Arene thiocyanation

Arene thiocyanation. Thiocyanation of arenes with metal thiocyanates usu-illy results in both arenethiocyanates and the more stable areneisothiocyanates. The reaction can be effected with CuSCN supported on charcoal. Thus iodo- and romoarenes react with this supported reagent (excess) in f-butylbenzene at 150° v give the corresponding thiocyanates in 70-80% yield. 

However, lithinm aluminum hydride or zinc metal and HCl (5) are required as reducing agents to reduce the thiocyanate to the thiol. These reducing agents are stoichiometric reagents and aren t environmentally acceptable at this time because of their hazardous properties and waste disposal problems on a large manufacturing scale. 

The conversion of functionalized arenes as represented by the general formula 97, into isothiazolium compounds (99) has been achieved by the sequence shown in Scheme 117.180 From a synthetic viewpoint, transformation of cyclopalladated products into thiocyanate derivatives is more efficiently achieved using monomeric dithiocarbamato complexes (98) rather than dimeric compounds. The generation of analogous dithiolylium perchlorates by a related procedure is described later (see Section IV,H). 

Halide displacement by thioanions such as thioalkoxides, thiocyanate and sulfite, can be readily carried out under PTC conditions in activated arenes. The reaction of nitro- and dinitro-aryl halides with thiophenol and NaOH in the presence of an ammonium or phosphonium salt catalyst proceeds readily in toluene at room temperature to give the phenyl aryl sulfides in nearly quantitative yield.189 Excellent yields of thiocyanoarenes were obtained from the reaction of the 2,4-dinitrohalobenzenes with KSCN in toluene at 90 C with a tetraalkyl onium salt PTC catalyst.190... 

The exposure of aromatic ethers to BTIB in (CF3)2CHOH or CF3CH2OH (TFE) leads to arene cation-radical intermediates and permits the introduction of nucleophiles (N, AcO-, NCS-, ArS-) into the alkoxyarene nucleus (94JA3684, 95JOC7144). For example, the treatment of / -substituted anisoles with BTIB in the presence of trimethylsilyl azide or -isothiocyanate affords the 2-anisyl azides 98 or 2-anisyl thiocyanates 99, respectively (Scheme 30). 

Solvent extraction of Fe(III) with calix(6)arene carboxylate derivative followed by spectrophotometric determination with thiocyanate was examined [1]. The developed method was recommended for determination of Fe(III) in samples containing Al, Mn(II), Mo(VI) and V(V). The extraction of Fe(III) with 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester followed by the determination with thiocyanate was employed to determine Fe in pharmaceuticals, metal and ores [2]. Solvent extraction separation of iron(III) with Cyanex 302 prior to the detection as the thiocyanate complex was applied to determine Fe(III) in multicomponent mixtures and ores, alloys and pharmaceuticals [3]. 

From Hydrazonyl Bromides and Thiocyanates (Fragments C—N-N-Arene and S)... 

The cerium(IV)-mediated generation of heteroatom radicals by oxidation of anions such as azides was discovered many years ago [10], However, Nair et al. applied this strategy for a C-S bond-forming reaction by oxidation of ammonium thiocyanate le only recently [11], Addition of thiocyanate radical to indole 18 provides an intermediate radical, which is further oxidized to the cation by CAN. Loss of proton from the cationic intermediate provides the substituted arene 19 in excellent yield (Scheme 6). 

Thiocyanic esters can also be obtained by treating arene-364 or alkane-sulfenyl chlorides,365 including trichloromethanesulfenyl chloride,366 with potassium cyanide ... 

The reaction of polycyclic aromatic hydrocarbons with [hydroxy(tosyloxy)iodo]benzene in the presence of trimethylsilyl isothiocyanate leads to the regioselective thiocyanation of an arene nucleus, as illustrated by the reaction of anthracene shown in Scheme 3.213 [274],... 

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