Environ. Sci. Technol. 1982, 16, 627-632
(3) Banerjee, S.;Yalkowsky, S. H.; Valvani, S. C. Environ. Sci. Technol. 1980,14,1227. ( 4 ) Hwang, S. T.; Fahrenthold, P. AIChE Symp. Ser. 1980,76, 37. (5) Sekine, T.; Suzuki, Y.; Ihara, N. Bull. Chem. SOC.Jpn. 1973, 46, 995. (6) Leo, A.; Hansch, C.; Elkins, D. Chem. Rev. 1971, 71,525.
(7) Ewell, R. H.; Harrison, J. M.; Berg, L. Znd. Eng. Chem. 1944, 36, 871.
Received for review September 21,1981. Accepted May 3,1982. This work was supported as part of Grant No, R807027from the U.S. Environmental Protection Agency, through the Robert S. Kerr Environmental Research Laboratory, Ada, OK.
Kinetics and Products of Hydrolysis of 1,2-Dibromo-3-chloropropane Nlcholas E. Burlinson," Lester A. Lee, and David H. Rosenblattt
Naval Surface Weapons Center, White Oak Laboratory, Silver Spring, Maryland 20910 The kinetics of hydrolysis of the nematocide 1,2-dibromo-3-chloropropane (DBCP) were studied in several aqueous buffers in the pH range 4-9 and in the temperature range 40-100 "C. The rate data suggest a mechanism that, at pH >7, is first order in hydroxide ion and first order in DBCP, but below pH 5 hydrolysis appears to be due solely to water. Product studies reveal formation of essentially two intermediates, 2-bromo-3-chloropropene (-95%) and 2,3-dibromopropene (-5%), by E2 elimination of HBr and HC1, respectively. Both of these allylic halide intermediates solvolyze in relatively fast steps to form the stable 2-bromoallyl alcohol. Arrhenius plots allowed extrapolation to environmental conditions (pH 7 and 15 "C) where the half-life of DBCP is estimated to be 141 years.
1,2-Dibromo-3-chloropropane (DBCP) has b.een widely used in agricultural regions of this country for many decades, mainly as a soil fumigant nematocide (1). Due to DBCP's low vapor pressure (0.8 mmHg at 20 "C ( I ) , moderate solubility in water (700 mg/L at 20 "C), resistance to biodegradation (2-4), and hydrolytic stability (5), it is quite persistent in the environment. Recently, an increase in DBCP concentration has been observed in ground waters in many agricultural regions (6, 7). In addition, DBCP has been shown to cause sterility in male chemical workers (6,8,9) and to be a potent carcinogen in lab animals ( 6 , 1 0 , 1 1 ) . Since DBCP's major environmental pathway appears to be via water, it is important to determine accurately its hydrolysis kinetics and the products of hydrolysis in order to assist in environmental fate predictions which are used in risk assessments by the Environmental Protection Agency (12). The predicted half-life for DBCP hydrolysis in water at pH 7 and 25 "C, assuming displacement of Br by OH, ranges anywhere from 280 days to hundreds of years. These predictions were based on Taft linear free energy relationships (p*,a*) for hydrolysis of model alkyl bromides (1). A few orienting experiments on the disappearance rates of DBCP have been carried out at one elevated temperature and several pHs (5). Use of a "theoretical" activation energy of 23.3 kcal/mol permitted extrapolation to a rate constant at 30 "C; this gave a l-year approximate half-life at pH 7. However, a small error in the predicted US. Army Medical Bioengineering Research and Development Laboratory, Fort Detrick, Frederick, MD 21701.
activation energy can give a large error in such an extrapolated constant. A more detailed study was necessary, both to identify produds and to obtain reliable kinetic rate laws and rate constants at ground-water temperatures. In the present kinetic study, we have endeavored to determine accurately the second-order hydrolysis rate constants for DBCP at several elevated temperatures in the temperature range 40-100 "C and at buffered pHs in the range 4-9. The resulting information is sufficient to provide relatively accurate half-life estimates for groundwater temperatures and pH levels. We have determined the pH hydrolysis profile for DBCP at 85 "C in the pH range 4-9 and have also identified the major intermediates, their hydrolysis rate constants, and the final product of their hydrolysis.
