Oxidation reactions belong to the group of the most commonly used processes in both organic and inorganic chemistry. The main issues in such transformation are usually safe handling of the oxidants as well as waste generation. Peroxymonosulfuric acid is one of the strongest oxidants. It was described for the first time in 1898 by Heinrich Caro. Nowadays, the commercial sources of KHSO5 are low-cost industrial bulk chemicals, e.g., the triple salt Oxone® (2KHSO5· KHSO4·K2SO4). These products are stable oxidizing agents commonly used in fine chemicals synthesis, and are easy to handle, non-toxic as well as generate non-polluting by-products. Over the past several years the scope of its use has extended. One of the most important transformation that have been made possible with the use of Oxone® are epoxidation and ketone formation. Epoxides and ketones are important synthetic building blocks widely used in the chemical industry for the production of pharmaceutical products, flavours, fragrances, resins, adhesives and paints. The use of Oxone® was demonstrated in several combinations both in classical methods that involved metal catalysis as well as in novel approaches with the use of microwaves and ionic liquids. Over the past 20 years, ionic liquids, together with supercritical fluids and water, have become powerful alternatives to conventional organic solvents. Ionic liquids are salts having in the structure an organic cation and an inorganic or organic anion, with a melting point below 100°C. The advantage of using ionic liquids is a big variety of available structures. Combinations of both ionic liquids and Oxone® offer an interesting alternative to classical oxidation methods used in industry.
The main advantage of biotransformation involving enzymes, compared to chemical processes, is a highly selective formation of products with precise configuration. Herein we describe enzymes participating in the oxidation processes, especially dehydrogenases and monooxygenases. Dehydrogenases are not only able to catalyze the enantioselective reduction of prochiral ketones, but they can also desymmetrize meso and prochiral diols through the enantioselective oxidation. As a result of this processes, optically active hydroxyketones, hydroxycarboxylic acids, and their derivatives are obtained. Cytochrome P450 monooxygenases (CYPs) constitute a family of heme-containing enzymes which exhibits a variety of catalytic activities. They catalyze different reactions, such as hydroxylation, epoxidation, oxidative deamination, or N- and (S)-oxidation. In the oxidation reaction with monooxygenases, the whole cells are commonly used as catalysts. The use of monooxygenases in the oxidation reaction of prochiral alkanes provides the optically active alcohols. It is very significant that these transformations are still difficult to carry out by chemical methods. Baeyer-Villiger monooxygenases (BVMO EC 1.14.13.X) effectively catalyze the nucleophilic and electrophilic oxidation reactions of various functional groups. BVMO are highly regio- and stereoselective enzymes, and their catalytic potential is used in the synthesis of optically pure lactones and esters. Keywords:
In continuation of our work, we herein describe next enzyme classes applied for oxidation reaction. Dioxygenases, oxidases, and peroxidases are successfully used in the synthesis of desymmetrization products with high yields and enantiomeric excesses. Aromatic dioxygenases, such as toluene dioxygenase (TDO), naphthalene dioxygenase (NDO), and biphenyl dioxygenase (BPDO) found in the prokaryotic microorganisms are enzymes belonging to the dioxygenase class and are the most commonly used in organic synthesis. The α-oxidation of various fatty acids in the presence of an α-oxidase from germinating peas is one of the few examples of oxidases application in asymmetric organic synthesis. The intermediary α-hydroxyperoxyacids can undergo two competing reactions: decarboxylation of the corresponding aldehydes or reduction to the (R)-2-hydroxy acids. In order to eliminate the competitive decarboxylation reaction tin(II) chloride is used as an in situ reducing agent. Peroxidases are the redox enzymes found in various sources such as animals, plants, and microorganisms. Due to the fact that, in contrast to monooxygenases, no additional cofactors are required, peroxidases are highly attractive for the preparative biotransformation. Oxidation reactions catalyzed by (halo)peroxydases are also often used in organic synthesis. N-Oxidation of amines, for instance, leads to the formation of the corresponding aliphatic N-oxides, aromatic nitro-, or nitrosocompounds. From a preparative synthesis standpoint, however, sulfoxidation of thioether is important since it was proven to proceed in a highly stereo- and enantioselective manner. Furthermore, depending on the source of haloperoxidase, chiral sulfoxides of opposite configurations can be obtained.
This paper presents methods of the synthesis and applications of biomimetic catalytic systems produced from molecularly imprinted polymers (MIP). MIPs contain cavities, which are complementary to the imprinted template, thus possess high selectivity and affinity for the molecules resembling template. MIPs have various applications such as: sorption, chromatography, solid phase extraction, drugs transport and catalysis. However, this article is a review of catalytic systems containing in their active sides one of the selected metal ions: copper(II), cobalt(II), zinc(II), iron(III) or nickel(II). Presented catalytic systems are used in hydrolysis, oxidations, hydrogenations and aldol condensation reactions. This review deals with papers published till 2013.
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The service life of magnesium anode cathodic protection systems have been in many instances, less than design calculations would predict. Testing of high potential magnesium alloys from various suppliers using the ASTM G97-89 test method indicates that efficiencies are widely variable. The literature shows that various factors such as anode current density, anode oxidation reaction, anolyte chemistry, alloy chemical composition, and alloy microstructure can affect anode efficiency. Utilities are advised to conduct tests for alloy composition, microstructure, and backfill composition on anodes from industry suppliers in order to ensure anode quality and to maximize system life. But even with constant quality control efforts the efficiency can still be low owing to operating factors. From an efficiency perspective packaged zinc anodes would be a better option under some application conditions.
