[506-64-9] · CAgN · Silver(I) Cyanide · (MW 133.89)
Physical Data: mp >300 °C; dec 320 °C; d 3.95 g cm-3.
Solubility: sol nitric acid, ammonium hydroxide; slightly sol cold water; sparingly sol methylene chloride.
Form Supplied in: white to off-white powder.
Handling, Storage, and Precautions: may be fatal if inhaled, swallowed, or absorbed through the skin. It causes eye and skin irritation and may cause argyria (blackening of the skin). It is highly toxic and light sensitive; contact with acids should be avoided (releases HCN gas). The solid should be stored in a cool dry place under an inert atmosphere. Use in a fume hood.
Silver cyanide can be used to prepare a number of isocyanides. Ethyl isocyanide,1 for example, can be prepared by heating Ethyl Iodide with silver cyanide (eq 1). This reaction should be carried out in a well ventilated area because of its vile odor. Ethyl isocyanide has also been known to explode, so all heated operations should be done behind a safety shield. N-Acyl isocyanides2 are highly unstable compounds which can be readily prepared by the reaction of acyl iodides with AgCN (eq 2). These compounds are capable of reacting as
electrophilic carbenes, unlike alkyl and aryl isocyanides, which makes them attractive for cycloadditions (eq 3).2 Silver cyanide also reacts with 4-ethoxybromobutane to give the corresponding isocyanide.3
1-Isocyano sugars can be prepared in good yields by the reaction of AgCN with benzyl-protected halogenated glycosides at room temperature (eq 4).4
The conventional method for preparing esters by the reaction of an acyl chloride with an alcohol in the presence of pyridine is not useful in certain hindered ester cases, where this method is too slow and incomplete. Hindered esters can generally be synthesized rapidly and in higher yields by reacting an acyl chloride with an alcohol in the presence of AgCN.5 Highly hindered steroidal esters,6 for example, have been prepared from the appropriate steroidal alcohol and a hindered acid chloride, such as pivaloyl chloride, using AgCN (eq 5).
Treatment of o-hydroxyamines with t-Butyl Isocyanide in the presence of AgCN yields cyclized products in high yields. By varying the structure of the starting material, a wide variety of heterocycles are available including 2-oxazolines, 2-imidazolines, tetrahydro-2-pyrimidines, thiazolines, and dihydro-1,3-oxazines (eq 6).7
Silver cyanide can also be used as a catalyst in the reactions of organomagnesium reagents with chlorosilanes, which afford tetraorganosilanes8 in higher yields than in the uncatalyzed reactions. When dioctylmagnesium reacts with Methyltrichlorosilane in the presence of AgCN (eq 7) an 80% yield is achieved while in the uncatalyzed reaction the product yield is only 16%.
Although phosphoroisothiocyanatidates (1) are readily accessible compounds, an isomer9 (eq 8) was first prepared in 1972 by the reaction of AgCN and bis(neopentyloxy)phosphorosulfenyl chloride which yielded dineopentyl phosphorothiocyanatidate.
The first trifluoromethyl-iodine compound with more than one iodine-carbon bond was obtained by the reaction of AgCN with trifluoromethyliodine dichloride in methylene chloride (eq 9).10 Silver cyanide reacts with difluoroaminocarbonyl chloride (eq 10) to give N,N-difluoroaminocarbonyl cyanide.11
Darlene A. Cothron & Eric J. Stoner
Abbott Laboratories, North Chicago, IL, USA