Rare earth metal salts

Against this background it is important that—quite fitting in this still new millennium— the first catalytic Friedel-Crafts acylations of (still relatively electron-rich) aromatic compounds were reported (Figure 5.35). Trifluoromethane sulfonates ( triflates ) of rare-earth metals, e. g., scandium(III)triflate, accomplish Friedel-Crafts acylations with amounts of as little as 1 mole percent. Something similar is true of the tris(trifluoromethanesulfonyl)-methides ( triflides ) of rare-earth metals. Unlike conventional Lewis acids, the cited rare-earth metal salts can form 1 1 complexes with the ketone produced, but these are so unstable that the Lewis acid can re-enter the reaction. Whether this works analogously for the third catalytic system of Figure 5.35 is unclear. 

The selectivity of the reaction of crotylmagnesium chloride with benzaldehyde in the presence of various rare earth metal chlorides was studied by Imamoto. Interestingly, the ratio of a to 7 products can be switched to the opposite simply by using of another rare earth metal salt. Yttrium gives exclusively 7-product, whereas neodymium leads to 89% of a-attack (with 92% of ( )-isomer).258 Scandium behaves like yttrium, other lanthanides give intermediate results (Scheme 86). 

Thus the peculiar titration results were due to the heterogeneous catalysis, not of the original reaction, but of a new reaction that had arisen from the analytical procedure. Precipitates formed by the reagents themselves can also prove catalytically active. For instance, the catalysis by rare earth metal salts of the hydrolysis of acid phosphonate esters was actually due to the development of metal hydroxide gels [159], A quite different example concerns reactions of mercury salts where the disproportionation... 

In recent years, the use of rare earth metal salts as inhibitors has been gaining attention. Rare earth metal salts have been found to be effective inhibitors for the protection of aluminium alloys, mild steel and zinc. 

The formation of a rare earth metal oxide on the metal surface, impedes the cathodic reduction of oxygen and thus cathodic inhibition is achieved by the addition of a rare earth metal salt to a system. The surface atom concentration ratio, [Ce/Ce + M], where M is Fe, Al or Zn, is a function of cerium oxide film thickness determined by AES depth profiles as shown in Fig. 12.2. 

Based on the electrochemical polarization and surface analytical data available, it is possible to surmise the following mechanism for inhibition by rare earth metal salts ... 

Corrosion inhibition by rare earth metal salts... 

Rare earth metal salts Aircraft industry. Effective for pitting corrosion, stress corrosion cracking, corrosion fatigue, galvanic corrosion and crevice corrosion by using rare earth metal salts in waters for washing aircraft. Disposal of the waters is environmentally safe [4,6]... 

Rare earth metal salts Recirculating water systems ... 

Molybdates of the Rare Earth Metals. —Salts of the type M2(Mo04)3 have been described. The cerous salt is obtained as yellow crystals by fusing together anhydrous cerous chloride and sodium molybdate. The density of the molten salt is 4-56. The crystals are similar to those of lead and bismuth molybdates, as also are those of didymium molybdate. ... 

Kobayashi et al. have demonstrated fhat some metal salts (e.g. Fe(II), Cu(II), Zn(II), Cd(II), and Pb(II) perchlorates) other fhan rare earth metal salts are also water-stable Lewis acids and work as catalysts of fhe aqueous aldol reaction of SEE [75]. Metal salts wifh good catalytic activity have pKh values (/hydrolysis constant) from 4.3 to 10.08 and WERC (water exchange rate constant) greater than 3.2 X10 m s . If p/metal cations are readily hydrolyzed to give oxo-nium ions, which promote hydrolysis of SEE. Metal cations with pKh> 10.08 do not have sufficient Lewis acidity to promote the aldol reaction. When fhe WERC... 

Rare earth metal salts produced at mines... 

A useful Mannich-type reaction can be carried out in an fluorous biphasic system, by use of perfluorodecalin (Ci0Fi8, cis- and trans mixture) as the fluorous solvent and hexane as the organic solvent and perfluorinated rare earth metal salts such as Sc(0S02C8F17)3 or Yb(0S02C8Fi7)3 (2.0mol%) as the catalyst. The Mannich-type reaction of arylaldehydes with aromatic amines and (l-methoxy-2-methylpropeny-loxy)trimethylsilane can be carried out many times without reloading the catalyst and the fluorous solvent (Equation 4.27) [48]. 

Amoco researchers began to research various catalytic additives that could prevent Mn02 precipitation while permitting one to operate at a lower Br/Co -I- Mn ratio. Rare earth metal salts, particularly Ce(OAc)3 at Co/Ce =10 1, were discovered to inhibit Mn02 precipitation even when very low Br/(Co + Mn) ratio was employed (<0.5) [62, 63]. A fundamental study of the unwanted production of Mn02 was later pursued by the group of Bakac [56]. Mn indeed can access the oxidation state by either direct oxidation of Mn(lll) or reduction from Mn(VII). Mn(IV) can also oxidize bromides andMn(ll). 

