Order Of OH Research Articles

Dissolution/precipitation kinetics of boehmite and gibbsite: Application of a pH-relaxation technique to study near-equilibrium rates

The dissolution and precipitation rates of boehmite, AlOOH, at 100.3°C and limited precipitation kinetics of gibbsite, Al(OH)3, at 50.0°C were measured in neutral to basic solutions at 0.1 molal ionic strength (NaCl+NaOH+NaAl(OH)4) near-equilibrium using a pH-jump technique with a hydrogen-electrode concentration cell. This approach allowed relatively rapid reactions to be studied from under- and over-saturation by continuous in situ pH monitoring after addition of basic or acidic titrant, respectively, to a pre-equilibrated, well-stirred suspension of the solid powder. The magnitude of each perturbation was kept small to maintain near-equilibrium conditions. For the case of boehmite, multiple pH-jumps at different starting pHs from over- and under-saturated solutions gave the same observed, first order rate constant consistent with the simple or elementary reaction: Al(OOH)(cr)+H2O(l)+OH-⇄Al(OH)4-.This relaxation technique allowed us to apply a steady-state approximation to the change in aluminum concentration within the overall principle of detailed balancing and gave a resulting mean rate constant, (2.2±0.3)×10−5kgm−2s−1, corresponding to a 1σ uncertainty of 15%, in good agreement with those obtained from the traditional approach of considering the rate of reaction as a function of saturation index. Using the more traditional treatment, all dissolution and precipitation data for boehmite at 100.3°C were found to follow closely the simple rate expression:Rnet,boehmite=10-5.485{mOH-}{1-exp(ΔGr/RT)}, with Rnet in units of molm−2s−1. This is consistent with Transition State Theory for a reversible elementary reaction that is first order in OH− concentration involving a single critical activated complex. The relationship applies over the experimental ΔGr range of 0.4–5.5kJmol−1 for precipitation and −0.1 to −1.9kJmol−1 for dissolution, and the pHm≡−log(mH+) range of 6–9.6. The gibbsite precipitation data at 50°C could also be treated adequately with the same model:Rnet,gibbsite=10-5.86{mOH-}{1-exp(ΔGr/RT)}, over a more limited experimental range of ΔGr (0.7–3.7kJmol−1) and pHm (8.2–9.7).

Suppression of free-radicals and protection against H 2O 2-induced oxidative damage in HPF-1 cell by oxidized phenolic compounds present in black tea

Whereas catechins are the most abundant polyphenols in green tea, the typical pigments in black tea are theaflavins (TF), thearubigins (TR) and theabrownins (TB), which are derived from the oxidation of catechins and their gallates during the fermentation stage of black tea processing. In this study, oxidized phenolic compounds (TF, TR and TB) present in black tea were obtained from a model oxidation system, using immobile enzyme. The order of OH − and 2,2-diphenyl-1-picrylhydrazyl-scavenging ability of these oxidation products was TF > TB > TR. These oxidized phenolic compounds showed protection against H 2O 2-induced damage in HPF-1 cells and suppressed the accumulation of intracellular reactive oxygen species in H 2O 2-induced damage of HPF-1 cells. Interestingly, TB, as a further oxidative product from TF or TR, showed potent activity, followed TF in the above four systems.

Electrochemical kinetics of gold dissolving in alkaline thiourea solution

Kinetic parameters of the electrode reactions were measured by investigating steady-state current-potential behaviors. The results show that the apparent transfer coefficient of anodic process is 0.0582, diffusion coefficient of thiourea gold complex is 6.04 × 10−6 cm2/s, anodic reaction order of thiourea is 2.0183, and anodic reaction order of OH− is 0.0166. The theoretical kinetics equation of gold dissoving in alkaline thiourea solution is deduced, which indicates that anodic reaction order of thiourea is 2, and anodic reaction order of OH− is 0. The theoretical values of the kinetic parameters are consistent with experimental values very well. The correctness of the mechanism is further demonstrated using apparent transfer coefficient according to the electrochemical dynamic equation of multi-electron reaction.

