Cesium salt

Example Shaking 50 mL of 0.001 Af cesium salt solution with 1.0 g of a strong cation exchanger in the H-form (with a capacity of 3.0 mequiv g ) removes the following amount of cesium. The... 

The quaHtative determination of water-soluble perchlorates by precipitation using methylene blue yields a violet precipitate (105). Using potassium, mbidium, or cesium salts for precipitation from ethanol—water solutions can serve as a quaHtative determination of perchlorates (106). 

Cesium, first discovered by Bunsen and Kirchoff ia 1860 while examining spring water, was the first element discovered spectroscopically (1). The name, comes from the Latin caesius, sky blue, and refers to the characteristic blue spectral lines of the element. Cesium salts were not successfully reduced to metal until 1881. Electrolysis of the molten chloride did not yield cesium metal under the same conditions that led to the reduction of the other alkaU metal chlorides. 

The carboxamidomethyl ester was prepared for use in peptide synthesis. It is formed from the cesium salt of an A-protected amino acid and a-chloroacetamide (60-85% yield). It is cleaved with 0.5 M NaOH or NaHCOa in DMF/H2O. It is stable to the conditions required to remove BOC, Cbz, Fmoc, and r-butyl esters. It cannot be selectively cleaved in the presence of a benzyl ester of aspartic acid. ... 

The Tcrom ester is prepared from the cesium salt of an N-protected amino acid by reaction with 2-(trifluoromethyl)-6-chromylmethyl bromide (DMF, 25°, 4 h, 53-89% yield). Cleavage of the Tcrom group is effected by brief treatment with n-propylamine (2 min, 25°, 96% yield). It is stable to HCl/dioxane, used to cleave a BOC group. ... 

Sulfobenzyl esters were prepared (cesium salt or dicyclohexylammonium salt, Na03SC6H4CH2Br, DMF, 37-95% yield) from A -protected amino acids. They are cleaved by hydrogenolysis (H2/Pd), or hydrolysis (NaOH, dioxane/water). Treatment with ammonia-or hydrazine results in formation of the amide or hydrazide. The ester is stable to 2 M HBr/AcOH and to CF3SO3H in CF3CO2H. The relative rates of hydrolysis and hydrazinolysis for different esters are as follows ... 

Cesium Salts in Crown Synthesis 3.14 Organometallic Derivatives of Crowns... 

Using cesium carbonate in methanol, Kellogg and coworkers were able to convert catechol and pentaethylene glycol into benzo-18-crown-6 in 74% yield. They found that the cesium salts in these reactions were usually equal or superior to the potassium salts. 

The most demanding test of cesium carbonate as base was with 2,3-dihydroxypyridine (3-hydroxypyridone). The cesium salt was found to be fairly unstable, apparently oxidizing quite rapidly. Model reactions suggested that alkylation would occur 1,3 (N, 0) to give the substituted pyridone. Nevertheless, on the basis of UV and H-nmr analysis, the product of reaction between 2,3-dihydroxypyridine and tetraethylene glycol dibromide was assigned as the pyridocrown (23% yield, mp 77—78.5°) as shown in Eq. (3.60). 

Although cesium salts appear to be excellent reagents for the formation of crown ethers, it should be noted that such salts are used at least in equivalent amounts or in excess (4 eq.) . These salts are relatively expensive and will probably be reserved for use in the synthesis of less readily accessible crowns. 

Similar compounds to those described above have been prepared by the same group using the bis-cesium salts of pyridine-3,5-dicarboxylic acids. In a number of experiments Piepers and Kellogg showed that Cs plays an irreplacable role as compared with Na", K and Rb for the formation of [the macrocycle shown below] . 

The Tcrom ester is prepared from the cesium salt of an A-protected amino acid by reaction with 2-(trifluoromonethyl)-6-chromonylmethyl brormde (DMF, 25°,... 

Returning to the observed values for these cesium salts, plotted as dark circles in Fig. 57, we must conclude that the position of the experimental points—nearer the diagonal than any salt of Rb, K, or Na—does not indicate anything unusual about the aqueous solution of the cesium salts, but merely arises from the fact that these cesium salts happen to crystallize in a more compact lattice structure, with less void space between the ions. We cannot make a similar remark about the points for the lithium salts, which lie astride the diagonal the interpretation of these values will be discussed later. 

