045
Ind. Eng. Chem. Prod. Res. Dev. 1986, 25, 645-649
Kokotailo, 0. T.; Lawton, S. L.; Olson, D. H.; Meier, W. M. Nature (London) 1978, 272, 437. ~ ~ J.~p.; a~ o b w~n , J,~J . i power i , 1979, 155,
C k n , N. Y.; Oerwood, W. E. Ind. Eng. Chem. Process Des. Dev. 1978, 17, 513. C k n , N. Y.; OoWing. R. L.; Ireland, H. R.; Stein, T. R. Oil Gas J . 1977, 75, 165. Clapetta. F. G.; Coonradt, H. L.;Garwood, W. E. (to Mobil Oil Corp.) U S . Patent 3 150071, Sept 22, 1964. Coonradt. H. L.; Garwood, W. E. Prepr.-Am. Chem. Soc., Div. Pet. Chem. 1967, 72(4), E-17.
Received for review October 25, 1985 Accepted May 19, 1986
Kinetic Study of 4-Chloro-2-methylphenoxyacetic Acid Photodegradation Jaime Soley, Manuel Vlcente, Pedro Clapgs, and Santiago Esplugas" Department de Qdmica Tacnica, Facunat de Qdmica, Unlversitat de Barcelona, Marti FranqAs 1, 08028 Barcelona, Spain
Photodegradation of MCPA (khloro-2-methylphenoxyacetic acid) in aqueous solutions has been studied by using UV radiation and simulated sunlight and sensitizers. The main photodegradation products have been characterized, and the kinetic study has been carried out in both processes for initial reaction times.
Introduction The presence of pesticides in water has increased in the last few years (Edwards, 1978; Medved, 1982). In fact, the extension of this effect is actually increasing both because of widespread use of these compounds and because of their high stability in aqueous medium. All these reasons together with the toxicity of the products have brought serious changes and ecological imbalances about in the zones where these compounds have been used, such as deltas and estuaries (Chunderova, 1970). In addition there is a clash between the interest of agriculture and fishing, which are the traditional activities of these areas. Photochemical treatment is one of the methods that gives good results for the degradation of this kind of effluents by means of UV or solar radiation with the aid of sensitizers. The conventional methods such as activated sludges, chemical treatment, etc. generally are difficult to apply (Meallier and Coste, 1981). One of the most used herbicides in rice cultivation is 4-chloro-2-methylphenoxyacetic acid (MCPA). In spite of the fact that MCPA has a moderate toxicity level, the pesticide treatment, which is carried out during certain periods of the year, affecta the ecosystem zones (Soderquist and Crosby, 1975). It is important to note that only photosensitizers with triplet-state energy similar to MCPA activation energy can be used successfully. Among the possible sensitizers having these energy conditions, it is preferable to select them from agricultural wastes. The use of these kinds of substances as sensitizers presents several advantages: utilization of a wide zone of the solar spectrum; low cost treatment; direct use in cultivations; and, finally, exploitation of agricultural wastes (Ivie and Casida, 1971). In this work the characterization of the main photoproducts and a kinetic study of MCPA photodecomposition have been carried out. UV radiation and simulated sunlight have been used as radiation sources.
