Silver acetate, decomposition

For primary and secondary bromides base-catalysis is required, while for tertiary bromides silver acetate or silver oxide are more effective cyclization catalysts. For tertiary substrates dehydrobromination leading to allylic hydroperoxides is a serious side reaction when base-catalysis is employed and, thus, silver ion catalysis is essential. Furthermore, the silver salts must be freshly prepared because metallic silver that might be present due to exposure to light causes decomposition of the dioxetane. The tetramethyl-l,2-dioxetane (7) was the first example prepared in this way (Eq. 13). For primary substrates, abstraction of the base-sensitive dioxetanyl hydrogens are probably responsible for the low yields. For secondary substrates, both side reactions might operate. 

Crystals of benzyl iodide when gently heated become red in colour owing to incipient decomposition. By the action of silver acetate in presence of acetic acid, silver iodide and benzyl acetate are formed (Lieben). 

The latter is observed in comparing the acetolysis of iodides 350 and 351 with the above reactions of the same substrates with bromine where the stereospecificity was observed not only in the shifting of bonds but in the addition of a nucleophile, i.e. ions 347 and 348 are the only product-forming ions. This difference in the rate ratio of the 1,2-bond shift and in the capture of ions 347 and 348 in reactions of iodides 350 and 351 with bromine and silver acetate can be accounted for as follows. Upon decomposition of the initially formed iodide-bromine complex the anion JBr is not only part of the ion pair, but it interacts further with the cation within the same ion pair to yield bromide. When the same iodide reacts with silver acetate... 

Applications of thallium bases to other palladium(0)-mediated couplings are rare. A noteworthy example is the use of thallium(i) acetate as a base in Heck coupling to promote the stereoselective synthesis of polyenes though the yields were quite low. Whereas silver acetate was a more effective base to produce J7,i7-polyenes from E-iodides in about 56% yield, it failed in the Heck reaction with Z-iodides since this substrate readily decomposes in the presence of silver acetate. Thallium(i) acetate solved the decomposition problem, however, the product was isolated in poor yield (Scheme 20.20). 

Formation of Cyclic Ethers. Alcohols that have a hydrogen in the 5-position can be cyclized with silver acetate and bromine (eq 1). The ring closure occurs via an intermediate hy-pobromite. The reaction can be run under a variety of conditions (presence/absence of light, acidity, solvent, temperature). Because of this variety and the products formed, there has been some disagreement about the role silver plays in the hypobromite decomposition. ... 

Some small molecules exert a profound influence on the mode of decomposition of PMMA. Silver acetate has been found to greatly accelerate depolymerization zinc bromide changes the entire character of the degradation reaction, with the formation of various volatile products, notably methyl bromide. The fire retardant additive ammonium polyphosphate acts by reaction with the polymer so as to interfere with the monomer-producing reaction. ... 

The 5-isobutoxymethyl monothioacetal is stable io2N hydrochloric acid and to 50% acetic acid some decomposition occurs in 2 A sodium hydroxide. The monothioacetal is also stable to 12 A hydrochloric acid in acetone (used to remove an A -triphenylmethyl group) and to hydrazine hydrate in refluxing ethanol (used to cleave an A-phthaloyl group). It is cleaved by boron trifluoride etherate in acetic acid, by silver nitrate in ethanol, and by trifluoroacetic acid. The monothioacetal is oxidized to a disulfide by thiocyanogen, (SCN)2. ... 

A. J. Balard,9 in 1821, also prepared hypobromous acid in a similar manner, namely, by the gradual addition of mercuric oxide of bromine water, and thoroughly shaking the mixture after each addition. Further, quantities of bromine and mercuric oxide can be added until the yellow fluid contains between 6 and 7 parts of HOBr per 100 c.c. The mercuric oxide can be replaced by silver oxide, silver or mercuric nitrate, mercuric acetate, etc. The soln. with 6-7 parts of HOBr per 100 c.c. decomposes at 30°, but more dil. soln. when distilled under ordinary atm. press, give a distillate of bromine followed by a straw-yellow fraction which is a dil. aq. soln. of hypobromous acid. The decomposition is not so pronounced if it be conducted at 40° under a press, of, say, 50 mm. of mercury. 

E. P. Alvarez 2 found that the pemitrates react with soln. of lead acetate (white precipitate), silver nitrate (white precipitate), mercurous nitrate (white precipitate with rapid decomposition), mercuric chloride (red precipitate), copper sulphate (blue precipitate), zinc and cadmium sulphates (white precipitate), bismuth nitrate (white precipitate), gold chloride (slight effervescence and escape of oxygen), manganous chloride (pink precipitate), nickelous chloride or sulphate (greenish-white precipitate), cobaltous nitrate and chloride (pink precipitate), ferrous sulphate (green or bluish-green precipitate), ferric chloride (red ferric hydroxide), and alkaline earth chlorides (white precipitates). The precipitates are all per-salts of the bases in question. 

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