Patented June 15, 1926. 1,589,041 UNITED STATES PATENT office. GEORGE BARSKY, OF NEw YORK, N. Y., ASSIGNOR TO AMERICAN CYANAMID COMI PANY, OF NEW YORK, N. Y., A CORPORATION OF MANE, METHOD or MAKING POTASSIUM FERRICYANIDE. Application filed October 2, 1925. Serial No. 60,046. This invention relates to the production of potassium ferricyanide by the oxidation of tals which may be further purified by re ferrocyanide by chemical reagents. w crystallization. I do not carry the reaction It has been customary to make potassium to absolute completion but stop the intro 55 5 ferricyanide by providing a solution of po duction of chlorine at a convenient point and tassium ferrocyanide and passing chlorine thus avoid the formation of the undesirable therethrough, keeping the solution cold green compounds incident to over-chlorina throughout the operation until conversion tion. I have discovered that, contrary to was complete. An excess of chlorine should the prior methods, it is not essential to keep 60 10 not be used, nor should the solution be al the solution cool, but that decomposition lowed to become warm as such conditions during the reaction may be prevented by the tend to the formation of complex, insoluble, addition of a small amount of a protective green compounds, which are difficult to re alkaline material, such as potassium hydrox move. The solution was then evaporated ide, to the reacting mixture. The mother 65 ls and the ferricyanide allowed to crystallize on liquor from the crystallized product, con cooling; the mother liquor was again evap taining a number of constituents, is treated orated and the salt crystallized therefrom, to reduce the ferricyanide content to ferro but it was contaminated with potassium cyanide, and it then reenters the process, and chloride. This method was fairly success accomplishedI have found in that a very this satisfactory reduction maymanner be 70 20 ful but great care was necessary to prevent by the use of calcium formate. the solution from heating up and forming The accompanying drawing is a flow sheet the undesirable green compounds, and the showing the adaptation of my improvements introduction of chlorine into the solution to the production of potassium ferricyanide had to be carefully regulated to convert all from calcium ferrocyanide. of the ferrocyanide without adding an ex I first prepare a solution 1 of calcium fer cess thereof. The cost of evaporation of rocyanide to which is added a sufficient the resulting solution was considerable. amount of potassium chloride 2 to form cal The present invention is adapted to over cium potassium ferrocyanide 3, which pre come these difficulties, it being among the cipitates out and is removed by filtration. . 0 objects of this invention to provide a method It is then digested with potassium carbonate of making potassium ferricyanide in which 4 to produce potassium ferrocyanide solu it shall not be necessary to maintain the solu tion 5 and calcium carbonate which is re tion very cold during the reaction period, moved by filtration, and the solution is evap which shall avoid the necessity of evaporat orated in 6 to crystallize at least ing the solution, and in which the control of ferrocyanide 1 into the resultingpart slurry,of the the various factors entering into the reaction which contains a small quantity of potassium 14needIt isnot also be amongvery close. the objects of my inven hydroxide, say 4% of the ferrocyanide pres tion to provide a substantially continuous ent to prevent decomposition, chlorine is process and one in which the various mother passed causing oxidation of the ferrocyanide liquors are completely utilized in the reac and conversion to potassium ferricyanide 8, tion. butbefore the allintroduction the ferrocyanide of chlorine is isconverted. stopped In practicing my invention I provide a Crystals of ferricyanide are formed during solution of potassium ferrocyanide into the reaction and the crystals of ferrocyanide which chlorine is passed as heretofore, but go into solution. The mixture is subjected I utilize a saturated solution containing an to filtration, and the crystals are purified, excess of solid potassium ferrocyanide and, if desired, by recrystallization in the pres as a result, as the reaction, proceeds the po ence of a small amount of potassium hydrox tassium ferricyanide produced crystallizes ide 9. The mother liquor 10 resulting from out of the solution while the excess of potas the recrystallization of the ferricyanide is sium ferrocyanide is dissolved, giving sub returned to the potassium ferrocyanide solu stantially pure potassium ferricyanide crys tion which is then subjected to the action 1,589,041 scope of my invention being defined in the of the chlorine, and its contained potassium claims appended hereto. hydroxide furnishes the alkalinity necessary What I claim is: to prevent decomposition during the chlori 1. The method of making potassium fer nation.The mother liquor 11 from the filtration- ricyanide which comprises providing a solu 70 of the potassium ferricyanide crystals con tion of potassium ferrocyanide, adding a small amount of alkali thereto, and oxidiz tains potassium ferricyanide and potassium ing the solution to ferricyanide. chloride, is treated with calcium formate 12 2. The method of making potassium fer and lime 13 in the presence of steam 14, re ricyanide which comprises providing a solu s 0. sulting in the production of calcium potas tion of potassium ferrocyanide, adding a sium ferrocyanide 15 together with other small amount of alkali thereto, and oxidizing soluble and insoluble compounds, the whole the solution to ferricyanide by passing potassiumbeing added ferrocyanide to the vesselin is being which precipitated. calcium chlorine thereinto. s The cycle of operations is then repeated. 