Oligomérisation anionique de l'ethylène. III. Application à la synthèse d'alcools à longue chaine

Living oligomers of ethylene obtained by n-BuLi complexed with TMEDA have been deactivated by ethylene oxide. The nuclear magnetic resonance study of the product obtained allowed us to follow the influence of TMEDA toward the functionalization. Three products have been characterized: By increasing the ratio [TMEDA]/[n-BuLi] one obtains a decrease of the functionalization reaction.     

Oligomérisation anionique de l'ethylène. II. Etude des paramètres thermodynamiques

A kinetic study, as a function of temperature, of ethylene oligomerization by the n-BuLi–TMEDA complex allowed us to evaluate the thermodynamic parameters (ΔS^? < ?23.7 u.e.) and thus to support a transition state where the ethylene is coordinated to the lithium atom.     

New telechelic polymers and sequential copolymers by polyfunctional initiator-transfer agents (inifers). LIII. Lithiation of 2,4,4-trimethyl-1-pentene and isopropylidene-capped polyisobutylenes by butyllithiums in the presence of complexing agents

Lithiated isopropylidene-telechelic polyisobutylenes (i.e., PIBs capped with end groups) are most interesting novel intermediates for further transformations, e.g., functionalization, polymerization. This report concerns model lithiation experiments of 2,4,4-trimethyl-1-pentene (TM1P) that guided us toward the subsequent quantitative lithiation of isopropylidene-telechelic PIBs. Thus, lithiation of TM1P with, n-, s-, and t-butyllithium, in the presence of various complexing agents (i.e., TMEDA, t-BuOK, 1,2-DPE, CH₃OCH₂CH₂OCH₃, THF, and 12-crown-4) followed by silylation with Me₃SiCl (for the purpose of quantitation) gave three products: 2(trimethylsilylmethyl)-4,4-dimethyl-1-pentene (TM1P-Si), 2(trimethylsilylmethyl)-4,4-dimethyl-2-pentene (TM2P-Si₂). The relative product composition strongly depends on the BuLi/complexing agent ratio and temperature. Among the different butyllithiums and complexing agents the best overall results were obtained with the s-BuLi/TMEDA combination. Complete lithiation of TM1P with minimum dilithiation was obtained using the molar ratio [s-BuLi]: [TMEDA]: [TM1P] = 2 : 2 : 1. The apparent activation energy of lithiation by s-BuLi/TMEDA was found to be 6.7 ± 0.8 kcal/mol. Guided by TM1P model experiments, quantitative monolithiation of isopropylidene-capped polyisobutylene (including ca. 4% chain and isomerization) was achieved using the molar ratio [s-BuLi] : [TMEDA] : [C? C] = 5 : 4 : 1.     

Cluster ions in the secondary ion mass spectrometry of choline and acetylcholine halides

Liquid secondary ion mass spectra of choline and acetylcholine halides exhibit several series of cluster ions whose origins were investigated using B/E and B²/E linked-scan techniques. In the case of choline halides three series of cluster ions were identified as (Me₃$ \mathop {\rm N}\limits^ + $CH₂CH₂OH + nM), (Me₃$ \mathop {\rm N}\limits^ + $CH₂CH₂OMe + nM) and (Me₃N$ \mathop {\rm N}\limits^ + $CH₂CH₂OH · Me₃$ \mathop {\rm N}\limits^ + $CH₂CH₂O^? + nM), while (CH₃COOCH₂CH₂$ \mathop {\rm N}\limits^ + $Me₃ + nM), (Me₃$ \mathop {\rm N}\limits^ + $CH₂CH₂OH + nM) and (CH₂ = CH$ \mathop {\rm N}\limits^ + $Me₃ + nM) were observed in the spectra of acetylcholine halides. For these cluster ions, bimolecular reactions induced on ion bombardment under secondary ion mass spectrometric conditions are discussed.     

