Mercuric iodide, reaction

The most common colorimetric technique involves a reaction between ammonia and a reagent containing mercuric iodide in potassium iodide (Messier reagent) to form a reddish-brown complex. Turbidity, color, and hardness are possible interferences that can be removed by preliminary distiHation at pH 9.5. 

Iodine acetate would seem to be unambiguously present in the iodination of pentamethylbenzene in acetic acid by iodine and mercuric acetate, since the latter components form an equilibrium mixture of iodine acetate and acetoxy-mercuric iodide and mercuric acetate speeds up the iodination332. Second-order rate coefficients of 0.078 (25 °C) and 0.299 (45 °C) were obtained, and these values are intermediate between those obtained for the reaction of bromine acetate with benzene (2.5 xlO-3) and toluene (1.2) at 25 °C, indicating that bromine acetate is the stronger electrophile. 

The reactions of mercuric iodide, mercuric bromide, and mercuric chloride with the excited species produced in the hexafluoroethane plasma were examined first, as the expected products were known to be stable and had been well characterized 13). Thus, these reactions constituted a "calibration of the system. Bis(trifluoromethyl)mercury was obtained from the reaction of all of the mercuric halides, but the highest yield (95%, based on the amount of metal halide consumed) was obtained with mercuric iodide. The mole ratios of bis(trifluoro-methyDmercury to (trifluoromethyl)mercuric halides formed by the respective halides is presented in Table I, along with the weight in grams of the trifluoromethyl mercurials recovered from a typical, five-hour run. 

In our laboratory, we find that the plasma reaction of trifiuoro-methyl radicals with mercuric iodide is an excellent source of bis(tri-fluoromethyDmercury. For those laboratories that lack access to radiofrequency (rf) equipment (a 100-W, rf source can at present be purchased for less than 1,000), synthesis of bis(trifluoromethyl)mercury by the thermal decarboxylation of (CFgCOjlzHg is also a functional, and quite convenient, source of bis(trifiuoromethyl)mercury (23). 

Sulfoxides are known to form both 0-alkyl and S-alkyl derivatives. The latter are obtained when so-called soft alkylating agents are employed. This behavior of sulfoxides was utilized (172) in the stereospecific synthesis of chiral 135. The reaction of the optically active (+)-ethyl phenyl sulfoxide 136 with methyl iodide in the presence of mercuric iodide followed by anion exchange was found to give the optically active salt 135. 

The reaction with mercury gave as the initial product trifluoromethyl mercuric iodide, CFsHgl, a white crystalline solid very similar to methyl mercuric iodide. From it, the free base, CFjHgOH, and a number of salts were prepared. 

Prepared by reaction (I) of iodine and mercuric oxide (see also Mercury) suspension in water, mercuric iodide being simultaneously formed. (2) of sodium hypoiodite and an acid, excess acid yielding iodine. 

Abraham and Spalding16 have shown that tetraethyltin reacts with mercuric iodide in solvent 96 % methanol -4 % water by the rate-determining bimolecular reaction (8), followed by the rapid, reversible reaction (9), viz. 

In equations (10) and (11), the initial concentrations of tetraethyltin and mercuric iodide are denoted by A and B respectively, the concentration of ethylmercuric iodide at time t is denoted by X, and the concentration of Et3Sn+ (and also of Hgl3 ) at any time t is denoted by Y. The equilibrium constant for reaction (9) is K, and k2 is the second-order rate coefficient for the electrophilic substitution (8). Equations (10) and (11) can be solved by the method of numerical analysis17 and values of k2 were thus obtained (values of K were determined16 by direct experiments). It was shown that k2 remained constant over a ten-fold range of initial concentration of tetraethyltin and of mercuric iodide. Values of the second-order rate coefficient and of the associated activation parameters are given in Table 5. Reaction (8) is thus characterised by a very negative activation entropy... 

In subsequent work, the substitution of a number of tetraalkyltins by mercuric iodide was investigated18. All of the substitutions proceeded by the rate-determining bimolecular reaction... 