PL
Czas pracy systemów ochrony katodowej z anodami magnezowymi jest w wielu przypadkach krótszy niż wskazują na to obliczenia. Testy wysokopotencjałowych stopów magnezu, pochodzących od różnych dostawców, wykonane zgodnie z ASTM G97-89, wskazują na bardzo zróżnicowaną efektywność. Zgodnie z literaturą, na wydajność anody ma wpływ szereg czynników, takich jak: gęstość prądu, anodowa reakcja utleniania, charakterystyka środowiska anodowego oraz skład chemiczny i mikrostruktura stopu. Dla zapewnienia odpowiedniej jakości i maksymalizacji czasu pracy, zaleca się wykonywanie badań składu i mikrostruktury stopu anody oraz składu zasypki. Jednak nawet przy ciągłej kontroli jakości wydajność może być niska z uwagi na czynniki zewnętrzne. Z perspektywy efektywności anody cynkowe w zasypce byłyby lepszym wyborem w niektórych aplikacjach.
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Praca miała na celu przebadanie labilnych kompleksów żelaza (III, II) jako aktywatorów tlenu cząsteczkowego w reakcjach utleniania węglowodorów nienasyconych, jak również zbadanie wpływu antyutleniaczy na tego typu procesy. Podjęto również próby ustalenia fizykochemicznych właściwości stosowanych antyutleniaczy oraz opracowanie metod oceny ich właściwości antyutleniających.
EN
The goal of present work was limited to: investigation of activation of dioxygen by iron (III, II) complexes for oxygenation of organic compounds; investigation of influence of antioxidants on this processes; correlation of the physicochemical properties of antioxidants with theis antioxidative properties.
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This review shows examples of application of Et3N in oxidations, eliminations, substitutions, and addition reactions. Triethylamine (Et3N) appears to be most popular organic amine base in organic synthetic chemistry. The popularity comes from its low price along with easiness of removal by distillation. However, Et3N is a very dangerous fire hazard when exposed to the heat, flame, or oxidizers. Their salts with inorganic acids are somewhat insoluble in most organic solvents of low polarity and for that reason may by removed from the reaction media by simple filtration. Examples of application of Et3N in oxidation reactions are shown in ozonolysis of cycloalkene 1-8 [3-5] (figs 1-4-5), and figs 1-6-8 show oxidation of 1-14, 1-16, and 1-18 alcohols, employing activated DMSO [6-12]. Various oxidation processes of hydrazones with iodide in the presence of Et3N are presented in fig. 1-9 [13]. Elimination reactions, concerned mainly with dehydrohalogenations, are described in examples of halogen derivatives of lactone 2-1 [17], ketone 2-3 [18,19], sulfone 2-6 [20], and acids 2-9 and 2-11 [21,22] (figs 2-1-5). Dehalogenation of 2-13 [23], 2-17 [26-28], and 2-22 [31-37] acid chlorides are presented in figs 2-6-8, while formation of nitrile oxides in figs 2-11-13 [38-42]. Competitive dehydrobromination and dehydrochlorination reaction occurs in the presence of Et3N in 1,1,1-trichloro-3-bromo-3-fenylopropane (2-35) is described in fig. 2-15 [44]. Mechanizm and examples of transformation of chlorosulfonyl chlorides are presented in figs 2-17-20 [47-51], and dimerization of aldiminium salts [63] in fig. 2-25 as well. Applications of Et3N in carbon-carbon bond formation in an intramolecular Heck reaction are shown in fig. 3-1 [70-74]. Example of use of Et3N in enolboronation of carbonyl compounds is described in fig. 3-2 [75-78], and additionally, in synthesis of silyl enol ethers can be found in figs 3-3-6 [89-104]. Application of Et3N as the base in neutralizing the acids liberated in preparing diazo ketones and mixed anhydrides are indicated in fig. 3-7 [105-107] and fig. 3-8 [108-117] respectively, while in protecting of hydroxy group in figs 3-9-11 [118-126]. Use of Et3N as the effective catalyst in cyjanoethylation reaction of active methyl group in acetylacetone (4-2) [130] and alkylpyridine methiodides 4-4-5, 4-8-9 [131] are shown in figs 4-1-3, and in isomerization reaction of pyrazolines 4-14 [133] and cycloaddition of indane-1,3-dione (4-16) [134] in figs.4-5?6.
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The survey applies to oxidation reaction of substituent phenols in the presence of catalysts. The transition metal complexes with various types of attached to polymer support ligands were used as these catalysts. Especially, we have paid attention to the hydroquinone oxidation to p-benzoquinone using hydrogen peroxide and atmospheric oxygen in the presence of Cu(II) complexes with ligands containing nitrogen (for example: pirydyl, aminoamidyl or guanidyl groups). Oxidation reactions of substituent phenols proceeds in accordance with Michealis-Menten kinetic in all of described systems. It can preclude neither an influence of support kind applied to the catalyst preparation nor an influence of ligand kind chelating metal ions on oxidation kinetic. The comparison of the oxidation kinetic in several systems showed the domination of polymer-metal complexes over the native metal ions and also over the catalysts being the metal complexes with the low molecular compounds (containing the same ligands as these, which were attached to polymer support).
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The conversion of NADH to NAD+ and of the reverse reaction, in the coenzyme as well as in its synthetic analogues, 1,4-dihydropyridines and 9,10-dihydroanthracenes is discussed. Two mechanisms of the NADHŰNAD+ conversion are compared: one-step hydride transfer and stepwise electron-proton-electron transfer. Direct characterization of transient species in the stepwise process, namely radical cations and radicals, is presented based on the pulse radiolysis and laser flash photolysis studies both in solution and low-temperature matrices. On ionization of NADH and 1,4-dihydropyridines the stability order of the keto and enol tautomers is inversed as compared to their neutral precursors. Both types of radical cations are characterized and their role in the stepwise process is discussed.
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