On the Gas‐Phase Reactivity of Complexed OH+ with Halogenated Alkanes

OH⁺ is an extraordinarily strong oxidant. Complexed forms (L? OH⁺), such as H₂OOH⁺, H₃NOH⁺, or iron–porphyrin‐OH⁺ are the anticipated oxidants in many chemical reactions. While these molecules are typically not stable in solution, their isolation can be achieved in the gas phase. We report a systematic survey of the influence on L on the reactivity of L? OH⁺ towards alkanes and halogenated alkanes, showing the tremendous influence of L on the reactivity of L? OH⁺. With the help of with quantum chemical calculations, detailed mechanistic insights on these very general reactions are gained. The gas‐phase pseudo‐first‐order reaction rates of H₂OOH⁺, H₃NOH⁺, and protonated 4‐picoline‐N‐oxide towards isobutane and different halogenated alkanes C_nH_2n+1Cl (n=1–4), HCF₃, CF₄, and CF₂Cl₂ have been determined by means of Fourier transform ion cyclotron resonance meaurements. Reaction rates for H₂OOH⁺ are generally fast (7.2×10^?10–3.0×10^?9 cm³ mol^?1 s^?1) and only in the cases HCF₃ and CF₄ no reactivity is observed. In contrast to this H₃NOH⁺ only reacts with tC₄H₉Cl (k_obs=9.2×10^?10), while 4‐CH₃‐C₅H₄N‐OH⁺ is completely unreactive. While H₂OOH⁺ oxidizes alkanes by an initial hydride abstraction upon formation of a carbocation, it reacts with halogenated alkanes at the chlorine atom. Two mechanistic scenarios, namely oxidation at the halogen atom or proton transfer are found. Accurate proton affinities for HOOH, NH₂OH, a series of alkanes C_nH_2n+2 (n=1–4), and halogenated alkanes C_nH_2n+1Cl (n=1–4), HCF₃, CF₄, and CF₂Cl₂, were calculated by using the G3 method and are in excellent agreement with experimental values, where available. The G3 enthalpies of reaction are also consistent with the observed products. The tendency for oxidation of alkanes by hydride abstraction is expressed in terms of G3 hydride affinities of the corresponding cationic products C_nH_2n+1⁺ (n=1–4) and C_nH_2nCl⁺ (n=1–4). The hypersurface for the reaction of H₂OOH⁺ with CH₃Cl and C₂H₅Cl was calculated at the B3 LYP, MP2, and G3_m* level, underlining the three mechanistic scenarios in which the reaction is either induced by oxidation at the hydrogen or the halogen atom, or by proton transfer.     

The Uptake and Assembly of Alkanes within a Porous Nanocapsule in Water: New Information about Hydrophobic Confinement

In Nature, enzymes provide hydrophobic cavities and channels for sequestering small alkanes or long‐chain alkyl groups from water. Similarly, the porous metal oxide capsule [{Mo^VI₆O₂₁(H₂O)₆}₁₂{(Mo^V₂O₄)₃₀(L)₂₉(H₂O)₂}]^41? (L=propionate ligand) features distinct domains for sequestering differently sized alkanes (as in Nature) as well as internal dimensions suitable for multi‐alkane clustering. The ethyl tails of the 29 endohedrally coordinated ligands, L, form a spherical, hydrophobic “shell”, while their methyl end groups generate a hydrophobic cavity with a diameter of 11 Å at the center of the capsule. As such, C₇ to C₃ straight‐chain alkanes are tightly intercalated between the ethyl tails, giving assemblies containing 90 to 110 methyl and methylene units, whereas two or three ethane molecules reside in the central cavity of the capsule, where they are free to rotate rapidly, a phenomenon never before observed for the uptake of alkanes from water by molecular cages or containers.     

Functionalization of saturated hydrocarbons by aprotic superacids 4. Ionic bromination of ethane and other alkanes and cycloalkanes with molecular bromine in the presence of systems based on polyhalomethanes and AlBr3 under mild conditions

Aprotic organic superacids CBr₄ · 2AlBr3, CBr₄ · AIBr₃, CHBr₃ · 2AlBr₃, CCl₄ · 2AlBr3, and C₆F₅CF₃ -2AlBr3 efficiently catalyze the bromination of alkanes and cycloalkanes with Br₂. Ethane is selectively brominated at 55–65 °C to give mostly 1,2-dibromoethane (stoichiometric reaction). Propane, butane, cyclopentane, cyclohexane, and methylcyclopentane react with Br₂ at -40 to -20 °C with good selectivity affording monobromides in high yields (catalytic reactions).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1208–1213, May, 1996.     

