Ultrasonic and photochemical degradation of chlorpropham and 3-chloroaniline in aqueous solution

Article abstract of DOI:10.1016/S0043-1354(97)00477-6

Sonolysis and photolysis are compared for the transformation of chlorpropham, a systemic herbicide belonging to the carbamate group, and 3-chloroaniline, the main intermediate often observed in the degradation of chlorpropham. In both cases the ultrasonic degradation is much more efficient at 482 kHz than at 20 kHz. The main identified sonoproducts formed in the degradation of chlorpropham are 3-chloroaniline, formic acid, carbon monoxide and dioxide and chloride ions. The degradation of 3-chloroaniline also leads to Cl^-, CO and CO₂ but chlorohydroquine was also detected as an intermediate. Two different mechanisms are involved in the ultrasonic transformation: pyrolysis resulting from the implosion of cavitation microbubbles and oxidation by hydroxyl radicals formed by sonolysis of water. Photolysis is more specific: 3-chloroaniline is initially quantitatively transformed into 3-aminophenol. A heterolytic mechanism is suggested. Resorcinol and some unidentified photoproducts are formed in a second stage. The same type of reaction is involved in the photo-transformation of chlorpropham, but the reaction is not so specific. In both cases the photolysis at 254 nm leads to a complete disappearance of phenolic and quinonic compounds. Sonolysis and photolysis are compared for the transformation of chlorpropham, a systemic herbicide belonging to the carbamate group, and 3-chloroaniline, the main intermediate often observed in the degradation of chlorpropham. In both cases the ultrasonic degradation is much more efficient at 482 kHz than at 20 kHz. The main identified sonoproducts formed in the degradation of chlorpropham are 3-chloroaniline, formic acid, carbon monoxide and dioxide and chloride ions. The degradation of 3-chloroaniline also leads to Cl^-, CO and CO₂ but chlorohydroquine was also detected as an intermediate. Two different mechanisms are involved in the ultrasonic transformation: pyrolysis resulting from the implosion of cavitation microbubbles and oxidation by hydroxyl radicals formed by sonolysis of water. Photolysis is more specific: 3-chloroaniline is initially quantitatively transformed into 3-amino-phenol. A heterolytic mechanism is suggested. Resorcinol and some unidentified photoproducts are formed in a second stage. The same type of reaction is involved in the photo-transformation of chlorpropham, but the reaction is not so specific. In both cases the photolysis at 254 nm leads to a complete disappearance of phenolic and quinonic compounds.

