[540-72-7] · CNNaS · Sodium Thiocyanate · (MW 81.08)
Physical Data: mp 287 °C.
Solubility: v sol H2O (139 g/100 mL at 21 °C); sol acetone, EtOH; partially sol CH2Cl2.
Form Supplied in: colorless to white deliquescent crystals; widely available.
Purification: recrystallization from water, MeCN, or MeOH, followed by washing with ether and drying at 130 °C.
Handling, Storage, and Precautions: contact with acids liberates toxic gas. Keep container well sealed during storage.
Sodium thiocyanate is primarily a reagent for the thiocyanation or isothiocyanation of organic compounds by nucleophilic chemistry. It acts as a thiocyanating agent by nucleophilic attack via its sulfur while attachment by nitrogen affords isothiocyanates.1 The ambident character of thiocyanate ion is explained in more detail in the description of Potassium Thiocyanate. Sodium thiocyanate is not often employed for the thiocyanation of organic compounds, although there are some instances of its use.1 It is preferred over KSCN for the formation of PhSeSCN from PhSeCl,2 but TMSNCS is the best reagent since the product is not contaminated with thiocyanate ion residues.3 NaSCN has been employed to introduce a thiocyanate group into a nitroxyl spin label (eq 1).4 NaSCN is rarely utilized for the thiocyanation of saccharides; potassium, ammonium, silver, and lead thiocyanates are employed instead.5
The primary use of sodium thiocyanate is as a reagent for the isothiocyanation of unsaturated compounds. For instance, the reaction of alkyl carbonochloridothioates with NaSCN followed by an alcohol quench affords O,O-dialkyl imidodithiocarbonothioates via an intermediate isothiocyanate. KSCN and NH4SCN give lower yields (eq 2).6 The identity of the base is also important in these and related isothiocyanate syntheses.6,7
In addition to alkoxycarbonyl halides, compounds such as imidoyl chlorides8 and aminocarbonyl chlorides9 react with NaSCN to afford isothiocyanates; in many cases, the isothiocyanates are intermediates on the path to substituted thioureas (eq 3). The reaction of NaSCN with imidoyl chlorides attached to a phosphonium salt affords substituted thioimidazolones by nitrogen attack and cyclization.10 Thioacyl halides may give the isothiocyanate or the thiocyanate, depending on the reaction conditions.1,11 In some instances, the organic thiocyanate can be converted to the isothiocyanate by thermolysis.1
The reaction of 2 equiv of NaSCN with aryl and alkyl dichloromethyl disulfides is an effective means of synthesizing 2-alkyl(aryl)thio-4l4-[1,2,4]dithiazolo[1,5-b][1,2,4]dithiazoles (eq 4).12
NaSCN is one of a collection of pseudohalides or halides that has been used in conjunction with a metal halide for the reductive dehalogenation of a-halo ketones (eq 5).13 NaSCN does not seem to have any particular advantage over the other reagents; all achieve the reduction in >90% yield.
Adrian L. Schwan
University of Guelph, Ontario, Canada