Corrosion inhibition of zinc in aqueous acidic media using a novel synthesized Schiff base – an experimental and theoretical study

Abstract

The kinetics of H₂ production during Zn corrosion in 0.5?M HCl without and with various additives of N,N'-bis-(1-hydroxyphenylimine)-2,5-thiophenedicarboxaldehyde (HPTD) was studied using gasometry and electrochemical techniques. The surface of the corroded Zn samples was investigated using SEM and Optical Profilometry. The rate of H₂ production (RHP) increased with the immersion time and temperature. Presence of HPTD mitigated RHP due to an adsorption process. The electrochemical impedance spectroscopy showed that HPTD had a good inhibitive effect. Polarization data proved that HPTD acted as a surface-active mixed-type inhibitor. Some thermodynamic parameters were deduced and discussed. Theoretical calculations were also conducted to corroborate the capability of HPTD to protect Zn surface from corrosion process.     

Kinetic surface roughening of electrodeposited amorphous PdP and NiP films – A comparative study

Kinetic surface roughening of electrodeposited PdP and NiP amorphous films were investigated by atomic force microscopy and X-rays phase-contrast radiography. Anomalous scaling of the interface width was observed for PdP system, with H = 0.75 ± 0.06, β_loc = 0.49 ± 0.07 and β = 0.38 ± 0.08. In contrast, NiP system shows normal scaling behavior, with H = 0.70 ± 0.02 and β = 0.16 ± 0.03. The results suggest that surface roughening during film growth is strongly influenced by local behaviors like hydrogen evolution reaction, which shifts surface roughening from normal scaling in NiP to anomalous scaling in PdP.     

α-Picolinic acid as a colorimetric reagent : A comparative study

The amount of iron in several naturally occuring samples has been determined colorimetrically with the reagent α-picolinic acid and the results obtained have been found to compare favourably with those due to o-phenanthioline     

Synthesis of β-fluoroenones and their reductive rearrangement in aqueous media

In this paper, a simple and efficient preparation of β-fluoroenones, as a mixture of E/Z isomers with the E-isomer as the main product, from 1,2-allenic ketones by using TBAF·3H₂O in water as a nucleophilic fluorination agent has been developed. Moreover, in exploring the synthetic applications of β-fluoroenones, an unprecedented reductive defluorination rearrangement of β-fluoroenones toward enones under mild conditions in aqueous media was also discovered.     

A comparative study of the structure and properties of β-galactosidases

A comparative study of β-galactosidase amino acid sequences of E. coli and another four out of 11 microorganisms selected at the first stage was performed. It was shown that the functional amino acid residues in the catalytic domain and the ligand environment of the magnesium cation for all five sequences are identical. The mechanism of the catalytic action of E. coli and K. lactis β-galactosidases was investigated by the method of nucleophilic competition. It was shown that the mechanism of the effects of nucleophilic agents is kinetically identical both enzymes: the presence of methanol or butanediols affects the stage of degalactosylation; the presence of magnesium cations promotes the activity of both β-galactosidases; and the mechanisms of the thermal inactivation of E. coli and K. lactis β-galactosidases are different.     

Kinetic and mechanism of oxidation of thiocarbohydrazide and its metal complex by acid bromate in aqueous and partial aqueous media

The kinetics of oxidation of thiocarbohydrazide in the free and zinc(Ⅱ)-bound states byacid bromate have been studied in aqueous and water-acetic acid(1:1,V/V)media under varyingconditions,both in the absence and presence of added bromide ion.The rates of oxidations show firstorder kinetics in[bromate]in all the cases,but exhibit different kinetic behaviour in[substrate]and[H~+].Oxidation of TCH in aqueous medium shows zero order in[TCH]and nearly second order in[H~+],while oxidation in aqueous acetic acid shows two ranges in[H~+].The rate shows first and fractionalorder kinetics in[TCH]in the first and second acid ranges.Kinetics observed in the presence of Br~-are similar to those observed for oxidation of TCH in second acid range.In addition,the reactionshows fractional order in[Br~-].Oxidation of TCH in Zn(Ⅱ)-bound state exhibits first order kinetics in[substrate]and second order in[H~+].Increase in ionic strength of the medium decreases the rate in allthe cases.Increase in acetic acid composition of the solvent increases the rate.Mechanisms consistentwith the observed results have been considered and the rate laws deduced.The rate limiting steps havebeen identified and the coefficients of these steps have been calculated at different temperatures.Therelated activation parameters have also been computed.The validity of the deduced rate laws has alsobeen tested by recalculating the rate constants from them as[TCH]and[H~+]are varied.     

