Automation of an experimental system for the microbial epoxidation of propene and 1-butene

An experimental set-up for automatic gas chromatographic analysis of circulation gas in a batch-reactor system is described. Gas sampling, substrate addition, data acquisition and data reduction are done with a coupled programmable integrator and microcomputer. On-line monitoring of the microbial oxidation of the gaseous alkenes, propene and 1- butene, to the corresponding epoxides is used to illustrate the operation of the experimental system. Measured gas concentrations of alkene and alkene oxide can be converted readily to quantify the reaction course in the liquid phase(s) of the circulation system. Results are presented for both one liquid phase (water) and two liquid phases (water and organic solvent) present in the reactor. The operational stability of the immobilized-cell system used for the epoxidations can be assessed by computer-controlled addition of gaseous alkene.     

Production of propene from 1-butene metathesis reaction on tungsten based heterogeneous catalysts

A new propene production route from 1-butene metathesis has been developed on heterogeneous 10WO₃/Al₂O₃-HY catalysts with different HY contents. It is found that the catalysts play bi-functionally first for the isomerization of 1-butene to 2-butene and then for the cross-metathesis between 1-butene and 2-butene to propene and 2-pentene. The combination of HY zeolite and Al₂O₃ is prerequisite for the production of propene. The propene yield keeps increasing with the HY content in the range of 10–70 wt%, where 10WO₃/Al₂O₃-70HY exhibits the highest propene yield. The MS-H₂-TPR and MS-O₂-TPO characterizations indicate that the increase of HY content in the catalysts weakens the interaction between W species and supports, whereas enhance the probability of coking on the metal species and acid sites.     

Conformational studies of aliphatic secondary ozonides (propene, 1-butene and 1-heptene) by means of FTIR spectroscopy

Ozonization reaction of simple alkenes was studied by means of FT infrared absorption gas spectroscopy. The reaction was performed at 95 K in neat films of the reactants. IR absorption spectra of the gaseous products were recorded. The spectra were analyzed combining experimental results with theoretical calculations performed at B3LYP 6-311++G (3df, 3pd) level. We found that among all theoretically predicted conformers of propene secondary ozonide, only one which has the O-O half-chair configuration for the five membered ring and the radical attached in the equatorial position was present in the sample. Samples of 1-butene and 1-heptene secondary ozonides consist from two conformers of very similar energy (ΔH=0.3 kJ/mol). The most stable conformer for both ozonides is the one with O-O half-chair configuration of the five membered ring and the radical attached in equatorial position and the aliphatic chain in gauche position. The second stable conformer has the aliphatic chain in anti position.     

Zirconocenium cation catalysis of propene polymerization

rac-Ethylenebis(1-η⁵-indenyl)dimethylzirconium (1) was reacted with triphenylcarbenium tetrakis(pentafluorophenyl)borate (2) to produce in situ the rac-ethylenebis(indenyl)methylzirconium cation (3). This aluminium-free catalyst showed propene polymerization activity (A) and stereoselectivity which both increase with the decrease of polymerization temperature (T_p). At very low T_p, 3 behaved as a “single-site” catalyst. An efficient way to produce such cation is to react ansa-zirconocene dichloride with 2 in the presence of TEA (=triethylaluminium). A superior cationic catalyst was obtained from rac-dimethylsilylenebis(1-η⁵-indenyl)dichlorozirconium, 2, and TEA, which polymerizes propene at −20°C(−55°C) with activity of 2×10⁹ (3×10⁸) g polypropene per (mol Zr η mol C₃H₆ η h) to polypropenes which are 93.8% (99.4%) isotactic with melting temperature T_m = 152.6°C (159.9°C) and viscosity-average molecular weight M_v = 1.4×10⁵ (2.2×10⁵). The addition of methylaluminoxane lowers the A of the cationic catalyst especially at low T_p. Rigorously speaking, the cation derived from 1 or 3 behaves as a “single site” catalyst only at very low T_p. The use of TEA significantly and unexpectedly enhances the efficiency of the zirconocenium catalyst system.     

In situ switching of sorbent functionality as monitored with hyperpolarized (129)Xe NMR spectroscopy

In this contribution, we demonstrate that a material (organic zeolite mimetic coordination polymer [CuL(2)], where L = L(-) = CF(3)COCHCOC(OCH(3))(CH(3))(2)) can be endowed with its functionality in situ under molecular-level control. This process involves the isomerization of the ligands followed by phase interconversion from a dense to an open, porous form. The porous (beta) form of the complex reveals zeolite-like behavior but, unlike zeolites and many other hard porous frameworks, porosity may be created or destroyed at will by the application of suitable external stimuli. Contact with methylene chloride vapor was used to switch on the sorbent functionality, whereas switching off was accomplished with a temperature pulse. The transformations between functionally inactive alpha and active beta forms, as well as the amount of vacant pore space, were monitored in situ by observing the NMR spectrum of hyperpolarized (HP) Xe atom probes. For methylene chloride, the chemical shift of the coabsorbed HP Xe correlated directly with the amount of adsorbate in the pore system of the open framework, illustrating the use of HP Xe for following sorption kinetics. The adsorption of propane, as an inert adsorbate, was also monitored directly with (1)H NMR, with HP Xe and by BET measurements, revealing more complex behavior.     