Support for this conclusion was provided by Abraham and Spalding19, who estimated the expected activity coefficients for a transition state such as (IX). These coefficients are also plotted in Fig. 2, and clearly do not agree at all with the observed transition state activity coefficients. It was thus concluded that the substitution of tetraalkyltins by mercuric iodide in solvent 96 % methanol-4 % water proceeds by a rate-determining step, reaction (12), which follows mechanism SE2(open) through a transition state of type (VIII). 

It is possible that such a set of reactions was in force for the related cleavages of allyl-silicon and allyl-germanium compounds studied by Roberts2-3 with mercuric iodide as the electrophile. 

The reaction of mercuric iodide with the chelating diphosphine bis(diphenyl-phosphinoethyl)sulphide gives the complex [(Ph2PC2H4)2S]HgI2.184 Structural analysis shows the mercury to be in a distorted tetrahedral co-ordination, with formation of an eight-membered puckered chelate ring. 

Fia. 5. Reaction rates in concentrated perchloric acid as a function of Ha. The circles are the experimentally obtained rate data. The dashed lines represent unit correlations with the hydronium ion concentration, while the solid lines represent unit correlations with Ho. (a) Methylmercuric iodide cleavage at 100° (Kreevoy, 1957). (b) Cyclopropyl-mercuric iodide cleavage at 25° (Kreevoy and Thoreen, unpublished results), (c) Vinyl-mercuric iodide cleavage at 25° (Kreevoy and Kretchmer, 1964). 

Even on a liquid surface, reactions may be catalysed at the boundary of a crystal touching the surface, e.g. the combination of iodine with mercury proceeds very fast at the region where a crystal of mercuric iodide touches the surface,1 and slowly elsewhere, although the iodine may be covering nearly all the mercury surface. 

AMMONIA CONTENT. The concentration of ammonia nitrogen in the water-extractable components of the fabric was determined colorimetrically by Nesslers reaction (23). Under alkaline conditions, Nesslers reagent (mercuric iodide-potassium iodide solution) reacts with ammonia that has been released from ammonium salts by the alkali present to produce a yellow compound by the following reaction ... 

These reactions proceed so regularly that they may be followed up quantitatively. Ferric salts have no catalytic influence upon these reactions.1 Iron salts, however, can act as oxygen-carriers in the absence of such powerful oxidisers as hydrogen peroxide and potassium permanganate. Thus, for example, it is well known that, upon exposure to sunlight, iodine is ordinarily liberated from a solution of mercuric iodide in potassium iodide. Curiously enough, if traces of iron salts are rigidly excluded, the liberation of iodine does not take place.2... 

One further reaction of this type studied by Kreevoy and his group [50] is the acid catalysed cleavage of unsaturated compounds containing a carbon—mercury bond, for example, allyl mercuric iodide (29). The important conclusion is that rate-determining proton transfer to unsaturated carbon occurs as a first step (A—SE2 mechanism) and as expected the reactions are catalysed by general acids. 

The mechanisms of two other reactions described in Sect. 2.2 involve slow proton transfer to unsaturated carbon. The general acid catalysed cleavage of vinyl mercuric halides [42, 50] for example, allyl mercuric iodide, CH2=CHCH2HgI (XXII), gives Bronsted exponents around 0.7. Linear Bronsted plots are obtained with carboxylic acid catalysts but, as observed in other A—SE 2 reactions, general acids of different structural types (for example, hydronium ion or bisulphate ion) show substantial deviations. Bronsted catalysis of the hydrolysis of diazo compounds (N2 =CR X) has been studied by the groups of Albery and Kreevoy. With... 

Seyferth concludes that phenyl(lrifluoromethyl)mercury is an excellent precursor for difluorocarbene. In the general procedure, 1 molar eq. of CeHjHgCFj, 2.5-3.0 molar eq. of well-dried sodium iodide, and 3.0 molar eq. of the dried olefin are used (N2). Benzene is distilled into the reaction flask directly from sodium benzophenone ketyl. The reaction mixture is stirred and heated at reflux under Nj for 12 18 hr. Filtration removes phenyl mercuric iodide and Nal and Nab" the gem-difluorocyclo-propanes are isolated by distillation or by gas chromatography, usually in good yield. 

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