Eutectic melting reaction

Lithium Chloride. Lithium chloride [7447- 1-8], LiCl, is produced from the reaction of Hthium carbonate or hydroxide with hydrochloric acid. The salt melts at 608°C and bods at 1382°C. The 41-mol % LiCl—59-mol % KCl eutectic (melting point, 352°C) is employed as the electrolyte in the molten salt electrolysis production of Hthium metal. It is also used, often with other alkaH haHdes, in brazing flux eutectics and other molten salt appHcations such as electrolytes for high temperature Hthium batteries. 

Lithium hydride is perhaps the most usehil of the other metal hydrides. The principal limitation is poor solubiUty, which essentially limits reaction media to such solvents as dioxane and dibutyl ether. Sodium hydride, which is too insoluble to function efficiently in solvents, is an effective reducing agent for the production of silane when dissolved in a LiCl—KCl eutectic at 348°C (63—65). Magnesium hydride has also been shown to be effective in the reduction of chloro- and fluorosilanes in solvent systems (66) and eutectic melts (67). 

Electrolytic aluminum production is the most important process in both volume and significance. World production is about 15 megatons per year, consuming about 240 billion kilowatthours of electrical energy. Aluminum oxide (alumina), AI2O3, is subjected to electrolysis at a temperature of 950°C to this end it is dissolved in molten cryolite NujAlFg, with which it forms a eutectic melting at about 940°C. Carbon anodes that are anodically oxidized to CO2 in the process are employed. The overall electrolysis reaction can be written as... 

MW irradiation conditions [80]. More recently, however, Varma and Kocevar s group have shown that a solvent-free and catalyst-free reaction of hydrazines with carbonyl compounds is possible upon MW irradiation (Scheme 6.24) [81]. Interestingly, the general reaction proceeds smoothly even for solid reactants and is completed below the melting points of the two reactants possibly via the formation of a eutectic. The reactions have been conducted in household MW oven and the control experiments are conducted concurrently in separate open beakers the reactions can be essentially followed by visual observation when a melt is obtained [82],... 

The racemization of Diels-Alder adducts in the solid state appears to proceed via diradical or complete cycloreversion. For example, (-l-)-96 racemizes in the solid state from 130 to 155 °C (AH =40.0 kcal mol AS =14 cal mol K ) to give (-)-96 (Scheme 9), whereas the melt reaction (eutectic temperature is 165 °C) from 176 to 194 °C has much lower activation parameters (AfJ =... 

Uozumi, lizuka, and coauthors have published several studies on the electrochemical behavior of Pu at liquid cadmium cathodes in LiCl—KCl eutectic melts [128-130]. In one account [130] the authors studied the reduction of Pu " " to Pu° at the LiCl— KCl melt and liquid Cd interface and compared the results to those obtained at a solid Mo cathode surface. The electrode reaction at liquid Cd was found to be close to fully reversible with rapid. 

In some cases a liquid phase can be formed from two solid substrates by eutectic melting, when the reaction temperature lies below the melting points of the pure substrates, but above their eutectic temperature [6, 7, 37]. A small liquid phase may also be formed from two solid substrates because of traces of associated water... 

Eutectic melting (and also similar systems with added adjuvants/solvents) has been used to prepare homogeneous substrate mixtures with extremely high concentration levels as media for enzymatic reactions [37, 68, 69]. 

Up to now the so-called catalytic process is the only way to produce c-BN on an industrial scale. However, catalytic is not the correct scientific term, because the activation energy for transformation is not decreased by these substances. The substances which are used have the function of a solvent, and are responsible for the formation of c-BN. This method is successful because of the different solubilities of c-BN and h-BN in the flux. The precursor substances form a eutectic melt with the h-BN [152]. If the reaction conditions are in the domain of stable c-BN, spontaneous crystallization takes place and the c-BN growth rate is relatively high. 

C, appreciable yields of products were not produced until 750°C. Reaction of ethylene with pure CuF2 or CuF2 dissolved in a eutectic melt of alkali and alkaline earth fluorides between 450°C and 700°C yielded vinyl fluoride and HF and Cu metal. A similar reaction with propylene at 400°C yielded 2-fluoropropene [19]. The reaction cycle is shown in equations (7a) and (7b) and the net reaction scheme is shown in equation (7c). 

A second interpretation is that the liquid phase previously formed between dolomite and soda ash was required for the reaction endotherm peak at 706°C, implying a fusion reaction rather than eutectic melting amongst solids. This is refuted by evidence discussed subsequently where the disappearance of this endotherm with decreasing particle size (increasing volume of liquid phase) implies that interparticle contact was required for this reaction. 

