1761
Znd. E n g . C h e m . Res. 1990, 29, 1761-1765
CaO, the use of more robust elements against fluorine should be recommended. The present result only suggests the basic principle for the disposal of CFCs by combustion. Further investigation is needed concerning, for example, the possible formation of harmful byproducts and effect of the coexisting organics or water. Acknowledgment This research was partly supported by the Kajima Foundation’s Research Grant and partly by a grant from Nippon Fine Gas Co. Ltd. We thank H. Tarumoto for his kind cooperation in carrying out this work. Registry No. CC12F2,75-71-8; Ti02, 13463-67-7; Si02, 763186-9; A1203, 1344-28-1; ZnP20s, 13765-95-2; Cr203, 1308-38-9; Mn2O3, 11129-60-5; Co304, 1308-06-1; Fe203, 1309-37-1; Moo3, 1313-27-5; Zr02, 1314-23-4;CaO, 130578-8; mordenite, 12173-987.
Literature Cited Ackerman, D. G.; Fischer, H. J.; Johnson, R. J.; Maddalone, R. F.; Matthews, B. J.; Moon, E. L.; Scheyer, K. H.; Shih, C. C.; Tobias, R. F. At-sea Incineration of Herbicide Orange Onboard the M / T Vulcanus. Environmental Protection Technology Series, EPA600/2-78-086; U S . Environmental Protection Agency: Research Triangle Park, NC, April 1978. Arata, K. Synthesis of Solid Superacids of Molybdenum and Tungsten Oxides Supported on Zirconia. Shokubai 1989,31,477-480.
Blake, D. M. Solar Thermal Technology for the Destruction of CFC Waste. Int. J. Refrig. 1988, 1 1 , 239-242. Colussi, A. J.; Amorebieta, V. T. Heterogeneous Decomposition of Trichlorofluoromethane on Carbonaceous Surfaces. J. Catal. 1987,83, 3055-3059. Gladrow, E. M.; Krebs, R. W.; Kimberlin, C. N., Jr. Reaction of Hydrocarbons over Cracking Catalysts. Ind.Eng. Chem. 1953,45, 142-147. Graham, J. L.; Hall, D. L.; Dellinger, B. Laboratory Investigation of Thermal Degradation of a Mixture of Hazardous Organic Compounds. 1. Environ. Sci. Technol. 1986, 20, 703-710. Imamura, S.; Ikeda, T.; Ishida, S. Multiple-step Catalytic Combustion of 1,2-Dichloroethane. Nippon Kagaku Kaishi 1989a, 139-144. Imamura, S.; Tarumoto, H.; Ishida, S. Decomposition of 1,2-Dichloroethane on Ti02/Si02. Ind. Eng. Chem. Res. 198913, 28, 1449-1452. Kagiya, T.; Sano, T.; Shimizu, T.; Fukui, K. High Polymerization of Ethylene oxide on Metal phosphate Catalysts. Kogyo Kagaku Zasshi 1963,66, 1893-1896. Millard, M. M.; Pavlath, A. E. Surface Analysis of PlasmaPolymerized Fluorocarbon Films by X-ray Photoelectron Spectrometry. J. Macromol. Sei.-Chem. 1976, AI0 (3), 579-597. Oku, A.; Kimura, K.; Sato, M. Complete Destruction of Chlorofluorocarbons by Reductive Dehalogenation Using Sodium Naphthalenide. Ind. Eng. Chem. Res. 1989,28, 1055-1059. Witt, S. D.; Wu, E. C.; Loh, K. L.; Tang, Y. N. Heterogeneous hydrogenolysis of Some Fluorocarbons. J. Catal. 1981, 71,270-277.
