Dehydrogenation Agent Research Articles

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Functionalization of unactivated sp3 C—H bonds of cyclic and linear alkanes to high‐value‐added chemicals is one of the most important classes of chemical transformations and has high synthetic potential in synthetic chemistry. A metal‐free, green, and sustainable functionalization of unactivated alkyl sp3 C—H bonds is reported using iodine(III) as a feasible dehydrogenation agent under visible light or KBr, and alkyl chlorides, bromides, alcohols, and ketones could be constructed by addition of different coupling reagents. More details are discussed in the article by Zhai et al. on page 505—510.image

Efficient Photolytic Halogenation and Oxidation of Unactivated Alkyl sp3 C—H Bonds with Iodine(III)

Comprehensive SummaryA metal‐free, green, and sustainable functionalization of unactivated alkyl sp3 C—H bonds is reported using iodine(III) as a feasible dehydrogenation agent under visible light or KBr, and alkyl chlorides, bromides, alcohols, and ketones could be constructed by addition of different coupling reagents. Cheap and safe iodobenzene diacetate was used to form a radical to activate the alkyl sp3 C—H bond in a highly efficient manner, which can construct different alkylation products by adding corresponding coupling reagents.

Engineering doping and defect in graphitic carbon nitride by one-pot method for enhanced photocatalytic hydrogen evolution

Hydrogen energy, as one clean energy, is one of the important ways to decarbonize in the future. The advancement of doping and constructing defect engineering in graphitic carbon nitride (g-C3N4) show promise for artificial photosynthesis for H2 evolution using solar energy. Unfortunately, it is still difficult to generate g-C3N4 that has been co-modified by doping and defect and investigate their synergistic effects. In this study, potassium thioacetate was used first-time as a potassium source and dehydrogenation agent to prepare g-C3N4 decorated by K+ ions and cyano groups with enhanced H2 evolution by a one-step method in an air atmosphere. The presence of K+ ions can increase the density of electron clouds in the delocalized π bond of the heptazine ring. The cyano group may successfully delocalize the solitary valence electrons in conjugated heterocycles since it is a potent electron-withdrawing group. These outcomes allow the modified catalysts to achieve improved H2 evolution activity, reduced interfacial transfer resistance, and increased light absorption and photocurrent. Finally, K(0.05)-CN's photocatalytic hydrogen evolution rate (HER) rose to 1319 μmol h−1 g−1, which is five-fold better than that of CN, and the normalized HER reached 118 μmol h−1 m−2, which was much higher than other reports. This research not only offers a fresh approach to creating photocatalysts with good H2 evolution efficiency but also advances a deep understanding of how structural defects and alkali metal doping affect photocatalytic activity.

Fullerene Black: Relationship between Catalytic Activity in n-alkanes Dehydrocyclization and Reactivity in Oxidation, Bromination and Hydrogenolysis

<p>The reactivity of fullerene black in oxidation (by air oxygen or ions MnO<sub>4</sub><sup>–</sup> or Cr<sub>2</sub>O<sub>7</sub><sup>2–</sup> in solution), bromination (by Br<sub>2</sub> or (C<sub>4</sub>H<sub>9</sub>)<sub>4</sub>NBr<sub>3</sub>) and hydrogenolysis (without hydrogenation catalyst) are studied. The dehydrocyclization of <em>n</em>-alkanes over fullerene black is realized via the monofunctional mechanism, <em>i.e. </em>the dehydrogenation and cyclization stages proceed on the same catalytic center. The addition of alumina to the catalyst transforms dehydrocyclization mechanism to bifunctional one, when fullerene black acts as dehydrogenation agent. Reactivity studies and ESR spectroscopy data for initial and annealed fullerene black show the presence in fullerene black structure of both non-conjugated multiple and dangling bonds. Nonconjugated bonds determine catalytic activity and reactivity of fullerene black. They are localized in amorphous part of fullerene black. Technological aspects of fullerene black as alkanes dehydrocyclization catalyst are discussed.</p>

Metal-free dehydrogenation of amine–boranes by an N-heterocyclic carbene

The dehydrogenation of primary and secondary amine-boranes (RNH(2)·BH(3) and R(2)NH·BH(3); R = alkyl groups) was studied using the bulky N-heterocyclic carbene IPr (IPr = [(HCNDipp)C:]; Dipp = 2,6-(i)Pr(2)C(6)H(3)) as a stoichiometric dehydrogenation agent. In the case of primary amine-boranes, carbene-bound adducts IPr·BH(2)-NH(R)-BH(3) were obtained in place of the desired polymers [RNH-BH(2)](n). The secondary amine-borane (i)Pr(2)NH·BH(3) participated in dehydrogenation chemistry with IPr to afford the aminoborane [(i)Pr(2)N=BH(2)] and the dihydroaminal IPrH(2) as products. Attempts to induce H(2) elimination from the arylamine-borane DippNH(2)·BH(3) yielded a reaction mixture containing the known species IPr·BH(2)NHDipp, IPr·BH(2)NH(Dipp)-BH(3), free DippNH(2) and IPrH(2). The new hindered aryl-amine borane adduct Ar*NH(2)·BH(3) [Ar* = 2,6-(Ph(2)CH)(2)-4-MeC(6)H(2)] underwent a reaction with IPr to give IPr·BH(3) and free Ar*NH(2), consistent with the presence of a weaker N-B dative bond in Ar*NH(2)·BH(3) relative to its less hindered amine-borane analogues.