3. The method of making potassium fer In the practice of my invention I need not ricyanide which comprises providing a solu start with calcium ferrocyanide. For in tion of potassium ferrocyanide, adding a stance, Idissolved 9.3 kilograms of ground small amount of alkali thereto, oxidizing potassium ferrocyanide in 10 liters of water the solution to ferricyanide by passing 20 and added 200 grams of potassium hy chlorine thereinto, filtering off the crystals droxide, the amount of potassium ferrocy formed and recovering the ferro- and ferri anide present being in excess of its solubil cyanides from the filtrate. ity. The mixture was agitated, and chlorine 4. The method of making potassium fer was passed in until the solution began to ricyanide which comprises providing a solu 25 darken. Crystals of potassium ferricyanide tion of potassium ferrocyanide, adding a were formed and were filtered off and dried small amount of alkali thereto, oxidizing in a vacuum oven. The filtrate was boiled the solution to ferricyanide by passing with 280 grams of calcium formate, (60% chlorine thereinto, filtering off the crystals pure), and 200 grams of lime, for two hours formed and treating the filtrate to reduce the Os 30 with constant stirring. The mass was fil ferricyanide therein to ferrocyanide. tered and then digested with potassium car 5. The method of making potassium fer bonate, giving a solution of potassium ferro ricyanide which comprises providing a solu cyanide which may be utilized for the pro tion of potassium ferrocyanide, adding a duction of potassium ferricyanide as above small amount of alkali thereto, oxidizing 00 35 described, or for other purposes. the solution to ferricyanide by passing It will be noted that my process produces chlorine thercinto, filtering off the crystals crystalline potassium ferricyanide directly formed and treating the filtrate to reduce the without the necessity of evaporating solu ferricyanide therein to ferrocyanide by add tions thereof with the consequent decomposi ing an organic reducing agent thereto. 40 tion of ferricyanide which can only be avoid 6. The method of making potassium fer 05 ed by evaporation in a vacuum, a relatively ricyanide which comprises providing a solu expensive rocedure. There is no substan tion of potassium ferrocyanide, adding a tial loss of cyanide in the process since the small amount of alkali thereto, oxidizing mother liquors produced are re-circulated in the solution to ferricyanide by passing the system and I have obtained a total re chlorine thereinto, filtering off the crystals 110 covery of materials of 98%, although the re formed and treating the filtrate to reduce the covery of ferricyanide at each operation is ferricyanide therein to ferrocyanide by add only 70% to 75% of the total cyanide pres ing calcium formate thereto. ent. The proportions of ingredients used 7. The method of making potassium ferri SO may be varied within wide limits with good cyanide which comprises providing a solu 5 results and no close control of the details of tion of potassium ferrocyanide, adding a the process is necessary as the addition of small amount of alkali thereto, oxidizing a small amount (2%-10%) of potassium hy the solution to ferricyanide by passing droxide to the reaction mixture prevents de chlorine thereinto, filtering off the crystals 35 composition without the necessity of artifi formed and treating the filtrate to reduce the 120 cial cooling of the solution other than by use ferricyanide therein to ferrocyanide by add of ordinary cooling water. The product is ing calcium formate and lime thereto. relatively pure, even the first crude crystals 8. The method of making potassium fer containining less than 3% of potassium chlo ricyanide which comprises providing a solu 60 ride and about 0.8% of potassium ferrocyan tion of potassium ferrocyanide, adding a ide; a simple recrystallization of the product small amount of alkali thereto, oxidizing reduces the said impurities to 0.3% and the solution to ferricyanide by passing 0.2%, respectively. Various changes may be chlorine thereinto, filtering off the crystals made in the details of the process as will be formed, treating the filtrate to reduce the 65 understood by those skilled in the art, the ferricyanide therein to ferrocyanide, and 80 1,589,041 8 converting the same to potassium ferrocy- idizing the solution to ferricyanide by pass anide. - ing chlorine thereinto. 9. The method of making potassium fer- In testimony whereof, I have hereunto 10 tionricyanide of potassium which comprises ferrocyanide providing containing a solu- an subscribed1925. my name this 30th day of Sept., excess of solid potassium ferrocyanide, add ing a small amount of alkali thereto and ox- GEORGE BARSKY.