In a literal sense, the term earth signifies an oxide and rare earth an oxide of a particular group of elements. Hence, one should speak of the salts of this group of elements as the rare earth metal salts. However, usage permits one to speak of the rare earth salts, rare earth ions, etc. This practice wiU be followed here. 

Inorganic metal salts can induce secondary metabolism in plant cell cultures, such as Cu and Ag. Cu elicited phytoalexin production in rice plants. Adding AgNOs induced taxol biosynthesis. Rare earth metal salts, such as (NH4)2Ce(N03)6, can also increase the accumulation of paclitaxel in Taxus cells. Ginsenoside biosynthesis was elicited in cell cultures of Panax ginseng by vanadate. The metabolic action of inorganic metal salts inducing the accumulation of secondary metabolites may be similar to other natural chemical elicitors. ... 

Ferromagnetism of the transition and rare-earth metal salts and complexes is due to high-spin states of those atoms. The electronic structure of these metal atoms is open-shell, with d-orbitals and f-orbitals containing several unpaired electrons [1-3]. 

The phagocytic potential of the liver and the spleen could be temporarily blocked by using different substances (such as rare-earth metal salts or carbon colloids). For example, injected liposome blood clearance can be reduced after MPS blockade with dextran sulfate or carbon (Souhami et al, 1981). MPS blockade was also achieved by progressively increasing intravenous (i.v.) dosages of liposomes liver saturation was first observed, followed by localization in the spleen and eventually accumulation in the bone marrow (Poste, 1983). 

Hinton, B.R.W., (1992). Corrosion inhibition with rare earth metal salts. Journal of Alloys and Compounds, Vol. 180, No. 1-2, (25 March 1992), pp. 15-25, ISSN 0925-8388... 

The Mannich and related reactions provide one of the most fundamental and useful methods for the synthesis of P-amino ketones or P-amino esters. Three-component Mannich-type reactions of aldehydes, amines, and silyl enol ethers have been developed. With the development of green solvent systems, this reaction was also examined in a fluorous phase using perfluorinated rare earth metal salts including Sc(0S02C8Fi7)3 [5]. A characteristic point of this system is that it can be reused many times without reloading a new catalyst. There are also many reports on other scandium-catalyzed Mannich reactions. For example, Sc(OTf)3 was found to be an efficient catalyst for the three-component Mannich-type reactions of aromatic aldehydes, ketones, and nitriles in the presence of acetyl chloride (Scheme 12.3) [6]. 

General uniform corrosion on pure magnesium has been drastically reduced by the use of inhibitors sueh as ehromate, dichromate, molybdate, nitrate, phosphates and vanadates that promote the formation of a protective layer, tend to retard corrosion (Ghali, 2006). Addition of substances that can form soluble complexes as tartrate, metaphosphate, etc. or insoluble salts as oxalate, carbonate, phosphate, fluoride, etc. is efficient at reducing corrosion. Adding soluble chromates, neutral fluorides or rare earth metal salts is effective in reducing magnesium-base metal corrosion (Schmutz et al, 2003). 

A variation of metathesis equation (Eq. 1.6) is the reaction between a rare earth metal salt and a carboxylic acid followed by addition of an alkali metal hydroxide imtil precipitation of the rare earth caiboxylate occius (Eq. 1.7), normally at pH = 5-7. 

B. R. W. Hinton, New approaches to corrosion inhibition with rare earth metal salts , NACE Corrosion/1989, paper no. 170 (1989). 

F. Mansfeld, C. Chen, C. B. Breslin and D. Dull, Sealing of anodized aluminum alloys with rare earth metal salt solutions , J. Electrochem. Soc. 145,2792 (1998). 

Development of new inorganic REM salt corrosion inhibitors has been slow and has not reached the same level of sophistication as that of organic inhibitors, although important contributions have appeared recently. In this chapter, an overview of inorganic corrosion inhibitors based on rare earth metal salts is presented. 

Hinton BRW (1989b) New Approaches to Corrosion Inhibition with Rare Earth Metal Salts , NACE Conference 1989, April 17-21, New Orleans, Paper 170. 

Hinton BRW (1992) Corrosion irrhibition with rare earths metal salts , J. Alloys and Compounds 180,15—25. 

Hinton, B.R.W., Corrosion Inhibition With Rare-Earth-Metal Salts. Journal of Alloys and Compounds, 1992. 180 15—25. 

Mansfield, F., Use of rare earth metal salt solutions for corrosion protection of aluminium alloys and mild steel. Russian Journal of Electrochemistry, 2000. 36(10) 1063-1071. 

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