Received for review February 26, 1990 Accepted May 16, 1990
Kinetics of the Diazo Coupling between l-Naphthol and Diazotized Sulfanilic Acid John
R.Bourne, Oemer M.K u t , J o a c h i m Lenzner,* and H o r s t
Maire
Technisch-Chemisches Laboratorium, E T H , CH-8092 Zurich, Switzerland
In previous publications, the diazo coupling of l-naphthol with diazotized sulfanilic acid was described by a two-reaction scheme. Primary coupling in the ortho position was neglected. The ratio of reactivities in the para and ortho positions is, however, only about 12. A four-reaction scheme gives a more accurate description of these couplings. The four rate constants have been determined by the stopped-flow method under standard conditions (25 O C , p H = 9.9, I = 444.4 m ~ l - m - ~ Spec). trophotometric and HPLC methods have been used to analyze product mixtures. Extinction coefficients for the two monoazo dyes and the bisazo dye are tabulated under the above conditions. Differences of up to 8.5% for the bisazo dye exist relative to our earlier (1985) publication. In the range of product distributions up to Xs= 0.15, the new spectrophotometric analytical method leads to somewhat higher Xs values.
1. Introduction The diazo coupling of l-naphthol with diazotized sulfanilic acid in alkaline solution at room temperature has been in use for some years as a test reaction to investigate the micromixing in various reactors (Bourne et al., 1981). The product distribution between mono- and bisazo dyes is sensitive to mixing and can be used to determine the rate of turbulent energy dissipation in the reaction zone. The couplings have previously been represented by a simplified two-reaction scheme: kl
A+B-R
(1)
k2
R+B-S
(2)
* Author, to whom correspondence should be addressed. Present address: Department of Chemical Engineering, Swiss Federal Institute of Technology Ziirich, Univenitiitsstr. 6, CH-8092 Zurich, Switzerland. 0888-5885/ 9012629- 1761$02.50/ 0
whereby in reaction 1only coupling in the para or 4 position of l-naphthol was considered. The extinction coefficients and rate constants are available (Bourne et al., 1985). Spectrophotometric determination of the concentrations of the two reaction products, cR and cs, required extinction measurements at several (e.g., 6-20) wavelengths in the range 400-640 nm and a two-parameter regression, based on E(X) = dcR(X)cR + dts(X)cs
(3)
The product distribution, after the limiting reagent (diazotized sulfanilic acid) had been fully consumed, was expressed by Xs’, which is the fraction of this reagent reacting to bisazo dye:
XS’ = 2cS/(cR + 2cS)
(4)
Representation of these couplings by the two-reaction scheme ignores primary coupling in the ortho or 2 position 0 1990 American Chemical Society
1762 Ind. Eng. Chem. Res., Vol. 29, No. 9, 1990
o-R
0
B
A
.o;
Figure 1. Diazo coupling reactions between l-naphthol and diazotized sulfanilic acid.
followed by secondary coupling in the para or 4 position of l-naphthol (Figure 1)and is not in agreement with the following observations. (a) Thin-layer chromatography indicates a few percent of the monoazo dye coupled in the ortho position (Bourne et al., 1985). (b) With reactors having high rates of energy dissipation and values of Xs'below 0.1, the two-component analytical method gives too low values of Xs',sometimes even negative ones (Studer, 1989). (c) By using l-naphthol and diazotized sulfanilic acid as starting materials in measurements of k2,values of k2 exceeded those starting from purified R (coupled in the para position) and B (Bourne et al., 1985). The reason, correctly given at that time, is that o-R reacts faster than p-R to S. Taking advantage of recent advances in instrumental analysis, it is the objective of this paper to drop the assumption that the concentration of R coupled in the ortho position is negligible. The four-reaction scheme, given in Figure 1, will be used to represent the reactions. Extinction coefficients for R coupled in the ortho and in the para position as well as for the bisazo dye will be tabulated. The rate constants of all four reactions in Figure 1will be given. These new analytical and kinetic data are essential to support more precise micromixing studies. 2. Experimental Section 2.1. Preparation of Dyes. 2.1.1. 4-[(4-Sulfophenyl)azo]-l-naphthol (p-R). Sulfanilic acid (Fluka 86090) was diazotized and 0.1 mol was added dropwise at room temperature to 0.1 mol of l-naphthol (Fluka 70440) dissolved in 150 mL of ethanol. The dark-brown solution was left for 2 h, heated up to 60 "C, and finally cooled over
