H2SO4 Mixtures Research Articles

Amperometric sulfur dioxide gas sensor with dimethyl sulfoxide as solvent for internal electrolyte solution

An amperometric sensor for atmospheric sulfur dioxide based on a classical three-electrode cell configuration equipped with a microporous Teflon membrane is presented. The measured current, directly associated with oxidation of SO2 on a gold electrode, is related to the SO2 level. Various electrolyte solutions, including aqueous H2SO4, HClO4, HClO4–H2SO4 mixtures and Li2SO4 and also solutions of H2SO4 and HClO4 in dimethyl sulfoxide (DMSO)–water solvent mixture, were tested. The high sensitivity, up to 45 nA ppm–1 (0.9 µA cm–2 ppm–1) SO2, was achieved when the sensor was filled with 5 M H2SO4 in DMSO–H2O with an H2O:DMSO mole ratio of 2. The respective value for standard 5 M H2SO4 electrolyte solution was only 0.5 nA ppm–1 SO2. The high sensitivity and advantages resulting from the use of an organic solvent (DMSO) are discussed.

Millimeter wave spectroscopic measurements over the South Pole: 3. The behavior of stratospheric nitric acid through polar fall, winter, and spring

We present data from a 9‐month series of ground‐based measurements of stratospheric nitric acid, made over the South Pole from mid‐April 1993 to mid‐January 1994. Observations were typically made at 3‐ to 6‐day intervals. Both profiles and column densities have been retrieved from pressure‐broadened millimeter‐wave emission spectra. These measurements provide the first quasi‐continuous series of vertical mixing ratio profiles for this species in the heart of the south polar votex. Conversion of NOx to nitric acid by heterogeneous reactions, and its incorporation into polar stratospheric cloud (PSC) particles, along with subsequent gravitational settling, is considered to be the main denitrifying mechanism in the Antarctic stratosphere, setting up conditions for ozone destruction at the end of winter. In our observations, a small increase in HNO3 was seen between April and the end of May, after which a rapid loss took place below 25 km. Column density above ∼15 km decreased to ≤1/4 its maximum within 30 days, and depletion continued until middle to late July, by which time the nitric acid column above 15 km had diminished by more than a factor of 10. The initial depletion was coincident with the onset of a rapid increase in lidar backscatter from polar stratospheric cloud formation at the same altitude range. Gas‐phase depletion was tracked as a function of altitude and temperature and found to be consistent with the temperature and partial pressure relationship for formation of ternary mixtures of HNO3, H2SO4, and H2O. Depletion occurred ∼3 weeks earlier in 1993 than was seen in 1992 column density measurements by Van Allen et al. [1995]. In late June a new layer of HNO3 was generated in the vicinity of 40‐km altitude and, subsequently, appeared to be carried downward with general vertical transport of air within the vortex. In spring, as temperatures increased, no rapid increase of gas‐phase HNO3 was seen, indicating that gravitational settling had carried PSC‐accreted nitric acid to low altitudes. By the end of observations in January 1994, mixing ratios and column densities above ∼15 km had not yet reached more than about half the values seen the previous April, indicating that a rather large increase in stratospheric HNO3 occurs in the early austral fall over the south polar region.

Effects of the Absorption of Artificial Acidic Solutions on the Root Systems of Japanese Red Cedar (Cryptomeria japonica D. Don) Cuttings and Saplings

The effects of the absorption of artificial acidic solutions only from below-ground parts on root systems were examined for 60 days in summer and 72 days in fall using cuttings and saplings of Japanese red cedar (Cryptomeria japonica D. Don). Cuttings and saplings absorbed the solutions through the potted soils from the reservoir of an autoirrigator and/or a simplified-autoirrigator. Nitric acid solutions of pH 2.0, 4.0 and 6.0 and distilled water (control) were used in summer, mixtures of H2SO4 and HNO3 solutions of pH 2.0, 3.0 and 4.0, HNO3 solution of pH 3.0, H2SO4 solution of pH 3.0 and distilled water (control) were used in fall. Although no detrimental effects of acidic solutions on saplings were observed, the rooting rate of cuttings treated at pH 2.0 in summer was significantly lower than that of the control. Root lengths and root dry weight per cutting at pH 2.0 in summer and fall were smaller than those of the control, and the difference in fall was significant. The present study revealed that the acidic treatment only from below-ground parts had detrimental effects on the root systems of cuttings, suggesting the importance of quantification of the effects on below-ground parts, as well as on above-ground parts, to evaluate the effects of acidic precipitation on trees.

