Aqueous Strong Acid Research Articles

Salt forms of amides: protonation of acetanilide.

Treating the amide acetanilide (N-phenylacetamide, C8H9NO) with aqueous strong acids allowed the structures of five hemi-protonated salt forms of acetanilide to be elucidated. N-(1-Hydroxyethylidene)anilinium chloride-N-phenylacetamide (1/1), [(C8H9NO)2H][Cl], and the bromide, [(C8H9NO)2H][Br], triiodide, [(C8H9NO)2H][I3], tetrafluoroborate, [(C8H9NO)2H][BF4], and diiodobromide hemi(diiodine), [(C8H9NO)2H][I2Br]·0.5I2, analogues all feature centrosymmetric dimeric units linked by O-H...O hydrogen bonds that extend into one-dimensional hydrogen-bonded chains through N-H...X interactions, where X is the halide atom of the anion. Protonation occurs at the amide O atom and results in systematic lengthening of the C=O bond and a corresponding shortening of the C-N bond. The size of these geometric changes is similar to those found for hemi-protonated paracetamol structures, but less than those in fully protonated paracetamol structures. The bond angles of the amide fragments are also found to change on protonation, but these angular changes are also influenced by conformation, namely, whether the amide group is coplanar with the phenyl ring or twisted out of plane.

Synthesis and structural characterisation of trivalent halidoantimonates and bismuthates of 2-methyl-2-benzoxazole (box): Reactivity and solid-state structural diversity within the [MX(6 – n)] [boxH](3 – n) series (M = Sb or Bi; X = Cl, Br, I; n = 0 or 1)

The structural characterisation (X-ray diffraction) of a series of anionic antimony (III) and bismuth (III) halide complexes containing protonated 2-methyl-1,3-benzoxazole (boxH) countercations are reported. Treatment of aqueous strong acid (HCl or HBr) or strong acid/additional solvent mixtures of box with MX3 (M = Sb, Bi; X = Cl, Br) leads to the isolation of known compounds BiCl5(boxH)2 (6: 33%) and SbBr5(boxH)2 (7: 31%) and the novel material BiBr5(boxH)2 (8: 57%). In the solid state, 6–8 all display an anionic portion consisting of edge sharing infinite zig-zag chains of the metallic [(MX5)2–]∞ units classified as Type A in structure. In contrast, mixtures of box, conc. HCl and SbCl3 yield, following recrystallization, to small quantities of Sb2OCl6(boxH)2 (2: 0.4%); a hitherto unknown complex containing the less common Sb2OCl62− anion. Hypotheses as to the origin of 2 are presented including its formation by hydrolysis of known SbCl4(boxH). Hydroiodic acid solutions of box treated with SbI3 leads to the isolation of the SbI6(boxH)3·(H2O) (9: 42%) which displays a rare example of the isolated SbI63− anion. The treatment BiI3 under similar conditions leads to the precipitation of previously known Bi2I9(boxH)3 (10: 54%) as a major product. Further evaporation of the reaction mixture from which 10 was obtained yields a second minor product, 11 (3%), identified as the Bi analogue of 9: BiI6(boxH)3·(H2O). The species described herein are further discussed in terms of their general coordination properties and relevance to related complexes under current scrutiny for their solid-state materials properties.

Photoelectrochemical oxidation of anions by WO3 in aqueous and nonaqueous electrolytes

The behavior of WO3 photoanodes has been investigated in contact with a combination of four anions (Cl−, CH3SO3−, HSO4−, and ClO4−) and three solvents (water, acetonitrile, and propylene carbonate), to elucidate the role of the semiconductor surface, the electrolyte, and redox kinetics on the current density vs. potential properties of n-type WO3. In 1.0 M aqueous strong acids, although the flat-band potential (Efb) of WO3 was dominated by electrochemical intercalation of protons into WO3, the nature of the electrolyte influenced the onset potential (Eon) of the anodic photocurrent. In aprotic solvents, the electrolyte anion shifted both Efb and Eon, but did not significantly alter the overall profile of the voltammetric data. For 0.50 M tetra(n-butyl)ammonium perchlorate in propylene carbonate, the internal quantum yield exceeded unity at excitation wavelengths of 300–390 nm, indicative of current doubling. A regenerative photoelectrochemical cell based on the reversible redox couple B10Br10˙−/2− in acetonitrile, with a solution potential of ∼1.7 V vs. the normal hydrogen electrode, exhibited an open-circuit photovoltage of 1.32 V under 100 mW cm−2 of simulated Air Mass 1.5 global illumination.

