Catalytic dechlorination of organochlorine compounds VI. Mass spectral identification of aldrin and dieldrin products

Chemosphere No. 4, pp 191 - 1 9 9 .

0045-6535/79/0401-0191502.00/0

©Pergamon Press Ltd. 1979. Printed in Great Britain.

CATALYTIC DECHLORINATION OF ORGANOCHLORINE COMPOUNDS VI.

MASSSPECTRAL IDENTIFICATIONOF ALDRINAND DIELDRIN PRODUCTS

W.J. Cooper and W.H. Dennis, Jr. US Amy Medical Bioengineering Research and Development Laboratory Fort Detrick, Frederick, Maryland 21701 I.R. DeLeon and J.L. Laseter Center for BiD-Organic Studies, University of New Orleans, Lakefront New Orleans, Louisiana 70122

INTRODUCTION As part of a continuing study to develop environmentally safe methods for the chemical degradation and disposal o f excess pesticides and of pesticides l e f t over after routine pest management operations, we have studied the reductive dechlorination of various organochlorine insecticides. I-4 Reductivedehalogenations have been applied for conformational analysis of naturally occurring halogenated residues, s and can also serve as convenient syntheses for p a r t i a l l y dechlorinated organochlorine pesticides. For example, chemical dehalogenation of two organochlorine pesticides, aldrin (1) and dieldrin (7), has been accomplished with alkoxide bases,6 lithium and t-butyl alcohol ,7,8 and cobalt with sodium borohydride.9, IO In the present work, the reductive dechlorination of aldrin and dieldrin by the in s~tu generation of Ni2B with excess NaBH4 resulted in mixtures of p a r t i a l l y dechlorinated products. The mixtures were analyzed by gas chromatography/mass spectrometry using both packed and high-resolution glass capillary columns. The major products were isolated and confirmed by nuclear magnetic resonance spectroscopy. MATERIALS AND METHODS Mass spectra were obtained on two instruments. One was a DuPont 21-490B gas chromatograph/ mass spectrometer (GC/MS) equipped with a DuPont 21-094 data system; the other, a HewlettPackard (HP) 5982A gas chromatograph/mass spectrometer equipped with a high-resolution glass capillary column. For the DuPont instrument, the conditions were the following: electron energy, 70 eV; accelerating voltage, 1.4 Kv; source temperature, 250°C; and transfer lines and glass j e t separator, 250°C. The gas chromatographic (GC) separations were performed on a 6' x I/4" glass column (2 mm I.D.) packed with IO% OV-I on l O0/200mesh Gas-Chrom Q. For the HP instrument the following conditions were used: electron energy, 70 eV; and source temperature, 150°C. The GC separations were performed on a 28 m x 0.3 mm SE-52-coated glass capillary column, programmed from 80° to 240°C at 2°/min, and with a flow rate of 2 ml/minute.

igi

192

No. 4

The nuclear magnetic resonance (NMR) data were obtained on a Varian T-6OA, 60 MHz, using deuteriochloroform and deuteriobenzene as solvents. Aldrin ( l ) , l ,2,3,4,10,I O-hexachloro-1,4,4a,5,8,0a-hexahydro-endo-1,4-exo-5,8-dimethanonaphthalene, and dieldrin (7), 1,2,3,4,10,10-hexachloro-exo-6,7-epoxy-l,4,4a,5,6,7,8,8aoctahydro-e~do- 1,4,-exo- 5,8-di methanonaphthal ene were obtained commercially and recrys tal I i zed from alcohol. For each reduction experiment, l mmol of the pesticide was dissolved in 30 ml of alcohol. Nickel chloride (0.Smmol) was added as a 2M aqueous solution; NaBH4 (15mmol), as a 5M aqueous solution. After 30 minutes the reaction was quenchedby the addition of lO0 to 200 ml of water. The product mixture was then extracted into benzene/hexane ( I / l , v/v) for GC/MS analysis. To insure that all minor products were detected, high-resolution gas chromatography was also employed during GC/MSanalysis. For the purpose of GC/MS identification of the product mixtures, additional NaBH4 was Used in order to give a yield of dechlorinated products in sufficient quantity for obtaining good mass spectra. Figure l shows the high-resolution gas chromatograms of the mixtures examined by GC/MS.

