Presence Of CBr4 Research Articles

Base-promoted triple cleavage of CCl2Br: a direct one-pot synthesis of unsymmetrical oxalamide derivatives.

We present a novel, eco-friendly and one-pot approach for synthesizing unsymmetrical oxalamides with the aid of dichloroacetamide and amine/amides in the presence of CBr4 in a basic medium. The use of water as a potent supplement for the oxygen atom source and the detailed mechanism have been disclosed. Moreover, the protocol involves triple cleavage of CCl2Br and the formation of new C-O/C-N bonds, with the advantage of achieving selective bromination using CBr4 with good to excellent yield under mild conditions. The method also demonstrates promise for industrial use, as proven by its effective implementation in gram-scale synthesis conducted in a batch process, along with its utilization in a continuous-flow system.

Base-promoted, CBr4-mediated tandem bromination/intramolecular Friedel-Crafts alkylation of N-aryl enamines: a facile access to 1H- and 3H-indoles.

Described here is a general and highly efficient method for the synthesis of 1H- and 3H-indoles. In the presence of CBr4 and a suitable base, the cyclization of N-aryl enamines proceeds with high efficiency. Unlike previous intramolecular cross dehydrogenative coupling (CDC) of the same substrates, this process does not require the use of either a transition metal or a stoichiometric amount of oxidant. This method also features operational simplicity, easy scalability and good substrate tolerability. Control experiments indicate the reactions may proceed in a tandem sequence of bromination and intramolecular Friedel-Crafts alkylation in a simple one-pot procedure.

Amidation of Diamantane with Organic Nitriles and CBr4 Under the Action of Granulated Zeolite FeHY

N-(1- and 4-diamantyl)amides have been synthesized by the reaction of diamantane with organic nitriles in the presence of CBr4 under the action of granulated zeolite FeHY. The optimal ratios of the catalyst, reagents and the conditions for preparation of 1-N-diamantylamides in high yield have been found.

The Role of Chain Transfer Agent in Reducing Branching Content in Radical Polymerization of Acrylates

Intramolecular transfer to polymer, and the reactions of the resulting midchain radical, are important processes in determining both the reaction kinetics and microstructure of acrylic polymers produced by radical polymerization. Herein, the causes of the reduction in branching content when adding chain transfer agent (CTA) to the polymerization mixture are unveiled. Quantitative NMR spectroscopy is used to determine the distribution of product species from the reaction of n-butyl acrylate in the presence of CBr4. It is shown that the reduction of branching is the result of the combined effect of a lower backbiting rate and the removal of the resulting midchain radical via transfer to CTA. The first effect is due to the minimum chain length required for backbiting to occur, and the second one is operative at high CTA/monomer ratios but becomes negligible at high concentrations of monomer.

Copper-catalyzed intermolecular amidation and imidation of unactivated alkanes.

We report a set of rare copper-catalyzed reactions of alkanes with simple amides, sulfonamides, and imides (i.e., benzamides, tosylamides, carbamates, and phthalimide) to form the corresponding N-alkyl products. The reactions lead to functionalization at secondary C–H bonds over tertiary C–H bonds and even occur at primary C–H bonds. [(phen)Cu(phth)] (1-phth) and [(phen)Cu(phth)2] (1-phth2), which are potential intermediates in the reaction, have been isolated and fully characterized. The stoichiometric reactions of 1-phth and 1-phth2 with alkanes, alkyl radicals, and radical probes were investigated to elucidate the mechanism of the amidation. The catalytic and stoichiometric reactions require both copper and tBuOOtBu for the generation of N-alkyl product. Neither 1-phth nor 1-phth2 reacted with excess cyclohexane at 100 °C without tBuOOtBu. However, the reactions of 1-phth and 1-phth2 with tBuOOtBu afforded N-cyclohexylphthalimide (Cy-phth), N-methylphthalimide, and tert-butoxycyclohexane (Cy-OtBu) in approximate ratios of 70:20:30, respectively. Reactions with radical traps support the intermediacy of a tert-butoxy radical, which forms an alkyl radical intermediate. The intermediacy of an alkyl radical was evidenced by the catalytic reaction of cyclohexane with benzamide in the presence of CBr4, which formed exclusively bromocyclohexane. Furthermore, stoichiometric reactions of [(phen)Cu(phth)2] with tBuOOtBu and (Ph(Me)2CO)2 at 100 °C without cyclohexane afforded N-methylphthalimide (Me-phth) from β-Me scission of the alkoxy radicals to form a methyl radical. Separate reactions of cyclohexane and d12-cyclohexane with benzamide showed that the turnover-limiting step in the catalytic reaction is the C–H cleavage of cyclohexane by a tert-butoxy radical. These mechanistic data imply that the tert-butoxy radical reacts with the C–H bonds of alkanes, and the subsequent alkyl radical combines with 1-phth2 to form the corresponding N-alkyl imide product.

