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Allyl thiocyanate isomerizes to the isothiocyanate: [8] CH 2 =CHCH 2 SCN → CH 2 =CHCH 2 NCS. Allyl isothiocyanate can also be liberated by dry distillation of the seeds. The product obtained in this fashion is known as volatile oil of mustard. It is used principally as a flavoring agent in foods.
The enzyme myrosinase removes the glucose group in sinigrin to give an intermediate which spontaneously rearranges to allyl isothiocyanate, the compound responsible for the pungent taste of Dijon mustard. This is a reactive material which is toxic to many insect predators and its production is triggered when the plant is damaged. [8]
Allyl thiocyanate isomerizes to the isothiocyanate: [4] CH 2 =CHCH 2 SCN → CH 2 =CHCH 2 NCS. Isothiocyanates can be prepared by treating organic dithiocarbamate salts with lead nitrate or tosyl chloride. [5] [6] Synthesis of phenyl isothiocyanate. Isothiocyanates may also be accessed by the fragmentation reactions of 1,4,2-oxathiazoles. [7]
For example, allylglucosinolate and allyl glucosinolate refer to the same compound: both versions are found in the literature. [5] Isothiocyanates are conventionally written as two words. [4] The following are some glucosinolates and their isothiocyanate products: [4] Allylglucosinolate is the precursor of allyl isothiocyanate
Despite this low acute toxicity, an extremely low short-term exposure limit (STEL) of 0.07 mg/m 3 is the legal limit for all isocyanates (except methyl isocyanate: 0.02 mg/m 3) in the United Kingdom. [22]
"SN1-type" substrates (e.g., benzyl halides) tend to give the isothiocyanate derivatives. Some organic thiocyanates are generated by cyanation of some organosulfur compounds. Sulfenyl thiosulfates (RSSO 3 −) react with alkali metal cyanides to give thiocyanates with displacement of sulfite. This approach has been applied to allyl thiocyanate: [6]
Allyl isothiocyanate is the pungent ingredient in fresh horseradish sauce. The distinctive pungent taste of horseradish is from the compound allyl isothiocyanate. Upon crushing the flesh of horseradish, the enzyme myrosinase is released and acts on the glucosinolates sinigrin and gluconasturtiin, which are precursors to the allyl isothiocyanate.
Examples include rosin, which inhibits attack on trees, and many alkaloids, which are highly toxic to specific insect species, [2] such as quassinoids (extracts from Quassia trees) against the diamondback moth (Plutela xylostella). [3] Samadera indica also has quassinoids used for insect antifeedant uses. [4]