Experimental Section
Procedure. Hydrolysis kinetics for DBCP were carried out in buffered aqueous solutions sealed in 15-mL glass ampuls at several temperatures (range 40-100 "C). The approximate DBCP starting concentration was 1 mg/L. Two constant-temperature baths were used: (1)a Braun Thermomix 1460 3-gallon 1000-W bath, with f0.05 "C temperature stability; (2) a modified Sargent Welch Thermoniter ST unit with 1500 W of proportional heating elements in a 16-gallon American Instrument constant temperature bath with fO.O1 "C temperature stability. The NBS-calibrated thermometers were readable to f0.02 "C. Materials,Reagents and pH Determination. For the majority of the kinetic runs, three NBS standard buffers were used. They were 0.01 M potassium acid phthalate (KHPhth) for pH 4, equivalent moles of KH,PO,/ Na2HP04(0.005, 0.025, 0.05 M) for pH 6.8, and 0.01 M Na2B40,.1OH20for pH 9.18. The actual pH value of each experiment was measured at the experimental temperature to allow exact calculation of hydroxide concentration. A Model No. 130 Corning pH meter was used, having an accuracy of fO.001 pH units, along with a Corning Ag/ AgCl combination electrode (No. 476115). The pH meter was calibrated in the usual way at ambient temperature with the appropriate NBS buffer standard. Then 25-mL samples of the kinetic stock solutions were added to a small (50 mL) insulated glass constant-temperature bath that contained the combination electrode and thermometer. The solutions and electrode and thermometer were allowed to equilibrate for 20 min after the thermometer had reached temperature before a
Not subject to U.S. Copyright. Published 1982 by the American Chemical Society
Environ. Sci. Technol., Vol. 16,No. 9, 1982 627
pH reading was taken. The system was sealed so no evaporation occurred. Since most of the kinetic stock solutions were made up with NBS buffers to standard concentrations, we could check our values against the standard pH tables (13). Our pH measurements were within 0.03 units of those in the standard tables. The samples of DBCP used for this study was supplied by Adrian Burns (EPA, Beltsville, MD). For the kinetic work, 99% pure DBCP was used, and technical grade (95%) DBCP was used for the product study. Commercial samples of 2-bromo-3-chloropropene (BCP) and 2,3-dibromopropene (DBP) were obtained from Pfaltz and Bauer. Analytical Method for DBCP. Aliquots (5 mL) were removed from the glass ampuls and extracted with 5-mL portions of benzene (shaken for 60 s in a 25-mL volumetric flask). The extraction efficiency was 99.99% by GC/EC analysis. The concentration of DBCP in the benzene extract was determined in a Hewlett-Packard Model 5750 research gas chromatograph, which was equipped with e3Ni electron capture detector and a 4 ft X l/* in. glass column packed with 3.52% Dexsil GC on 80/100 Chromosorb W AW DBCS. The carrier gas was 95:5 (v/v) argon/methane at 83 mL/min; the column temperature was 108 "C; the injection port was at 130 "C and the detector at 280 "C. The retention time for DBCP was 40 s, and for p-nitrotoluene (p-NT) (internal standard) it was 100 s. Our limit of detection for DBCP using the above method without further concentration of the benzene extract was 0.3 pg/L. The change in concentration of DBCP during the hydrolysis kinetics was generally followed from 1 to 0.001 mg/L for the fast reactions at high pH and temperature and from 1to 0.1 mg/L for the slow (tlj2 -2 weeks) reactions at low pH and temperature. A known amount of p-NT dissolved in benzene was added to each benzene extract of DBCP as an internal standard. Peak heights