Ab initio molecular orbital study on the structures and energetics of CH3OH\documentclass{article}\pagestyle{empty}\begin{document}$_{2}^{+}$\end{document}(H2O)n and CH3SH\documentclass{article}\pagestyle{empty}\begin{document}$_{2}^{+}$\end{document}(H2O)n in the gas phase

The purpose of this study was to calculate the structures and energetics of CH₃OH$_{2}^{+}$(H₂O)_n and CH₃SH$_{2}^{+}$(H₂O)_n in the gas phase: we asked how the CH₃OH$_{2}^{+}$ and CH₃SH$_{2}^{+}$ moieties of CH₃OH$_{2}^{+}$(H₂O)_n and CH₃SH$_{2}^{+}$(H₂O)_n change with an increase in n and how can we reproduce the experimental values ΔH°_n−1,n. For this purpose, we carried out full geometry optimizations with MP2/6‐31+G(d,p) for CH₃OH$_{2}^{+}$(H₂O)_n (n=0,1,2,3,4,5) and CH₃SH$_{2}^{+}$(H₂O)_n (n=0,1,2,3,4). We also performed a vibrational analysis for all clusters in the optimized structures to confirm that all vibrational frequencies are real. All of the vibrational frequencies of these clusters are real, and they correspond to equilibrium structures. For CH₃OH$_{2}^{+}$(H₂O)_n, when n increases, (1) the C O bond length decreases, (2) the C H bond lengths do not change, (3) the O H bond lengths increase, (4) the OCH bond angles increase, (5) the COH bond angles decrease, (6) the charge on CH₃ becomes less positive, and (7) these predicted values, except for the O H bond lengths of CH₃OH$_{2}^{+}$(H₂O)_n, approach the corresponding values in CH₃OH. The C O bond length in CH₃OH$_{2}^{+}$(H₂O)₅ is shorter than that in CH₃OH$_{2}^{+}$ in the gas phase by 0.061 Å at the MP2/6‐31+G(d,p) level. Except for the S H bond lengths in CH₃SH$_{2}^{+}$(H₂O)_n, however, the structure of the CH₃SH$_{2}^{+}$ moiety does not change with an increase in n. © 2000 John Wiley & Sons, Inc. J Comput Chem 22: 125–131, 2001     

Reactions of methyl radicals with acetaldehyde and acetaldehyde-d1. I. relative rates of atom abstraction reactions at 785°K

The role of ethenoxy radicals in the pyrolysis of CH₃CDO was studied by mass spectrometric analysis of the isotopic composition of the methane, ethane, and recovered aldehyde. Experimental evidence was obtained for the formation of ethenoxy radicals and for their reaction with acetaldehyde. Mixtures of CH₃CHO and CH₃CDO were pyrolyzed in order to minimize H-D scrambling in the methyl group of the aldehyde. A kinetic treatment of the methyl radical reactions and furnished the rate constant ratios (k_2a + k_2b)/k_1a = 2.7 and k_1b/k_1a = 0.62 at 785°K. It is concluded that at the usual temperatures of CH₃CHO pyrolysis the rate of alkyl hydrogen capture is comparable to that of formyl hydrogen abstraction. The results and conclusions are discussed and compared with previous work.     

Electron impact ionization of ethylene–methanol heteroclusters: Stable configurations and mechanisms in intracluster ion–molecule reactions

Reactions that proceed within mixed ethylene–methanol cluster ions were studied using an electron impact time-of-flight mass spectrometer. The ion abundance ratio, [(C₂H₄)_n(CH₃OH)_mH⁺]/[(C₂H₄)_n(CH₃OH)_m⁺], shows a propensity to increase as the ethylene/methanol mixing ratio increases, indicating that the proton is preferentially bound to a methanol molecule in the heterocluster ions. The results from isotope-labelling experiments indicate that the effective formation of a protonated heterocluster is responsible for ethylene molecules in the clusters. The observed (C₂H₄)_n(CH₃OH)_m⁺ and (C₂H₄)_n(CH₃OH)_m–1CH₃O⁺ ions are interpreted as a consequence of the ion–neutral complex and intracluster ion–molecule reaction, respectively. Experimental evidence for the stable configurations of heterocluster species is found from the distinct abundance distributions of these ions and also from the observation of fragment peaks in the mass spectra. Investigations on the relative cluster ion distribution under various conditions suggest that (C₂H₄)_n(CH₃OH)_mH⁺ ions with n + m ≤ 3 have particularly stable structures. The result is understood on the basis of ion–molecule condensation reactions, leading to the formation of fragment ions, $ {\rm CH}_2=\!=\mathop {\rm O}\limits^ + {\rm CH}_3 $ and (CH₃OH)H₃O⁺, and the effective stabilization by a polar molecule. The reaction energies of proposed mechanisms are presented for (C₂H₄)_n(CH₃OH)_mH⁺(n + m ≤ 3) using semi-empirical molecular orbital calculations.     

