Zinc In Acid Research Articles

Identification of a reduction product of aristolochic acid: implications for the metabolic activation of carcinogenic aristolochic acid.

Aristolochic acids are nephrotoxic and carcinogenic natural products that have been implicated both in endemic nephropathy in the Balkan region and in ailments caused by ingestion of herbal remedies. Aristolochic acids are metabolized to active intermediates that bind to DNA. In this study, reduction of aristolochic acid I with zinc in acetic acid afforded a new product that was characterized as 9-methoxy-7-methyl-2H-1,3-oxazolo[5',4'-10,9]phenanthro[3,4-d]-1,3-dioxolane-5-carboxylic acid, designated as aristoxazole, along with the expected aristolactam I. This new compound is a condensation product of aristolochic acid and acetic acid that may be related to the aristolochic acid-DNA adducts. The proposed mechanism of formation of aristoxazole involves nucleophilic attack of acetic acid on the nitrenium ion of aristolochic acid I. On the basis of these studies, a route to the metabolic activation of aristolochic acids and formation of adducts with DNA in in vitro systems is proposed and discussed.

Neutralization of a sec‐Ammonium Group Unusually Stabilized by the “Rotaxane Effect”: Synthesis, Structure, and Dynamic Nature of a “Free” sec‐Amine/Crown Ether‐Type Rotaxane

A fifteen-year riddle has been settled: neutralization, the most popular chemical event, of a crown ether/sec-ammonium salt-type rotaxane has been achieved and a completely nonionic crown ether/sec-amine-type rotaxane isolated. A [2]rotaxane was prepared as a typical substrate from a mixture of dibenzo[24]crown-8 ether (DB24C8) and sec-ammonium hexafluorophosphate (PF(6)) with a terminal hydroxy group through end-capping with 3,5-dimethylbenzoic anhydride in the presence of tributylphosphane as a catalyst in 90% yield. A couple of approaches to the neutralization of the ammonium rotaxane were investigated to isolate the free sec-amine-type rotaxane by decreasing the degree of thermodynamic and kinetic stabilities. One approach was the counteranion-exchange method in which the soft counterion PF(6)(-) was replaced with the fluoride anion by mixing with tetrabutylammonium fluoride, thus decreasing the cationic character of the ammonium moiety. Subsequent simple washing with a base allowed us to isolate the free sec-amine-type rotaxane in a quantitative yield. The other approach was a synthesis based on a protection/deprotection protocol. The acylation of the sec-ammonium moiety with 2,2,2-trichloroethyl chloroformate gave an N-carbamated rotaxane that could be deprotected by treating with zinc in acetic acid to afford the corresponding free sec-amine-type rotaxane in a quantitative yield. The structure of the free sec-amine-type rotaxane was fully confirmed by spectral and analytical data. The generality of the counteranion-exchange method was also confirmed through the neutralization of a bisammonium-type [3]rotaxane. The mechanism was studied from the proposed potential-energy diagram of the rotaxanes with special emphasis on the role of the PF(6)(-) counterion.

Synthesis and Characterization of Methionine- and Cysteine-Substituted Phosphazenes

The preparation of phosphazenes that possess reversible cross-linking groups to control mechanical stability and hydrolysis has been accomplished using cysteine and methionine amino acid side groups. Small molecule models and linear polymeric phosphazenes that contain methionine ethyl ester and cysteine ethyl disulfide ethyl ester side groups were synthesized. Protection of the free thiol groups was carried out to circumvent unwanted cross-linking of the phosphazenes through the cysteine ethyl ester N- and S-termini. Cyclic trimeric cysteine ethyl disulfide ethyl ester model compounds were deprotected by S−S bond cleavage using β-mercaptoethanol, dithiothreitol (DTT), and zinc in aqueous hydrochloric acid. For the high polymeric derivatives, the extent of S−S bond cleavage varied depending on the deprotection method used. With the exception of the Zn/HCl method, the resultant deprotected polymers were soluble in common organic solvents and underwent minimal chain cleavage during the reaction sequence. The...