for each sample (DBCP and p-NT) were compared with peak heights for a standard (benzene solution containing a known amount of DBCP and p-NT) for each analysis. This procedure was tedious but allowed for accurate GC/EC analysis by peak height. The quantity of DBCP and p-NT in the final diluted samples was adjusted by microliter syringe amounts so that their peak heights would approximate those in the standard. This procedure eliminated errors that might have arisen from nonlinearity in the EC detector response or from injection volume errors. Calculation of DBCP Concentration. The concentration (mg/L) of DBCP is calculated from
where PHIS.= peak height of internal standard, PHDBCP = peak height of DBCP, a = microliters of internal standard in unknown solution, b = microliters of internal standard in standard solution, and c = concentration of DBCP in mg/L in standard solution. Analysis of Hydrolysis Products. For the identification and kinetics of hydrolysis of the intermediates, the following instrumentation and materials were used: a Hewlett-Packard Model 5750 research gas chromatograph was used with a 4 f t X 1/4 in. glass column packed with A-71 Poly Pak I (polystyrene-divinyl benzene), 80/ 120 mesh; the column temperature was 200 "C; helium, hydrogen, and air flow rates were 84,38, and 305 mL/min, respectively;the flame ionization detector temperature was 250 "C; the injection port temperature was 150 "C. Analysis was by direct injection of the aqueous solution. The GC/MS analyses were performed on a Finnigan 3200 E with a 5 f t X 2 mm i.d. glass GC column packed with 10% SP-1000 on 80/100 mesh Supelocoport, tem-
Table I. Kinetic Data for Hydrolysis of DBCP in Buffered Aqueous Solutions temp, "C
pH ( k O . 0 1 )
buffer
no. of points
10j k o b d , h ''
corr coeff
0.72' zero buffer 0.759 t 0.064 0.9965 8 0.005 M PO,' 0.881 f 0.047 0.9986 8 0.05 M PO, 0.9991 71.46 i 0.92 5 0.01 M borax 0.9978 3.13 f 0.24 8 0.01 M borax 4.00' zero buffer 4.50 k 0.11 0.9991 14 0.005 M PO, 0.9965 6.30 k 0.35 15 0.025 M PO, 0.9993 9.00 i 0.30 9 0.05 M PO, 0.970 4 0.69 i 0.05 0.01 M KHPhth 0.62 t 0.03 0.9975 12 0.05 M KHPhth 0.9996 298f 15 5 0.01 M borax 0.9917 314 * 56 7 0.01 M borax 0.9982 2 7 5 i 23 6 0.005 M borax 0.9955 2.904 * 0.84 4 0.05 M KHPhth 24.30' zero buffer 27.65 k 3.70 0.9990 4 0.005 M PO, 26.61 f 2.73 0.9991 5 0.005 M PO, 0.973 43.96 t 3.19 4 0.025 M PO, 0.9953 35.44 i 5.51 6 0.025 M PO; 0.9989 46.07 k 6.45 4 0.05 M PO, 0.9983 46.31 i: 3.80 7 0.05 M PO, 0.9994 4.20 f 0.14 8 0.025 M KH-PO, 0.9988 1646 * 109 6 0.01 M borax 0.9983 179.6 k 15.5 7 0.025 M borax + 0.1 M HCl 170.0' zero buffer 6.89' 100 0.9998 182.3 i 4.6 6 6.8gb 0.005 M PO, 100 0.9956 1 7 1 . 1 i: 22 6 6.8gb 0.005 M PO, 100 0.9979 6 246.7 k 29.5 6.90b 0.05 M PO, 100 pH values estimated for 100 "C (ref 13). ' Extrapolated value at a PO, = equimolar amounts of KH,PO,/Na,HPO,. zero buffer strength. 60 60 60 60 40 72 72 12 72 72 72 72 72 12 85 85 85 85 85 85 85 85 85 85 85
628
6.84' 6.84 6.85 8.97 9.07 6.85' 6.85 6.85 6.86 4.01 4.01 8.93 8.91 8.90 4.01 6.84' 6.84 6.84 6.85 6.85 6.88 6.89 5.68 8.86 1.85
Environ. Sci. Technol., Vol. 16, No. 9, 1982
L
/
t,,? = 38 YRS @ 25OC
L
0
I
,
,
I
I
1
2
3
4
I
5
6
/
7
8
9
10
PH
Flgure 1. Profile of pH vs. rate for DBCP hydrolysis at 85 "C.
