Synthesis of potassium dithionate

Preparation of potassium dithionate dihydrate

Preparation of potassium dithionate dihydrate

Preparation of potassium dithionate dihydrate

44g of potassium metabisulfite are added in a solution of 100g of potassium hydroxide in one liter of water, add 5 drops of phenolphthalein indicator and then more of the 10% potash solution until a pink color just forms. The obtained solution is diluted to 500ml with water and the solution stirred mechanically while a solution of 65g of silver nitrate in 75ml water is added. The temperature of the agitated mixture is slowly raised to the boiling point over a flame. In the course of 20-30 minutes the white precipitate of silver sulfite disappears and a greyish mass of crystalline silver settles sharply at the bottom of the reaction vessel. The hot solution is filtered through a large suction funnel and the silver residue washed twice with 50ml of boiling water. The combined filtrate and washings are concentrated with continual stirring over a free flame to a volume of about 350-400ml. During the evaporation any small amounts of colloidal silver that settle out are filtered off. The solution is cooled in running water and crystallization is induced by scratching the walls of the vessel. The precipitated crystals are filtered on a large funnel and allowed to remain there without washing. The filtrate is heated to 75-80°C and 100ml of boiling 95% alcohol is added. The solution is cooled as above and the deposited solid is added to the first batch on the filter. The combined product is pressed well, washed first with 95% alcohol and then with acetone, and dried in air. Yield about 40g.

Inorganic laboratory preparations, by G. G. Schlessinger, 60-61, 1962

Preparation of potassium dithionate dihydrate

Preparation of potassium dithionate dihydrate

50g of highest quality (>95%) finely powdered manganese dioxide are placed in a 500ml suction flask with 250ml of water. The flask is fitted with an inlet tube leading almost to the bottom of the vessel. The mixture is cooled in an ice-water bath and a stream of sulfur dioxide is led in (3 bubbles/sec) for a period of about two hours, during which time the flask is frequently swirled and good cooling maintained. The black dioxide disappears gradually in the course of the reaction, leaving a light brown slurry. The crude manganese dithionate solution is heated to boiling and small portions of powdered barium hydroxide are added until a sample of the mixture, when filtered and acidified slightly with hydrochloric acid, gives no more test for sulfate ion with dilute barium chloride solution. (Sulfate is formed as a by-product in the oxidation of the sulfur dioxide by pyrolusite. Low temperatures of reaction minimize the formation of it) . An excess of barium hydroxide does no harm as it is removed later. The sulfate-free mixture is kept hot and stirred while about 52g of anhydrous potassium carbonate is added in 2g portions until the liquid is just alkaline (pale blue) to red litmus paper. The hot slurry is suction-filtered and the residue is stirred up with 200ml of hot water and refiltered. The combined washings and main filtrate must be slightly alkaline; otherwise a little more potassium carbonate is added and the solution refiltered through a clean paper. The potassium dithionate is recovered by evaporation on the steam bath to a final volume of about 10ml. Successive crops of crystals are isolated by cooling and filtering without washing. Any insoluble material that forms during the initial concentration is filtered off.

Inorganic laboratory preparations, by G. G. Schlessinger, 60-61, 1962



InChI Key


Canonical SMILES


Depositor-Supplied Synonyms

dipotassium dithionate, Potassium dithionate, 13455-20-4, AC1L4YQH, AC1Q1TT5, CTK4B9265, EINECS 236-649-3, AR-1I6195, Dithionic acid,potassium salt (1:2), IN004332

Removed Synonyms

Sodium dithionate, 14970-71-9 (Parent), CID166813, 178979-74-3

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