A convenient synthesis of ( Z)-4-hydroxy- N-desmethyltamoxifen (endoxifen)

A mixture of the ( Z)- and ( E)-isomers of 4-hydroxy- N-desmethyltamoxifen was conveniently prepared in four steps. These geometrical isomers were then neatly separated by semi-preparative Reverse Phase High Performance Liquid Chromatography (RP-HPLC) using specified conditions. Additionally, the isolated E-isomer could be equilibrated in aqueous strong acid in acetonitrile or trifluoroacetic acid/dichloromethane to give a clean 1:1 mixture of Z/ E isomers that was re-subjected to HPLC separation. In this way, most of the undesired ( E)-isomer could be readily converted to the desired ( Z)-isomer providing quick access to over 200 mg quantities of pure endoxifen ( Z-isomer), a potent antiestrogenic metabolite of tamoxifen traditionally used in breast cancer treatment.

Isomeric Effects on Structures and Properties of Polyaminophenols Synthesized in Basic Medium

The oxidative chemical polymerizations of three isomers of aminophenol, ortho, meta, and para (PoAP, PmAP, PpAP) were performed in aqueous NaOH using ammonium persulfate (APS) as oxidant. Solubility tests for the synthesized polymers were performed in various solvents and it was found that all three polymers are soluble in DMSO and DMF. PpAP is soluble in aqueous strong acid, as well as in base, but PoAP is soluble in acid, whereas PmAP is soluble in base. The difference in their solubility is due to their structural difference, which can be supported by the proposed mechanisms of polymerizations. The film casting from the DMF or DMSO solution of PoAP and PpAP is difficult due to the presence of quinone impurity while casting of PmAP film from DMSO solution is possible. The intrinsic viscosities of the polymers were determined from the DMSO solution. The polymers were characterized by UV-VIS, FTIR and1H-NMR spectroscopy and elemental analyses. From structural analysis, it is found that PoAP and PpAP do not contain π -electron conjugation due to ether linkage in the backbone chain. So, PoAP and PpAP do not show any conductivity like sulfuric acid doped PmAP.

Keto–enol/enolate equilibria in the 2-acetylcyclopentanone system. An unusual reaction mechanism in enol nitrosation

The keto–enol equilibrium of 2-acetylcyclopentanone (ACPE) was studied in water by analysing the effect that aqueous micellar solutions produce in the UV absorption spectrum of this compound. Aqueous solutions of anionic, cationic, or nonionic surfactants forming micelles have been used. The quantitative treatment of absorbance changes measured at the maximum absorption wavelength as a function of surfactant concentration gave the keto–enol equilibrium constant, KE. In the same sense, the analysis of spectral changes measured as a function of pH in aqueous basic media allowed us to determine the acidity equilibrium constant, Ka. The combination of both equilibrium constants gives the acidity constant of the enol ionizing as an oxygen acid, pKEa=7.72 and the acidity constant of the ketone ionizing as a carbon acid, pKKa=8.12. The kinetic study of the nitrosation reaction of ACPE has been realized in aqueous strong acid media under several experimental conditions. As expected, the reaction is first-order with respect to ACPE concentration, but in sharp contrast to other β-dicarbonyl compounds, the dependence of both [H+] or [X−] (X−=Cl−, Br−, or SCN−) is not simple first-order; instead a fractional order which varied from 1 to 0 was observed. The kinetic interpretation of these experimental facts has been done on the basis of a reaction mechanism that considers the formation of an intermediate in steady-state, which has been postulated as a chelate-nitrosyl complex. The quantitative treatment of the experimental data gave the values of every rate constant appearing in the proposed reaction mechanism.