1H NMR studies of molecular relaxations of poly-1-butene

The temperature dependance of the proton NMR line shape, T₁ and T_1ρ of isotactic poly-1-butene forms I, I′, II, and III have been studied between 100 and 400 K (up to melting). The usual line shape decompositions concerning rigid vs. crystalline and mobile vs. amorphous phases are discussed. The rigid-lattice second moments were calculated introducing a fast rotation of the methyl group. Complex spin-lattice decays were analyzed as a continuous distribution of rates. Relaxation behavior was analyzed in terms of a Williams-Watt correlation function. Motions in the crystalline parts of samples in forms II and III very similar to the amorphous one were revealed, leading us to compare form II to a condis crystal during the crystal form transformation. © 1995 John Wiley & Sons, Inc.     

Preparation of mesoporous alumina with large pore size and their supported rhenium oxide catalysts in metathesis of 1-butene and 2-butene to propene

Mesoporous γ-aluminas with large pore size(up to 19 nm,denoted as MA19) are prepared from dispersed pseudo-boehmite using pluronic P123 as template.It is found that these mesoporous alumina supported rhenium oxide catalysts were more active and have far longer working life-span in gas-phase metathesis of 1-butene and 2-butene to propene than rhenium oxide on conventional alumina with small pore size(5 nm).At 60°C and atmospheric pressure with WHSV = 1 h-1,the similar stable conversions of butene(ca.55%) for all the 13 wt% Re 2 O 7 /alumina catalysts were obtained near the chemical equilibrium,and the stable working life-spans of Re 2 O 7 /MA19 were far longer than that of Re 2 O 7 /Al 2 O 3,being about 70 h and 20 h,respectively.     

Photodissociation of 1-bromo-2-butene, 4-bromo-1-butene, and cyclopropylmethyl bromide at 234 nm studied using velocity map imaging

We present photofragment imaging experiments to characterize potential photolytic precursors of three C4H7 radical isomers: 1-methylallyl, cyclopropylmethyl, and 3-buten-1-yl radicals. The experiments use 2+1 resonance enhanced multiphoton ionization (REMPI) with velocity map imaging to state-selectively detect the Br(2P(3/2)) and Br(2P(1/2)) atoms as a function of their recoil velocity imparted upon photodissociation of 1-bromo-2-butene, cyclopropylmethyl bromide, and 4-bromo-1-butene at 234 nm as well as the angular distributions of the photofragments. Energy and momentum conservation allows the internal energy distribution of the nascent momentum-matched radicals to be derived. The radicals are detected with single photon photoionization at 157 nm. In the case of the 1-methylallyl radical the photoionization cross section is expected to be independent of internal energy in the range of 7-30 kcal/mol. Thus, comparison of the product recoil kinetic energy distribution derived from the measurement of the 1-methylallyl velocity distribution, detecting the radicals with 157 nm photoionization, with a linear combination of the Br atom recoil kinetic energy distributions allows us to derive reliable REMPI line strength ratios for the detection of Br atoms and to test the assumption that the photoionization cross section does not strongly depend on the internal energy of the radical. This line strength ratio is then used to determine the branching to the Br(2P(3/2)) and Br(2P(1/2)) product channels for the other two photolytic systems and to determine the internal energy distribution of their momentum-matched radicals. (We also revisit earlier work on the photodissociation of cyclobutyl bromide which detected the Br atoms and momentum-matched cyclobutyl radicals.) This allows us to test whether the 157 nm photoionization of these radicals is insensitive to internal energy for the distribution of total internal (vibrational+rotational) energy produced. We find that 157 nm photoionization of cyclopropylmethyl radicals is relatively insensitive to internal energy, while 3-buten-1-yl radicals show a photoionization cross section that is markedly dependent on internal energy with the lowest internal energy radicals not efficiently detected by photoionization at 157 nm. We present electronic structure calculations of the radicals and their cations to understand the experimental results.     

