Most important Chemical Compound: Sodium Hypochlorite

History & Production & Application

Sodium hypochlorite, commonly known as bleach, is present in aqueous solutions ranging from 5% to 15% NaOCl. Household bleach typically constitutes a 5.25% solution, while industrial bleach is marketed as a 12% solution. When referring to sodium hypochlorite in this context, it is assumed to be the aqueous solution, exhibiting clarity, a slight yellowish tint, corrosiveness, and a distinctive chlorine odor. The discovery of chlorine gas is credited to Carl Wilhelm Scheele (1742–1786) in 1774, initially known as dephlogisticated salt spirit. By 1787, the French chemist Claude Louis Berthollet (1749–1822) explored the application of an aqueous solution of chlorine gas as a bleaching agent, leading to the production of bleaches by the Javel Company near Paris in 1788.

Bleaching powders, borax, lye, and blueing were prevalent bleach agents during the 19th century. The adoption of Louis Pasteur's (1822–1895) germ theory in the latter half of the century emphasized the necessity for sanitation and hygiene. Although hypochlorite solutions and bleaching powders were employed as general disinfectants in the early 19th century, the routine use of chlorine and its compounds in public water systems commenced towards the century's end. The first wastewater treatment plants utilizing chlorine were established in 1893 in Hamburg, Germany, and in 1894 in Brewster, New York. The inaugural drinking water plant in the United States employing chlorine was inaugurated in Chicago in 1908.

The surge in sodium hypochlorite production for bleaching and disinfection spurred large-scale industrial manufacturing. The prevalent method involved absorbing chlorine gas in a sodium hydroxide solution, a process represented by the chemical equation:Cl2(g) +NaOH(aq) → NaOCl(aq) + NaCl(aq) + H2O. . Dow Chemical Company, founded by Herbert Henry Dow (1866–1930), emerged as one of the initial major bleach producers, adopting electrolysis for chemical extraction.

Clorox, the prominent U.S. household bleach producer, traces its origins to 1913 when it was founded as The Electro-Alkaline Company in Oakland, California. Its original bleach solution comprised 21% sodium hypochlorite (NaOCl) and was later reformulated to 5.25% in 1916. Sodium hypochlorite's disinfection property, shared with calcium hypochlorite, stems from its ability to form hypochlorous acid (HOCl), a potent oxidizing agent. The equation NaOCl(aq) + H2O(l) → HOCl(aq) + NaOH(aq). outlines the generation of hypochlorous acid.

The bleaching efficacy of sodium hypochlorite arises from its capability to disrupt chromophores, the light-absorbing structures in organic molecules. Chromophores, often linked to conjugated systems featuring alternating single and double bonds, absorb specific wavelengths of light, leading to visible color. Sodium hypochlorite's oxidizing action breaks the double bonds in chromophores, either destroying or altering them to eliminate visible light absorption.

Sodium hypochlorite stands as the primary hypochlorite utilized for bleaching and disinfection, commanding 83% of global hypochlorite use. The remaining 17% is attributed to calcium hypochlorite. Approximately 1 million tons of sodium hypochlorite were globally consumed in 2005, with half employed in households for laundry purposes and disinfection. The remaining usage was predominantly in wastewater and drinking water treatment, alongside applications in pool sanitation, bleaching of pulp, paper, textiles, and as an industrial chemical.

Reference

Richard L. Myers (2009). The 100 Most Important Chemical Compounds: A Reference Guide. Greenwood Publishing Group. October 1, 2009. https://doi.org/10.1021/ed086p1182