Multibrominated Hyperbranched Polymers: Synthesis and Further Functionalizations by ARGET ATRP or Click Chemistry

Hyperbranched polymers with multiple alkyl bromide peripheral groups were synthesized by the copolymerization of styrene with ethylene glycol dimethacrylate (2.5, 5.0, 7.5, or 10.0 mol% relative to styrene) in the presence of CBr(4) (10-20-fold excess vs. the radical initiator). The latter compound markedly delayed the gelation and served as the source of terminal bromine atoms via transfer to the propagating radicals. The degree of branching increased with the amount of crosslinker. The alkyl bromide groups were used in further chemical modifications (ATRP at low catalyst concentration or azidation with NaN(3) followed by CuBr-catalyzed click coupling of an alkyne-terminated polymer) that yielded star copolymers with hyperbranched cores.

Effect of carbon tetrabromide on the morphology of GaAs nanowires

Carbon is a commonly used p-type dopant in planar III–V semiconductors, however its usein nanowire (NW) growth has been much less reported. In this work we show that themorphology of gold assisted GaAs NWs can be strongly modified by the presence ofCBr4 vapor during growth by metalorganic vapor phase epitaxy. GaAs NWs were grownunder conditions which result in strong tapering and lateral growth at low growthtemperatures by the use of triethylgallium (TEGa) instead of the more usual precursor,trimethylgallium (TMGa). Under these conditions, NWs grown in the presence ofCBr4 exhibithigher axial and lower radial growth rates, and negligible tapering compared with NWs grown in the absenceof CBr4 under the same conditions. We attribute this primarily to the suppression of the 2d growth rate byCBr4, which enhances the axial growth rate of the nanowires. NWs grown withCBr4 show stacking-fault-free zincblende structure, while the NWs grown withoutCBr4 show a high density of stacking faults. This work underlines the striking effects whichprecursor chemistry can have on nanowire morphology.

ChemInform Abstract: Photochemical Oxidation of 4H-Seleno(thio)pyrans.

Oxidation of solutions of 4H-thiopyrans and 4H-selenopyrans to the corresponding heteroaromatic cation bromide occurs on irradiation with ultraviolet light in the presence of CBr4. Reaction takes place by a free radical chain mechanism. The presence of CHBr3 and C2Br6 in the reaction mixture was detected chromatographically.

Reactions Starting from Diiron Propanedithiolate [(μ-SCH2)2CH(OH)]Fe2(CO)6 Leading to Malonyl-, PPh3-, and [60]Fullerene-Containing Compounds Relevant to the Active Site of FeFe-Hydrogenases

As the active site models of FeFe-hydrogenases, a series of new diiron propanedithiolate compounds (1−7) have been synthesized starting from [(μ-SCH2)2CH(OH)]Fe2(CO)6 (A). Treatment of A with ethyl malonyl chloride or malonyl dichloride in the presence of pyridine gave the malonyl-containing compounds [(μ-SCH2)2CHO2CCH2CO2Et]Fe2(CO)6 (1) and [Fe2(CO)6(μ-SCH2)2CHO2C]2CH2 (2) in 64% and 55% yields, respectively. While A reacted with PPh3 in the presence of Me3NO to give the PPh3-substituted compound [(μ-SCH2)2CH(OH)]Fe2(CO)5(PPh3) (3) in 91% yield, reaction of 3 with malonyl dichloride in the presence of pyridine produced the malonyl-containing compound [Fe2(CO)5(PPh3)(μ-SCH2)2CHO2C]2CH2 (4) in 67% yield. More interestingly, compounds 1, 2, and 4 could react with C60 in the presence of CBr4 and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) via Bingel−Hirsch reaction to afford the [60]fullerene compounds [(μ-SCH2)2CHO2CC(C60)CO2Et]Fe2(CO)6 (5), [Fe2(CO)6(μ-SCH2)2CHO2C]2C(C60) (6), and [Fe2(CO)5(PPh3)(μ-SCH2)2CHO2C]2C(C60) (7) in 36−39% yields. While new compounds 1−7 were characterized by elemental analysis and various spectroscopic methods, 1−4 were further characterized by X-ray crystallography, and the photoinduced H2 evolution catalyzed by 5 was preliminarily investigated.