Trägerfixierte Organometallkomplexe. VI. Charakterisierung und Reaktivität Polysiloxan-gebundener (Ether-phosphan)ruthenium(II)-Komplexe

Supported Organometallic Complexes. VI. Characterization und Reactivity of Polysiloxane-Bound (Ether-phosphane)ruthenium(II) Complexes The ligands PhP(R)CH₂D [R = (CH₃O)₃Si(CH₂)₃; D = CH₂OCH₃ ( 1b ); D = tetrahydrofuryl ( 1c ); D = 1,4-dioxanyl ( 1d )] have been used to synthesize (ether-phosphane)ruthenium(II) complexes, which have been copolymerized with Si(OEt)₄ to yield polysiloxane-bound complexes. The monomers cis,cis,trans-Cl₂Ru(CO)₂(P ～ O)₂ ( 3b ) and HRuCl(CO)(P ～ O)₃ ( 5b ) were treated with NaBH₄ to form cis,cis,trans-H₂Ru(CO)₂(P ～ O)₂ ( 4b ) and H₂Ru(CO)(P ～ O)₃ ( 6b ), respectively (P ～ O = η¹-P coordinated; = η²- coordinated). Addition of Si(OEt)₄ and water leads to a base catalyzed hydrolysis of the silicon alkoxy-functions and a precipitation of the immobilized counterparts 4b ′, 6b ′. The polysiloxane matrix resulting by this new sol gel route has been described under quantitative aspects by ²⁹Si CP-MAS NMR spectroscopy. 4b ′ reacts with carbon monoxide to form Ru(CO)₃(P ～ O)₂ ( 7b ′). Chelated polysiloxane-bound complexes Cl₂Ru( )₂ ( 9c ′, d ′) and Cl₂Ru( )(P ～ O)₂ ( 10b ′, c ′) have been synthesized by the reaction of 1b–c with Cl₂Ru(PPh₃)₃ ( 8 ) followed by a copolymerization with Si(OEt)₄. The polysiloxane-bound complexes 9c ′, d ′ and 10b ′, c ′ react with one equivalent of CO to give Cl₂Ru(CO)( )(P ～ O) ( 12b ′– d ′). Excess CO leads to the all-trans-complexes Cl₂Ru(CO)₂(P ～ O)₂ ( 14b ′– d ′), which are thermally isomerized to cis,cis,trans- 3b ′– d ′. The chemical shift anisotropy of ³¹P in crystalline Cl₂Ru( )₂ ( 9a , R = Ph, D = CH₂OCH₃) has been compared with polysiloxane-bound 9d ′ indicating a non-rigid behavior of the complexes in the matrix.     

Iodostannate(II) mit kettenförmigen [SnI3]–‐Anionen – der Übergang von fünffach zu sechsfach koordinierten SnII‐Zentralatomen