Materials and Methods Two kinds of photochemical reactors have been used in this experimental study: an annular photoreactor (Figure 2) and a plane photoreactor (Figure 5). The operation was batch in both cases. The annular photoreactor was made of quartz with the lamp placed in the center of the annulus. The inner and outer radii of the photoreactor were R1 = 3.0 cm and R,, = 5.6 cm, respectively. The thickness of the filter solution jacket, df, was 1.5 cm. The height of the reactor, H, was 6.0 cm. The source of the radiation was a mercury lamp (Philips, HPK-125 W), which was L = 3 cm long. A filter of solution (25 g/L CuS04)was used so that the incident radiation was practically 290 nm. The plane photoreactor was a parallelepipedal device with the lamp outside it and without reflector. There was only direct radiation from the lamp to the reactor. The dimensions of the reactor were A = 21.1 cm long, B = 14.0 cm wide, and C = 3.0 cm deep. The lamp, with a length of L = 4.5 cm, was an Osram HQIT-400W/DH placed zo = 34 cm above the reactor. Liquid chromatography was performed with a PerkinElmer S-2 Model, a Model LC 75 variable wavelength detector, a Spherisorb C-8 (10 pm) 250 X 46 mm column, and a Rheodyne 7125 loop injector; it was eluted with isocratic mode. Chromatography conditions were as follows: eluent acetonitrile/buffer (trifluoroacetic acid, pH 2.2) 50150; flow 0.8 mL/min; and wavelength 228 nm. A MS-9 VG updated mass spectrometer with a VG/250 data system was used for mass spectrometric measurements. GC/MS analyses were carried out with a DB-1 fused silica capillary column coupled directly to the ion source. Helium was the carrier gas with a back pressure of 0.8 bar. The temperature program was from 700 (3 min) to 275 "C (25 min) at 2 OC/min. For the E1 mode, the conditions were as follows: ionization energy 70 eV; mass range 40-500 amu; scan time 4 s; and 1000 of resolving power. Actinometry. Before beginning a kinetic study attempting to fiid quantum yield or any other measurement, it is necessary to carry out an actinometry in order to measure the energy emitted by the source of radiation. Of
*Towhom any correspondence should be addressed. 0196-432118811225-0645$01.50/0
0
1986 American Chemical Society
646
Ind. Eng. Chern. Prod. Res. Dev., Vol. 25, No. 4, 1986
OH
I
hu
f
Figure 1. Scheme of MCPA photodecomposition.
the various chemical actinometers, the photochemical decomposition of aqueous solutions of oxalic acid in the presence of uranyl salts was chosen (Cassano, 1968). The flux of photons emitted by the lamp was determined, and einstein/s (UV lamp) it is as follows: WL = 5.85 X and WL = 3.29 X lo4 einstein/s (simulated sunlight lamp). In the same way the flux of photons entering the reaction chamber was calculated (Esplugas et al., 1983).
Photodecomposition with UV Radiation A series of experiments at 3, 6, 12, and 20 min were carried out in the annular photoreactor to identify the photodecomposition products by using GC/MS technique. In these experiments the initial concentration of MCPA was 120 ppm, the temperature was 25 "C, and the pH was 5.4. Analysis proved that after 3 min of radiation the chloride compounds 4-chloro-2-methylphenol (11) and 4-chloro-2methylphenyl formate (I) were present but disappeared after 6 min. At this time the compound 2-methylphenol (IV) was not detected; the major product was 1,4-dihydroxy-2-methylbenzene (111) and the lesser was 2methyl-2,5-cyclohexadiene-1,4-dione (111bis). Taking into account these results, it is possible to suggest the scheme of MCPA photodecomposition shown in Figure 1 (Clap& et al., 1986). MCPA yields compound I1 by the breakdown of the ether bond or by a double decarboxylation. Compounds I11 and IV are obtained from I1 by a substitution of the chloro by a hydroxyl group or by dehalogenation. Finally, there is a redox tautomerism, depending on pH, between compounds I11 and I11 bis. Kinetic Study. The mechanism of any photochemical process is usually complex because the excited states of the molecules give different kinds of reactions. However, for this reaction, regarding the obtained results, the kinetic mechanism proposed is a simple scheme of three steps: MCPA (MCPA)* rl = k,pI (MCPA)* MCPA r2 = kdC(MCpA)* (MCPA)* products r3 = k,C(MCpA)* The first step consists in the excitation of MCPA by the absorption of one photon, the second step is the deactivation of this excited state to its ground state, and the thud one is the real photodecomposition of MCPA. The kinetic constant kd includes the constants of monomolecular deactivation processes, which can be radiatives or not, and the constants of pseudo first order corresponding to the quenching processes with the medium impurities. kl includes the primary constants of the photochemical degradation processes, and ke includes the constants of the
-
+
-+
activation step and the intersystem crossing. Applying a mass balance and assuming the pseudostationary state for the activated species, the kinetic equation is
where V is the reaction volume. The decomposition quantum yield of MCPA, +MCpA, can be expressed by
The expression of the radiation flow rate absorbed, Wab, is (3)
where p is the MCPA absorbance and I the radiation intensity in each point of the reactor. In order to evaluate Wab it is necessary to establish and to solve the radiation balance (Cassano, 1968). Because of the geometric characteristics of the reactor and the lamp system used, a linear spherical model for the lamp emission was assumed (Jacob and Dranoff, 1968, 1970). If p is constant with the position, Wabs is Wabs= 2 ~ p & ~ L ~ ~ I ( rdr, zdz) r
(4)
1
where I(r,z) = 4lrL
'o+Lexp((-pLrdf+ p ( r - R , ) ) c ) dl (5) r2 + ( z - L)*
and c = (r2
+ ( z - l)2)1/2/r
(6)
r and z are radial and axial coordinates of the point; pfy d p are the absorbance of the filter solution and the reaction medium, respectively; and W, is the radiation emission of the lamp per unit time. The remaining geometrical parameters used in eq 5 and 6 are explained in Figure 2. When the conversion of the reaction is low, W, can be considered constant, that is to say, independent of the time. In this case, the kinetic equation results to be zero order with respect to MCPA concentration. The integration of eq 1 gives (7)
which is a lineal variation of MCPA concentration according to the irradiation time.
