American Journal of Anal yt ical Chemistry, 2011, 2, 809-813
doi:10.4236/ajac.2011.27092 Published Online November 2011 (http://www.SciRP.org/journal/ajac)
Copyright © 2011 SciRes. AJAC
Analysis and Characterization of Isopropyl Carbanilate
Herbicide and Its Photoproducts
Mohammed Fehmi Zaater
Department of Chemical Sciences, Jordan University of Science and Technology, Irbid, Jordan
Received January 17, 2011; revised May 20, 2011; accepted June 19, 2011
The phototransformation of the herbicide Isopropyl carbanilate (IPC) has been investigated under UV light.
Irradiation of the herbicide at room temperature in aqueous and organic solvents such as hexane and metha-
nol afforded new photo-products formed as a consequence of various processes including photo-Fries rear-
rangement, ring solvolysis, hydrolysis of the amide/carbamoyl and ester bonds, ring coupling and polymeri-
zation. The percentage remaining of the herbicide as a function of time was followed periodically starting
from zero time up to three hours. Analyses were performed by GC-FID equipped with a semipolar glass
column operated at 170˚C. The rate of photo disappearance of IPC under controlled lab condition followed
1st order kinetics and found to be solvent dependent in the manner of non polar > polar solvents. The
photo-products were successfully separated by GC and preparative TLC (Silica gel F-254) and were identi-
fied using either GC-MS and/or MS. Identifications were assigned on the bases of molecular ions, mass
fragmentation pattern and whenever possible by comparison with the mass spectra of literature analogues.
Keywords: Phototransformation, Isopropyl carbanilate, Isopropyl-N-Phenylcarbamate, Propham, IPC and
Isopropyl carbanilate or Isopropyl N-phenylcarbamate,
also known as propham, Turberite® or IPC, is a xeno-
biotic urethane derivative with Kow = 2.6 (pH 7 and
20˚C), Log P = 2.58 and LD50 ≥ 5000 mg/kg. Propham
has the formula of C10H12NO2 shown in Figure 1.
IPC has been widely used as a soil acting herbicide
with selectivity towards weeds and grasses in broad-
leaved crop vegetables [1,2]. Once IPC finds its way into
the environment, it undergoes biological, chemical and
photochemical transformation , producing eventually
the same or similar degradation products, indicating dif-
ficulties in judging the cause for a specific transforma-
Regarding biodegradation of the herbicide, it has been
Figure 1. Chemical structure of Isopropyl-N-phenylcar-
reported that hydrolysis to the respective aniline and iso-
propanol in a reverse manner to its synthesis constitutes
the major metabolic pathway especially in tolerant plants
and soil [4-10]. Molecular modification into more polar
derivatives through hydroxylation of the aromatic and
side alky moieties with subsequent conjugation to en-
dogenous matter constitutes the principal transformation
route of IPC in animals [10-12]. Additionally, a minor
route for propham metabolism in animals include hy-
drolysis into aniline with subsequent acylation, hy-
droxylation and finally conjugation to qlucuronide or
sulfate , N-hydroxylation and ring methoxylation of
the intact IPC were also reported to occur in animals
Previous studies pertaining to the photolysis of IPC
revealed that it was highly resistant and photolysed very
slowly even at short UV radiation [16,17]. Other studies
in this context showed that IPC photolysed very slowly
in a reverse manner to its synthesis giving aniline, phenyli-
socyanate, isopropanol and diphenylurea, all in accor-
dance to its thermal degradation or pyrolysis products
[18,19]. Investigations in relation to IPC persistence in
the environment indicated a half-life of 254 days with
M. F. ZAATER
unidentified metabolites in water under simulated sum-
mer sunshine . However, in presence of TiO2/H2O2
and UV, the half-life of IPC was shortened to few hours
[20,21], giving a variety of degradation products includ-
ing ortho- and para-hydroxy analogues, benzoquenone,
isopropyl aminobenzoate and aminophenol derivatives
[22-27]. In view of these conflicting reports and inade-
quate data on propham photo-product, herein we report
the IPC photodegradation in various media with its re-
spective photoproducts; however, such data are not fully
available and the demand for it is important both to
chemists and environmentalists.