The Role of Substitutional Defects in Order/Disorder Phenomena of OH− Ions in Hydroxyapatite

AbstractWe report on density functional quantum mechanical calculations of hydroxyapatite. The central focus is dedicated to the local arrangement of hydroxide ions in proximity of defects originating from substituting OH− by F− or O2− ions. At ambient conditions the preferred structure of bulk hydroxyapatite exhibits an ordering of OH− ions oriented in rows along the [001] direction. From zero Kelvin geometry optimizations the orientation inversion of a hydroxide ion was found to be disfavored by 0.165 eV. This picture changes dramatically when replacing one of the OH− ions by a fluoride ion. The preferred hydroxide ion arrangement next to the F− defect was identified as an OH−··F−··HO− constellation, which implies the orientation inversion of one of the neighboring hydroxide ions. An analogous phenomenon was observed for O2− defects.

Origin of diffuse superstructure reflections in labuntsovite-group minerals

The average crystal structures of two natural porous titanosilicates of the labuntsovite group, lemmleinite-Ba and lemmleinite-K, ideally Na 4 K 4 Ba 2 Ti 8 (Si 4 O 12 ) 4 O 4 (OH) 4 ·8H 2 O and Na 4 K 4 K 2 Ti 8 (Si 4 O 12 ) 4 O 2 (OH) 6 ·8H 2 O, respectively, have been refined from single crystal X-ray diffraction data. Both samples represent an extensive solid solution with labuntsovite sensu strictu Na 4 K 4 D 2 Ti 8 (Si 4 O 12 ) 4 O 4 (O H) 4 ·10H 2 O where D = Mn, Fe, and Mg. In addition to the sharp Bragg reflections both crystals, space group C 2/ m , a = 14.3, b =13.8, c = 7.75 A, β= 117°, exhibit diffuse layers at c */2 intervals indicating faulty superstructures with c = 15.7 A. The diffuse layers consist of two types of reflections. The dominant type is strongly diffuse and smeared along a * indicating an I -centered Bravais lattice. The other type is very sharp but also weak and is in agreement with a C -centered lattice. Models for both superstructures have been developed on the basis of crystal-chemical principles and their theoretical diffraction patterns have been calculated and compared with the observed diffuse layers yielding excellent qualitative agreement. X-ray structure refinements of the average structure at −160 and 22 °C indicate temperature in-dependent (static) disorder of Ti within rather rigid TiO 6 octahedra connected to chains that extend along a. This Ti disorder is interpreted in terms of long-range order of OH and O in the superstructures where these anions occupy the corner-connecting octahedral apices in an ordered fashion. An additional effect of OH, O order is an ordered arrangement of extraframework Ba (K) that only bonds to O but not to OH sites exposed on the channel walls. Temperature dependent cell dimensions between −160 and +200 °C suggest a phase transition at ca. −80 °C. However, the structural data obtained from the average structures, refined at −160 and 22 °C, did not allow us to draw crystal-chemical conclusions about the nature of the phase transition. Dehydration of the investigated lemmleinite-Ba starts at ca. 150 °C leading to increasing extraframework disorder and decreasing crystal quality as evidenced by strong smearing of the originally sharp Bragg reflections.

Oxidation of L-tyrosine by sodium N-bromobenzenesulfonamide in alkaline medium : a kinetic and mechanistic study

The kinetics of oxidation of L-tyrosine (Tyr) by sodium N-bromobenzenesulfonamide or bromamine-B (BAB) has been studied in NaOH medium at 283 K. The rates are first order in both BABo and Tyr o and inverse fractional order in OH-. Ionic strength and halide ion variations or the presence of added reaction product, benzenesulfonamide, has no pronounced effect on the rate. The dielectric effect is positive. The reaction has been studied at different temperatures and activation parameters for the composite reaction are computed. Solvent isotope effect is also studied. The thermodynamic parameters for the equilibrium step and activation parameters for the rate determining step are evaluated. A plausible mechanism consistent with the observed kinetics is proposed.