perature programmed at 15 "C/min from 50 to 200 "C. The helium carrier gas flow was 25 mL/min. Injection port and separator temperatures were 250 and 280 "C, respectively. MS ionization conditions were electron impact (70 eV) with a spectral range of 25-300 mass units. Proton NMR spectra were recorded on a Varian Model XL-200 superconducting FT spectrometer. Chemical shifts are reported in ppm relative to tetramethylsilane as internal standard. 2-Bromoallyl Alcohol (14). This compound was synthesized by the hydrolysis of 2,3-dibromo-l-propene in aqueous borax buffer at pH 9 and 85 OC for 23 h. The aqueous hydrolysate was extracted with ethyl ether and the extract dried over anhydrous magnesium sulfate. After concentration of the extract on a rotary evaporator, a gas chromatogram of the concentrate gave one peak. lH NMR (benzene-dJ gave 6 3.81 (br t, 2 H), 5.34 (9, 1H), and 5.62 (9, 1 H). The mass spectrum (EI) gave M+ 138 with the major peak at (M+ - 81).
Results and Discussion Kinetics of Hydrolysis of DBCP. All the kinetic experiments for DBCP (Table I) were done under buffered aqueous conditions and followed a simple pseudo-firstorder disappearance. Several kinetic runs at 85 and 100 "C showed good first-order plots for over 9 half-lives of DBCP (99.8% disappearance). Tenfold changes in DBCP starting concentration (14.1mg/L) showed no change in the first-order rate constant. Because of the relative stability of DBCP to hydrolysis at room temperature and neutral pH the hydrolysis kinetics were performed in sealed glass ampuls at 40,60,72,85, and 100 "C in the pH range 4-9. Some runs required almost 3 months to collect sufficient rate data at the lower temperatures and lower pHs, whereas at 85 OC and pH 9.2 the half-life was approximately 1 h. In each experiment 15 mL of DBCP solution in a sealed glass ampul were allowed to equilibrate in the constant-temperature bath for at least 30 min before the first analysis. The rate data in Table I reveal buffer catalysis in the phosphate buffers. A tenfold increase in phosphate buffer concentration gave a twofold increase in rate at pH 6.5 and 72 OC. Therefore the rate constants for DBCP hydrolysis in pH 6.8 buffers were determined by extrapolation of the first-order rates to zero phosphate concentration. Phosphate catalysis was less pronounced at lower temperatures (see 60 "C data). Buffer catalysis was not observed with the borax or phthalate buffers. A plot of pH vs. log k,bd for the hydrolysis of DBCP at
i
l o o - l L L L ' ~ ' 2.5 2.7
2.9 3.1 1000/TInKI
3.3
5
Flgure 2. Arrhenlus plot of In k , vs. 1/Tfor the hydrolysis of DBCP.
85 "C is shown in Figure 1. The straight line portion above pH 5 has a slope of 1.05, indicating a first-order dependency on hydroxide ion over the range pH 5-10. The fact that the curve does not flatten out until pH 4 indicates that the specific rate constant for hydroxide, kOH,is much larger than that for water, ItHzo. This would be expected for an E2-type elimination where hydrogen ion abstraction is followed by halide elimination. Although further kinetic runs were not carried out at more acidic pHs, acid hydrolysis is not expected since DBCP has been reported to be stable in acid (15). Pseudo-first-orderrate constants (kow) were determined from plots of In [DBCP] vs. time. Linear regression equations for the data were calculated by a least-squares method, which also gave the error in the rate constant and the correlation coefficient. The rate constants in Table I represent a 95% confidence interval by use of Student's t test. The correlation coefficients for 95% of the rate constants were better than 0.99. In summary, the kinetic data for the hydrolysis of DBCP suggest a rate law that is first order in DBCP and first order in hydroxide ion down to pH 7. Below pH 7 the rate depends in part on hydrolysis by water (eq 1). -d[DBCP] = ~oH-[DBCP] [OH-] + ~ H ~ [ D B C P ] [ H , O ] dt (1) Values of [OH-] were calculated according to eq 2, where [OH-] = K,/[H+]
(2)
[H+] values were experimental and the equation of Marshall (16) was used to calculate K, as a function of temperature and density (see Appendix A). Equation 3 was used to obtain ItoH-.