Electrolytic Conductivities and Mixing Coefficients of the Aqueous HCl−H2SO4 System

The coefficients of the conductivity theory for the multicomponent system of Onsager−Fuoss−Kim−Chen−Quint−Viallard for aqueous HCl−H2SO4 mixtures have been computed. The experimental results for the mixtures of equal molarity and equal ionic strength of the same system agree well with the theory. The excess conductivity of mixing is calculated. The mixing coefficients of Friedman and of Timmermann are derived. These two sets of coefficients agree with those derived from the excess conductivity of mixing. The extrema of the mixing coefficients as predicted by Friedman are observed.

Osmotic and Activity Coefficients of Aqueous (NH4)2SO4 as a Function of Temperature, and Aqueous (NH4)2SO4−H2SO4 Mixtures at 298.15 K and 323.15 K

Osmotic coefficients of (NH4)2SO4(aq), and aqueous (NH4)2SO4−H2SO4 mixtures at 298.15 K and 323.15 K, and H2SO4(aq) at 323.15 K have been determined by an isopiestic method. Using the Pitzer molality-based thermodynamic model, the measurements are combined with other literature data to obtain osmotic and activity coefficients of, first, (NH4)2SO4(aq) from <273 K to ∼373 K and, second, aqueous (NH4)2SO4−H2SO4 over the entire composition range at 298.15 K.

Anion-exchange behaviour of 12 elements in H2SO4 and HF−H2SO4 medium

Anion-exchange data have been obtained for the elements As, Hf, Mo, Nb, Pa, Re, Sb, Sn, Ta, Tc, W, and Zr in 0.1 to 10M H2SO4 and in HF−H2SO4 mixtures of combination extending from 0.1 to 10M HF and from 0.1 to 10M H2SO4. The distribution ratios for mixed solutions are presented in form of adsorption contour lines.