In Table 40 the values for the cesium salts show that, if a zero value or a positive value of the activity /l-cocflicient is used, approximate agreement with experiment can be obtained only by introducing a value of a that is smaller than the lattice spacing in the crystal- an impossibly small value. Figure 74 indicates that this situation may have arisen because a mutual attraction between the Cs+ ion and the halide ion is superimposed on their electrostatic attraction. We may tentatively look for the source of this additional attraction in the situation depicted in Fig. 69. 

Kinetic studies of the polymerization of mono-functional polymethyl methacrylate led to the determination of the propagation constants, k , of the sodium, potassium, and cesium salts 29- 35 36) of polymethyl methacrylates anions. Surprisingly, they... 

An iron phosphate catalyst with a P/Fe atomic ratio of 1.2 used in this study was prepared according to the procedures described in the previous studies [6-8]. On the other hand, a V-P oxide catalyst with a P/V atomic ratio of 1.06 and pumice supported 12-molybdophosphoric acid (H3PM012O40) and its cesium salt (CS2HPM012O40) catalysts were the same as used in a previous study [9]. Pumice supported W03-based mixed oxide catalysts were the same as used in a previous study [10]. 

Especially for large-scale work, esters may be more safely and efficiently prepared by reaction of carboxylate salts with alkyl halides or tosylates. Carboxylate anions are not very reactive nucleophiles so the best results are obtained in polar aprotic solvents45 or with crown ether catalysts.46 The reactivity order for carboxylate salts is Na+ < K+ < Rb+ < Cs+. Cesium carboxylates are especially useful in polar aprotic solvents. The enhanced reactivity of the cesium salts is due to both high solubility and minimal ion pairing with the anion 47 Acetone is a good solvent for reaction of carboxylate anions with alkyl iodides48 Cesium fluoride in DMF is another useful... 

Carboxylate anions derived from somewhat stronger acids, such as p-nilrobcnzoic acid and chloroacetic acid, seem to be particularly useful in this Mitsunobu inversion reaction.53 Inversion can also be carried out on sulfonate esters using cesium carboxy-lates and DMAP as a catalyst in toluene.54 The effect of the DMAP seems to involve complexation and solubilization of the cesium salts. 

As a suitable model reaction, the coupling of various substituted carboxylic acids to polymer resins has been investigated by Stadler and Kappe (Scheme 7.8) [28]. The resulting polymer-bound esters served as useful building blocks in a variety of further solid-phase transformations. In a preliminary experiment, benzoic acid was attached to Merrifield resin under microwave conditions within 5 min (Scheme 7.8 a). This functionalization was additionally used to determine the effect of micro-wave irradiation on the cleavage of substrates from polymer supports (see Section 7.1.10). The benzoic acid was quantitatively coupled within 5 min via its cesium salt utilizing standard glassware under atmospheric reflux conditions at 200 °C. 

A rapid and efficient procedure for flash heating by microwave been described for attachment of aromatic and aliphatic carboxylic lrra< iation las methylated polystyrene resins via their cesium salts (Eq. 3) [17], aQ s to chloro-... 

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]. 

Cesium salts of 12-tungstophosphoric acid have been compared to the pure acid and to a sulfated zirconia sample for isobutane/1-butene alkylation at room temperature. The salt was found to be much more active than either the acid or sulfated zirconia (201). Heteropolyacids have also been supported on sulfated zirconia catalysts. The combination was found to be superior to heteropolyacid supported on pure zirconia and on zirconia and other supports that had been treated with a variety of mineral acids (202). Solutions of heteropolyacids (containing phosphorus or silicon) in acetic acid were tested as alkylation catalysts at 323 K by Zhao et al. (203). The system was sensitive to the heteropoly acid/acetic acid ratio and the amount of crystalline water. As observed in the alkylation with conventional liquid acids, a polymer was formed, which enhanced the catalytic activity. 

The propensity of the cesium salts of week acids to accelerate SN2 type displacement reactions was exploited for the stereodirected conversion of glycosyl nitrates into anomeric phosphotriesters by exposure of phosphoric acid diesters to cesium salts (Scheme 9).16 Thus, glycosyl nitrate 50, obtained by azidonitration of 3,4-di-O-acetyl-L-fucal, was treated with... 

Gomplexation of cesium at a tetracarbaborane cage was achieved in the reaction of [ / >-2,4,6,12-(SiMe3)4-2,4,6,12-C4B8H8] with an excess quantity of cesium metal in THF. In the polymeric structure of the cesium salt, one cesium atom occupies an apical position above an open six-membered C3B3 face 5.19... 

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