Environ. Sci. Technol. 1988, 22, 92-99
(18) Callahan, M. A.; Slimak, M. W.; Gabel, M. W.; May, I. P.; Fowler, C.; Freed, J. R.; Jennings, P.; Durfee, R. L.; Whitmore, F. C.; Maestri, B.; Mabey, W. R.; Holt, B. R.; Gould, C. Water-Related Environmental Fate of 129 Priority Pollutants;U.S. Environmental Protection Agency:
Washington, DC, 1979;Vol. I and 11, EPA-440/4A-79-029a and EPA-440/4-79-029b. (19) Albert, A,; Serjeant, E. P. Ionization Constants of Acids and Bases; Methuen: London, 1962; p 14. (20) Williams, A. In The Chemistry of Enzyme Action; Page, M. I., Ed.; Elsevier: Amsterdam, 1984; pp 127-201. (21) Hansch, C.; Leo, A. Substituent Constants for Correlation Analysis in Chemistry and Biology; Elsevier: Amsterdam, 1979. (22) Cessna, A. J.; Grover, R. J. Agric. Food Chem. 1978, 26, 289-292. (23) Barlin, G. B.; Perrin, D. D. Q. Rev. Chem. SOC.1966,20, 75-101. (24) Faust, B.; Tremp, J.; Hoign6, J.; Giger, W., unpublished results. (25) Zeyer, J.; Kocher, H. P.; Timmis, K. N. Appl. Environ. Microbiol. 1986, 52, 334-339. (26) Chiou, C. T.; Schmedding, D. W.; Manes, M. Enuiron. Sci. Technol. 1982,16, 4-10. (27) Hashimoto, Y.; Tohura, K.; Kishi, H.; Strochan, W. M. J. Chemosphere 1984, 13, 881-888.
(28) Mackay, D.; Bobra, A,; Chan, D. W.; Shiu, W. Y. Environ. Sci. Technol. 1979, 13, 333-337. (29) Przyjazny, A.; Janicki, W.; Chrzanowski, W.; Staszewki,R.
J . Chromatogr. 1983, 280, 249-260. (30) Munz, C.; Roberts, P. V. Environ. Sci. Technol. 1986,20, 830-836. (31) MacKay, D.; Bobra, A,; Shiu, W. Y.; Yalkowski, S. M. Chemosphere 1980,9,701-711. (32) Westall, J. C.; Grieder, E.; Schwarzenbach, R. P., to be submitted for publication in Environ. Sci. Technol. (33) Lyman, W. J. In Handbook of Chemical Property Estimation Methods; Lyman, W. J., Reehl, W. F., Rosenblatt, D. M., Eds.; McGraw-Hill: New York, 1982; pp 1.1-1.54. (34) Leuenberger, C.; Ligocki, M. P.; Pankow, J. F. Environ. Sci. Technol. 1985, 19, 1053-1058. (35) Mackay, D.; Shiu, W. Y. J . Phys. Chem. Ref. Data 1981, 10, 1175-1199. (36) Smith, J. H.; Bomberger, D. C., Jr.; Haynes, D. L. Chemosphere 1981, 10, 281-289. (37) Seinfeld, J. H.; Atmospheric Chemistry and Physics of Air Pollution; Wiley-Interscience: New York, 1986; p 213. Received for review April 6, 1987. Accepted August 19, 1987. This work was partially funded by Project COST 641 in the framework of the European Cooperation for Scientific and Technical Research.
Aldehyde-Bisulfite Adducts: Prediction of Some of Their Thermodynamic and Kinetic Properties Eric A. Betterton, Ylgal Erei, and Mlchael R. Hoffmann"
Environmental Engineering Science, W. M. Keck Laboratories 138-78, California Institute of Technology, Pasadena, Callfornia 91 125
stabi1%' constants (K1) for the reaction of acetaldehyde and hydroxyacetaldehyde with NaHS03, determined s~ectro~hotometricall~ in a ueous solution, were found to be (6'90 0*54) lo5M-7 and (2*o Oa5) lo6M-19 where K1 (corrected for hydration) 25 = [RCH(0H)S03-1~[RCH01[HS03-1 (' = Oa2 Acid dissociation 'Onstants ( P K d Of a series Of a-hydroxydkanesulfonate RCH(0H)S03-, were found to be 11.46 (CH3-), 11.28 (H-), 10.30 (HOCH,-), 10.33 (C6~ ~ - 10.31 1 , (cH,co-),and 7.21 (cl3c-)(' = 0 M; 25 OC). Simple straight-line relationships were found to exist between Taft's u* parameter and a number of thermodynamic and kinetic properties of some aldehydes. K1,K , , and the rate constant for nucleophilic addition of SO$all increase linearly with u*. Carbonyl species such as halogenated derivatives of acetaldehyde, certain 0-and y-dicarbonyl aldehydes, and perhaps also some highly (halogen) substituted ketones, Le., all those species with x u * 1 -1.5 (aldehydes) or x u * I-2.5 (ketones), could be important S(1V) reservoirs.
