Silver, photolytic

The Ritter reaction with unsaturated carbenium ions under either silver-assisted solvolysis or photolytic conditions leads to excellent yields of isoquiaolines (173). The ease of preparation of the requited vinyl bromides makes an attractive route to highly substituted isoquiaolines. 

Scheme 10.14 gives some other examples of Wolff rearrangement reactions. Entries 1 and 2 are reactions carried out under the classical silver ion catalysis conditions. Entry 3 is an example of a thermolysis. Entries 4 to 7 are ring contractions done under photolytic conditions. Entry 8, done using a silver catalyst, was a step in the synthesis of macbecin, an antitumor antibiotic. Entry 9, a step in the synthesis of a drug candidate, illustrates direct formation of an amide by trapping the ketene intermediate with an amine. 

If the photolytic silver is added on to the material of the speck, the nuclei which are responsible for making a grain developable consist... 

AgBr films could be made in the same manner using various bromo-alco-hols. AgBr is colorless but is usually slightly brownish due to photolytic formation of small particles of metallic silver (this occurs much more strongly if deposition is carried out in room light, but formation of some brown coloration is stiU noticeable even if deposition is carried out in the dark). This coloration masked the optical absorption, which occurs mainly in the UV for AgBr. For bromides, triethanolamine was not needed. 

A very important photographic reaction is the photolytic decomposition of silver br< rude described approximately by the following equation ... 

Pyridine 20 has been prepared by the silver- or acid-catalyzed isomerization of 1-aza-bicyclo[2.2.0]hexadiene 22, which in turn was obtained in a [2 + 2]-cycloaddition reaction of tris(to7-butyl)azete with hexafluorobut-2-yne. Irradiation of Dewar pyridine 22 gives a high yield of azaprismane 23, which isomerizes thermally to rearranged pyridine 24. Finally, pyridine 24 yields 1-aza Dewar pyridine 25 photolytically.34... 

The electron, if not lost by recombination or some secondary process, can combine with an interstitial silver ion or possibly a surface silver ion to form a silver atom. The photolytic silver is formed as, or aggregates to form, nuclei rather than existing as individual atoms distributed throughout the crystal. Only one nucleus consisting of a few silver atoms is needed to produce a detectable photographic effect. 

Why and how are nuclei of silver formed by the photolysis What becomes of the other photolytic product, the hole or halogen, and how important is it to photographic sensitivity How do crystal defects and impurities influence sensitivity and latent image formation How can radiation absorbed by dyes at the crystal surface induce formation of silver My intention in this chapter is to review recent experimental and theoretical work bearing on these questions and to offer some conclusions as to what we know, what we think we know, and what can be decided only by future investigations. 

Latent preimage center is a photolytic silver atom located where a latent image center can form upon further exposure to radiation. 

Both reduction centers and latent image centers are composed of silver, and to Moisar "it seems safe to assume that the silver specks formed by reduction are identical to those which somehow appear as subspecks and alleged intermediate entities during photolytic silver formation" (93). He proposed that Ag2 centers formed by exposure by light can act as hole traps and Agj centers act as subdevelopable precursors of latent image centers but, as Hamilton and Baetzold comment (96),... 

In summary, there is evidence that the multitalented sulfur sensitization product can trap electrons, can trap holes to reduce recombination, can stabilize photolytic silver atoms, and can accelerate reduction sensitization. Conceivably, each of these properties could be of importance for latent image formation under at least some conditions. The silver sulfide centers are not of uniform size, they probably are not uniformly related energetically to the silver halide matrix, and they may differ in chemical consititution. 

The favored formation of acetylated l-a-deuterio-l,5-anhydro-D-glucitol 78 in labeling experiments has been put forward to support the occurrence of carbohydrate radicals as intermediates in the photolytic decomposition of glucopyranosyl phenyl sulfone acetates104 as well as the Cp2TiBD4193 and zinc-silver/graphite-197 mediated reduction of glycosyl halides. Cationic intermediates would have favored the opposite stereochemistry 26... 

Photolysis of metal compounds is a method of historical dimension as it has been used since the middle of the nineteenth century, when the light-sensitivity of silver salts was used for photographic purposes. Novel research, especially linked with the names Henglein and Belloni, led to a large extended field in the science of nanoparticles. UV-visible irradiation of Au, Ag, and Pt salts in surfactant or polymer solutions end up with nanoparticle formation. " Compared with hydrogen reduction, photolytic reactions usually give smaller particles with narrower size distribution. ... 

Saegmueller B, Brehm G, Schneider S (2000) In situ generated photolytic silver in a gelatin matrix an approach for high-throughput SERS spectroscopy applying microtiter plates. Appl Spectrosc 54(12) 1849-1856... 

DIBAL-H/n-butyllithium, in cyclic and acyclic systems with iron pentacarbonyl, in cyclodecanes with lithium dihydrodimethoxyaluminate(III)/copper(I) iodide, and in cyclohexane and cyclopentane systems with NaH/sodium r-butylpentyl/Ni(OAc)2. ° The monoreduction of 1,3-diketones can be carried out under similar conditions, as illustrated by the reaction of a substituted cyclohexane-1,3-dione with oxalyl chloride to give the corresponding 1-chlorocyclohexenone, which was subsequently reduced to the enone with zinc-silver couple (Scheme 45). Kropp et al. have reported the photolytic reduction of vinyl iodides in acyclic systems however, when an a-hydrogen is present, formation of the diene product is a limiting side reaction (Scheme 46). For a more extensive discussion of vinyl halide reductions, see the preceding chapter in this volume. 

Kawasaki et al. [91] looked at the oxidation kinetics of large photolytic silver clusters in redox buffer solutions. The process was analyzed in terms of a series of stepwise reactions involving electron transfer and silver ion elimination. It was shown that the single-step oxidation ... 

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