Carbon Tetrabromide-A New Brominating Agent for Alkanes and Arylalkanes

Quantitative catalytic bromination of alkanes, cycloalkanes, and arylalkanes with carbon tetrabromide as brominating agent was accomplished for the first time.     

Oligomerization,Isomerization and Carboxylation of Alkanes and Alkenes with Galvanostatically Generated Superoxide in the Al/O2 Electrochemical Cell

Conversion of low‐value, but thermodynamically stable chemical byproducts such as alkanes or CO₂ to more valuable feedstocks is of broad‐based interest. These so‐called up‐conversion processes are expensive because they require energy‐intensive and catalytic interventions to drive reactions against thermodynamic gradients. Here we show that the nucleophilic characteristics of superoxides, generated galvanostatically in an Aluminum/O₂ electrochemical cell, can be used in tandem with the intrinsic catalytic properties of an imidazolium/AlCl₃ electrolyte to facilely upgrade alkanes (n‐decane), alkenes (1‐decene), and CO₂ feedstocks. The aluminum/O₂ electrochemical cell used to generate the superoxide intermediate is also reported to deliver large amounts of electrical energy and therefore offers a system for high‐energy density storage and for chemical up‐conversion of low‐value compounds. Chronopotentiometry, mass spectrometry and nuclear magnetic resonance were used to investigate the electrochemical features of the system and to analyze the discharge products. We find that even at room temperature, alkanes and alkenes are facilely oligomerized and isomerized at high conversions (>97 %), mimicking the traditionally produced refined products. Incorporating CO₂ in the alkane feed leads to formation of esters and formates at moderate yields (21 %).     

Oligomerization,Isomerization and Carboxylation of Alkanes and Alkenes with Galvanostatically Generated Superoxide in the Al/O2 Electrochemical Cell

Conversion of low‐value, but thermodynamically stable chemical byproducts such as alkanes or CO₂ to more valuable feedstocks is of broad‐based interest. These so‐called up‐conversion processes are expensive because they require energy‐intensive and catalytic interventions to drive reactions against thermodynamic gradients. Here we show that the nucleophilic characteristics of superoxides, generated galvanostatically in an Aluminum/O₂ electrochemical cell, can be used in tandem with the intrinsic catalytic properties of an imidazolium/AlCl₃ electrolyte to facilely upgrade alkanes (n‐decane), alkenes (1‐decene), and CO₂ feedstocks. The aluminum/O₂ electrochemical cell used to generate the superoxide intermediate is also reported to deliver large amounts of electrical energy and therefore offers a system for high‐energy density storage and for chemical up‐conversion of low‐value compounds. Chronopotentiometry, mass spectrometry and nuclear magnetic resonance were used to investigate the electrochemical features of the system and to analyze the discharge products. We find that even at room temperature, alkanes and alkenes are facilely oligomerized and isomerized at high conversions (>97 %), mimicking the traditionally produced refined products. Incorporating CO₂ in the alkane feed leads to formation of esters and formates at moderate yields (21 %).     

Biocatalytic Oxidative Cascade for the Conversion of Fatty Acids into α‐Ketoacids via Internal H2O2 Recycling

The functionalization of bio‐based chemicals is essential to allow valorization of natural carbon sources. An atom‐efficient biocatalytic oxidative cascade was developed for the conversion of saturated fatty acids to α‐ketoacids. Employment of P450 monooxygenase in the peroxygenase mode for regioselective α‐hydroxylation of fatty acids combined with enantioselective oxidation by α‐hydroxyacid oxidase(s) resulted in internal recycling of the oxidant H₂O₂, thus minimizing degradation of ketoacid product and maximizing biocatalyst lifetime. The O₂‐dependent cascade relies on catalytic amounts of H₂O₂ and releases water as sole by‐product. Octanoic acid was converted under mild conditions in aqueous buffer to 2‐oxooctanoic acid in a simultaneous one‐pot two‐step cascade in up to >99 % conversion without accumulation of hydroxyacid intermediate. Scale‐up allowed isolation of final product in 91 % yield and the cascade was applied to fatty acids of various chain lengths (C6:0 to C10:0).     