Iodostannates(II) with Anionic [SnI₃]^– Chains – the Transition from Five to Six‐coordinated Sn^II The iodostannates (Me₄N) [SnI₃] ( 1 ), [Et₃N–(CH₂)₄–NEt₃] [SnI₃]₂ ( 2 ), [EtMe₂N–(CH₂)₂–NEtMe₂] [SnI₃]₂ ( 3 ), [Me₂HN–(CH₂)₂–NH–(CH₂)₂–NMe₂H] [SnI₃]₂ ( 4 ), [Et₃N–(CH₂)₆–NEt₃] [SnI₃]₂ ( 5 ) and [Pr₃N–(CH₂)₄–NPr₃]‐ [SnI₃]₂ · 2 DMF ( 6 ) with the same composition of the anionic [SnI₃]^– chains show differences in the coordination of the Sn^II central atoms. Whereas the Sn atoms in 1 and 2 are coordinated in an approximately regular octahedral fashion, in compounds 3 – 6 the continuous transition to coordination number five in (Pr₄N) [SnI₃] ( 7 ) or [Fe(dmf)₆] [SnI₃]₂ ( 8 ) can be observed. Together with the shortening of two or three Sn–I bonds, the bonds in trans position are elongated. Thus weak, long‐range Sn…I interactions complete the distorted octahedral environment of SnI₄ groups in 3 and 4 and SnI₃ groups in 5 and 6 . Obviously the shape, size and charge of the counterions and the related cation‐anion interactions are responsible for the variants in structure and distortion.     

Thermal decomposition of 2,2-propane-d2. CH3CDCH3 radical isomerization

The decomposition of CH₃CD₂CH₃ was studied from 713 to 853 K at pressures of 98–466 torr. The values of k₁/k₂ = 2.08 ± 0.05 and k₃/k₄ = 2.04 ± 0.66 were found independent of temperature by measuring the ratios of CH₄/CH₃D and CH₃CHD₂/CH₃CD₃, respectively, for the following reactions: . Isomerization of CH₃CDCH₃ was detected by measuring CHDCH₂ formed from the isomerized radical. The expression of k₂₁/k₂₂ was found to be where k₂₁ and k₂₂ are the rate constants of . The results and conclusions are discussed and compared with previous works.     

Incorporating glycidyl methacrylate into block copolymers using poly(methacrylate‐ran‐styrene) macroinitiators synthesized by nitroxide‐mediated polymerization

Methyl methacrylate/styrene (MMA/S), ethyl methacrylate/styrene (EMA/S) and butyl methacrylate/styrene (BMA/S) feeds (>90 mol % methacrylate) were copolymerized in 50 wt % p‐xylene at 90 °C with 10 mol % of additional SG1‐free nitroxide mediator relative to unimolecular initiator (BlocBuilder^®) to yield methacrylate rich copolymers with polydispersities _w/ _n = 1.23–1.46. k_pK values (k_p = propagation rate constant, K = equilibrium constant) for MMA/S copolymerizations were comparable with previous literature, whereas EMA/S and BMA/S copolymerizations were characterized by slightly higher k_pK's. Chain extensions with styrene at 110 °C initiated by the methacrylate‐rich macroinitiators (number average molecular weight _n = 12.9–33.5 kg mol^?1) resulted in slightly broader molecular weight distributions with _w/ _n = 1.24–1.86 and were often bimodal. Chain extensions with glycidyl methacrylate/styrene/methacrylate (GMA/S/XMA where XMA = MMA, EMA or BMA) mixtures at 90 °C using the same macroinitiators resulted frequently in bimodal molecular weight distributions with many inactive macroinitiators and higher _w/ _n = 2.01–2.48. P(XMA/S) macroinitiators ( _n = 4.9–8.9 kg mol^?1), polymerized to low conversion and purified to remove “dead” chains, initiated chain extensions with GMA/MMA/S and GMA/EMA/S giving products with _w/ _n ～ 1.5 and much fewer unreacted macroinitiators (<5%), whereas the GMA/BMA/S chain extension was characterized by slightly more unreacted macroinitiators (～20%). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2574–2588, 2009     

Gas‐phase intramolecular anion rearrangements of some trimethylsilyl‐containing systems revisited. A theoretical approach

Ab initio calculations at the CCSD(T)/6‐311++G(2d,p)//B3LYP/6‐311++G(d,p) level of theory have been carried out for three prototypical rearrangement processes of organosilicon anion systems. The first two are reactions of enolate ions which involve oxygen–silicon bond formation via three‐ and four‐membered states, respectively. The overall reactions are: The ΔG (reaction) values for the two processes are +175 and +51 kJ mol^?1, with maximum barriers (to the highest transition state) of +55 and +159 kJ mol^?1, respectively. The third studied process is the following: (CH₃O)C(?CH₂)Si(CH₃)₂CH → (CH₃)₂(C₂H₅)Si^? + CH₂CO, a process involving an S_Ni reaction between ‐CH and CH₃O‐ followed by silicon–carbon bond cleavage. The reaction is favourable [ΔG(reaction) = ?39 kJ mol^?1] with the barrier for the S_Ni process being 175 kJ mol^?1. The previous experimental and the current theoretical data are complementary and in agreement. Copyright © 2009 John Wiley & Sons, Ltd.     