2. Experimental Studies
2.1. Material and Equipments
Isopropyl- N-penylcarbamate technical grade of purity >
99% from Sigma, solvents and reagents were of analyti-
cal grade or Analar and used as such, water used was
deionised. Thin layer chromatography plates of silica gel
with fluorescent indicator GF254 (20 × 20 cm, 2 mm
thickness) were used. The plates were developed with
hexane-toluene- acetone (7:2:1, v/v/v). Irradiation in
solution was performed with UV light from Hanova
mercury lamp (125 W) with two band-passes at 280/254
nm and equipped with internal water cooled quartz im-
mersing jacket. The photolysed solutions were open to
Analysis of the remaining IPC was made by GC-FID
(Pye Unicam) fitted with semipolar packed OV-17 col-
umn (1.8 m, 4 mm i.d) operated at 170˚C. Mass spectra
for identification were conducted on GC-MS (Hewlett
Packard/5890) and MS. UV spectra were performed on
UV-VIS spectrophotometer (Perkin Elmer).
2.2. UV Spectra
In an attempt to evaluate photolabilaty of IPC and deter-
mine its characteristics absorption maximum, a prelimi-
nary investigation on UV spectra of IPC in methanol and
hexane were taken.
2.2.1. Photoirradiation in Aqueous Solution
One litre solution of 200 mg/L in water was introduced
into a UV reactor system and exposed to UV at 254 nm
for 3 hours at room temperature. The reactor was shield-
ed with aluminium foil for protection. Aliquots of 25 mL
were taken periodically every 30 min starting from zero
time, followed by extraction with methylene chloride.
The combined organic extract was washed with deion-
ized water, dried over anhydrous Na2SO4, filtered and
finally evaporated under reduced pressure using rotary
evaporator. The remaining brown red viscous residue
was reconstituted in a small amount of methanol and
completed to 5 mL volume. The collected samples were
analysed for the disappearance of IPC using GC-FID
which was checked periodically for linearity using stan-
dards of the herbicide in methlyne chloride. Portions of
the collected samples were also subjected for qualitative
analysis by GC-MS. To examine the effect of acetone as
a co-solvent and photosensitizer, the above experiment
was repeated in presence of 3% acetone. The change of
propham amount with time of irradiation is shown in
2.2.2. Photoirradiation in Organic Solvents
One litre solution of 200 mg/L IPC in hexane, methanol
was similarly irradiated at room temperature for 3 hours.
Aliquots of 5 mL were withdrawn periodically and ana-
lysed for disappearance of the herbicide. After the ter-
mination period the remaining solution was evaporated
to dryness. Eventually the red viscous residue was redis-
solved in methanol and qualitatively analysed using
Propham in methanol was similarly irradiated and
analysed. Controlled blank experiments were reserved in
a dark room.
2.2.3. Separation and Identification of Photoproducts
The photolysate from different solvents used were care-
fully chromatogrammed on preparative TLC plates with
fluorescent indicator. Plates were developed in a mixture
of hexane-toulene-acetone (7:2:1, v/v/v) respectively.
Following development, plates were visualised under UV
light, the localised bands were scrapped, taken in
methanol and finally analysed by MS spectrometer.
Figure 1. Photodegradation profile of ln IPC (y) with time
value (x) in various media with regression equations for
y = 0.002x + 4.95, r2 = 0.990, y = 0.003x + 5.88,
r2 = 0.977, y = 0.009x + 4.52, r2 = 0.974, y =
0.012x + 4.58, r2 = 0.997.
Copyright © 2011 SciRes. AJAC
M. F. ZAATER 811
Identifications were made on the basis of parent molecu-
lar ions (M+), mass fragmentation pattern and whenever
possible by comparison with mass spectra of literature
3. Results and Discussion
From the spectral data of propham in hexane and methanol
it was expected that the herbicide was not a good candi-
date for direct photolysis. As it showed negligible ab-
sorbance above solar cut off wavelength and down to the
maximum output of UV mercury lamp used. This is in
accordance to the fact that only absorbed radiation is
effective in producing chemical changes (Grothuss-Drapper
Law). However, IPC in hexane and methanol showed
two intense maxima at λ (ε × 106) 203(18.0), 233(16.5)
and 205(14.2), 236(16.4), respectively and were assigned
to π – π* transition of the carbonyl bond.