4 h to room temperature. The dark-green precipitate was filtered, rinsed with acetone, and recrystallized three times from 50% aqueous ethanol (Slotta and Franke, 1931; Belevi et al., 1981). 2.1.2. 2 4 (4-Sulfophenyl)azo]-l-naphthol(O-R). Naphthoquinone (Fluka 70360) (0.1 mol) was dispersed in 160 g of glacial acetic acid at room temperature and then poured into a suspension of phenylhydrazine-p-sulfonic acid (TCI H 0176) in 150 mL of water. After stirring for 24 h, the partly precipitated dye was dissolved in a little water and separated from unconverted reagents by filtration. The dye was precipitated by adding sodium chloride and then was recrystallized three times from warm water (Grandmougin and Noelting, 1891). 2.1.3. 2,4-Bis[(4-sulfophenyl)azo]-l-naphthol(S). This dye could not be isolated as a stable, pure crystalline solid. It was prepared in solution by adding diazotized sulfanilic acid to a purified o-R solution at low concentrations to avoid decomposition reactions (Bourne et al., 1985). Further details are given later. 2.2. Identification of Dyes. The monoazo dyes were identified by thin-layer chromatography, 'H NMR, elementary analysis, spectrophotometry (UV and vis), highperformance liquid chromatography (HPLC), and atomic absorption spectrometry. Their purities exceeded 99.5%. p-R was in the form of the free acid with a molar mass of 328.35 g, whereas o-R was formed as its monosodium salt, having a molar mass of 350.33 g. Bisazo dye was characterized by using thin-layer chromatography, HPLC, and UV/vis spectrophotometry. Excellent agreement for Rfvalues and the identical form of the absorption spectra compared to earlier investigations were obtained (Belevi et al., 1981; Bourne et al., 1981, 1985). 2.3. Stability of Dyes. The monoazo dyes have been kept unchanged for many months in a drying oven (45 "C, 100 mbar) and in brown glass bottles. In neutral solution (approximately 0.5 mol~m-~) after 2-3 months o-R showed no additional peaks in a high-performance liquid chromatogram, whereas several small peaks appeared with p-R, indicating its partial decomposition. Bisazo dye solutions have much lower stability. Those having concentrations near 3 m o l ~ m were - ~ stable for 1-2 h, whereas with concentrations for the spectrophotometric analysis (near 0.035 m~lem-~) they can be kept for 4-5 h. 3. Analysis 3.1. Spectrophotometric Analysis. A diode array spectrophotometer (Hewlett-Packard 8452A with Workstation 9153C) was used to cover the UV/vis range of wavelengths from 190 to 800 nm (2-nm steps) in a single measurement. The HP software allowed the measurement and storage of calibration spectra, the subtraction of spectra, the calculation from the calibration spectra of the spectrum of an arbitrary mixture, etc. The analysis of the composition of a solution containing known dyes was made by a standard, multiparameter linear regression (based on the extension of eq 3 for any number of dyes) using 156 stored absorptions in the range of wavelengths from 390 to 700 nm. A standard set of conditions was defined as 25 "C and 111.1 m ~ l . m -each ~ of sodium carbonate and sodium bicarbonate, giving an ionic strength of 444.4 m ~ l . m -and ~ a pH of 9.9. As explained later, a few analyses were made at pH = 1.2 to obtain better resolution of isomers (o-R and p-R). This solution was prepared from 100 mL of alkaline dye solution by adding 33.3 mL of 1 N HC1 and making up to 200 mL with KCl/HCl buffer (pH = 0.95, I = 200 m01.m-3).
