alphamethrin mukesh research paper

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This article was downloaded by:[Florida State University Libraries] On: 15 April 2008 Access Details: [subscription number 789349894] Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Journal of Environmental Science and Health, Part B Pesticides, Food Contaminants, and Agricultural Wastes Publication details, including instructions for authors and subscription information: http://www.informaworld.com/smpp/title~content=t713597269 Phototransformation of Alphacypermethrin as Thin Film on Glass and Soil Surface Mukesh Kumar Raikwar a ; Subir Kumar Nag a a Plant Animal Relationship Division, Indian Grassland and Fodder Research Institute, U.P., India Online Publication Date: 01 September 2006 To cite this Article: Raikwar, Mukesh Kumar and Nag, Subir Kumar (2006) 'Phototransformation of Alphacypermethrin as Thin Film on Glass and Soil Surface ', Journal of Environmental Science and Health, Part B, 41:6, 973 - 988 To link to this article: DOI: 10.1080/03601230600806186 URL: http://dx.doi.org/10.1080/03601230600806186 PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdf This article maybe used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.

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This article was downloaded by:[Florida State University Libraries]On: 15 April 2008Access Details: [subscription number 789349894]Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

Journal of Environmental Scienceand Health, Part BPesticides, Food Contaminants, and AgriculturalWastesPublication details, including instructions for authors and subscription information:http://www.informaworld.com/smpp/title~content=t713597269

Phototransformation of Alphacypermethrin as Thin Filmon Glass and Soil SurfaceMukesh Kumar Raikwar a; Subir Kumar Nag aa Plant Animal Relationship Division, Indian Grassland and Fodder ResearchInstitute, U.P., India

Online Publication Date: 01 September 2006To cite this Article: Raikwar, Mukesh Kumar and Nag, Subir Kumar (2006)

'Phototransformation of Alphacypermethrin as Thin Film on Glass and Soil Surface ', Journal of Environmental Scienceand Health, Part B, 41:6, 973 - 988To link to this article: DOI: 10.1080/03601230600806186URL: http://dx.doi.org/10.1080/03601230600806186

PLEASE SCROLL DOWN FOR ARTICLE

Full terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdf

This article maybe used for research, teaching and private study purposes. Any substantial or systematic reproduction,re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expresslyforbidden.

The publisher does not give any warranty express or implied or make any representation that the contents will becomplete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should beindependently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings,demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with orarising out of the use of this material.

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Journal of Environmental Science and Health Part B, 41:973–988, 2006Copyright C© Taylor & Francis Group, LLCISSN: 0360-1234 (Print); 1532-4109 (Online)DOI: 10.1080/03601230600806186

Phototransformationof Alphacypermethrin as ThinFilm on Glass and Soil Surface*

Mukesh Kumar Raikwar and Subir Kumar Nag

Plant Animal Relationship Division, Indian Grassland and Fodder Research Institute,U.P., India

Photodegradation of alphacypermethrin ((RS)-α cyano-3-phenoxy benzyl (1RS) cis-3-(2,2,dichlorovinyl)-2,2-dimethyl cyclopropane carboxylate) was studied as a thin film onglass surface and on black and red soil surfaces. A number of photoproducts from glasssurfaces have been isolated, characterized and identified by gas chromatography-massspectroscopy (GC-MS). However, only two of them viz. 3-phenoxy benzyl alcohol and[2,2-dichlorovinyl-3(2,2,dimethyl) cyclopropane carboxylate] could be identified fromboth the soil. Rate of photodegradation on glass and soil surface under UV andsunlight followed first order kinetics with significant correlation coefficients. The rateof photodegradation was greater on black than on red soil.

KeyWords: Photodegradation; Black soil; Red soil; UV; Sunlight; Alphacypermethrin.