Molecular structures of isobutene and 2,3-dimethyl-2-butene as studied by gas electron diffraction

The structures of isobutene and 2,3-dimethyl-2-butene have been studied by gas electron diffraction. For isobutene the rotational constants obtained by Laurie by microwave spectroscopy have also been taken into account. Leastsquares analyses have given the following r_g bond distances and valence angles (r_av for isobutene and r_α for dimethylbutene): for isobutene, r(CC) = 1.342±0.003 Å, r(C-C)= 1.508±0.002Å, r(C-H, methyl) = 1.119±0.007 Å, r(C-H, methylene) = 1.095±0.020 Å, ∠(C-CC) = 122.2±0.2°, ∠(H-C-H) = 107.9±0.8°, and ∠(C-C-H) 121.3±1.5°; for dimethylbutene, r(CC)= 1.353 ±0.004 Å, r(C-C) = 1.511±0.002 Å, r(C-H) = 1.118± 0.004 Å, ∠(C-CC)= 123.9±0.5°, and ∠(H-C-H)= 107.0±1.0°, where the uncertainties represent estimated limits of experimental error. The bond distances and valence angles in these molecules and in related molecules are compared with one another. The CC and C-C bond distances increase almost regularly with the number of methyl groups, and the C-C bonds in isobutene and dimethylbutene are shorter than those in acetaldehyde and acetone by about 0.01 Å. Systematic variations in the C-CC angles suggest the steric influence of methyl groups.     

Molecular dynamics in polyethylene and ethylene-1-butene copolymer investigated by NMR methods

1H and 13C NMR spectra and 1H spin-lattice relaxation times T₁ and T_1ρ have been employed to study the structure and molecular dynamics in polyethylene and ethylene-1-butene copolymer in the temperature range from 100 to 370 K. Results are interpreted in terms of α, β and γ -relaxation, as well as methyl group rotation. The activation energies for all motions were established. The incorporation of 1-butene into ethylene chain leads to an increase of mobility in amorphous and crystalline phases as well as appearance the 13C resonance characteristic to the monoclinic structure in addition to the orthorhombic observed in both polymers. The crystallinity degree derived from T_1ρ in studied polymers is close to that determined using DSC method.     

Copolymerization of propene and 1-hexene using metallocene amide compounds

Copolymerization of propene and 1-hexene has been carried out at 30°C in toluene under atmospheric pressure by using three isospecific metallocene amide compounds, rac-(EBI)Zr(NMe₂₎₂ (EBI = ethylenebis(1-indenyl), rac- 1 ), rac-(EBI)Zr(NC₄H₈₎₂ (rac- 2 ), and rac-Me₂Si(1-C₅H₂-2-Me-4-t-Bu)₂Zr(NMe₂₎₂ (rac- 3 ), in the presence of methylaluminoxane (MAO) or [Ph₃C][B(C₆F₅)₄]. The rate enhancements in the presence of 1-hexene were recorded as a function of the catalytic systems. The incorporation of 1-hexene decreases in the following order: rac- 2 /MAO > rac- 3 /Al(i-Bu)₃/[Ph₃C][B(C₆F₅)₄] > rac- 1 /MAO. All copolymers investigated in this study have a nearly random sequence distribution.     

Kinetics from indirectly detected hyperpolarized NMR spectroscopy by using spatially selective coherence transfers

An important recent development in NMR spectroscopy is the advent of ex situ dynamic nuclear polarization (DNP) approaches, which are capable of yielding liquid‐state sensitivities that exceed considerably those afforded by the highest‐field spectrometers. This increase in sensitivity has triggered new research avenues, particularly concerning the in vivo monitoring of metabolism and disease by NMR spectroscopy. So far such gains have mainly materialized for experiments that focus on nonprotonated, low‐γ nuclei; targets favored by relatively long relaxation times T₁, which enable them to withstand the transfer from the cryogenic hyperpolarizer to the reacting centers of interest. Recent studies have also shown that transferring this hyperpolarization to protons by indirectly detected methods could successfully give rise to ¹H NMR spectra of hyperpolarized compounds with a high sensitivity. The present study demonstrates that, when merged with spatially encoded methods, indirectly detected ¹H NMR spectroscopy can also be exploited as time‐resolved hyperpolarized spectroscopy. A methodology is thus introduced that can successfully deliver a series of hyperpolarized ¹H NMR spectra over a minutes‐long timescale. The principles and opportunities presented by this approach are exemplified by following the in vitro phosphorylation of choline by choline kinase, a potential metabolic marker of cancer; and by tracking acetylcholine’s hydrolysis by acetylcholine esterase, an important enzyme partaking in synaptic transmission and neuronal degradation.     

