Transformation Of Alkenes Research Articles

ChemInform Abstract: Copper‐Catalyzed Electrophilic Amination of Organoboron Compounds

AbstractReview: ca. 100 refs.

An Efficient Synthesis of Fluorinated Azaheterocycles by Aminocyclization of Alkenes

A general and efficient approach to important fluorinated azaheterocycles has been developed by incorporating nucleophilic fluorination into alkene difunctionalization. This intramolecular aminofluorination transformation of alkenes has been achieved via the aminocyclization of reactive unsaturated N-iodoamines, which can be generated in situ from either unsaturated N-chloramines or their amine precursors in a one-pot protocol.

BNBTS More than Brominating Agent: Green and One-pot Route for the C-N Bond Formation in Water from Alkenes

E-mail: Kazemi_f@iasbs.ac.irReceived October 27, 2012, Accepted November 19, 2012In this paper, in addition to introducing efficient method for bromohydrin and bromoether preparation, simple,green and efficient method to C-N bond formation from alkene and N,N'-Dibromo-N,N'-1,2-ethanediyl-bis(p-toluenesulfonamide) [BNBTS] in water was investigated. The reaction between alkenes, β-cyclodexterin, andBNBTS took place in water afterward, by making media basic; it will give the corresponding valuable buildingblocks in good yields (45-79%).Key Words : C-N bond formation, BNBTS, N-bromo sulfonamide, Bromo hydrin, Building blocksIntroductionThe regioselective electrophilic addition to alkenes is ofimportance process in organic synthesis and several meth-odologies have been described in the literature. The trans-formation of alkenes into the corresponding halohydrins andhaloethers is frequently practiced in organic synthesis.

Copper-Catalyzed Electrophilic Amination of Organoboron Compounds

A new procedure for direct transformation of alkenes to tertiary alkylamines based on hydroboration and copper-catalyzed amination of alkylboranes is described. The new method is presented in a broader context provided by a brief analysis of various approaches to the formation of anti-Markovnikov hydroamination products. A short discussion of the reaction development, scope, and the mechanism are also provided. Finally, the extension of this methodology to the preparation of hindered anilines from aryl ­boronic esters is presented.

Envirocat (K10-MX)–Catalyzed Regioselective Transformation of Alkenes into Iodohydrins and β-Iodo Ethers and Further Conversion of Iodohydrins to Epoxides Using Al2O3-Na2CO3 Under MWI

Commercial K10 clay was converted to extremely efficient and environmentally friendly catalyst K10-MX for the preparation of iodohydrins and β-iodo ethers from alkenes (terminal as well as internal) using microwave irradiation. This method was further extended for the conversion of alkenes to epoxides via iodohydrin intermediate in a one-pot reaction system.

C–H Bond Activation by Oxygen-Centered Radicals over Atomic Clusters

Saturated hydrocarbons, or alkanes, are major constituents of natural gas and oil. Directly transforming alkanes into more complex organic compounds is a value-adding process, but the task is very difficult to achieve, especially at low temperature. Alkanes can react at high temperature, but these reactions (with oxygen, for example) are difficult to control and usually proceed to carbon dioxide and water, the thermodynamically stable byproducts. Consequently, a great deal of research effort has been focused on generating and studying chemical entities that are able to react with alkanes or efficiently activate C-H bonds at lower temperatures, preferably room temperature. To identify low-temperature methods of C-H bond activation, researchers have investigated free radicals, that is, species with open-shell electronic structures. Oxygen-centered radicals are typical of the open-shell species that naturally occur in atmospheric, chemical, and biological systems. In this Account, we survey atomic clusters that contain oxygen-centered radicals (O(-•)), with an emphasis on radical generation and reaction with alkanes near room temperature. Atomic clusters are an intermediate state of matter, situated between isolated atoms and condensed-phase materials. Atomic clusters containing the O(-•) moiety have generated promising results for low-temperature C-H bond activation. After a brief introduction to the experimental methods and the compositions of atomic clusters that contain O(-•) radicals, we focus on two important factors that can dramatically influence C-H bond activation. The first factor is spin. The O(-•)-containing clusters have unpaired spin density distributions over the oxygen atoms. We show that the nature of the unpaired spin density distribution, such as localization and delocalization within the clusters, heavily influences the reactivity of O(-•) radicals in C-H bond activation. The second factor is charge. The O(-•)-containing clusters can be negatively charged, positively charged, or neutral overall. We discuss how the charge state may influence C-H bond activation. Moreover, for a given charge state, such as the cationic state, it can be demonstrated that local charge distribution around the O(-•) centers can also significantly change the reactivity in C-H bond activation. Through judicious synthetic choices, spin and charge can be readily controllable physical quantities in atomic clusters. The adjustment of these two properties can impact C-H bond activation, thus constituting an important consideration in the rational design of catalysts for practical alkane transformations.

