Concentrated H2SO4 Solutions Research Articles

Synthesis of derivatives of new heterocyclic system 5,7-dioxo(4h,6h)-1,3-dithiolo[4,5-d]pyrimidine on the basis of barbituric acid

The 5-phenyliodonium betaine of barbituric acid reacts with sodium diethyldithiocarbamate to form 5-(diethylaminothiocarbonylthio)barbituric acid, which is cyclized in concentrated H2SO4 solution to form the cation of 5,7-dioxo(4H,6H)-1,3-dithiolo[4,5-d]pyrimidine, isolated in the form of the perchlorate and the chloride. These salts are split by sodium sulflde or selenide, forming 5-[diethylaminothio (seleno)carbonylthio]-4-thiobarbituric acids, which are cyclized by the action of concentrated HCl in an organic solvent to form 5,7-dioxo(4H,6H)-1,3-dithiolo[4,5-d]pyrimidinethione (selenone)-2. The thione and the selenone, as NH acids, form salts; alkylation of the tetrabutylammonium salt affords N(4)-alkyl and N,N′-dialkyl derivatives. The compounds that were obtained have been characterized by IR and PMR spectra.

Mn基合金の機械的性質と耐食性

The mechanical properties and corrosion resistance of manganese-base alloys cold-rolled in concentrated and 10% HCl, HNO3, H2SO4, HF and H3PO4, and other acidic solutions were examined.The maximum tensile strength of 1370 MPa was obtained by the cold-rolled Mn-Cu-C alloys. The strength of the Mn-Cr-Ni-Cu alloys showed an intermediate value, that of the Mn-Cu aloys giving a minimum value. The alloys cold-rolled after heating at 1173 K showed embrittlement. Such embrittlement, however, was prevented in most cases by a presolution-treatment prior to heating at lower temperatures. Addition of copper or nickel or both showed a tendency to suppress the embrittlement or to depress the temperature at which the embrittlement would occur.In the corrosion test, the chromium element was effective for the attack of acidic solutions, in particular for that of nitric solutions; nickel and copper elements were corrosion resistant for reducing solutions. Most of the manganese-base alloys formed corrosion resisting films in the concentrated H2SO4 solution.

A chemically regenerative redox fuel cell. II

Our previous paper [1] has described an unconventional chemically regenerative redox fuel cell, including a modest amount of performance data, and has pointed out a number of problem areas. This paper describes additional work and some attempts that have been made to improve the cell performance in several of the problem areas described in the first paper. Two different redox fuel cell systems employing the V2+/V3+ and Mo3+Mo4+ redox couples as the anolyte, and a new NO 3 −/NO catalyst system for VO2+ oxidation were explored and described. The reduction of Na2MoO4 to Mo4+ and Mo3+ by H2 in concentrated H2SO4 solution was studied in small scale laboratory experiments and discussed. The performance of a redox cell in which H2 was obtained from the Pd-catalysed decomposition of formic acid, HCOOH, is described and the results of experiments with different membranes are reported. The results of experiments using WC as a hydrogenation catalyst at a temperature of 70–90° C with mixed molybdo-tungsto-silicic acids are reported and discussed.

Hydrolysis of trioxaadamantane ortho esters. I. Dialkoxycarbocation – ortho ester equilibrium and acidity function

3-Aryl-2,4,10-trioxaadamantane ortho esters (T) undergo a rapid equilibration with a ring-opened dioxan-2-ylium ion (DH+) prior to hydrolysis to product (a 1,3,5-cyclohexanetriol monobenzoate). The cation is stable in concentrated H2SO4 solutions where it has been characterized by nmr spectroscopy. It is observed using uv spectroscopy in dilute acids, and the ratio [DH+]/[T] at equilibrium has been measured as a function of acidity. Reversibility of the ring opening is established by the pattern of plots of cation absorbance versus acid concentration and by the observation that solutions containing cation on neutralization or dilution yield ortho ester, not hydrolysis product. Equilibrium constants for the reaction [Formula: see text] have been measured by obtaining the acidity function HT for this system. The effects of the aromatic substituent and the steepness of the acidity function plot versus acid concentration are interpreted in terms of a strong intramolecular interaction in the cation between the cationic center and the hydroxyl oxygen.

Investigation of acid-base interaction in H2SO4-diethyl ether system by means oe MFTIR infrared spectroscopy

1. By means of multiple-frustrated total internal reflection (MFTIR) infrared spectroscopy at 30°C, the equilibrium concentrations have been determined for the components forming the system H2SO4,-Et2O. The species existing in the system consist primarily of addition products with a 1∶1 composition, and also the complexes B·2H2SO4, and 2B·H2SO4. 2. In the region of concentrations close to 100% H2SO4, the complexes are completely dissociated into ions. Dilute solutions of H2SO4, in ether are made up of complexes of the molecular type and contact ion pairs. With an equimolar ratio of components, an equilibrium exists among the molecular complexes, contact ion pairs, and individual ions. 3. It is suggested that current transport in concentrated H2SO4 solutions is accomplished primarily by a hopping mechanism, owing to the presence of complexes B·2H2SO4 with a well-developed tructure of hydrogen bonds. 4. The optical density of continuous absorption has been measured at a frequency of 2000 cm−1, in relation to the composition of the H2SO4,-Et2O system, and molar extinction coefficients have been measured for dilute and concentration solutions of acid: 50 ± 10 and 120 ± 10 liters/mole · cm, respectively.