Acid‐Catalyzed [3,3]‐Sigmatropic Rearrangements of N‐Propargylanilines

AbstractThe acid‐catalyzed rearrangement of N‐(1′,1′‐dimethylprop‐2′‐ynyl)‐, N‐(1′‐methylprop‐2′‐ynyl)‐, and N‐(1′‐arylprop‐2′‐ynyl)‐2,6‐, 2,4,6‐, 2,3,5,6‐, and 2,3,4,5,6‐substituted anilines in mixtures of 1N aqueous H2SO4 and ROH such as EtOH, PrOH, BuOH etc., or in CDCl3 or CCl4 in the presence of 4 to 9 mol‐equiv. trifluoroacetic acid (TFA)has been investigated (cf. Scheme 12‐25 and Tables 6 and 7). The rearrangement of N‐(3′‐X‐1′,1′‐dimethyl‐prop‐2′‐ynyl)‐2,6‐ and 2,4,6‐trimethylanilines (X = Cl, Br, I) in CDCl3/TFA occurs already at 20° with τ1/2 of ca. 1 to 5 h to yield the corresponding 6‐(1‐X‐3′‐methylbuta‐1,2′‐dienyl)‐2,6‐dimethyl‐ or 2,4,6‐trimethylcyclohexa‐2,4‐dien‐1‐iminium ions (cf. Scheme 13 and Footnotes 26 and 34) When the 4 position is not substituted, a consecutive [3,3]‐sigmatropic rearrangement takes place to yield 2,6‐dimethyl‐4‐(3′‐X‐1′,1′‐dimethylprop‐2′‐ynyl)anilines (cf. Footnotes 26 and 34). A comparable behavior is exhibited by N‐(3′‐chloro‐1′‐phenylprop‐2′‐ynyl)‐2,6‐dimethylaniline (45., cf. Table 7). The acid‐catalyzed rearrangement of the anilines with a Cl substituent at C(3′) in 1N aqueous H2SO4/ROH at 85‐95°, in addition, leads to the formation of 7‐chlorotricyclo[3.2.1.02,7]oct‐3‐en‐8‐ones as the result of an intramolecular Diels‐Alder reaction of the primarily formed iminium ions followed by hydrolysis of the iminium function (or vice versa; cf. Schemes 13,23, and 25 as well as Table 7). When there is no X substituent at C(1′) of the iminium‐ion intermediate, a [1,2]‐sigmatropic shift of the allenyl moiety at C(6) occurs in competition to the [3,3]‐sigmatropic rearrangement to yield the corresponding 3‐allenyl‐substituted anilines (cf. Schemes 12,14–18, and 20 as well as Tables 6 and 7). The rearrangement of (−)−(S)‐N‐(1′‐phenylprop‐2′‐ynyl)‐2,6‐dimethylaniline ((−)‐38; cf. Table 7) in a mixture of 1N H2SO4/PrOH at 86° leads to the formation of (−)‐(R)‐3‐(3′‐phenylpropa‐1′,2′‐dienyl)‐2,6‐dimethylaniline ((−)‐91), (+)‐(E)‐ and (−)‐(Z)‐6‐benzylidene‐1,5‐dimethyltricyclo[3.2.1.02′7]oct‐3‐en‐8‐one ((+)‐(E)‐ and (−)‐(Z)‐92, respectively), and (−)‐(S)‐2,6‐dimethyl‐4‐( 1′‐phenylprop‐2′‐ynyl)aniline((−)‐93). Recovered starting material (10%) showed a loss of 18% of its original optical purity. On the other hand, (+)‐(E)‐ and (−)‐(Z)‐92 showed the same optical purity as (minus;)‐38, as expected for intramolecular concerted processes. The CD of (+)‐(E)‐ and (−)‐(Z)‐92 clearly showed that their tricyclic skeletons possess enantiomorphic structures (cf. Fig. 1). Similar results were obtained from the acid‐catalyzed rearrangement of (−)‐(S)‐N‐(3′‐chloro‐1′phenylprop‐2′‐ynyl)‐2,6‐dimethylaniline ((−)‐45; cf. Table 7). The recovered starting material exhibited in this case a loss of 48% of its original optical purity, showing that the Cl substituent favors the heterolytic cleavage of the N–C(1′) bond in (−)‐45. A still higher degree (78%) of loss of optical activity of the starting aniline was observed in the acid‐catalyzed rearrangement of (−)‐(S)‐2,6‐dimethyl‐N‐[1′‐(p‐tolyl)prop‐2′‐ynyl]aniline ((−)‐42; cf. Scheme 25). N‐[1′‐(p‐anisyl)prop‐2‐ynyl]‐2,4,6‐trimethylaniline(43; cf. Scheme 25) underwent no acid‐catalyzed [3,3]‐sigmatropic rearrangement at all. The acid‐catalyzed rearrangement of N‐(1′,1′‐dimethylprop‐2′‐ynyl)aniline (25; cf. Scheme 10) in 1N H2SO4/BuOH at 100° led to no product formation due to the sensitivity of the expected product 53 against the reaction conditions. On the other hand, the acid‐catalyzed rearrangement of the corresponding 3′‐Cl derivative at 130° in aqueous H2SO4 in ethylene glycol led to the formation of 1,2,3,4‐tetrahydro‐2,2‐dimethylquinolin‐4‐on (54; cf. Scheme 10), the hydrolysis product of the expected 4‐chloro‐1,2‐dihydro‐2,2‐dimethylquinoline (56). Similarly, the acid‐catalyzed rearrangement of N‐(3′‐bromo‐1′‐methylprop‐2′‐ynyl)‐2,6‐diisopropylaniline (37; cf. Scheme 21) yielded, by loss of one i‐Pr group, 1,2,3,4‐tetrahydro‐8‐isopropyl‐2‐methylquinolin‐4‐one (59).

Ionization of sulfonic acids and dimethylsulfoxide basicity. A 13C nuclear magnetic resonance and calorimetric study

The ionization of trifluoromethane-, methane-, and benzene-sulfonic acids in Me2SO and in water has been studied by 13C nuclear magnetic resonance. While the protonation shifts of CF3SO3− and CH3SO3− in both solvents are too small to make a quantitative interpretation possible, the C6H5SO3− shift data in H2O–H2SO4 mixtures, when treated by the method of Cox and Yates, gave a pKa value of −2.5 for the ionization of C6H5SO3H. Our results are discussed in relation to those of other workers. Enthalpies of solution and of ionization of these acids and related compounds have been obtained in both solvents. Single ion enthalpies of transfer from water to Me2SO have been calculated from our data and from a transfer value for CF3SO3− (+1.9 kJ mol−1) based on the tetraphenylarsonium–tetraphenylborate extrathermodynamic assumption. The transfers are endothermic processes for the anions CH3SO3− (+29.6 kJ mol−1), C6H5SO3− (+ 20.2 kJ mol−1), and p-CH3C6H4SO3− (+ 21.8 kJ mol−1), and exothermic for H+(−27.4 kJ mol−1). These results are discussed in terms of the properties of the ions and solvents. The transfer value for H+ is a valuable measure of the basicity difference between bulk water and Me2SO. Keywords: sulfonic acids, ionization, dimethylsulfoxide, 13C NMR, calorimetry.