FTIR and 27Al MAS NMR analysis of the effect of framework Al- and Si-defects in micro- and micro-mesoporous H-ZSM-5 on conversion of methanol to hydrocarbons

A series of micro- and micro-mesoporous H-ZSM-5 zeolites with highly regular and, on the other side, a defective framework were prepared by synthesis and post-synthesis treatment, and their activity was investigated in transformation of methanol to low olefins, aromatics and paraffins. 27Al MAS NMR and FTIR spectroscopy of OH groups and C N groups of adsorbed d 3-acetonitrile were used for analysis of the population of framework Al- and Si-related defective sites. Beside framework Al atoms in regular Td coordination, perturbed Td coordinated Al atoms and partly extra-framework Al species, and the internal Si–OH groups as Si-related defects were identified. The increase in the concentration of framework Al- and Si-defective sites in microporous H-ZSM-5 was manifested in methanol transformation in the increased yields of aromatics and paraffins, while highly regular framework preferred formation of low C 2 and C 3 olefins. The non-defective micro-mesoporous H-ZSM-5 prepared by alkaline and subsequent oxalic acid leaching of the zeolite with silanols typical for external crystal surface gave substantially longer catalyst life-time. The micro-mesoporous H-ZSM-5 (synthesized by using carbon particles) exhibited high content of defective sites, i.e., inner silanols, interacting OH groups, perturbed framework Al atoms and Al-Lewis sites, provided a slight increase in the yield of paraffins and C 6 + aromatics, and particularly much lower catalyst life-time compared to the sample of similar composition and synthesis procedure carried out without carbon presence. These findings point out on the importance of highly regular framework of H-ZSM-5 for methanol to olefin transformation, and on the way of preparation of micro-mesoporous H-ZSM-5 by desilication with alkaline solution followed by acid leaching of electron acceptor sites, resulting in the high life-time of the catalyst.

Alkane-oxidizing metalloenzymes in the carbon cycle

This review examines the metalloenzymes that catalyze the oxidation of alkanes in the environment. The focus of the review is on what is known about the relative abundances of these metalloenzymes, their metal ion requirements, and their reaction mechanisms. The relative significance of these reactions in the global transformation of alkanes is discussed.

ChemInform Abstract: Palladium‐Catalyzed Allylic C—H Bond Functionalization of Olefins

AbstractReview: 36 refs.

Scope and Mechanism of Allylic C−H Amination of Terminal Alkenes by the Palladium/PhI(OPiv)2Catalyst System: Insights into the Effect of Naphthoquinone

Palladium-catalyzed oxidative amination of unactivated alkyl olefins has been developed to produce linear (E)-allylimides with high regioselectivity. This highly efficient transformation of alkenes has been achieved by enhancing the reoxidation of palladium with the strong oxidant PhI(OPiv)(2). The present work also provides the first systematic analysis of the mechanism of the allylic C-H oxidative amination. It has been found that naphthoquinone (NQ) plays a vital role in promoting olefin coordination to the palladium catalyst: in the absence of NQ, the turnover-limiting step is olefin coordination to palladium catalyst; in the presence of NQ, the reaction involves a rapid equilibration to give a nitrogen-coordinated olefin-Pd(NQ) complex that undergoes turnover-limiting allylic C-H bond activation to generate a pi-allyl-Pd intermediate. This work provides valuable insights for further studies on the functionalization of unactivated olefins.

