Soil Degradation of Trifluralin: Mass Spectrometry of Products and Potential Products Tomasz Golab and J. L. Occolowitz~ Lilly Research Laboratories, Division of Eli Lilly and Company, Indianapolis, Indiana 46206, USA
The examination of soil which has been treated with trifluralin (TREFLANm a,a,a-trifluoro-2,6-dinitroN,N-dipropyl-ptoluidine) has resulted in the identification of 28 degradation products. This paper presents the mass spectra of these products and a number of related compounds which were suspected products but were not found in trifluralin-treated soil. The mass spectra of the N,N-dialkylamines, with one exception, show major peaks due to amine or-cleavage and due to amine a-cleavage followed by carbon-nitrogen bond fission with rearrangement of a hydrogen atom. Compounds having nitro groups yield mass spectra containing peaks due to intra-ionic oxidation by the nitro groups. In some cases, propionyl ions formed by this process are major ions in the spectra. Azo and azoxybenzenes resulting from condensation of two trifluralin moieties through nitronitrogens fragment mainly through the nitrogen-nitrogen bond.
INTRODUCTION
EXPERIMENTAL
Trifluralin (TR-l), is the most prominent member of a series of selective dinitroaniline herbicides introduced to agriculture in the 1 9 6 0 ~ . ” ~
The degradation study of trifluralin in soil under field conditions was performed over a three year period after initial application of the herbicide. [“C] Trifluralin uniformly labeled in the aromatic ring and the trifluoromethyl group was used in the study. The compound was incorporated in the soil to a depth of 7.5 cm and the sampling for degradation products was performed periodically to a depth of 15 cm. Soil samples were extracted with methanol and aqueous methanol, and the extracts were purified using column, thin-layer and high pressure chromatographies. Detailed procedures are given elsewhere.” EI spectra were determined either by GCMS using an LKB-9000 mass spectrometer, or by direct inlet using a C E C 21-1 10A or Varian-MAT 731 mass spectrometer. In those cases where GCMS did not yield a molecular ion, the sample was re-examined using the direct inlet technique. Accurate mass measurements were made from photoplates or peak matching using the 731 mass spectrometer. The same instrument was used to determine FD spectra from carbon dendrite emitters. Apart from TR-43 and TR-44, which were kindly provided by Dr J. 0.Nelson, University of Maryland, all compounds were synthesized at these laboratories by the most obvious procedure. The sole exceptioY2is T R 38, which was obtained by photolysis of TR-2. Structures were checked by NMR, IR, UV and microanalysis, as well as by MS.
”;”o”’. cF
-3
The fate of trifluralin and other related herbicides in soil, plants, animals, water and air has been investigated3-’ and the mass spectrometry of several degradation products described.’ In soil, 28 products derived from trifluralin have been detected. The identities of these compounds have been determined either by synthesizing possible candidates and matching these chromatographically and by spectral methods with soil products, or by direct spectral structure determination followed by comparison with synthetic compounds. In the course of this investigation, 49 compounds have been examined. The purpose of this paper is twofold; viz. to examine the mass spectrometry of this somewhat chemically heterogeneous group, and to present the spectra to other workers in this field. Only the spectra needed to achieve the first purpose are presented here. However, a compilation of those compounds examined but whose spectra are not presented is included. All spectra will be submitted to the MSDC/EPA/NIH9 and Cornell“’ collections. t Author to whom correspondence should be addressed.
RESULTS The spectra of the compounds necessary for the ensuing discussion, together with structures and designations,
CCC-0306-042X/79/0006-0001$04.50 @ Heyden & Son Ltd, 1979
BIOMEDICAL MASS SPECTROMETRY, VOL. 6, NO. 1, 1979
1
T. GOLAB AND J. L. OCCOLOWITZ
are presented in Figs. 1-28. The designations and structures of the remaining compounds are listed in Table 1. Of the foregoing compounds, TRs 1,2,13,15,17,20, 28 and 32 were isolated from soil in sufficient quantity for identification by spectroscopic techniques. The most abundant degradation product was TR-2, which resulted from decomposition of 2% of the applied trifluralin. Products identified by chromatographic comparison
L
I
50
I50 m/z
I00
250
200
300
Figure 6. Mass spectrum of TR-7, a,a,a-trifluoro-N4,N4-dipropyltoluene-3,4,5-triamine.
0
b 20
I
LY
150
100
50
200
250
I,
[Mlr3S5
l " " 1
300
I
350
m /I
Figure 1. Mass spectrum of TR-1, a,a,a-trifluoro-2,6-dinitro-N, N-dipropyl-p-toluidine (trifluralin).
50
150
100
250
200
300
1 350
mh
Figure 7. Mass spectrum of TR-10, a,a,a-trifluoro-2'-hydroxyamino-6-nitro-N-propyl-p-propionotoluidide.
50
100
200
I50 m/z
250
300 [MI+ 317
Figure 2. Mass spectrum of TR-2, a,a,a-trifluoro-2,6-dinitro-Npropyl-p-toluidine.
/
50
100
200
150
'
'
I
250
I " " I
300
350
m/z
Figure 8. Mass spectrum of TR-11, 2-ethyl-7-nitro-l-propyl-5(trifluoromethyl) benzimidazole 3-oxide.
g
20
I. , 50
100
150 rn/z
200
_1
250
300
Figure 3. Mass spectrum of TR-3, a,a,a-trifluoro-2,6-dinitro-p toluidine.
e
9
joi ,,I, i.;
40-
,
258
I
j'
+r+++++
,,
50
150
100
1'1
200
Figure 9. Mass spectrum of TR-12, (trifluoromethy1)benzimidazole 3-oxide.
o
J
[MI+ 275
250
' 1
300
2-ethyl-7-nitro-5-
I
60
234
40-
ii
I
212
r" 80-
20-
(MI'
-
l d
[ I
50
100
150
m/z
200
250
I
Y
Y
5
305
300
I
21b
$+O
-
60-
1
Ch
[MI' 301
350
Figure 4. Mass spectrum of TR-4, a,a,a-trifluoro-5-nitro-N4,N4dipropyltoluene-3,4-diamine.
with previously synthesized compounds are TRs 3 through 12,14,16,18,19,21,29,31,36,39,40 and41.
50
100
150
260
250
300
Substituted benzenes
rn /z
Figure 5. Mass spectrum of TR-5, a,a,a-trifluoro-5-nitro-N4propyltoluene-3,4-diamine.
2 BIOMEDICAL MASS SPECTROMETRY, VOL. 6, NO. 1 , 1979
The spectrum of the parent compound, trifluralin (TRl), is shown in Fig. 1. The spectrum is typical of an @ Heyden & Son Ltd, 1979
SOIL DEGRADATION OF TRIFLURALIN
E'5
-
1
a0STR-14 80
60
El
.'
40
.-
B u"
20
m/z
50
I00
150
200
300
250
m/z
Figure 16. Mass spectrum of TR-28, 2,2'-azoxybis trifluoro-6-nitro-N-propyl-ptoluidine).
(a,a,a-
Figure 11. Mass spectrum of TR-14,7-amino-2-ethyl-l-propyl-5-
(trifluoromethyl)benzimadazole.
m/z
Figure 17. Mass spectrum of TR-29, N-propyl-2,2'-azoxybis(a,a,a-trifluoro-6-nitro-p-toluidine). 50
100
150
200
250
300
m/z
Figure 12. Mass spectrum of TR-15, 2-ethyl-7-nitro-5-(trifluoromethy1)benzimidazole.
-., -j
Iool
-bp 80 I
TA-'7
186
1'
I00
I50 m/z
Figure 13. Mass spectrum of (trifluoromethyl) benzimdazole.
200
TR-17,
250
1
50
100
150
ZOO 250 m/z
, 300
[MI+ 4% 477
,it,
400
450
-4 500
300
7-nitro-l-propyl-5-
Figure 19. Mass spectrum of TR-31, 2,2'-azoxybis trifluoro-6-nitro-p-toluidine).
i 'ml 1
u r L ; L 7
Figure 18. Mass spectrum of TR-30, N'-propyl-2,2'-azoxybis(a,a,a-trifluoro-6-nitro-p-toluidine).