Mirror formation by chemical etching and microcleaving of InP-based lasers

This paper outlines two chemical-etch techniques by which processed laser mirrors can be obtained. These are (i) direct etching and (ii) the etching of bridges or cantilevers that can be "microcleaved" to produce small local mirror surfaces. Both techniques rely on the crystallographic selectivity of chemical etchants.Direct etching of mirrors is accomplished using HCl–HNO3–H3PO4–H2SO4 mixtures. This approach produces smooth surfaces with vertical walls in InP and a slight bevel in the GaInAsP active layers. Lasers made with direct etched mirrors showed threshold currents comparable to normal cleaved mirror lasers.For microcleaving, cantilevers were etched in 1–2% Br2–CH3OH solutions initially in InP wafers. Cantilevers, however, could not be obtained directly on double heterostructure InP–InGaAsP lasers with a ternary (GaInAs) capping layer. Owing to severe sideways etching of the ternary under the SiO2 mask, the negative slopes necessary for cantilever formation never developed. To form laser structures, we had to completely remove the ternary top layer from all areas exposed to the Br2– CH3OH etch solution. Properly formed cantilevers were then obtained.

Soil Cation Leaching by “Acid Rain” with Varying Nitrate‐to‐Sulfate Ratios

AbstractThe influence of the anion composition of simulated “acid rain” on cation leaching of three soils with different surface‐charge properties was examined. Four acid mixtures of H2SO4 and HNO3, all with pH 3.5, but with varying NO3−/SO42− mole ratios of 1.00:0.00, 0.75:0.25, 0.55:0.45, and 0.00:1.00, were used to leach an Ultic‐Alfisol, an Oxisol, and an Entisol. The taxonomic names of these three soils are (i) Cornutt series: fine, mixed, mesic Ultic Haploxeralfs, (ii) unnamed Rhodustox, and (iii) Hanford series: coarse‐loamy, mixed, nonacid, thermic Typic Xerorthents. The Alfisol had a high SO42− adsorption capacity because of its high Fe2O3 content of 12 g kg−1 and high point‐of‐zero charge (PZC) of 6.0. The Oxisol, although strongly weathered, had a lower Fe2O3 content of 5 g kg−1 and PZC of 4.5. The Entisol was a relatively unweathered soil derived from silicaceous alluvium, with even less Fe2O3 of 3 g kg−1 and a lower PZC of 3.5, and represented a soil of fixed charge. Cation leaching of the Alfisol varied directly with the NO3− content of the leaching input due to the higher mobility of NO3− compared with SO42− that was adsorbed. The relative NO3−/SO42− contents of inputs had no effects on cation leaching of the Entisol. Effects on leaching of the Oxisol were intermediate between those of the Alfisol and Entisol. It was clearly demonstrated that the anion composition of “acid rain” plays a significant role in the cation leaching of soils with amphoteric‐charge properties, which are able to adsorb S42−. Some practical implications are also discussed.

Die chemische Hydrolyse von Reisschalen und das Wachstum einer Candida tropicalis‐Kultur auf den Reaktionsprodukten

AbstractThe kinetics of the prehydrolysis of rice hulls where investigated with different concentrations of H2SO4 and temperatures by modified ARRHENIUS–equation in relation to the degradation of pentosans and the formation of reducing sugars. The determination of the activation energy, the frequency‐factor and the orden of reaction in relation to the concentration of the acid results for the formation of the reducing sugars in 60.3 kJ/mol, 5.28 ×. 107 and 1.76, for the degradation of the pentosans in 59‐ and 69.9 kJ/mol, 3.08 × 107 and 6.03 times; 107 as well as 0.76 and 0.85The discontinuous growth of the yeast Candida tropicalis QML 7601, isolated from a biotop in Cuba, on the products of the prehydrolysis of the rice hulls with H2SO4 (0.1‐ and 0.2 N) and different mixtures of H2SO4 and HNO3 yield values of μmax = 0.3 – 0.6 h‐1 in relation to the conditiones.