Acid strength of solids probed by catalytic isobutane conversion

The literature is controversial on whether sulfated zirconia (SZ) is “just” as strong acid as H-zeolites, or a strong superacid. Spectroscopic studies of adsorbed probe molecules concluded that SZ is not a superacid, whereas acidity measurements based on Hammett indicators, alkane transformations and the 1/2% isobutane conversion test [B. Umansky, J. Engelhardt, W.K. Hall, J. Catal. 127 (1991) 128; D. Fraenkel, Chem. Lett. (1999) 917] indicated that SZ is superacidic. We for the first time applied direct acidity measurements under comparative conditions for SZ and common H-zeolites in a single series and found that the apparent acid strength order is SZ ( H 0 ∼ −18) ≫ HM (−14) > HZSM-5 (−10) ≈ HY (−9), in agreement with previous studies employing the zeolites and SZ separately. Product distribution at 1/2% isobutane conversion is in full agreement with the acid ranking and strength; SZ gives the typical pattern of known superacids (Magic Acid®, HCl–AlCl 3), whereas the weaker acid zeolites’ pattern is consistent with that of other weaker acids.

Light olefin transformation over ZSM-5 zeolites with different acid strengths – A kinetic model

In this study, we analysed the influence of the acidity of a ZSM-5 catalyst on the catalytic transformation of various short-chain olefins (ethylene, propylene and 1-butene). Four ZMS-5 catalysts with different acid strength distributions were studied at different temperatures and partial pressures. The results were fitted using a kinetic model based on a network mechanism, which details the products by type (olefins, paraffins and aromatics) and number of carbon atoms. Polanyi-type equations, supported on quantum chemical calculations, were used to derive quantitative relations between the ammonia adsorption energy, used as a measure of the acidity of a given acid site, and the energetics of the various steps involved in the reaction. It was observed that, although the qualitative aspects of the reactivity differs from olefin to olefin and according to the catalyst's acidity, the model is able to describe both activity and product distribution for all catalysts, reactants and conditions using a single reaction scheme and a single set of kinetic parameters.

ChemInform Abstract: Reactions of Nitrosonium Ethyl Sulfate with Olefins and Dienes: An Experimental and Theoretical Study.

Nitrosonium ethyl sulfate (1), which is generated in situ from ethyl nitrite and sulfur trioxide, is a convenient reagent for the one-pot transformation of olefins and dienes into substituted aldeh...

Metathesis of Alkanes and Related Reactions

The transformation of alkanes remains a difficult challenge because of the relative inertness of the C-H and C-C bonds. The rewards for asserting synthetic control over unfunctionalized, saturated hydrocarbons are considerable, however, because converting short alkanes into longer chain analogues is usually a value-adding process. Alkane metathesis is a novel catalytic and direct transformation of two molecules of a given alkane into its lower and higher homologues; moreover, the process proceeds at relatively low temperature (ambient conditions or higher). It was discovered through the use of a silica-supported tantalum hydride, ([triple bond]SiO)(2)TaH, a multifunctional catalyst with a single site of action. This reaction completes the story of the metathesis reactions discovered over the past 40 years: olefin metathesis, alkyne metathesis, and ene-yne cyclizations. In this Account, we examine the fundamental mechanistic aspects of alkane metathesis as well as the novel reactions that have been derived from its study. The silica-supported tantalum hydride catalyst was developed as the result of systematic and meticulous studies of the interaction between oxide supports and organometallic complexes, a field of study denoted surface organometallic chemistry (SOMC). A careful examination of this surface-supported tantalum hydride led to the later discovery of alumina-supported tungsten hydride, W(H)(3)/Al(2)O(3), which proved to be an even better catalyst for alkane metathesis. Supported tantalum and tungsten hydrides are highly unsaturated, electron-deficient species that are very reactive toward the C-H and C-C bonds of alkanes. They show a great versatility in various other reactions, such as cross-metathesis between methane and alkanes, cross-metathesis between toluene and ethane, or even methane nonoxidative coupling. Moreover, tungsten hydride exhibits a specific ability in the transformation of isobutane into 2,3-dimethylbutane as well as in the metathesis of olefins or the selective transformation of ethylene into propylene. Alkane metathesis represents a powerful tool for making progress in a variety of areas, perhaps most notably in the petroleum and petrochemical fields. Modern civilization is currently confronting a host of problems that relate to energy production and its effects on the environment, and judicious application of alkane metathesis to the processing of fuels such as crude oil and natural gas may well afford solutions to these difficulties.

