Promoter cesium

Type Potassiiun promoted Potassium- promoted high vanadium Cesium promoted Cesium- promoted high vanadium... 

However, for Cs+ some comments are possible. Formation of crown ether complexes promotes cesium extraction (Vendilo, et al, 2009) into hydrophobic RTIL from water if the complex stability in RTIL is higher than in water. Table 8. Indeed for [BMIM][N(Tf)2], [HMIM][N(Tf)2], [EtHMIM][N(Tf)2], [BMiMIpFg] and [TOMA][Sal] logKiRTiL > logKi i --... 

Ethylene oxide is produced in large, multitubular reactors cooled by pressurized boiling Hquids, eg, kerosene and water. Up to 100 metric tons of catalyst may be used in a plant. Typical feed stream contains about 30% ethylene, 7—9% oxygen, 5—7% carbon dioxide the balance is diluent plus 2—5 ppmw of a halogenated moderator. Typical reactor temperatures are in the range 230—300°C. Most producers use newer versions of the Shell cesium-promoted silver on alumina catalyst developed in the mid-1970s. 

Silver alone on a support does not give rise to a good catalyst (150). However, addition of minor amounts of promoter enhance the activity and the selectivity of the catalyst, and improve its long-term stabiHty. Excess addition lowers the catalyst performance (151,152). Promoter formulations have been studied extensively in the chemical industry. The most commonly used promoters are alkaline-earth metals, such as calcium or barium, and alkaH metals such as cesium, mbidium, or potassium (153). Using these metals in conjunction with various counter anions, selectivities as high as 82—87% were reported. Precise information on commercial catalyst promoter formulations is proprietary (154—156). 

Cesium fluoride-promoted telomenzation of equimolar amounts of perfluoro 2-butyne and 2-bromoperfluoro-2-butene gives a mixture of hexadienes or, with... 

Among the many methods of generating difluorocarbene, the treatment of bromodifluoromethylphosphonium bromides with potassium or cesium fluoride is particularly useful at room temperature or below [II, 12 13] The sodium iodide promoted decomposition of phenyl(trifluoromethyl)mercury is very effective at moderate temperatures [S, 14] Hexafluoropropylene oxide [/5] and chlorodifluo-roacetate salts [7] are excellent higher temperature sources of difluorocarbene... 

M.V. Badani, and M.A. Vannice, Effects of cesium and chlorine on oxygen adsorption on promoted Ag/a AI203 catalysts, Appl. Catal. A 204, 129-142 (2000). 

GP 2] [R 3a] A Shell Series catalyst was measured in a fixed-bed configuration and deposited in micro channels electrophoretically (20 vol.-% ethylene, 80 vol.-% oxygen 0.3 MPa 230 °C) [101]. The selectivity was lower in the micro channels (51%) than in the fixed bed (57%) at a conversion of 17%. In a further investigation, a sputtered silver catalyst (cesium promoted) was better than both systems (68%) at higher conversion (25%). 

In contrast, perfluoromethylenecyclopropane (105) failed to give any thermal dimerization (cesium fluoride promotes its dimerization, but not in a [2 + 2] fashion) [29], while tetrafluoroethylene and other 1,1-difluoroalkenes readily undergo thermal [2 + 2] dimerization [123]. 

An 8000-member library of trisamino- and aminooxy-l,3,5-triazines has been prepared by use of highly effective, microwave-assisted nucleophilic substitution of polypropylene (PP) or cellulose membrane-bound monochlorotriazines. The key step relied on the microwave-promoted substitution of the chlorine atom in monochlorotriazines (Scheme 12.7) [35]. Whereas the conventional procedure required relatively harsh conditions such as 80 °C for 5 h or very long reaction times (4 days), all substitution reactions were found to proceed within 6 min, with both amines and solutions of cesium salts of phenols, and use of microwave irradiation in a domestic oven under atmospheric reaction conditions. The reactions were conducted by applying a SPOT-synthesis technique [36] on 18 x 26 cm cellulose membranes leading to a spatially addressed parallel assembly of the desired triazines after cleavage with TFA vapor. This concept was later also extended to other halogenated heterocycles, such as 2,4,6-trichloropyrimidine, 4,6-dichloro-5-nitropyrimidine, and 2,6,8-trichloro-7-methylpurine, and applied to the synthesis of macrocyclic peptidomimetics [37]. 

It is important to note that not all cations promote Prussian blue/Prussian white electroactivity. Except for potassium, only ammonium (NH4+), cesium (Cs+), and rubidium (Rb+) were found able to penetrate the Prussian blue lattice. Other mono-and divalent cations are considered as blocking ones. 