Gold Recovery from Nickel Catalyzed Ammonium Thiosulfate Solution by Strongly Basic Anion Exchange Resin

Copper catalyzed ammonium thiosulfate leaching process has been proposed as an alternative gold extraction process to cyanidation. In order to recover gold from the ammonium thiosulfate solution, ion exchange process has been proposed as a gold recovery method using strongly basic anion exchange resin. However, the co-adsorption of copper along with gold causes difficulty in separating gold and copper at the gold elution stage. Our previous study has demonstrated that nickel catalyzed ammonium thiosulfate solution for gold extraction has the advantage of reducing thiosulfate consumption. In this study, the results also demonstrated the advantage of gold recovery from the nickel catalyzed ammonium thiosulfate solution by strongly basic anion exchange resin. The optimal gold loading conditions on a 1 g/dm 3 strongly base anion exchange resin (wet base value) are investigated in several ion concentrations and 95 kg-Au/t-resin has been obtained. The alternative gold eluant was investigated as the gold loaded resin cannot be eluted by conventional hydrochloric acid. Results showed that the elution efficiency was in the order of OH � < Cl � � NO3 � < Br � � I � < ClO4 � . The maximum gold recovery by using 2.5 mol/dm 3 ClO4 � was around 98% with the stripped resin assayed as 0.2 kg/t Au. The feasibility of resin recycling has demonstrated that there was no deterioration in gold adsorption and desorption for four cycles.

Kinetics and mechanisms of catalyzed and noncatalyzed reactions of OH and NCO in acrylic polyol–1,6‐hexamethylene diisocyanate (HDI) polyurethanes. VI

AbstractFourier transform infrared spectroscopy was used to study the kinetics of noncatalyzed and catalyzed polyurethanes. These studies show that for noncatalyzed acrylic polyol–hexamethylene diisocyanate (HDI) trimer reactions, the reactions between OH and NCO of HDI exhibit second‐order kinetics, with first‐order kinetics with respect to NCO and OH. On the other hand, when dibutyltin dilaurate (DBTDL) is used as a catalyst in acrylic polyol–HDI trimer reactions, the reaction rate is first order with respect to NCO and 0.5 order in OH and DBTDL concentrations. A mechanism for the catalyzed acrylic polyol–HDI trimer crosslinking reactions is proposed and it appears that an equilibrium involving associations between OH and DBTDL exists, resulting in the formation of an active anion, which interacts with NCO to generate polyurethanes. To further verify this mechanism, the influence of acidity on the reaction rate constant was investigated. When the acidity of the system is increased, retardation of urethane formation occurs. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2322–2329, 2002

A theoretical study of the [formula omitted] reaction I

The reactions are assumed to proceed through an insertion mechanism on the CH 3OH ground state potential energy surface. The rate constants of CH 3OH dissociation at a O( 1 D)+ CH 4 collision energy of 6.6 kcal/mol are obtained by the RRKM and variational RRKM theory based on our ab initio potential energy surface. The rate constants of the primary reactions suggest their branching ratios are in the order of OH>H>H 2>H 2O, consistent with the experimental findings. The predicted rate constant of the OH radical channel indicates a likely nonstatistical behavior. The derived bimolecular rate constant for O( 1 D)+ CH 4 at 300 K agrees reasonably well with the experiments.