The gas-phase decomposition of methylsilane. Part I. Mechanism of decomposition under shock-tube conditions

The gas-phase decompositions of methylsilane and methylsilane-d₃ have been investigated in a single-pulse shock tube at 4700 torr total pressure in the temperature range of 1125–1250 K. For CH₃SiD₃ at 1200 K three primary steps occur in the homogeneous decomposition with efficiencies in parentheses: , , and . For CH₃SiH₃ at 1200 K the primary CH₄ elimination efficiency is 0.09 while the total primary H₂ elimination efficiency is 0.91. Minor product formations of C₂H₄, acetylene, dimethylsilane, and SiH₄ are discussed.     

Kinetic investigation of the bromate–ascorbic acid–malonic acid system

According to our experiments the bromide ion concentration exhibits in the bromate–ascorbic acid–malonic acid–perchloric acid system three extrema as a function of time. To describe this peculiar phenomenon, the kinetics of four component reactions have been studied separately. The following rate equations were obtained: Bromate–ascorbic acid reaction: Bromate–bromide ion reaction: Bromide–ascorbic acid reaction: Bromine–malonic acid reaction: k₄ = 6 × 10^?3 s^?1, k_-4 ≥ 1.7 × 10³ s^?1, k₅ ≥ 1 × 10⁷M^?1 · s^?1 Taking into account the stoichiometry of the component reactions and using these rate equations, the concentration versus time curves of the composite system were calculated. Although the agreement is not as good as in the case of the component reactions, it is remarkable that this kinetic structure exhibits the three extrema found.     

Absolute rate constants for the reactions of O(3P) atoms and OH radicals with SiH4 over the temperature range of 297–438°K

Absolute rate constants for the reaction of SiH₄ with O(³P) atoms and OH radicals have been determined over the temperature range 297°–438°K using flash photolysis–NO₂ chemiluminescence and flash photolysis–resonance fluorescence techniques, respectively. The Arrhenius expressions obtained are where the error limits in the Arrhenius activation energies are the estimated overall error limits. Rate data for the reactions of SiH₄, CH₄, and H₂S with O(³P), H, and F atoms and with OH, CH₃, and CF₃ radicals are compared, showing that H₂S and SiH₄, which have similar bond energies, have reasonably similar reactivities toward these atoms and radicals.     

Kinetics of the gas-phase reaction CH3F + I2 ⇆ CH2FI + HI: The C?H bond dissociation energy in methyl and methylene fluorides

The kinetics of the gas-phase reaction of CH₃F with I₂ have been studied spectrophotometrically from 629 to 710 K, and were determined to be consistent with the following mechanism: (1) A least-squares analysis of the kinetic data taken in the initial stages of reaction resulted in where θ = 4.575T/1000 kcal/mol. The errors represent one standard deviation. The experimental activation energy E₄ = 30.8 ± 0.2 kcal/mol was combined with the assumption E₃ = 1 ± 1 kcal/mol and estimated heat capacities to obtain The enthalpy change at 298 K was combined with selected thermochemical data to derive The kinetic studies of ?HF₂ and CH₂F₂ have been reevaluated to yield These results are combined with literature data to yield the C? H, C? F, and C? Cl bond dissociation energies in their respective fluoromethanes, and the effect of α-fluorine substitution is discussed.     