P‐Nitrobenzyl protection for cysteine and selenocysteine: A more stable alternative to the acetamidomethyl group

This study evaluated the acidic lability of the acetamidomethyl (Acm), trimethylacetamidomethyl (Tacm), and the p-nitrobenzyl (pNB) as protecting groups for cysteine and selenocysteine (Sec) during the tert-butyloxycarbonyl (Boc)-chemistry solid-phase peptide synthesis of oxytocin (OT). Two novel Sec building blocks (Nalpha-tert-butyloxycarbonyl-Se(acetamidomethyl)-L-selenocysteine (Boc-L-Sec(Acm)-OH) and Nalpha-tert-butyloxycarbonyl-S(4-nitrobenzyl)-L-selenocysteine (Boc-L-Sec(pNB)-OH)) were developed for this study. Six partially protected thio- and seleno-OT analogues were synthesized, purified, and exposed to neat trifluoroacetic acid (TFA) at temperatures of 25, 40, 50, and 60 degrees C for 1 h, and HF treatment at 0 degrees C for 1 h. Significant losses were observed for the Acm and Tacm group in TFA at temperatures greater than 25 degrees C and during HF treatment at 0 degrees C, whereas the pNB group remained intact. Removal of the pNB was achieved via reduction to the p-aminobenzyl group either with zinc in acetic acid in solution or via tin chloride in hydrochloric acid on solid support, followed by oxidative cleavage with iodine yielding the corresponding disulfide or diselenide bond. No major side reactions were observed. This study confirms the occasionally described Acm instability and underpins the development of the pNB group as an alternative for cysteine and Sec protection.

Hexamine as Corrosion Inhibitors forZinc in Phosphoric Acid

The corrosion of zinc in phosphoric acid containing hexamine has been studied at different acid concentrations, inhibitor concentration and temperatures. Corrosion increases with the concentration of acid and the temperature. The inhibition efficiency (IE) of hexamine increases with the concentration of inhibitor. The IE decreases with the increase in concentration of acid. As temperature increases, percentage of inhibition decreases. The plot of log (Θ/1‐Θ) versus log C results in a straight line suggest that the inhibitors cover both the anodic and cathodic regions through general adsorption following Longmuir isotherm. Galvenostatic polarization curves show polarization of both anodes as well as cathodes.

A tribute to Rolf Neeb (1929–2006) on the 80th anniversary of his birth

The year 2009 marks the 80th anniversary of the birth of the eminent German analytical chemist Rolf Neeb (Fig. 1). Sadly, Rolf Neeb passed away 3 years ago; however, the 80th anniversary of his birth is an appropriate occasion to remember his many scientific achievements, especially his contributions to electroanalytical chemistry. Rolf Neeb was born on January 7, 1929, in Mainz, the only child of the merchant Arthur Neeb and his wife Anna, nee Lerch. In Mainz he went to the Leibnitz-Volksschule from 1935 to 1939, and then until 1945 to the GutenbergOberrealschule. The war forced the Neeb family to leave Mainz and to settle temporarily in the village of Nierstein. However, Rolf Neeb was able to attend the Gymnasium (grammar school) in the nearby town of Oppenheim, and left with his Abitur (German school-leaving certificate) in 1948. In the same year he began to study chemistry at the reopened Johannes Gutenberg University in Mainz, where his teachers were W. Geilmann, F. Strassmann, T. Wieland, L. Horner, and G.V. Schulz. Neeb was a student with very wide interests, and even started to learn Arabic (personal information from T. Steudel). He finished his studies with a diploma, which was achieved under the guidance of the well-known analytical chemist Wilhelm Geilmann (May 16, 1891 to May 24, 1967) [1, 2]. Geilmann had been taught by Otto Wallach, Gustav Tammann, Richard Zsigmondy [3], and Carl Mannich [4, 5], and Mannich had supervised Geilmann’s PhD work in Hannover. Thus, one can trace Rolf Neeb’s scientific genealogy back in a straight line to the great Johann Wolfgang Dobereiner [6], who was largely self-taught (see Fig. 2). The German writer and poet Johann Wolfgang von Goethe frequently consulted Dobereiner on chemical issues, and he strongly supported his work at Jena [7]. Rolf Neeb’s diploma thesis (1954) concerned the separation of zinc from complex matrices. To achieve this he used a stream of hydrogen gas to reductively evaporate zinc metal—together with other reducible metals—and deposit them onto the cold parts of a quartz capillary. From there it was comparatively straightforward to dissolve the zinc in acid, and then determine the concentration using spectrophotometry or polarography [8, 9]. This was an early example of his scientific creativity, since we know that it was Neeb’s idea to develop such a method, not that of his supervisor (personal information from T. Steudel). Neeb stayed in Geilmann’s group and completed his PhD Anal Bioanal Chem (2009) 395:1571–1573 DOI 10.1007/s00216-009-2801-1

Complex formation of tetra(3,5-di-tert-butylphenyl)porphine with copper(II) and zinc(II) acetates in organic solvents

The effect of accumulation of the tert-butyl groups in the phenyl rings of tetraphenylporphine on the complex formation rate of tetra(3,5-di-tert-butylphenyl)porphine (I) with copper(II), zinc(II), and cadmium(II) acetates in acetic acid and in a mixed ethanol-benzene solvent was studied by the chemical kinetics method with spectrophotometric monitoring. The activation characteristics of the complex formation were calculated. The complex with zinc was found to form three times more slowly that the copper complex. Benzene additives to the organic solvent decreased the reaction rate because of steric hindrance created by the benzene molecules that formed stable solvates with compound I.