Ordering of hydroxyl defects in hydrous wadsleyite (β-Mg2SiO4)

Samples of wadsleyite (β-Mg 2 SiO 4 ) containing a range of dissolved water concentrations up to 1.5 wt% were synthesized at 1300 °C and 15 GPa. The samples were studied using 1 H MAS NMR and FTIR spectroscopy to determine the ordering of OH within the structure. As the 1 H NMR chemical shift and O-H stretching frequency are both known to be correlated with the O-H···O distances in silicate and other materials, the spectroscopic data were compared with O­···O distances calculated from the published crystal structure of hydrous wadsleyite. Using this approach we show that the hydroxyl ions in wadsleyite containing 0.8-1.5 wt% H 2 O are highly disordered, occupying at least 14 of the 17 possible O-H···O environments, including some with strong hydrogen bonding. In contrast, for low water concentrations (&lt;0.4 wt%) the hydroxyl ions are less disordered, with four environments being much more abundant than the others are. Three of these environments appear to involve protonation of O1, in agreement with most previous suggestions, and the fourth is probably O2-H···O2. It is probable that the degree of disorder will increase with increasing temperature, so it should be taken into account when predicting phase equilibria involving hydrous wadsleyite and when extrapolating data on density and elastic properties from room temperature measurements.

The hydrothermolysis of the picrate anion: kinetics and mechanism

The hydrothermolysis of the picrate anion in aqueous solution has been studied at 260–325 °C in liquid water. At starting pH values above 12, the disappearance of picrate begins immediately and is first order in OH −. At lower pH, there is an induction period preceding the disappearance, and over the pH range 6.7–11.9 there is no pH dependence in the developed reaction phase. Added borate and silicate salts promote the reaction, suggesting their acting as nucleophiles at hydrothermal conditions. Nitrite is an initial product, while acetate is a final product and reflective of a vigorous oxidative sequence consuming the intermediate products. A reaction sequence consistent with the results at the lower pH includes initiation of a chain process by displacement of nitrite by water, followed by nucleophilic displacement of nitrite by nitrite such that a nitro group is replaced by an ONO group. The ester then rapidly hydrolyzes, and the net reaction is the production of an additional nitrite with each cycle. A simple modeling of this system satisfactorily fits the experimental findings.

Multiple changes in rate-determining step in the acid and base catalyzed cyclizations of ethyl N-(p-nitrophenyl)hydantoates caused by methyl substitution

The slopes of the pH-rate profiles for the cyclization of 2-methyl- and 2,3-dimethyl hydantoates 1-NPU and 2-NPU between pH 1 and 7 change from 1 to 0 and then back to 1. A reaction first order in H+ was observed with the latter compound. The 2,2,3-trimethyl derivative 3-NPU showed only one reaction first order in OH-, but complex acid catalysis is described by slopes 0, -1, 0, and finally -1 again. The cyclizations were general base catalyzed, with Brønsted β values of 0.5-0.6. The OH- catalysis at higher pH for 1-NPU and 2-NPU showed inverse solvent kinetic isotope effects and deviated from the Brønsted relationships, while that for 3-NPU showed a normal effect and complied with the Brønsted relationship. The accelerations due to the gem-dimethyl effect were lost with the OH- and general base-catalyzed reactions of 3-NPU. This behaviour is due to a change from the rate-determining formation of the tetrahedral intermediate with 1-NPU and 2-NPU to the rate-determining breakdown with 3-NPU, due to steric hindrance to protonation of the leaving ethoxy group. The OH- reaction at higher pH involves attack of the ureide anion with 1-NPU and 2- NPU, becoming concerted with deprotonation when catalyzed by general bases and changing to acid inhibition of the anion of the tetrahedral intermediate at low pH. With 3-NPU at higher pH, T- is in equilibrium and the conjugate acids of the general bases accelerate its breakdown by protonating the ethoxy group. Acid catalysis of the cyclization of 3-NPU at higher pH is also protonation of the leaving group from T0 changing to the rate-determining formation of T at lower pH. The latter mechanism is preferred for the cyclization of 2-NPU.Key words: gem-dimethyl effect, mechanism, general base catalysis, proton transfer, steric hindrance.

