Sodium Hydroxide—4-Nitrobenzaldehyde —1,2-Dinitrobenzene

Synthetic pyrethroids with a-cyano ester group react with sodium hydroxide to yield hydrogen cyanide, which reacts with 4-nitrobenzaldehyde and 1,2-dinitrobenzene to yield a pink-colored derivative (o-quinonoid di-anion) according to the following scheme ... 

Mix together 5 drops of a 1.5 per cent solution of p-nitrobenzaldehyde in 2-methoxyethanol, 5 drops of a 1.7 per cent solution of o-dinitrobenzene in 2-methoxyethanol and 2 drops of a 2.0 per cent aqueous solution of sodium hydroxide. To this mixture add 1 drop of fusion solution. A deep purple coloration is positive for cyanide ions, a yellow or tan colour is negative. Neither halide ions nor sulphide ions interfere. 

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