Ind. Eng. Chem. Res., Vol. 29, No. 9, 1990 1763 Tnble I. Molar Extinction Coefficients of the Three Dyesa A, nm e@-R), m2.mol-' 40-R), m2.mol-' c(S), m2.mol-' 390 400 410 420 430 440 450 460 470 480 490 500 510 520 530 540 550 560 570 580 590 600 610 620 630 640 650 660 670 680 690 700 0
277.6 411.2 588.7 794.2 1009.6 1227.8 1456.9 1717.1 2025.7 2382.1 2728.4 3009.6 3158.5 3140.3 2959.1 2618.4 2133.5 1583.6 1057.6 609.6 302.7 130.2 54.1 23.2 11.6 7.9 4.7 4.4 4.1 2.5 2.2 1.6
400.6 395.5 463.6 576.6 722.5 901.8 1110.6 1345.8 1611.5 1892.3 2140.4 2317.9 2381.6 2308.0 2108.3 1809.4 1431.3 1018.4 638.6 343.8 166.1 74.8 35.3 15.7 8.7 6.6 4.2 4.2 4.4 2.7 2.8 2.1
654.7 761.3 972.2 1246.9 1544.1 1830.4 2074.9 2245.5 2318.7 2311.7 2246.2 2157.5 2116.9 2175.0 2311.4 2467.4 2590.4 2647.4 2618.8 2486.1 2259.7 1964.2 1618.4 1265.7 936.1 652.1 428.7 271.9 161.2 89.1 48.9 28.3
wavelength
Figure 2. Comparison between cs values obtained in this work and cs values of earlier publications. Bourne et al. (1981); Bourne et al. (1985); (--) this work. (-e-)
3500
1
(e-.)
n
2 5 0 3 5 0 4 5 0 5 5 0 6 5 0 7 5 0
T = 25 oc, I = 444.4 m01.m-3, PH = 9.9.
wavelength
3.1.1. Calibration Spectra. Solutions having concentrations of the individual purified monoazo dyes in the range 0.02-0.04 m ~ l - m -(buffered ~ to pH = 9.9, 444.4 m~l-m-~ were ) scanned a t 25 "C and their extinction coefficients determined and stored. Extinction coefficients a t a given wavelength but for different solutions differed by a few parts per thousand. Average values were stored in the spectrophotometer to give the calibration spectra. It was noted that the ionic strength had a significant effect on the absorption and that it was therefore essential to maintain the standard conditions. Table I reports extinction coefficients for the two monoazo dyes. Bisazo dye could not be isolated but was prepared by diazo coupling as outlined earlier. This procedure is associated with at least two risks (Dreher et al., 1981). The diazonium ion, which is more stable in acidic solution, can react with the huge excess of hydroxyl ions in the alkaline-buffered 1-naphthol solution, giving (via the diazo hydroxide) the diazotate form. Reagent B can thus be converted into a form that is very inactive in diazo coupling. Further, the higher the yield of S becomes, the greater is the risk of its reaction with freshly added diazonium ions. This leads to a loss of S and the formation of unstable products (diazo ether, radicals, etc.). The earlier assumption that S can be formed by coupling from A (Bourne et al., 1985) or p-R with 100% yield (Bourne et al., 1981) is now thought to be unjustified. The yield was almost certainly less than 100%. The strategy in the present work was therefore (a) to prepare S in solution from o-R, which (as shown in detail later) couples much faster than p R , and (b) to restrict the conversion of o-R to less than loo%, which requires subtraction of the absorption of the unconverted o-R from the measured absorption to give that due to S. Due to advances in spectrophotometry, these calculations could be easily programmed. By varying the stoi-
[nml
[nm]
Figure 3. New molar extinction coefficients for all three dyes and also for 1-naphtholat pH 9.9, I = 444.4 mol~m-~, and T = 25 O C . (-) p-R; o-R; (-.-) S; ( - - - ) 1-naphthol. (..a)
chiometric ratio of B to o-R, conversions of some 20%, 45%,6090, and 75% o-R were obtained. The calculated extinction coefficients attributed to S differed only by a few parts per thousand, despite widely different yields. They are given in Table I as the values for S. Figure 2 summarizes the new values of es (from Table I), comparing them with those found by assuming 100% yield of S in solution (Bourne et al., 1981) as well as those obtained by isolating by thick-layer chromatography (Bourne et al., 1985) a small quantity of S having an unknown purity. The difference between the 1985 and the new values suggests no increase in purity (both curves have the same form) but an earlier inaccuracy in isolating and weighing the purified solid S. The maximum difference between these two sets of eS values is 8.5%. Figure 3 presents the new extinction coefficients (from Table I) for all three dyes and also for 1-naphthol. The maximum value for 1-naphthol was 586.7 m2.mol-' at 332 nm (under standard conditions), which can be used to check the concentration of the A-reagent solutions before reaction. The strong overlap of the absorption spectra of o-R and p-R is considered in detail later. 