[MI+'P73
50
204
LL
(a,a,a-
80
TR-20
50
260
100
250
300
m/z
Figure 14. Mass spectrum.of TR-20, a,a,a-trifluoro-2,6-dinitro-pcresol.
m/z
Figure 20. Mass spectrum of TR-32, 2,2'-azobis (a,a,a-trifluoro6-nitro-N-propyl-p-toluidine).
N'-dipropylamines, as well as the N-propanol-N-propylamines TR-41 and TR-42 (Table l),exhibit analogous behavior; i.e.
R4p': '4GRz ' H
\ +//
CH,
N
Figure 15. Mass spectrum of TR-21, 4-(dipropylamino)-3, 5-dinitrobenzoic acid.
aliphatic amine13 insofar as major fragments involve arnine a-cleavage, to yield m / z 306, followed by carbon-nitrogen bond fission with hydrogen rearrangement, to yield m / t 264. Apart from TR-39 (Fig. 25), whose spectrum is discussed below, all of the N, @ Heyden & Son Ltd, 1979
+
'4QRz
' R3
--*
\
R5
R3
R5
R3
R I = CHzCHzCH3, CHzCH(OH)CH3, CHzCHzCHzOH Rz # NHOH Scheme 1
BIOMEDICAL MASS SPECTROMETRY, VOL. 6, NO. 1, 1979 3
T. GOLAB AND J. L. OCCOLOWITZ
$
‘E
f
60 40
20
190
1
50
Figure 21. M a s s spectrum of TR-34, a,a,a,a’,cu’,cu’-hexafluoro2,2’,6,6’-tetranitro-p-p’-azotoluene.
4 4 L t ’ C
50
100
&,-,GI,,, 150
100
200
150
250
300
350
rn/z
Figure27. M a s s spectrum of TR-43, a,cu,a-trifluoro-2,6-dinitro-N(propan-2-ol)-p-toluidine.
-
!
[MI+ 3C9
L-t--
d
rnh
-
40
250
XK, m/z
50
100
Figure 22. M a s s spectrum of TR-35, 1,2-bis(a,~,a,-trifluoro2,6-dinitro-p-tolyl) hydrazine.
150
200
250
300
350
rn/z
Figure28. M a s s spectrum of TR-44, a,a,a-trifluoro-2,B-dinitro-N(propan-3-ol)-p-toluidine.
Scheme 1is applicable to TRs 1(Fig. l ) , 4 (Fig. 4), 7 (Fig. 6), 21 (Fig. 15), 21M, 24,36,36M, 41 and 42 (Table 1). Not unexpectedly, amine (Y -cleavage yields major peaks in the spectra of the N-propylamines and the N-propanols; i.e. 50
100
150
200
250
300
350
H
rnh
Figure23. M a s s spectrum of TR-37, a,a,a-trifluor0-2,6-dinitro-Nnitroso-N-propyl-p-toluidine.
100
50
150
L 200
250
300
m/r
Figure 24. M a s s spectrum of TR-38, a,a,a-trifluoro-6-nitro-2nitroso-p-toluidine.
50
100
150
200
250
300
350
rnn
Figure 25. M a s s spectrum of TR-39, a,a,a-trifluoro-2-hydroxyamino-6-nitro-N,N-dipropyl-p-toluidine.
,
;
5
T
“
60
p 40
= d
20
I,, 50
100
150
200
250
,3y;
300
[;+;I*?
350
m/z
Figure 26. M a s s spectrum of TR-40, a,a,a-trifluoro-2’.6‘-dinitroN-propyl-p-propionotoluidide.
4
BIOMEDICAL MASS SPECTROMETRY, VOL. 6, NO. 1, 1979
\+. /
N
R,
H
\+/ N
CH,
Scheme 2 is applicable to TRs 2 (Fig. 2), 5 (Fig. 5), 8,22, 22M, 25 (Table l), 4 3 (Fig. 27) and 44 (Fig. 28). In contrast to the above, the EI fragmentation of TR-39 (Fig. 25) involves the loss of 0. and OH- to give m / z 305 and 304, respectively. Accurate mass measurements show that m / z 276 and 275 have compositions C2H50and CzH60 less than the molecular ion. They presumably arise by the loss of C2H5.from m l z 305 and 304. The subsequent loss of Ha from mlz 275 (m*, found 273.0) followed by elimination of C3H6 (m”, found m / z 196.5) yields m l z 232, the base peak. The ion m / z 43, which has the composition C3H7 (found 43.0546, calc. 43.0548), is abundant in the spectrum of TR-1 (Fig. 1). Its relative intensity is decreased fivefold in the spectrum of TR-7 (Fig. 6), where both nitro groups of TR-1 have been reduced to amino groups. Likewise, the relative intensity of the C3H7 ion from TR-2 (Fig. 2) is considerably greater than from TR-8. A number of the compounds studied, possessing at least one N-propyl group and an o-substituted nitro group, show intense peaks at m / z 57 in their spectra; e.g. TR-2, Fig. 2. This ion has the composition C3H50 (found 57.0343 TR-1, and 57.0346 TR-2; calculated for C3H50, 57.0340) and must arise by a skeletal rearrangement. The skeletal rearrangement of o-nitrobenzenes has been reported previously; l4 however, we @ Heyden & Son Ltd, 1979
SOIL DEGRADATION OF TRIFLURALIN
Table 1. Compounds whose spectra are not presented herein Cornpound
Structure and nomenclature
TR-6
Compound
Structure and nomenclature
Cornpound
TR-19
No
TR-26 HN-CH
Qk
NH,
O2
Structure and nomenclature
NHz
CF,
7-Amino-5-(trifluoromethyl)benzimidazole TR-2OM Methyl ether of TR-20 TR-21M Methyl ester of TR-21
a,a,a,-Trifluoro-5-nitrotoluene3.4-diamine
TR-8
TR-27
TR-22 HN-n-Pr
p P r
"'"0""
2,2'-Azoxybis (a,a,a-trifluoro-6-nitro-
"."5""'
CF3
N,N-dipropyl-p-toluidine)
TR-33
COOH
a,a,a,Trifluoro-N4-propyltoluene3,4,5-triamine
3,5-Dinitro-4-(propylamino) benzoic acid TR-22M Methyl ester of TR-22
3.3'-Azobis(N'-propyl-6-trifluoromethyl-o-phenylenediamine)
TR-9 TR-23
""'0"
TR-36
OH
N(n-Pr),
HZ
C F3
COOH
a,a,a-Trifluorotoluene-3,4,5-triamine
""QNoz CF3 OH
4-Hydroxy-3.5-dinitrobenzoicacid TR-23M Methyl etherjester of TR-23
c~,a,u,Trifluoro-4,6-dinitro-5(dipropy1amino)-o-cresol TR-36M Methyl ether of TR-36
TR-16 HN-C-Et
""@
TR-41 TR-24
(n-Pr)
\
CH,CH(OH)CH,
ozNo
CF3
O Z N e N o 2
7-Amino-2-ethyl-5-(trifluoromethyl) benzimidazole
/
2.6-Dinitro-N,N-dipropylaniline
?J
TR-42 TR- 18
(n-Pr)
TR-25
\
HN-CH
N
/
(CH,),OH
n-Pr 02N&N02
OZN@
I
CF3
c F3 a,cu,cr,-Trifluoro-2,6-dinitro-N-(propan-
7-Nitro-5-(trifluoromethyl)benzimidazole
@ Heyden & Son Ltd, 1979
BIOMEDICAL MASS SPECTROMETRY, VOL. 6, NO. 1, 1979 5
T. GOLAB AND J. L. OCCOLOWITZ
believe that the intra-ionic oxidation of an aliphatic group to yield an intense alkanoyl peak in a mass spectrum is unprecedented. The relative intensity of m / r 57 is quite dependent on changes in substitution of the aromatic ring. Thus, in the spectrum of TR-1 (Fig. l), it has a relative intensity of 13% ; but in the spectrum of TR-2 (Fig. 2), in which one n -propyl group of TR-1 has been replaced by hydrogen, the relative intensity of m / z 57 is 100%. Reduction of one nitro group of TR-2 to an amino group to give TR-5 (Fig. 5) reduces the relative intensity of m / r 57 to 18%. TR-43 (Fig. 27) and TR-44 (Fig. 28) contain N-(propan-2-01) and N-(propan-3-01) moieties, respectively. Intra-ionic oxidation as described above would yield a C3H502, m / r 73, ion in each case. In the spectrum of TR-43 (Fig. 27), m / z 73 is of low intensity, whereas it is quite intense in the spectrum of TR-44 (Fig. 28). We have advanced the following mechanism (Scheme 3), using TR-2 as model, to explain the formation of m / z 57:
presence of a propionyl group in the nonionized molecule. For reactions in Scheme 4,it is of interest to speculate on the reasons for the changes in the relative intensities
\
\
1
N'
H7C3\ N'
CF,
Scheme 4
H
O2
0Hlz 1. N
-
C -C, H
m / z 57
02NoN:oH
Scheme 3
The spectrum of the deuterated analog of TR-2, H
\
/