INTRODUCTION

Alphacypermethrin (1R cis, αS and 1S cis αR enantiomeric pair ofα-cyano-3-phenoxy benzyl-3-(2,2-dichlorovinyl)-2,2-dimethyl cyclopropanecarboxylate) is a synthetic pyrethroid insecticide having a broad spectrumof activity. It is a stereo selective compound consisting of the mixture offour stereoisomers owing to the presence of two chiral carbon atoms. Thestereo selectivity of alphacypermethrin is very high. It is effective againsta wide range of insect pests of agricultural importance, particularly ofLepidoptera & Coleoptera order, in different crops at a very small doseof 5–30 g a.i./ha.[1] It is also used to protect seeds during storage, toeradicate vectors of endemic diseases like malaria, and to fight householdinsects.[2–4] Its persistence and residues have been evaluated only on a few

∗A part of Ph.D. thesis of the first author in the Department of Chemistry submitted tothe Bundelkhand University, Jhansi, U.P., India.Address correspondence to Subir Kumar Nag, Senior Scientist, PAR Division, IGFRI,Jhansi-284003, U.P., India. E-mail: [email protected] or nagsk [email protected]

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crops in Indian condition.[5–8] From the view point of environmental safetythe metabolism of cypermethrin [(RS)-α-cyano-3-phenoxybenzyl (1RS)-Cis,trans-3-(2,2-dichlorovinyl)-2,2-dimethyl cyclopropane carboxylate] has beenstudied in mammals,[9–11] soils[12–14] and plants.[8,15,16] The photodegradationof cypermethrin studied by Takahashi et al.[17] in water and on soil surfacesrevealed that both cis and trans isomers rapidly degraded on soil with initialhalf-life of 0.6–1.9 days. The main reactions involved in degradation werecleavage of ester or diphenyl ether linkage, oxidation of –CHO, hydration of–CN, oxidative cleavage, dehalogenation etc. As little published literatureabout photodegradation of alphacypermethrin was available, the presentexperiment was conducted to see the rate of photolysis and the nature ofphotoproducts of alphacypermethrin formed when irradiated as thin film onglass and soil surfaces under ultra-violet light (UV) and sunlight.

MATERIAL AND METHODS

ChemicalsTechnical grade (99%) alphacypermethrin was obtained by courtsey of

M/s. Meghamani Organics Ltd. Ahmedabad, India. It was further purified byrepeated crystallization from hexane. The purity of the compound was checkedby m.p. (80◦C), thin layer chromatography (solvent system, hexane: acetone2:1 v/v, Rf 0.57) and gas liquid chromatography.

Solvents and ReagentsAll the solvents used in the experiment were Laboratory Grade Regents

(LR) or commercial grade. Hexane was distilled over anhydrous sodium sulfatein the boiling range 60–80◦C before use. Acetone was refluxed over KMnO4 andthen distilled.

Soil CharacteristicsTwo types, black soil and red soil, were used in the experiment. Their

properties are given in Table 1.

Chromatography

Gas Liquid Chromatography (GLC)Alphacypermethrin degradation rates were determined using a PC based

gas liquid chromatograph (Varian CP–3800) equipped with an electron capturedetector (ECD, Ni63) and a capillary column (CP SIL 5CB, 30 m × 0.53 mm i.d.

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Table 1: Physicochemical properties of the soils used in the experiment.

Soil properties Black soil Red soil

pH (1:2.5) 7.62 6.72EC (1:2.5) 0.87 dSm−1 0.76 dSm−1

Organic carbon 0.6 0.47Soil order Inceptisol AlfisolParticle size analysis

Silt (%) 49.5 30.0Clay (%) 27.2 28.3Sand (%) 23.3 41.7

Soil Texture Loam Clay loamAvailable Nitrogen (Kg/ha) 288.24 185.02Available P2O5(Kg/ha) 22.27 12.23Available K2O (Kg/ha) 476 280

× 0.25 mm film thickness). The operating conditions were as follows: Columntemperature: 250◦C for 1 min, then 5◦C/min up to 280◦C (5 min), Injectionport temperature: 280◦C, Detector temperature: 300◦C. Nitrogen was used asthe carrier gas with the flow rate of 1 mL/mins. through column and make up30 mL/min.

Thin Layer Chromatography (TLC)Thin layer chromatography plates were prepared by spreading a slurry of

silica gel G containing 10% gypsum (as binder) in water on 5 cm × 20 cm and20 cm × 20 cm plates, maintaining a uniform thickness of 0.25 mm using aTLC applicator. The mobile phase used for TLC were hexane + acetone (2:1,4:1, 9:1 v/v), with iodine vapour used as the chromogenic reagent.

