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N-Alkyl-N-nitrosoamides undergo competitive reactions whose rates are dependent upon the interplay of a number of factors. There already exists a significant body of work delineating the effects of pH on the partitioning of the nitrosoamides along their deaminative (-N(2)) and denitrosative (-"NO(+)") pathways. In this paper, the issue of pH dependence is discussed with particular attention to nitrosoamide decompositions in nonaqueous media. The role of the acidity of the medium in the partitioning of the nitrosoamide between deamination and denitrosation and in the choice of deaminative pathways is revisited. In nonaqueous media under near-neutral conditions, the partitioning's pH dependence is evidently accompanied by a sensitivity to structural features in the nitrosoamide. Thus, diminution of steric crowding around the N-nitroso moiety as well as the presence of strongly electron-withdrawing acyl units (i.e., those derived from strong acids, e.g., tosyl and trifyl) increase the relative yield of amides by encouraging the denitrosative pathway. A mechanism for thermal denitrosation of nitrosoamides under near-neutral conditions is proposed in which rapid protonation at the acyl O rather than slow protonation at the amidic N is the first step in the reaction profile. A rate-limiting, bimolecular reaction between the O-conjugate acid and adventitious nucleophiles at the nitrosyl group then occurs followed by rapid tautomerization to amide.

VTEC ™ PI-1388 and 20 wt% (Al) NH 2 -MIL-53/VTEC ™ PI-1388 mixed-matrix membranes (MMMs) with different thicknesses were tested for gas permeation of H 2 and CO 2 from 5 to 30 bar and from 35 to 300 °C. 50/50 H 2 /CO 2 mixtures were also tested at 30 bar and 250 °C with stage cuts that ranged from 0.05 to 1. Gas permeation data show that the affinity of (Al) NH 2 -MIL-53 for VTEC ™ PI-1388 is strong enough to perform gas separations under these conditions. At 30 bar and at temperatures above 200 °C, the performance of the MMMs for H 2 /CO 2 separation improved significantly with increasing temperature. Specifically, the H 2 permeability of the MMM at 300 °C increased by 70% with respect to that of VTEC ™ PI-1388 (VTEC ™ PI-1388: H 2 = 85 Barrer, H 2 /CO 2 = 4.0; MMM: H 2 = 144 Barrer, H 2 /CO 2 = 5.8). Gas mixture separations using VTEC ™ PI-1388 and the MMM depended on the stage cut and reached a maximum H 2 /CO 2 separation of 7.2 for VTEC ™ PI-1388 and 7.5 for the MMM at a stage cut of 0.05.(MOFs) [31][32][33][34][35][36][37][38] and metal organic polyhedra (MOPs) [39][40][41], is promising. These membranes typically exhibit strong additive/polymer interfaces and high loadings. Herein, we report the preparation and testing of VTEC ™ PI-1388 and (Al) NH 2 -MIL-53/VTEC ™ MMMs at pressures up to 30 bar and at temperatures up to 300 °C with pure H 2 and CO 2 and with H 2 /CO 2 mixtures at stage cuts ranging from 0.05 to 1 to minimize concentration polarization. VTEC ™ PI-1388 (referred to as VTEC ™ in this work) is a commercially available polyimide with a structure similar to Kapton. The (Al) NH 2 -MIL-53 MOF (referred to as NH 2 -MIL-53 in this work) ( Figure 1) [42][43][44][45] was used as the additive due to its high thermal stability to 400 °C, stability in water, and high ideal H 2 /CO 2 selectivity of 27 [46]. Previously, this MOF was also used in the fabrication of MMMs with polysulfone (PSf) [47], a polymer with low T g (170 -185 °C).Improved CO 2 /CH 4 selectivity at 25 wt% MOF loading and pressures up to 12 bar was reported.These results suggest that (Al) NH 2 -MIL-53 might be a good additive for VTEC ™ -based MMMs for high temperature and high pressure H 2 /CO 2 separations. EXPERIMENTAL MaterialsVTEC ™ polyamic acid (20 wt% in N, DMAc) was purchased from RBI Inc. and used as received. Mylar ® (polyethylene terephthalate) A92 (25 µm) sheets were purchased from Active Industries. Molecular sieves type 4A were purchased from Aldrich, washed with deionized water, and activated at 400 °C for 1 d. HPLC grade DMAc (99.8%), N,N-dimethylformamide (DMF, 99.8%), and acetone (99.8%) were purchased from Fisher Scientific and dried over activated 4A molecular sieves. Aluminum nitrate hexahydrate Al(NO 3 ) 3 ·6H 2 O, 2-aminobenzene-1,4-dicarboxylic acid (abdc), HPLC grade water,

A series of N-4-R-benzylpivalamides (R = MeO, Me, H, CF(3), and NO(2)) was nitrosated using a standardized solution of N(2)O(4) in CDCl(3) at -40 degrees C. The reactions, which produced the corresponding N-4-R-benzyl-N-nitrosopivalamides, were followed by (1)H NMR spectroscopy. The rate of nitrosation was found to vary in a systematic way with the nature of the 4-R-group on the aromatic ring. Thus, electron-releasing groups increased the rate of the reaction, whereas electron-withdrawing ones decelerated N-nitrosation. In a similar fashion, the nitrosations were accelerated in polar solvents but were slower in solvents of low polarity. The sensitivities of N-nitrosation to these intra- and intermolecular electronic effects are compared to those from a previous study examining the dependence of the kinetics of nitrosoamide thermolyses on the same factors.

Abstract:Gas separation for industrial, energy, and environmental applications requires low energy consumption and small footprint technology to minimize operating and capital costs for the processing of large volumes of gases. Among the separation methods currently being used, like distillation, amine scrubbing, and pressure and temperature swing adsorption, membrane-based gas separation has the potential to meet these demands. The key component, the membrane, must then be engineered to allow for high gas flux, high selectivity, and chemical and mechanical stability at the operating conditions of feed composition, pressure, and temperature. Among the new type of membranes studied that show promising results are the inorganic-based and the metal-organic framework-based mixed-matrix membranes (MOF-MMMs). A MOF is a unique material that offers the possibility of tuning the porosity of a membrane by introducing diffusional channels and forming a compatible interface with the polymer. This review details the origins of these membranes and their evolution since the first inorganic/polymer and MOF/polymer MMMs were reported in the open literature. The most significant advancements made in terms of materials, properties, and testing conditions are described in a chronological fashion.

An instrument was built for the permeation testing of flat polymer membranes under pressures up to 3.0 MPa and temperatures up to 300 °C. The high pressure, high temperature cell uses aluminum tape and a graphite gasket to minimize the leak from the high pressure side to the low pressure side, making possible the permeability measurements of slow diffusing gases such as N2. A computer program developed on a LabVIEW platform fully controls the instrument and data acquisition. It incorporates algorithms to automatically adjust the downstream volume, repressurize the upstream volume, vent the downstream volume to prevent over pressurization, and change the temperature of the permeation cell. The percent relative standard deviation of the permeability measurements was <5.5%. Flat membranes of VTEC PI-1388 polymer were tested from 0.3 to 3.0 MPa and from 35 to 300 °C. The permeabilities and fluxes of H2, CO2, and N2 increased with increasing temperature, while the H2∕CO2 ideal selectivity remained unchanged. The major contribution to increased flux arose from increments in temperature rather than pressure.

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