Separation of zinc and nickel ions in a strong acid through liquid–liquid extraction

Many solid wastes contain both zinc and nickel at the same time. For recycling or recovery of metals, it is essential to separate materials. Among those materials, zinc and nickel are very difficult to be separated because there is not so much difference in the chemical and physical properties. This paper focuses on the separation of zinc and nickel ions in a diluted aqua regia solution. Liquid–liquid extraction by TBP, Cyanex 272 and Cyanex 301 was used and a distribution coefficient ( D), a separation factor ( S) and a relative purity ( R) were induced to evaluate the degree of separation. All of the extractions were proportional to the concentration of the extractants, and zinc ions were extracted more easily than nickel ions. Among the extractants, Cyanex 301 showed the best characteristics regarding Zn/Ni separation. In particular, the extraction of zinc ions in the range of pH ≤ 6 was constantly over 99 wt.%, whilst that of nickel ions was less than 20 wt.%, when 100 vol.% Cyanex 301 was used. The maximum S Zn,Ni value was about 21,700 at pH 6.0 and the highest relative purity ( R) of zinc was about 99 wt.% without a pH control, pH −1.1.

Schiff bases of ethylenediamine/triethylenetetramine with benzaldehyde/cinnamic aldehyde/salicylaldehyde as corrosion inhibitors of zinc in sulphuric acid

PurposeA survey of technical literature indicates that there is a shortage of excellent corrosion inhibitors for zinc in non‐oxidizing acids, particularly sulphuric acid. This paper aims to describe the behaviour of ethylenediamine‐N‐N′‐dibenzylidene, ethylenediamine‐N‐N′‐disalicylidene, ethylenediamine‐N‐N′‐dicinnamylidene, triethylenetetramine tribenzylidene and triethylenetetramine trisalicylidene as corrosion inhibitors for zinc in sulphuric acid solutions. The objective of this research work also is to have an insight into the action mechanism of these inhibitors.Design/methodology/approachThe effect of the various parameters affecting the action of the above‐mentioned corrosion inhibitors has been studied using weight‐loss data and polarisation measurements. Adsorption data also were utilized.FindingsThe inhibitors showed excellent corrosion inhibition (>99 per cent) at effective inhibitor concentrations. The two salicylidenes were better corrosion inhibitors than were corresponding benzylidenes. It appeared from this study that an efficient inhibitor is characterised by a relatively greater decrease in free energy of adsorption, lower entropy of adsorption and relatively lower heat of adsorption. Basically, these inhibitors were cathodic, as was revealed by polarisation data, and the inhibitors followed Langmuir adsorption isotherm behaviour. In general, the conjoint action of the inhibitor and the cathodic current was synergistic.Research limitations/implicationsPowerful Schiff bases still need to be synthesized so as to be effective at extremely low concentrations. The behaviour with other metals and alloys in diverse media also requires to be investigated.Originality/valueVery few inhibitors demonstrate such excellent corrosion inhibition of zinc in aggressive corrosive media. Such detailed investigations on corrosion inhibitors are unusual.

Hydrophobic-tailed bicycloisoxazolidines: A comparative study of the newly synthesized compounds on the inhibition of mild steel corrosion in hydrochloric and sulfuric acid media

The cycloaddition reactions of the cyclic nitrones 1-pyrroline 1-oxide and 3,4,5,6-tetrahydropyridine 1-oxide with alkenes, 11-phenoxy-1-undecene and 11- p-methoxyphenoxy-1-undecene, afforded cycloaddition products (bicyclic isoxazolidines) in excellent yields. One of the cycloadducts on reaction with propargyl chloride and ring opening with zinc in acetic acid afforded quaternary ammonium salt and aminoalcohol, respectively. All the new inhibitor molecules in the presence of 400 ppm at 60 °C achieved inhibition efficiencies, determined by gravimetric method, in the range 99–99.6% and 85–99% for mild steel in 1 M HCl and 0.5 M H 2SO 4, respectively. Comparable results were obtained by the electrochemical methods using Tafel plots and electrochemical impedance spectroscopy for the synthesized compounds. The isoxazolidine derivatives were also found to be good inhibitors of mold steel corrosion in synthetic brine. Negative values of Δ G ads ∘ in the acidic media ensured the spontaneity of the adsorption process. While the corrosion inhibition by these molecules was predominantly under cathodic control in 1 M HCl, the inhibition in 0.5 M H 2SO 4 was found to be under anodic control. The isoxazolidines and their derivatives were found to be among a rare class of molecules, which provide suitable inhibition mechanism for the corrosion inhibition in HCl as well as in H 2SO 4 media.