The undertaken preliminary lab investigation in this
context suggested that IPC is a photo-susceptible com-
pound as its solution in aqueous and organic solvents
became increasingly yellow and turbid with some ad-
hered to the wall of the photoreaction vessel, in contrast
to its intact solution.
Initially the use of aqueous solvents was used because
water is the most universal polar solvent available and
might come into contact with the applied herbicides in
the environment. The addition of acetone to aqueous
solution of IPC was chosen to act as a co-solvent and a
triplet photo-sensitizer that mimics the sensitising effect
of humic matter in natural water [28,29]. However, the
use of organic solvents was conducted to enhance the
solubility of IPC and facilitate its direct injection into the
The mode of degradation was carried out by monitor-
ing its remaining concentration as a function of time
compared to its initial concentration. Figure 2 demon-
strates the photolysis of IPC in aqueous and organic sol-
vents at a concentration of 200 mg/L. From the repre-
sentative graph it is clear that the disappearance of IPC
follows 1st order kinetic in agreement to what has been
reported for most herbicides [30,31]. The photolysis rate
of IPC in different solvents demonstrated similar behav-
iour with an order of hexane > aqueous acetone > metha-
nol > water. This trend is due to differences in the routes
followed for transformation . Homolytic cleavage
with subsequent hydrogen or solvent abstraction was a
general and dominant mechanism in organic solvents
. The slower rate in polar solvents as compared to
that in hexane could be assigned to the association of the
herbicide with protic solvent via hydrogen bond in
agreement with literature report , or due to stabiliza-
tion of the excited state of its bi-radical cage [ArNH
ĊOOR] [19,33,34]. The higher rate of disappearance in
hexane is attributed to its hydrogen radical donating abil-
ity as compared to that of methanol and water. The GC-
MS and mass spectral analysis of the photolysates to-
gether with the separated photo-products revealed the
formation of various compounds. The major photo-prod-
ucts in hexane were two isomers of IPC with molecular
ions, m/z+, 197 with different Rf values and were as-
signed as isopropyl ortho- and para-aminobenzoate, ad-
ditionally two solvolysis isomers with molecular ion
m/z+, 263 were identified as hexylpropham.
Those products were expected to proceed via homlytic
cleavage of the carbamoyl bond giving either a bi-radical
cage [ArN˙H ĊOOR] or normal free radicals ArN˙H &
ĊOOR [33,34]. In both cases the radicals were able to
abstract hydrogen atom and undergo concerted photo-
Fries intramolecular rearrangements to ortho or para
positions or else the radical may delocalise over the en-
tire ring and abstract solvent molecules.
The photoirradiation of IPC in methanol provided va-
riety of products including two isomers of ortho- and
para-methoxy IPC with m/z+, 209, two coupled dimers
with m/z+, 356 in contrast to the situation in hexane, hy-
droxyaminophenol m/z+, 123, aminoqinone derivative
with m/z+, 193 and isopropyl aminobenzoate isomers,
Eventually, the photolysis of IPC in aqueous media
afforded two isomers of ortho- and para- hydroxy IPC,
m/z+, 195 with different Rf and tr values, two coupled
derivatives with m/z+, 356, two isomers of IPC m/z+, 179
and benzazolone, m/z+, 135, together with an unidenti-
fied polymeric matter. The formation of benzazolone
derivative is a result from internal thermal cyclisation of
the respective hydroxy-IPC .
In this context it is worth noting that the demonstrated
modes of IPC phototransformation i.e. solvolysis, photo-
Fries intramolecular rearrangement and dimerization
were not reported in any previous study. However, these
have similarities with other photolysed herbicides [21,
22,33-35] or some have been reported to occur for IPC in
animals [13-15]. Additionally phenylisocyanate, isopro-
panol, di-isopropyl ether and amino phenols were also
identified from the MS spectra and could be attributed to
the hydrolysis of the carbamoyl and ester bond as previ-
ously reported .
The result of this investigation revealed the photolabilaty
of IPC under the influence of short UV radiation in polar
and non polar media. The rate and route of IPC photode-
gradation were affected by the nature and polarity of the
photolysed media. The principal routes of IPC disap-
Copyright © 2011 SciRes. AJAC
M. F. ZAATER
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certed rearrangement and dimarization. These finding
indicate the photolabilaty of IPC under UV exposure and
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