The endotherm that peaked at 706°C was correlated to eutectic melting between CaCOj, Na2C03, and MgO. It could also be interpreted as a fusion reaction involving these phases and pre-existing liquid phase. This endotherm appears in the 90-125 /xm and 63-90 /xm particle size mixtures as well, albeit more diffusely, but does not appear in DTA traces for the two finest particle size mixtures. It is interpreted that for the 45-63 /xm particle size and smaller, an adequate quantity of liquid phase was formed (associated with the peak at 651°C) to have prevented the solid particle contact necessary for CaCC>3-Na2C03-Mg0 eutectic melting. This further implies that preexisting liquid phase was not a participant in this reaction. 

The results of the test showed that the uranium dioxide produced a vigorous reaction with the nitrate melt, beginning at approximately 400°C. At this time the melt was open to the atmosphere, and no nitric acid was being added. Nitrogen dioxide was evolved as a gaseous product of the reaction, but there was no visual indication of any uranium solubility in the molten nitrate eutectic. Complete reaction, indicated by the cessation of gas evolution, required approximately 2.5 hours at 500°C. 

The kinetics of the oxidation of Br by BrOj, in the eutectic melt NaN03-KN03, have been studied in the presence of Ba2+ and C02.153 The reaction order with respect to C02, Ba2+, and Br- is 0.6, 0.6, and 1.0, respectively. Pergola154 has shown that the voltammetric reduction of per-bromate at Pt is described by the equation ... 

In the presence of 02, I- is oxidized in such melts to I2 and Li5I06.159 However, IOiT reacts with I- in the presence of C02 to form I2 and C03 - A similar reaction was found to occur in a eutectic melt of NaN03 and KN03 at 340 °C.160 The reaction proceeds according to ... 

Molten Na[AlCl4] catalyses the reaction at 600 C, in a three-phase system with gaseous COCl and solid y-AIjOj, to give very high purity aluminium(III) chloride [962], and this reaction (in the presence of carbon) has formed the basis of a patent for the industrial scale production of aluminium(III) chloride [909]. The chlorination of AljOj by phosgene has been studied in a LiCl-KCl eutectic melt at 470 C as a function of pO it is essentially a two-step process [1842] ... 

The oxidative protocol simply involves grinding of the two solid substrates using a pestle and mortar a mildly exothermic reaction results in the formation of a yellowish eutectic melt and the reaction gets completed in a few minutes. The work has now been extended to the synthesis of p-ketosulfones from ketones employing another hypervalent iodine reagent. 

The only example of a reaction between two solids, under solvent-free and catalyst-free environment, was demonstrated by Varma et al. when the reaction of neat 5- or 8-oxobenzopyran-2(177)-ones with a variety of aromatic and heteroaromatic hydrazines provided rapid access to several synthetically useful heterocyclic hydrazones (Scheme 5) via the formation of a eutectic melt below the melting point of either of the reactants. ... 

The reaction exhibited a marked temperature dependence. The highest level of methane conversion occurred at a temperature of approximately 345°C. This temperature is slightly below the eutectic melting point of the supported catalyst. If the catalyst temperature is allowed to exceed about 350°C, a decrease in conversion is observed, probably owing to loss of active surface... 

The direction of reaction (2.4.37) is confirmed by the results obtained by Laitinen and Bhatia [230], who found that the solubility of NiO in the KCl-LiCl eutectic melts was considerably lower than that of PtO. Of course, such a sequence of solubilities remains unchanged in other melts. 

G. Picard, F. Seon and B. Tremillon, Reactions of Formation and Stability of Iron(II) and (III) Oxides in LiCl-KCl Eutectic Melt at 470 °C, Electrochim. Acta 22 (1978) 1291-1300. 

Solutions of dicyclohexyl-18 crown 6 in DMSO have been used to prepare pale yellow 0.15 mol P solutions of KO2 which contain the O2 anion in approximately the same concentration. The specificity of the superoxide dismutase enzyme was used to show that the solution did indeed contain the superoxide ion in solution. I hc redox potentials of the superoxide and hydroperoxy free radicals, O2 and HO2, have been measured by the fast reaction technique of pulse radiolysis and kinetic absorption spectrophotometry. A d.t.a. study has shown that, during the heating of LiC104-K02 mixtures containing <30% KO2, a eutectic melt occurred at 100—250 C with the loss of superoxide oxygen. At 250—300 °C the mixture melted with loss of peroxide oxygen and at 360— 500 °C the perchlorate decomposed with the loss of all the perchlorate oxygen. 

---