3a Aldrin

6

43s ! L~ C~

J m,m r~

8s

lO

0 0 L~ r~

Ba

9

Dieldrin

II

L u

I

150

Figure 1.

170

190

i

n

v

210

230

240

TEMPERATURE FID high-resolution gas chromatograms of the reduction mixtures examined by GC/MS. Compoundidentifications are as follows (numbers correspond to those in Figs. 2 and 7). (3a) CI2HIICI5, (3s) Cl2HllCl5, (4) Cl2Hl2Cl4, (5) Cl2Hl5Cl3, (6) C12H16C12, (8a) CI2HgCI50, (Ss) CI2HgCI5O, (g) CI2HIoCI40, (lO) Cl2Hl3Cl30, and ( l l ) Cl2Hl4Cl20. The separations were performed on an SE-52 coated glass capillary column programmed from 50° to 240°C at 2°/minute.

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The major products of the aldrin and dieldrin dechlorination reactions were isolated by passing the product mixtures through a 30 cm x l cm column of Woelm acidic alumina. The compounds were eluted with ether and the fractions collected, concentrated, and monitored by GC.I RESULTS AND DISCUSSION I t had been shown previously that the solvent used in the catalyzed dechlorination of organochlorine compounds can affect the extent of dechlorination.l,2 For this work, the dechlorinations of aldrin and dieldrin were studied as a function of the solvent used and the amount of sodium borohydride added. Table I shows the results of these experiments.

Table I. Productionof Chloride from the Dechlorination of l mmol of Pesticide with 0.5 mmol NiCl and 15 mmol 2 of NaBH4 as a Function of Solvent Solvent (30 ml)

Pesticide

Chloride Produced (mmol)

Methanol

Al dri n Dieldrin

l . 50 l .46

Ethanol

Al dri n Dieldrin

O.81 l .12

2-Propanol

Al dri n Di el dri n

O.67 O. 63

Under optimum conditions, only 1.5 mmol of chloride (6 mn~l are possible) were produced from both aldrin and dieldrin. The GC examination of the mixtures showed one major product and minor amounts of dechlorinated products for each pesticide. The structural determination of these is discussed below. ALDRIN A probable reaction pathway for the reductive dechlorination of aldrin is shown in Figure 2. The presence of dihydro-aldrin (2) in the product mixture, suggests that the f i r s t step involves the hydrogenation of the C'-C7b double bond. This is very l i k e l y since the NiB2/NaBH4 catalytic system has been shown to hydrogenate double bonds effectively. 11-13 The major product, 3~, had a melting point of 94-95.5°C and represented 74% of the product mixture under optimum dechlorination conditions. The yield was determined by the flame ionization detector response (uncorrected for detector response factor and based only on percent of the total area of the detector response). The major product, 3a, was characterized by i t s mass and NMR spectra. Several minor products (2,3s, 4,5, and 6), which were also observed, were identified by their mass spectra. In general, the mass spectra of the reduction products are typified by ring opening decompositions which resemble the retro-Diels-Alder (RDA) reaction, accompanied or preceded by the elimination of Cl or HCI. The ring opening decompositions are of three types: (1) a chlorinated norbornadiene neutral fragment is eliminated with the formation of the very stable and + intense cyclopentadienyl ion at m/c 66 (C5H6) ; (2) a cyclopentadiene neutral fragment is eliminated with the formation of a chlorinated-n6rbornadienyl ion; and (3) a norbornadiene neutral fragment is eliminated with the formation of a chlorinated cyclopentadienyl ion. All of these ring opening decompositions, along with the eliminations of Cl and HCl, originate with the molecular ion.

194

~o. 4

]1

O0 (C5H6)+

RDA + (C5HCIs)'M 7 +

(-1)

(M'35)+

200 250 300 350 m/z Mass spectrum of dechlorination product of aldrin, Cl2HllCl5, 3~I (tool. wt. 330).

50

150

1O0

Figure 3.

l

]oo

M-35)+

e-

(M-71)+

e-'

I, .

.

.

.

.

