Benzyl cyanide

Benzyl cyanide is an organic nitrile that does not ionize to free cyanide in solution but slowly releases cyanide during metabolism. The compound is prohibited or strictly restricted by IFRA, the EU and Health Canada in fragrance applications.

Skin. Reports of irritation exist but specific supporting data are lacking.

Acute toxicity. Acute intraperitoneal LD50 in rats is 75 mg/kg. Oral LD50 is 211 mg/kg (female rats) and 304 mg/kg (male rats). Sublethal doses are nephrotoxic, increasing excretion of protein, amino acids and glucose.

Metabolism. Dermal application of 150 mg/kg in rats under 24-hour occlusion markedly increased urinary thiocyanate, equivalent to 32–37 percent of the dose.

The compound appears in floral absolutes at below 5 percent, so practical risk is limited by the finished-product cap of 100 ppm (0.01 percent).

Benzyl cyanide is metabolized in rat liver by at least two CYP isozymes to cyanide ions, then excreted as cyanide and thiocyanate. Inhaled benzyl cyanide is substantially detoxified in the nasal cavity.

Karo karoundé absolute has an oral LD50 of 1.4 g/kg in rats, suggesting that benzyl cyanide content in the absolute does not raise practical acute toxicity concerns. Some authors view the IFRA limit as overly restrictive.