Full text of DOI:10.1016/S0043-1354(97)00477-6

Wat. Res. Vol. 32, No. 8, pp. 2451±2461, 1998
# 1998 Elsevier Science Ltd. All rights reserved
Printed in Great Britain
PII: S0043-1354(97)00477-6
0043-1354/98 $19.00 + 0.00
ULTRASONIC AND PHOTOCHEMICAL DEGRADATION
OF CHLORPROPHAM AND 3-CHLOROANILINE IN
AQUEOUS SOLUTION
B. DAVID1*, M. LHOTE1, V. FAURE2 and P. BOULE2
1Laboratoire de Chimie Moleculaire et Environnement, ESIGEC, Universite de Savoie, 73376 Le Bourget
du Lac Cedex, France and Laboratoire de Photochimie Moleculaire et Macromoleculaire, URA CNRS
433, Universite Blaise Pascal (Clermont±Ferrand), 63177 Aubiere Cedex, France
2
(First received March 1997; accepted in revised form November 1997)
AbstractÐSonolysis and photolysis are compared for the transformation of chlorpropham, a systemic
herbicide belonging to the carbamate group, and 3-chloroaniline, the main intermediate often observed
in the degradation of chlorpropham. In both cases the ultrasonic degradation is much more ecient at
482 kHz than at 20 kHz. The main identi®ed sonoproducts formed in the degradation of chlorpropham
are 3-chloroaniline, formic acid, carbon monoxide and dioxide and chloride ions. The degradation of 3-
chloroaniline also leads to Cl , CO and CO2 but chlorohydroquine was also detected as an intermedi-
ate. Two di€erent mechanisms are involved in the ultrasonic transformation: pyrolysis resulting from
the implosion of cavitation microbubbles and oxidation by hydroxyl radicals formed by sonolysis of
water. Photolysis is more speci®c: 3-chloroaniline is initially quantitatively transformed into 3-amino-
phenol. A heterolytic mechanism is suggested. Resorcinol and some unidenti®ed photoproducts are
formed in a second stage. The same type of reaction is involved in the photo-transformation of chlor-
propham, but the reaction is not so speci®c. In both cases the photolysis at 254 nm leads to a complete
disappearance of phenolic and quinonic compounds. # 1998 Elsevier Science Ltd. All rights reserved
Key wordsÐultrasound, photolysis, herbicide, chlorpropham, CIPC, 3-chloroaniline, mineralization
INTRODUCTION
treatment, photodegradation is one of the main
natural processes of elimination of xenobiotic pollu-
Several studies have already demonstrated that
tants. It can also be used for the decontamination
ultrasound is an ecient method for the degra-
of polluted waters, in association with other pro-
dation of organic pollutants in aqueous solution
cesses: UV/H2O2, UV/O3 and photo-Fenton. The
(Kotronarou et al., 1992; Serpone et al., 1994;
photolysis consists in exciting the substrate by
Petrier et al., 1992b, 1994). The applied pressure
absorption of a photon. Then several processes may
®eld induces the formation of microbubbles which
be involved according to the structure of the com-
oscillate and collapse. The implosion of the cavita-
pound. With chloroaromatic derivatives in dilute
tion bubbles generates high energy reactions due to
aqueous solution, photooxidation and heterolytic
the local increase of temperature and pressure, that
scission of the C±Cl bond with formation of the
is the hot spot theory (Suslick and Hammerton,
corresponding hydroxylated product and hydro-
1986; Suslick, 1988). The high energy phenomena
chloric acid, are the most frequent reactions (Boule
can also be attributed to electrical discharges
(Margulis, 1990) and/or corona e€ect (Lepoint and
et al., 1982, 1985; Lipczynska-Kochany and Bolton,
1991).
Mullie, 1994). In these conditions the homolytic
The aim of the present work is to compare the
.
.
cleavage of water yields OH and H which recom-
bine or di€use in the bulk.
ultrasonic degradation with the photodegradation
of chlorpropham (also called CIPC) and 3-chloro-
aniline.
.
.
†††
H2O‰ 4 ŠH ‡ OH
Hydroxyl radicals lead to the oxidation of most
of the organic compounds present in the solution.
Besides, if the vapour pressure of substrates is su-
cient for their di€usion in the short lived bubbles, a
thermal degradation, assisted or not by electric dis-
charges and/or corona e€ect also occurs.
If the ultimate purpose of sonochemistry is water
*Author to whom all correspondence should be addressed.
2451