.

i

200 250 300 m/e Figure 4. Mass spectrum of dihydro-aldrin CI2HIoCl6, 2 (mol. wt. 364). O0 RDA

~ 5o

l O0

150

350

(C5H2C14)+ "G

(C5H6)+ c

(M-35)+

J

J

50

200 250 300 m/e Figure 5. Mass spectrum of dechlorination product of aldrin, C 2H12C14, 4 (mol. wt. 296).

~=il

1O0

150

:(M_35) +

O0

(M.71)+ R D A ,+ • .., 50

Figure 6.

,L ,I.L ]00

,ll, :,,.L.., .... ,•,,I,L~L, 150

m/~

. . ,I, 20o

. i.~.

250

300

Mass spectrum of dechlorination product of aldrin, CI2H]5CI3, 5 (mol. wt. 264).

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195

Cf C

>

I

i

c

c

3a

~

3s

C

5

6

The mass spectrum of 3a is shown in Figure 3. The molecular ion, (M)-, was observed at m/e 330 and was typical for a 5-chlorine atom isotopic cluster. A 5-chlorine atom isotopic cluster which presumably resulted from+ a RDA-type decomposi• tion to glve (C5HCI5) , was present at m/e 236. The base peak at m/e 66 is somewhat unexpected in that the C6-C7 bond is hydrogenated, in contrast to the same bond in aldrin where the s~L1e base peak is observed.14 Because the empirical formula for 3awas Cl2HliCl 5, and two isomers were possible at the Clo, i t was necessary to examine the compound by NMR spectroscopy to establish the structure of 3a. The NMR spectrum in CDCI3 showed a multiplet at 0.8-I.6 ppm, a singlet at 2.38 ppm, and a singlet at 4.15 ppm, which integrated to 6, 4, and l protons, respect i v e l y . Whenthe solvent was changed to deuteriobenzene, the singlet, Hi 0, was shifted 0.62 ppm upfield, indicating that the a~-assignment of the proton is correct. 15-I~ The absence of H6 at 6.50 ppm, and the appearance of the multiplet substantiate the hydrogenation of the C6-C7 double bond. This product was therefore identified as 1,2,3,4, lO pentachloro-I ,4,4,4a,5,5,8,8a-octahydroanX:£-l O-hydro-endo-I ,4- exo-5,8dimethanonophthalene (where the lO-hydro is a~:.~l with respect to the C2-C3 double bond).

The GC peak that was el uted before the major product gave a mass spectrum nearly Probable reaction pathway for the reductive dechlorination of aldrin. identical to the one shown in Figure 3, and is presumably the "syn-lO-hydro" isomer (3s). These results are similar to those observed in the reductive dechlorination of heptachlor.2, W In a previous study, the "syn-lOmhydro" isomer was isolated when Co+2 and NaBH4 were used to reductively dechlorinate aldrin; however, no mention was made of the "a~-lO-hydro" compound.9 Figure 2.

Figure 4 shows the mass spectrum of dihydro-aldrin (2). The molecular ion, (M)+, was observed at m/e 364. The (M-35)+ ion at m/e 329 gave the base peak. The subsequent losses of HCI account for the ion clusters at m/e 293 and m/e 257. Highmass ions attributable to the retro Diels-Alder type decompositions were not observed; however, an ion at m/e 68 (C5H8)+ was present. This ion is absent in the spectrum of aldrin. Figure 5 shows the mass spectrum of compound 4, CI2H Cl The molecular ion, (M)+, was 12 4" present at m/e .296 and exhibited a typical 4-chlorine atom isotopic cluster. The loss of t chlorine (M-35) at m/e 261 gave a typical 3-chlorine atom isotopic cluster. The ion cluster at m/e 202 gave the base peak. This ion is probably the result of a RDA-type process leading to

(C5H2C14)*.

Figure 6 shows the mass spectrum of compound 5, C12H15C13. The molecular ion, (M)+, was observed at m/e 264, with the base peak (M-35)+ at m/e 229. The (M)+ and (M-35)+ ions show clusters typical of 3- and 2-chlorine atoms, respectively. The relative contributions of the RDA-type decomposition ions at m/e 196, (C7H7C13)÷, and m/e 66, (C5H6)+, were much less than those observed in other spectra.