Observation of the Type of Hydrogen Bonds in Coal by FTIR

It is hard to distinguish the type of hydrogen bonds formed by hydroxyl groups by normal FTIR methods because of the interference of water in samples. In this work, a method is proposed for the clear observation of the types of hydrogen bonds by FTIR. The method involves the evaporation of water in a vacuum chamber with CaF2 windows (vacuum level, 4 × 10-3 kPa) followed by in situ scanning of the IR spectrum. Five types of hydrogen bonds were found in coal and its extracts. The hydroxyl groups in coal mainly exist as self-associated OH and OH−N hydrogen-bonded pairs. The thermal stability of these hydrogen bonds was investigated by means of in-situ pyrolysis FTIR. It follows the order of OH−ether O > self-associated OH ≈ cyclic OH > OH−N > OH−π.

Studies on Structure of Cuprammonium Cellulose II. Structural Change of Cellulose–Cuprammonium Complex as a Function of Hydroxyl Ion Concentration

As an extension of our previous study on cellulose–cuprammonium system,1 an attempt was made to clarify the structure of cellulose–cuprammonium complex in the solid–liquid coexisting system by applying the fact that dissolution of cellulose into cuprammonium solution depends strongly on OH− concentration in the system. Electro-conductivity measurements on aqueous (aq) cuprammonium complex revealed that the complex existed as dissociated type at COH (OH concentration for aq solution) 0.5. Absorption reaction of aq cuprammonium complex on solid cellulose was also dependent on COH, revealing that the reaction order of OH− ion for the solid–liquid absorption reaction is unity and 0 for the system with COH less than 0.3 mol l−1 and for the system with COH>0.5 mol l−1, respectively. Meanwhile, the reaction order of copper to cellulose was found unity regardless the COH value. The latter fact might deny the random reaction of 3 OH groups in glucopyranose unit with copper ion and suggests indirectly the regio-selective complex formation of cuprammine and OH groups at C2 and C3 as previously proved. It was found that even if the molar ratio of copper ion in aq cuprammine complex to solid cellulose is more than unity, copper absorbed on solid cellulose is at most 0.65 mol mol−1. This value is quite near to that evaluated for the cellulose dissolved in cuprammonium solution. Using the above results a tentative new cellulose dissolving process is proposed, in which the less amount of copper and NH3 are employed, compared with those used for conventional process.

Modelling anion amelioration of aluminium phytotoxicity

There is good evidence for the ameliorating effect of SO42- and F- on the expression of Al phytotoxicity in acidic solutions. The role of OH-, in both shifting Al speciation towards hydroxy-Al species and decreasing activities of H+ with increasing pH, is still controversially discussed. Grauer and Horst (1992) proposed a model based on the assumption that Al phytotoxicity is a function of the Al saturation (AlS) of exchange sites in the root apoplast and analyzed the predictions of the model in the case of cation amelioration, with special emphasis on H+. In this study the model is further developed by considering, in addition to Al3+, the complexation of Al with the anions OH-, F-, SO42-, and Cl- to form potentially toxic Al species. Association constants of these Al complexes with a ligand (L-) which is assumed to simulate the cation exchange sites in the root apoplast, were estimated. Affinity factors for binding to L- compared to Al3+ were derived from these estimated association constants, and values were, in a first approach, 0.79 for AlOH2+, 0.02 for Al(OH)2+, and 0.13 for Al(OH)30 (or 0.03 choosing another hydrolysis constant). High toxicity of Al13 (AlO4Al12(OH)24(H2O)127+) could be explained by diminished H+ amelioration and a high association constant to L-. From estimated association constants for Al-Cl complexes, low affinity factors for L- for these complexes were derived. Since the formation of these Al-Cl complexes is not favoured, Cl- is predicted to have very little ameliorating effect. In the case of SO42− and F- complexes with Al, the derived affinity factors never exceeded 0.05 and, since formation of these complexes is favoured by high association constants, are thus in agreement with experimental results on ameliorating effects. The ranking of the anions for ameliorative effectiveness was estimated to be in the order of OH->F->SO42−>Cl-. Hydroxy amelioration in this context is restricted to the speciation effect, which is only significant above pH 4.

