United States Patent Office

3,189,410 United States Patent Office Patiented June 15, 1965 2 ganic liquid reaction medium, under anhydrous condi 3,189,410 tions, in accordance with the equation METHOD OF PRODUCING ANHYDROUS ALKAL METAL CYANDE ral Brown Johns, Marblehead, Mass., assignor to where M is an alkali metal with an atomic weight below Monsanto Research Corporation, St. Louis, Mo., 40 and R is an inert organic radical. a corporation of Delaware The stated method is particularly conveniently adapted No Drawing. Filed Mar. 29, 1963, Ser. No. 269,177 for production of the hydrolysis-sensitive cyanides of the 7 Claims. (CI. 23-79) lower atomic weight alkali metals, sodium and lithium, This invention relates to alkali metal salts and more O and especially so for lithium cyanide preparation. particularly, provides a novel method for the preparation The organolithium compounds such as the lithium alkyls of an alkali metal cyanide. are Soluble in organic hydrocarbon solvents such as pen The cyanides of the alkali metals vary quite markedly tane and hexane, providing desirable homogeneity of the in the ease with which they undergo hydrolysis. Potas reaction mixture thereof with the hydrogen cyanide react sium cyanide is relatively resistant to hydrolysis, and can 5 ant. The reaction proceeds smoothly and readily to com be obtained in pure form from the reaction of potassium pletion, which is in contrast to the reaction of metallic carbonate with carbon and ammonia, or from the reac lithium with anhydrous HCN, wherein reaction is in tion of potassium hydroxide with hydrogen cyanide. complete in the absence of a liquid organic reaction medi Moreover, the anhydrous salt is the stable form at con tin, and in presence of a solvent, must be effected with veniently low temperatures, so that it can be precipitated particular rapidity to avoid the appearance of HCN poly from aqueous solutions without difficulty. For sodium mer. The lithium cyanide product of the present novel cyanide, the reaction of sodium carbonate with carbon method precipitates from the liquid reaction medium as and ammonia gives impure product, and the sodium hy a fine crystalline mass which is readily separated from droxide reaction with HCN gives product which is only other reaction mixture components to provide 100% yields about 90% NaCN, the rest consisting of hydrolysis and 25 of pure anhydrous product. The freedom of this product oxidation products. HCN released by hydrolysis of a from contaminants is such that it can be stored for weeks lower atomic weight alkali metal cyanide tends to polym in dry air without discoloration. erize, the polymerization being catalyzed by base, with Lithium cyanide is very soluble in alcohol, insoluble the result that the black polymer of HCN is formed. in hydrocarbon solvents, and somewhat soluble in oxy This is a particularly objectionable, discoloring organic 30 genated Solvents such as dimethylformamide, dimethyl impurity in a cyanide salt product. Sulfoxide and dimethylacetamide. Slurries of the anhy Lithium cyanide is even more hydrolysis-sensitive than drous salt in these solvents have been found to be re sodium cyanide. In the reaction of solid lithium hydrox markably reactive with compounds containing replace ide and hydrogen cyanide gas, the product is only about able halogen atoms, and are especially useful for replac 40% LiCN. When the reaction of lithium hydroxide and 35 ing halogen with CN in compounds of boron, silicon and hydrogen cyanide is conducted under anhydrous conditions phosphorous. in ether, the product obtained is still only about 60% Although boron trichloride does not react with silver lithium cyanide, the rest consisting of undesirable con cyanide, it reacts vigorously with lithium cyanide, and taminants which are difficult to separate, such as the black indeed, moderation of the reaction by means of a solvent polymer of hydrogen cyanide. is necessary to prevent decomposition. Chlorodiphen Valuable uses exist for pure, anhydrous form of the ylphosphine oxide in benzene or xylene reacts neither with lower atomic weight alkali metal cyanides which make it potassium cyanide nor with silver cyanide, but with lithi desirable to develop methods for providing these cyanides um cyanide the cyano derivative is obtained in 80% yield. essentially free of contaminants. Thus, use has been When acetonitrile is used as solvent, the yield increases to made of the metallic element as a starting material, in the 95%. Displacement of the halogen atoms of diphenyldi manufacture of sodium cyanide employing metallic sodi cholorosilane by lithium cyanide proceeds vigorously in um, ammonia and carbon, for example. Lithium cyanide dimethylformamide. The lithium cyanide product of the in pure, anhydrous form can be used to effect unique re present invention can also be used to displace the halogen actions, as further set forth hereinafter. - atom of a reactive organic halide such as co-bromoaceto Provision of these lower atomic weight alkali metal 50 phenone to provide the corresponding cyano derivative. cyanides