The effect of bath additives on the electrocodeposition of alumina-copper has been studied. Chloride ion was found to significantly inhibit incorporation of alpha alumina in an acidic copper bath [27, 51], whereas thallium ions, cesium ions, and tetra-ethylene pentamine were promoters [25, 32]. 

Fluoride ion is effective in promoting the reduction of aldehydes by organosil-icon hydrides (Eq. 161). The source of fluoride ion is important to the efficiency of reduction. Triethylsilane reduces benzaldehyde to triethylbenzyloxysilane in 36% yield within 10-12 hours in anhydrous acetonitrile solvent at room temperature when tetraethylammonium fluoride (TEAF) is used as the fluoride ion source and in 96% yield when cesium fluoride is used.83 The carbonyl functions of both p-anisaldehyde and cinnamaldehyde are reduced under similar conditions. Potassium bromide or chloride, or tetramethylammonium bromide or chloride are not effective at promoting similar behavior under these reaction conditions.83 Moderate yields of alcohols are obtained by the KF-catalyzed PMHS, (EtO SiH, or Me(EtO)2SiH reduction of aldehydes.80,83,79... 

Diphenylsilane reacts with two equivalents of neat n-heptanal in the presence of anhydrous cesium fluoride within three minutes at room temperature to form di-n-hep toxy diphenylsilane quantitatively (Eq. 162).319 Potassium fluoride and potassium phthalate are considerably less effective promoters, even at temperatures up to 140°.319... 

Diphenylsilane catalyzed by various salts promotes the 1,2-reduction of cinnamaldehyde.318 Cesium fluoride catalysis is particularly effective.320 It is possible to stop these reactions at the silyl ether stage.73,320 The 1,2-reduction of citral is accomplished in high yield with diphenylsilane and Wilkinson s catalyst (Eq. 262) 435 Interestingly, the trialkylsilanes, ethyldimethylsilane and triethylsilane, give high yields of the 1,4-reduction product whereas diisopropylsilane gives a 1 1 mixture of 1,2- and 1,4-reduction (Eq. 263)435... 

It is thought that these trialkonolamine borates may enhance the reactivity of the rhodium carbonyl anions by minimizing their tendency to form contact ion pairs in solution under the reaction conditions employed. The same patent discloses that ammonium salts and salts of Groups I and II, especially cesium and ammonium carboxylate salts, function as promoters (63). 

Knochel demonstrated the effectiveness of soluble potassium or cesium alkoxides such as KO Bu or CsO Bu as well as KH in iV-methylpyrrolidinone (NMP) for promoting the 5-endo-dig cyclizations of 2-alkynylanilines to 2-substituted indoles in solution or the solid-phase <00AG(E)2488>. Alternatively, Cacchi coupled a palladium-catalyzed cyclization of o-alkynyltrifluoroacetanilides with the addition of benzyl bromide or ethyl iodoacetate to afford 2-substituted-3-benzyl or 3-indolylcarboxylate esters, respectively <00SL394>. Yamamoto reported a new palladium catalyzed indole synthesis in which 2-(l-alkynyl)-Ar-alkylideneanilines 117 give 2-substituted-3-(l-alkenyl)indoles 118 directly from the imine by the in situ coupling of an aldehyde with the alkynylaniline <00JA5662>. 

Chiral diester diamide macrocycles such as ll-180 have been synthesized (181) from esters of L-valine by, first of all, forming acyclic bisamides and then hydrolyzing the ester functions prior to template-promoted cyclization with cesium carbonate (182) and the appropriate dibromide. L-Tartaric acid has also been incorporated into a macrocycle, i.e., lll-181, of this type. 

Ru/Rh/Promoter/HOAc Catalyst Compositions. The behavior described in the previous section is however by no means limited to cesium ions as promoters, nor is it confined to cations of the alkali metal group. 

A chemist prepares an aqueous solution of cesium sulfate, 082(804)3, swirling the beaker in her gloved hand to promote dissolution. She notices something, momentarily furrows her brow, and then smiles knowingly. She nestles the beaker into a bed of crushed ice within a bucket. What did the chemist notice, why was she briefly confused, and why did she place the dissolving cesium sulfate on ice ... 

Fig. 8. Plot of rates as a function of Cst/Rh ratio ( ) methanol ( ) ethylene glycol. Reaction conditions 75 ml tetraglyme solvent, 3 mmol Rh, 10 mmol 2-hydroxypyridine, 544 atm, H2/CO = 1, 220 C, cesium formate promoter as indicated, 4 hr (88). Methanol and ethylene glycol rates at Cs+/Rh = 0 are 5.21 and 1.34 hr-1, respectively.

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