Column Chromatography (CC)Photoproducts were separated by column chromatography (CC) using a

glass column of 75 cm × 2 cm id containing 500 g of 60–100 mesh silica gel forcolumn chromatography (preactivated at 120◦C) in hexane. The column wassuccessively eluted with hexane, hexane and toluene and toluene and acetonein different proportions. Different fractions (25 mL) were collected and distilledon a rotary vacuum evaporator. The fractions containing same product werecombined and purified further.

Preparative TLCSingle or mixtures of a few compounds of different polarity, obtained earlier

through column chromatography, were spotted in 20 × 20 cm plates coatedwith silica gel G and run in a suitable solvent system as mentioned above.After running of plates and visualization, spots appearing at the same position(i.e. same Rf value) were marked, scratched along with the coated silica gel

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and put in a small conical flask. They were dissolved in a small quantity ofacetone, filtered and concentrated to get the pure isolated compound. A numberof plates was used to get the whole quantity obtained from the column isolatedand/or separated.

SpectroscopyThe ultraviolet and visible (UV-VIS) spectrum of alphacypermethrin was

recorded on a Perkin-Elmer Lambda UV/VIS spectrophotometer in methanoland water, using a quartz cuvette (1 cm path length).

Gas Chromatography–Mass Spectroscopy (GC-MS)The GC-MS spectra were performed on Fison gas chromatograph (trace

GC) connected with an electron impact mass detector (MD–800) and fitted witha capillary Column (BD-17, J&W Scientific, 30 m × 0.32 mm i.d.× 0.25 µmfilm). The conditions were as follows. Injection port temperature: 260◦C (Split1:10); Oven temperature: 150–250◦C, 2◦C/min, Helium was used as the carriergas.

Photolysis on Glass SurfaceFor studies on glass surface, a solution of alphacypermethrin in hexane (10

mL, 1000 mg/L) was applied uniformly on petriplates (20 cm diameter). Thesolvent was allowed to evaporate off at room temperature leaving behind a thinlayer of alphacypermethrin on the surface of the petriplates which were thenexposed to UV light by placing them under the ultraviolet lamp (λ-254 nm) ata distance of 30 cm for one hour. The temperature at the test surface variedfrom 25–30◦C. A set of petriplates was also exposed to sunlight in the monthsof April-May for 7–8 hours (9.30 AM–5.30 PM). The temperature at the testsurface varied from 30–40◦C. Sunlight intensity at wavelength between 300and 400 nm was approximately 720, 780 and 350 m Wcm−2 at the beginning,middle and end of the day, respectively.

To get a sufficient quantity of photoproducts a number of plates wereirradiated. After irradiation the plates were extracted with hexane (5 × 5 mL).The combined hexane extracts from different plates were concentrated at alow temperature under vacuum. Photoproducts thus formed were separatedby column chromatography, purified by preparative TLC, recrystallisation andsubsequently identified by GC-MS.

Photolysis on Soil SurfaceSoil samples collected from the Central Research Farm of the Institute

were dried in air under shade. They were pulverized and passed through a2 mm sieve. Soils were also sterilized in an autoclave for two hours at a

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temperature of 121◦C and pressure of 15 lb/sq inch. A slurry of soil (50 g)was made with double distilled water and sprayed uniformly on to petri plates(20 cm dia.) to give a layer of 2 mm thickness which was then dried in air.Alphacypermethrin in hexane (10 ml, 1 mg/ml) was applied uniformly to thesurface of the soil using a pipette. The plates were again dried in air andthen irradiated under UV light for four hours and under sunlight for 18–20 hours. After irradiation the soil was removed from the plates and extractedwith hexane (5 × 5 mL). The extracts from several plates were combined andconcentrated at low temperature. Photoproducts thus formed were separatedby column chromatography, preparative TLC and identified by GC-MS.

Rate of Photodegradation of Alphacypermethrinon Glass SurfaceA solution of alphacypermethrin (1 mL of 10 mg/L) in hexane was

uniformly applied on petriplates of 5 cm diameter, with a pipette. The solventfrom the petriplates was evaporated off at room temperature leaving behinda thin film of alphacypermethrin. Plates were exposed to UV Light (λ-254nm) at a distance of 30 cm and also to sunlight for different durations. Oneset of petriplates were covered with aluminum foil and kept in the dark ascontrol. Sample plates were withdrawn from the light source at random (threereplicates) at different intervals. Samples irradiated under UV light werewithdrawn at 0, 5, 10, 20, 30, 45 and 60 mins and those from sunlight werewithdrawn at 0, 15, 30, 45, 75, 90, 105 and 120 mins. The content of eachpetriplate was extracted thoroughly with hexane (5 × 3 mL). The solvent wasevaporated to dryness and residues were diluted with hexane (1 mL) for GLCanalysis.