Palladium-Catalysed Oxidation of Bicycle Monoterpenes by Hydrogen Peroxide in Acetonitrile Solutions: A Metal Reoxidant-Free and Environmentally Benign Oxidative Process

Currently, the oxidative transformations of natural olefins are complicated for competitive reactions such as isomerization, skeletal rearrangements and nucleophilic addition. These concurrent reactions are promoted by metal reoxidant, normally a Lewis acid, and by protic solvent. In this article, the oxidation of terpenes, namely camphene, β-pinene, α-pinene and 3-carene were performed in PdCl2/H2O2/CH3CN system. This metal reoxidant-free system showed highly efficient, especially on camphene and β-pinene oxidation, which resulted in the selective conversion of these substrates into epoxy-derivates and allylic oxidation products, respectively. Additionally, the effects of the principal reactional parameters such as the peroxide/catalyst and substrate/catalyst molar ratio were also investigated.

State of the metal and the mechanism of transformations of alkanes on platinum-containing zeolite catalysts

The structure and reactivity of Pt6 particles in silicalite and the sodium and hydrogen forms of zeolite ZSM-5 were investigated by density functional theory. In the case of adsorption on the sodium form and silicalite, the interaction energy is 15 and 9 kcal/mol, respectively, and a negative charge appears on the metal cluster. In the channels of the hydrogen form, the energy of absorption of a metal particle increases to 45 kcal/mol and oxidized platinum species is formed. The formation of the active center on the zeolite H-form involves the interaction of the platinum particle with an acid site, resulting in the suppression of the acidity of the support. An alternative alkane conversion mechanism is proposed, which avoids the involvement of the acid sites. Predictability of the direction of transformation of alkanes adsorbed on metal particles is shown.

Chemoselective and biomimetic hydroxylation of hydrocarbons by non-heme μ-oxo-bridged diiron(iii) catalysts using m-CPBA as oxidant

Three novel non-heme micro-oxo-bridged diiron(III) complexes [Fe2(micro-O)(L1)2] 2, where H2(L1) is N,N'-o-phenylenebis(salicylideneimine), [Fe2(micro-O)(L2)2].2H2O 4, where H2(L2) is N,N'-o-phenylenebis(3,5-di-tert-butylsalicylideneimine), and [Fe2(micro-O)(L3)2] 6, where H2(L3)=1,4-bis(2-hydroxybenzyl)-1,4-diazepane, have been isolated and studied as catalysts for the selective oxidative transformation of alkanes into alcohols using m-choloroperbenzoic acid (m-CPBA) as co-oxidant. The mononuclear iron(III) complexes [Fe(L1)Cl] 1 and [Fe(L4)Cl] 7, where H2(L4)=1,4-bis(2-hydroxy-3,5-di-tert-butylbenzyl)-1,4-diazepane, have been also isolated and those corresponding to the dimeric complexes 4 and 6 have been generated in CH3CN solution and characterized as [Fe(L2)Cl] 3 and [Fe(L3)Cl] 5 by using ESI-MS, absorption and EPR spectral and electrochemical methods. The molecular structures of 4 and 6 have been successfully determined by single crystal X-ray diffraction. Both 4 and 6 possess the Fe-O-Fe structural motif with each iron atom possessing a distorted square pyramidal coordination geometry. The steric constraint at the iron(III) center in 6 is higher than that in 4 as understood from the values of the trigonality structural index (tau: 4, 0.226, 0.273; 6, 0.449) due to the higher steric congestion built by the diazapane back bone. The micro-oxo-to-Fe(III) LMCT band for 4 is observed around 622 nm (epsilon, 1830 M(-1) cm(-1)) in methanol but is not observed in CH3CN solution and it is blue-shifted to around 485 nm (epsilon, 5760 M(-1) cm(-1)) in 6, possibly due to the higher Fe-O-Fe bond angle in the latter (4, 177.4; 6, 180 degrees). The Fe(III)/Fe(II) redox potentials of the dinuclear complexes (E1/2: 2, -0.606; 4, -0.329; 6, -0.889 V) are more negative than those for their corresponding mononuclear complexes (E1/2: 1, -0.300 V; 3, -0.269; 5, -0.289 V) due to O2- coordination. Interestingly, upon addition of peroxides (H2O2, t-BuOOH) and the peracid m-CPBA, the intensity of the phenolate-to-Fe(III) LMCT band for 2 and 6 decreases but does not exhibit any appreciable change for 4. In the presence of m-CPBA cyclohexane is selectively (A/K, 12.2) oxidized by the dimeric complex to cyclohexanol (A, CyOH) and a small amount of the further oxidized product cyclohexanone (K, CyO). However, interestingly, the corresponding monomeric complex affords enhanced yields of both CyOH and CyO but with a lower selectivity (A/K=1.7) and also 1-chlorocyclohexane via oxidative ligand transfer (OLT). The oxidation of adamantane by 4 affords exclusively 1-adamantanol (50.5%) and 2-adamantanol (9.5%) with enhanced yields over 12 h. In contrast, 3 provides 1-adamantanol (32.4%) and 2-adamantanol (14.8%) and adamantanone (14.6%) in addition to 1-chloroadamantane (14.1%) as the OLT product. The secondary C-H bond of ethylbenzene is randomly activated by both 3 and 4 to give 1-phenylethanol and acetophenone. Also, oxidation of cumene with tertiary C-H bonds to give 2-phenyl-2-propanol and the further oxidized product acetophenone is illustrated by invoking the iron-phenoxyl radical species as invoked for metalloporphyrin-catalyzed systems. The strong chemoselectivity in C-H bond activation of alkanes by 4has been illustrated by invoking the involvement of a high-valent iron-oxo intermediate generated by using m-CPBA rather than the conventional oxidants H2O2 and t-BuOOH. In contrast to 4, the complexes 2 and 6 fail to effect the oxidation of hydrocarbons in the presence of H2O2, t-BuOOH and m-CPBA as the co-oxidant.

