Manganese dioxide, reaction with hydrochloric acid

Carl Wilhelm Scheele (1742-1786) discovered chlorine in the reaction of hydrochloric acid with manganese dioxide (pyrolusite or brownstone ore). Recognized as an element by Sir Humphry Davy (1778-1829). 

Synthesis and Reactivity Chlorine was first prepared by the Swedish chemist K.W. Scheele in 1774 using the reaction of manganese dioxide with hydrochloric acid. Erroneously, he thought that it was a compound of oxygen, and ultimately it was named and identified as an element by Sir Humphry Davy in 1810. The reaction of hydrochloric acid with potassium permanganate provides a second convenient route to small quantities of chlorine. 

Chlorine is one of the halogen family of elements and the first of that family to be discovered. Swedish chemist Carl Wilhelm Scheele prodnced chlorine in 1774 by the reaction of manganese dioxide (Mn02) with a solntion of hydrochloric acid (HCl). In 1810 English chemist Sir Hnmphry Davy determined chlorine to be an element and named it for the color of the gas (the Greek word chloros means pale green ). 

At the end of the reaction time there was no unreacted amine as shown by the following test A 10-ml. aliquot was filtered through Supercel to remove the manganese dioxide, and the filtrate was added to a mixture of 25 ml. of benzene and 25 ml. of water. Extraction of the benzene layer with 10% hydrochloric acid, followed by the addition of sodium hydroxide, gave no oil layer or characteristic odor of the free amine. 

The reaction mixture is cooled somewhat (Note 5) and filtered through a large Buchner funnel. The manganese dioxide cake is removed from the funnel and stirred to a smooth paste with 1 1. of fresh water. The slurry is filtered, and the washing is repeated. The total filtrate, about 10 1., is evaporated under reduced pressure on the steam bath to a volume of approximately 3 1. (Note 6). The solution is swirled or stirred gently while 550 ml. (6.6 moles) of 36% hydrochloric acid is cautiously added (Note 7). Evaporation under reduced pressure is then continued imtil a moist cake of solid potassium chloride and 2,3-pyrazinedicar-boxylic acid remains in the flask (Note 8). 

Preparation of Chlorine from Hydrochloric Acid by the Action of Various Oxidizing Agents. 1. Spill a small amount of manganese dioxide into a test tube and add concentrated hydrochloric acid. Carefully smell the chlorine by directing a stream of it toward your face with a wave of your hand. Write the equation of the reaction. 

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