CBr4 Catalyzed Synthesis of Aryl-14H-dibenzo[a, j] Xanthenes Under Solvent-free Conditions

A convenient procedure has been developed for the synthesis of heteroaryl, aryl and alkyl 14-[H]-dibenzo [a,j] xanthenes by one-pot condensation of β-naphthol with heteroaryl, aryl and alkyl aldehydes in the presence of CBr4, under solvent free conditions in very good yields. The catalyst is readily available and is inexpensive to promote the synthesis of xanthenes. Keywords: Xanthenes, aldehydes, β-naphthol, CBr4, one-pot condensation, metal free conditions

Novel flexible network polymers consisting of oligomeric primary polymer chains originated in the mechanistic discussion of multiallyl crosslinking polymerization

It is well known that allyl monomers polymerize only with difficulty and yield polymers having low molecular weights, i.e., oligomers. Inevitably, free-radical multiallyl crosslinking polymerization provides network polymers consisting of oligomeric primary polymer chains, i.e., having abundant dangling chains. This led to the development of novel flexible network polymers such as amphiphilic network polymers (I) consisting of short primary polymer chains and long crosslink units with opposite polarities, simultaneous interpenetrating networks (II) consisting of both polyurethane (PU) and polymethacrylate (PM) networks with oligomeric primary polymer chains, and network polymers (III) consisting of centipede-type primary polymer chains. Thus, the solution copolymerizations of benzyl methacrylate with tricosaethylene glycol dimethacrylate in the presence of lauryl mercaptan yielded I consisting of nonpolar, short primary polymer chains and polar, long crosslink units. The opposite type of I was prepared by the copolymerization of 2-hydroxyethyl methacrylate, a polar monomer having a hydroxyl group, with heneicosapropylene glycol dimethacrylate, a nonpolar monomer having a poly(oxypropylene) unit. The equimolar polyaddition crosslinking reaction of poly(methyl methacrylate-co-2-methacryloyloxyethyl isocyanate) with tri(oxytetramethylene) glycol, leading to PU networks, and the free-radical crosslinking copolymerization of methyl methacrylate with tri(oxytetramethylene) dimethacrylate in the presence of CBr4, leading to PM networks, were progressed simultaneously, providing II formed via the topological crosslink between PU and PM network structures. The post-copolymerizations of oligomeric allyl methacrylate/alkyl methacrylate precopolymers, having different amounts of pendant allyl groups and different molecular weights, with allyl benzoate/vinyl benzoate monomer mixtures were conducted to give III.

Approach to Ideal Simultaneous Interpenetrating Network Formation via Topological Cross-Links between Polyurethane and Polymethacrylate Network Polymer Precursors

The equimolar polyaddition cross-linking reaction of poly(methyl methacrylate-co-2-methacryloyloxyethyl isocyanate) with tri(oxytetramethylene) glycol leading to polyurethane (PU) networks was carried out in methyl benzoate at a 0.1 mol/L concentration of functional groups at 80 °C. Simultaneously, the free-radical cross-linking copolymerization of methyl methacrylate with tri(oxytetramethylene) dimethacrylate leading to polymethacrylate (PM) networks was progressed at a dilution of 1/10 in the presence of CBr4 as a chain transfer agent. The simultaneous interpenetrating networks (SINs) were formed via the topological cross-links between PU and PM network structures introduced by the respective intramolecular cross-linking reactions. Under the same polymerization conditions, no gelation was observed for respective cross-linking homopolymerizations leading to PU and PM homo-networks because respective intramolecular cross-linking reactions would be enhanced at a diluted solution. The topological cross-link...

