Molecular weight distribution characterization of reactive higher ethyleneamines using size-exclusion chromatography with conventional calibration.

Ethyleneamines have been produced and commercialized for decades in the chemical industry for a diverse range of applications. The presence of amine functional groups provides them opportunity to adsorb onto surfaces which can make them a very challenging sample matrix to analyze using separation techniques. In the present report, a new aqueous SEC-RI method, which enables MWD characterization of higher ethyleneamines, is described. The sample preparation was based on the dilute-and-shoot methodology. A surface-modified SEC column with positively charged groups attached to the stationary phase was used. The mobile phase composition (salt concentration, pH) was optimized to suppress interaction between the ethyleneamines and the packing material. Very symmetrical peak shapes were achieved for low MW monodisperse ethyleneamines despite their high primary amine content. MWD calculations were conducted using conventional narrow standard calibration with partial linear extrapolation of the calibration curve. The narrow standards were of the same chemistry as the samples of interest. Consequently, the standard components display a consistent behaviour towards the column packing as the sample components which makes the present method more robust and the interpretation of the quantitative results more convenient. Effect on the measured MW averages and MW distribution due to various experimental parameters (e.g., system variability, mobile phase preparation, sample concentration) were investigated showing good repeatability (RSD < 2%) for Mn, Mw, and Mz.

Catalytic and mechanistic insights of the low-temperature selective oxidation of methane over Cu-promoted Fe-ZSM-5.

The partial oxidation of methane to methanol presents one of the most challenging targets in catalysis. Although this is the focus of much research, until recently, approaches had proceeded at low catalytic rates (<10 h(-1)), not resulted in a closed catalytic cycle, or were unable to produce methanol with a reasonable selectivity. Recent research has demonstrated, however, that a system composed of an iron- and copper-containing zeolite is able to catalytically convert methane to methanol with turnover frequencies (TOFs) of over 14,000 h(-1) by using H(2)O(2) as terminal oxidant. However, the precise roles of the catalyst and the full mechanistic cycle remain unclear. We hereby report a systematic study of the kinetic parameters and mechanistic features of the process, and present a reaction network consisting of the activation of methane, the formation of an activated hydroperoxy species, and the by-production of hydroxyl radicals. The catalytic system in question results in a low-energy methane activation route, and allows selective C(1)-oxidation to proceed under intrinsically mild reaction conditions.

Telomerisation of buta-1,3-diene and methanol: superiority of chromanyl-type phosphines in the Dow process for the industrial production of 1-MOD.

Butadiene and methanol were telomerised in the presence of palladium catalysts with ligands containing 8-diphenylphosphinochromane-like substituents at phosphorus. MonoXantphos and monoSPANphos afforded the most active, stable and selective catalysts known to date under commercially relevant production conditions for 1-methoxyocta-2,7-diene, the precursor to oct-1-ene.

Efficient bulky phosphines for the selective telomerization of 1,3-butadiene with methanol.

A series of bulky phosphines containing substituted biphenyl, 2-methylnaphthyl, or 2,7-di-tert-butyl-9,9-dimethylxanthene moiety were prepared. They were used in the preparation of new monophosphine-palladium(0)-dvds complexes, which were employed as catalysts for the selective telomerization of 1,3-butadiene with methanol to obtain 1-methoxyocta-2,7-diene (1-MOD), the key intermediate in the Dow 1-octene process. Several ligands showed improved selectivity and yield compared to that of the benchmark ligand PPh(3). Especially 2,7-di-tert-butyl-9,9-dimethylxanthen-4-yl-diphenylphosphine (4, "mono-xantphos") stands out as an excellent ligand in terms of yield, selectivity, and stability.

Homogeneous vanadium-based catalysts for the Ziegler-Natta polymerization of alpha-olefins.

Although their activity is often inferior to that of other systems, the use of vanadium-based catalysts in homogeneous Ziegler-Natta polymerizations allows the preparation of high-molecular-weight polymers with narrow molecular-weight distributions, ethene/alpha-olefin copolymers with high alpha-olefin incorporation, and syndiotactic polypropene. The main reason for the low activity of these catalysts is their deactivation during catalysis by reduction of active vanadium species to low-valent, less active or inactive species. We here present an up-to-date review of this area with particular emphasis on the attempts to improve catalyst performance and stability by the use of additives or ancillary ligands.