Description
Empenthrin, also known as vaporthrin, (2E)-1-ethynyl-2-methyl-2-penten-1-yl 2,2-
dimethyl-3-(2-methyl-1-propen-1-yl) cyclopropanecarboxylate, is a derivative of 1-ethynyl-
2-methyl penten-2-ol. The vapor pressure of empenthrin at room temperature is suitable and therefore
it has a natural volatility. At 30 °C, the vapor pressures of empenthrin and allethrin
are 1.62?×?10?3 and 1.20?×?10?4 mmHg, respectively. Thus, the vapor pressure of empenthrin is about 10 times more than that of allethrin. Moreover, empenthrin is odorless.
It has strong killing activity and repellent effect on pests and is very suitable for textile
mothproofing.
Chemical Properties
Empenthrin is a light yellow and oily liquid with a boiling point of 346°C and
a flash point of 144°C. Its density is 0.999 g.cm
–3 at 20°C. The refractive index of
empenthrin is 1.5270 at 20°C. It has low acute mammalian toxicity (its oral LD50 is
>5,000 mg.kg
–1 in male rats, >3,500 mg.kg
–1 in female rats and >3,500 mg.kg
–1 in mice). It is, however, very toxic to fish and other aquatic organisms.
Uses
Empenthrin is an insecticidal pyrethroid compound.
Uses
Empenthrin is used as a domestic insecticide, especially against
moths and other insects which attack fabrics.
Definition
ChEBI: Empenthrin is a monoterpenoid.
Preparation
About 3.72 g (0.03 mol) of 2-methyl-1-ethynyl-2-pentenol and 3.16 g (0.04 mol) of pyridine were added to toluene to form a solution. A toluene solution containing 5.6 g
(0.03 mol) of Chrysanthemoyl chloride was added in a dropwise manner. The reaction was carried out at a temperature of 40–50°C for 6h. After reaction, the reaction
solution was washed with water until neutral, dried and then subjected to distillation
under reduced pressure. About 5.7 g of empenthrin was collected from a fraction of
120–126°C (0.03 mmHg). The yield of empenthrin was 69%.
Metabolic pathway
Empenthrin is a low molecular weight ester of (1R)-chrysanthemic acid
(2,2-dimethyl-3-(2-methylprop-1-enyl)cyclopropanecarboxylic acid). It
has a relatively high vapour pressure and, unlike most pyrethroids, it is
effective against flying insects. The molecule has three chiral centres and
geometric isomerism in the alcohol group but, with the exception of the
1R acid, the full isomer mixture is used. As the insecticide has been
developed for domestic use, it is unlikely that there will be a requirement
for metabolism studies in plants or for extensive environmental fate studies.
Its metabolism in rats has been reported, with particular attention
paid to the fate of the novel alcohol moiety. As with other pyrethroids,
ester cleavage and oxidation and conjugation of the alcohol metabolite
predominated. The fate of the chrysanthemic acids can be assessed by
reference to phenothrin.
Degradation
Empenthrin is a stable molecule but it would be expected to be labile at
pH values above 10.