NMR spectrum of poly(propene sulfide)

The 100 MHz spectra of polymers of propene sulfide and propene-2-d₁ sulfide have been determined in CDCl₃, CCl₄, and C₆D₆. In the deuterated polymer the main-chain protons give rise to two overlapping AB quartets in which the two pairs of upfield B lines are coincident and the two pairs of downfield A lines are resolved. With CdCO₃ as polymerization catalyst the downfield quartet is twice as strong as the upfield quartet. The former is ascribed to an isotactic dyad: and the latter to a syndiotactic dyad: Other catalysts (ZnCO₃, CuCO₃, SiO₂/Al₂O₃, Na) produce an essentially atactic structure. The values τ_A = 7.125, τ_A′ = 7.155, τ_B = 7.45, J_AB = ?12.9 Hz, derived from the spectrum of the deuterated polymer (in CCl₄) were used to obtain the following values from the spectrum of the undeuterated polymer (tertiary proton = Hc): τ_C = 7.131, J_BC = 10.0 Hz, J_CA = 4.1 Hz. The magnitudes of the vicinal coupling constants indicate a preferred trans conformation for the mainchain C? C bond. τ_A, τ_B, and τ_C are somewhat dependent on solvent; τCH₃ = 8.63, independent of solvent, and JCH₃, H_C = 6.2 Hz.     

Solid phase β-lactams synthesis using the Staudinger reaction, monitored by F NMR spectroscopy

We report the use of ¹⁹F NMR as a simple means to monitor reactions on a solid phase. Multi-step sequences including protection, coupling, deprotection, condensation, cycloaddition and cleavage steps are described in the case of multicomponent reactions involving fluorinated α-aminoesters, aldehydes and acid chlorides.     

Metathesis of 1-butene and 2-butene to propene over Re2O7 supported on macro-mesoporous γ-alumina prepared via a dual template method

Macro-mesoporous γ-alumina support(MMA) was prepared by a sol-gel route in aqueous medium using pseudo-boehmite as aluminum source and polystyrene microspheres and Pluronic P123 as hard and soft dual templates,respectively.MMA had a BET specific surface area of about 259 m2 g-1,total pore volume of about 1.61 cm3 g-1,macropore diameter of about 102 nm,and mesopore diameter of about 14 nm.Re2O7/MMA and conventional Re2O7/Al2O3 were prepared by a incipient-wetness impregnation method,and their catalytic performances in the metathesis of 1-butene and 2-butene were tested in a fixed-bed tubular reactor.The result showed that Re2O7/MMA possessed higher activity and far longer working life-span than conventional Re2O7/Al2O3.     

Probing the geometry and interconnectivity of pores in organic aerogels using hyperpolarized 129XE NMR spectroscopy

Hyperpolarized (HP) 129Xe NMR was used for the first time to probe the geometry and interconnectivity of pores in RF aerogels and to correlate them with the [resorcinol]/[catalyst] (R/C) ratio. We have demonstrated that HP 129Xe NMR is an ideal method for accurately measuring the volume-to-surface-area (Vg/S) ratios for soft mesoporous materials without using any geometric models. The Vg/S parameter, which is related both to the geometry and the interconnectivity of the porous space, has been found to correlate strongly with the R/C ratio and exhibits an unusually large span: an increase in the R/C ratio from 50 to 500 results in about 5-fold rise in Vg/S. Unlike conventional techniques, HP 129Xe NMR spectroscopy probes the geometry and interconnectivity of the nano- or mesopores in soft materials, providing new insights into the pore structure.     

Vibrational assignment and rotational isomerism of 2-chloro-1-butene and 2-bromo-1-butene

Infrared spectra were obtained for 2-chloro-l-butene and 2-bromo-l-butene that show the presence of trans and gauche rotamers in both compounds. Vibrational assignments were made with the aid of normal coordinate calculations that utilized a thirty-eight parameter valence force field.     

The Radiation Polymerization of 4-Methyl-1-pentene, 2-Methyl-1-butene,and 2,3-Dimethyl-1-butene under Conditions of Extreme Dryness

The γ-ray initiated polymerization of 4-methyl-1-pentene, 2-methyl-1-butene, and 2,3-dimethyl-1-butene has been studied under conditions of extreme dryness. Only low yields of oily low molecular weight polymers were obtained. It is suggested that the low propagation rate constants are responsible for the results obtained.     

Stopped-flow studies of the mechanisms of ozone–alkene reactions in the gas phase propene and isobutene

The reactions of ozone with propene and isobutene have been studied in the gas phase at 298°K and 530 Pa (4 torr) using a stopped-flow reactor coupled to a photoionization mass spectrometer. Reactant and product concentrations were followed as a function of reaction time. The major reaction products monitored were CH₂O, CH₃CHO, CO₂, and H₂O from the propene reaction, and CH₂O, (CH₃)₂CO, CO₂, and H₂O from the isobutene reaction. The observations were interpreted on the basis of the Criegee mechanism for ozonolysis in solution: for which we find k_A≈k_B.In the gas phase the carbene peroxy radical is postulated to isomerize and decompose into molecular and free-radical products.