NOVELTY - Improved process for preparing deltamethrin, comprises e.g. (a) preparing delta-3-carene-5-one, and (b) subjecting delta-3-carene-5-one in polar/non-polar solvent to ozonolysis at -5 to -12 degrees C followed by quenching with aqueous sodium sulfite solution, purifying obtained crude 9C-ketoacid chemically by forming alkali metal salt of acid, extracting out non-acidic impurities with water immiscible polar/non-polar solvent, isolating purified 9C-ketoacid by acidification with aqueous mineral acid, followed by extraction and finally stripping off polar/non-polar solvent under reduced pressure.    USE - The process is useful for preparing deltamethrin which is useful as an insecticide (all claimed). No biological data given.    ADVANTAGE - The process: is improved (claimed) due to improved yield; is more simple and more economically viable, and continuous, thus avoiding thermal degradation of the precious and thermolabile delta-3-carene-5-one in a batch process; eliminates the need for a sophisticated and expensive spinning band fractionating column; eliminates capital and energy intensive reduced pressure distillation of 9C-ketoacid, instead introduced an economical, chemical purification method; reduces the quantity of aqueous sodium bicarbonate solution (reduced effluent load) during isolation of the product; avoids the possibility of formation of undesired byproducts by using a soluble acidic catalyst (PTSA); eliminates the use of dimethyl sulfide; reduces the quantity of bromoform as 1.39-1.03 moles; recovers the tetrahydrofuran-methanol solvent mixture and recycles it successfully; eliminates the use of chlorinated aliphatic hydrocarbon and dichloromethane, and replaces by a safer aromatic hydrocarbon (toluene); and reduces the quantity and environmental hazard of liquid effluent.    DETAILED DESCRIPTION - Improved process for preparing deltamethrin, comprises (a) preparing delta-3-carene-5-one by oxidizing delta-3-carene in the presence of air/oxygen and cobalt pyridinium halide catalyst and subsequently isolating delta-3-carene-5-one through continuous distillation and fractionation at 0.5-1 mm of mercury, (b) subjecting the delta-3-carene-5-one in a polar/non-polar solvent to ozonolysis at -5 to -12 degrees C followed by quenching with aqueous sodium sulfite solution to obtain crude 9C-ketoacid, purifying the 9C-ketoacid chemically by forming alkali metal salt of the acid, extracting out the non-acidic impurities with a water immiscible polar/non-polar solvent and isolating the purified 9C-ketoacid by acidification with aqueous mineral acid, followed by extraction with a water immiscible polar/non-polar solvent and finally stripping off the polar/non-polar solvent under reduced pressure (60-70 degrees C/50-200 mm of mercury), (c) stirring the purified 9C-ketoacid with an acid anhydride (1-1.5 mole with respect to 9C-ketoacid) and para-toluene sulfonic acid catalyst (PTSA) (4-5 mole% with respect to 9C-ketoacid) at 15 plus minus 5 degrees C until lactonization is complete, adding an alkali metal acetate in predetermined quantity to neutralize PTSA and distilling off the acid along with un-reacted acid anhydride under reduced pressure (70-90 degrees C/60-90 mm of mercury), extracting the residual mass with a water immiscible polar/non-polar solvent and washing off the acidic impurities with aqueous alkali metal carbonate/bicarbonate solution, isolating the crude 9C-enol lactone by removal of the polar/non-polar solvent under reduced pressure (60-70 degrees C/50-200 mm of mercury) and purifying it by distillation under reduced pressure (68-70 degrees C/1 mm of mercury), (d) subjecting the 9C-enol lactone to ozonolysis in solvents followed by quenching the reaction mass, at low temperature, with an alcoholic or aqueous solution of a reducing agent that gets easily oxidized under these conditions, to obtain the methyl ether of hemiacetal and hydrolyzing the methyl ether of hemiacetal into hemiacetal by treatment with aqueous oxalic acid solution and isolating the hemiacetal by extraction with a water immiscible solvent, followed by removal of the solvent under reduced pressure, (e) adding simultaneously the hemiacetal and bromoform from separate addition points to a solution of an alkali metal hydroxide in an alcohol along with an organic ether such as tetrahydrofuran (in which hemiacetal is added at a slightly faster rate with respect to bromoform) at -10 to 0 degrees C, stirring the reaction mass at low temperature until the completion of the reaction, diluting the mixture with water, recovering the solvent mixture at 60-80 degrees C/760 mm of mercury for reuse, dissolving the alkali metal salt of the bromoacid by addition of required amount of water, extracting the impurities with a water immiscible solvent, acidifying the aqueous mass with mineral acid to pH of 2, and isolating the precipitated bromoacid either by filtration or by extraction with a water immiscible solvent, (f) heating a solution of the bromoacid in solvents and PTSA at 80-120 degrees C and continuously removing water to form bromolactone, removing the PTSA using 2-5% aqueous alkali metal carbonate/bicarbonate solution followed by azeotropic water removal and then partial solvent stripping under reduced pressure (70-75 degrees C/350-600 mm of mercury) to have a solution of the bromolactone of a known concentration in the solvent, (g) adding aqueous acetic acid to a solution of the bromolactone in the solvent, stirring at 25 plus minus 5 degrees C, then adding zinc powder in a known manner and stirring until the reaction is complete, diluting the reaction mixture with water, extracting the crude deltamethric acid with a water immiscible solvent, adding aqueous alkali metal hydroxide solution to the solvent layer to extract deltamethric acid as its alkali metal salt, acidifying the alkali metal salt solution with aqueous mineral acid to pH of 2 and isolating the precipitated deltamethric acid by filtration or by extraction with a water immiscible solvent followed by removal of the solvent under reduced pressure, and (h) preparing deltamethric acid chloride from the deltamethric acid by reacting it with thionyl chloride and a catalyst, dimethyl formamide, reacting the acid chloride with sodium cyanide and meta-phenoxy benzaldehyde to get crude deltamethrin along with R-diastereoisomer and epimerizing the mixture to deltamethrin in isopropanol in the presence of a base, triethyl amine, at 20-25 degrees C for 20-30 hours in a known manner and isolating pure deltamethrin by filtration followed by drying.