A comparative adsorption study of β-naphthol on four polymeric adsorbents from aqueous solutions

Adsorptive removal of aromatic compounds from aqueous solutions by polymeric adsorbents has attracted many concerns in recent years. A comparative adsorption study including equilibria, kinetics and column dynamics of β-naphthol from aqueous solutions was carried out using two hypercrosslinked polymeric adsorbents (HJ-1 and TEPA) we developed and two commercial polymeric adsorbents (XAD-4 and XAD-7). The adsorption isotherms could be well described by the Freundlich equation, and the adsorption equilibrium capacities of β-naphthol followed an order of q(e)((TEPA))>q(e)((HJ-1))>q(e)((XAD-4))>q(e)((XAD-7)). The isosteric adsorption enthalpies on HJ-1 and TEPA decreased with increasing adsorption fractional loading, while a constant enthalpy was observed for XAD-4 and XAD-7, implying that HJ-1 and TEPA had a heterogeneous surface while XAD-4 and XAD-7 possessed a homogenous surface. The surface energetic heterogeneity of HJ-1 and TEPA could be well characterized by the Do's model. The adsorption kinetics were fitted by both pseudo-first-order and pseudo-second-order rate equations, and the intra-particle diffusion was found to be the rate-limiting step. The adsorption breakthrough data were well correlated by the Thomas and Clark models, and the dynamic capacities for TEPA, HJ-1, XAD-4 and XAD-7 adsorbents were calculated to be 341.7, 321.6, 268.0 and 173.8 mg/g dry resin, which were within 90% of the corresponding equilibrium capacities obtained in the batch experiments.     

Oxidation of aniline and some para-substituted anilines by benzimidazolium fluorochromate in aqueous acetic acid medium – A kinetic and mechanistic study

The oxidation kinetics of some para-substituted anilines by benzimidazolium fluorochromate (BIFC) have been studied in aqueous acetic acid media in the presence of perchloric acid. The reaction is first order with respect to both aniline and BIFC and is catalysed by a hydrogen ion. The rate data obey Hammett relationship. The products of oxidation are the corresponding azo benzenes. Based on the kinetic results and product analysis, a suitable mechanism has been proposed for the reaction of BIFC with anilines.     

A comparative study in structure and reactivity of “FeO_x-on-Pt” and “NiO_x-on-Pt” catalysts

Oxide nanostructures grown on noble metal surfaces are often highly active in many reactions,in which the oxide/metal interfaces play an important role.In the present work,we studied the surface structures of Fe Ox-on-Pt and Ni Ox-on-Pt catalysts and their activity to CO oxidation reactions using both model catalysts and supported nanocatalysts.Although the active Fe O1x structure is stabilized on the Pt surface in a reductive reaction atmosphere,it is prone to change to an Fe O2x structure in oxidative reaction gases and becomes deactivated.In contrast,a Ni O1x surface structure supported on Pt is stable in both reductive and oxidative CO oxidation atmospheres.Consequently,CO oxidation over the Ni O1x-on-Pt catalyst is further enhanced in the CO oxidation atmosphere with an excess of O2.The present results demonstrate that the stability of the active oxide surface phases depends on the stabilization effect of the substrate surface and is also related to whether the oxide exhibits a variable oxidation state.     

Indium-mediated allylation of aryl trichloromethyl ketones in aqueous media

It is described that indium-mediated allylation of trichloromethyl ketones could afford the corresponding homoallylic alcohols smoothly in aqueous media.     

