Zinc: amalgamated activation

Mossy zinc is activated by converting to zinc amalgam by brief immersion in amalgam solution. (Use 40 g mossy zinc immersed in 4 g mercuric chloride, 4 ml concentrated HCl acid, and 40 ml of water.) This type of amalgam can be used with powdered zinc also. 

Another Zinc Reduction. Prepare or activate the zinc as follows 400 g of mossy zinc is treated with 800 ml of 5% aqueous solution of mercuric chloride for 1 hour. Decant the solution off and use the zinc right away. Add. 834 mole of compound to be reduced to the zinc amalgam, followed by as much HCl acid (.834 mole) diluted in as much water as is required to cover all the zinc. Reflux for 6 hours while adding small portions of dilute HCL acid. Cool, separate the upper, wash free of acid (a few portions of dilute sodium hydroxide), dry and distill to get about a 79% yield of product. 

An example of this type is a cell in which two zinc amalgams, differing in concentration (al > a.,), are dipped into a zinc salt solution with the zinc ions activity hZii,... 

The easiest way to introduce a nitrogen substituent into an arene is by nitration. Yet many desired substituted benzenes have amino functions. Moreover, the nitro group is a meta director, poorly suited for preparing ortho, para-substituted systems. A solution to these problems is provided by the availability of simple reagents that reversibly convert -NO2, a meta director, into -NH2, an ortho, para director. Thus, the nitro group can be reduced to the amino function by either catalytic hydrogenation or exposure to acid in the presence of active metals such as iron or zinc amalgam. The reverse, oxidation of aniline to nitrobenzene, employs trifluoroperacetic acid. 

The simplest way to illustrate the influence of the availability of suitable sites on the electrode on an electrode reaction is to add to the solution a known amount of material which adsorbs to a known extent and study the reaction with and without the presence of this known surface active substance. The inhibiting effect of the adsorbed film is shown in Fig. 38. This curve shows the effect of adsorption of cyclohexanol on the reduction of zinc at a zinc amalgam electrode. One clearly sees that when 6 reaches 0 = 0 5, the inhibiting effect of the cyclohexanol is total, i.e. no current is observed. On the other hand, adsorbed species can provide a way for an alternative path for the mechanism of the reaction studied and may, as a result, act as a catalyst rather than as an Inhibitor. The catalytic effect of diphenylamine on the reduction of water is shown in Fig. 39 hydrogen is... 

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... 

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, ... 

Assuming the concentrations of zinc in the amalgam to be very small and the solution fairly ideal, the activity terms in the above equation can be replaced by concentration terms, and the final relationship can be expressed as ... 

The zinc will be inclined to depart spontaneously from the high-activity amalgam to that with a corresponding low activity. For example, if c1 is greater than c2, E is positive and the reaction advances in the direction specified. It may be added that metals in mercury constitute fairly ideal solutions, and that the emfs are almost correctly calculated by using concentrations instead of activities. 

The formation of dimers by reduction of a,p-unsaturated ketones in aqueous media is well documented in the early literature of electrochemistry. Reductants include sodium or aluminium amalgams [58], dissolving zinc and a lead cathode in both acid and alkaline conditions [59,60]. Mixtures of dimers and dihydro derivatives were isolated. As the concept of the hydrodimerization of activated alkenes... 

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