Mechanism of Acid Neutralization by Overbased Colloidal Additives in Hydrocarbon Media

Stopped-flow kinetic studies have been employed to study the mechanism of acid neutralization for the reaction between overbased commercial detergent additives, used as crankcase lubricants, and aqueous strong acids (e.g., HCl and H2SO4) dispersed in the form of water-in-oil microemulsion droplets. Three water-soluble pH indicators, including methyl orange, 4-nitrophenyl-2-sulfonate, and nile blue have been used to monitor the change in pH accompanying the neutralization reaction. This process represents a model reaction involving communication between a nanometer-sized colloidal particle and a similar-sized aqueous droplet with the reactants solubilized inside the respective colloidal speciesdynamic processes in such systems have rarely been studied previously in a systematic way. The state of the system at the end of the neutralization reaction was monitored by the techniques of small angle neutron scattering (SANS) and ultracentrifugation. The rate was studied as a function of the initial concentration...

Deuteration of amino acids in acidic deuterium oxide solution at supercritical temperatures

The deuterations of a number of the common amino acids at 400 °C and 390 bars in aqueous strong acid are reported. Protium/deuterium exchange is found to be rapid at the α carbon in all examples. Decarboxylation occurred in most cases at a sufficiently rapid rate that the reaction could not be used for deuteration at other sites in most cases. Exchange was accompanied by racemization of the α chiral center as was previously observed for reaction in supercritical base. While rapid α deuteration was noted for all the amino acids, slower deuteration of alkyl chains was not observed because of decomposition. Electrophilic substitution of activated aromatic groups, however, was more rapid than decomposition leading to the production of some products deuterated at sites other than the α carbon. Several of the decomposition products are identified and a general scheme for the deuteration and decomposition reactions is suggested.

Deuteration of amino acids in basic deuterium oxide solution at supercritical temperatures

The deuterations of the common amino acids at 400°C in aqueous base are reported. Protium-deuterium exchange is found to be rapid at the a carbon in all examples where decomposition was unimportant. Exchange was accompanied by racemization of the a chiral center, however. While rapid α deuteration was noted for all the amino acids, slower deuteration was also observed for some alkyl chains and aromatic groups as well. Amino acids having OH, SH, SS, or CN groups on alkyl chains decomposed rapidly to multiple, uncertain products while OH substituted aromatic groups and proline survived the reaction conditions.

A new approach to the analysis of the UV absorption spectra of ketones in aqueous sulfuric acid

Abstract Using the measured UV absorption spectra of 2-pentanone and cyclopentanone (33,000–53,000 cm−1) in 0–99% H2SO4 (w/w) as an example, a new approach to the analysis of ketone UV absorption spectra in aqueous strong acid solutions has been suggested. According to this approach, in 0–65% H2SO4 the changes in the ketone spectra are due mainly to the H-bond strengthening (CO⋯H—) and may be quantitatively interpreted by the increase in the medium electrophilicity (ΔE). In more concentrated acid solutions the H-bond strengthening continues to occur but the protonation of the carbonyl group predominates. Applying a nonlinear least squares iteration method, all the parameters needed to describe changes in the set of measured spectra were obtained. Also among them were the estimated values of the basicity constant pKBH+ and slope parameter m*: pKBH+ = −5.51, m*= 0.76 for 2-pentanone; and pKBH+ = −5.88, m*= 0.77 for cyclopentanone.

Determination of oxygen concentrations by luminescence quenching of a polymer-immobilized transition-metal complex

Oxygen quenching of the luminescence of the tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) perchlorate immobilized in a silicone rubber is shown to be an accurate and precise method for measuring oxygen concentrations in solutions and in the gas phase. Quenching can be quantitated by either lifetime or intensity quenching measurements. Aqueous strong acids, bases, complexing agents, oxidants, and reductants do not penetrate the hydrophobic polymer and, therefore, do not affect the response. Gaseous interferents, such as H/sub 2/S, anesthetic gases (e.g., N/sub 2/O, halothane), and fluorocarbons do not affect the response. Chlorine and especially SO/sub 2/ are strong, but fully reversible, interferents. A system was developed with a response time of less than 0.2 s, which is adequate for the monitoring of breathing subjects.