2452
B. David et al.
Fig. 1. Kinetics of ultrasonic transformation of chlorpropham (CIPC) at 20 and 482 kHz in air-equili-
brated solution (100 ml).
lary column Supelco SE 52) was used for the identi®cation
of some of the products.
Chlorpropham (isopropyl-3-chlorocarbanilate) is
a selective systemic herbicide and growth regulator.
It is also used as a sprouting inhibitor for ware
potatoes and sucker control agent in tobacco
(Metcalf, 1971; Tsumura-Hasegawa et al., 1992;
Carbon dioxide and monoxide analyses were carried out
after head space sampling on an Intersmat I.G.16 chro-
matograph equipped with a Porapak Q 2 m  2 mm id.
column. Identi®cation and calibration were obtained with
gas standards.
1
Tomlin, 1994). As its solubility in water is 80 mg l
and it is resistant to hydrolysis and oxidation, the
bacterial degradation of chlorpropham is probably
the dominant elimination pathway in the environ-
Ultrasonic treatments
Degradation was performed at two frequencies. At low
frequency, 20 kHz, a commercial titanium probe system of
ment. It leads to the formation of the toxic 3-chlor- 35 mm diameter was connected to a Branson Soni®er 450
generator. High frequency was obtained with a transducer
emitting at 482 kHz. Both reactors have been previously
described (Petrier et al., 1994). They were calibrated by de-
termination of the calorimetric power which was 20 W for
oaniline (Wolfe et al., 1978) listed on the European
Community priority pollutant Circular No 90±55
(1990). So it is important to study and compare
di€erent processes to eliminate these compounds
from water and analyse the intermediate products
involved in their degradation.
the two frequencies corresponding to 40 W electric. Most
of these experiments were carried out in air-equilibrated
solutions at 208C and constant pressure.
Photochemical irradiations
Several devices were used to study the photochemical
transformations. Solutions were irradiated at 254 nm with
a low pressure mercury lamp germicide Mazda TG-15 W
surrounded by an elliptical mirror, the lamp being located
along one focal axis and the reactor in quartz along the
other. A device in which the reactor was surrounded by 6
lamps in a cylindrical mirror was used to study the com-
plete phototransformation of substrates. In the latter, the
EXPERIMENTAL SECTION
Reagents
Chlorpropham (99%) was provided by Chem Service
and used as received, 3-chloroaniline (>99%) by Aldrich,
3-aminophenol (>98%) and resorcinol (>99%) by
Merck. Water used for solutions and HPLC was puri®ed
with a Milli-Q apparatus. Methanol was of HPLC grade.
incident photon ¯ow in 25 ml was evaluated at about
2Â 10 6 Einstein s
1
using uranyl oxalate actinometry
Analyses
(Calvert and Pitts, 1966).
A monochromator Schoe€el equipped with a xenon
lamp (1600 W) was used for irradiations at 270 nm, and a
monochromator Bausch and Lomb with a high pressure
mercury lamp (Ushio USM-200 DP) at 296 nm. For the
isolation of photoproducts, solutions were irradiated in
the range 290±340 nm with 6 low pressure UVB lamps
Duke GL 20 W.
UV spectra of solutions were recorded on a CARY 13,
Varian Spectrophotometer.
Separations and titrations of products were carried out
on HPLC chromatographs (Waters 600E model and
Beckman 420 model) equipped with C18 columns, 5 mm
250 mm 4.6 mm. The eluent was a mixture MeOH/H2O
(usually 60/40). Acetic acid (0.1%) was added to water to
prevent ionisation of phenolic derivatives. Nitrate, nitrite
and chloride ions were analysed by ionic liquid chroma-
tography on a Waters ILC1 apparatus equipped with a
conductimeter 430.
Photochemical reactions were carried out in unbu€ered
solution at room temperature.
Identi®cation of the main sonoproducts was obtained
by GC-MS (Carlo Erba Instruments QMD 1000) on a
CP-SIL8 column. Photoproducts were identi®ed by 1H
NMR on a Bruker AC400 spectrometer and by mass spec-
trometry on Fison type EB (70E) or Nermag R10-10C
RESULTS
Ultrasonic transformation of chlorpropham
The disappearance of chlorpropham at 20 and
spectrometers; GC-MS (Hewlett-Packard 5985 with capil- 482 kHz is compared in Fig. 1.

Ultrasonic and photodegradation of chlorpropham
2453
Fig. 2. Kinetics of formation of the main sonoproducts of chlorpropham at 482 kHz in air-equilibrated
solution (100 ml, 0.1 mM). (a) Organic and ionic products; (b) carbon monoxide and dioxide.
The treatment at high frequency (initial rate not result from the sonication of chlorpropham
13.0 Â10 8 M s 1) is much more ecient than at
because their formation was not observed when
20 kHz (initial rate 4.2 Â10 8 M s 1). The complete
nitrogen was eliminated from the solution by oxy-
degradation was obtained after 45 min at 482 kHz
whereas about 1/3 of chlorpropham remained after
60 min at 20 kHz. The kinetics of formation of
ionic species, 3-chloroaniline and formic acid at
482 kHz are reported in Fig. 2(a). Formation of 3-
chlorohydroquinone has been observed on the
HPLC chromatogram, but not quanti®ed. It can be
noted that the same sonoproducts were obtained at
20 kHz but in lower amounts.
gen purging whereas chloropropham was comple-
tely degradated. Moreover it appears in Fig. 2(a)
that the sum of nitrite and nitrate ions formed is
quite higher than the amount of chlorpropham con-
verted.
Nitrite ions are formed as primary sonoproduct
whereas nitrate ions appear as secondary product.
This is consistent with the oxidation of nitrite by
hydroxyl radicals formed in the sonolysis of water.
In the ®rst stage of the reaction, when the concen-
The C±Cl bond cleavage is the major primary
process. The yield of Cl is about 98% after 80 min
at 482 kHz. Ultrasound does not only lead to a
dechlorination but also to a drastic degradation of
the herbicide. During the course of the reaction,
nitrite and nitrate ions are formed. Both ions do
.
tration of nitrite is too low to quench OH, the for-
mation of hydrogen peroxide was observed
(iodometric test) and attributed to recombination of
.
OH.