Crosslinking polymerization leading to interpenetrating polymer network formation. 3. Polyaddition crosslinking reaction of poly(methyl methacrylate-co-2-methacryloyloxyethyl isocyanate) with poly(oxytetramethylene) glycol in the presence of linear polymethacrylate resulting in semi-interpenetrating polymer network

As part of a series of our works concerned with the elucidation of the crosslinking polymerization mechanism leading to the interpenetrating polymer network (IPN) formation, in which IPN consists of both polyurethane (PU) and polymethacrylate (PM) networks, this article deals with the polyaddition crosslinking reactions of poly(methyl methacrylate-co-2-methacryloyloxyethyl isocyanate) poly(MMA-co-MOI) [MMA/MOI = 99/1] as a novel multifunctional polyisocyanate with poly(oxytetramethylene) glycol [H-(OCH2CH2CH2CH2)n-OH (n = 28)] (POTMG-28) in the presence of two types of linear PMs, differently miscible with the resulting PU networks, leading to semi-IPN formation. Thus, poly(MMA-co-MOI) was prepared by the radical copolymerization of MOI with MMA in the presence of CBr4 as a chain-transfer agent. No influence of the linear PM on the rate of polyaddition crosslinking reaction was observed. The actual gel points were compared with the theoretical ones calculated according to Macosko's equation: the deviation of the actual gel point from the theoretical one was rather small, close to the ideality, and the delayed gelation from theory tended to become a little smaller in the presence of PM. These are discussed mechanistically to deepen the understanding of the PU network formation in the presence of a linear PM resulting in semi-IPN, along with the data of the intrinsic viscosities of resulting prepolymers. To collect a direct evidence of semi-IPN formation, we attempted to pursue the incorporation of the linear PM into the resulting PU networks by 1H-NMR and UV-vis spectroscopy; in the latter case, the copolymers containing a small amount of pyrenyl methacrylate were used as linear PMs because the pyrenyl group was employed as the probe for UV-vis spectroscopic determination of the amount of the incorporated PM. The swelling ratio of the gel became lower in the presence of a linear PM. All data for the polyaddition crosslinking reactions of poly(MMA-co-MOI) with POTMG-28 in the presence of PM, along with the mechanistic discussion, demonstrate that the freely compatible molecular interaction would lead to a true semi-IPN formation as a result of the good miscibility between PU networks and a linear PM. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1198–1208, 2004

Crosslinking polymerization leading to interpenetrating polymer network formation. I. Polyaddition crosslinking reactions of poly(methyl methacrylate‐co‐2‐methacryloyloxyethyl isocyanate)s with ethylene glycol resulting in polyurethane networks

AbstractAt the start of our research program concerned with the elucidation of the crosslinking polymerization mechanism leading to interpenetrating polymer network (IPN) formation, in which IPNs consist of both polymethacrylates and polyurethane (PU) networks, this article deals with the polyaddition crosslinking reaction leading to PU network formation. Therefore, 2‐methacryloyloxyethyl isocyanate (MOI) was radically copolymerized with methyl methacrylate (MMA) in the presence of CBr4 as a chain‐transfer agent. The resulting poly(MMA‐co‐MOI)s, having pendant isocyanate (NCO) groups as novel multifunctional polyisocyanates, were used for polyaddition crosslinking reactions with ethylene glycol as a typical diol. The second‐order rate constants depended on both the functionality of poly(MMA‐co‐MOI) and the NCO group concentration. The actual gel points were compared with the theoretical ones calculated according to Macosko's equation; the deviation of the actual gel point from the theoretical value became more remarkable for a greater functionality of poly(MMA‐co‐MOI) and at a lower NCO group concentration or at a lower poly(MMA‐co‐MOI) concentration. These are discussed mechanistically, with consideration given to the significance of intramolecular cyclization and intramolecular crosslinking reactions leading to the shrinkage of the molecular size of the prepolymer, along with the data of the intrinsic viscosities of resulting prepolymers and the swelling ratios of resulting gels. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 606–615, 2003

First examples of the selective carbonylation of C 6[sbnd]C 10 linear alkanes to tertiary carbonyl-containing compounds

The carbonylation of C6–C10n-alkanes with CO in the presence of CBr4·2AlBr3 at –40 °C and 1 atm CO leads to the products of non-destructive carbonylation, i.e., the esters of tertiary carboxylic acids, R1C(Me)2COOR and R2(Et)C(Me)COOR, after the workup of reaction mixtures with ROH.