Significant Influence of Zn on Activation of the C‐H Bonds of Small Alkanes by Brønsted Acid Sites of Zeolite

Herein, we analyze earlier obtained and new data about peculiarities of the H/D hydrogen exchange of small C₁–n‐C₄ alkanes on Zn‐modified high‐silica zeolites ZSM‐5 and BEA in comparison with the exchange for corresponding purely acidic forms of these zeolites. This allows us to identify an evident promoting effect of Zn on the activation of C? H bonds of alkanes by zeolite Brønsted sites. The effect of Zn is demonstrated by observing the regioselectivity of the H/D exchange for propane and n‐butane as well as by the increase in the rate and a decrease in the apparent activation energy of the exchange for all C₁–n‐C₄ alkanes upon modification of zeolites with Zn. The influence of Zn on alkane activation has been rationalized by dissociative adsorption of alkanes on Zn oxide species inside zeolite pores, which precedes the interaction of alkane with Brønsted acid sites.     

Ruthenium‐Catalyzed meta‐Selective C?H Bromination

The first example of a transition‐metal‐catalyzed, meta‐selective C H bromination procedure is reported. In the presence of catalytic [{Ru(p‐cymene)Cl₂}₂], tetrabutylammonium tribromide can be used to functionalize the meta C H bond of 2‐phenylpyridine derivatives, thus affording difficult to access products which are highly predisposed to further derivatization. We demonstrate this utility with one‐pot bromination/arylation and bromination/alkenylation procedures to deliver meta‐arylated and meta‐alkenylated products, respectively, in a single step.     

Ruthenium‐Catalyzed meta‐Selective CH Bromination

The first example of a transition‐metal‐catalyzed, meta‐selective C? H bromination procedure is reported. In the presence of catalytic [{Ru(p‐cymene)Cl₂}₂], tetrabutylammonium tribromide can be used to functionalize the meta C? H bond of 2‐phenylpyridine derivatives, thus affording difficult to access products which are highly predisposed to further derivatization. We demonstrate this utility with one‐pot bromination/arylation and bromination/alkenylation procedures to deliver meta‐arylated and meta‐alkenylated products, respectively, in a single step.     

A Novel Hydrogen Peroxide Amperometric Sensor Based on Hierarchical 3D Porous MnO2−TiO2 Composites

A novel nanocomposite electrode based on hierarchical 3D porous MnO₂?TiO₂ for the application in hydrogen peroxide (H₂O₂) sensors has been explored. This electrode was fabricated by growing TiO₂ cross‐linked nanowires on a commercial fluorine tin oxide (FTO) glass via a hydrothermal process and subsequent deposition of 3D honeycomb‐like MnO₂ nanowalls using an electrodeposition method (denoted as 3D MNS‐TNW@FTO). The obtained 3D MNS‐TNW@FTO electrode was characterized by scanning electron microscopy (SEM), Raman spectroscopy, X‐ray diffraction (XRD), and X‐ray photoelectron spectroscopy (XPS). Based on such a unique 3D porous framework and the existence of MnO₂, the electrode demonstrates a good performance in the detection of H₂O₂, with two linear ranges from 9.8 to 125 μM and 125 μM–1.0 mM, a good selectivity of 8.02 μA mM^?1 cm^?2, and a low detection limit of 4.5 μM. In addition, the simplicity of the developed low‐cost fabrication process provides an efficient method for the mass production of electrocatalytical MnO₂?TiO₂ nanocomposites on commercial FTO glass for H₂O₂ sensing applications and can be adapted for other electrochemical sensors for various biochemical targets. It thus is beneficial for the practical usage in bioanalysis.     

Low Temperature n-alkanes Bromination without Catalysts

It has been observed that Ba (BrF₄)₂ demonstrated a high reactivity towards normal alkanes from C₆H₁₄ to C₁₆H₃₄. It has been found that the reactions ran with intensive self-heating and release of elemental bromine. The GC-MS analysis showed that the main product of Ba (BrF₄)₂ interaction with each alkane was its 3-bromoderivative. The optimal interaction parameters have been found. The heat effects of the reaction have been determined by the isothermal calorimetric method, it has been found that the heat effect of the bromination increased with the increase of the length of carbon chain of alkane.     

Synthesis of Ag Nanoparticle Doped MnO2/GO Nanocomposites at a Gas/Liquid Interface and its Application in H2O2 Detection

Ag/MnO₂/GO nanocomposites were synthesized via the method of gas/liquid interface based on silver mirror reaction, and a non‐enzymatic H₂O₂ sensor was fabricated through immobilizing Ag/MnO₂/GO nanocomposites on GCE. The composition and morphology of the nanocomposites were studied by energy‐dispersive X‐ray spectroscopy (EDS), X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Electrochemical investigation indicated that it exhibited a favorable performance for the H₂O₂ detection. Its linear detection range was from 3 μM to 7 mM with a correlation coefficient of 0.9960; the sensitivity was 105.40 μA mM^?1 cm^?2 and the detection limit was estimated to be 0.7 μM at a signal‐to‐noise ratio of 3.     

