Here is a complete recipe on how to make sodium cyanide.
First, 100 g of sodium hydroxide is mixed with 43g of cyanuric acid and 12g of carbon. This is heated to 600 Celsius with occasional stirring for at least an hour. If the bubbling goes out of control, turn down the temperature and let it come back under control before raising it again.
After the mixture is cooled, it is broken up and dissolved in methanol. After all the large chunks are converted to a powder, 100g of sodium bicarbonate is added to convert the excess sodium hydroxide into sodium carbonate. The solution is allowed to stir for 30 minutes and then filtered.
The filtrate maybe tested for cyanide by reacting a few drops with a solution of ferrous sulfate. A deep blue color of Prussian blue indicates cyanide ions are present.
The filtrate is then dried to obtain crude sodium cyanide. Approximate yield 19g.
The various processes for the manufacture of cyanide may be classified according to the source from which the nitrogen is derived. The principal methods in use are:
(a) Those in which refuse animal matter is used as the nitrogenous raw material, ferrocyanide being generally produced as an intermediate product.
(b) Those in which atmospheric nitrogen is employed to form cyanide compounds, directly or indirectly.
(c) Those in which ammonia or ammonium compounds form the nitrogenous raw material, including methods which utilize residues from gas-works.
PRODUCTION OF CYANIDES FROM REFUSE ANIMAL MATTER
Until about the year 1890, this was the method almost universally used. The raw materials required are: (1) Nitrogenous animal matter, such as horns, hoofs, dried blood, wool, woollen rags, hair, feathers, leather-clippings, etc. (2) An alkaline carbonate, such as pearl-ash, soda-ash, etc. (3) Iron filings or borings.
The alkali and the iron are first fused together at a moderate heat in an iron pan, or other suitable vessel, contained in a reverberatory furnace. The well-dried animal matter is then introduced in small quantities at a time and stirred in. The heat is then raised and the furnace closed so as to maintain a reducing atmosphere. The hard black mass which forms is then taken out and lixiviated with nearly boiling water. The crude ferrocyanide containing sulphides, sulphates, carbonates and thiocyanates, is crystallized out and purified by recrystallization. The ferrocyanide was formerly converted into cyanide by first dehydrating and then fusing, either alone or with alkaline carbonate:
K4Fe(CN)6+K2CO3 = 5KCN+KCNO+Fe+CO2
The cyanide so formed is always contaminated with cyanates and carbonates, and generally with small amounts of other salts (sulphides, chlorides, thiocyanates, etc.).
The procedure frequently adopted at present is to fuse with metallic sodium:
K4FeCy6 + 2Na = 4KCy + 2NaCy + Fe;
thus yielding a mixture of potassium and sodium cyanides free from cyanates, etc. The presence of sulphides and thiocyanates in the product is due chiefly to the sulphur contained in the organic matter. These compounds are partially decomposed and removed by metallic iron during the fusion. When the cyanide is made by direct fusion of ferrocyanide, the product contains carbide of iron, some nitrogen being given off in the process. Most of the volatile organic nitrogen is lost in the form of ammonia or nitrogen gas during the fusion for ferrocyanides, in the first stage of the process.
PRODUCTION OF CYANIDES FROM ATMOSPHERIC NITROGEN
It was observed by Scheele that when nitrogen is passed over a mixture of K2CO3 and charcoal heated to redness, a cyanide of potassium is formed. Many attempts were made throughout the nineteenth century to utilize this reaction for industrial purposes. One of the earliest was that of Possoz and Boissiere, who used a mixture of charcoal with 30 per cent. of potassium carbonate. This was kept at a red heat in fire-clay cylinders, through which a mixture of N and CO, produced by passing air over red-hot alkalized carbon, was allowed to pass for about 10 hours. The product was then lixiviated with water in presence of ferrous carbonate (spathic iron ore) to give a ferrocyanide.