The structure and activity of Pt 6 particles in ZSM-5 type zeolites

Density functional theory was applied to investigate the nature of active sites formed by the interaction of a Pt 6 guest particle with the silicalite and H-form of ZSM-5 as the host zeolites. Interaction of metal cluster with silicalite shows a slight stabilization (36 kJ/mol) and formation of a negatively charged Pt entity. When a metal particle is arranged in the channel of H-form substantial stabilization (187 kJ/mol) and generation of an oxidized Pt 6H + species are observed. The formation of an active site includes interaction between a platinum particle and an acid site accompanied by the suppression of zeolite acidity. The suggestion is made that the alkane transformation on supported platinum particles proceeds via metal–cyclobutane and metal–carbene intermediates and does not need the direct involvement of acid sites. The difference in catalytic behavior of the Pt 6/HZSM-5 and Pt 6/ZSM-5 systems is discussed.

N-Heptane and methylcyclohexane transformation over a HMCM-22 zeolite. Origin of the features typical of large-or of medium-pore zeolites

The main features of methylcyclohexane (mch) and n-heptane (n-C7) transformation at 350°C were compared for fresh samples of HMWW, HMFI and HFAU zeolites. With both reactions, the behavior of HMWW was between those of the medium HMFI and large pore HFAU zeolites. Thus, the values of turnover frequency (TOF) and of the TOFmch/n-C7 ratio were similar with HMWW and HMFI and much higher with HFAU. In contrast, small differences were found between product distributions over HMWW and HFAU but large differences between HMWW and HMFI. These observations can be explained by alkane transformation in the large supercages with 10-MR apertures of HMWW: the narrow apertures limit diffusion of the mch within the supercages, but not the diffusion of the products which are therefore typical of the transformation within large cages hence without any steric limitation.

Kinetic modelling of methane decomposition in a tubular solar reactor

Solar methane cracking is a promising pathway to produce hydrogen and carbon black with the bonus of zero CO 2 emission. A kinetic simulation of the methane decomposition in a tubular solar chemical reactor prototype is presented. This reactor is composed of four independent tubular reaction zones inserted in a graphite cavity receiver. Chemical reaction modelling is carried out thanks to the Dsmoke software, using a detailed kinetic scheme for the wide range modelling of alkane transformation. First, a kinetic analysis of the chemical system is presented to determine the sequence of methane cracking and a sensitivity analysis of the results on temperature (in the range 1500-2300 K) and on natural gas composition is performed. Then, a kinetic simulation of the solar reactor is proposed and implemented, in which each tubular reaction zone is modelled by three plug-flow reactors in series representing the pre-heating, isothermal, and cooling zones of the reactor. It predicts the evolution of gas species concentrations as a function of residence time. Comparisons with experimental results between 1670 K and 1770 K show good agreement for CH 4 conversion, and CH 4 and H 2 off-gas compositions.