Use of metal salts

Separation Techniques. Current methods for separating fatty acids are by solvent crystaUi2ation or by the hydrophili2ation process. Other methods that have been used in the past, or perhaps could be used in the future, are panning and pressing, solvent extraction, supercritical fluid extraction, the use of metal salts in assisting in separation, separations using urea complexes, and adsorption/desorption. 

Note that the use of metal salts for coagulation may increase the quantity of dissolved solids. One must consider the downstream impact of these dissolved solids. In addition, the impact of carryover of suspended Al. .. and Fe... compounds and their related effect on downstream processes must be considered. 

In 1801 the French pyrotechnist Claude-Fortune Ruggieri described the use of metal salts in the production of coloured flames. By the early nineteenth century the firework maker had at his disposal a diverse arsenal of materials, many of which are still in use today. The following substances were documented by Audot and others at around that time ... 

In general, the reaction is run with an excess of the metal halide. The use of metal salts that have a high lattice energy require the addition of a crown ether. 

The above conventional synthetic methods are based on the use of metal salts or carbonyls as complex-formers. At the same time, as far back as at the end of the nineteenth century [504], the possibility of use of compact elemental metals for obtaining complex compounds was shown. This circumstance served as a basis for development of the electrochemical [10,24,201,202,206,505-507], gas-phase [201,202,508-512], and liquid-phase [201,202,513] syntheses of metal complexes using zero-valent metals. All these syntheses are united as direct synthesis of metal complexes [201,202,513]. Much literature is devoted to this area, generalized in a series of reviews [505-507,510-513] and monographs [10,201,202,206,508]. In this respect, only principal aspects of the direct synthesis and the most recent achievements of its application for obtaining various types of coordination and organometallic compounds will be discussed in this section. 

The solid-phase reactions starting from metal powders in conditions of friction (Examples 8 and 9) are described in two recent monographs [201,202] (see the scheme of the mechanochemical reactor in Ref. 202). In this respect, we note the possibility of a solid-state synthesis with the use of metal salts. In particular, mechanochemical syntheses are widely used for obtaining acetylacetonates [698-70Id] by the method of ligand exchange, for example (3.277) [701a] ... 

In general, carbenoid reactions in which an organic molecule decomposes thermally or photochemically without the use of metal salts or organometallic reagents are thought to involve free carbenes base-induced reactions more often involve carbenoids. However, both halves of this generalization have their exceptions. 

Todorovic et al. [21] gave the synthesis of a library of 3-aryl-pyrimido [5,4-e] [l,2,4]-triazine-5,7-(lH,6H)-dione (v) following microwave approach. The use of microwave irradiation allowed the rapid reaction times and good yields of products. It also avoids the use of metal salts. 

The understanding of direct-initation mechanisms. In this context, tire use of metal salts of strong acids has opened a new area of fundamental studies. Indeed, we believe that the chemical insertion of the olefin between the metal cation and the anion following its adsorption on the salt surface closely resembles recent mechanistic proposals put forward by Zambelli and collaborators to rationalise initiation in stereospecific polymerisation (propene with vanadium-based catalysts). We are inclined to conclude that the cationic nature of stereospecific polymerisations of the Ziegler-Natta type is supported by our findings , viz. electrophilic attack by... 

In addition to the catalyst and base (if required), the use of metal-salt additives is very conunon for enhancing cross coupling and other reactions. Cul is the most common additive and in many cases it may operate as an intermediate transmetallating agent RM RCu —> RPdR. In other cases, it has been said to remove excess phosphine, thus increasing the reactivity of the palladium. Ag20 is sometimes used and may act by transmetallation or as a halide trap. 

The work of Myers et al. [6] illustrates the synthetic potential of the use of metal salts (instead of HMPA ) in alkylation reactions of enolates, employing easily accessible amide, enolates of the chiral auxiliary pseudoephed-rine. It is not surprising that the mechanism of chiral induction is not yet fully understood further investigations are necessary. Nonetheless, unanswered questions in enolate chemistry remain even for tailor-made, well-established auxiliaries, whose asymmetric induction can be explained convincingly by working models on monomer enolate structures, considering chelation control and steric factors. 

Oxidations in Bronsted Acid Media Oxidation by Lewis Acids Oxidation by Halogens Use of Metal Salts. ... 

Utilizing an inorganic salt in this manner requires obtaining a stable solution of the alkoxide and the salt. Metal salts are less expansive than alkoxide, so the use of metal salts compensates for a disadvantage of the sol-gel method. 

The use of metal salts such as copper sulfate increase the sensitivity of the reaction (see below). 

Recently, considerable attention has been focused on the use of metal salts, such as lanthanide or scandium triflates, as water-tolerant, recyclable Lewis-acid catalysts for C-C bond formation [6, 7]. When reactions are conducted in water, several limitations have to be overcome. Even if these salts are described as compatible with water, they can undergo slow hydrolysis. Water can solvate the metal center and may compete with the reactants. It modifies its acidity and infiuences the catalytic performances. Moreover, the solubility problem of organic substrates in water has to be overcome. Most commonly, reaction products are extracted from water with organic solvents, since the Lewis acid remains in the aqueous phase and can be re-used. 

Faraday does not comment on the fact that when acid and alkali are formed as primary products in the electrolysis of a solution of a salt (e.g. sulphate of soda), at the same time hydrogen and oxygen are evolved as primary products from the water, so that the same current seems to be doing double work on the basis of his law. He made no quantitative experiments in this field (see Daniell, p. 128). Faraday s view precluded the use of metal salt solutions in determining, e.g., the equivalent of copper by electrolysing copper sulphate... 

Initially, the chentical compoimds termed precursors, which contained the catimis M from which an oxide gel was made, were essentially metallic salts. The sodium metasUicate Na2Si03, initially used by Kistler [1], was cheap. Hence, an industrial process based on this precursor was developed for some time by BASF [19]. Simple metallic salts also remained interesting when a more elaborate precursor was not easily available. More recently, the use of metallic salts as sol-gel precursors has seen a renewed interest when hydrolyzed in solution in an organic solvent, in which a slow proton scavenger such as an epoxide was added [3] (Chap. 8). Nice aerogel monoliths were obtained in this way with Cr, Fe, Al, Zr, and other cations. 

Polymerizable compound route (PCR) based on the use of metal salts such as precursors, citric acid, and ethylene glycol as a chelating agent such as polyesterificatiOTi... 

With the exception of direct insertion into CO and isocyanides [51], carbon-carbon bond formation from organozirconocenes requires the use of metal salts for transmetalation or (chloride) ligand abstraction. The former protocol has been successfully applied for many carbonyl additions and crosscouplings, whereas the latter strategy is particularly useful for conversions with electrophiles such as epoxides and aldehydes. 

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