Rate of Photodegradation of Alphacypermethrin on Soil SurfaceThe rate of photodegradation of alphacypermethrin was studied on black

and red soil. Soil passed through a 2 mm sieve was suspended in distilledwater (1 g in 2 mL) and the suspension was used to prepare a thin layer onthe bottom of a petriplate (5 cm dia). Air drying of the plates resulted in a thinuniform layer of soil on the glass surface. A solution of alphacypermethrin (10mg/L, 1 mL) was uniformly applied on the petri plates and the solvent wasallowed to evaporate at room temperature. The plates were exposed to UVlight and sunlight for different durations. In case of UV irradiation, sampleswere withdrawn at random in triplicate at intervals of 0, 30, 60, 90, 120, 150and 180 mins (black soil) and 0, 30, 60, 90, 120, 180, 240 and 300 mins (redsoil). Samples irradiated under sunlight were withdrawn at 0, 1, 2, 3, 4, 5, 6and 7 days (black soil) and 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 days (red soil).After irradiation, soil was scraped from each plate and extracted with hexane

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(5 × 3 mL). The combined extracts were then centrifuged. The supernatantwas then concentrated to 1 mL at a low temperature and analysed in GLC.

RESULTS

Rate of Photodegradation of AlphacypermethrinThe rate of photodegradation of alphacypermethrin was studied on a glass

surface and also on black and red soil surface under UV light as well as undersunlight. Results showed that no degradation of alphacypermethrin occurredin the dark, since more than 90 percent of the applied alphacypermethrin wasrecovered unchanged during the time frame of the study which indicated thatalphacypermethrin was stable under these conditions and the degradationobserved in the study to the samples can be attributed to photolysis only.The rate of photodegradation followed first order kinetics with significantcorrelation coefficients (Figs. 1–4). The rate constant and half-life values aregiven in Table 2.

Isolation and Identification of Photoproducts Formedon Glass SurfaceThe UV spectrum of alphacypermethrin in methanol and water exhibited

bands at 245.6 nm (ε = 24,560) for the allowed π-π∗ transition of the phenylrings and a band at 276 nm (ε = 27,600), which is essentially n-π∗ in characterresulting from the combined transition of the carbonyl group and the lowerenergy bond of the aromatic rings. These π-π∗ and n-π∗ transition can leadto the production of either singlet or triplet excited states. So no uniqueexcited state can be invoked to explain the variety of photochemical reactions

Figure 1: Linear plot for first order kinetics of alphacypermethrin as thin film on glass surfaceunder ultraviolet light.

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Figure 2: Linear plot for first order kinetics of alphacypermethrin as thin film on glass surfaceunder sunlight.

under gone by various functional groups of alphacypermethrin. The possiblephotodegradation products of alphacypermethrin as thin film on glass surfaceunder UV light is shown in Figure 5.

Elution of column with hexane (fraction I–V) gave a viscous liquid, whichwas further purified by preparative TLC (solvent system, hexane: acetone

Figure 3: Linear plot for first order kinetics of alphacypermethrin as thin film on black and redsoil under Ultraviolet light.

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Figure 4: Linear plot for first order kinetics of alphacypermethrin as thin film on black and redsoil under sunlight.

9:1, Rf 0.65). The compound was eluted at 17.35 mins and gave a parent ionpeak at m/z 209, which was also the base peak, with fragment ion peaks at183 (M+-CN), 169 (M+-CH2CN), 141, 133, 116 on the basis of which it wasidentified as 2-(3 phenoxy)-benzyl cyanide (II). Further elution of column withhexane and toluene (7:3 v/v, fractions I–VI) and distillation of the eluate gavepale yellow viscous oil, which was further purified by short path distillationunder reduced pressure (120◦C bath temperature). On TLC it gave a singlespot (solvent system hexane: acetone 9:1, Rf 0.51). It eluted at 14.83 mins and

Table 2: Rate constants and half-life values for alphacypermethrin on glass anddifferent soil surface under UV and sunlight.