One-pot tandem Barbier-Prins synthesis of tetrahydropyrans in aqueous media

Tetrahydropyran is an important structural core ofmany carbohydrates and their polymers. Its structure ispresent in numerous natural compounds such as poly-ether antibiotics, marine toxins and pheromones[1,2].Thus many reactions have been developed toward…     

A comparative study of the thermodynamic properties at the air–water interface and in the bulk of structurally related phenothiazine drugs aqueous solutions

Surface tension, conductivity, density, and ultrasound velocity measurements have been performed in order to determine in a systematic manner some of the aggregation properties of the phenothiazine drugs promazine and triflupromazine hydrochlorides. Both drugs are structurally related, differing in an extra CF₃ group in the triflupromazine molecular structure. Surface tension data showed that the presence of an extra CF₃ in the molecular structure of triflupromazine involves a higher hydrophobicity of this drug and a restriction in the number of conformations molecules can adopt due to the presence of this bulkier atomic group. This involves a larger surface area in order to accommodate triflupromazine molecules at the interface. From conductivity measurements at different temperatures, the thermodynamic quantities of the micellization process of these drugs indicate that the aggregation is a spontaneous process, mainly enthalpic, where the London-dispersion forces play an active role. Using density and ultrasound velocity measurements, apparent molar volume and adiabatic compressibility of aqueous solutions of the amphiphilic cationic drugs have been determined. Positive deviations from the Debye–Hückel limiting law of the apparent molar volume were obtained from both drugs over the whole temperature range, which provides evidence of possible pre-association at concentrations below the critical concentration. Apparent molar adiabatic compressibility of the aggregates formed by these drugs was typical of those corresponding for an aggregate formed by a stacking process.     

A novel synthesis of allyl and benzyl selenides via Sm/SbCl_3 system in aqueous media

Allyl and benzyl selenides were synthesized via reactions of allyl and benzyl bromides and diselenides promoted by Sm/Sb-Cl3 system in aqueous media in moderate to good yields.     

Synthesis and use of a cost-effective,aqueous soluble diazo transfer reagent – m-carboxybenzenesulfonyl azide

Herein, we report the preparation and use of m-carboxybenzenesulfonyl azide as a diazo transfer reagent. This compound is an inexpensive and potentially scalable alternative to many of the diazo transfer reagents currently available, most of which have hazards associated with their use. Its usefulness and suitability as a diazo transfer reagent was assessed on the basis of cost, safety and its effectiveness in diazo transfer to a variety of different substrates.     

A comparative study of the multicomponent Ugi reactions of an oxabicycloheptene-based β-amino acid in water and in methanol

Di-exo-3-amino-7-oxabicyclo[2.2.1]hept-5-ene-2-carboxylic acid 1, five aldehydes and two isocyanides were reacted both in methanol and in water to prepare a 10-membered β-lactam library via a Ugi-4-centre-3-component reaction. The yields were found to be similar in water and methanol. The diastereoselectivities of the aqueous reactions were similar, though in a few cases higher than those in methanol. The benefits of water are the facile isolation of the precipitated product and the shorter reaction time.     

Cyclization of N-alkyldithiocarbamates in alkaline media,a counter example of well-known chemistry – an experimental and theoretical study

In strong alkaline media, the reaction of 2-(tert-butylamino)ethanol (3: R?=?Bu^t) with CS₂ at 0°C produced a cyclic dithiocarbamate, 3-tert-butylthiazolidine-2-thione (1: R?=?Bu^t), rather than alkaline metal or ammonium salts of [S₂CN(Bu^t)CH₂CH₂OH]^?. This is in contrast to isolation of stable alkaline metal or ammonium salts of [S₂CN(R)CH₂CH₂OH]^? (R?=?Me, Et, Pr, or CH₂CH₂OH) obtained in analogous reactions. The use of Ni(OAc)₂, both as a source of Ni(II) and a weaker base, in a one-pot reaction with (3: R?=?Bu^t) and CS₂, successfully gave the first reported metal complex of [S₂CN(Bu^t)CH₂CH₂OH]^?, namely [Ni{S₂CN(Bu^t)CH₂CH₂OH}₂] (2: R?=?Bu^t). Compounds 1 and 2 have been fully characterized by infrared and NMR spectroscopies, and by X-ray crystallography. DFT calculations on the cyclization and stabilities of [S₂CN(R)CH₂CH₂OH]^? (R?=?Pr and Bu^t) have been carried out.     

Polarographic behaviour of α- and γ-substituted acetoacetanilide derivatives in alcoholic aqueous media

A polarographic study on a series of newly synthesized compounds, namely N-(3-pyridyl)-2,3-dioxobutanamide-2-arylhydrazones (1 a–f) in a wide range ofpH is reported and discussed. CPE indicated that these compounds are reduced in the hydrazono form. A scheme is proposed and confirmed through isolation and identification of 2,5-dimethyl-3,6-di[N-(3-pyridyl)amide]-1,4-dihydro-pyrazine as an electrolysis product.

