Cyanation of aromatic hydrocarbons

Cyanation of aromatic hydrocarbons, also a carbon-carbon coupling reaction, is achieved in the case of anthracene in MeCN-Et4NCN to yield 54% 9,10-dicyanoanthracene [165]. The cyanation is simplified when it is carried out in an emulsion system (aqueous sodium cyanide, dichloromethane, and TBAHSO4). Its synthetic utility in this mode has been demonstrated for the preparation of 4-alkoxy-4-cyanobiphenyls, a class of liquid crystals [166]. 

There have been several recent investigations into the mechanism of photo-cyanation of aromatic hydrocarbons. The process with naphthalene, biphenyl, and phenanthrene has been subjected to a kinetic analysis the reactions in dry or aqueous methyl cyanide are shown to involve two transient species, the first of which is an ionic complex formed from a triplet excimer of the arene, or, in the presence of an electron acceptor, from a triplet exciplex. Reaction of the transient complex with the cyanide ion yields the radical ArHCN, and in aqueous methyl cyanide this second transient reacts with itself to produce dihydrocyano- and cyano-compounds. In dry methyl cyanide the radical species is oxidized to the cyano product. 

Photochemical cyanation of aromatic hydrocarbons in acetonitrile solution is a higher yield process when the potassium cyanide complex of 18-crown-6 is the cyanide ion source [31] compared to similar reactions in mixed organic aqueous solvent systems [32] (see Eq. 7.16). A ten-fold excess of 18-crown-6/KCN over the aromatic hydrocarbon (present in 10 " M) was used. The yield improvements were attributed to increased activity of cyanide due to diminished hydration of the ion. Biphenyl, naphthalene, phenanthrene, and anthracene were photocyanated in 50%, 15%, 25% and 20% yields respectively the latter being an equimolar mixture of mono and dicyanation products [31]. 

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See also in sourсe #XX -- [ , ]

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