in pure, anhydrous form as accomplished here The presently provided novel method for anhydrous tofore has involved undesirable and hazardous practices alkali metal salt synthesis is also applicable, as stated such as handling of the metallic element, a requirement above, to the production of anhydrous sodium cyanide. that the conversion of the element to the cyanide be ef The organo-Sodium compounds such as the sodium alkyls, fected rapidly if byproduct formation is to be avoided, by contrast to the corresponding lithium alkyls, are in and so forth. Thus, a need exists for a convenient method Soluble, or practically insoluble, in inert organic solvents for preparing the really anhydrous cyanides of these alkali Such as hydrocarbons like benzene and hexane. However, metals, and particularly so in the case of lithium cyanide, it has now been established that a slurry of such a sodium in view of the extreme ease of its hydrolysis and polymer hydrocarbyl in an inert hydrocarbon diluent will react ization of the resulting HCN. 60 with hydrogen cyanide to completion, yielding the desired It is an object of this invention to provide an improved anhydrous inorganic cyanide, free of hydrolysis products. method for the preparation of a lower atomic weight Thus, whereas the stated insolubility could have been alkali metal cyanide. expected to produce a less complete conversion than the A particular object of this invention is to provide a lithium alkyls give, the present method is in fact found convenient method for the preparation of a lower atomic 65 to be usefully applicable for production of the anhydrous weight alkali metal cyanide which avoids hydrolysis and cyanide of sodium, also. The present method can be produces substantially pure product. practiced using readily handled organic solvent/diluent These and other objects will become evident upon con reaction media, avoiding the high temperatures and the sideration of the following specification and claims. other inconveniences of operating with the ammonia proc In accordance with the present invention, an alkali 70 ess for anhydrous sodium cyanide manufacture. metal cyanide is prepared by contacting an alkali metal The method of this invention may also be used for prep organic derivative with hydrogen cyanide in an inert or aration of pure anhydrous potassium cyanide from an 3,189,420 3. 4. organo-potassium compound such as a potassium alkyl, hexane, light petroleum, kerosene and the like. Ethers by reaction with hydrogen cyanide, where for some reason such as diethyl ether and tetrahydrofuran dissolve lithium ... the present method is the procedure of choice for this alkyls, but tend to form complexes with them, making is cyanide. - . these less desirable solvents. - Referring now to the organometallic compounds em 5 The procedure used in conducting the method of the ployed in conducting the present novel method, these are invention consists in contacting hydrogen cyanide with the alkali metal organic compounds represented by the the organometallic compound of the alkali metal in pres formula R-M where M is an alkali metal with an atomic ence of the inert organic liquid reaction medium. The weight below 40 and R is a monovalent inert organic rad hydrogen cyanide is introduced gradually into a solution tical. In the cyanide-forming reaction - O or dispersion of the organometallic, in a presently pre ferred procedure. This is not critical, however, and the R-M+HCN->R-H+M-CN organometallic can alternatively be added to a solution where R and M are as defined above, the organic radical of the HCN, the addition can be made all at once, and : R is converted to an organic compound R-H, which is a so forth. Though approximately the stoichiometric pro byproduct of the reaction. - - - portions, a 1:1 molar ratio, are desirable for economy, The organic alkali metal compound employed as Start this is not essential... It is found that excess HCN, which ing material may include any organic radical which is free. is soluble in an organic solvent like benzene, can readily of interfering substituents and which, on formation of an be washed out of the metal cyanide product with such organic compound by displacement of its bond to the solvents. That gradual addition of the hydrogen cyanide ... alkali metal radical, can be removed from the reaction is effective shows that presence of excess organometallic mixture by procedures not deleterious to the desired alkali does not interfere with the reaction, and at least with metal cyanide product, such as volatilization at tempera organometallics like lithium alkyls, which are soluble in tures below the decomposition temperature of the cya a hydrocarbon solvent whereas lithium cyanide is not, nide. In general, the useful compounds are those in which excess organometallic can also readily be removed from the stated organic radical is of moderate to low molecular the metal cyanide product by washing with organic sol weight, preferably containing up to about 12 carbon atoms, vents.

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