2454
B. David et al.
Table 1. Main products of ultrasonic transformation of chlorpropham (482 kHz) identi®ed by GC-MS
The pH decrease observed with unbu€ered sol- observed that the transformation is 65% inhibited
by addition of isopropanol 0.1 M.
utions results from the formation of HCl, HNO2,
HNO3, formic and carbonic acids.
Gases formed in the ultrasonic degradation of
chlorpropham were analysed by the head space
method. Kinetics are reported in Fig. 2(b). It
appears that CO2 is formed as both a primary and
a secondary product.
The main organic sonoproduct is 3-chloroaniline.
It was identi®ed by its HPLC retention time (com-
parison with a standard) and by GC-MS. The yield
reached 12.5% after sonication at 482 kHz during
45 min and decreased afterwards. Other products
were identi®ed from GC-MS spectra by comparison
with NBS library, namely carbamic acid isopropyl
ester, the four isomeric 3-chlorohydroxyphenylcar-
bamic acid isopropyl esters and 3-chlorohydroqui-
none. The main values of m/e are given in Table 1.
Ultrasonic transformation of 3-chloroaniline
As it was observed with chlorpropham the degra-
dation of 3-chloroaniline is more ecient at
482 kHz than at 20 kHz and this e€ect is much
more important: the ratio of initial rates is about 8
as it appears in Fig. 3. The main sonoproducts are
Cl , NO2, NO3, CO and CO2. Kinetics are given in
Fig. 4 for sonolysis at 482 kHz.
Isopropanol was also detected by GC on
a
Gaschrom 254 column at the end of the experiment,
but it was not quanti®ed.
The formation of hydroxylated products indicates
that hydroxyl radicals are involved in the ultrasonic
degradation of chlorpropham. Actually, it was The commercial compound was characterised by
Another product formed was identi®ed as chloro-
hydroquinone (m/e = 144) by means of GC-MS.

Ultrasonic and photodegradation of chlorpropham
2455
Fig. 3. Kinetics of ultrasonic transformation of 3-chloroaniline at 20 and 482 kHz in air-equilibrated
solution (100 ml).
Fig. 4. Kinetics of formation of the main sonoproducts of 3-chloroaniline at 482 kHz in air-equilibrated
solution (100 ml). (a) Organic and ionic products; (b) carbon monoxide and dioxide.