4-Hydroxy-2-quinolones 132. Synthesis, chemical, and biological properties of 1-R-4-hydroxy-2-oxo-1,2-dihydroquinoline-3-carboxylic acids 2-nitrobenzylidenehydrazides

1-R-4-Hydroxy-2-oxo-1,2-dihydroquinoline-3-carboxylic acids 2-nitrobenzylidenehydrazides are reduced to the corresponding quinoline-3-carboxamides by zinc in glacial acetic acid but in refluxing triethylphosphite they are converted to the symmetrical N,N′-di(4-hydroxy-2-oxo-1,2-dihydro-3-quinolinoyl)hydrazines. A study of the antitubercular activity of the synthetic compounds has been carried out.

N-Bromosuccinimide assisted oxidation of 5-aminopyrazoles: formation of bis diazenylderivatives

Treatment of 5-amino-4-cyanopyrazoles with N-bromosuccinimide, in DMF at rt gave azo dyes resulting from dimerization through the amino groups and further oxidation.With bromine water the dimer was also formed but, bromination occurred on the aryl ring, either at reflux or rt. Reduction of the azo group with zinc in acetic acid originated the corresponding pyrazoles.

Synthesis of 2‐Alkyl‐1,2,4‐benzotriazin‐3(2H)‐ones and 2‐Alkyl‐1,4‐dihydro‐1,2,4‐benzotriazin‐3(2H)‐ones

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Synthesis of 2-alkyl-1,2,4-benzotriazin-3(2h)-ones and 2-alkyl-1,4-dihydro-1,2,4-benzotriazin-3(2h)-ones

A preparative method for the synthesis of 2-alkyl-1,2,4-benzotriazin-3(2H)-ones 3 was developed. The method involves treatment with sodium cyanate of 2-alkylbenzotetrazinium tetrafluoroborates, which exist in solutions in equilibrium with o-(alkylazo)aryldiazonium tetrafluoroborates. Reduction of compounds 3 with zinc in acetic acid afforded 2-alkyl-1,4-dihydro-1,2,4-benzotriazin-3(2H)-ones.

Synthesis of β-Amino Ketones and β-Amino Alcohols

Reductive ring opening of 3,5-di­substituted 2,3-dihydroisoxazoles using sodium borohydride in acetic acid followed by zinc in acetic acid gave the corresponding syn-β-amino alcohols with good yields and diastereoselectivity. The reaction can be performed in one pot. Treatment of the 3,5-disubstituted 2,3-dihydroisoxazoles with zinc and acetic acid gave the β-amino ketone in good to excellent yield. Lower yields were obtained when R1 = Ph, due to the formation of an competing α,β-unsatured ketone. An anomalous result was observed with R2 = Ph: treatment of the 2,3-dihydroisoxazole with zinc in acetic acid produced the anti-β-amino alcohol rather than the expected β-amino ketone.

Fused Supracyclopentadienyl Ligand Precursors. Synthesis, Structure, and Some Reactions of 1,3-Diphenylcyclopenta[l]phenanthrene-2-one, 1,2,3-Triphenylcyclopenta[l]phenanthrene-2-ol, 1-Chloro-1,2,3-triphenylcyclopenta[l]phenanthrene, 1-Bromo-1,2,3-triphenylcyclopenta[l]phenanthrene, and 1,2,3-Triphenyl-1H-cyclopenta[l]phenanthrene

