Molecular sieving temperature effects

The completely resolved spectrum of the free radical, a triplet of triplets, could be recorded at room temperature for NF2/N2F4equilibrium mixturesdissolved in perfluoro-2,3-dimethylhexane, in 2,2-dichloro-3-chloroperfluorobutane and in various Kel-F oils [3] and, even with better resolution, for NF2 introduced into molecular sieves with effective pore diameters of 5 to 9 A [4]. 

Some workers avoid delay. Pai)adium-on-carbon was used effectively for the reductive amination of ethyl 2-oxo-4-phenyl butanoate with L-alanyl-L-proline in a synthesis of the antihyperlensive, enalapril maleate. SchifTs base formation and reduction were carried out in a single step as Schiff bases of a-amino acids and esters are known to be susceptible to racemization. To a solution of 4,54 g ethyl 2-oxO 4-phenylbutanoate and 1.86 g L-alanyl-L-proline was added 16 g 4A molecular sieve and 1.0 g 10% Pd-on-C The mixture was hydrogenated for 15 hr at room temperature and 40 psig H2. Excess a-keto ester was required as reduction to the a-hydroxy ester was a serious side reaction. The yield was 77% with a diastereomeric ratio of 62 38 (SSS RSS)((55). 

Sigman et al. have optimized their system too [45]. A study of different solvents showed that the best solvent was f-BuOH instead of 1,2-dichloroethane, which increased the conversion and the ee. To ensure that the best conditions were selected, several other reaction variables were evaluated. Reducing the catalyst loading to 2.5 mol % led to a slower conversion, and varying temperature from 50 °C to 70 °C had little effect on the selectivity factor s. Overall, the optimal conditions for this oxidative kinetic resolution were 5 mol % of Pd[(-)-sparteine]Cl2, 20 mol % of (-)-sparteine, 0.25 M alcohol in f-BuOH, molecular sieves (3 A) at 65 °C under a balloon pressure of O2. 

Thus, there are two limitations of the pycnometric technique mentioned possible adsorption of guest molecules and a molecular sieving effect. It is noteworthy that some PSs, e.g., with a core-shell structure, can include some void volume that can be inaccessible to the guest molecules. In this case, the measured excluded volume will be the sum of the true volume of the solid phase and the volume of inaccessible pores. One should not absolutely equalize the true density and the density measured by a pycnometric technique (the pycnometric density) because of the three factors mentioned earlier. Conventionally, presenting the results of measurements one should define the conditions of a pycnometric experiment (at least the type of guest and temperature). For example, the definition p shows that the density was measured at 298 K using helium as a probe gas. Unfortunately, use of He as a pycnometric fluid is not a panacea since adsorption of He cannot be absolutely excluded by some PSs (e.g., carbons) even at 293 K (see van der Plas in Ref. [2]). Nevertheless, in most practically important cases the values of the true and pycnometric densities are very close [2,7],... 

The catalyst was prepared from the corresponding chiral diol and TiCl2(OPr-/)2 at room temperature in the presence of 4 A molecular sieves. Without molecular sieves, stoichiometric amounts of the titanium complex were required to obtain an equally high enantioselectivity. A remarkable solvent effect was observed. Various cycloadducts were only obtained with high optical yields when non-polar solvents were employed252,253. For example, 4-substituted 4-cyclohexene-1,2-dicarboxylate derivatives 408 were obtained with ee values ranging from 91 to 94% in the reactions of 91a, 399 and 407 with 17b in toluene/... 

Molecular sieving, 18 269-272 effect of temperature, 18 271, 272 sorbate structure, 18 270, 271 molecular dimensions, 18 270, 271 polarity, 18 271 zeolitic, 39 352 structure, 18 269, 270 effect of cation, 18 269, 270 of solvation, 18 270 ring shape, 18 269 ring size, 18 269 silicon aluminum ratio, 18 270... 

The process for isomerization of EB requires that some fraction of the feed be maintained in a saturated state, as described in Sections 14.4.1.1 and 14.4.1.2. The ability to isomerize the EB is affected by the naphthene concentration and constrained by the equilibrium ratio of EB/xylenes at the reaction temperature. Use of a pore-restricted molecular sieve can be used to eliminate more sterically demanding species from the reaction network and can effectively remove these from consideration. In this maimer, one can achieve higher levels of a desired species, such as PX from EB, than could ordinarily be obtained by isomerization over a larger-pore zeolite. 

Several preparation methods have been reported for the synthesis of TS-1. In this work, we have investigated the physicochemical properties of TS-1 samples synthesized by different preparation metiiods and tested these materials as catalysts for the oxidation of n-octane, 1-hexene and phenol using aqueous hydrogen peroxide (30 wt%) as oxidant at temperatures below 100 C. For comparison, Ti02 (anatase) and the octahedral titanium-containing silicate molecular sieve (ETS-10) (5) have been studied. The effect of the presence of aluminum and/or sodium on the catalytic activity of TS-1 is also discussed. 

It is the purpose of the present paper to study the effect of pore size on the adsorption of xenon on mesoporous MCM-41 molecular sieves. In particular, much attention will be focused on the temperature variation of l2,Xe NMR chemical shifts at low Xe loading to realize the characteristics of the Xe-wall interactions. 

Figure 15.3. Effects of temperature, pressure, and kind of adsorbent on the amount of ethane adsorbed (1) activated carbon at 25°C (2) type 4A molecular sieve (MS) at 0°C (3) type 5A MS at 25°C (4) type 4A MS at 25°C (5) type 4A MS at 75°C (6) silica gel at 25°C (7) type 4A MS at 150°C. (Data from Union Carbide Corp.)...

Figure 15.11. Effect of temperature on molecular sieve type 5A, silica gel and activated alumina at water vapor pressure, 13.3 kPa (lOOmmHg). A, molecular sieve type 5A B, silica-type adsorbent C, alumina-type adsorbent. (Chi and Cummings, 1978).

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