Photolysis halides

Also included are some of the chemical and physical steps which immediately follow the initial interaction of silver halide materials with fight The story of these imaging processes would not be complete without them and they serve to illustrate the diverse applications of the common photochemical process of silver halide photolysis. 

Before we look in detail at the core photochemical process of silver halide photolysis and the amplification of the photochemical response resulting from chemical development we will first explore the early history of imaging technology. By doing so will introduce the essential elements of modern photographic systems. 

W. Braun and W. Tsang, Mechanism of alkyl halide photolysis by... 

Kropp and his co-workers reported competing ionic and radical photobehavior for a number of alkyl halides. Photolysis of a-halo ketones (ROCCX) is understood to proceed via competing homolysis of CC and CX bonds as the primary processes. Tomioka et al. also proposed that irradiation of a-halo ketones in alcohols brings about competition between ionic and radical reaction paths with the formation of photoalcoholysis and photoreduction products. During the course of our studies, it was found that irradiation of a-iodocycloalkanones in the nonpolar solvents (e.g., hexane) afforded mainly the elimination product, an a,(3-unsaturated cyclic ketone, accompanied by a small amount of photoreduction product. " Therefore, it is considered that this photochemical behavior can be explained as shown in Figure 56.1 on the basis of the results mentioned above. 

The primary product of hypohalite photolysis is a 1,5-halohydrin, the stability of which increases on passing from iodo- to bromo- to chloro-hydrins. If spontaneous elimination of hydrogen halide does not occur, the halohydrins can be converted into tetrahydrofurans by base treatment. In several instances it has been possible to isolate the intermediate... 

The halide groups can be replaced by other substituents like hydride or alkyl [86]. When the naphthyl (np) RuHnp(dmpe)2 is heated, the ligand undergoes an internal metallation to afford a dimer [87] (it was originally believed to be a monomer), though Ru(dmpe)2 has been isolated by photolysis of its dihydride, in matrixes at 12K (Figure 1.29) [88],... 

Thermolysis rates are enhanced substantially by the presence of certain Lewis acids (e.g. boron and aluminum halides), and transition metal salts (e.g. Cu ", Ag1).46 There is also evidence that complexes formed between azo-compounds and Lewis acids (e.g. ethyl aluminum scsquichloridc) undergo thermolysis or photolysis to give complexed radicals which have different specificity to uncomplexed radicals.81 83... 

We start the discussion of the group (2) of photo-de-diazoniations in imaging processes by noting that, after silver halide photography, systems based on the photolysis of diazo compounds form the second most important group of imaging processes. 

Very much more persistent radicals, with a half-life of up to a year, and with the structures [(Me3Si)2CH]3Sn- and [(MejSiljCHljRSn-(R = Pr , Bu , Me, Et, Bu, or cyclopentadienyl) have been prepared by the photolysis of [(Me3Si)2CH]2Sn(II), or by photolyzing a mixture of the appropriate halide [ Me3Si)2CH]2RSnX with an "electron rich olefin (299, 300). 

Primary alkyl amines RNHi can be convertedto alkyl halides by (1) conversion to RNTs2 (p. 447) and treatment of this with I or Br in DMF, or to N(Ts)—NH2 derivatives followed by treatment with NBS under photolysis conditions, (2) diazotization with terr-butyl nitrite and a metal halide such as TiCU in DMF, or (3) the Katritzky pyrylium-pyridinium method (pp. 447,489). Alkyl groups can be cleaved from secondary and tertiary aromatic amines by concentrated HBr in a reaction similar to 10-71, for example,... 

In another reductive coupling, substituted alkenes (CH2=CH Y Y = R, COOMe, OAc, CN, etc.) can be dimerized to substituted alkanes (CH3CHYCHYCH3) by photolysis in an H2 atmosphere, using Hg as a photosensitizer. Still another procedure involves palladium-catalyzed addition of vinylic halides to triple bonds to give 1,3-dienes. ... 

Koplitz and co-workers have studied the photolysis of C2H5 via the A2A (3s) state by using 248-nm photolysis radiation and hot ethyl radicals generated from photolysis of ethyl halides.125,126 Chen and co-workers have investigated the photodissociation of jet-cooled ethyl (produced by flash pyrolysis of ethyl iodide and n-propylnitrite) in the region of 245-264 nm... 

The formation of hydrated electrons by the photolysis of halide ions in solution may be envisaged in two steps. The first step is the CTTS absorption leading to (X -). The second step is a slow, thermal process releasing the electron in competition with degradation and recapture. In the presence of acid and alcohol, photolysis of halide solutions generates H2 with a yield that increases both with acid and alcohol concentrations (seejortner et al., 1962, 1963, 1964). At 25°, the limiting quantum yields are 0.98 for Cl- at 185 nm, 0.6 and 0.5 for Brat 185 and 229 nm, respectively, and 0.3 and 0.25 for I- at 254 and 229 nm, respectively. Since most of these yields are less than 1, the direct reaction of HsO and (Xaq-) is ruled out. Instead, it is proposed that eh is produced from the... 

Hydrogen halides will easily add to unsaturated compounds under radiolysis or photolysis. The free-radical chain reaction process is initiated by the dissociation of the halide or by the radiolytic production of radicals from the halide or the organic compound. Thus, for the radiolysis of a mixture of HBr and ethene the postulated initiation is... 

Allenyl cations have been generated by solvolysis of allenic derivatives, by photolysis of allenyl halides and by reaction of metal salts with allenyl and propargyl halides. This review will delineate these reactions. The related butatrienyl cations are not many and they will be only briefly described. 

The photolysis of CpPbR3 in the presence of various reagents was also investigated. Some differences were observed compared with the analogous tin compounds. The chemistry observed is summarized in Scheme 14, the main differences from CpSnR3 being the lack of reaction with alkyl halides or alkenes. 

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