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Das polarographische Verhalten von - und -substituierten Acetoacetanilid-Derivaten in alkoholisch-wäßrigem Medium

Zusammenfassung Es wird über eine polarographische Untersuchung einer Reihe von neu synthetisierten Verbindungen, die N-(3-pyridyl)-acetoacetamid--arylhydrazone1 a–fbd, in einem weitenpH-Bereich berichtet. Kontrollierte Potential-Elektrolyse (CPE) zeigte, daß diese Verbindungen in ihrer Hydrazonoform reduziert werden. Es wird ein Reaktionsschema vorgeschlagen und auch mit der Isolierung und Identifizierung von 2,5-Dimethyl-3,6-di[N-(3-pyridyl)amid]-1,4-dihydropyrazin als Elektrolyseprodukt belegt.

     

Single sensor for multiple analytes: fluorogenic detection of Al3+ in aqueous media and AcO− in organic media

A simple novel receptor, designed to have a combination of both oxygen and nitrogen-binding sites for metal ion and hydrogen bond donor sites for anion, was synthesised. The receptor has been explored for the selective detection of cation Al³⁺ over the other interfering metal ions and anion AcO^?  against a range of physiologically relevant anions in the fluorescence spectroscopy. The receptor shows a different response to aluminium and acetate in the emission spectra. The binding isotherm and detection limit demonstrate that the receptor is an excellent fluorometric probe for Al³⁺ and AcO^? .     

Nanotubes as polymer composite reinforcing additive materials – A comparative study

Nitrogen-doped bamboo-shaped carbon nanotubes (N-BCNTs) and their non-doped conventional counterparts, multiwalled carbon nanotubes (MWCNTs) were compared as polymer reinforcing additives in polyvinyl chloride (PVC) matrix. The nanotubes were synthetized by catalytic chemical vapor deposition (CCVD) method. The purity of both nanotubes was measured by thermogravimetric analysis (TGA) and found to be >91%. Further analysis on the morphology and size of the carbon nanotubes (CNTs) were performed by transmission electron microscopy (TEM). The PVC powder was impregnated with CNTs in ethanol by using tip ultrasonicator. The dispersion media was evaporated, and the CNT/PVC powder was used to produce polymer fibers. The orientation of carbon nanotubes in the PVC matrix was characterized by scanning electron microscopy (SEM), and the presence of nanotubes were confirmed in case of all PVC samples. It can be observed on the SEM images that the nanotubes are fully covered with PVC. The tensile strength of the nanotube containing samples was tested and the N-BCNT/PVC composite was found to be better in this sense, thanks to the extraordinary structure of the nanotube. In case of the N-BCNT/PVC composite the measured young modulus was 39.7% higher, while the elongation at brake decreased by 33.6% compare to the MWCNT/PVC composite. These significant differences in the mechanical properties of the composites can be explained with the stronger interaction between N-BCNTs and PVC.     

Gas chromatographic determination of perfluorocarboxylic acids in aqueous samples – A tutorial review

Determination of perfluorocarboxylic acids (PFCAs) by gas chromatography (GC) has been undertaken since 1980. However, only small number of studies can be found in the literature due to the major drawbacks associated with the GC determination of PFCAs such as high detection limits, a small range of analytes, long analysis time, and laborious derivatization prior to chromatographic separation. Liquid chromatography-tandem mass spectrometry (LC–MS²) can overcome these limitations of GC, and therefore has become the method of choice for the determination of PFCAs since 2001. Nevertheless, GC as a low-cost and commonly available analytical technique should not be ignored because of its inherent advantage over LC to identify PFCA isomers in environmental and biological matrices owing to its high-resolution power. In addition, GC provides an opportunity to crosscheck LC–MS² results that are often suspicious due to background contamination. This tutorial provides an overview of GC methods that have been used for the determination of PFCAs after derivatization. Moreover, performance characteristics of GC–MS are compared with that of LC–MS². PFCAs in aqueous samples were determined by both analytical techniques, and two sets of measurements were compared using the Bland-Altman plot. For both methods, reasons for false-positive and false-negative results (overestimation and underestimation of the PFCA concentration, respectively) are discussed, and accordingly some advice is offered on how to avoid erroneous results. Finally, major applications of GC and its future perspectives for the determination of PFCAs are discussed.