It was also observed at an early date (by Clark, in 1837), that cyanides are formed as an efflorescence in blast-furnaces, and that the gases of these furnaces contain cyanogen. Bunsen proposed a special blast-furnace for the production of cyanide, in which coke and potash in alternate layers were to be heated by a strong blast, the fused cyanide running off at the bottom of the furnace. It was found, however, that a very high temperature was necessary, as the potassium compound must be reduced to metallic potassium before combination with atmospheric nitrogen takes place.
Better results were obtained by substituting barium carbonate for K2CO3, as in the process of Margueritte and DeSourdeval (1861). Air (deoxygenated by hot carbon) was passed over a previously ignited mixture of BaCO3, iron-filings, coal tar, and sawdust, whereby barium cyanide is produced. This is converted into sodium cyanide by fusion with sodium carbonate. The BaCO3 is first reduced to barium carbide (BaC2):
BaCO2 + 4C = BaC2 + 3CO.
This then combines with nitrogen to form Ba(CN)2. It has been found, however, that only about 30 per cent, of the barium is converted to cyanide, the remainder forming barium cyanamide by a secondary reaction:
Ba(CN)2 = C + BaCN2.
When calcium is substituted for barium in this process, practically the whole is converted into calcium cyanamide:
CaC2 + N2 = C + CaCN2.
Calcium cyanamide is also formed in the electric resistance furnace by passing nitrogen over a mixture of lime and charcoal:
CaO + 2C + N2 = CaCN2 + CO.
By heating the product at a high temperature with a further quantity of carbon, with the addition of salt-to prevent frothing and facilitate the reaction, the cyanamide is converted into cyanide as follows:
CaCN2 + C = Ca(CN)2.
The crude mixture so formed has been used as a substitute for potassium cyanide under the name of “ Cyankalium surrogat,” and is equivalent in cyanogen contents to about 30 per cent. KCN. [See Erlwein and Frank, U. S. patent, 708,333.]
An improved method more recently introduced is to convert the calcium cyanamide into sodium cyanide by the following series of reactions:
(1) By leaching with water, a crystallizable, easily purified salt is obtained, known as dicyan-diamide:
2CaCN2 + 4H2O = (CN · NH2)2 + 2Ca(OH)2.
(2) This, when fused with sodium carbonate and carbon, is largely converted into sodium cyanide:
(CN · NH2)2 + Na2CO3 + 2C = 2NaCN + NH3 + N + H + 3CO
A portion of the dicyan-diamide sublimes and polymerizes; this is recovered and re-treated with Na2CO3 in a subsequent operation. The cyanamide and dicyan-diamide are also utilized as sources of products valuable as manures, as they can be readily converted into ammonia, ammonium carbonate, urea, etc.
Cyanides may also be formed by the action of metallic sodium and carbon on atmospheric nitrogen (Castner); but it is preferable to use ammonia as the source of nitrogen in this reaction (see below).
PRODUCTION OF CYANIDES FROM AMMONIA OR AMMONIUM COMPOUNDS
When ammonia is passed over mixtures of heated alkali and carbon, only small quantities are converted into cyanide; better results are obtained by passing CO and NH3 through a molten mixture of KOH and carbon, but even by this means much of the ammonia is dissociated into N and H, owing to the great heat which is necessary. It is supposed that potassamide is an intermediate product:
In Castner’s process (Brit, patents, 12,218, 12,219, of 1894), molten sodium is allowed to flow through a mass of heated coke while ammonia gas is passed upward, the reaction being
2NH3 + 2C + 2Na = 2NaCN + 3H2.
The reaction takes place at a much lower temperature than in the previous process with KOH, and the losses by dissociation of NH3 and volatilization of the cyanide are consequently smaller. It probably takes place in two stages, forming sodamide as an intermediate product:
(1) NH3 + Na = NaNH3 + H (at 300° to 400° C).
(2) NaNH2 + C = NaCN + H2 (at dull red heat).