2456
B. David et al.
Fig. 5. UV spectrum of chlorpropham and 3-chloroaniline in aqueous solution.
the same retention time and the same fragmenta- located at dppm: 6.63 (dd); 6.99 (dd); 7.20 (s) and
tion.
7.23 (t) in the 1H 400 MHz NMR spectrum in
It was observed that the inhibition of the ultra- CD3OD. The protons of isopropyl group are at
sonic transformation of 3-chloroaniline by isopro- 5.2 ppm (1H) and 1.5 ppm (6H). From these results
panol (85% inhibition with isopropanol 0.1 M) is the product can be identi®ed as isopropyl 3-hydro-
more ecient than the inhibition of chlorpropham. xycarbanilate (HIPC). The fragment at m/z = 153
Thus it can be deduced that hydroxyl radicals play corresponds to the loss of the isopropyl group and
a major role in the degradation compared with m/e = 109 corresponds to aminophenol.
direct pyrolysis.
Phototransformation of chlorpropham
The UV spectrum of chlorpropham is given in
Fig. 5. The maximum absorption is located at
A few mg of this product was isolated and a sol-
277 nm with a molar absorption coecient e evalu-
ution of known concentration was used to calibrate
ated at 606 5 M 1 cm 1. At 300 nm the absorp-
the HPLC chromatogram. The initial yield was
evaluated at more than 70%. The formation of the
tion is rather low (e = 53.0 0.5 M 1 cm 1), but
sucient to induce a photochemical transformation
chloride ion was experimentally proved using a
in summer sunlight. It was experimentally observed
speci®c electrode.
that a solution 1.7Â 10 4 M is about 80% trans-
A device with 6 germicide lamps was used to
study the ®nal photodegradation at 254 nm. As it
appears in Fig. 7, chlorpropham is almost comple-
tely transformed after about 20 min and the main
photoproduct (HIPC) after about 80 min. No or-
formed after 53 days in summer sunlight (latitude
468N, 420 m over sea level).
Unbu€ered aqueous solutions 5.7 Â10 4 M were
irradiated at 254 and 270 nm. The quantum yield at
254 nm was evaluated at 0.14 0.02 in both air-
ganic species absorbing at 250 nm were detected in
saturated and deoxygenated solutions, and at
the chromatogram after 90 min.
0.10 0.02 at 270 nm. The di€erence is not signi®-
cant because of the error due to the sharp decrease
of absorption in this range.
Phototransformation of 3-chloroaniline
Three photoproducts appear on the HPLC chro-
matogram of a solution of chlorpropham irradiated observed in the direct photolysis of chlorpropham
at 254 nm (Fig. 6). but it occurs in its biotransformation. So it is useful
The formation of 3-chloroaniline was not
The main product (III) was extracted with ethyl to study its photochemical behaviour. Figure 5
ether from a solution irradiated until complete shows that 3-chloroaniline absorbs at longer wave-
transformation. The parent peak in the mass spec- lengths than chlorpropham. The maximal absorp-
trum obtained by electron impact was located at m/ tion of the neutral form is located at 286 nm with a
z = 195. It corresponds to a non-chlorinated com- molar
absorption
coecient
evaluated
at
pound. The main fragments correspond to m/ 1730 15 M 1 cm 1. The protonated form of 3-
z = 153 and 109. Four aromatic protons are chloroaniline has only a very low absorption in the

Ultrasonic and photodegradation of chlorpropham
2457
Fig. 6. HPLC chromatogram of an unbu€ered air-saturated solution of chlorpropham 1.7 Â10 4 M. (a)
1
Non-irradiated; (b) irradiated during 1 min at 254 nm (photon rate 1.6 Â 10 7 Einstein s in 10 ml, con-
version 36%) eluent MeOH/H2O, 68/32, detection 270 nm.
Fig. 7. Kinetics of phototransformation of a solution of chlorpropham 1.45Â 10 4 M, irradiated at
254 nm (detection at 250 nm, photon rate received in 25 ml 2Â 10 6 Einstein s 1).

2458
B. David et al.
Fig. 8. Kinetics of transformation of 3-chloroaniline 1.2Â 10 4 M and formation of the main photopro-
ducts by irradiation at 254 nm (detection at 270 nm, photon rate received in 25 ml
1.8Â 10 6 Einstein s 1).
UV. It plays a minor role in environmental con- transformation was quanti®ed by calibration of
ditions, since the pKa was evaluated at 3.2 by spec- HPLC. It clearly appears in Fig. 8 that the trans-
formation
is
initially
almost
quantitative.
trophotometric measurements.
An unbu€ered solution (1.1 Â10 3 M, pH = 5.5)
was irradiated at 254 and 296 nm. The quantum
yield was evaluated at 0.12 0.02 at these two
wavelengths. This value and the data about the sun-
light spectrum (see, for instance, Frank and
Klop€er, 1988), make it possible to evaluate the
photochemical half-life in sunlight using the re-
lationship proposed by the European Chemical
Resorcinol and several unidenti®ed photoproducts
are formed in a second stage of the reaction. The
phototransformation of 3-aminophenol is slower
and not so speci®c as the transformation of 3-chlor-
oaniline. Under the conditions given in Fig. 8, i.e.
25 ml of solution of 1.2 Â10 4 M irradiated with 6
germicide lamps, 3-chloroaniline disappeared in
3 min, 3-aminophenol in 30 min and no aromatic or
quinonic compound could be detected after 3 h. In
sunlight irradiation (summer time) most of photo-
products absorbing at 280 nm disappeared after
40 days.
Industry Ecology
(ECETOC, 1984).
and
Toxicology
Centre
ln2
l2
t1=2
ˆ
2300f
Iꢀl†eꢀl† dl
l1
Eciency of both processes
where t1/2 is the half-life in seconds, f the quantum
yield, l1±l2 the absorption range (nm) and I(l) and
The devices used in the present work for the
degradation of chlorpropham and 3-chloroaniline
were not optimised for practical application since
the aim of this study was focused on the com-
parison of the mechanisms involved. However,
the energy eciencies were approximately evalu-
ated for both techniques. For complete degra-
dation of chlorpropham in aqueous solution
(0.1 mM), ultrasonic treatment needs ca. 0.4 kWh
for 1 L. The photolysis of the same solution
needs about 0.15 kWh for the elimination of
chlorpropham, but about 9 times more energy
for the transformation of aromatic products. The
eciencies of both devices could be greatly
e(l)
the
incident
photon
rate
(Einstein cm 2 s 1 nm 1) and molar absorption coef-
®cient (l mol 1 cm 1) at wavelength l (nm).
The half-life was evaluated at a few hours in
summer and a few days in winter. Actually it was
experimentally observed that in
a solution of
7.2 Â10 4 M, 3-chloroaniline was 98% transformed
after 8 days in summer sunlight. This calculation is
not very accurate with chlorpropham which absorbs
only a very low percentage of sunlight.
The main photoproduct initially formed from 3-
chloroaniline was identi®ed as 3-aminophenol by
comparison of HPLC retention times and UV spec- increased by designing them for applied purposes.
tra of irradiated solution and authentic sample. The For the sonolysis treatment: optimisation of geo-