3.2. Analysis with HPLC. Samples containing an unknown mixture of dyes, reagents, and byproducts, having ionic strengths below 80 m o l ~ m and - ~ dye concentrations of around 0.4 m ~ l . m - were ~ , analyzed by HPLC (Hewlett-Packard 1090 M). The stationary phase was ODS-Hypersil C18 (column NC-04, 250 X 4 mm from Innovativ Bischoff, Wallisellen, Switzerland). The mobile phase was a variable mixture of double-distilled water (solvent A) and acetonitrile (solvent B), each containing
1764 Ind. Eng. Chem. Res., Vol. 29, No. 9, 1990 Table 11. Gradients for HPLC Analysis
start separation cleaning of column start
time, min 0.0 1.0 13.0 15.0 17.0 18.0
solvent A, 90 75.0 60.0 58.0 30.0 30.0 75.0
solvent B, 70 25.0 40.0 42.0 70.0 70.0 25.0
2 g/L TBAB (tetra-n-butylammonium bromide from Serva 35853). The gradients are given in Table 11. The flow and pressure drop were 1.2 mL/min and 200 bar at 40 "C. The injected volume was 20 pL. Each substance was detected at that wavelength for which its extinction coefficient was independent of pH. These values were p-R 493 nm; o-R 480 nm; S 524 nm, and A (l-naphthol) 303 nm. The retention time of l-naphthol was 7 min; the retention times of the dyes were p-R 5.7 min, o-R 12.1 min, and S 10.9 min. A direct proportionality was found between the peak area (in counts) a t the selected wavelength and the dye concentration.
Table 111. Comparison between the Two Spectrophotometric Methods method P-R, m ~ l - m - ~o-R, m ~ l - m - ~ S. m ~ l - m - ~ XP old 0.033 3 0.000 4452 0.0264 0.030 95 0.003 144 0.000 731 0.0412 new ~
3500
~~~
I
350
400
450
500 550 600 650 700
wavelength [ n mI Figure 4. Molar extinction coefficients for all three dyes at pH 1.2, I = 280 m o l ~ m -and ~ , T = 25 "C. (--) p-R; o-R; (---) S. (a*.)
4. Kinetic Measurements Reaction kinetics were determined with the help of a specially designed stopped-flow apparatus in the group of Prof. P. L. Luisi, Institute of Polymers, ETH Ziirich. This is equipped with a signal memory recorder, allowing 512 measurements with a minimum time step of 2 ps to be carried out and stored. Sixty microliters of each of the two reagent solutions was driven through the mixing head into an observation chamber, having a capacity of 34 pL. The light path was 10 mm, and the wavelengths could be selected in the range 230-800 nm. A tungsten lamp (75 w) was the light source. By using a driving pressure of 1.7 bar, the mixing time in the mixing head did not exceed 0.2 ms. Standard conditions were again 25 "C , I = 444.4 m ~ l a m -and ~ , pH = 9.9. To investigate the primary couplings, the following reagent concentrations were employed: l-naphthol 0.018-0.02 m o l ~ m -and ~ diazotized sulfanilic acid 5.54 X 10-3-8.88 X mol.m+. The partial reaction orders were taken to be one (Bourne et al., 1985). Absorptions at 500 and 510 nm were recorded as functions of time. For the secondary couplings, which were measured in turn, the concentrations of purified monoazo dye and diazonium salt were 0.09 and 0.068 m ~ l - m -respectively. ~, Absorptions were measured as functions of time a t eight wavelengths in the range 595-630 nm (in steps of 5 nm). The partial reaction orders were set equal to one (Bourne et al., 1985). The primary coupling formed the monoazo dyes (o-R and p-R) simultaneously. The rate constants of the primary coupling reactions could not be determined individually. Therefore, a total rate constant (klo + kip) was calculated from the kinetic runs. According to the selectivity (c,R/c,,-R) determined in this work (analysis at pH 1.2; HPLC) the total rate constant could be divided into the desired individual primary rate constants. 5. Results 5.1. Spectrophotometric Analysis. The definition of the product distribution, eq 4, was extended to include
both monoazo dyes, giving XS = 2cS/(co.R + C p . R + 2cS) (5) Accounting for o-R and improving the extinction coefficient for S raised the accuracy of the spectrophotometric analysis of product mixtures up to X s values of about 0.15.
