Mercuric process

The ratio of the two products is primarily affected by the nature of the mercury(II) salt and also by the reaction conditions. Since the formation of these compounds could result from either a kinetically or a thermodynamically controlled mercuration process, a study of the mercuration of 3 in the presence of aromatic amines using various mer-cury(II) salts has been more recently carried out in order to determine the conditions under which aminomercuration is reversible, and the results have been compared to those of the oxymercuration170. 

Many catalytic systems have been described acidic solutions of mercuric salts are the most generally used. This process has long been superseded by more economical routes involving oxidation of ethylene or other hydrocarbons. 

Protonic initiation is also the end result of a large number of other initiating systems. Strong acids are generated in situ by a variety of different chemistries (6). These include initiation by carbenium ions, eg, trityl or diazonium salts (151) by an electric current in the presence of a quartenary ammonium salt (152) by halonium, triaryl sulfonium, and triaryl selenonium salts with uv irradiation (153—155) by mercuric perchlorate, nitrosyl hexafluorophosphate, or nitryl hexafluorophosphate (156) and by interaction of free radicals with certain metal salts (157). Reports of "new" initiating systems are often the result of such secondary reactions. Other reports suggest standard polymerization processes with perhaps novel anions. These latter include (Tf)4Al (158) heteropoly acids, eg, tungstophosphate anion (159,160) transition-metal-based systems, eg, Pt (161) or rare earths (162) and numerous systems based on tri flic acid (158,163—166). Coordination polymerization of THF may be in a different class (167). 

Halogenation and dehalogenation are catalyzed by substances that exist in more than one valence state and are able to donate and accept halogens freely. Silver and copper hahdes are used for gas-phase reactions, and ferric chloride commonly for hquid phase. Hydrochlorination (the absoration of HCl) is promoted by BiCb or SbCl3 and hydrofluorination by sodium fluoride or chromia catalysts that form fluorides under reaction conditions. Mercuric chloride promotes addition of HCl to acetylene to make vinyl chloride. Oxychlori-nation in the Stauffer process for vinyl chloride from ethylene is catalyzed by CuCL with some KCl to retard its vaporization. 

Hydrochloric acid may conveniently be prepared by combustion of hydrogen with chlorine. In a typical process dry hydrogen chloride is passed into a vapour blender to be mixed with an equimolar proportion of dry acetylene. The presence of chlorine may cause an explosion and thus a device is used to detect any sudden rise in temperature. In such circumstances the hydrogen chloride is automatically diverted to the atmosphere. The mixture of gases is then led to a multi-tubular reactor, each tube of which is packed with a mercuric chloride catalyst on an activated carbon support. The reaction is initiated by heat but once it has started cooling has to be applied to control the highly exothermic reaction at about 90-100°C. In addition to the main reaction the side reactions shown in Figure 12.6 may occur. 

The best characterized of these reactions involve the mercuric ion, Hg ", as the cation. The same process occurs for other transition-metal cations, especially Pd, but the products often go on to react fiirther. Synthetically important reactions involving Pd will be discussed in Section 8.2 of Part B. The mercuration products are stable, and this allows a relatively uncomplicated study of the addition reaction itself The usual nucleophile is the solvent, either water or an alcohol. The tenn oxymercuration is used to refer to reactions in... 

Diphenylthioalkanes react with mercuric fluoride to give 1-fluoro-l-phenylthio-alkanes. Provide a detailed description of a likely mechanism for this reaction. Consider such questions as (1) Is an SnI or an Sn2 process most likely to be involved (2) Would NaF cause the same reaction to occur (3) Why is only one of the phenylthio groups replaced ... 

Cmchonine, C19H22ON2. This alkaloid is usually present in cinchona and cuprea barks. One of the best sources is Cinchona micrantha bark. It occurs in the crude quinine sulphate mother liquors. The mixed alkaloids recovered from these may be extracted with ether to remove quinidine and cinchonidine and the insoluble residue boiled with successive small quantities of alcohol, from which cinchonine crystallises on cooling. The crude alkaloid is neutralised with dilute sulphuric acid and the sulphate recrystallised from boiling water. Cinchonine so prepared contains quinidine, from which it may be freed by crystallisation from boiling alcohol until it ceases to exhibit fluorescence in dilute sulphuric acid. It will then still contain 10 to 15 per cent, of dihydrocinchonine, which may be removed by reprecipitation as the cuprichloride, B. 2HC1. CuClj, or by the simpler mercuric acetate process of Thron and Dirscherl. ... 