kOH- = k,bsd/[OH-] above pH = 7 (3) Arrhenius plots of In kOH vs. 1/T (K) for the kinetics experiments at pH 6.8 and 8.9 are shown in Figure 2. The energy of activation (E,) for the base-catalyzed hydrolysis of DBCP can be calculated from the integrated form of the Arrhenius equation (4) or from the slope of In kl/k2 = -E,(T2 - Tl)/RT2Tl (4) In k = -E,/RT
+ constant
(5)
a plot of In kOH- vs. 1/T (K) (Figure 2), which is based on the Arrhenius equation (5). The energy of activation for the pH 6.8 Arrhenius plot is 22.34 kcal/mol. Environ. Sci. Technol., Vol. 16, No. 9, 1982
629
Scheme I
24
Br I CH2 = C - CHZCI I \
22 20
f
0
DBCP l6
CH,
14
s 12
CH, = C - CH,OH
~r =
,,/
BAA
C - CH2Br DBP
3
a 10
BCP
~
8 6
4
2 0
\
BrCH2CHBrCH2CI
18
l
l
2
~
l
4
l
l
6
l
,
l
10
8
I
l
12
14
TIME (MINI
Figure 3. Gas chromatogram of 752 mg/L technical grade DBCP in water (pH 9) after 1.5 h at 85 "C.
*
BCP IpH 9) AT 85OC
+ BCP IpH 71 AT 85% 0
DBP IpH 7) AT 6OoC
ESTIMATED: FOR BCP. t i 1 2 = 0.38 YR AT
c
Flgure 4. Plot of In peak height vs. time for the hydrolysis of BCP and DBP at 60 and 85 "C.
If the hydrolysis mechanism is the same over the whole temperature range, then a straight-line plot should be obtained with a slope equal to -E,/R. Either extrapolation from the plot or substitution into eq 4 allows the calculation of the rate constant, lz, at environmental temperatures. Extrapolation of the results of the Arrhenius plot in Figure 2 to 25 "C at pH 7 gives kOH-= 20.6 h-' M-' and a half-life of t I j z= 38 f 4 years. However at 15 "C and pH 7, tl12 = 141 years. Ground-water temperatures are generally between 10 and 20 "C in the US. (17). It should be also noted that at pH 4 and 85 OC the kobsd for DBCP hydrolysis is actually kH,o[HzO]from eq 1and h-l. This value represents 11.9% of is equal to 2.9 X h-') obtained at pH 6.86 the komrate constant (24.3 X and 85 OC. This accounts somewhat for the difference in intercepts in Figure 2, where the contribution to kobsd by the k ~ ~ o [ H 2term 0 ] would raise the intercept for the pH 6.8 data by approximately 12% but have no effect on pH 9 since the contribution from the lzH,o[HzO]term would be negligible. 630 Envlron. Sci. Technol., Vol. 16, No. 9, 1982
Since the DBCP hydrolysis kinetics were run at high temperature in sealed ampuls, a question arose as to the concentration of DBCP found in the vapor phase in the 5% void volume left in the ampul. If the amount was considerable, this would change the kinetics and make the hydrolysis rate constants lower than they actually should be. Using Henry's law and the method of Mackay (18)for estimating Henry's law constant, we estimated the ratio of vapor DBCP/solution DBCP to be less than 0.00074 at 20 "C (see Appendix B). Since the solubility of DBCP also increases with temperature, as does its vapor pressure, we would not expect the Henry's law constant for DBCP to significantly change even at 100 OC, the boiling point of DBCP being 196 OC. Therefore, the amount of DBCP in the vapor is expected to be negligible and have little effect on the value of k0bsd. DBCP Hydrolysis Products. In an effort to identify the hydrolysis products of DBCP we adjusted a 752 mg/L aqueous solution of technical grade DBCP to pH 9 with a borax buffer. Three sealed glass ampuls containing this solution were placed in an 85 "C bath. Gas chromatograms of these DBCP solutions, at 0, 1.5, 5, and 20 h, revealed the formation of two intermediates, one major and one minor, and the subsequent disappearance of these intermediates to yield a single stable product. A GC trace of the 1.5-h sample, containing four components, is shown in Figure 3. GC/MS and NMR analysis of each component allowed us to identify the major intermediate as 2bromo-3-chloropropene(BCP), the minor intermediate as 2,3-dibromopropene (DBP), and the final hydrolysis product was 2-bromo-2-propeno1, commonly known as 2-bromoallyl alcohol (BAA). The assigned structures (Scheme I) of BCP, DBP, and BAA were confirmed by comparisons of GC retention times, mass spectral fragmentation patterns, and lH NMR data of