Table I11 gives an example of the analysis of a solution. "Old" refers to the extinction coefficients from 1985 (the basis of which was the two-reaction scheme), whereas %ew" refers to the values in Table I (four-reaction scheme). Xs according to the old method was too low. An extensive evaluation of the former two-component analysis (Bourne et al., 1985) and the present three-component one, which has applied both methods to some 100 samples, having 0.01 < Xs < 0.25, was carried out (Lips, 1989). With XS> 0.15, both methods gave the same result within the experimental limits (i0.005 in Xs)of spectrophotometric analysis. The old and new methods may be applied provided X s < 0.4. With Xs < 0.15, the following empirical correlation between the 1985 and the present methods was obtained: Xs = 0.884Xs' 0.0203 (6) As in Table 111, this shows that the old method underestimated Xswhen X s C 0.15. This has been confirmed by independent HPLC measurements (Studer, 1989). The new three-component spectrophotometric analysis a t pH 9.9 has been found to give inadequate resolution between the monoazo isomers because of their overlapping spectra (Figure 3). In a few cases, negative values were obtained for o-R. It was found, however, that the sum of the concentrations of o-R and p-R was correctly determined. This sum has also been verified by HPLC and by spectrophotometry at pH 1.2 (Figure 4). No corresponding difficulty was noted in determining Xs,since this requires only the sum of the isomer concentrations-refer to eq 5. 5.2. Rate Constants. At 25 "C, I = 444.4 mol.mg, and pH = 9.9, the following second-order rate constants and their standard deviations [m3.mol-'.s-'] were obtained: kl, = 921 f 31, k1, = 12 238 f 446, k2, = 22.25 f 0.25, k2, = 1.835 f 0.018. The activation energy of 12% was previously found to be 3.874 X lo4J-mol-' (Bourne et al., 1985), and the same value is recommended for k, in the range 293-303 K. The previous value of the activation energy for the primary couplings, 3.05 X lo4 J-mol-' (Bourne et al., 1985) refers to 7% coupling in the ortho position and 93% in the para. Again over the small range of temperatures 293-303 K, it seems reasonable to use this activation energy for k l , and kip. The composite value kl was previously given as 11300 m3.mol-'-s-' a t 293 K, pH = 10.0, and I = 40 mol~m-~.
+
Ind. Eng. Chem. Res., Vol. 29, No. 9, 1990 1765 Calculating 0.07kl, + 0.93kl, gives kl = 11500 m3-mol-'-s-' The earlier at 298 K, pH = 9.9, and I = 444.4 m~lam-~. result (Bourne et al., 1985) was measured at the optimum pH for maximum reaction rate but was less accurate than the new value, because there was evidence of prereaction in the former stopped-flow apparatus; i.e., mixing was too slow for such a fast reaction. The new composite value agrees well with recent measurements using another technique (Andrigo et al., 1988). At 298 K, pH = 10.0, and I = 40 mol~m-~, kzo was previously found to be 1.7 m3* mol-'&. The new value (1.84 m3.mol-'.s-') refers to pH = 9.9, I = 444.4 m ~ l - m -and ~ , 298 K and was obtained by using the t S values in Table I. 6. Conclusions The diazo coupling of l-naphthol with diazotized sulfanilic acid proceeds first by two parallel primary reactions to give monoazo dyes coupled in the ortho and para positions and then by the corresponding secondary reactions, taking place at the para and ortho positions of the corresponding monoazo dye, to give the bisazo dye. Under well-mixed conditions, the ortho monoazo dye amounts to 7 % of the products and is not negligible. (This result was established by