Ind. Eng. Chem. Prod. Res. Dev., Vol. 25, No. 4, 1986
647
MCPA + C h l o r o p h y l l
(ppm) 150
1
100 l
I
-d
f
5
n
MCPA c Antraquinone MCPA + Riboflavine
3
O
P
*
*-
e-
w-
-
Figure 2. Annular photoreactor geometry. In this figure (r,z)are the cylindrical coordinates of the point considered; L and I , are the length and the axial position of the lamp; R1and Ro me the internal and external radii of the reactor chamber; H is the reactor height; and df is the filter solution thickness.
n
0:
li
t
m)”’
20
Figure 3. MCPA concentration as function of irradiation time using UV radiation. Table I. PhotodecomDosition of MCPA by UV Radiation CMCPA~ ppm t , min t , min &PA, ppm 0 119.6 10 103.5 2 117.5 15 94.9 5 111.0 20 81.4
To test the kinetic equation, an additional experiment at short irradiation times was carried out in the following conditions: initial concentration of MCPA 120 ppm; temperature 25 OC; and pH 5.4. The result of this experiment is shown in Table I and Figure 3. According to eq 7, the results, MCPA concentration and irradiation time, were fitted to a line by the square method. Both the adjustment and the estimation of the parameters were significant with a confidence coefficient of 95%. Taking into account the value of Wab, we calculated the quantum yield of the MCPA photodecomposition from the slope: c$MC~A = 0.53 f 0.03 mol/einstein
Experiments with Sensitizers and Simulated Sunlight Because MCPA does not absorb radiation above 300 nm, it is necessary to use sensitizers to carry out its photodecomposition in the wavelength range of the solar spectrum. Sodium anthraquinonesulfonate, chlorophyll, and riboflavin have been chosen to be used among the suitable sensitizers. Series of experiments were carried out to test the capacity of the sensitizers to degrade MCPA. In all cases, the MCPA and the sensitizer initial concentrations were 120 and 40 ppm, respectively. The results are shown in Figure 4. It can be observed that riboflavin is the sensitizer that gives a bigger MCPA degradation rate. That is the reason
7--7
0
50
100
I
I
150
200
250
500 t ‘ m m
Figure 4. Evolution of MCPA concentration with irradiation time using visible radiation and different sensitizers.
this compound was chosen for the kinetic study and the main products determination of the sensitized MCPA photodegradation. When the riboflavin was used as sensitizer, the major photoproduct obtained was 4-chloro-2-methylphenol (11). Its concentration increases with irradiation time. The lesser product was 4-chloro-2-methylphenyl formiate (I), and its concentration decreases with the time. The sensitized decomposition of MCPA corresponds to the first steps of Figure 1. After chlorinated compounds I and 11, no other reactions take place. Kinetic Study. The mechanism of any sensitization process is usually very complex and cannot be represented by a simple scheme. The mechanism suggested for this reaction when the reaction conversions are low is shown in Scheme I. Scheme I F -F* r1 = k,pI F* F r2 = k,Cp F* products r3 = k,Cp F* + MCPA (MCPA)* F r4 = k4CMCpACF’ (MCPA)* MCPA ~5 = ~ ~ C ( M C P A ) *
--
4
+
(MCPA)* -* products
= k&(~cp~)* The step of photochemical decomposition of riboflavin has to be included because the photodecomposition process of this sensitizer has been verified by the irradiation of riboflavin in the same experimental conditions. Using the stationary assumption for the activated species and a mass balance, we find the kinetic equation for MCPA is r6
where
and for the riboflavin it is
where
In both cases, Wabsis the flow rate of the radiation absorbed by the riboflavin.
