Analysis of primary amines as mustard oils

The mustard oil reaction is a well known test for the presence of primary amines. By the action of carbon disulfide under mild conditions (room temperature), the 

The conversion of the weakly UV-absorbing primary and secondary amines to the more strongly absorbing dithiocarbamic acids has been used to reveal the firee amines on thin-layer plates [47]. The plates were sprayed with dilute ammonia to free the bases from their salts before exposure to carbon disulfide. 

In 1967, we found that -aryl-substituted alkylamines and carbon disulfide react at room temp erature with the direct formation of the corresponding isothiocyanates [48,49]. There is reason to believe that this reaction proceeds according to a ketone—base condensation (reaction 6). 

In the field of chromatography, the mustard oils of primary amines have substantial analytical value. 

Many of the biologically important -phenylalkyl-amines and also indolylalkylamines contain alcoholic and/or phenolic hydroxyls. For a separation by GC, these polar groups must be derivatized. This can be done by silylation. We use a one-step method [49], Both reagents, carbon disulfide and the silylating agent (usually trimethylsilylimidazole), are added to a solution of the amine in a polar solvent such as dimethylforma-mide or pyridine. A two-step procedure has also been described [56, 57]. The free bases are dissolved in ethyl acetate and treated with carbon disulfide, the solution is evaporated to dryness, and mustard oil is dissolved in pyridine and silylated at 100 °C. If the reaction time is sufficiently long, this procedure also silylates the indole nitrogen. Trifluoroacetylation has also been used to block the hydroxyls of the mustard oils [60]. 

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