Amalgams, activities

In many cases the formation of amalgams, active metals, hydrogen peroxide, halogens, or hydroxyl radicals has been postulated as the electrochemical step which then is followed by a purely chemical reaction. One of the usual arguments for these intermediates is that the reaction follows a route which may be duplicated by the chemical reagent, but this does not prove the presence of these intermediates in the electrolytic reaction. 

Mercury layers plated onto the surface of analytical electrodes serve as Hquid metal coatings. These function as analytical sensors (qv) because sodium and other metals can be electroplated into the amalgam, then deplated and measured (see Electro analytical techniques). This is one of the few ways that sodium, potassium, calcium, and other active metals can be electroplated from aqueous solution. In one modification of this technique, a Hquid sample can be purified of trace metals by extended electrolysis in the presence of a mercury coating (35). 

Cesium forms simple alkyl and aryl compounds that are similar to those of the other alkah metals (6). They are colorless, sohd, amorphous, nonvolatile, and insoluble, except by decomposition, in most solvents except diethylzinc. As a result of exceptional reactivity, cesium aryls should be effective in alkylations wherever other alkaline alkyls or Grignard reagents have failed (see Grignard reactions). Cesium reacts with hydrocarbons in which the activity of a C—H link is increased by attachment to the carbon atom of doubly linked or aromatic radicals. A brown, sohd addition product is formed when cesium reacts with ethylene, and a very reactive dark red powder, triphenylmethylcesium [76-83-5] (C H )2CCs, is formed by the reaction of cesium amalgam and a solution of triphenylmethyl chloride in anhydrous ether. 

The exchange of aromatic protons can be effected in the absence of any -OH or —NH2 activating group during the course of a Clemmensen reduction in deuteriochloric and deuterioacetic acid mixture (see section Ill-D). This reaction has been carried out with various tricyclic diterpenes and is best illustrated by the conversion of dehydroabietic acid into its 12,14-d2-labeled analog (40 -+ 41).Amalgamated zinc is reportedly necessary for the exchange reaction since the results are less satisfactory when a zinc chloride-mercuric chloride mixture is used. 

Reductive cleavages of carbon-chlorine bonds by active metals and with photochemical activation figure in recent studies aimed at HFCs and HCFCs Sodium amalgam [3J] (equation 25), zinc powder [34] (equation 26), and alumi-mun/tin chloride [35] (equation 26) are all used in conjunction with protic solvents in reactions giving high yields and conversions... 

Dose-response curves quantify drag activity. The maximal asymptote is totally dependent on efficacy, while potency is due to an amalgam of affinity and efficacy. 

The extended ternary complex model [23] was conceived after it was clear that receptors could spontaneously activate G-proteins in the absence of agonist. It is an amalgam of the ternary complex model [12] and two-state theory that allows proteins to spontaneously exist in two conformations, each having different properties with respect to other proteins and to ligands. Thus, two receptor species are described [Ra] (active state receptor able to activate G-proteins) and [RJ (inactive state receptors). These coexist according to an allosteric constant (L = [Ra]/[Ri]) ... 

The loss of active zinc and the evolution of hydrogen, causing an intolerable rise of internal pressure, were retarded by amalgamation of zinc particles. For quite long time (up to about 1982) mercury contents of 6% (in some cases up to 8%) were regarded as normal [21]. Then a rapid decrease in the mercury content took place (Fig. 1). 

For a couple of years 0.25% Hg became the technical standard. It has to be pointed out that the mercury content of the metallic zinc has to be divided by a factor of roughly 10 to give the mercury content based on the total cell weight of an AA (LR-6) cell. These values are sometimes indicated on the cell labels. With decreasing amalgamation, other corrosion inhibitors had to take over the role of mercury. There are numerous papers and patents claiming corrosion-inhibiting activities of elements like A1, In, T1, Cd, Ga, Na, ... 

The diastereomeric lactones could be separated by chromatography and converted into optically active lactones by desulfurization with sodium amalgam or by pyrolysis to the corresponding butenolides. 

---