of the products when the aromatic substituents are changed. Using group equivalent values for heats of formation, together with the heats of formation of [C3H7]+, [C2H5CO]' and the [M-H]+ ion from dimethyl aniline listed in Ref. 15, and neglecting any reverse activation energy, one can calculate that reaction (3) requires the least activation energy and reaction (2) the most. Consequently, for reactions (1 and 2), which are simple cleavage reactions, populations of molecular ions whose internal energy distribution is biased toward lower energies will favor reaction ( l ) , while an increase in the relative number of ions having higher energies will make reaction (2) more competitive. This is in agreement with observation; when R1= NOz (TR-1, Fig. 1), the ionization potential of the molecular ion will be higher (for example, the ionization potential of aniline is 7.70eV, and that of o-nitroaniline is 8.66eV1') and reaction (2) will become more prominent, whereas when R1=NH2 (TR-4, Fig. 4), a decrease in molecular ionization energy will decrease the relative importance of (2). For TR-7 (Fig. 6), this reasoning would predict reaction (2) to be less prominent than for TR-4 (Fig. 4), as is observed. The above reasoning cannot be applied to reaction (3) because it involves considerable rearrangement. It is likely that its relatively low activation energy makes it competitive when other factors, e.g. geometry of the molecular ion, are favorable. A referee has pointed out that reaction (2) is an example of a charge site reaction;16 i.e.
CD2CH2CH3
CF.3
obtained on the 73 1 mass spectrometer, shows a peak at m l z 57 and no evidence of any shift to m / z 58 or 59. This is in agreement with the above mechanism insofar as the itinerant hydrogens involved in the formation of [C3H50]+ arise solely from the a-carbon of the N propyl group. The spectrum of the deuterated analog of TR-2, obtained by GCMS using the LKB-9000, gave m / z 57 and m / z 59 in the ratio 4 : 1. Although this mechanism does not explain all that is known about the rearrangement, it is not at odds with the experimental observations. It is perhaps sufficient to show, within the scope of this paper, that the observation of an intense propionyl peak in the spectrum of a trifluralin metabolite is not necessarily indicative of the 6 BIOMEDICAL MASS SPECTROMETRY, VOL. 6, NO. 1, 1979
H7C3y+. /c 4%
/C&
+[C3H71"+
ozN+No2
ozN+Noz CF,
-3
Scheme 5
@ Heyden & Son Ltd, 1979
SOIL DEGRADATION OF TRIFLURALIN
The electron-withdrawing nitro groups destabilize the radical cation [MIC',and this condition is relieved by the charge site reaction which leaves the radical on the aromatic moiety. This theory also explains the lesser importance of this reaction in TR-7. The nitrosamine TR-37 (Fig. 23) and the nitrosobenzene TR-38 (Fig. 24) are interesting model compounds, although they were not detected in soil during the three-year study. Both compounds show molecular ions in their E I spectra. The FD spectrum of TR-37 has two main peaks, m / z 322 ([MI+', 100%) and m / z 293 ([M-C~HS]+,15%). Major peaks at m / z 292 and 264 in the E I spectrum of TR-37 arise by the sequential loss of N O and C2H4, as evidenced by accurate mass measurement and the presence of the appropriate metastable peak (found 292.0545, calc. for C10H9N304F3, 292.0545; found 264.0230, calc. for CSHsN304F3, 264.0232; for m / z 292 + 264, found 238.5, calc. 238.7.) Other major peaks are the skeletal rearrangement ion, m / z 57 (found 57.0340, calc. for C3Hs0,57.0340) m / z 43 (C3H7) and m / z 30 (NO). Compounds which possess an N-propionyl moiety, viz. TRs 10 (Fig. 7) and 40 (Fig. 26), not unexpectedly have intense peaks due to the [C3H50]+ion in their spectra. TR-40 has no molecular ion in its EI spectrum, but a relatively intense molecular ion is produced by FD. Of the 28 degradation products of TR-1, TR-20 (Fig. 14) is unique insofar as it is the only compound in which an atom directly attached to the aromatic ring of TR-1 has been eliminated. The EI fragmentation of TR-20 can be rationalized in terms of known fragmentations of its substituents; e.g. m / z 194, which has the composition C6H3N03F3,is due to the elimination of NO, a fra mentation undergone by aromatic nitro compounds,% followed by the elimination of CO, which is typical of phen01s.l~ The m l z 159 ion has the composition C7H20F3and arises by the elimination of both nitro groups plus a hydrogen atom, while the m / z 132 ion, which has the composition C6H3F3, results from the elimination of both nitro groups and a CO molecule.
Benzimidazoles Intra-ionic oxygen transfer is not confined to the compounds mentioned above. It is also evident in the spectra of benzimidazole N-oxides TR-11 (Fig. 8) and TR-12 (Fig. 9) which have base peaks due to the [C3H50]' ion. In the case of TR-11, the [C3H50]+ ion (found 57.0342, calc. 57.0340) can arise from the propyl group as described above or from the C-ethyl moiety. It is likely that oxygen transfer to the C-ethyl moiety plays a prominent part in the formation of [C3H50]+,because TR-12, which has no propyl group, gives a spectrum in which [C3H50]+ is the most abundant ion. Relatively smaller contributions by m / z 57 occur in the benzimidazoles TR-13 (Fig. 10) and TR-17 (Fig. 13), both of which possess an N-propyl group and an o-nitro group. More prominent in the spectra of these compounds are peaks resulting from the loss of C3Hs0-, m / z 224 and 216, respectively. The alternate route to these ions by the successive elimination of CzHS' and C2H4 was excluded by accurate mass determination, @ Heyden & Son Ltd, 1979
although this process gives rise to m / z 214 in the spectrum of TR-14 (Fig. 11) which has no oxygen function. The spectra of benzimidazoles not having an N-alkyl function, TRs 15, 16, 18 and 19, are relatively straightforward; and as an example, the spectrum of TR-15 is included in the figures (Fig. 12). Accurate mass measurement shows that m / z 212 and 213 are due to the elimination of H N 0 2 and NO2, respectively. TR-10 (Fig. 7) was formerly assigned' the structure
The formation of m / z 279 by a single-step elimination of C3H40, as evidenced by the appropriate metastable peak and accurate mass measurement of m / z 279, however, suggests the presence of an N-propionyl group which can eliminate methyl ketene in a manner analogous to the elimination of ketene from the molecular ion of a~etani1ide.l~ More definitive evidence for the structure of TR-10, as shown in Fig. 7, comes from its IR spectrum which shows absorptions at 3320 cm-' (-NHOH stretch) and 1675 cm-' (=C=O stretch). When left in solution for a few days, TR-10 loses water to give TR-11, possibly via an intermediate with the structure formerly assigned to TR-10. The IR spectrum of TR-11 shows no carbonyl absorption.
