Mercury sensitivity

Mercury-sensitized irradiation of 1,2,3-triphenylisoindole (65) in the presence of oxygen gives a peroxide (103). This peroxide is relatively stable compared with the peroxide (104) derived from similar oxidation of 1,3-diphenylisobenzofuran and can be reconverted to the isoindole (65) by pyrolysis or by treatment with zinc and acetic acid. Reduction of 103 under mild conditions affords o-dibenzoylbenzene (46) and aniline. Aerial oxidation of 47 gives 46 and methylamine, presumably via a peroxide intermediate similar to 103. °... 

Mercury-sensitized irradiation of 3-methylfuran gave 2-butyne, 1,2-pentadiene, 1-methylcyclopropene, 1-butyne, and 1,3-butadiene (Scheme 6) (68JA2720 70JPC574). In the direct irradiation, 1-methylcyclopropene was obtained in lower yields while both 3-methylcyclopropene and 2-methylfuran appeared (Scheme 6) (70JPC574). 

In the analogous studies of the photolysis of sulfolane (31), the work of Honda and coworkers66 was carried out in the gas phase at 70-130 °C and established the formation of S02, ethylene, cyclobutane and acetylene as the major products, on mercury-sensitized photolysis. In considerable contrast, photolysis of sulfolane at 185 nm in the liquid phase67 produced ethylene( = 0.22), the sultine (32) (parallel experiments on aqueous solutions of sulfolane, a sulfinic acid is also believed to be formed. The authors believe that both four-membered (33) and six-membered (32) sultines may be formed during these photolyses. Further work in this area would appear to be necessary to unravel the full mechanistic details. 

Delahoy, A., Doele, B., Ellis, F., Ramaprasad, K., Tonon, T., and Van Dine, J., Amorphous Silicon Films and Solar Cells Prepared by Mercury-Sensitized Photo-CVD of Silane and Disilane, Materials Issues in Applications of Amorphous Silicon Technology, (D. Adler, et al., eds), MRS Proc., (49) 33-39 (1985)... 

Cohen and Heicklen 46 investigated the mercury-sensitized photolysis of C2F4 and were able to determine the rate constant for the reaction... 

Birse and Melville55 measured the disappearance of N2H4 in the presence of hydrogen atoms generated by mercury-sensitized photolysis of H255. They could not discriminate between reactions (4) and (5) and assumed that the H atoms were removed by reaction (4). In view of the more recent experiments with D atoms it is, however, more likely that they determined the rate of reaction (5). They report a rate coefficient... 

Further observations on the effect of light on diborane(6) did not appear until the 1950 s. At that time, Hirata and Gunning studied the mercury-sensitized de-... 

The influence of mercury sensitization on the exchange rate was checked by Nadler and Turbini using a Vycor filter to eliminate light absorbed by borazine. In both cases the effect of mercury-sensitized photolysis was small compared to the effect of direct photolysis. 

Taylor in 1925 demonstrated that hydrogen atoms generated by the mercury sensitized photodecomposition of hydrogen gas add to ethylene to form ethyl radicals, which were proposed to react with H2 to give the observed ethane and another hydrogen atom. Evidence that polymerization could occur by free radical reactions was found by Taylor and Jones in 1930, by the observation that ethyl radicals formed by the gas phase pyrolysis of diethylmercury or tetraethyllead initiated the polymerization of ethylene, and this process was extended to the solution phase by Cramer. The mechanism of equation (37) (with participation by a third body) was presented for the reaction, - which is in accord with current views, and the mechanism of equation (38) was shown for disproportionation. Staudinger in 1932 wrote a mechanism for free radical polymerization of styrene,but just as did Rice and Rice (equation 32), showed the radical attack on the most substituted carbon (anti-Markovnikov attack). The correct orientation was shown by Flory in 1937. In 1935, O.K. Rice and Sickman reported that ethylene polymerization was also induced by methyl radicals generated from thermolysis of azomethane. 

The mercury sensitized emission, (process (b)) from TI and Na vapour has been discussed in Section 6.6.6. The quenching to 63P0 (process (d)) by CO, N2 and N O, NH3 are presented in Section 6.2. In presence of H2, the possible photochemical reactions are... 

In order to understand the mercury-sensitized oxidation, it is first necessary to discuss the sensitized reaction in the absence of 02. The reaction has been studied in a series of papers and the general overall mechanism has been developed... 

The state is definitely excluded as it reacts with ground state 02 to give 03 with a quantum yield of two.1740 From mercury sensitization 0(03) is only 0.03.173... 

Fig. 6. Log-log plot of (CF3CF0) 1 -I- (AS6[C4Fs-2]/A52[021) / (A56[C4F8-2]/ B2[OJ) + ArBs[C4Fe-2]/(A 65[C4F2-2] + A53[02]) vs. [02] in the mercury-sensitized photolysis of trans-C4Fe-2 at room temperature. [C4Fa], torr (O) 7 (A) 20 ( ) 60 ( ) 200. From Johnston and Heicklen.93...

Gozzo and Camaggi64 photolyzed 02-C2F4 mixtures at 2537 A, supposedly in the absence of Hg. However, since neither gas absorbs the radiation, and c-C3F6 was formed even in the absence of 02, it is almost certain that they were inadvertently examining the mercury-sensitized reaction. Their qualitative results agreed with the more detailed studies of Heicklen et al.83,85 However, they also found that with ppm of 02, the polymerization of C2F4 was induced. 

Laidler83 points out the possibility of mercury-sensitized photoexcitation in a spin-allowed, energy-exchange process. 

Although no suggestion appeared initially that O Ag) could be a product of reactions (23) and (24), there seems to be no reason why it should not, although Gill and Laidler125 subsequently showed that OaCA,) was a less probable product of the mercury-sensitized reaction. 

There has been some speculation as to whether the mercury-sensitized decomposition of cyclopropane involves energy transfer or radical formation in the primary process.508... 

The quenching cross section for cyclopropane is considerably smaller than those for olefins.497 However, the fact that cyclopropane-de is, if anything, a more effective quencher of triplet mercury than cyclopropane-/ 6497 favors an energy transfer process over a hydrogen abstraction process. Recently Gunning has reported that methylene-cyclobutane is the major high-pressure product in the mercury-sensitized decomposition of spiropentane.509 This result provides very compelling support for the intermediacy of a biradical species. 

Recent evidence supports the hypothesis that NO (a4 II,) is produced by mercury sensitization... 

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