the hydrolysis products with authentic samples of each. A gas chromatogram of the 20-h sample revealed that all DBCP and DBP were gone, only 2% BCP remained, and almost a quantitative yield of BAA was present and stable to further hydrolysis or reaction at 85 "C and pH 9. Further confirmation of the above-mentioned reactions was obtained with NMR spectroscopy. A similar sealedtube experiment with approximately 500 mg of DBCP/L in 0.01 M borax/D20 was carried out in an NMR tube place in the 85 OC constant-temperature bath. Over a 50-h period the tube was removed at certain intervals and cooled and the NMR spectrum taken of the starting DBCP and products. DBP could not be observed by this technique owing to its low concentration, but BCP formation and disappearance and BAA formation could easily be monitored. As expected, E2 elimination of HBr from DBCP is the major mechanism, forming BCP; however, a small amount of HC1 elimination also occurs to yield DBP. Time did not allow a detailed kinetic study of the individual rates
Table 11. Kinetic Data for Hydrolysis of 2-Bromo-3-chloropropene(BCP) and 2,3-Dibromopropene (DBP) at 60 and 85 "C compd temp, "C PH k o b d , h-' no. of points t,,,, h corr coeff
BCP BCP BCP DBP
60 85 85 60
0.0115 0.1249 0.1076 0.1786
6.86 6.86 9.18 6.86
7
t 0.0086 t 0.018
I 5
0.016
9
i
60.2 5.5 6.4 3.8
0.995 0.998 0.996 0.995
or
Table I11
a
i 0.0013
T,'C
T,K
40 60 72 85 100
313 333 345 358 373
d, g/mLa 0.99224 0.98322 0.97662 0.96864 0.95838
[BCP] -- kOH-[OH-l + ~ H , O
log Kw -13.482 -13.037 -12.776 -12.523 -12.270
Reference 20.
of formation of BCP or DBP, but a limited set of hydrolysis kinetics on the disappearance of BCP and DBP were carried out (see below). Kinetics of Hydrolysis of 2-Bromo-3-chloro-lpropene (BCP) and 2,3-Dibromo-l-propene (DBP). Individual aqueous solutions of BCP and DBP, ranging in concentration from 300 to 600 mg/L, buffered at pH 7 and 9, were placed in sealed glass ampuls. The ampuls were placed in 60 and 85 "C constant-temperature baths. Their rates of hydrolysis were monitored by direct injection of the aqueous hydrolysate into the gas chromatograph with a flame ionization detector. A plot of the log of the peak height vs. time for four runs (Figure 4) gave straight-line plots over several half-lives: (BCP) 60 OC, pH 7; (BCP) 85 "C, pH 7; (BCP) 85 "C, pH 9; (DBP) 60 "C, pH 7. DBP solvolyzed to BAA 16 times faster than did BCP. The kinetic data are shown in Table 11. The fiist-order rate constants for disappearance of BCP in buffered aqueous solutions for 85 "C at pH 6.86 and 9.18 are about the same. This is expected if an SN1solvolysis type mechanism is operating where the rate is not dependent on hydroxide ion concentration, typical of an allyl halide (19). Plotting the data for BCP at pH 6.86 at 85 and 60 "C (In kobsdvs. 1/T) allowed for a rough estimate of the Arrhenius energy of activation: Ea = 22.6 kcal/mol. From this value, the rate constant for BCP hydrolysis at h-' or tl/z 25 "C (pH 7) was estimated as kl = 2.1 X = 0.38 years. This is a 100-fold faster rate of disappearance than that of DBCP. Consequently, environmental accumulation of the intermediates BCP or DBP would not be expected. The actual steady-state ratio of [BCP]/ [DBCP] can be roughly calculated from the above kinetic data by the following:
[DBCP]
kHz0
Note: on the basis of the product study, 95% of DBCP goes to BCP, therefore at 25 "C and pH 7 kOH- = 20.6 h-l M-l from Figure 2 kHzO = 7 3 X 10" h-l (calculated from DBCP kinetic data at 72 and 85 "C at pH 4 where E, = 27.4 kcal/mol) and kHzO = 2.1 X h-l (calculated from BCP kinetic data at 60 and 85 "C where E, = 22.6 kcal/mol) gives [BCP]/ [DBCP] FV 0.016 at pH 7 and 25 "C (estimated value). It should also be mentioned that, under these kinetic conditions, no other products were observed forming. We looked very closely for SN2type products, which could be formed from attack by hydroxide on DBCP (e.g., saturated alcohols and epichlorohydrin),and for E2 elimination-type products other than those identified; none were found by GC/MS methods.
