The History of Hypochlorite

Some years after the discovery in 1774 of the gas called 'dephlogisticated salt spirit' by the Swedish chemist Carl Wilhelm Scheele, another chemist, the

Frenchman Claude-Louis Bertholet obtained in 1787 some bleaching solutions of this gas dissolved in water. In 1810 this gas was renamed 'Chlorine' by the Englishman Davy.

A small chemical industry in Paris directed by Leonard Alban, the 'Societe Javel', adopted the Bertholet process for the industrial production of a bleaching solution produced by dissolving gaseous chlorine (Cl2) in water. The factory was built in 1778 on the banks of the Seine. The financial partners were a group of court nobles, and the Count of Artois, brother of King Louis XVI, gave his name to the company. In 1787 the process was modified, and the chlorine, rather than being dissolved in water (to form an unstable though very active solution of hypochlorous acid [HOCl]), was made to react in a suspension of 'washing soda'. After filtration, a solution is obtained that is still effective in bleaching and much more stable, to which Alban gave the name of 'Eau de Javel'. This product, a solution of potassium hypochlorite, had immediate success both in France and in England, in as much as it was easily transported and stored. Curiously, Bertholet initially was reluctant to accept that the chlorine molecule (called 'Oxidizing Muriatic Acid') was bi-atomic. He accepted this fact only after a publication on the subject by Davy in 1816. Bertholet established that chlorine in solution produces a molecule called 'HOCl'. Davy and Bertholet discovered, in fact, the two forms of chlorine: in aqueous solution with pH < 7, it is mainly HOCl; whereas, in gaseous form, it is Cl2. In 1820 Labarraque replaced the potash solution with the more economical solution of caustic soda (NaOH) and obtained the solution of NaOCl that was called 'Eau de Labarraque', which found wide use as a disinfectant and bleaching agent.

Its uses are innumerable from industrial disinfection, to household use, but above all its germicidal properties were exploited in the food and hospital sectors.

NaOCl in itself is a relatively weak disinfectant compared to HOCl, but it functions as a reservoir for the successive formation of the acid by hydrolysis. The precise mechanism by which the HOCl kills microorganisms is not yet completely elucidated, but there are sufficient experimental data to affirm with certainty that the mechanism of action begins with permeation of the cell membrane, and thus the reaction with the enzymatic system of the microorganism attacked. NaOCl is the most widespread and commonly used household disinfectant in the world.

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