
ClO2 is a very small molecule, e.g., it can penetrate into very small areas. As a gas Cl02 will completely and evenly fill any space, giving it unmatched distribution and diffusion.
Cl02 is much smaller than other particles and molecules. Because of its size, Cl02 is a stronger oxidizer and works at much lower concentrations. Because ClO2 works at much lower concentrations, it is also less corrosive.
As a true gas, Cl02 is able to contact organisms wherever they are located and penetrate into tight, hidden or difficult to reach areas, including microscopic cracks and crevices.