Azo and azoxy compounds The major fragments in the spectra of the azo and azoxy compounds TR-27 through TR-33 arise from fission of the nitrogen-nitrogen bond, followed by fragmentation of the ions so formed. Fragmentation of the 'head to head' azo compound TR-34 occurs predominantly through the azo-nitrogen-carbon bonds to yield m / z 263 (Fig. 21). Skeletal rearrangements observed in the spectrum of az~xybenzene'~ are not evident in the substituted azoxybenzenes TR-27 to TR-3 1.Compounds having an N-propyl moiety and an o-nitro substituent have m / z 57 peaks in their spectra formed by the intra-ionic oxidation discussed earlier. The spectra of the isomers TR-29 and TR-30, Figs. 17 and 18, illustrate the fragmentation of the azoxy compounds and indicate the ability of mass spectrometry to distinguish between their structures. Both TR-29 and TR-30 show molecular ions in their spectra; however, the molecular ion of TR-29 is of such low relative intensity that it can be hidden easily among peaks due to impurities in samples isolated from soil. Accurate mass measurements of the more intense peaks at [M-OH]", m / z 479, and [M-F]+', m / z 477, proved instrumental in establishing the molecular BIOMEDICAL MASS SPECTROMETRY, VOL. 6, NO. 1, 1979 7
T. GOLAB AND J. L. OCCOLOWITZ
formula, and ultimately the structure of TR-29. The F D spectrum of TR-29 consists substantially of two peaks: the molecular ion, m/z 496 (100"/0), and (M-OH]+', m f z 479 (20%). Fission of the nitrogen-nitrogen bond of TR-29 with hydrogen transfer yields m / t 276. The fragmentation of TR-29 is rationalized in Scheme 6. An elemental composition below a postulated structure indicates that the composition of that ion was established by accurate mass measurement. An asterisk indicates that a metastable peak was observed for the ionic reaction shown. H
CH,CH,CH,,
\+./
AH,
I H,
/CHCH,CH,
' i
arise by nitrogen-nitrogen bond fission of the molecular ion of TR-30, it is to be expected that the spectra of TR-29 and TR-30 would have common peaks, as is observed. Substitution of a primary amino-hydrogen of TR-29 with an n-propyl group to give TR-28, the most abundant dimeric degradation product, largely suppresses those ionic reactions leading to m/z-276, 258 and 248 which indicate the presence of the azoxy function. Apart from a peak at m/z 290 in the spectrum of TR-28 (Fig. 16), which can result from fission of either or both of the azo-nitrogen-carbon bonds with hydrogen rearrangement, the fragmentation of TR-28 is generally qualitatively similar to the corresponding azo compound TR32 (Fig. 20). TR-31 (Fig. 19) contains n o N-alkyl moieties, and its spectrum is relatively straightforward. Fission of the nitrogen-nitrogen bond yields m/z 235 and 219, each of which eliminates NO2 to give m/z 189 and 173, respectively. The spectrum of the symmetrical substituted diphenyl hydrazine TR-35 is shown in Fig. 22, The electron impact induced formation of the [M-H20]" ion, m / z 482, from the molecular ion is supported by the presence of the appropriate metastable peak. The only major peak shifted in the s ectrum of TR-35 after exchange with methanol-0-[9HI] is the molecular ion. Consequently, the elimination of water from the molecular ion involves both hydrazine-hydrogens, and the
R=HorD
NO,
NO,
NO
NO,
1'
m l z 482
m / z 235
m/z 263
-NO21
Scheme 6
m / z 189
The peaks at m/z 276, 258 and 248 define the position of the azoxy-oxygen in TR-29. Both m / z 276 and m/z 248 are absent from the spectrum of TR-30, and m / z 258 has a low relative intensity. Since m/z 260 can 8
BIOMEDICAL MASS SPECTROMETRY, VOL. 6, NO. 1, 1979
/-NO2
m / z 143
:NO, m / z 159 I-CO
m / z 131
Scheme 7
@ Heyden & Son Ltd, 1979
SOIL DEGRADATION OF TRIFLURALIN
major fragments in the spectrum likely arise by fragmentation of the [M - H20]+‘ ion. This explanation accounts for the qualitative similarity between the spectra of TR-35 and TR-34 (Fig. 21), Scheme 7. In conclusion, apart from a few exceptions, the molecular ions of the trifluralin degradation products are accessible by EI mass spectrometry. For the exceptions, molecular ions can be obtained by FD mass spectrometry. The o-nitroanilines of the group exhibit typical aliphatic amine fragmentation, insofar as those having N-alkyl or N-alkanol groups fragment by amine a cleavage or carbon-nitrogen fission, or both. Intra-ionic oxidation of N-alkyl or N-propanol groups by nitro groups gives rise to propionyl ions or ions from which a propionyl group has been lost. This skeletal rearrangement could result in misinterpretation of the spectra of compounds of unknown structure. Similarly, intra-ionic oxygen transfer in the EI fragmentation of the 2-ethyl benzimidazole N-oxides could
result in misinterpretation of their spectra. T h e relative importance of the peaks d u e to intra-ionic oxidations appears to be a function of the electron density on the aromatic ring, as well as other structural features. T h e major fragmentation of azo and azoxy compounds resulting from the condensation of trifluralin through two nitro groups is through the nitrogen-nitrogen bond. ‘Head to head’ azo and hydrazo compounds resulting from the condensation of trifluralin through two amino-nitrogens fragment by fission of azo-nitrogen-carbon bonds.
Acknowledgments The authors are indebted to G. G . Cooke, J. W. Mosier, D. G. Saunders and J. M. Gilliam for their recording of mass spectra; to R. P. Gajewski, J. L. Miesel, G. 0. P. O’Doherty and N. H. Terando for syntheses of numerous model compounds; and to P. L. Unger for recording and interpretation of the NMR and IR spectra.
REFERENCES 1. E. F. Alder, W. L. Wright and Q. F. Soper, Proc. North Cent. Weed Control Conf. 17,23 (1960). 2 Q.F. Soper, E. F. Alder and W. L. Wright, Proc. South Weed Conf. 14,86 (1961). 3. G. W. Probst, T. Golab and W. L. Wright, in Herbicides (Chemistry,Degradation andMode ofAction),Vol. 1, ed. by P. C. Kearney and D. D. Kaufman, p. 453.Marcel Dekker, New York (1975). 4. C. S. Helling, J. Envirun. Qual. 1, 1 (1976). 5. T. Golab and W. A. Althaus, WeedSci. 23,165 (1975). 6. T. Golab, C. E. Bishop, A. L. Donoho, J. A. Manthey and L. L. Zornes, Pestic. Biochem. Physiol. 5, 196 (1975). 7. T. Golab and M. E. Amundson, in Environmental Qualityand Safefy, Supplement Vol. 111, ed. by F. Coulston and F. Korte p. 258.Georg Thieme, Stuttgart (1975). 8. J. R. Plimmer and U. 1. Klingebiel, in Massspecfrometryand NMR Spectroscopy in Pesticide Chemistry, ed. by R. Hague and F. J. Biros, p. 99,Plenum Press, New York (1974). 9. G. W. A. Milne and S. R. Heller, Am. Lab. 8,43 (1976). 10. F. W. McLafferty, H. E. Dayringer and R. Venkataraghaven, Ind. Res. 18,78 (1976).
0Heyden & Son Ltd,
1979
11. T. Golab, W. A. Althaus and H. L. Wooten, J. Agric. Food Chem. in press.
12. R. E. McMahon, Tetrahedron Lett. 21,2307 (1966). 13. H. Budzikiewicz, C. Djerassi and D. H. Williams, Mass Spectrometryof Organic Compounds, Holden-Day, San Francisco
(1967). 14. P. C. Vijfhuizen, W. Heerrna and N. M. M. Nibbering, Org. Mass Spectrom. 11, 787 (1976)and references contained therein.