*
*
Introduction Aldehyde-bisulfite adducts, particularly a-hydroxymethanesulfonate [HCH(OH)SO,-], may be important reservoirs for S(IV), i.e., S02.H20,HS03-, and SO?-, in naturally occurring water droplets such as fog, mist, cloud, and rain but little is known about their thermodynamic and kinetic properties and so far only one S(1V) adduct has been positively identified ( I , 2) in a natural sample, viz,, a-hydroxymethanesulfonate in fog. Until recently, only the reaction of formaldehyde ( 3 ) , isobutyraldehyde ( 4 ) , and benzaldehyde (5) (and its derivatives) with S(1V) had been studied in any detail, 92
Environ. Sci. Technol., Vol.
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whereas at least nine aldehydes have been identified (6-8) in polluted urban environments: formaldehyde, aldehyde, propanal, n-butanal, n-pentanal, n-hexanal, glyoxal (CHOCHO), methy~g~yoxal (CH,COCHO), and benzaldehyde. It is difficult to predict the affinity of all these aldehydes for S(IV) with only the three examples studied, especially since benzaldehyde, one of the best an aromatic ring that studied of d l the aldehydes, can give rise to effectsand perhaps also to steric repulsion. Consequently, it is difficult to Pinpoint Potentially important (or as yet unidentified) aldehydes as targets for further research. In our recent study (9) of the methylglyoxal-S(1V) system, we pointed out that any aldehyde that (a) occurs in the environment at a significant concentration, (b) has a high effective Henry's law constant (the combination of the intrinsic Henry's law constant and the hydration constant), and (c) has high stability constants and rate constants for reaction with S(1V) could form an important S(1V) reservoir. The discrepancy between the number of aldehydes identified in the environment and the number of a-hydroxyalkanesulfonatesactually found is partly due to analytical difficulties (IO),but it is also partly due to the inability of many of these aldehydes to fulfill the three conditions necessary for being a significant s(IV) reservoir-as we will show. The primary aim of this work is to correlate the electron-withdrawing ability of the substituent R, in a series of aldehydes RCHO, with some important thermodynamic and kinetic parameters for their reactions with S(1V) and H 2 0 so that potentially important S(1V) reservoirs can be identified and actively sought in natural samples. These correlations may also be useful in estimating other thermodynamic and kinetic parameters, for improving ana-
0013-936X/88/0922-0092$01.50/0
0 1987 American Chemical Society
Table I. Elemental Analysis of Aldehyde-Bisulfite Adducts %C adduct CH3CH(OH)SO3Naa1/2HZO HOCH2CH(OH)S03Na (CH(OH)S03Na)2.Hz0 C13CCH(OH)S03Na
%O
%H
% S
found
calcd
found
calcd
found
calcd
found
calcd
15.03 14.67 8.54 9.91
15.29 14.64 8.45 9.55
3.82 3.11
3.21 3.07 2.11 0.80
47.37 49.23 50.42
40.73 48.75 50.69 25.46
20.47 19.51 22.31 13.95
20.41 19.54 22.57 12.75
2.29 0.87
Mr 157.1 164.1 284.1 251.4
Table 11. Experimental and Corrected Equilibrium Constants at 25 "C"
R CH3HHOCHZCGH5CH(0H)Z-O CHSCOCHBCOC1&-
R CH3HOCHZ-
g, M
3.0 0.3 0.3 3.0 0.3 0.3 0.01 0.01 P, M 0.2
0.2
Ka3, M
X
K,l, M
10"
PKn?
0.343 f 0.042 0.528 f 0.054 4.99 i 0.82 4.65 f 0.87
0.304 f 0.038 0.188 f 0.019 1.77 f 0.29 4.12 f 0.77 530 1.75 f 0.41 6.54 f 0.69 4508 f 145
K ~M-I , x
X 10"
11.4 (6) 11.2 (8) 10.3 (0) 10.3 (3)
4.92 f 1.15 8.94 f 0.94 6163 f 199 10-5
6.90 f 0.54 16.2 f 0.99: 23.7 f 2.1e
10.3 (1) 10.0 (5) 7.2 (1)
K,E,~
-
x1 10-5
2.67 f 0.21 1.47 f 0.09: 2.15 f O.lge
nError limits throughout this work are f one standard deviation. See eq 9 and eq 1-6 for definitions of the equilibrium constants. *Corrected to p = 0 using Davies' equation (see text), The monobisulfite adduct of glyoxal is assumed to be in the diol form. Ka3could not be determined for the reasons given in the text. dBy the spectrophotometric method. "By the stopped-flow acid-quench method.