Surface Source of irradiation Rate constant (k) Half-life R2

Glass UV 0.0486 min−1 14.26 min 0.95Glass Sunlight 0.0191 min−1 36.26 min 0.95Black soil UV 0.0122 min−1 56.8 min 0.98Black soil Sunlight 0.3084 day−1 2.24 d 0.96Red soil UV 0.0073 min−1 94.07 min 0.99Red soil Sunlight 0.2181 day−1 3.17 d 0.99

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Figure 5: Possible photodegradation products of alphacypermethrin on thin film on solidsurface under ultraviolet light.

gave a molecular ion peak at m/z 198 with the base peak at m/z 197 (M+-1)and a fragment peak m/z 169 (M+-CHO), 141 (M+-CHOCO), 115, 77 and onthe basis of it the compound was identified as 3-phenoxy-benzaldehyde (III).

Elution of column with toluene (fraction I–V) gave colorless viscous liquidwhich was further purified by preparative TLC (solvent system hexane:acetone 8.5: 1.5, Rf 0.73, It eluted at 8.89 mins and gave a parent ion peakat m/z 225 with base peak at m/z 198 (M+-HCN) and fragment ion peaksat m/z 182 (M+ –CNOH), 169, 141, 77, 55. The compound was identified asα-cyano–3–phenoxy benzyl alcohol (IV).

Elution of column with toluene and acetone (99:1, v/v, fraction I–VII) gave asolid, purified by preparative TLC (solvent system hexane: acetone 8.5: 1.5, Rf.0.56). It eluted at 51.74 mins and gave the molecular ion peak at m/z 208 (M+)indicating the presence of chlorine atom. The fragment ion peaks appeared at

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191 (M+-OH), 180 (M+-CO), 163, 140, 128, 123, 107 indicating the presenceof the chlorine atom. It was identified as 3-(2, 2–dichlorovinyl)-2, 2-dimethyl-cyclopropane carboxylic acid (V).

Further elution of the column with toluene and acetone (98:2 v/v, fractionI–VI) gave a white crystalline solid, which was further purified by preparativeTLC (solvent system, hexane: acetone 8:2, Rf 0.62). The compound was elutedat 55.49 mins, showed the molecular ion peak at m/z 391 and other fragmention peaks at 315 (M+-C6H5), 298, 207, 191, 183, 169, 123, 107. It was identifiedas 3-phenoxy benzyl–3-(2, 2-dichlorovinyl)-2, 2-dimethyl cyclopropane carboxy-late (VI).

Figure 6: Proposed photochemical pathways to accounts for the observed photoproducts.

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Next few fractions (VI–XII) of the column eluted with toluene and acetone(98:2 v/v) gave solid substance, purified by preparative TLC. The compoundwas eluted at 16.05 mins. The mass spectrum of the compound showedmolecular ion peak at m/z 435 (M+) and other fragment ion peaks at 391

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(M+-COO), 356, 207, 183, 169, 163, 127, 77, 51. The compound was identified asα-carboxy-3phenoxybenzyl-3-(2,2-dichlororvinyl)-2, 2 dimethyl cyclopropanecarboxylate (VII).

Further elution of the column with toluene and acetone (97:3 v/v, fractionsI–V) gave a yellow liquid, purified by preparative TLC (solvent system hexane:acetone 7.5: 2.5, Rf 0.48). The compound showed molecular ion peak at m/z371(M+) and eluted at 14.98 mins. The mass spectrum indicated the presenceof chlorine atom and fragment ions appeared at 300 (M+-2Cl), 208, 169, 163,127, 91, 77, 51. The compound was identified as 1-(α-cyano-3-phenoxy) benzyl-3(2,2-dichlorovinyl)-2,2-dimethylcyclopropane (VIII).

Further elution of the column with toluene and acetone (96:4 v/v, fractionsI–IV) gave a colorless solid substance, purified by preparative TLC. Thecompound was eluted at 59.55 mins and gave the molecular ion peak at m/z381(M+). The mass spectrum indicated the presence of chlorine atom. Thefragments appeared at 346 (M+-Cl), 305 (M+-C6H5), 298, 288, 227, 208, 173,140, 129, 115. The compound was identified as α-cyano-3-phenoxy benzyl-3(2-chloro vinyl)-2, 2-dimethyl cyclopropane carboxylate (IX).