15. J. L. Franklin, J. G. Dillard, H. M. Rosenstock, J. T. Herron and
K. Draxl, Ionization Potentials, Appearance Potentials and Heats of Formation of Gaseous Ions. US Department of Commerce, Washington, DC (1969). 16. F. W. McLafferty, Interpretation of Mass Spectra, 2nd Edn, W. A. Benjamin, Reading (1973).
Received 10 April 1978
0Heyden & Son Ltd, 1979
BIOMEDICAL MASS SPECTROMETRY, VOL. 6, NO. 1, 1979 9
The examination of soil which has been treated with trifluralin (TREFLANm a,a,a-trifluoro-2,6-dinitroN,N-dipropyl-ptoluidine) has resulted in the identification of 28 degradation products. This paper presents the mass spectra of these products and a number of related compounds which were suspected products but were not found in trifluralin-treated soil. The mass spectra of the N,N-dialkylamines, with one exception, show major peaks due to amine or-cleavage and due to amine a-cleavage followed by carbon-nitrogen bond fission with rearrangement of a hydrogen atom. Compounds having nitro groups yield mass spectra containing peaks due to intra-ionic oxidation by the nitro groups. In some cases, propionyl ions formed by this process are major ions in the spectra. Azo and azoxybenzenes resulting from condensation of two trifluralin moieties through nitronitrogens fragment mainly through the nitrogen-nitrogen bond.
INTRODUCTION
EXPERIMENTAL
Trifluralin (TR-l), is the most prominent member of a series of selective dinitroaniline herbicides introduced to agriculture in the 1 9 6 0 ~ . ” ~
The degradation study of trifluralin in soil under field conditions was performed over a three year period after initial application of the herbicide. [“C] Trifluralin uniformly labeled in the aromatic ring and the trifluoromethyl group was used in the study. The compound was incorporated in the soil to a depth of 7.5 cm and the sampling for degradation products was performed periodically to a depth of 15 cm. Soil samples were extracted with methanol and aqueous methanol, and the extracts were purified using column, thin-layer and high pressure chromatographies. Detailed procedures are given elsewhere.” EI spectra were determined either by GCMS using an LKB-9000 mass spectrometer, or by direct inlet using a C E C 21-1 10A or Varian-MAT 731 mass spectrometer. In those cases where GCMS did not yield a molecular ion, the sample was re-examined using the direct inlet technique. Accurate mass measurements were made from photoplates or peak matching using the 731 mass spectrometer. The same instrument was used to determine FD spectra from carbon dendrite emitters. Apart from TR-43 and TR-44, which were kindly provided by Dr J. 0.Nelson, University of Maryland, all compounds were synthesized at these laboratories by the most obvious procedure. The sole exceptioY2is T R 38, which was obtained by photolysis of TR-2. Structures were checked by NMR, IR, UV and microanalysis, as well as by MS.
”;”o”’. cF
-3
The fate of trifluralin and other related herbicides in soil, plants, animals, water and air has been investigated3-’ and the mass spectrometry of several degradation products described.’ In soil, 28 products derived from trifluralin have been detected. The identities of these compounds have been determined either by synthesizing possible candidates and matching these chromatographically and by spectral methods with soil products, or by direct spectral structure determination followed by comparison with synthetic compounds. In the course of this investigation, 49 compounds have been examined. The purpose of this paper is twofold; viz. to examine the mass spectrometry of this somewhat chemically heterogeneous group, and to present the spectra to other workers in this field. Only the spectra needed to achieve the first purpose are presented here. However, a compilation of those compounds examined but whose spectra are not presented is included. All spectra will be submitted to the MSDC/EPA/NIH9 and Cornell“’ collections. t Author to whom correspondence should be addressed.
RESULTS The spectra of the compounds necessary for the ensuing discussion, together with structures and designations,
CCC-0306-042X/79/0006-0001$04.50 @ Heyden & Son Ltd, 1979
BIOMEDICAL MASS SPECTROMETRY, VOL. 6, NO. 1, 1979
1
T. GOLAB AND J. L. OCCOLOWITZ
are presented in Figs. 1-28. The designations and structures of the remaining compounds are listed in Table 1. Of the foregoing compounds, TRs 1,2,13,15,17,20, 28 and 32 were isolated from soil in sufficient quantity for identification by spectroscopic techniques. The most abundant degradation product was TR-2, which resulted from decomposition of 2% of the applied trifluralin. Products identified by chromatographic comparison
L
I
50
I50 m/z
I00
250
200
300
Figure 6. Mass spectrum of TR-7, a,a,a-trifluoro-N4,N4-dipropyltoluene-3,4,5-triamine.
0
b 20
I
LY
150
100
50
200
250
I,
[Mlr3S5
l " " 1
300
I
350
m /I
Figure 1. Mass spectrum of TR-1, a,a,a-trifluoro-2,6-dinitro-N, N-dipropyl-p-toluidine (trifluralin).
50
150
100
250
200
300
1 350
mh
Figure 7. Mass spectrum of TR-10, a,a,a-trifluoro-2'-hydroxyamino-6-nitro-N-propyl-p-propionotoluidide.
50
100
200
I50 m/z
250
300 [MI+ 317
Figure 2. Mass spectrum of TR-2, a,a,a-trifluoro-2,6-dinitro-Npropyl-p-toluidine.
/
50
100
200
150
'
'
I
250
I " " I
300
350
m/z
Figure 8. Mass spectrum of TR-11, 2-ethyl-7-nitro-l-propyl-5(trifluoromethyl) benzimidazole 3-oxide.
g
20
I. , 50
100
150 rn/z
200
_1
250
300
Figure 3. Mass spectrum of TR-3, a,a,a-trifluoro-2,6-dinitro-p toluidine.
e
9
joi ,,I, i.;
40-
,
258
I
j'
+r+++++
,,
50
150
100
1'1
200
Figure 9. Mass spectrum of TR-12, (trifluoromethy1)benzimidazole 3-oxide.
o
J
[MI+ 275
250
' 1
300
2-ethyl-7-nitro-5-
I
60
234
40-
ii
I
212
r" 80-
20-
(MI'
-
l d
[ I
50
100
150
m/z
200
250
I
Y
Y
5
305
300
I
21b
$+O
-
60-
1
Ch
[MI' 301
350
Figure 4. Mass spectrum of TR-4, a,a,a-trifluoro-5-nitro-N4,N4dipropyltoluene-3,4-diamine.
with previously synthesized compounds are TRs 3 through 12,14,16,18,19,21,29,31,36,39,40 and41.
50
100
150
260
250
300
Substituted benzenes
rn /z
Figure 5. Mass spectrum of TR-5, a,a,a-trifluoro-5-nitro-N4propyltoluene-3,4-diamine.
2 BIOMEDICAL MASS SPECTROMETRY, VOL. 6, NO. 1 , 1979
The spectrum of the parent compound, trifluralin (TRl), is shown in Fig. 1. The spectrum is typical of an @ Heyden & Son Ltd, 1979
SOIL DEGRADATION OF TRIFLURALIN
E'5
-
1
a0STR-14 80
60
El
.'
40
.-
B u"
20
m/z
50
I00
150
200
300
250
m/z
Figure 16. Mass spectrum of TR-28, 2,2'-azoxybis trifluoro-6-nitro-N-propyl-ptoluidine).
(a,a,a-
Figure 11. Mass spectrum of TR-14,7-amino-2-ethyl-l-propyl-5-
(trifluoromethyl)benzimadazole.
m/z
Figure 17. Mass spectrum of TR-29, N-propyl-2,2'-azoxybis(a,a,a-trifluoro-6-nitro-p-toluidine). 50
100
150
200
250
300
m/z
Figure 12. Mass spectrum of TR-15, 2-ethyl-7-nitro-5-(trifluoromethy1)benzimidazole.
-., -j
Iool
-bp 80 I
TA-'7
186
1'
I00
I50 m/z
Figure 13. Mass spectrum of (trifluoromethyl) benzimdazole.
