Europium salt

Urbain and Botjrion [186] first prepared the divalent europium salt EuGla. In weakly acidic aqueous solution Eu2+ is quite stable in the absence of oxidizing agents. The divalent ions of Sm, Eu and Yb are strong reducing agents and follow the order Sm2+ > Yb2- > Eu2+. The oxidation potentials (E°) for the reaction... 

The lanthanum or europium atoms had no interaction with the gold and silver centers, and the determined crystal structures exhibited hexagonal arrays of metal-metal interactions with diagonal interactions in the layer and the lanthanoids in the middle of the hexagonal prisms. In both examples, the lanthanum and the europium salts were isostructural (Fig. 5). 

However, excellent simple (exo endo = 95 5) and induced diastereoselectivity (94 6) was obtained by Jurczak [88] by applying the bornane sulfone amide derivative of glyoxylic acid 2-23 in the presence of a catalytic amount of a europium salt. Reaction of 2-23 with 1-methoxy-1,3-butadiene 2-24 gave predominantly 2-25 a which was transformed into the lactone 2-26 aiming towards the synthesis of compactin (Fig. 2-7)[89]. 

Based on the work of Danishefsky [70] on the cycloaddition of aldehydes to dienes bearing various menthyl auxiliaries, Stoodley et al. have used butadienyl glycosides 2-58 with the aim to synthesise (1—>l)-linked disaccharides [103]. The reaction was performed with p-nitrobenzaldehyde 2-57 in the presence of an europium salt since benzaldehyde itself did not react. Reasonable induction was obtained in the presence of the chiral (-)-Eu(hfc)3 as a matched pair to give 2-59 as the major product (Fig. 2-17). 

Freeman, Crosby, Lawson (13), Kropp, and Windsor 17, 18) had reported that hydrated europium chloride crystals and aqueous solutions of europium salts, respectively, showed considerable enhancement of ion fluorescence and lifetimes upon substitution of H2O by D2O, the latter workers have reported (37) that wet hydrocarbon solutions of the thenoyltrifluoroacetone chelate of europium showed no enhancement of quantum yield and lifetime upon replacing the H2O present by D2O. They suggested that whereas deuteration enhanced the fluorescent properties of the free ions by inhibiting nonradiative deactivation of the Do level, the quantum efficiency of Do luminescence obtained upon direct excitation of this level (JO, 11) is already so high in the fluorinated diketone chelates e.g. thenoyltrifluoroacetone) that deuteration of the environment should have little further enhancing effect. 

The same effect can be observed if the stage of spin-on deposition of sol is replaced by immersion of the sample in solution of europium salt. These examinations show that porous anodic alumina grown in oxalic acid which displays inherent blue PL can be used for fabrication of dichromatic luminescent images only, while red luminescence related to Eu is not observed from the same area of the sample. 

The fluoride electrode is the best known of the ISEs. Its sensitive membrane is a mono-crystal of lanthanum trifluride doped with a europium salt, which allows the fluorine atoms to migrate within the cristalline network (Figure 19.3). The OH ion can cause interference with the F ions at alkaline pH. 

The application of Lewis acids, such as the europium salt Eu(fod)3, in [4+2] cycloadditions of carbonyl compounds (e.g. glyoxylates and aldehydes) with 1-methoxy-3-trimethylsilyloxy-l,3-butadiene (Danishefsky s diene) has been intensively examined by Danishefsky et al. and employed in natural product synthesis. ... 

To prepare europium(III) acetate from a solution of a soluble europium salt, the oxalate is first precipitated from an acidified dilute solution of a soluble europium(III) salt at 50 to 70° by the slow addition of a 5 per cent solution of oxalic acid while the reaction mixture is stirred. The amorphous precipitate first formed soon becomes crystalline. It is filtered and washed with water and methanol. The product is converted to the oxide by ignition in a muffle furnace at 900°. 

The reduction of europium(III) to europium(II) may be accomplished simply with a Jones reductor or, more elaborately, by the action of hydrogen on the chloride at 700°. In the three procedures below the preparation of (1) europium(II) sulfate, (2) europium(II) carbonate, and (3) europium(II) chloride are described. Fortunately, these europium salts when dry are not appreciably oxidized by dry air and hence may be handled and stored conveniently. The first procedure is based on the preparation of insoluble europium(II) sulfate after reduction of europium(III) in... 

In the case of complexation of europium salts, the N/Eu molar ratio was found to be 6.5 and 4.8 for materials obtained from 3-aminopropyltrimethoxysilane and A -(6-aminohexyl)-3-aminopropyltrimethoxysilane, respectively. ... 

Scheme 12.21. Chelating ability of M1K-M3K toward europium salts.

This synthesis was repeated by Carri re and Eisenbach, who were able to prepare an a-phenyl-a-ethyl-3-propiolactone with an enantiomeric excess of 95%. This value was determined by NMR spectroscopy after complexation of the aminoester with a chiral europium salt shift reagent. 

Acetylacetone reacts with an ethanol solution containing a salt of europium to give a compound that is 40.1% C and 4.71% H by mass. Combustion of 0.286 g of the compound gives 0.112 g EU2O3. Assuming the compound contains only C, H, O, and Eu, determine the formula of the compound formed from the reaction of acetylacetone and the europium salt. (Assume that the compound contains one europium ion.)... 

H N.m.r. spectra of potassium and calcium salts of gluconic acid in the presence of europium salts have shown that the former are selectively bound to the europium, a function of conformation. ... 

Werts and co-workers tested the validity of these calculations by comparing experimental and calculated parameters for well-studied systems, the europium salts of dipicolinic acid [59]. They found an error of about 15% between experimentally determined and calculated branching ratios and radiative lifetimes. 

Similar NMR studies of MTPA esters showed that there was a correlation between the shape of the signals due to the CH2OH (C-26) group in the R) and (5)-MTPA esters and the absolute configuration at C-25. This new approach (i.e., comparison of the chemical shifts of the methylene protons at C-26 in the spectra of the R) and (S)-MTPA esters) has the advantage of avoiding the use of europium salts and has been widely used by researchers interested in the stereochemistry of steroid side chains. ... 

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