As hazardous chemicals go, chlorine gas ranks as one of the more unpleasant to work with. Chlorine gas was the first chemical weapon deployed in WW1, when the German Army used it against Allied troops near Ypres in April 1915. One soldier later described his brush with chlorine gas:
“I got several breathes [sic] of the strong solution right from the shell before it got diluted with much air. If it hadn’t been for the fellow with me I probably wouldn’t be writing this letter because I couldn’t see, my eyes were running water and burning, so was my nose and I could hardly breathe. I gasped, choked and felt the extreme terror of the man who goes under in the water and will clutch at a straw.”
Just the idea of coming into contact with corrosive, toxic chlorine gas caused some infantrymen “illness.” For some scientists, that’s Tuesday. Not only is elemental chlorine a cheap, effective reagent used to chlorinate organic compounds and create a number of useful synthetic compounds, but it’s highly dangerous– reacting with water and cellular fluid to form hydrochloric acid if inhaled at concentrations greater than 30 ppm. As a result, it must be stored and handled carefully due to the risk to personnel. Chlorine’s high reactivity can result in poor reagent selectivity if not managed correctly, and its exothermic nature can set off a thermal explosion. As such, specialized training and equipment is required to use and store chlorine gas, but Austrian researchers have developed a pioneering method to streamline this process (published in Reaction Chemistry & Engineering).
Using a flow chemistry reactor, the team from the University of Graz combined hydrochloric acid with sodium hypochlorite, producing small amounts of chlorine gas as needed, with water and salt the only by-products. By producing only the amount needed, it can be “produced in place, separated and can then be consumed immediately,” according to Chemistry World. This eliminates the need to store chlorine cylinders and adhere to the complicated safety regulations required to do so. The method appears to be as effective as the traditional method, as “Kappe and his group tested their equipment on a number of standard organic chemistry reactions, for example the oxidation of secondary alcohols, which produced excellent yields.”
Additional study will be needed to replicate the findings, and it’ll be some time before this method can be widely adopted, but as we’ll see in future posts, scientists are developing innovative methods of on-demand production using raw materials stored at the site of use. Method development and emerging technologies will combine to make possible things we previously only dreamed of – like making chlorine gas user-friendly.