200
TR-17,
250
1
50
100
150
ZOO 250 m/z
, 300
[MI+ 4% 477
,it,
400
450
-4 500
300
7-nitro-l-propyl-5-
Figure 19. Mass spectrum of TR-31, 2,2'-azoxybis trifluoro-6-nitro-p-toluidine).
i 'ml 1
u r L ; L 7
Figure 18. Mass spectrum of TR-30, N'-propyl-2,2'-azoxybis(a,a,a-trifluoro-6-nitro-p-toluidine).
[MI+'P73
50
204
LL
(a,a,a-
80
TR-20
50
260
100
250
300
m/z
Figure 14. Mass spectrum.of TR-20, a,a,a-trifluoro-2,6-dinitro-pcresol.
m/z
Figure 20. Mass spectrum of TR-32, 2,2'-azobis (a,a,a-trifluoro6-nitro-N-propyl-p-toluidine).
N'-dipropylamines, as well as the N-propanol-N-propylamines TR-41 and TR-42 (Table l),exhibit analogous behavior; i.e.
R4p': '4GRz ' H
\ +//
CH,
N
Figure 15. Mass spectrum of TR-21, 4-(dipropylamino)-3, 5-dinitrobenzoic acid.
aliphatic amine13 insofar as major fragments involve arnine a-cleavage, to yield m / z 306, followed by carbon-nitrogen bond fission with hydrogen rearrangement, to yield m / t 264. Apart from TR-39 (Fig. 25), whose spectrum is discussed below, all of the N, @ Heyden & Son Ltd, 1979
+
'4QRz
' R3
--*
\
R5
R3
R5
R3
R I = CHzCHzCH3, CHzCH(OH)CH3, CHzCHzCHzOH Rz # NHOH Scheme 1
BIOMEDICAL MASS SPECTROMETRY, VOL. 6, NO. 1, 1979 3
T. GOLAB AND J. L. OCCOLOWITZ
$
‘E
f
60 40
20
190
1
50
Figure 21. M a s s spectrum of TR-34, a,a,a,a’,cu’,cu’-hexafluoro2,2’,6,6’-tetranitro-p-p’-azotoluene.
4 4 L t ’ C
50
100
&,-,GI,,, 150
100
200
150
250
300
350
rn/z
Figure27. M a s s spectrum of TR-43, a,cu,a-trifluoro-2,6-dinitro-N(propan-2-ol)-p-toluidine.
-
!
[MI+ 3C9
L-t--
d
rnh
-
40
250
XK, m/z
50
100
Figure 22. M a s s spectrum of TR-35, 1,2-bis(a,~,a,-trifluoro2,6-dinitro-p-tolyl) hydrazine.
150
200
250
300
350
rn/z
Figure28. M a s s spectrum of TR-44, a,a,a-trifluoro-2,B-dinitro-N(propan-3-ol)-p-toluidine.
Scheme 1is applicable to TRs 1(Fig. l ) , 4 (Fig. 4), 7 (Fig. 6), 21 (Fig. 15), 21M, 24,36,36M, 41 and 42 (Table 1). Not unexpectedly, amine (Y -cleavage yields major peaks in the spectra of the N-propylamines and the N-propanols; i.e. 50
100
150
200
250
300
350
H
rnh
Figure23. M a s s spectrum of TR-37, a,a,a-trifluor0-2,6-dinitro-Nnitroso-N-propyl-p-toluidine.
100
50
150
L 200
250
300
m/r
Figure 24. M a s s spectrum of TR-38, a,a,a-trifluoro-6-nitro-2nitroso-p-toluidine.
50
100
150
200
250
300
350
rnn
Figure 25. M a s s spectrum of TR-39, a,a,a-trifluoro-2-hydroxyamino-6-nitro-N,N-dipropyl-p-toluidine.
,
;
5
T
“
60
p 40
= d
20
I,, 50
100
150
200
250
,3y;
300
[;+;I*?
350
m/z
Figure 26. M a s s spectrum of TR-40, a,a,a-trifluoro-2’.6‘-dinitroN-propyl-p-propionotoluidide.
4
BIOMEDICAL MASS SPECTROMETRY, VOL. 6, NO. 1, 1979
\+. /
N
R,
H
\+/ N
CH,
Scheme 2 is applicable to TRs 2 (Fig. 2), 5 (Fig. 5), 8,22, 22M, 25 (Table l), 4 3 (Fig. 27) and 44 (Fig. 28). In contrast to the above, the EI fragmentation of TR-39 (Fig. 25) involves the loss of 0. and OH- to give m / z 305 and 304, respectively. Accurate mass measurements show that m / z 276 and 275 have compositions C2H50and CzH60 less than the molecular ion. They presumably arise by the loss of C2H5.from m l z 305 and 304. The subsequent loss of Ha from mlz 275 (m*, found 273.0) followed by elimination of C3H6 (m”, found m / z 196.5) yields m l z 232, the base peak. The ion m / z 43, which has the composition C3H7 (found 43.0546, calc. 43.0548), is abundant in the spectrum of TR-1 (Fig. 1). Its relative intensity is decreased fivefold in the spectrum of TR-7 (Fig. 6), where both nitro groups of TR-1 have been reduced to amino groups. Likewise, the relative intensity of the C3H7 ion from TR-2 (Fig. 2) is considerably greater than from TR-8. A number of the compounds studied, possessing at least one N-propyl group and an o-substituted nitro group, show intense peaks at m / z 57 in their spectra; e.g. TR-2, Fig. 2. This ion has the composition C3H50 (found 57.0343 TR-1, and 57.0346 TR-2; calculated for C3H50, 57.0340) and must arise by a skeletal rearrangement. The skeletal rearrangement of o-nitrobenzenes has been reported previously; l4 however, we @ Heyden & Son Ltd, 1979
SOIL DEGRADATION OF TRIFLURALIN
Table 1. Compounds whose spectra are not presented herein Cornpound
Structure and nomenclature
TR-6
Compound
Structure and nomenclature
Cornpound
TR-19
No
TR-26 HN-CH
Qk
NH,
O2
Structure and nomenclature
NHz
CF,
7-Amino-5-(trifluoromethyl)benzimidazole TR-2OM Methyl ether of TR-20 TR-21M Methyl ester of TR-21
a,a,a,-Trifluoro-5-nitrotoluene3.4-diamine
TR-8
TR-27
TR-22 HN-n-Pr
p P r
"'"0""
2,2'-Azoxybis (a,a,a-trifluoro-6-nitro-
"."5""'
CF3
N,N-dipropyl-p-toluidine)
TR-33
COOH
a,a,a,Trifluoro-N4-propyltoluene3,4,5-triamine
3,5-Dinitro-4-(propylamino) benzoic acid TR-22M Methyl ester of TR-22
3.3'-Azobis(N'-propyl-6-trifluoromethyl-o-phenylenediamine)
TR-9 TR-23
""'0"
TR-36
OH
N(n-Pr),
HZ
C F3
COOH
a,a,a-Trifluorotoluene-3,4,5-triamine
""QNoz CF3 OH
4-Hydroxy-3.5-dinitrobenzoicacid TR-23M Methyl etherjester of TR-23
c~,a,u,Trifluoro-4,6-dinitro-5(dipropy1amino)-o-cresol TR-36M Methyl ether of TR-36
TR-16 HN-C-Et
""@
TR-41 TR-24
(n-Pr)
\
CH,CH(OH)CH,
ozNo
CF3
O Z N e N o 2
7-Amino-2-ethyl-5-(trifluoromethyl) benzimidazole
/
2.6-Dinitro-N,N-dipropylaniline
?J
TR-42 TR- 18
(n-Pr)
TR-25
\
HN-CH
N
/
(CH,),OH
n-Pr 02N&N02
OZN@
I
CF3
c F3 a,cu,cr,-Trifluoro-2,6-dinitro-N-(propan-
7-Nitro-5-(trifluoromethyl)benzimidazole
@ Heyden & Son Ltd, 1979
BIOMEDICAL MASS SPECTROMETRY, VOL. 6, NO. 1, 1979 5
T. GOLAB AND J. L. OCCOLOWITZ
believe that the intra-ionic oxidation of an aliphatic group to yield an intense alkanoyl peak in a mass spectrum is unprecedented. The relative intensity of m / r 57 is quite dependent on changes in substitution of the aromatic ring. Thus, in the spectrum of TR-1 (Fig. l), it has a relative intensity of 13% ; but in the spectrum of TR-2 (Fig. 2), in which one n -propyl group of TR-1 has been replaced by hydrogen, the relative intensity of m / z 57 is 100%. Reduction of one nitro group of TR-2 to an amino group to give TR-5 (Fig. 5) reduces the relative intensity of m / r 57 to 18%. TR-43 (Fig. 27) and TR-44 (Fig. 28) contain N-(propan-2-01) and N-(propan-3-01) moieties, respectively. Intra-ionic oxidation as described above would yield a C3H502, m / r 73, ion in each case. In the spectrum of TR-43 (Fig. 27), m / z 73 is of low intensity, whereas it is quite intense in the spectrum of TR-44 (Fig. 28). We have advanced the following mechanism (Scheme 3), using TR-2 as model, to explain the formation of m / z 57:
presence of a propionyl group in the nonionized molecule. For reactions in Scheme 4,it is of interest to speculate on the reasons for the changes in the relative intensities
\
\
1
N'
H7C3\ N'
CF,
Scheme 4
H
O2
0Hlz 1. N
-
C -C, H
m / z 57
02NoN:oH
Scheme 3
The spectrum of the deuterated analog of TR-2, H
\
/
