Thiocyanates reaction with aromatic compounds

Alkylation of metal thiocyanates has been known to produce isothiocyanates, and this can be followed by treatment with carbon nucleophiles to give thioamides. Alternatively, metal thiocyanates can be used in the Friedel-Crafts reactions of aromatic compounds. For example, the reactions of aromatic compounds bearing alkoxy groups and heteroaromatic compounds with potassium thiocyanate under acidic conditions are carried out at 30 °C (Eq. 11) [34]. In the reaction a large excess of methanesulfonic acid is used. 

In organo-fluorine compounds fluorine atoms can be eliminated by nucleophilic sulfur species to form C —S bonds. In principle, the fluorine to be eliminated can be bonded to aliphatic or araliphatic compounds, as well as to aromatic or heterocyclic compounds however, the replacement proceeds more efficiently the more the fluorine is activated. Therefore, the synthetic usefulness of these reactions is the broadest with fluoroaromatic compounds, including heteroaromatics, with which the reactions often proceed smoothly under mild conditions. The nucleophilic sulfur compound to be reacted is. in most cases, an aliphatic or aromatic thiol or a metal sulfide, but reactions with, for example, thiourea or ammonium thiocyanate have also been described. The sulfur introduced this way can be either oxidized or removed by reduction, opening additional possibilities for modifications of the original fluoro compounds. 

Although thiocyanogen does not react with benzene or naphthalene, it does react with more highly condensed aromatic compounds such as anthracene benzopyrene, etc.761 The substance may be added to a solution of thiocyanogen (for its preparation see page 104), but it is simpler to generate the thiocyanogen in situ. The (SCN)2 is produced in the reaction mixture from alkali thiocyanate and bromine or chlorine or from Cu(SCN)2. Suitable solvents for work with bromine or chlorine are acetic acid, methanol, and methyl acetate, the last two saturated with NaBr or NaCl. 

For introduction of SCN into aromatic compounds the Sandmeyer reaction or its Gattermann variant is much more widely applicable than direct replacement of H by SCN (see page 202). An aqueous thiocyanate solution and CuSCN are added to a diazonium salt solution prepared in the usual way, or the addition is made gradually in the reverse direction — the diazonium salt to an aqueous solution of K3[Cu(SCN)4] copper powder can also be used.1264-1266 Reaction, with evolution of nitrogen, often occurs at room temperature or on... 

Absolute rate constants have been determined for the reaction of the hydroxyl radical with a variety of aromatic compounds in aqueous solution. The rate constants obtained are significantly higher than values previously reported. Rate constants for the reaction of the hydroxyl radical with methyl alcohol and ethyl alcohol have also been determined by competition kinetics using three of these absolute rate constants as reference values. Comparison of our results with the published values from competition kinetics suggests that the rate constants for the reaction of hydroxyl radicals with iodide ion and thiocyanate ion are significantly higher than reported in earlier work. The ultraviolet absorption bands of the various substituted hydroxycyclohexadienyl radicals formed have been observed. 

---