Further elution of the column with toluene and acetone (95:5 v/v, fractionsI–V) yielded a compound, purified by preparative TLC. The compound waseluted at 29.00 mins. and gave the molecular ion peak at m/z 339 (M+) andother fragments at 295 (M+-COO), 269 (M+-2Cl), 261, 245, 227, 207, 191, 149,123, 107. It was identified as α-cyano-3-hydroxy benzyl 3-(2, 2-dichlorovinyl)-2,2-dimethyl cyclopropane carboxylate (X).

Elution of the column with toluene and acetone (94:6 v/v, fractions I–III)gave a yellowish liquid, which was further purified by preparative TLC. Thecompound was eluted at 12.88 mins. and gave the molecular ion peak at m/z223 (M+) and others at 197 (M+-CN), 169 (M+-COCN), 149, 132, 123, 105, 77,65 and identified as 3-phenoxy benzoyl cyanide (XI).

A few more compounds were also obtained as a result of photo irradiationof alphacypermethrin under UV Light. However those compounds could notbe separated from the mixture through column chromatography. They wereidentified in the mixture by GC-MS.

Photoproduct XII eluted at 9.42 mins and showed molecular ion peak atm/z 200 (M+) with base peak at 198 (M+-2H) due to 3-phenoxy benzaldehyde,169(M+- CH2OH) due to formation of phenoxy phenyl cation, 141 due to C6H5-C5H4

+. From the mass fragmentation the compound was tentatively identifiedon 3-phenoxy benzyl alcohol (XII).

Photoproduct XIII was eluted at 13.97 mins. Its mass spectrum showedmolecular ion peak at m/z 366 (M+). Different mass fragments appeared atm/z 183, 169, and 141. On the basis of molecular ion and mass fragmentationpattern the molecule was tentatively identified as 1, 2-bis- (3-phenoxy phenyl)ethane (XIII).

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The mass spectrum of photoproduct XIV (Rt 25.369 min) showed molecularion peak at m/z 327 (M++1). Different mass fragments of the compound cameat 291, 256, 221, 190, 156, 163 and 129. The mass spectrum indicated thepresence of chlorine atoms in the molecule. On the basis of the mass spectrumthe compound was tentatively identified as bis-3 (2, 2-dichloro)-2, 2-dimethylcyclopropane (XIV).

Photoproduct (XV) was eluted at 72.44 mins and gave the molecular ionpeak at m/z 273. Different mass fragments of the photoproduct appeared atm/z 246 (M+- CH2·CH), 229 (M+- CONH2), 202, 185, 151, 135 (base peak)attributed to phenyl acetamide, 123, 111 and 107. On the basis of thisinformation the compound was tentatively identified as α-carbomoyl benzyl-3-vinyl-2, 2-dimethyl cyclopropane carboxylate (XV).

The same compounds were also identified after sunlight irradiation ofalphacypermethrin. However, the rate of formation of these photoproducts wasslow a under sunlight than under UV light.

Identification of Photoproducts Formed on Soil SurfaceCompounds III and V were detected in both types of soil i.e. black and red

soil under both UV and sunlight irradiation.

DISCUSSION

Photolysis on Glass and Soil SurfaceThe identification of photoproducts of alphacypermethrin formed as thin

film on glass surface can be rationalized as originating from any one ofthe following photochemical processes like cleavage of ester linkage, cleav-age of diphenyl ether linkage, hydration of CN group to CONH2 group,hydrolysis of CONH2 group to COOH group, dehaloganation, decarboxylation,self-coupling of fragment radicals, oxidation etc (Fig. 2). The photochemicalcleavage via pathway A involves bond breaking between carbonyl carbon andoxygen atom of the ester group (Ia) leading to formation of two radicalswhich can subsequently form product V [2,2-dichlorovinyl-3 (2,2-dimethyl)-cyclopropane carboxylate] and IV (α-cyano-3-phenoxy benzyl alcohol). ProductIII (3-phenoxy benzaldehyde) is formed by removal of HCN from photoproductIV. Photoproduct III is then reduced to give photoproduct XII (3-phenoxybenzylalcohol). Product III and V were also formed in both black and red soils underboth UV and sunlight.