648
Ind. Eng. Chem. Prod. Res. Dev., Vol. 25, No. 4, 1986
Table 11. Photodecomposition of MCPA with Riboflavin and Simulated Sunlight" E-1 E-2 E-3 t , min 0 5 15 23 30
CMCPA 118.5 100.3 81.2 65.7 54.9
CMCPA 86.5 69.5 37.9 27.9 20.5
CF 39.4 37.9 33.8 30.8 26.8
CF 28.8 27.9 20.5 14.8 10.4
CMCPA 56.9 41.4 27.3 15.4 9.8
CF 19.6 19.1 16.6 15.0 14.1
"In all experiments the temperature was 25 "C, the pH 5.4, and the initial MCPA concentration 3 times the initial riboflavin concentration (Co~cpA/COF = 3). Concentrations are expressed in PPm.
'1 Figure 5. Plane photoreactor geometry. In this figure (z,y,z) are the Cartesian coordinates of the point considered; (AB$) are the reactor dimensions; (x,,y,,z,) are the lamp positions; and L is the length of the lamp.
For the plane photoreactor (Figure 5) applying a mathematical model similar to that utilized previously gives Wabs as
where Z(x,y,z) =
Joyo+L
4irL wL
exp(-pz/sin p) ( x - x,)2
2,
cp
=
(tx,
- x)2
dl
(13)
and sin
+ ( E - y)* + ( 2 , + 2)2
+ (E -
+z
Figure 6. Evolution of MCPA concentration vs. irradiation time for the experiments E-1, E-2, and E-3, in which visible radiation and riboflavin as sensitizer are used.
0
+ ( 2 , + 2)2)1'2
F-.
(14)
When the irradiation time is not very high (low reaction conversions), Wabscan be considered as constant. In this case, the rate equation of MCPA is of zero order in relation to the riboflavin concentration and of first order with regard to the MCPA concentration. The rate equation of riboflavin is of zero order in both species. By integration of these kinetics equations, the following expressions are obtained
which show the evolution of MCPA and riboflavin concentration according to the irradiation time. In order to find out if these equations correspond to the experimental photodecomposition, a series of batch experiments, measuring the MCPA and riboflavin concentrations, were carried out. The experimental conditions and the results obtained are shown in Table 11. For each experiment, data concentrations of MCPA and riboflavin and reaction time were fitted to eq 15 and 16. In each case, both the adjustment and the estimation of K M and KFwere significant with a confidence coefficient of 95%. The variations of K M and KFare not significant; therefore, the average value of those obtained has been taken: KM = 67.5 f 0.1 L/einstein KF = 4.41
X
f2 X
mol/einstein
I
I
zn
t
mln
an
Figure 7. Evolution of riboflavin concentration vs. irradiation time for the experiments E-1 and E-2.
Figures 6 and 7 show the evolution of MCPA and riboflavin concentrations vs. the irradiation time and the fitted equations. Conclusions From the analysis of the results presented in this paper the following conclusions may be drawn: The photodecomposition of aqueous solutions of MCPA at atmospheric pressure and 25 "C using the radiation of 290 nm leads to photoproducts, the major ones being 1,4-dihydroxy-2-methylbenzeneand 2-methyl-2,5-cyclohexadiene-194-dioneand a minor one, 2-methylphenol.