Ultrasonic and photodegradation of chlorpropham
2459
metrical parameters of the reactor and ultrasonic
The amount of isopropanol formed is too
frequency; for photochemical treatment: insertion low ( 10 4 M) to signi®cantly inhibit the degra-
of the lamp into the contaminated solution to dation.
minimise photonic losses.
A similar mechanism has been suggested for the
transformation of other carbamates, particularly on
TiO2 (Pramauro et al., 1993) and bentonite
(Sabadie and Coste, 1985). The thermal degradation
could be attributed to the local increase of tempera-
ture resulting from the implosion of the cavitation
bubble. This means that some molecules of chlor-
propham are surrounding the cavitation bubbles in
DISCUSSION AND MECHANISMS
Ultrasonic transformation
Two mechanisms are involved in the ultrasonic
transformation of chlorpropham and 3-chloroani-
line. With chlorpropham, the initial formation of
CO2 is too high to result only from the cleavage of
carbamate function. Moreover, the transformation
is partly inhibited by isopropanol. With 3-chloroa-
niline, the eciency of the inhibition is higher than
with chlorpropham and CO2 formed appears as a
secondary sonoproduct.
The ®rst mechanism involves hydroxyl radicals
formed by sonolysis of water. It is inhibited by
alcohols and it explains the formation of hydroxyl-
ated compounds as primary products and the for-
mation of CO2 in the last stage of the reaction.
Both compounds are concerned by this oxidative
pathway which leads to the complete mineralisation
in many steps. The ®nal one is the oxidation of for-
mic acid according to the following reactions:
a
layer of 250 nm thickness (Suslick and
Hammerton, 1986). This bubble jacket can be con-
sidered as an intermediate region where temperature
goes down from several thousand degrees Kelvin to
the ambient liquid temperature.
Comparing Figs 2 and 4 it can be noticed that
the disappearance is slower with 3-chloroaniline
than with chlorpropham. This phenomenon is
attributed to a higher thermal stability of 3-chloroa-
niline. It was also observed that the inhibiting e€ect
of alcohols is more signi®cant with 3-chloroaniline
than with chlorpropham. Thus the oxidation by hy-
droxyl radicals plays a more important role with 3-
chloroaniline. Moreover, the thermal degradation
into CO2 is much lower with 3-chloroaniline than
with chlorpropham. In both cases, the minor for-
mation of carbon monoxide can be attributed either
to the thermal degradation of formic acid (Tsang
and Lifohitz, 1990) or to a possible reduction of
CO2 (Henglein, 1985).
.
.
HCOOH + OH 4 HCOO + H2O
(k = 1.3Á108 mol-1 l) (Buxton et al., 1988),
.
.
HCOO + OH 4 CO2+H2O (minor pathway)
.
or HCOO ; + O24CO2+HO2
But oxidation by hydroxyl radicals does not
explain the initial formation of CO2 (see Fig. 2).
The second mechanism which provides CO2 as a
primary product is most likely a thermal degra-
dation. Actually it was shown that chlorpropham
was degraded into 3-chlorophenyl±isocyanate and
isopropanol at 2508C (Somda, 1986). It was
observed that in aqueous solution 3-chlorophenyli-
socyanate is completely hydrolysed into 3-chloroa-
niline and CO2. The following mechanism is
proposed:
HCOOH 4CO ‡ H2O
CO2 ‡ H 4CO ‡ OH
The following mechanism is proposed for the