196

No. 4

Compound 6, Cl2Hl6Cl2, was also observed. The molecular ion, (M)+, at m/¢ 230 and the (M-35)+ ion at m/e 195 were consistent with two- and one-chlorine atom isotopic clusters, respectively. The monochlorinated dimethanonaphthalene C12Hl7cl, not shown in the dechlorination pathway of Figure 2, was observed only after very exien~ive dechlorination in Ni2B/NaBH4, and resulted from the loss.of one of the bridgehead chlorine atoms (based on chemical inference). The molecular ion, (M)+, was observed at m/e 196 and had a typical one-chlorine atom isotopic cluster. The spectra of 6 and the monochlorinated compound have an ion at (M-28). This ion is probably a result of a-RDA-type decomposition which eliminates C2H4. Further studies are needed to confirm this hypothesis. The contribution of the ions + resulting from RDA type processes in these molecules is of interest. In compound 3a, (C~HA) corresponds to the base peak, and predominates over the formation of the stericaTly h{ndered (CsHCI5)+ planar 5-membered ring. I° In compound 4 the base peak represents the ion resulting from the RDA type process that gives (C~H~CIa)+, a much less sterically hindered planar ion. The virtual absence of ions resulting frUm~a RDA process for compounds 5 and 6 results in the (M-35)+ ion being the base peak; this is probably related to the relative instability of the odd-electron cyclopentane cation. DIELDRIN A probable reaction scheme for the reductive dechlorination of dieldrin is shown in Figure 7. As in the case of aldrin, the product mixture consisted of one major product (8a_) and several minor components (8~, 9, lO, and l l ) .

c

I

7~

>

8a

cl

8s

9

The major product, 8a, had a melting point of 137-138.5°C7 At optimum dechlorination, this product represented 71% of the reaction product mixture (uncorrected for detector response factor and based only on percent total area of flame ionization detector). The major product (8a) was characterized by its mass and NMR spectra. The minor products were identified by their mass spectra. As in the case of the al dri n dechlori nation products, the mass spectra of the dieldrin reductive dechlorination are also typified by ring opening decompositions which resemble the retro-DielsAlder (RDA) reaction.

The mass spectrum of compound 8a is shown in Figure 8. The molecular ion, (M)+ was observed at m/e 344 and H H is consistent with a 5-chlorine atom isotopic cluster. The (M-35)+ had a < 4-chlorine atom isotopic cluster at m/e 309. Ions resulting from RDA type processes appeared at m/e l 08~t (C7H80)+, and m/e 82, (C5H60)-. A I0 11 chlorinated ion resulting from a similar process was observed at m/¢ 236. Figure 7. Probable reaction pathway for the reductive The base peak, m/e 79, arises from the dechlorination of dieldrin. loss of CHO from (C7H80)+.14

Mo. 4

197

E

I

O0

I

XlO

.F-

e-

(C5H60) 50 Figure

RDA +

Li,(c7"8°I....

...........l,li ......

n,

.

.

150

l O0

,l (~-3S)+ ,~,I

RDA (C5HC15)+

RDA +

II.Lhl:,

,..

.

.

200 m/e

)

.

3O0

250

350

Mass spectrum of dechlorination product of dieldrin, CI2H9CI5O, 8a (mol. wt. 344).

8°

1l°° XlO

I

(M-35~+

RDA . RDA ~ (C=HcO)* u (C7H80)I . 50

Figure 9.

.. I ! L .

l O0

RDA + (C5H2C14)

...........

,.,;...... .

......,.,.,:,

150

, r,l~,

....

200

J

250

Jr,, 300

m/¢ Mass spectrum of dechlorination product of dieldrin, Cl2HloCl40, 9 (mol. wt. 310). 100

v

RDA + (C5H60)

C

XlO

(M-71)+ > ~

~ J,I,,...~.l,,.,;,.LI, i..,1. ,J,I.,,,..,l. L,,~.. ].,~b,.,?.,,..,.,.,.. ~,..,LI, .,,~. ,,..,J ........ 50

1O0

150

200

> (M-35)+

L,,,.U.,..... 250

.

,,I..

: 300

m/¢ Figure lO.

Massspectrum of dechlorination product of dieldrin, Cl2Hl3Cl3O, lO (mol. wt. 278).

-llOO

)

c

RDA .+ C5H601

=A

X4

IIL

" 50 ""

Figure I I .