The partitioning of tetrahedral intermediates of the hydrolysis of benzimidatonium ions in acid solutions

The products (a benzoate ester or an N,N-dimethylbenzamide) have been accurately determined for the hydrolysis of the O-ethyl-N,N-dimethylbenzimidatonium ion (1) and its 4-nitro derivative (2) in dilute and moderately concentrated H2SO4 solutions. In dilute acid the ratio of amide:ester is very small (0.0005–0.001). It is proposed that the ester product arises from the zwitterionic form of the tetrahedral intermediate of the hydrolysis. The small amount of amide is due to an SN2 hydrolysis reaction and to the non-catalyzed breakdown of the neutral form of the tetrahedral intermediate, the relative contributions of the two being unknown. Although ester remains the major product throughout, at some intermediate acid concentration (20% H2SO4 for 1 and 35% H2SO4 for 2) a sharp increase in the amide:ester ratio is observed, followed by a levelling-off. This change is shown to be associated with tetrahedral intermediate partitioning, and not the SN2 reaction. It is argued that the strong acid product ratio represents the breakdown of the tetrahedral intermediate via cationic transition States. Two kinetically equivalent reactions are involved, the breakdown of the N-protonated tetrahedral intermediate producing a protonated ester and amine and the H+-catalyzed breakdown of the neutral tetrahedral intermediate producing a protonated amide and alcohol. Analogous pathways are also observed for the decomposition in acid of the amide acetals ArC(OMe)2NMe2, and the two systems are compared. A similar effect of the aromatic substituent on the partitioning ratio is noted, but the tetrahedral intermediate exhibits a greater tendency for amine expulsion. A kinetic analysis produces the estimate of 1011 s−1 for the rate constant for the breakdown of the zwitterionic form of the tetrahedral intermediate. This very large rate explains why its decomposition remains important even in concentrated acids, where the amount of tetrahedral intermediate which actually exists as zwitterion must be extremely low.

Structure and properties of poly(2,5‐dimethylterephthalamides)

AbstractSix methyl‐substituted wholly aromatic polyamides were synthesized from the reaction of 2,5‐dimethylterephthaloyl chloride with p‐phenylenediamine, its 2,5‐dimethyl and 2‐methyl derivatives, m‐phenylenediamine, or its 2‐methyl and 4‐methyl derivatives by solution polycondensation at low temperature. The x‐ray diffraction diagrams of the polyamides obtained exhibit crystal patterns. Density values range from 1.26 to 1.37 g/cm3. NMR spectra determined in concentrated H2SO4 solution are reported. Poly(2,5‐dimethylterephthalamides) have lower thermal stability than the corresponding polyterephthalamides. The increase in solubility of polyamide by the introduction of the 2,5‐dimethylterephthaloyl linkage is accompanied by a decrease in thermal stability. The effect of methyl substituents on thermal properties and solubility is discussed in terms of the packing of polymeric molecules and the extent of hydrogen bonding of the amide groups.

Study of the adsorption of chloride ions on platinum electrodes from concentrated solutions of H2SO4, H3PO4 and HClO4

Study of the adsorption of chloride ions on platinum electrodes from concentrated solutions of H2SO4, H3PO4 and HClO4

The solubilities of Fe, Ni, V and Na salts in concentrated aqueous H2SO4 solutions at temperatures between 400 and 460 K

When residual fuel oil, which contains up to 4 wt% S, is burned in boiler plant, H2SO4 is formed which condenses as aqueous solutions (65–90 wt% H2SO4) on surfaces in the cool back-end. The oil contains traces of other elements, in particular Na, V, Fe and Ni, which also deposit on these surfaces as either sulphates (Na, Fe, Ni,) or oxides (V). When designing techniques to control acid deposition and the corrosion which it subsequently causes, account must be taken of the degree to which the acid properties can be modified by taking these compounds into solution. A series of measurements of the solubilities of relevant compounds in acid solutions within the appropriate ranges of concentration and temperature (400–460 K) have been made. Sodium sulphate has by far the highest solubility (55 wt% in a solution originally containing 85 wt% H2SO4 at 423 K). Of the other compounds considered, only V2O5 exhibits a solubility of more than 2 wt%; for example, at 463 K, in 75 wt% H2SO4, solutions containing up to 16 wt% V2O5 can be formed. Solutions with up to 23 wt% V2O5 can be stabilised by the presence in solution of small amounts (∼0.5 wt%) of Fe3+ ions. The structure of these solutions is discussed.

Nuclear magnetic resonance study of the ionization kinetics of tri-phenylmethanols in concentrated acid solutions

The n.m.r. line shape method is used to determine the rate constants for the appearance and disappearance of substituted triphenylmethyl ions in concentrated H2SO4 and HClO4 solutions. The ionization reaction of tris-(4-methylphenyl)methanol is studied in 60%(w/w) dioxan–water solutions and that of tris-(4-methyl-3-sulphophenyl)methanol in water. From the closer correlation of log kf(for ion formation) with H0 than with HR, it is concluded that the transition state approximates much more closely to a protonated alcohol than to the carbonium ion structure. Further evidence for a special interaction between perchlorate and triphenylmethyl ions is also provided by the n.m.r. chemical shifts observed in solutions of tris-(4-methylphenyl) and triphenymethyl carbonium ions in mixtures of 98% H2SO4 with 70% HClO4. The shifts observed are concordant with those calculated from Buckingham's equation when the perchlorate ion is assumed to be ca. 6 A from the charged carbon atom.

The hydrolysis of amides, esters, and related compounds in acid solution. Part IV. Phenyl chloroformate and the 1-(methoxycarbonyl)-imidazolium and -pyridinium ions

The kinetics of hydrolysis of these three substrates in moderately concentrated solutions of H2SO4, HClO4, and HCl has been studied. None of these reactions is acid catalysed. Medium effects are compared with those found in similar but acid-catalysed reactions. The reactivity of the cations, which serve as models for N-protonated carbamates, are compared with those of similar models for N-protonated amides, and in the light of the comparison the mechanism of hydrolysis of protonated carbamates is discussed.