Time lag in nucleation: A variational treatment of relaxation times in the binary sulfuric acid–water system

A method for evaluating a lower bound to the time required for the establishment of steady state nucleation in binary mixtures of water and sulfuric acid vapors is described. The method is an extension of an earlier approach devised by Reiss and Katz for unary systems, and involves matrix algebra and the Rayleigh–Ritz variation principle. The mathematical development is described at some length. Application to laboratory-type mixtures of H2O and H2 SO4 indicate that times to the steady state may be very long and should seriously impede the measurements of critical supersaturations in both expansion cloud chamber and nozzle experiments.

Separation of europium and thulium from mixed KI−H2SO4 solutions

The extraction of Tm with HDEHP from H2SO4, HCl and HBr is inversely proportional to the third power of the hydrogen ion concentration while the extraction is small with HDEHP, LA-2 and TBP from binary mixtures of acids. The extraction of both Eu and Tm with HDEHP from KI solutions decreases in the presence of small concentrations of H2SO4. The decrease is sharper in case of Eu leading to high separation factors between Eu and Tm from KI−H2SO4 mixtures.

Transient nucleation in H2O–H2SO4 mixtures: A stochastic approach

Transient phenomena in the rate of nucleation are of importance in the interpretation of experimental data on nucleation in the H2SO4–H2O vapor system. Furthermore, fluctuations in the rate of nucleation can actually be measured. In view of these facts, a stochastic approach to the theory of nucleation is developed with eventual application to the H2SO4–H2O system. The central goal of the theory is the evaluation of the distribution of ’’first passage times,’’ for a nucleus, over the relevant free energy barrier. This distribution is calculated from the distribution of a ’’walker’’ on a lattice. However, the distribution of the walker is derived from a ’’master equation,’’ and for this purpose it is demonstrated that walks on lattices and master equations are, in this sense, ’’equivalent’’ even for a lattice which is not translationally invariant. Given the distribution of first passage times, it is possible to compute the transient rate of nucleation, as well as the distribution of fluctuations of the rate about some instantaneous mean. This theory is then applied to the H2SO4–H2O vapor system, and the results indicate that, under many typical experimental conditions, the time to reach the steady state may be quite long (hundreds or thousands of seconds), but that nevertheless, some nucleation should be observed in the laboratory time frame (in agreement with experiment). The character of nucleation as an ’’extreme event’’ is demonstrated by the appearance of a large band gap in the spectrum of relaxation times for the process.

Studies on the extraction behaviour of zirconium from mixed aqueous media with TBP

A systematic study is presented on the extraction of Zr(IV) by tri-n-butylphosphate from H2SO4, HNO3, HCl and HBr solutions as well from binary mixtures of H2SO4 and halogen acids. It has been found that Zr(IV) extraction is appreciably increased by addition of halogen acid to sulphuric acid solutions. On the other hand, the presence of water-miscible alcohols and acetone was found to enhance Zr(IV) extraction from HCl and HNO3 solutions. An investigation of extracted Zr complexes from pure acids and mixed aqueous media enabled an explanation of the observed enhancements. In the light of the obtained results, an extraction mechanism is suggested.

Hydrates in supersaturated binary sulfuric acid-water vapor

Portions of the free energy surface giving the reversible work W required to form a droplet containing n1 molecules of H2O and n2 molecules of H2SO4 from an initially homogeneous vapor have been calculated for a variety of relative humidities and H2SO4 vapor concentrations. These surfaces are displayed as three dimensional perspective plots. The surfaces predict the existence of stable H2SO4 hydrates in the vapor phase, and the number of hydrates, Nh, with h molecules of H2O per hydrate has been calculated for three different values of the relative humidity. The results of these calculations indicate that virtually all the H2SO4 present, especially for relative humidities greater than 100%, exists in hydrate form. As the relative humidity is increased (i.e., greater than 200%), the distribution of hydrate sized agrees well with that found by Giauque et al. for solid H2O–H2SO4 mixtures. Hydrate formation can exert an appreciable effect on the process of vapor phase nucleation in H2O–H2SO4 mixtures, and must be considered in any theory of nucleation rate.

E.m.f. studies of electrolytic dissociation. Part 11.—The bisulphate ion at 25°C

A Pt,H2—AgCl,Ag e.m.f. cell is described whereby accurate measurements may be obtained from additions of stock solutions. Measurements with HCl + H2SO4 mixtures are used to evaluate the dissociation constant of the HSO–4 ion at 25°C. A method of extrapolation is described which aims at reducing uncertainties due to the ion size parameter. Some previous measurements with e.m.f. cells are also re-examined.