Silver carbonate decomposition

Preliminary experiments on the coupling of the chloride (lb) with digitoxigenin (3/ ,14,/ -dihydroxy-5/ -card-20(22)-enolide) in the presence of silver carbonate, led to gross decomposition of the halide, and it was suspected that, under the conditions of the experiments, the silver carbonate was causing elimination of hydrogen chloride. When, however, digitoxigenin was treated with an excess of lb in a small volume of... 

Two plausible mechanistic pathways have been proposed for the thermal decomposition of alkylsilver compounds either a radically-mediated cleavage of the carbon-silver bond or a process by which the breaking of the silver-carbon bond and formation of the carbon-carbon bond are concerted. Mechanistic studies by Whitesides and coworkers in which the product ratios obtained for the thermal process... 

Glycosides from the Dihalides.—By the decomposition of the dihalides with silver carbonate or oxide in methanol, followed by deacetylation of the product, the corresponding methyl 2-desoxy-2-halogeno-glycosides are formed. 

AH° for this reaction is 79.14 kj/mol in the temperature range of 25°C-125°C. Given that the partial pressure of carbon dioxide in equilibrium with pure solid silver carbonate is 6.23 X 10 3 torr at 25°C, calculate the partial pressure of C02 necessary to prevent decomposition of Ag2C03 at 110.°C. 

Phenylmercuric carbonate is prepared from the chloride in a similar manner to the nitrate using silver carbonate. It forms small, white needles, very slightly soluble in boiling water, easily soluble in boiling alcohol or benzene. When heated it melts with decomposition, and with strong acids gives carbon dioxide and the corresponding salts. 

McCowan [38] used electron microscopic and X-ray measurements to study the thermal decomposition of silver acetylide. Although detailed or-time relationships could not be established, the value of was estimated to be 170 kJ mol in the interval 388 to 408 K. The rate-limiting step was identified as the production of an electron and an acetylide radical that react fiirther to yield amorphous carbon. Decomposition is catalyzed by the product, probably metallic silver, and explosion was ascribed to the accumulation of catalyst rather than heat. 

The thermal decomposition kinetics of silver carbonate using the disk technique was reported by Wvdenen and Leban (59). Continuous, in siru quantitative analysis of infrared active reactants and products of the decomposition reactions was made possible by use of a heated cell. The cell was constructed of stainless steel and could be heated to 500 C with the KRS-5 cell windows maintained at room temperature by cooling water. A similar approach was used by Wendlandt (60). 

HAZARD RISK Stable under normal conditions explosive reactions with trialkylphos-phines and silver chlorite decomposition emits toxic fiimes of carbon dioxide, hydrogen iodide and iodine NFPA Code not available. 

EXPLOSION and FIRE CONCERNS NFPA rating (not available) reacts violently with oxygen at 300 C violent reaction with sodium reacts explosively with trialkylphosphines and silver chlorite decomposition emits toxic fumes of F use water spray, carbon dioxide, dry chemical powder, or appropriate foam for firefighting purposes. 

The bottom example in Fig. 4.193 represents the thermal decomposition of a silver carbonate, AgjCOj, in helium. At about 400-550 K, the carbonate loses carbon dioxide and changes into the oxide Ag20. A second, smaller loss of mass begins at a temperature of 675 K. Both mass losses are accompanied by an endotherm in the DTA trace, meaning that the reactions are entropy driven. The final decomposition product is metallic silver. 

The studies of the influence of foreign gases are very few however, frequently, a catalytic effect of the water vapor that seems to accelerate the reaction was noted. In the case of the decomposition of silver carbonate, the curve in Figure 13.5a shows this acceleration. The other gases often have, on the contrary, a reducer effect on the speed however, Bardel announces the presence of a minimum in the influence of the oxygen pressure on the rate of decomposition of silver carbonate [BAR 78] (Figure 13.5b). 

Figure 13.5. Influence of a foreign gas in the decomposition of silver carbonate...

In the decomposition of silver carbonate to form metallic silver, carbon dioxide gas, and oxygen gas, (a) one mol of oxygen gas is formed for every 2 mol of carbon dioxide gas (b) 2 mol of silver metal is formed for every 1 mol of oxygen gas (c) equal numbers of moles of carbon dioxide and oxygen gases are produced (d) the same number of moles of silver metal are formed as of the silver carbonate decomposed. 

The reaction is carried out over a supported metallic silver catalyst at 250—300°C and 1—2 MPa (10—20 bar). A few parts per million (ppm) of 1,2-dichloroethane are added to the ethylene to inhibit further oxidation to carbon dioxide and water. This results ia chlorine generation, which deactivates the surface of the catalyst. Chem Systems of the United States has developed a process that produces ethylene glycol monoacetate as an iatermediate, which on thermal decomposition yields ethylene oxide [75-21-8]. 

Bromocyclopropane has been prepared by the Hunsdiecker reaction by adding silver cyclopropanecarboxylate to bromine in dichlorodifluoromethane at —29° (53% yield) or in tetrachloro-ethane at —20° to —25° (15-20% yield).3 Decomposition of the peroxide of cyclopropanecarboxylic acid in the presence of carbon tetrabromide gave bromocyclopropane in 43% yield.4 An attempt to prepare the bromide via the von Braun reaction was unsuccessful.3... 

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