The photochemical reaction of 1,3-diphenylcyclopenta[l]phenanthrene-2-one 5 (phencyclone) with oxygen in acetone leads to the formation of 1,2,3-trihydro-1,2,3-triphenylcyclo-penta[l]phenanthrene 7 (9,10-dibenzoylphenanthrene) along with a trace of the lactone 1,4-diphenylcyclo-3-pyran[l]phenanthrene-2-one 8. An independent synthesis of 8 was achieved by the reaction of 5 with FeCl3 in CHCl3. The treatment of 5 with phenyllithium yields 1,2,3-triphenylcyclopenta[l]phenanthrene-2-ol 9-OH in good yield. Subsequent reaction of 9-OH with SOCl2 or SOBr2 in pyridine leads to the formation of the halo-analogues 1-chloro-1,2,3-triphenylcyclopenta[l]phenanthrene 9-Cl and 1-bromo-1,2,3-triphenylcyclopenta[l]phenanthrene 9-Br, respectively. Treatment of 9-OH with HBr in acetic acid affords the rearranged product 1,1,3-triphenylcyclopenta[l]phenanthrene-2-one 10 with a trace of 9-Br. Treatment of 9-Cl or 9-Br with zinc in acetic acid affords 1,2,3-tri-phenyl-1H-cyclopenta[l]phenanthrene 9-H. 9,10-Phenanthrenediylbis(phenyl)methanone 7 is formed in good yield upon treatment of 9-OH with HI in acetic acid followed by heating with H2PO4. Compounds 7, 8, 9-Cl, 9-Br, and 10 have been structurally characterized using X-ray crystallography.

Synthesis of 2,4,5‐Trisubstituted Oxazoles.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Corrosion Inhibition of Zinc on HCl using Nypa fruticans Wurmb Extract and 1,5 Diphenyl Carbazone

The corrosion inhibition of zinc in hydrochloric acid by extract of Nypa Fruticans Wurmb was studied using weight loss techniques. Maximum inhibition efficiency (and surface coverage) was obtained at an optimum concentration. However increase in temperature decreased the inhibition efficiency at the temperature range studied. The inhibition action of Nypa Fruticans Wurmb extract compared closely to that of 1, 5 Diphenyl Carbazone (DPC). Optimum inhibition efficiency for zinc in the presence of Nypa Fruticans Wurmb extract was 36.43% and 40.70% with DPC. The phenomenon of physical adsorption has been proposed from the activation energy values (19.33 kJ mol-1 and 21.11 kJ mol-1) with Nypa Fruticans Wurmb extract and DPC respectively. A first order kinetics has been deduced from the kinetic treatment of the results. The heat of adsorption, Qad range from (-33.63 to - 58.52 kJ mo l-1) for both additives studied. Mean ΔGoads values (-7.82 to 8.68 kJ mol-1) are negative and suggestive of adsorption on metal surface. The data obtained from this study fits well into the Langmuir isotherm. Evidence is hereby provided to show that Nypa Fruticans Wurmb extract and DPC inhibits the corrosion of zinc comparatively. Journal of Applied Sciences and Environmental Management Vol. 8 (1) 2004:57 - 61

Solvothermal Synthesis and Crystal Structure of One‐Dimensional Chains of Anhydrous Zinc and Magnesium Formate

AbstractReaction of the zinc or magnesium formate dihydrates in formic acid under solvothermal conditions results in the formation of single crystals of the anhydrous metal(II) formates β‐Zn(OOCH)2 and β‐Mg(OOCH)2. Both structures form one‐dimensional chains of μ‐oxygen‐bridged metal atoms. Single crystal diffraction studies reveal that β‐zinc formate represents the first structure in which chains of oxygen‐bridged metal atoms are connected by alternating single, double and triple oxygen atom bridges resulting in the first observation of corner, edge and face sharing coordination octahedra within a single chain. Polycrystalline material can be obtained by dehydration reaction of zinc formate dihydrate. β‐magnesium formate is the crystalline product that is obtained by annealing the amorphous intermediate phase after dehydration of magnesium formate dihydrate.

Meta-Substituted aniline- N-salicylidenes as corrosion inhibitors of zinc in sulphuric acid

The corrosion of zinc in sulphuric acid containing different m-substituted aniline- N-salicylidenes has been studied with respect to inhibitor and acid concentration, period of exposure and temperature. 99% inhibitor efficiencies have been observed. It appears that the salicylidene part of the inhibitor including the iminic group in the molecule plays a dominant role in the inhibition. As far as the effect of exposure period and temperature is concerned, m-CNS has turned out to be the best one. For all the five inhibitors, the heats of adsorption and free energies of adsorption are negative, while the entropies of adsorption are positive. The free energies of adsorption are more negative in the case of very good inhibitors like m-TNS and m-CNS, indicating a strong interaction of the inhibitor molecules with the metal surface. The activation energies in the presence of these inhibitors are higher than that in plain acid. The adsorption of these inhibitors follows Langmuir adsorption isotherm. The conjoint effect of external cathodic current and the inhibitor is observed to be either synergistic or additive. Galvanostatic polarization studies indicate that these are mixed type inhibitors with predominant action on the local cathodes. Mechanism of the action of inhibitors has been provided.