2460
B. David et al.
ultrasonic degradation of 3-chloroaniline:
The in¯uence of ultrasonic frequency on the e- cant in dilute solution (concentration around
ciency of chlorpropham and 3-chloroaniline degra- 10 4 M). Chlorinated substrates disappear in a few
dation may be mainly related to the OH minutes when solutions are irradiated with the
production. Actually it was reported that the for- device equipped with
6
germicide lamps.
mation of OH is more ecient at 482 kHz than at Photoproducts are transformed more slowly, but
20 kHz (Petrier et al., 1992a). At high frequency the after a few hours no quinonic or aromatic deriva-
collapse of microbubbles is too fast to allow the tives remain.
recombination:
.
.
CONCLUSIONS
H ‡ OH 4H2O
so di€usion of radicals in the bulk is favoured.
Ultrasound and light can transform chlorprop-
ham and 3-chloroaniline, but the intermediates are
di€erent.
Phototransformation
The ultrasonic degradation is more ecient at
482 kHz than at 20 kHz for both compounds. With
chlorpropham, intermediates are hydroxylated pro-
ducts and 3-chloroaniline. Two pathways are
involved, the oxidation by OH and pyrolysis near
the cavitation bubbles. 3-chloroaniline, which is a
toxic intermediate, does not accumulate and is
mineralised.
Ultrasonic treatment at 482 kHz appears to be an
ecient method for the elimination of both com-
pounds.
Photolysis is initially more speci®c. The main in-
itial reaction is a photohydrolysis of the C±Cl bond
The transformation of 3-chloroaniline into 3-ami-
nophenol is very speci®c and does not depend on
the presence of oxygen. Such a behaviour was pre-
viously observed with 3-chlorophenol (Boule et al.,
1982) and chlorobenzene (Boule et al., 1985). The
reaction cannot result from a radical mechanism
since the formation of 3-aminophenol is formed in
the absence of oxygen. Moreover, oxidation pro-
ducts resulting from the oxidation by oxygen or
chlorine atom should be expected. As it was
suggested for chlorobenzene and 3-chlorophenol the
reaction is explained by a heterolytic scission of the
C±Cl bond, concerted or not with hydrolysis:
A similar mechanism can be applied to the trans- leading to hydroxylated products. This reaction is
formation of 3-aminophenol into resorcinol and to quantitative with 3-chloroaniline in the ®rst stage of
the transformation of chlorpropham into the hy- the transformation. With chlorpropham some uni-
droxylated product (HIPC).
The photolysis involves the transformation of or-
denti®ed minor by-products are also formed.
Irradiation at 254 nm can be used to eliminate 3-
ganic chlorine into hydrochloric acid which leads to chloroaniline and chlorpropham from water. In the
a decrease of pH. Consequently, in unbu€ered sol- ®rst stage hydroxylated products are rapidly
utions, the protonation of 3-chloroaniline involves a formed. They may be more oxidable or biodegrad-
decrease in the fraction of absorbed radiation able than the starting material. For example 3-ami-
specially at l 275 nm, but this e€ect is not signi®- nophenol is easily oxidised in basic solution. In

Ultrasonic and photodegradation of chlorpropham
2461
Metcalf R. L. (1971) Pesticides in the environment. In:
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Keravis (Universite d'Orleans) and V. Jacob (Universite
de Grenoble, GRECA) for their help in mass spec-
trometry. They also thank the Service Central d'Analyse
du C.N.R.S. for GC-MS analyses.
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