of the products when the aromatic substituents are changed. Using group equivalent values for heats of formation, together with the heats of formation of [C3H7]+, [C2H5CO]' and the [M-H]+ ion from dimethyl aniline listed in Ref. 15, and neglecting any reverse activation energy, one can calculate that reaction (3) requires the least activation energy and reaction (2) the most. Consequently, for reactions (1 and 2), which are simple cleavage reactions, populations of molecular ions whose internal energy distribution is biased toward lower energies will favor reaction ( l ) , while an increase in the relative number of ions having higher energies will make reaction (2) more competitive. This is in agreement with observation; when R1= NOz (TR-1, Fig. 1), the ionization potential of the molecular ion will be higher (for example, the ionization potential of aniline is 7.70eV, and that of o-nitroaniline is 8.66eV1') and reaction (2) will become more prominent, whereas when R1=NH2 (TR-4, Fig. 4), a decrease in molecular ionization energy will decrease the relative importance of (2). For TR-7 (Fig. 6), this reasoning would predict reaction (2) to be less prominent than for TR-4 (Fig. 4), as is observed. The above reasoning cannot be applied to reaction (3) because it involves considerable rearrangement. It is likely that its relatively low activation energy makes it competitive when other factors, e.g. geometry of the molecular ion, are favorable. A referee has pointed out that reaction (2) is an example of a charge site reaction;16 i.e.
CD2CH2CH3
CF.3
obtained on the 73 1 mass spectrometer, shows a peak at m l z 57 and no evidence of any shift to m / z 58 or 59. This is in agreement with the above mechanism insofar as the itinerant hydrogens involved in the formation of [C3H50]+ arise solely from the a-carbon of the N propyl group. The spectrum of the deuterated analog of TR-2, obtained by GCMS using the LKB-9000, gave m / z 57 and m / z 59 in the ratio 4 : 1. Although this mechanism does not explain all that is known about the rearrangement, it is not at odds with the experimental observations. It is perhaps sufficient to show, within the scope of this paper, that the observation of an intense propionyl peak in the spectrum of a trifluralin metabolite is not necessarily indicative of the 6 BIOMEDICAL MASS SPECTROMETRY, VOL. 6, NO. 1, 1979
H7C3y+. /c 4%
/C&
+[C3H71"+
ozN+No2
ozN+Noz CF,
-3
Scheme 5
@ Heyden & Son Ltd, 1979
SOIL DEGRADATION OF TRIFLURALIN
The electron-withdrawing nitro groups destabilize the radical cation [MIC',and this condition is relieved by the charge site reaction which leaves the radical on the aromatic moiety. This theory also explains the lesser importance of this reaction in TR-7. The nitrosamine TR-37 (Fig. 23) and the nitrosobenzene TR-38 (Fig. 24) are interesting model compounds, although they were not detected in soil during the three-year study. Both compounds show molecular ions in their E I spectra. The FD spectrum of TR-37 has two main peaks, m / z 322 ([MI+', 100%) and m / z 293 ([M-C~HS]+,15%). Major peaks at m / z 292 and 264 in the E I spectrum of TR-37 arise by the sequential loss of N O and C2H4, as evidenced by accurate mass measurement and the presence of the appropriate metastable peak (found 292.0545, calc. for C10H9N304F3, 292.0545; found 264.0230, calc. for CSHsN304F3, 264.0232; for m / z 292 + 264, found 238.5, calc. 238.7.) Other major peaks are the skeletal rearrangement ion, m / z 57 (found 57.0340, calc. for C3Hs0,57.0340) m / z 43 (C3H7) and m / z 30 (NO). Compounds which possess an N-propionyl moiety, viz. TRs 10 (Fig. 7) and 40 (Fig. 26), not unexpectedly have intense peaks due to the [C3H50]+ion in their spectra. TR-40 has no molecular ion in its EI spectrum, but a relatively intense molecular ion is produced by FD. Of the 28 degradation products of TR-1, TR-20 (Fig. 14) is unique insofar as it is the only compound in which an atom directly attached to the aromatic ring of TR-1 has been eliminated. The EI fragmentation of TR-20 can be rationalized in terms of known fragmentations of its substituents; e.g. m / z 194, which has the composition C6H3N03F3,is due to the elimination of NO, a fra mentation undergone by aromatic nitro compounds,% followed by the elimination of CO, which is typical of phen01s.l~ The m l z 159 ion has the composition C7H20F3and arises by the elimination of both nitro groups plus a hydrogen atom, while the m / z 132 ion, which has the composition C6H3F3, results from the elimination of both nitro groups and a CO molecule.
Benzimidazoles Intra-ionic oxygen transfer is not confined to the compounds mentioned above. It is also evident in the spectra of benzimidazole N-oxides TR-11 (Fig. 8) and TR-12 (Fig. 9) which have base peaks due to the [C3H50]' ion. In the case of TR-11, the [C3H50]+ ion (found 57.0342, calc. 57.0340) can arise from the propyl group as described above or from the C-ethyl moiety. It is likely that oxygen transfer to the C-ethyl moiety plays a prominent part in the formation of [C3H50]+,because TR-12, which has no propyl group, gives a spectrum in which [C3H50]+ is the most abundant ion. Relatively smaller contributions by m / z 57 occur in the benzimidazoles TR-13 (Fig. 10) and TR-17 (Fig. 13), both of which possess an N-propyl group and an o-nitro group. More prominent in the spectra of these compounds are peaks resulting from the loss of C3Hs0-, m / z 224 and 216, respectively. The alternate route to these ions by the successive elimination of CzHS' and C2H4 was excluded by accurate mass determination, @ Heyden & Son Ltd, 1979
although this process gives rise to m / z 214 in the spectrum of TR-14 (Fig. 11) which has no oxygen function. The spectra of benzimidazoles not having an N-alkyl function, TRs 15, 16, 18 and 19, are relatively straightforward; and as an example, the spectrum of TR-15 is included in the figures (Fig. 12). Accurate mass measurement shows that m / z 212 and 213 are due to the elimination of H N 0 2 and NO2, respectively. TR-10 (Fig. 7) was formerly assigned' the structure
The formation of m / z 279 by a single-step elimination of C3H40, as evidenced by the appropriate metastable peak and accurate mass measurement of m / z 279, however, suggests the presence of an N-propionyl group which can eliminate methyl ketene in a manner analogous to the elimination of ketene from the molecular ion of a~etani1ide.l~ More definitive evidence for the structure of TR-10, as shown in Fig. 7, comes from its IR spectrum which shows absorptions at 3320 cm-' (-NHOH stretch) and 1675 cm-' (=C=O stretch). When left in solution for a few days, TR-10 loses water to give TR-11, possibly via an intermediate with the structure formerly assigned to TR-10. The IR spectrum of TR-11 shows no carbonyl absorption.