Bifunctional even-electron ions. II. Fragmentation behaviour of aliphatic ω-hydroxy and ω-methoxy methoxonium ions

Bifunctional methoxonium ions \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm R} -\mathop {\rm C}\limits^ + ({\rm OCH}_3 ) - ({\rm CH}_2 )_{\rm n} - {\rm OH}({\rm b}) $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm R} - \mathop {\rm C}\limits^ + ({\rm OCH}_3 ) - ({\rm CH}_2 )_{\rm n} - {\rm OCH}_3 ({\rm c}) $\end{document} (c) show as the main reactions those caused by functional group interaction, as has already been found for the analogous hydroxonium ions (g). Although there are similarities in the fragmentation behaviour of the isomeric ions b and g, their fragmentation pathways are different, proving b and g as distinct species. The dominant primary fragmentation for b and c is loss of CH₃OH. The hydrogen migrations prior to this reaction have been established by deuterium labelling. The findings on the fragmentation behaviour of the bifunctional methoxonium ions have been extended to the general behaviour of hydroxy and alkoxy substituted alkoxonium ions.     

Hydrogen/deuterium abstraction by chlorine atoms from gaseous ethyl chlorides. Secondary kinetic isotope effects in the system CH3CH2Cl,CH3CHDCl,CH3CD2Cl

The abstraction of hydrogen/deuterium from CH₃CH₂Cl, CH₃CHDCl, and CH₃CD₂Cl by photochemically generated ground-state chlorine atoms has been investigated over the temperature range of 8–94°C using methane as a competitor. Rate constant data for the following reactions have been obtained: The temperature dependence of the relative rate constants k_i/k_j was found to conform to the Arrhenius rate law, where the stated error limits are one standard deviation: and k_r is the rate constant for the reference reaction (CH₄ + Cl → CH₃ + HCl). The β secondary kinetic isotope effects (k₂/k₃/k₄) are close to unity and show a slight inverse temperature dependence. Both preexponential factors and activation energies decrease as a result of deuterium substitution in the adjacent chloromethyl group. The trends are well outside the limits of experimental error.     

The carbon–hydrogen bond strength in dimethyl ether and some properties of iodomethyl methyl ether

The kinetics and mechanism of the reaction between iodine and dimethyl ether (DME) have been studied spectrophotometrically from 515–630°K over the pressure ranges, I₂ 3.8–18.9 torr and DME 39.6–592 torr in a static system. The rate-determining step is, where k₁ is given by log (k₁/M^?1 sec^?1) = 11.5 ± 0.3 – 23.2 ± 0.7/θ, with θ = 2.303RT in kcal/mole. The ratio k₂/k_?1, is given by log (k₂/k_?1) = ?0.05 ± 0.19 + (0.9 ± 0.45)/θ, whence the carbon-hydrogen bond dissociation energy, DH° (H? CH₂OCH₃) = 93.3 ± 1 kcal/mole. From this, ΔH°_f(CH₂OCH₃) = ?2.8 kcal and DH°(CH₃? OCH₂) = 9.1 kcal/mole. Some nmr and uv spectral features of iodomethyl ether are reported.     

The gas phase reactions of hydroxyl radicals with a series of aliphatic ethers over the temperature range 240–440 K

Absolute rate constants were determined for the gas phase reactions of OH radicals with a series of linear aliphatic ethers using the flash photolysis resonance fluorescence technique. Experiments were performed over the temperature range 240–440 K at total pressures (using Ar diluent gas) between 25–50 Torr. The kinetic data for dimethylether (k₁), diethylether (k₂), and dipropylether (k₃) were used to derive the Arrhenius expressions and At 296 K, the measured rate constants (in units of 10^?13 cm³ molecule^?1 s^?1) were: k₁ = (24.9 ± 2.2), k₂ = (136 ± 9), and k₃ = (180 ± 22). Room temperature rate constants for the OH reactions with several other aliphatic ethers were also measured. These were (in the above units): di-n-butylether, (278 ± 36); di-n-pentylether, (347 ± 20); ethyleneoxide, (0.95 ± 0.05); propyleneoxide, (4.95 ± 0.52); and tetrahydrofuran, (178 ± 16). The results are discussed in terms of the mechanisms for these reactions and are compared to previous literature data.