FORM 2
THE PATENTS ACT, 1970
(39 OF 1970)
AND
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10 rule 13)
1. TITLE OF THE INVENTION
"Solvent-free process for the preparation of transfluthrin"
2. APPLICANT
(a) NAME: Heranba Industries Limited
(b) NATIONALITY: An Indian Company
(c) ADDRESS: 101/102, Kanchanganga, Factory Lane, Borivali (W), Mumbai 400 092
3. PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed.

Field of the Invention
The present invention relates, in general, to the field of synthetic pyrethroid insecticide and, in particular, relates to an eco-friendly process for the preparation of cyclopropanecarboxylic acid ester of formula (I),

generically referred as transfluthrin, having high degree of purity.
Description of the Prior Art
Pyrethroids, naturally occurring and synthetically derived from cyclopropanecarboxylic acid, have been long of interest as insecticides since they are effectively active against a wide spectrum of insect species, display relatively low toxicity toward mammals, and do not )eave harmful residues. The cyclopropanecarboxylic acid ester of formula (I),

generically referred as transfluthrin, as described in the U.S. Pat. No. 4,889,872 is a fast-acting pyrethroid insecticide with low persistency. It is a widely used household product effective against the flying insects, mosquitoes and cockroaches.
in the US Patent No. 4,889,872, transfluthrin is prepared by reacting (+) 1R-trans-permethrin acid chloride with 2, 3, 5, 6-tetrafluorobenzyl alcohol. In another variant process, potassium (+) 1R-transe-2, 3-dimethyi-3-dimethyl-3-dichlorovinyl-cyclopropanecarboxylate is reacted with 2, 3, 5, 6-tetrafluorobenzyl chloride in a polar organic solvent to give transfluthrin.

In the European Patent No. 0779269, transfluthrin is obtained by azeotrophic esterification of (+) 1R-trans-permethric acid with 2, 3, 5, 6-tetrafluorobenzyl alcohol using toluene as organic solvent.
In the Indian Patent No. 239904, the disclosed provide step of reacting (+) 1R-trans-permethric acid with chlorinating agent in the presence of toluene as organic solvent to obtain (+) 1R-trans-permethric acid chloride which is reacted insitu with 2, 3, 5, 6-tetrafluorobenzy! alcohol to give transfluthrin.
In the Indian Patent No. 225306, the disclosed process provide two step synthesis of chlorination of (+) 1R-trans-permethric acid with thionyl chloride to form (+) 1R-trans-permethric acid chloride which is reacted with 2, 3, 5, 6-tetrafluorobenzyl alcohol in the presence of toluene as organic solvent to give transfluthrin.
All above discussed prior art processes use one or more solvents which results into formation of impurities and may hamper the purity of the product. The applicants have devised a practical, eco-friendly solvent-free process for the preparation of transfluthrin having high degree of purity,
Summary of the Invention
Accordingly, the present invention provides a solvent free process for the preparation of transfluthrin which obviates the drawback of the prior art. The present invention further provides an eco-friendly process for the preparation of transfluthrin having high degree of purity.
Detailed Description of the Invention

is condensed with 2, 3, 5, 6-tetrafluorobenzyl alcohol of formula (III)
According to the present invention, RR-trans cypermethric acid chloride of formula (II)



to produce transfluthrin of formula (I)
having high degree of purity, being greater than 96%. The reaction is carried out without using solvent.
EXAMPLE 1
Preparation of transfluthrin
Step A
619 gms of RR-trans cypermethric acid chloride was charged and heated at 60°C in a 4
neck 3 lit round bottom flask fitted with mechanical stirrer, condenser and thermometer
pocket. 479 gms of 2, 3, 5, 6-tetrafluorobenzyl alcohol was added to the flask in the
interval of 2-2 Vi hrs and reaction mixture temperature was maintained at 60-65°C for 1
hr.
The reaction mixture was analyzed to obtain a reaction mass with less than 0.3% of RR-trans cypermethric acid chloride and 2, 3, 5, 6-tetrafluorobenzyl alcohol. The hydrochloride gas was then removed from the reaction mass by applying 700 mm/hg vacuum at 70-75°C and was analyzed to obtain a reaction product with less than 0.5% free acid content.
StepB
470ml of water was charged in round bottom flask. 16mg K2C03 was added to the flask,
stirred and heated at 60-65°C. The reaction product from Step A was then added to the

K2C03 solution which was stirred and allowed to settle for 1 hour at pH between 8.5 to 9.0.
The bottom organic layer was separated from the reaction solution at 60-65°C and was added and stirred with 470ml of water in round bottom flask. The organic solution was heated at 60-65°C and stirred for 30 mins and allowed to settle for 1 hour.
The bottom organic mass was separate from the organic solution at 60-65°C and heated at temperature 80°C and vacuum 745 mm/hg in a reactor for 2 hours for removal of water. After complete dehydration, the product (purity: 96%) was obtained.

Claims
1. A solvent free process for the preparation of transfluthrin, comprising the steps of:

in a round bottom flask at 60°C; (b) adding 479gm of 2, 3, 5, 6-tetrafluorobenzyl alcohol of formula (III)

(a) charging 619gm of RR-trans cypermethric acid chloride of formula (II)
to the round bottom flask in the interval of 2-2/4 hours to obtain a reaction mixture;
(c) removing hydrochloride gas from the reaction mixture by applying 700 mm/hg vacuum at 70-75°C to obtain a reaction mass;
(d) charging 470ml water in a separate round bottom flask and adding 16gm K2C03 at 60-65°C to obtain K2C03 solution;
(e) adding the reaction mass of step (c) to the K2C03 solution of step (d) to a reaction solution;
(f) allowing the reaction solution to settle for 1 hour to separate bottom organic layer at 60-65°C;
(g) adding the bottom organic layer to 470mg of water in a separate round bottom flask at 60-65°C to obtain an organic solution;
(h) allowing the organic solution to settle for 1 hour to separate bottom
organic mass at 60-65°C; and (i) heating the bottom organic mass in reactor at 80°C and 745 mm/hg
vacuum for 2 hours to obtain transfluthrin. 2. The process of claim 1, wherein transfluthrin have a purity of 96%.

3. The process of claim 1, wherein transfluthrin have a purity of more than 96%.