Replacement of halogen by thiocyanate

The classical, generally applicable method of preparing aliphatic thiocyanates (a) is to treat a halide with an alkali thiocyanate or ammonium thiocyanate  

General procedure An alkyl bromide (1 mole) is dropped into a stirred, boiling mixture of finely powdered KSCN (1.5 moles) and ethanol (340 ml about one-third of the KSCN dissolves), and the mixture is kept at the b.p. for 2 h. Then part of the solvent is distilled off, the remaining mixture is diluted with water, the thiocyanate is extracted in ether, and the ethereal solution is dried over CaCl2 or Na2S04 and worked up by vacuum-distillation. Yields for pentyl to tridecyl thiocyanate are about 80-90 %.850 

Alternatively ethanolic halide solutions, e.g.9 Cl(CH2) OH,851 and concentrated aqueous KSCN are mixed, boiled for some hours, diluted with water, and extracted with CHC13. Dioxan may also be used as solvent. Thiocyanatohydrin derivatives RO(CH2) SCN are of value as insecticides.852 

NaSCN in acetone can also be used, as in other halogen exchange reactions. For the preparation of cw-9-octadecenyl thiocyanate853 the bromide (54 g) and NaSCN 2H20 (75 g) in acetone (500 ml) are allowed to react in an autoclave at 80° for 20 hours. 

Lower alkyl thiocyanates are very simply obtained by gradually adding the dialkyl sulfate (1 mole) to KSCN (1 mole) in water (50 ml) with shaking and, if necessary, cooling.854 

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