Mercuric bromide, reaction

Unsaturation value can be determined by the reaction of the akyl or propenyl end group with mercuric acetate ia a methanolic solution to give acetoxymercuric methoxy compounds and acetic acid (ASTM D4671-87). The amount of acetic acid released ia this equimolar reaction is determined by titration with standard alcohoHc potassium hydroxide. Sodium bromide is normally added to convert the iasoluble mercuric oxide (a titration iaterference) to mercuric bromide. The value is usually expressed as meg KOH/g polyol which can be converted to OH No. units usiag multiplication by 56.1 or to percentage of vinyl usiag multiplication by 2.7. 

Tin tetrachloride has been used to prepare the stericaHy hindered triisopropylchlorosilane [13154-24-0] (119). Organobromosdanes are obtained under similar conditions through reaction with cupric and mercuric bromide. These reactions are most suitable for stepwise displacement of hydrogen to form mixed hydridochlorosilanes or in systems sensitive to halogen (120). Hydrides have also been displaced using organic bromides. Heating triethylsilane and... 

It has been reported recently that 17/ -acetoxy-5a,14a-androstan epimerizes at C-14 when photolyzed in cyclohexane solution in the presence of mercuric bromide. When the reaction is carried out in perdeuterated cyclohexane, the product consists of 55 % d - and 12% d2-labeled species. This reaction may develop into an interesting deuteration technique if the incorporated deuterium can be securely assigned to the epimerized position. 

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. ... 

Subsequent kinetic work has amply confirmed the mechanistic picture described above. For example, the reaction of diphenylmercury with Ph(COOEt).CH.HgBr gives an almost instantaneous reaction with precipitation of phenylmercuric bromide, whereas reaction of the soluble product with a second molar equivalent of mercuric bromide gave a very slow (ca. 2 weeks) precipitation of phenylmercuric bromide722, i.e. reaction involves (287) and (288)... 

The fast reaction clearly involves the transition state (XLVIII) as confirmed by the observation of Reutov etal.123 that all of the label in the mercuric bromide... 

The reaction starts spontaneously and is mildly exothermic. Moderating the temperature by use of a water bath diminishes the amount of bromine and product carried off by the carbon dioxide evolved. The reaction can be followed by use of a tetra-chloroethane bubbler, and at the end of the reaction the solvent in the bubbler can be used to wash the mercuric bromide. The checkers followed the reaction with a wet test meter presaturated with carbon dioxide 52-60% of the theoretical amount of carbon dioxide was evolved. 

CIDNP has also been reported in reactions of organomercurials. Emission is observed from the couphng product of p-methylbenzyl-mercuric bromide and triphenylmethyl bromide (Beletskaya et al., 1971), while thermolysis of organomercury derivatives of tin such as t-C4H9HgSn(CH3)3 gave mixtures of isobutene and isobutane (by disproportionation of uncorrelated pairs of t-butyl radicals) showing A/E polarization (Mitchell, 1972). 

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. 

Apart from the fluoride, mercuric halides react explosively with potassium like all analogues of the other metals already mentioned. With mercurous salts, the reaction seems less violent since with mercurous chloride, molten potassium causes the mixture to incandesce without ever combusting. It is likely that other metals react too an extreme violent reaction was mentioned between indium and mercuric bromide. 

Although aliphatic alcohols are typically poor acceptors in the Mitsunobu-type glycosylation, Szarek and coworkers have highlighted one advance to this end [95]. For the triphenylphosphine and diethylazodicarboxylate promoted glycosylation of a monosaccharide acceptor, the addition of mercuric bromide is necessary to promote the reaction. For example, the (1,6)-disaccharide 44 was obtained in 80% yield using this modified Mitsunobu protocol. Unlike previous examples with phenol or N-acceptors, preactivation of the hemiacetal donor was performed for 10 min at room temperature prior to addition of the aliphatic alcohol nucleophile. 

A second method is based on the abnormal course of the Koenigs-Knorr reaction with fluoroalkyl alcohols. Indeed, when there are two or three methylenes between the Rf group and the hydroxyl, the reaction does not lead to substitution of the anomeric bromide but instead affords an orthoester. In the presence of mercuric bromide, this orthoester can undergo a rearrangement into an (9-fluoroalkyl glycoside (Figure 6.47). 

H. Rose obtained a product approximating to a hemitrihydrate by the action of phosphine on an aq. or alcoholic soln. of mercuric chloride. A. Partheil and A. van Haaren worked with an alcoholic soln. and said that the phosphine should be diluted with an inert gas. D. Vitali obtained a similar substance. The yellow product is decomposed by heat by boiling water cone, alkali-lye hydrogen sulphide and by dil. nitric acid. For analogous reactions with mercuric bromide and iodide, vide infra. 

Meanwhile, Reutov et al.4 had reported that reaction (1) followed first-order kinetics, first-order in alkylmercuric bromide and zero-order in mercuric bromide, when anhydrous dimethylsulphoxide (DMSO) was used as the solvent. This report was confirmed by Ingold and co-workers3 and hence is the first authentic record of a reaction following mechanism SE1. Over a six-fold variation in the initial concentration of a-carbethoxybenzylmercuric bromide and a three-fold variation in that of mercuric bromide, only the first-order rate coefficient with respect to the alkylmercuric bromide remained constant3. The rate coefficients reported by the two sets of workers are given in Table 1, together with the reported Arrhenius equations. 

The rate of reaction (7) (R = Me, X = Br) was increased on addition of lithium nitrate or on addition of water to the solvent, and mechanism SE2(open) was therefore indicated5. The rate coefficients for reaction (7) (R = Me) increased in the sequence X = Br < I-C OAc < N03, again suggesting mechanism SE2(open) rather than mechanism SE2(cyclic). In Table 2 are collected the various rate coefficients reported5,12 for the substitution of methylmercuric bromide by mercuric bromide in ethanol the Arrhenius parameters5 were A = 5x 107l.mole-1. sec-1 and Ea = 19.8 kcal.mole-1, which I have calculated correspond to AH1 = 19.2 kcal.mole-1 and AS = —25 cal.deg-1.mole-1 at 333 °K. 

Reaction (14), in the solvents listed in Table 5, no doubt proceeds by mechanism SE2 Reutov et al.17 write a transition state corresponding to mechanism SE2(cyclic) for the reaction in pyridine and point out that the electrophile is probably a pyridine complex of mercuric bromide rather than the unsolvated bromide itself. 

Reaction (15) is the longest-known of the mercury redistributions, but was studied kinetically only as recently as 1959 by Ingold et al.26. These workers showed that the substitution of di-sec.-butylmercury by mercuric bromide in solvent acetone was first-order in each reactant, and that the second-order rate coefficient remained constant over a range of initial concentrations of the reactants. Substitutions by other mercuric salts also followed the second-order rate equation, and the various rate coefficients obtained are collected in Table 6. The... 

Hence the observation that, for example, mercuric acetate reacts with a given substrate in a given solvent faster than does mercuric bromide can be interpreted in at least two ways (i) the mechanism of reaction is SE2(open) and mercuric acetate is a more powerful electrophile than is mercuric bromide, and (ft) the mechanism of reaction is SE2(cyclic) and mercuric acetate is better able to act as a bridging group in a six-centred transition state than is mercuric bromide in a four-centred transition state. The possibility that the two salts might be reacting by different mechanisms must also be considered. 

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