Functionalization of alkanes and cycloalkanes by superelectrophiles. 15. Carbonylation of cycloheptane, cyclooctane, and isomeric monoalkylcyclohexanes with CO in the presence of CBr4·2AlBr3 to form individual esters of tertiary carboxylic acids of the cyclohexane series

Cycloheptane, methylcyclohexane, cyclooctane, and ethylcyclohexane were selectively carbonylated with CO. The reactions of cycloalkanes with CO at –40 °C in the presence of the superelectrophilic system CBr4·2AlBr3 in CH2Br2 followed by treatment of the reaction mixtures with alcohols afforded esters of 1-methylcyclohexanecarboxylic acid (in the reactions of cycloheptane and methylcyclohexane) or esters of 1-ethylcyclohexanecarboxylic acid (in the reactions of cyclooctane and ethylcyclohexane) in 70—80% yields with respect to CBr4·2AlBr3. The reaction of 1,3-dimethylcyclohexane at –40 °C and the reactions of cyclooctane and ethylcyclohexane and at –20 °C proceeded nonselectively to form four isomeric esters C8H15COOR.

Carbonylation of C7C8 cycloalkanes leading to individual tertiary carbonyl-containing compounds

Carbonylation of cycloheptane, methylcyclohexane, cyclooctane and ethylcyclohexane by CO in the presence of CBr4·2AlBr3 at −40°C and 1 atm was performed with good yields and selectivities. Individual esters of tertiary carboxylic acids of the cyclohexane series were the products of these cycloalkane carbonylations.

Photochemical oxidation of 4h-seleno(thio)pyrans

Oxidation of solutions of 4H-thiopyrans and 4H-selenopyrans to the corresponding heteroaromatic cation bromide occurs on irradiation with ultraviolet light in the presence of CBr4. Reaction takes place by a free radical chain mechanism. The presence of CHBr3 and C2Br6 in the reaction mixture was detected chromatographically.

A PHOTOCHEMICAL TECHNIQUE TO ENHANCE SENSITIVITY OF DETECTION OF FLUORESCENCE RESONANCE ENERGY TRANSFER

Abstract: A photochemical kinetic method of measuring small values of efficiency of fluorescence resonance energy transfer (FRET) between special probes is proposed. The FRET efficiency (ω) is determined from kinetics of the photochemical reaction of the energy acceptor sensitized by FRET from the energy donor. The choice of an appropriate donor‐acceptor pair permits the minimization of background reactions. Application of the method is demonstrated by the detection of FRET from 2,5‐bis(5‐tert‐butyl‐2‐benzoxasolyl)thiophen (BBOT) to acridine orange (AO) in phospholipid vesicles. Photobleaching of AO in the presence of CBr4 was applied as a photochemical reaction of the acceptor. The reaction was monitored by steady‐state fluorescence measurements. The FRET measurements were carried out by the proposed technique when the probe/lipid ratio and ω were as small as 1.1 × 10−5M/M and 0.0017, respectively. Under these conditions, the rate constant of AO photobleaching was increased by 26% as compared with that of the reference sample without BBOT. The results suggest that applications of the technique may be useful in the study of the membrane topography.

A PHOTOCHEMICAL TECHNIQUE TO ENHANCE SENSITIVITY OF DETECTION OF FLUORESCENCE RESONANCE ENERGY TRANSFER

Abstract –A photochemical kinetic method of measuring small values of efficiency of fluorescence resonance energy transfer (FRET) between special probes is proposed. The FRET efficiency (Ω) is determined from kinetics of the photochemical reaction of the energy acceptor sensitized by FRET from the energy donor. The choice of an appropriate donor‐acceptor pair permits the minimization of background reactions. Application of the method is demonstrated by the detection of FRET from 2,5‐W.s(5‐tert‐butyl‐2‐benzoxasolyl)thiophen (BBOT) to acridine orange (AO) in phospholipid vesicles. Photobleaching of AO in the presence of CBr4 was applied as a photochemical reaction of the acceptor. The reaction was monitored by steady‐state fluorescence measurements. The FRET measurements were carried out by the proposed technique when the probe/lipid ratio and Ω were as small as 1.1 times 10‐5M/Mand 0.0017, respectively. Under these conditions, the rate constant of AO photobleaching was increased by 26% as compared with that of the reference sample without BBOT. The results suggest that applications of the technique may be useful in the study of the membrane topography.