Azo and azoxy compounds The major fragments in the spectra of the azo and azoxy compounds TR-27 through TR-33 arise from fission of the nitrogen-nitrogen bond, followed by fragmentation of the ions so formed. Fragmentation of the 'head to head' azo compound TR-34 occurs predominantly through the azo-nitrogen-carbon bonds to yield m / z 263 (Fig. 21). Skeletal rearrangements observed in the spectrum of az~xybenzene'~ are not evident in the substituted azoxybenzenes TR-27 to TR-3 1.Compounds having an N-propyl moiety and an o-nitro substituent have m / z 57 peaks in their spectra formed by the intra-ionic oxidation discussed earlier. The spectra of the isomers TR-29 and TR-30, Figs. 17 and 18, illustrate the fragmentation of the azoxy compounds and indicate the ability of mass spectrometry to distinguish between their structures. Both TR-29 and TR-30 show molecular ions in their spectra; however, the molecular ion of TR-29 is of such low relative intensity that it can be hidden easily among peaks due to impurities in samples isolated from soil. Accurate mass measurements of the more intense peaks at [M-OH]", m / z 479, and [M-F]+', m / z 477, proved instrumental in establishing the molecular BIOMEDICAL MASS SPECTROMETRY, VOL. 6, NO. 1, 1979 7
T. GOLAB AND J. L. OCCOLOWITZ
formula, and ultimately the structure of TR-29. The F D spectrum of TR-29 consists substantially of two peaks: the molecular ion, m/z 496 (100"/0), and (M-OH]+', m f z 479 (20%). Fission of the nitrogen-nitrogen bond of TR-29 with hydrogen transfer yields m / t 276. The fragmentation of TR-29 is rationalized in Scheme 6. An elemental composition below a postulated structure indicates that the composition of that ion was established by accurate mass measurement. An asterisk indicates that a metastable peak was observed for the ionic reaction shown. H
CH,CH,CH,,
\+./
AH,
I H,
/CHCH,CH,
' i
arise by nitrogen-nitrogen bond fission of the molecular ion of TR-30, it is to be expected that the spectra of TR-29 and TR-30 would have common peaks, as is observed. Substitution of a primary amino-hydrogen of TR-29 with an n-propyl group to give TR-28, the most abundant dimeric degradation product, largely suppresses those ionic reactions leading to m/z-276, 258 and 248 which indicate the presence of the azoxy function. Apart from a peak at m/z 290 in the spectrum of TR-28 (Fig. 16), which can result from fission of either or both of the azo-nitrogen-carbon bonds with hydrogen rearrangement, the fragmentation of TR-28 is generally qualitatively similar to the corresponding azo compound TR32 (Fig. 20). TR-31 (Fig. 19) contains n o N-alkyl moieties, and its spectrum is relatively straightforward. Fission of the nitrogen-nitrogen bond yields m/z 235 and 219, each of which eliminates NO2 to give m/z 189 and 173, respectively. The spectrum of the symmetrical substituted diphenyl hydrazine TR-35 is shown in Fig. 22, The electron impact induced formation of the [M-H20]" ion, m / z 482, from the molecular ion is supported by the presence of the appropriate metastable peak. The only major peak shifted in the s ectrum of TR-35 after exchange with methanol-0-[9HI] is the molecular ion. Consequently, the elimination of water from the molecular ion involves both hydrazine-hydrogens, and the
R=HorD
NO,
NO,
NO
NO,
1'
m l z 482
m / z 235
m/z 263
-NO21
Scheme 6
m / z 189
The peaks at m/z 276, 258 and 248 define the position of the azoxy-oxygen in TR-29. Both m / z 276 and m/z 248 are absent from the spectrum of TR-30, and m / z 258 has a low relative intensity. Since m/z 260 can 8
BIOMEDICAL MASS SPECTROMETRY, VOL. 6, NO. 1, 1979
/-NO2
m / z 143
:NO, m / z 159 I-CO
m / z 131
Scheme 7
@ Heyden & Son Ltd, 1979
SOIL DEGRADATION OF TRIFLURALIN
major fragments in the spectrum likely arise by fragmentation of the [M - H20]+‘ ion. This explanation accounts for the qualitative similarity between the spectra of TR-35 and TR-34 (Fig. 21), Scheme 7. In conclusion, apart from a few exceptions, the molecular ions of the trifluralin degradation products are accessible by EI mass spectrometry. For the exceptions, molecular ions can be obtained by FD mass spectrometry. The o-nitroanilines of the group exhibit typical aliphatic amine fragmentation, insofar as those having N-alkyl or N-alkanol groups fragment by amine a cleavage or carbon-nitrogen fission, or both. Intra-ionic oxidation of N-alkyl or N-propanol groups by nitro groups gives rise to propionyl ions or ions from which a propionyl group has been lost. This skeletal rearrangement could result in misinterpretation of the spectra of compounds of unknown structure. Similarly, intra-ionic oxygen transfer in the EI fragmentation of the 2-ethyl benzimidazole N-oxides could
result in misinterpretation of their spectra. T h e relative importance of the peaks d u e to intra-ionic oxidations appears to be a function of the electron density on the aromatic ring, as well as other structural features. T h e major fragmentation of azo and azoxy compounds resulting from the condensation of trifluralin through two nitro groups is through the nitrogen-nitrogen bond. ‘Head to head’ azo and hydrazo compounds resulting from the condensation of trifluralin through two amino-nitrogens fragment by fission of azo-nitrogen-carbon bonds.
Acknowledgments The authors are indebted to G. G . Cooke, J. W. Mosier, D. G. Saunders and J. M. Gilliam for their recording of mass spectra; to R. P. Gajewski, J. L. Miesel, G. 0. P. O’Doherty and N. H. Terando for syntheses of numerous model compounds; and to P. L. Unger for recording and interpretation of the NMR and IR spectra.
REFERENCES 1. E. F. Alder, W. L. Wright and Q. F. Soper, Proc. North Cent. Weed Control Conf. 17,23 (1960). 2 Q.F. Soper, E. F. Alder and W. L. Wright, Proc. South Weed Conf. 14,86 (1961). 3. G. W. Probst, T. Golab and W. L. Wright, in Herbicides (Chemistry,Degradation andMode ofAction),Vol. 1, ed. by P. C. Kearney and D. D. Kaufman, p. 453.Marcel Dekker, New York (1975). 4. C. S. Helling, J. Envirun. Qual. 1, 1 (1976). 5. T. Golab and W. A. Althaus, WeedSci. 23,165 (1975). 6. T. Golab, C. E. Bishop, A. L. Donoho, J. A. Manthey and L. L. Zornes, Pestic. Biochem. Physiol. 5, 196 (1975). 7. T. Golab and M. E. Amundson, in Environmental Qualityand Safefy, Supplement Vol. 111, ed. by F. Coulston and F. Korte p. 258.Georg Thieme, Stuttgart (1975). 8. J. R. Plimmer and U. 1. Klingebiel, in Massspecfrometryand NMR Spectroscopy in Pesticide Chemistry, ed. by R. Hague and F. J. Biros, p. 99,Plenum Press, New York (1974). 9. G. W. A. Milne and S. R. Heller, Am. Lab. 8,43 (1976). 10. F. W. McLafferty, H. E. Dayringer and R. Venkataraghaven, Ind. Res. 18,78 (1976).
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11. T. Golab, W. A. Althaus and H. L. Wooten, J. Agric. Food Chem. in press.
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Received 10 April 1978
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