ChemInform Abstract: Synthesis of 2-Chloro-4,6-di(heteroaryl)pyrimidines.

A practical method for the preparation of 2-chloro-4,6-di(heteroaryl)pyrimidines and their 5-methyl homologues from readily available 2-chloropyrimidine and 2-chloro-5-methylpyrimidine, respectively, is described. The method is based on the addition reactions of heteroaryllithium reagents with chloropyrimidines followed by dehydrogenation of the resultant substituted dihydropyrimidines. The use of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone as the dehydrogenation agent gives the best results. Side reactions in the addition step are discussed.

First Ring Contraction-Desulfurization of 1-(Arylcarbonyl)pyrido[2,1-c]-1,4-thiazines to 1-(Arylcarbonyl)indolizines and Its Application to 3-Arylthieno[3,2-a]indolizine Synthesis

The ring contraction-desulfurization route from transient 1-(arylcarbonyl)pyrido[2,1-c]-1,4-thiazine intermediates, generated in situ from the treatment of the corresponding pyridinium salts with a base and then a dehydrogenation agent, to 1-(arylcarbonyl)indolizines was first observed. By using this route three l-arylcarbonyl-6,8-dimethylindolizines having the protected 2-thiol group were prepared and their transformation to 2-acyl-3-arylthieno[3,2-a]indolizine derivatives were performed in good yields.

Conversion of poly(1,3-dihydroisothianaphthene) into polyisothianaphthene with the new dehydrogenation agent, tert-butyl hypochlorite

The low band-gap conducting polymer, polyisothianaphthene (PITN), which is usually considered to be insoluble and cannot be processed into film, is prepared by dehydrogenation from its precursor polymer, poly(1,3-dihydroisothianaphthene) (PDHITN), in solution with the use of the new dehydrogenation agent, tert-butyl hypochlorite (tBHC), and pyridine as terminating and stabilizing agent. The PITN solution obtained is stable and a uniform PITN film can be obtained from it by casting. The resulting PITN film has less defects as reflected in its high optical absorption wavelength (λ max = 810 nm) and has good electrochromic property.

Synthesis of 2‐chloro‐4,6‐di(heteroaryl)pyrimidines

AbstractA practical method for the preparation of 2‐chloro‐4,6‐di(heteroaryl)pyrimidines and their 5‐methyl homologues from readily available 2‐chloropyrimidine and 2‐chloro‐5‐methylpyrimidine, respectively, is described. The method is based on the addition reactions of heteroaryllithium reagents with chloropyrimidines followed by dehydrogenation of the resultant substituted dihydropyrimidines. The use of 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone as the dehydrogenation agent gives the best results. Side reactions in the addition step are discussed.

Reaction of 1,1-dicyano-2,2-bis(trifluoromethyl)ethylene with arylamines

We have studied the nature and determined the application boundaries of C-alkylation of various arylamines and their derivatives with 1,1-dicyano-2,2-bis(trifluoromethyl)ethylene. The possibility of formation in these reactions of heterocyclic vicinal enaminonitriles has been shown. It has been found that in certain cases the reactions owe their complexity to oxidation- reduction process in which the electrophilic alkene plays the role of dehydrogenation agent.

New Applications of Tetracyanoethylene in Organic Chemistry

Recent applications of tetracyanoethylene in organic chemistry are reviewed; this survey is mainly concerned with selected reactions of tetracyanoethylene which have use or potential use in organic synthesis. Among other topics, this survey includes new information on molecular complexes, ozonization of alkenes and acetylenes (the Criegee reaction) dehydrogenation and tricyanovinylation reactions, reactions of tetracyanoethylene oxide, reactions with ketones and diketones, synthesis of heterocycles, cationic polymerization reactions, and industrial, and analytical applications. Cycloaddition reactions and reactions of tetracyanoethylene with organometallics are not included in this survey. 1. Introduction 2. Scope of the Review 3. Methods of Preparation 4. Toxicity and Handling 5. Chemical Reactivity 6. Tetracyanoethylene Oxide (Tetracyanooxirane); Chemical Reactivity 7. The Ozonization of Alkenes in the Presence of Tetracyanoethylene (The Criegee Reaction) 8. Tetracyanoethylene as a Dehydrogenation Agent 9. Molecular Complexes between Aromatic and Heterocyclic Compounds and Tetracyanoethylene 10. Reaction of Ketones and Diketones with Tetracyanoethylene 11. Tricyanovinylation Reactions via Tetracyanoethylene 12. Synthesis of Heterocycles via Tetracyanoethylene 13. Cationic Polymerization in the Presence of Tetracyanoethylene 14. Industrial Applications of Polymeric Tetracyanoethylene Complexes 15. Analytical Application of Tetracyanoethylene 16. Addenda

Reactivity and activation of dioxygen-derived species in aprotic media (a model matrix for biomembranes).