In a modification of this method used by the Deutsche Gold Silber Scheide-Anstalt, metallic sodium is melted with carbonaceous matter in a crucible, and then ammonia is led in at 400° C. — 600° O.; this forms disodium cyanamide:
Na2 + C + 2NH3 = Na2CN2 + 3H2.
By then raising the temperature to 700-800° C., the excess of C. interacts, forming sodium cyanide:
Na2CN2 + C = 2NaCN;
the whole operation being conducted in the same crucible.
Methods have also been proposed by J. Mactear, H. C. Woltereck, and others, in which cyanogen compounds are produced by the action of ammonia gas on gaseous carbon compounds at a high temperature.
In Mactear’s method (Brit, patent, No. 5037, of 1899) the reaction
2NH3 + CO = NH4CN + H2O
is supposed to take place in a closed chamber at 1800° to 2000° F., the products being condensed and absorbed in alkali hydrate and the ammonia liberated for reuse. Instead of CO, a mixture of CO with N and H (producer gas) may be used.
In Woltereck’s method (Brit, patent, No. 19,804, of 1902) “ perfectly dry ammonia and a volatilized or gaseous carbon compound, also perfectly dry, are passed together with hydrogen, in equal volumes, over a strongly heated catalytic agent, such as platinized pumice. One volume of NH3 and two volumes of ‘water-gas’ (CO + H2) make a convenient mixture. The HCN produced is absorbed in an alkaline solution.”
Cyanide has also been made from the trimethylamine (CH3)3N obtained by the distillation of beet-root molasses at a high temperature. This, at a red heat, decomposes, giving NH3, HCN, and H.
Another source of cyanogen compounds is the crude illuminating gas from the distillation of coal. In Knublauch’s method (Brit. patent, No. 15,164, of 1887) the gas is passed through a solution of an alkali or alkaline earth containing ferrous hydrate in suspension. The gas carries with it ammonium cyanide and thiocyanate, which are absorbed by the mixture and converted into ferrocyanide.
In Rowland’s process (U. S. patent, No. 465,600, of 1891) the gas is passed through a solution of an iron salt, thus forming ammonium ferrocyanide. This is converted into the calcium salt by boiling with lime. The calcium ferrocyanide may then be converted into the required alkali ferrocyanide by decomposing with an alkaline carbonate.
Bueb’s process (Brit, patent, No. 9075, of 1898) is a modification of the above, in which the cyanogen is separated in the form of an insoluble double compound by using a concentrated iron solution (FeSO4); the reactions said to take place are:
FeSO4 + H2S + 2NH3 = FeS + (NH4)2SO4.
2FeS + 6NH4CN = (NH4)2Fe2(CN)6 + 2(NH4)2S.
The insoluble product, known as ” cyanide mud,” is then treated to obtain marketable cyanogen compounds.
Many other modifications have been suggested.
Cyanides may also be obtained by desulphurizing thiocyanates by means of iron, or by zinc and carbon.
Manufacture of Cyanide from Beet-sugar Residues
C. A. Browne describes this process in Columbia School of Mines Quarterly (Ab3. Mining Magazine, Sept. 1913, p. 226).
The residue, containing 12 to 15 per cent, of potassium and 4 per cent, of nitrogen, is heated in retorts and yields a number of volatile products, including ammonia and methylamine. These gases are further heated in tubes to a temperature of 1000° C. whereby the nitrogenous compounds are converted into ammonium cyanide. After cooling and purifying, the gases are passed through sulphuric acid, thus yielding ammonium sulphate and hydrocyanic acid. The latter is absorbed in water, redistilled and collected in sodium hydroxide. This solution is evaporated and crystallized to obtain sodium cyanide.
The remaining combustible gases are led back to the furnace for heating the retorts. About three fourths of the nitrogen in the residues is recovered as ammonium sulphate and sodium cyanide, the remainder escaping as nitrogen gas.
About 5000 tons of sodium cyanide are produced annually by this process by two factories in Germany, the product being exported to the Transvaal.