Acidic and related constituents in liquid water stratiform clouds

Composition of cloud liquid water and interstitial air is reported for aircraft measurements near Charleston, South Carolina, in February 1982. Cloud water was collected by means of a slotted‐rod impactor. Cloud‐free interstitial air was obtained by a centrifugal separator. Principal ionic species in cloud water were H+, SO4=, NO3−, and NH4+. The relative acidity of cloud water, as measured by the ratio of H+ to NH4+, was much greater than that of the interstitial aerosol or of clear‐air aerosol samples. Gaseous O3, NOx (i.e., NO+NO2), and SO2 were present in interstitial air within clouds, whereas HNO3 and NH3 were below limit of detection (0.4 ppb for both species). Comparison of relative aciditiy of cloud water samples with that of clear‐air samples suggests that clear‐air aerosol and HNO3 are incapable of providing the levels of acidity observed in cloud water. Such acidity would be consistent with in‐cloud conversion of prevailing concentrations of SO2 or SO2+NOx to aqueous strong acid, although other hypotheses cannot be excluded. Comparison of absolute concentrations of cloudwater constituents to concentrations in clear‐air measurements gives no indication of accumulation of sulfur and nitrogen species by clouds.

ChemInform Abstract: THE STRUCTURE OF THE DOUBLE LAYER AT THE MERCURY‐PHOSPHORIC ACID INTERFACE FROM STUDIES OF ADSORPTION OF THIOUREA AND ITS IMPLICATIONS ON OXYGEN REDUCTION KINETICS

AbstractIm Hinblick auf den Wirkungsgrad‐Verlust von H3PO4‐Brennstoffzellen, der hauptsächlich durch die langsame Kinetik der Sauerstoff‐Reduktion bedingt ist, wurden Differentialkapazitäten bei 25°C als Funktion des Potentials für die Grenzfläche Hg‐ Elektrode/Elektrolyt (95proz. H3PO4) ohne und mit Thioharnstoff‐Zusätzen gemessen.

Tautomerism of 4-amino- and 4-arylamino-1,2-naphthoquinones.

The 13C chemical shifts of 4-amino- and 4-arylamino-1, 2-naphthoquinones measured in DMSO-d6, pyridine-d5 and a D2O solution of NaOD indicated that the predominant tautomer in neutral solvents is the 1, 2-dioxo-4-amino-naphthalene (Ia) form, while that in weak basic solvents is the 1-oxo-2-hydroxy-4-imino-naphthalene (Ib) form and that in an aqueous solution of NaOH is the anion of the Ib form. The electronic spectrum of 4-anilino-1, 2-naphthoquinone measured in a mixture of EtOH and 0.05M H3SO4 (1 : 4 by volume) indicated that its tautomeric form in an aqueous strong acid solution is the Ia form and that the compound is hydrolyzed quickly to produce 2-hydroxy-1, 4-naphtho-quinone. The magnitudes of substituent effects observed in the electronic spectra of 4-(4'-substituted)-anilino-1, 2-naphthoquinones measured in EtOH were found to be smaller than those measured in pyridine. This difference was considered to provide confirmation that the predominant tautomer in neutral solvents is the Ia form. The theoretical π-π* transition energies of 4-arylamino-1, 2-naphthoquinones were calculated for both the Ia and the Ib forms by means of Pariser-Parr-Pople type molecular orbital calculations.

Reactions of organic phosphates. Part VI. The hydrolysis of aryl phosphates

The hydrolysis of monoaryl phosphates shows acid catalysis only if an electron-attracting substituent (e.g., NO2–or CH3CO–) is present in the aryl group. There is then a rate maximum at a strong acid concentration in the range 3–6M. A typical rate maximum at ca. pH 4·0 due to hydrolysis via the monoanion species is observed in all cases. The reactions, both in aqueous strong acid and at pH 4, proceed by phosphorus–oxygen bond fission.Rate maxima in aqueous strong acid are also observed in the hydrolysis of diphenyl and triphenyl phosphates: the reactions also proceed by phosphorus–oxygen bond fission. The maxima do not arise from complete protonation of the substrate but are apparently the result of a powerful negative electrolyte effect.