Appendix A
Calculation of K,. The ion product for water (K,) is both temperature and density dependent. The equation of Marshall (16) is accurate in the temperature range 0-1000 "C and in the pressure range 1-10 000 bars. This equation is as follows:
where A = -4.098, B = -3245.2, C = +2.2362 X lo5, D = -3.984 X lo', E = +13.957, F = -1262.3, G = +8.5641 X los, d = density water, and T = temperature (K). Table I11 gives some of the calculated ion products for water from use of the Marshall equation.
Appendix B if
- slow
fast
DBCP BCP BAA then -d[BCP] dt ~H,o[BCP]- ko,-[DBCP][OH] - kHp[DBCP] If we assume the steady state condition of d[BCP]/dt = 0 then ~H,o[BCP]= ~oH-[DBCPI [OH-] + k~,o[DBcp]
Estimate of the Concentration of DBCP in the Vapor. Since the kinetics were carried out in 15-mL sealed glass ampuls with a 5% void volume, an estimate of the amount of DBCP in the gas phase was necessary to determine if a correction in the rate constants were needed. Henry's law gives
where the partial pressure of DBCP above the liquid is a product of Henry's law constant, Hc, and the concentration of DBCP in the liquid. H , can be estimated by the method of Mackay (18) by Environ. Sci. Technol., Vol. 16, No. 9, 1982
631
For DBCP (2) H, 0.8 mmHg for 0.700 g/L at 20 “C = 0.355 (atm L)/mol
=
for a 1mg/L solution, [DBCP] = 4.24 X lO* mol/L or 6.36 X mo1/15 mL; therefore
PDBCP = 1.51 X
lo*
atm at 20 “C
and
n = -PV =
RT
(1.51 X lo* atm)(0.75 mL) (82.05 mL atm/deg mol)(293 K) 4.71 X
mol
in vapor if V = 0.75 mL (5% void volume) or the ratio
Note: in actuality the void volume decreases as the sample is heated. At 100 “C the void volume decreased to -2%. Therefore, 0.00074 is an upper limit on the ratio.
Acknowledgments We express our thanks to Stuart Cohen (EPA, Washington, D.C.) for many helpful discussions,to Adrian Burns (EPA, Beltsville, MD) for supplying samples of DBCP, to N. Lee Wolfe (EPA, Athens, GA) for helpful suggestions, to Donald Glover and John Hoffsommer for mass spectral services and assistance on the analytical procedures for DBCP, and to James Wheeler of Howard University for mass spectral analysis of the products from DBCP.
Literature Cited (1) Berkowitz, J.; Goyer, M.; Harris, J. C.; Lyman, W. J.; Horne, R. A.; Nelken, L. H.; Harrison, J. E.; Rosenblatt, D. H., A. D.Little Report, ”Literature Review-Problem Definition Study on Selected Chemicals-Final Report Vol. 11,” U.S. Army Contract No. DA-MD-17-77-C-7037 (AD-B0529461), June 1978. (2) Hodges, L. R.; Lear, B. Nematologica 1973,19, 146-158. (3) Castro, C. E.; Belser, N. O., Environ. Sci. Technol. 1968, 2,779-783.
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Received for review September 18,1981. Accepted May 17,1982. This project was funded jointly by the US.Army Toxic and Hazardous Materials Agency and the Environmental Protection Agency.