有机化合物的氧化溴化研究进展

综述了几类在氧化剂存在下的羰基α位、芳环、烯烃双键、烷基苯苄位及烷烃上的氧化溴化反应。氧化溴化体系主要有Br-/H2O2和Br-/BrO3-体系。总结了不同反应条件对反应收率的影响,并展望了该领域的研究前景。     

n-Hexane Bromination Using Barium Fluorobromate Ba(BrF4)2

It was observed that Ba(BrF₄)₂ demonstrates a high reactivity towards n-hexane. It was found that the heating the reaction mass proceed with intensive self-heating up to 40 °C and release of elemental bromine. The GC-MS analysis showed that the main product of Ba(BrF₄)₂ interaction with n-hexane is 3-bromohexane. The optimal interaction parameters were found. The heat effect of the reaction was determined by isothermal calorimetric method, it was –1451 kJ/mole. The qualitative composition of solid precipitate was determined by EDXRF and XRD analyses. BaF₂ is formed as only solid product of the reaction between Ba(BrF₄)₂ and n-hexane. It was found that conditions of researched reaction are quite unusual for known free-radical hydrogen substitution processes in case of alkanes. Also we can conclude that Ba(BrF₄)₂ is much more soft reagent is case of interaction with alkanes in comparison with BrF₃ and it can provide more or less selective bromination of alkane unlikely to BrF_3.     

Solvent‐Free Photooxidation of Alkanes by Dioxygen with 2,3‐Dichloro‐5,6‐dicyano‐p‐benzoquinone via Photoinduced Electron Transfer

Photooxidation of alkanes by dioxygen occurred under visible light irradiation of 2,3‐dichloro‐5,6‐dicyano‐p‐benzoquinone (DDQ) which acts as a super photooxidant. Solvent‐free hydroxylation of cyclohexane and alkanes is initiated by electron transfer from alkanes to the singlet and triplet excited states of DDQ to afford the corresponding radical cations and DDQ^??, as revealed by femtosecond laser‐induced transient absorption measurements. Alkane radical cations readily deprotonate to produce alkyl radicals, which react with dioxygen to afford alkylperoxyl radicals. Alkylperoxyl radicals abstract hydrogen atoms from alkanes to yield alkyl hydroperoxides, accompanied by regeneration of alkyl radicals to constitute the radical chain reactions, so called autoxidation. The radical chain is terminated in the bimolecular reactions of alkylperoxyl radicals to yield the corresponding alcohols and ketones. DDQ^??, produced by the photoinduced electron transfer from alkanes to the excited state of DDQ, disproportionates with protons to yield DDQH₂.     

Zinc(II), Cadmium(II), and Mercury(II) Complexes with the 2, 2′‐Diamino‐4, 4′‐bithiazole (DABTZ) Ligand — Syntheses and X‐Ray Crystal Structure of [Hg(DABTZ)(SCN)2]

Reaction of the ligand 2, 2′‐diamino‐4, 4′‐bithiazole (DABTZ) with Zn(ClO₄)₂, CdCl₂, and Hg(SCN)₂ gives complexes with composition [Zn(DABTZ)₂](ClO₄)₂, [Cd(DABTZ)₂Cl₂], and [Hg(DABTZ)(SCN)₂]. The complexes were characterized by elemental analyses and infrared spectroscopy. The crystal structure of the [Hg(DABTZ)(SCN)₂] was determined by X‐ray crystallography. The complex is built up of a monomeric Hg(SCN)₂ unit with one 2, 2′‐diamino‐4, 4′‐bithiazole ligand coordinated to the Hg atom via the two N atoms giving rise to a five‐member chelate ring in a distorted tetrahedral environment. There is π‐π stacking interaction between the parallel aromatic rings belonging to adjacent chain as planar species in which the mean molecular planes are close to parallel and separated by a distance of ～ 3.5Å, close to that of the planes in graphite. The coordinated 2, 2′‐diamino‐4, 4′‐bithiazole molecule is involved in hydrogen bonding acting as hydrogen‐bond donors with N atoms from the SCN ligand as potential hydrogen‐bond acceptors. The hydrogen bonding yields infinite chains parallel to the crystallographic vectors a and b. Each molecule is bonded to three neighbours. Both amine H atoms are hydrogen bonded to N atoms.     

