Molecular sieves, addition with

This transformation has been applied to several chiral production processes, the first being the synthesis of a pheromone (Disparlure) intermediate (S) albeit with low turnover numbers and only 91 % ee. Another industrial product is the epoxide of allyl alcohol as developed by PPG-Sipsy, to give a process where catalyst loading was decreased by molecular sieve addition and the safety factors involving peroxide contamination were overcome. These examples are shown in Figure 1.46. 

Nickel catalysts on a support have been and continue to be a subject of multilateral studies, the results of which have helped the development of the theory of the polyfunctional catalyst. The catalytic properties of Ni molecular sieves in the presence of H2 2, 7, 8) have not been studied completely. Study of zeolite structural changes and the condition of the metal after thermal and hydrogen treatment have been comparatively poor. The same is true for the influence of zeolite type on the catalytic activity of the metal. This study aims to give additional information on the subject. As type A molecular sieve modified with Ni proves to be a suitable subject for clarifying some of the structural and catalytic peculiarities of zeolites, it is given main consideration. 

Allylic alcohols can be converted to epoxy-alcohols with tert-butyUiydro-peroxide on molecular sieves, or with peroxy acids. The addition of an appropriate chiral ligand to the metal-catalyzed hydroperoxide epoxidation of allylic alcohols leads to high enantioselectivity. This important modification is... 

The novel zeolite UTD-1 with titanium in the framework (up to 3.5% by weight) is an effective catalyst for the oxidation of cyclohexane, cyclohexene and 2,6-di-tert-butyl phenol. The catalytic behavior is similar to that of other large pore zeolites and mesoporous molecular sieves modified with titanium which includes solvents effects. Additionally, Ti-UTD-1 allows the use of oxidants and substrates too large for the commercial TS-1 catalyst. We are currently evaluating further the role of solvent and oxidant in an effort to improve selectivity as well as expand the utility of this material in oxidation catalysis. 

In addition to the solvent adsorbed on the AC, there is also moisture given up by the SLA. Owing to its volatility and low molecular weight, this is not strongly adsorbed and is desorbed preferentially. The desorption loop includes a molecular sieve dryer with sieves able to take up water but not solvent (Table 7.8). 

Catalytic system addition of molecular sieves to "soak" up any water with 3A sieves, 5-10 mol % catalyst is used,... 

The reaction of a halide with 2-butene-1,4-diol (104) affords the aldehyde 105, which is converted into the 4-substituted 2-hydroxytetrahydrofuran 106, and oxidized to the 3-aryl-7-butyrolactone 107[94], Asymmetric arylation of the cyclic acetal 108 with phenyl triflate[95] using Pd-BINAP afforded 109, which was converted into the 3-phenyllactone 110 in 72% ee[96]. Addition of a molecular sieve (MS3A) shows a favorable effect on this arylation. The reaction of the 3-siloxycyclopentene 111 with an alkenyl iodide affords the. silyl... 

Product recoveiy from reversed micellar solutions can often be attained by simple back extrac tion, by contacting with an aqueous solution having salt concentration and pH that disfavors protein solu-bihzation, but this is not always a reliable method. Addition of cosolvents such as ethyl acetate or alcohols can lead to a disruption of the micelles and expulsion of the protein species, but this may also lead to protein denaturation. These additives must be removed by distillation, for example, to enable reconstitution of the micellar phase. Temperature increases can similarly lead to product release as a concentrated aqueous solution. Removal of the water from the reversed micelles by molecular sieves or sihca gel has also been found to cause a precipitation of the protein from the organic phase. 

Ketones are more stable to oxidation than aldehydes and can be purified from oxidisable impurities by refluxing with potassium permanganate until the colour persists, followed by shaking with sodium carbonate (to remove acidic impurities) and distilling. Traces of water can be removed with type 4A Linde molecular sieves. Ketones which are solids can be purified by crystallisation from alcohol, toluene, or petroleum ether, and are usually sufficiently volatile for sublimation in vacuum. Ketones can be further purified via their bisulfite, semicarbazone or oxime derivatives (vide supra). The bisulfite addition compounds are formed only by aldehydes and methyl ketones but they are readily hydrolysed in dilute acid or alkali. 

The acetal (b 82.5°) is removed during fractional distn. Traces of benzene, if present, can be removed as the benzene/MeOH azeotrope by distn in the presence of MeOH. Distn from LiAlHa removes aldehydes, peroxides and water. Dioxane can be dried using Linde type 4X molecular sieves. Other purification procedures include distn from excess C2H5MgBr, refluxing with Pb02 to remove peroxides, fractional crystn by partial freezing and the addition of KI to dioxane acidified with aq HCl. Dioxane should be stored out of contact with air, preferably under N2. 

Dried with Linde type 5A molecular sieves or Na2S04 and fractionally distd at reduced pressure. Alternatively, it was refluxed with, and distd from, BaO. Also purified by fractional crystn from the melt and distd from zinc dust. Converted to its phosphate (m 135°) or picrate (m 223°), which were purified by crystn and the free base recovered and distd. [Packer, Vaughn and Wong J Am Chem Soc 80 905 1958.] The procedure for purifying via the picrate comprises the addition of quinoline to picric acid dissolved in the minimum volume of 95% EtOH to yield yellow crystals which are washed with EtOH and air dried before recrystn from acetonitrile. The crystals are dissolved in dimethyl sulfoxide (previously dried over 4A molecular sieves) and passed through a basic alumina column, on which picric acid is adsorbed. The free base in the effluent is extracted with n-pentane and distd under vacuum. Traces of solvent are removed by vapour phase chromatography. [Mooman and Anton J Phys Chem 80 2243 1976.]... 

A rather unexpected discovery was made in connection to these investigations [49]. When the 1,3-dipolar cycloaddition reaction of la with 19b mediated by catalyst 20 (X=I) was performed in the absence of MS 4 A a remarkable reversal of enantioselectivity was observed as the opposite enantiomer of ench-21 was obtained (Table 6.1, entries 1 and 2). This had not been observed for enantioselective catalytic reactions before and the role of molecular sieves cannot simply be ascribed to the removal of water by the MS, since the application of MS 4 A that were presaturated with water, also induced the reversal of enantioselectivity (Table 6.1, entries 3 and 4). Recently, Desimoni et al. also found that in addition to the presence of MS in the MgX2-Ph-BOX-catalyzed 1,3-dipolar addition shown in Scheme 6.17, the counter-ion for the magnesium catalyst also strongly affect the absolute stereoselectivity of the reac-... 

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