In aprotic media the electrochemical reduction of dioxygen yields superoxide ion (O2-), which is an effective Brønsted base, nucleophile, one-electron reductant, and one-electron oxidant of reduced transition metal ions. With electrophilic substrates (organic halides and carbonyl carbons) O2- displaces a leaving group to form a peroxy radical (ROO.) in the primary process. Superoxide ion oxidizes the activated hydrogen atoms of ascorbic acid, catechols, hydrophenazines and hydroflavins. Combination of O2- with 1,2-diphenylhydrazine yields the anion radical of azobenzene, which reacts with O2 to give azobenzene and O2- (an example of O2--induced autoxidation). With phenylhydrazine, O2- produces phenyl radicals. The in situ formation of HO2. (O2- plus a proton source) results in H-atom abstraction from allylic and other groups with weak heteroatom--H bonds (binding energy (b.e.) less than 335 kJ). This is a competitive process with the facile second-order disproportionation of HO2. to H2O2 and O2 (kbi approximately equal to 10(4) mol-1 s-1 in Me2SO). Addition of [FeII(MeCN)4] (ClO4)2 to solutions of hydrogen peroxide in dry acetonitrile catalyses a rapid disproportionation of H2O2 via the initial formation of an adduct [FeII(H2O2)2+----Fe(O)(H2O)2+], which oxidizes a second H2O2 to oxygen. In the presence of organic substrates such as 1,4-cyclohexadiene, 1,2-diphenylhydrazine, catechols and thiols the FeII-H2O2/MeCN system yields dehydrogenated products; with alcohols, aldehydes, methylstyrene, thioethers, sulphoxides, and phosphines, the FeII(H2O2)2+ adduct promotes their monoxygenation. The product from the FeO2+-H2O2 reaction, [FeII(H2O2)22+], exhibits chemistry that is closely similar to that for singlet oxygen (1O2), which has been confirmed by the stoichiometric dioxygenation of diphenylisobenzofuran, 9,10-diphenylanthracene, rubrene and electron-rich unsaturated carbon-carbon bonds (Ph2C = CPh2, PhC = CPh and cis-PhCH = CHPh). In dry ligand-free acetonitrile (MeCN), anhydrous ferric chloride (FeIIICl3) activates hydrogen peroxide for the efficient epoxidation of alkenes. The FeIIICl3 further catalyses the dimerization of the resulting epoxides to dioxanes. These observations indicate that strong Lewis acids that are coordinatively unsaturated, [FeII(MeCN)4]2+ and [FeIIICl3], activate H2O2 to form an effective oxygenation and dehydrogenation agent.(ABSTRACT TRUNCATED AT 400 WORDS)

Halbleiter‐Materialien aus der Pyrolyse von Polyphenylenen

Abstractp‐Polyphenylenes and o,m,p‐polyphenylenes are pyrolyzed at various temperatures up to 1500°C in a nitrogen atmosphere. The weight loss during the pyrolysis and the residues of pyrolysis are studied by gravimetric measurements, elemental analysis, X‐ray analysis and electrical conductivity. The results of the measurements are interpreted by correlating the mechanism of pyrolysis with the structure and the numerical values of the electrical conductivity of the corresponding residues of pyrolysis. The maximum temperature of pyrolysis has a very important meaning for the electrical conductivity of the residues of pyrolysis, where has the polymerization conditions of the various polyphenylenes play only a secondary role. Three ranges of the temperature are distinguished (up to 600°C, 600 – 800°C, above 800°C), in which the corresponding residues of the pyrolysis are novel semiconductor materials with different structures and properties. Also the significance of chlorine as dehydrogenation agent is explained; chlorine contributes to the connection of neighbouring macromolecules; thus the presence of small amounts of Cl in polyphenylenes in the first temperature range of the pyrolysis seems to be suitable.

Derivatives of 1.3-Benzdioxoles, 49 [1] Preparation and Reactions of 1.3-Benzdioxole-4.5-quinones / Derivatives of 1.3-Benzdioxoles, 49 [1] Preparation and Reactions of 1.3-Benzdioxole-4.5-quinones

Abstract Treatment of the subst. 4,5-Dihydroxy-1,3-benzdioxoles (1a-1m) with silver(I)-carbonate/Celite resp. tetrachloro-1,2-benzoquinone as dehydrogenation agent yields the 1,3-benzdioxol-4,5-quinones (2a-2m). These are darkblue or black coloured compounds with a different stability.

SO2 promoted oxidative dehydrogenation of ethylbenzene

AbstractIt has been demonstrated that SO2 acts as an efficient dehydrogenation agent in the conversion of ethylbenzene to styrene in the presence of alkali and alkaline earth metal oxide doped alumina and titania catalysts. Development of these catalysts, which give styrene yields of greater than 80% per pass, is described in the paper. The catalysts allow the use of close to stoichiometric amounts of sulphur dioxide, are active in the presence of steam diluent and show low deactivation with time. The effect of varying process conditions such as temperature, reactant concentration and diluent amount is also described.