HPLC and UV/vis spectrophotometry at pH 1.2.) The four second-order rate constants were measured in a stopped-flow apparatus under standard conditions (25 OC, pH = 9.9, and I = 444.4 m ~ l . m - ~ ) . Values at other temperatures in the range 293-303 K can be calculated from the activation energies. After synthesizing and purifying the two monoazo dyes, their extinction coefficients were measured under standard conditions. Those of the bisazo dye, which was prepared in various yields in solution, were up to 8.5% higher than our previously published values (Figure 2). The extinction coefficients for the monoazo isomers and the bisazo dye under the standard conditions are given in Table I and Figure 3. Those in acid solution (pH = 1.2) are in Figure 4. Spectrophotometric analysis of the alkaline-buffered dye solutions to determine Xsis possible, provided Xsdoes not exceed approximately 0.4. The concentrations of the two monoazo isomers cannot be determined accurately under the standard conditions because of overlapping absorption spectra (Figure 3), although their sum can be found. Values of Xs,defined in eq 5 for the new threecomponent analysis, exceed those defined in eq 4 for the old two-component analysis when Xs is less than approximately 0.15. Equation 6 is an empirical correlation between the old and new analyses. Acknowledgment We thank the following colleagues a t ETH: Prof. H. Zollinger for many discussion on dyestuff chemistry, Prof.
P. L. Luisi and K. Zeman for the use of their stopped-flow machine, S. Petrozzi for his help with HPLC measurements, and M. Lips for the results in eq 6. Nomenclature A = l-naphthol B = diazotized sulfanilic acid c = concentration d = light path E = extinction I = ionic strength k = rate constant k , = rate constant in two-reaction scheme (eq 1) k 2 = rate constant in two-reaction scheme (eq 2) o-R = 2-[(4-sulfophenyl)azo]-l-naphthol p-R = 4-[ (4-sulfophenyl)azo]- l-naphthol R = "old" definition for monoazo dye (p-R) S = 2,4-bis[(4-sulfophenyl)azo]-l-naphthol X s = product distribution, eq 5 Xs' = product distribution, eq 4 Greek L e t t e r s t
= molar extinction coefficient
X = wavelength
Subscripts o-R = 2-[ (4-sulfophenyl)azo]-l-naphthol
p-R = 4-[(4-sulfophenyl)azo]-l-naphthol S = 2,4-bis[(4-sulfophenyl)azo]-l-naphthol l o = describes reaction from A to o-R lp = describes reaction from A to p-R 20 = describes reaction from p-R to S 2p = describes reaction from o-R to S
Literature Cited Andrigo, P.; Bagatin, R.; Cavalieri d'Oro, P.; Perego, C.; Raimondi, L. Micromixing in a chemical quenching apparatus for fast kinetics. Chem. Eng. Sci. 1988, 43, 1923. Belevi, H.; Bourne, J. R.; Rys, P. Chemical selectivities disguised by mass diffusion. Helu. Chim. Acta 1981, 64, 1618. Bourne, J.R.; Kozicki, F.; Rys, P. Mixing and fast chemical reaction, part 1. Chem. Eng. Sci. 1981, 36, 1643. Bourne, J. R.; Hilber, C.; Tovstiga, G. Kinetics of azo coupling reactions between I-naphthol and diazotized sulfanilic acid. Chem. Eng. Commun. 1985, 37, 293. Dreher, E. L.; Niederer, P.; Rieker, A,; Schwarz, W.; Zollinger, H. Dediazonations of arenediazoniumions in homogeneous solution, part XIV. Helu. Chim. Acta,,1981,64, 488. Grandmougin, E.; Noelting, E. Uber einige Orthoazoverbindungen des a-Naphthol. Chem. Ber. 1891, 24, 1594. Lips, M. Private communication, ETH Zurich, Dec 1989. Slotta, K. H.; Franke, W. Zur Konstitution der Azo-Indikatoren. Ber. 1931, 64, 86. Studer, M. Ph.D. Thesis 9037, ETH Zurich, 1989.
Receiued for reuiew February 12, 1990 Reuised manuscript received May 22, 1990 Accepted June 8, 1990