Mechanistic Studies on the Gas‐Phase Dehydrogenation of Alkanes at Cyclometalated Platinum Complexes

In the ion/molecule reactions of the cyclometalated platinum complexes [Pt(L? H)]⁺ (L=2,2′‐bipyridine (bipy), 2‐phenylpyridine (phpy), and 7,8‐benzoquinoline (bq)) with linear and branched alkanes C_nH_2n+2 (n=2–4), the main reaction channels correspond to the eliminations of dihydrogen and the respective alkenes in varying ratios. For all three couples [Pt(L? H)]⁺/C₂H₆, loss of C₂H₄ dominates clearly over H₂ elimination; however, the mechanisms significantly differs for the reactions of the “rollover”‐cyclometalated bipy complex and the classically cyclometalated phpy and bq complexes. While double hydrogen‐atom transfer from C₂H₆ to [Pt(bipy? H)]⁺, followed by ring rotation, gives rise to the formation of [Pt(H)(bipy)]⁺, for the phpy and bq complexes [Pt(L? H)]⁺, the cyclometalated motif is conserved; rather, according to DFT calculations, formation of [Pt(L? H)(H₂)]⁺ as the ionic product accounts for C₂H₄ liberation. In the latter process, [Pt(L? H)(H₂)(C₂H₄)]⁺ (that carries H₂ trans to the nitrogen atom of the heterocyclic ligand) serves, according to DFT calculation, as a precursor from which, due to the electronic peculiarities of the cyclometalated ligand, C₂H₄ rather than H₂ is ejected. For both product‐ion types, [Pt(H)(bipy)]⁺ and [Pt(L? H)(H₂)]⁺ (L=phpy, bq), H₂ loss to close a catalytic dehydrogenation cycle is feasible. In the reactions of [Pt(bipy? H)]⁺ with the higher alkanes C_nH_2n+2 (n=3, 4), H₂ elimination dominates over alkene formation; most probably, this observation is a consequence of the generation of allyl complexes, such as [Pt(C₃H₅)(bipy)]⁺. In the reactions of [Pt(L? H)]⁺ (L=phpy, bq) with propane and n‐butane, the losses of the alkenes and dihydrogen are of comparable intensities. While in the reactions of “rollover”‐cyclometalated [Pt(bipy? H)]⁺ with C_nH_2n+2 (n=2–4) less than 15 % of the generated product ions are formed by C? C bond‐cleavage processes, this value is about 60 % for the reaction with neo‐pentane. The result that C? C bond cleavage gains in importance for this substrate is a consequence of the fact that 1,2‐elimination of two hydrogen atoms is no option; this observation may suggest that in the reactions with the smaller alkanes, 1,1‐ and 1,3‐elimination pathways are only of minor importance.     

Syntheses of Phosphoryl Chloro‐ and Bromofluorides and Crystal Structures of POFCl2 and POF2Cl

A simple procedure for the preparation of phosphoryl chlorofluorides, POFCl₂ and POF₂Cl, by chlorination of the appropriate potassium fluorophosphates, K₂PO₃F and KPO₂F₂, respectively, with PCl₅ is described. The analogous bromination with PBr₅ gives POFBr₂ and POF₂Br. However, due to low yields and high content of impurities, this method is not suitable for the synthesis of the former compound. Both chlorofluorides were crystallized from the melt at low temperatures and their crystal structures were determined by X‐ray diffraction at ?153 °C. Distorted tetrahedral molecules of POFCl₂ are only weakly associated through intermolecular O···Cl contacts forming infinite chains similarly as in crystalline POCl₃. In POF₂Cl, however, the chains are formed by the O···P contacts, and an additional P–O···Cl bridging leads to their linkage into a double‐chain structure.     

Modulating the Properties of Azulene‐containing Polymers Through Functionalization at the 2‐Position of Azulene

Poly(2‐arylazulene‐alt‐fluorene) and poly(2‐arylazulene‐alt‐thiophene) are synthesized via Suzuki and Stille cross‐coupling polymerization, respectively, using 1,3‐dibromo‐2‐arylazulenes as monomers, which are prepared by a novel directed C?H activation method of 2‐carboxylic azulene and subsequent bromination reaction. Our study shows that functionalization at the 2‐position of azulene monomers influences polymer properties. For instance, different from electron‐withdrawing groups that discourage the protonation of azulene, electron‐donating aryl groups, however, enhances the sensitivity of response to acid. Protonation of the polymers leads to significant shifts in absorption spectra accompanying with obvious color changes from green to brown in majority cases because of the formation of poly(azulenium cation). The electrochromic properties of polymers are examined, exhibiting that nature of aryl group at the 2‐position of azulene influences the stability of their electrochromic devices.