649
Ind. Eng. Chem. Prod. Res. Dev. 1986, 25, 649-653
The quantum yield of MCPA decomposition, at 25 "C, is 4 M p A = 0.53 f 0.03 mol/einstein. This decomposition does not take place at wavelengths longer than 310 nm. The results of MCPA photodecomposition using visible radiation and sensitizers are (1)riboflavin increases the rate of MCPA photodecomposition, (2) sodium anthraquinonesulfonate increases the rate of MCPA slightly, and (3) chlorophyll does not degrade the MCPA. The major product of the MCPA photodecomposition using visible radiation and riboflavin is 4-chloro-2methylphenol, and the kinetic equation for the decomposition of MCPA at initial times is
and for the riboflavin it is dCF
1
- = --(4.41 x 1 0 - 3 ) ~ ~ ~ dt V Nomenclature C = concentration, mol m-3 df = filter solution thickness, m H = reactor height, m I = radiation intensity, einstein-m-2-s-1 K = global kinetic constant k = kinetic constant L = lamp length, m 1 = lamp axial coordinate, m 1, = lamp axial position, m Ro = external radius of the annular photoreactor, m R1 = internal radius of the annular photoreactor, m r = cylindrical radial coordinate, m
t = time, s V = volume, m3 W = radiation flow rate, einstein-s-' x: = Cartesian coordinate, m
y = Cartesian coordinate, m z = Cartesian or cylindrical axial coordinate, m = absorbance, m-l 4 = quantum yield, mol-einstein-' Subscripts
abs = absorbed d = deactivation step F = riboflavin f = filter solution MCPA = 4-chloro-2-methylphenoxyaceticacid Superscripts 0 = initial * = activated species Registry No. I, 30114-33-1; 11,1570-64-5; 111,95-71-6; I11 bis, 553-97-9; IV,95-48-1; MCPA, 94-74-6;sodium anthraquinonechlorophyll, 479-61-8; riboflavin, 83-88-5. sulfonate, 27600-99-3;
Literature Cited Cassano, A. E. Rev. Fac. Ing. Qulm. (Unlv. Nac. Lnorai) 1988, 3 7 , 447. Chunderova, A. 1. Mlkrobiologlye 1970. 39(5), 887. Clap&. P.; Soley, J.; Vlcente. M.; Rivera. J.; Caixach, J.; Venture. F. Chemosphere 1986, 15, 395. Edwards, C. A. festic. Microblol. 1878, 603. Esplugas, S.; Ibarz, A.; Vlcente, M. Chem. Eng. J . 1883, 27, 107. Ivle, 0. N.; C a s h , J. E. J. Agric. FoodChem. 1971, 19, 405, 410. Jacob, S. M.; Dranoff, J. S. Chem. Eng. frog., Symp. Ser. 1988, 89(64), 54. Jacob, S. M.; Dranoff, J. S. A I C M J . 1870, 16, 359. Mealller, P.; Coste, C. M. Trav. SOC. phenn. Montpellier 1881, 41, 19. Medved, L. I. Glg. Sann. 1982, 6 , 62. Soderqulst, C. J.; Crosby, D. 0. festic. Sci. 1975, 6 , 17.
Received for reuiew September 24, 1985 Accepted July 28, 1986
Preparation of 3-Methyl-4-nitrophenol Ken Ito' and Hlroshl Kamlnaka Osaka Research Labofatow, Sumitom0 Chemical Company, Lfd., 3- 1-98 Kasugadenaka, Konohana-ku, Osaka, Japan
3Methyl4nitrophenol (abbreviated customarily as 4-NMP) is a key intermediate for the synthesis of fenitrothion, which is a major low-toxic organophosphorus insecticide. As a result of our studles on synthetic routes of CNMP on an lndustrlai scale, the following method was found to be the most suitable: m-cresol was first converted to m-cresol phosphate, nitrated with nitric acid, and then hydrolyzed under acldic condition to glve 3-methyl-4nitrophenol in the overall yield of 82%-85% based on m-cresol.
Introduction Fenitrothion (O,O-dimethyl0-(3-methyl-4-nitrophenyl) phosphorothioate) (see Figure 1)is a major low-toxic organophosphorus insecticide, and it is recommended as a malaria mosquito controller by the World Health Organization. 3-Methyl-4-nitrophenol (4-NMP) is a key intermediate for the synthesis of this insecticide. When m-cresol was nitrated by general nitration methods, byproducts which were nitrated a t the ortho positions with respect to the hydroxyl group of m-cresol were generated in almost the same amount as that of the target product, which was the nitration product at the para position of m-cresol (Hoffmann and Miller, 1883). Koelsch (1944) reported another O1964321/86/1225-O649$O1.5O/O
nitration method, which was to prepare first the nitroso compound and then to oxidize it to the nitro compound with nitric acid. The yield was 66% based on m-cresol. But, since nitroso-rn-creaolis an unstable compound which tends to decompose abruptly under dry conditions, it seemed impractical to adopt this procedure for industrial purposes. In an attempt to solve these problems, nitration was performed after esterification of m-cresol. In the case of the acetate ester, selectivity for 4-NMP was about 60%. In the case of the carbonate ester, selectivity for 4-NMP was about 80% (Faltis et al., 1944). Selectivity for nitration of the para position with respect to the hydroxyl group of phenol (Rapp, 1884) and chlo0 1986 American Chemical Society