Cinchotine (Hydrocinohonine, more correctly dihydrocinchonine, Cinchonifine, >fs-Cinchonine), C19H24ON2. This alkaloid occurs in commercial cinchonine to the extent of about 14 per cent. and may be prepared from this source by the mercuric acetate process, or more conveniently by the hydrogenation of commercial cinchonine previously freed from quinidine. ... 

Hydroquinine (Dihydroquinine), C20H26O2N2.2H2O. This base was isolated by Hesse from the mother liquors of quinine sulphate manufacture and is present to the extent of 5 to 6 per cent, in commercial sulphate of quinine, from which it is best isolated by the mercuric acetate process. The demand for hydroquinine as such and as a material for the preparation of hydrocupreine has led to its manufacture from quinine by catalytic hydrogenation. It crystallises from ether or benzene in needles, m.p. 173 5° (dry), — 235 7° (c = M/40, N/10 H2SO4) or... 

Swain and Eddy have queried the wide applicability of the S l and Sif2 mechanisms and favored a push-pull termolecular process for the reaction of pyridine with methyl bromide in benzene solution for example, they have suggested that the effects observed on the addition of methanol, phenol, p-nitrophenol, and mercuric bromide to the reaction mixture can be explained by an intermediate of type 168. ... 

However, in the case of stress-corrosion cracking of mild steel in some solutions, the potential band within which cracking occurs can be very narrow and an accurately known reference potential is required. A reference half cell of the calomel or mercury/mercurous sulphate type is therefore used with a liquid/liquid junction to separate the half-cell support electrolyte from the process fluid. The connections from the plant equipment and reference electrode are made to an impedance converter which ensures that only tiny currents flow in the circuit, thus causing the minimum polarisation of the reference electrode. The signal is then amplifled and displayed on a digital voltmeter or recorder. 

Vanadium pentoxide and mercuric oxide were used as catalysts for the hydrogen peroxide oxidation of bis(phenylthio)methane to its monooxide 17a31 (equation 5). From the synthetic point of view, it is interesting to note that vanadium pentoxide, in addition to its catalytic action, functions also as an indicator in this reaction. In the presence of hydrogen peroxide, the reaction mixture is orange while in the absence of hydrogen peroxide a pale yellow colour is observed. Thus, it is possible to perform the oxidation process as a titration ensuring that an excess of oxidant is never present. 

The general term metallation describes that process in which reaction of an unsaturated system with a metal or an electrophilic metal salt results in formation of an unsaturated organometallic compound by formal replacement of a C—H bond by a C—metal bond, as for example in the mercuration of benzene (Scheme 3). The term oxymetallation is used to describe the... 

The reactants can be made from allylic alcohols by mercuric ion-catalyzed exchange with ethyl vinyl ether.220 The allyl vinyl ether need not be isolated and is often prepared under conditions that lead to its rearrangement. The simplest of all Claisen rearrangements, the conversion of allyl vinyl ether to 4-pentenal, typifies this process. 

Chemical precipitations which are not dependent on pH are used in various processes. Sometimes the reagent is reasonably set for a certain metal and this is the situation in the precipitation of silver as silver chloride. The only other insoluble common metal chlorides of significance are lead chloride, cuprous chloride, and mercurous chloride. This implies that precipitation of cuprous and mercurous chlorides generally may be avoided by ensuring that the metals occur in their higher oxidation states, cupric and mercuric states. The separation of silver in its chloride form is rarely employed for bulk precipitation, but is quite useful for removing relatively small amounts of the metal when it occurs in minor amounts. 

One such process was developed by the Outokumpu Company in Finland and used in the company s zinc smelter at Kokkola. The gases are scrubbed with concentrated sulfuric acid, whereby mercury is dissolved as mercuric sulfate. After several recycling operations, the mercury concentration reaches saturation level such that crystals of mercuric sulfate form and can be removed. 

In the Odda process, used by Det Norske Zinkkompani in Norway in collaboration with Boliden Kemi, the gases are subjected to scrubbing with a mercuric chloride solution which reacts with mercury, yielding insoluble mercurous chloride this can be separated by filtering. 

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