The effect of various nucleophiles on the mutagenicity of softwood kraft chlorination effluent

The mutagenicity of softwood kraft chlorination effluent in the Ames Salmonella assay was measured in the presence of various added nucleophiles. The relative effectiveness of the applied nucleophiles in reducing the mutagenicity of the effluent was in the order of OH − > SO 2 (HSO 3 −, SO 3 =)>glutathione>pyrrolidine>S 2O 3, which appeared to follow in order of decreasing nucleophile basicity. Both the carbonyl group and organically bound chlorine contents of the effluent decreased upon addition of nucleophiles. In all cases, carbonyl loss appeared to be the more important factor in controlling mutagencity reduction. The conclusion can be drawn that deactivation of kraft chlorination effluent, and possibly the chlorination products of other types of naturally occurring organic material (e.g., humic acid), may be achieved by treatment with any appropriate nucleophile. Effective nucleophiles can include substances such as glutathione, which is endogenous to all mammals, and as such may represent the biochemical basis for a detoxication mechanism.

ChemInform Abstract: Kinetics of Base Hydrolysis of Cyanogen and 1‐Cyanoformamide.

AbstractThe rate of (CN)2 hydrolysis in base is first order in OH‐ and first order in (CN)2, but the reaction proceeds by two paths.

F faces of apatite and its morphology: Theory and observation

Eighteen connected nets have been determined for hydroxyapatite, and 12 different F faces run parallel to at least one of these connected nets. The order of morphological importance of these F faces is determined by the slice energy, E slice hkl and compared to the morphological data for natural apatites. It is found that there is a close agreement between predicted and observed morphology. It follows that the lowering of the apatite symmetry (P6 3/m → P2 1/b) due to the ordering of OH is not likely to be the cause of the occurence of plate like apatitic crystals in calcified tissues.

Kinetics of oxidation of some α‐amino acids L(−) arginine, L(−) histidine, L(+) ornithine, L(−) tryptophan, L(−) threonine by sodium N‐chloro‐4 methyl benzene sulphonamide (chloramine‐T) in alkaline medium

AbstractKinetic studies of oxidation of L(−) arginine, L(+) ornithine, L(−) histidine, L(−) tryptophan, L(−) threonine have been carried out in alkaline medium. The reaction showed an inverse fractional order in OH− and first‐order dependence on both amino acid and chloroamine‐T concentration. The effect of varying ionic strength (KCl) on the rate of oxidation is negligible. A general mechanism for the oxidation has been suggested by considering interaction between anionic species of amino acid and p‐toluene‐sulphochloramide. The effect of solvent and temperature have been also discussed. The fractional order obtained in OH− is due to the fact that a fraction of overall reaction proceeds via an alternative OH− independent path. The combined rate law in accordance to observed kinetics is derived as The rate constants predicted by the derived rate law as the concentration of OH− ions change, are in excellent agreement with the observed rate constants, thus further justifying these rate laws and hence the proposed mechanistic schemes.

Catalytic electro-oxidation of hydrazine on phthalocyanines deposited on graphite electrodes

The catalytic properties phthalocyanines of Fe, Co, Ni and Cu for the electro-oxidation of hydrazine have been examined. The metal chelates were deposited on ordinary pyrolytic graphite electrodes and their redox properties were studied by cyclic voltammetry. The catalytic activity was found to decrease as follows: FePc > CoPc > CuPc ∼ NiPc > graphite. The kinetics of the process with Fe-Pc and Co-Pc were examined. Tafel slopes of 40 mV for Fe-Pc, and of 60 m V for Co-Pc were obtained. The chemical order in N 2H 4 is 1 both complexes. The order in OH − is 2 for Fe-Pc and 1 for Co-Pc. With Fe-Pc, the transfer of a second electron seems to be rate determining. With Co-Pc, a slow chemical step preceded by a fast one-electron transfer seems to operate.