I'

I l O0

150

200

250

300

m/e.

Mass spectrum of dechlorination product of dieldrin, Cl2Hl4Cl2O, II (mol. wt. 244).

198

No. 4

The NMR spectrum of 8a in CDCI3 showed a singlet at 4.25 ppm, which shifted to 3.57 ppm when analyzed in deuteriobenzene. This s h i f t indicates an an~i-orientation of the C._ proton. Is Other features of the NMR spectrum in CDCI3 were three singlets at 3.07 ppm, 2 . ~ ppm and 2.45 ppm, and a multiplet between 0.80-I.33 ppm, each of which integrated as 2 protons. The 5,8- and 6,7-protons remained unchanged in the compound 8a (relative to dieldrin); however, the 4a,8a-protons shifted from 2.62 ppm in dieldrin to 2.42 ppm in the product, also indicating that the lO-proton was ant~L rather than syn. IB Basedon the above evidence, the compound was identified as l ,2,3,4,10-pentachloro-exo-6,7-epoxy-octahydro-anY~L-lO-hydro-e~do-l,4-exo-5,8dimethanonaphtha I ene. As in the dechlorination of hepachlor4 and aldrin, the GC peak which eluted prior to the major peak (using packed columns) had an identical mass spectrum. This compound was assumed to be the "syn-lO-hydro" isomer of the major product. Figure 9 shows the mass spectrum of compound 9 (Cl2HloCl40). The (M)+ appeared at m/e 310 and was consistent with a 4-chlorine atom isotopic cluster. The (M-35)+ ion at m/e 275 had a 3-chlorine atom isotopic cluster. A small ion at m/z 202~resumably resulted from a RDA tvpe process that favored the formation of (C7H80)+ and (C5H60)T at m/e i08 and 82, respectively. Figure lO shows the mass spectrum of compound lO, Cl2HI3CI30. The (M)+ ion was observed at m/e 278 and was a 3-chlorine atom isotopic cluster. The presence of a (M-HCO)+ ion at m/e 249 and (M-35)+ ion atm/e 243 were observed. A large (M-71)+ atm/¢ 207 had a l-chlorine atom isotopic cluster. The base peak, role 82, presumably arose from the RDA type process to give (C5H60)+. The low abundance of the ion resulting from a RDA-typedecomposition to give (C7H80)+, and consequently them/e 79 peak, has not been explained. Figure I I shows themass spectrum of compound I I , Cl2Hl4Cl20. The (M)+ ion was observed at m/e 244 with a (M-35)+ ion at m/e 209. The base peak at m/e 82 appears to be an ion similar to that of compound lO. The RDA-type decomposition process in the dechlorination products of dieldrin favors the elimination of the neutral chlorinated fragments with charge retention on the oxygen-containing ring. For example, the base peak at m/e 79 in dieldrin arises from the loss of CHO from the RDA type decomposition ion, m/e I08, (C7H80)+. This same base peak at m/e 79 was observed in compounds 8, 9 and lO where the C2-C3 bond was unsaturated. In compounds I I and 12 (not shown) where the C2-C3 bond was saturated, the base peak became (C5H60)+ ion at m/e 82. The presence of the C2-C3 double bond appears to favor the formation of the neutral cyclopentadiene fragment which i n i t i a l l y gives rise to the (C7H80)+ ion at m/e I08 and f i n a l l y the ion at m/e 79 with loss of HCO. Where the C2-C3 bond is-saturated, the loss of the C7HxCly moiety gives rise to the (C5H60)+ ion which is the favored RDA type decomposition product. CONCLUSION The major products of the reductive dehalogenations of aldrin and dieldrin using the Ni2B/NaBH4 system were the monodechlorinated products, 3a and 8a_. Thesewere produced in 74% and 71% yields, respectively. Both major products were assigned the a~X~i-10-hydro configuration based on their NMR spectra. Our results are in good agreement with the results obtained by others 18 using similar compounds. In this other work, the reductions were performed using the Zn/acetic acid and chromous acetate systems and the main products obtained were the monodechlorinated compounds in 70% and 78% yields, respectively. In both cases the hydrogen atom was also assigned the amPuLconfiguration, with respect to the double bond.

No. 4

199

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2.

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(Received in The Netherlands 16 February 1979)