lytical methodology, and for obtaining data for substitution into mathematical models. To this end, the stability constants of two more aldehyde-bisulfite adducts have been determined, and the acid dissociation constants of several a-hydroxyalkanesulfonatesalts have been measured. Besides being of intrinsic importance, the acid dissociation constants are relatively simple to measure, and they thus provide a good means of rapidly evaluating the expected chemical behavior of an a-hydroxyalkanesulfonate salt. It will be shown that the Taft u* parameter, which is documented (11) for a large number of substituents R and which is a measure of the electron-withdrawing power of R (12), can be used for correlating and making predictions of the chemical behavior of a closely related set of aldehydes of environmental significance. It will also become apparent that the correlations could usefully be extended to include ketones.
Experimental Procedures Materials. AR-grade reagents were used except where indicated, and high-purity (18Mncm) deionized water was obtained from a Millipore MilliRO-4 MilliQ system. Acetaldehyde (Aldrich, laboratory grade), hydroxyacetaldehyde (glycolaldehyde;Sigma, laboratory grade), chloral hydrate (Mallinckrodt, U.S.P.), glyoxal (40% aqueous solution; Aldrich, laboratory grade), and methylglyoxal (40% aqueous solution; Sigma, laboratory grade) were used without further purification. Benzaldehyde (MCB, laboratory grade) was redistilled under reduced pressure, and the sodium salt of hydroxymethanesulfonic acid (Kodak, laboratory grade) was used as received. The sodium bisulfite salt of glyoxal (CH(OH)S03Na)2.H20 was prepared by T. M. Olson in these laboratories in a manner similar to that described below. Full details will be published elsewhere. The S(IV) adducts were prepared by mixing the appropriate aldehyde with aqueous NaHSO, in a molar ratio of 1.O:O.g and allowing the mixture to equilibrate for 24 h under nitrogen in a sealed flask in the dark. [In the case of acetaldehyde (bp 21 "C) all reagents and glassware were cooled to 5 "C before mixing.] The product was isolated
by evaporating the solution to a syrup under reduced pressure (20 mbar; 40 "C), adding an equal volume of anhydrous ethanol, repeating the evaporation, and finally precipitating the white crystalline solid by stirring with ethanol. Filtration on sintered glass and washing with ethanol and anhydrous diethyl ether completed the preparation. Yields were usually >go%, and the salts were stored over silica gel in a desiccator. The adducts were analyzed for S(1V) by titration with excess As203-standardized Iz solution and back-titration with Na2S203(13, 14). Elemental analysis (by Galbraith Laboratories Inc.) gave the results shown in Table I. The similar preparation and analysis of the S(IV) adducts of methylglyoxal(9) and benzaldehyde (5) have been reported previously. The number of molecules of water per mole of adduct was based on the elemental analysis for C and was not determined directly. The calculated molecular weights are given in Table I. Methods. All experiments were performed a t 25.0 f 0.1 "C (Haake water baths). Water used to prepare the solutions was degassed under vacuum and saturated with nitrogen, and all solutions were stored under nitrogen. The acid dissociation constants of the a-hydroxyalkanesulfonate salts (Ka3in eq 19) were determined by potentiometric titration of a 0.01 M solution of the adduct under nitrogen with phthalic acid standardized 0.1 M NaOH using a Beckman 4 45 pH meter and a Beckman 39836 combination pH-electrode. The electrode was calibrated with pH 7.00 and 10.01 buffers. The titrations were performed in the presence of excess Na2S03[0.1 M when I.L (the ionic strength) = 0.3 M and 1.0 M when I.L = 3.0 M in Table 111 to prevent the dissociation of the conjugate base RCH(O-)S03-. The concentration of Na2S03 was chosen so that 199% of RCH(O-)S03-would remain at the end of the titration. Although the magnitude of K 2 in eq 15 (which is needed to calculate the required excess concentration of Na2S03)is not known for all the compounds titrated, we estimate that for R = H-, HOCH2-, CH(0HI2-, and CH3CO-, K2 2 lo3 M-l and that for R = CH,and C6H5-, K2 2 lo2 M-l. The acid dissociation constants were calculated from the raw data by the method described Envlron. Scl. Technol., Vol. 22, No. 1, 1988
93