Pathway B involved cleavage of ester oxygen and benzylic carbon bondyielding (Ib). The discrete radical intermediate thus produced by scissionof the bond abstracts proton to yield photoproduct II [2(3-phenoxy)-benzylcyanide]. Self-coupling of the radicals following the removal of CN group,

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on the other hand, resulted in the formation of product XIII [1,2-bis-3-phenoxy phenyl ethane]. Photoproduct VIII [α-cyano-3-phenoxy benzyl-3(2,2-dichlorovinyl)-2,2-dimethyl cyclopropane], which may also be called as de-carboxylated alphacypermethrin, was formed from the intermediate Ib bythe loss of carbon dioxide via photo-induced decarboxylation. This involvedsimple coupling of the discrete free radicals after loss of carbon dioxide fromintermediate Ib. Pathway A and B are the most important and dominantphotoreaction mechanisms of all ester group pyrethroids. Products II, III, IVand V also obtained in photo and other degradation studies of cypermethrinand other related pyrethroids.[16–21]

In pathway C intermediate Ic is formed by scission of diphenyletherlinkage. Subsequent abstraction of proton from the medium resulted in the for-mation of the photoproduct X [α-cyano-3-hydroxybenzyl-3(2,2-dichlorovinyl)-2,2-dimethyl cyclopropane carboxylate]. Similar cleavage of diphenyl etherlinkage i.e. bond between phenyl ring attached is benzylic carbon atom andether oxygen result in the formation of intermediate stage Id (Pathway D).The resultant fragment radical on abstraction of proton followed by photodehalogenation of vicinal dihalides by extrusion of two halogen atoms andhydration of the CN group gave the product XV (α-carbomoyl benzyl-3-vinyl-2,2-dimethyl cyclopropane carboxylate).

Photodehalogenation of I caused by homolytic cleavage of carbon-halogenbond following n-σ∗ excitation yielded the photoproduct IX [α-cyano-3-phenoxy-benzyl-3-(2-chlorovinyl)-2,2-dimethyl cyclopropane]. Reductive dehalogenationis an important photochemical reaction and degradation mechanism and wasobserved in case of other synthetic pyrethroids also.[17]

Hydration of CN group in 1 formed the carbamoyl derivative whichon hydrolysis gave the product VII [α-carboxy-3-phenoxy benzyl-3-(2,2-dichlorovinyl)-2, 2-dimethyl- cyclopropane carboxylate]. On photo induceddecarboxylation of VII product VI [3-phenoxy benzyl-3-(2,2-dichlorovinyl)-2,2-dimethyl cyclopropane carboxylate] was formed.

Cleavage of carbonyl carbon and C-1 of cyclopropane ring by homolyticfission and subsequent self-coupling of the discrete radical intermediatesthus produced formed the product XIV [bis-3 (2,2-dichloro)-2, 2-dimethylcyclopropane].

Rate of PhotodegradationThe rate of photodegradation was greater on glass than on soil surface.

This may be due to the fact that some pesticides get adsorbed on soil clays andother colloidal substances and so become less available to light. The rate ofdegradation was higher on black soil than red soil under both UV and sunlight(Table 2). This may be due to difference in organic matter content and pH ofthe soil (Table 1).

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CONCLUSION

Irradiation of alphacypermethrin as a thin film on glass surface under UVand sunlight has given basic information about photoreactivity, photoproductsand possible chemical pathways in the environment. Although, number ofphotoproducts were formed on the glass surface, only two major productscould be identified in the soil surface. Hydrolysis of ester bond, cleavage ofdiphenyl ether bond, dehalogenation, decarboxylation and hydration of CNgroups are some of the major process of formation of different products. Itmay be concluded that in the environment there will be rapid breakdown ofalphacypermethrin on glass and also on soil surface.

ACKNOWLEDGMENT

The authors are grateful to the Head, PAR Division and the Director,Indian Grassland and Fodder Research Institute, Jhansi, Uttar Pradesh,India for providing necessary facilities to carry out the experiment, constantencouragement and valuable suggestions.

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