by Albert and Serjeant (15),and the results (given in Table 11) are the average of at least three separate determinations. Calculations showed that the number of protons involved in the reaction was 1.0 f 0.1 in all cases. Na2S03 (pKd = 6.73 at p = 0.3 M) (16, 17) does not interfere with the determination [except for C1,CCH(OH)S03-] since it is fully deprotonated over the pH range of most of this work (pH 9-13). The pKa of C13CCH(OH)S03-was found to overlap with that of HS03- and in this case the excess M, which is sufficient if K2 1 lo5 M-l. Na2S03was only There was no added inert electrolyte. The pKa3of CH,COCH(0H)SOC was also determined under these conditions to confirm that no gross systematic errors had been introduced by this variation in experimental procedure. Prior to titration, ethylenediaminotetraacetic acid (EDTA) (lo4 M) was added to the a-hydroxyalkanesulfonatesalt solution to reduce the risk of trace metal catalyzed oxidation of S(1V) to S(V1). Experiments performed in the absence of EDTA showed that it had no effect on the titration results. The pH readings were stable between each addition of NaOH, indicating that S(1V) oxidation was minimal. We were unable to obtain acid dissociation constants for the dibisulfite adduct of glyoxal -SO3(0H)CzHz(0H)SO,-, since, soon after the beginning of the titration, the pH of the solution began to drift downward and an intense yellow color developed. This behavior is presumably due to a Cannizzaro reaction (18) (to produce a carboxylic acid and thus lower the pH) and to polymerization (to account for the yellow color), but no experiments were done to confirm this. By titrating rapidly, we were able to estimate that the apparent pKa3 is 19.5 but we could not determine if this was due to ionization of one or two hydroxyl groups. Stability constants for the reaction of acetaldehyde and hydroxyacetaldehyde with bisulfite (KIein eq 1) were determined spectrophotometrically by the method of Deister et al. (19). In addition, K I e for hydroxyacetaldehyde was checked with a stopped-flow acid-quenching procedure described later. Oxygen was rigorously excluded by using vacuum-line techniques and by manipulating the reagents in a glovebox under nitrogen. A series of four RCH(OH)S03Nasolutions (see below for concentrations) was equilibrated for 24 h (R = CH3-) or for 7 h (R = HOCH2-) at 25.0 "C in sealed flasks, and they were protected from the light. The ionic strength was 0.2 M (NaC1) and the pH was adjusted to 4.32 f 0.02 (CH3-) or to 4.59 f 0.01 (HOCH2-) with HC1. The pH of each solution was checked after equilibration by a Radiometer PHM 84 pH meter and GK 473901 combined pH-electrode calibrated with pH 7.00 and 4.10 buffers, In this pH region, and for the total S(1V) concentrations used here, >99% of the S(1V) is present as HS03-, and so no corrections for S(1V) speciation were necessary. All spectrophotometric measurements were made on a dual-beam Shimadzu MPS 2000 instrument fitted with a temperature-controlled cell holder. The concentrations of the a-hydroxyalkanesulfonatesalts used to determine Kle were 5.29, 7.94, 10.58, and 21.15 X M for CH,CH(OH)S03-, and they were 1.21, 4.84, 8.47, and 12.10 X M for HOCH,CH(OH)SO,-. The wavelength for the acetaldehyde system was 205 nm (using 1-cm quartz cuvettes), and the wavelength for the hydroxyacetaldehyde system was 210 nm (using 10-cm quartz cuvettes). The latter conditions were used because we expected the concentration of free HS03- to be very low. The equilibrated solutions were analyzed for HS03- by measuring their absorbance at a fixed wavelength and making the necessary corrections for absorbance due to 94
Environ. Scl. Technol., Vol. 22, No. 1, 1988
Table 111. Extinction Coefficients Used To Calculate K Le for Acetaldehyde and Hydroxyacetaldehyde S(IV) Adduct Formation t.
M-' cm-'
R
A, nm
HSO8-
RCHO
RCH(OHISO3-
CHSHOCHg-
205 210
(5.74 f 0.23) X lo2 (2.18 f 0.04) X 10'
0.5 3.8
3.6 1.0
free aldehyde and undissociated sulfonate RCH(OH)S03(see eq 3). The extinction coefficients of the free aldehyde and of HS03- were determined from the absorbance of standard solutions under identical conditions of pH, ionic strength, and wavelength, and the extinction coefficient of the a-hydroxyalkanesulfonatesalt was determined immediately after dissolving a known mass in an aliquot of acidic solution (0.2 M HC1). This was done to reduce the rate of dissociation of the adduct and to allow sufficient time for an absorbance measurement to be made. The following equations were used: Kle Kle
[RCH(OH)SO,-]/[RCHO]T[HSO
