Mercury sensitized photolysis

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. 

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... 

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. 

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...

A systematic restudy of the thermal and photolytic reactions of perlluorodiene 12 demonstrated that ring closure to the bicyclie isomer 13 is reversible at 250 C and that at higher temperatures crosswise cycloaddition takes place to give perfluorobicyclo[2.1.1 (hexane (14).40 Mercury-sensitized photolysis at 254 nm of diene 12 gives bicyclie isomers 13 and 14 in a ratio of 1 4.4,1... 

Perfluorohcpta-l,6-diene (15) requires about 1 day at 300 C in a Pyrex ampule for complete conversion and yields the crosswise cycloaddition product 16 and the parallel eycloaddition product 17 in a ratio of 9 I.41 Increasing the temperature to 450 C results in a product ratio of 1 1. Direct photolysis of diene 15 leads only to polymerization, but mercury-sensitized photolysis gives a mixture of 16, ra-fused 17, and /raw.wfused 17 in a ratio of 2.8 5.7 1.0. 

Photochemical behavior of monosilanes has been investigated by mercury-sensitized photolysis (15-19), flash photolysis (20, 21), vacuum ultraviolet photolysis (22-27), and matrix photolysis (28-30). The first examples of the photolysis of permethylated polysilanes were published in 1970 (14). All of the cyclic and acyclic permethylpolysilanes with the exception of hexamethyldisilane readily undergo photolysis on irradiation with ultraviolet light to give shorter chain compounds with the concurrent generation of the divalent silicon intermediate, dimethylsilylene (8). 

The mercury sensitized photolysis of a mixture of F3 SiSip3 and PF3 affords P(SiF3)3 as a colorless air-sensitive liquid. It reacts with a deficiency of water to give (F3Si)2PH and F3SiPH2 and with bromine to give PBrs and F3SiBr. ... 

Porter and Spear have reported the mass spectrum of aziridine 8 ) which shows HC=NH+ as the base peak in addition to peaks which correspond to (M—1)+, (M—2)+ and CH3. The mercury sensitized photolysis of aziridine 8 ) gives predominantly ethylene and nitrene. This heteroatom effect does not apply to the mass spectral photochemical correlation for ethylene oxide, which shows very similar behavior in both systems.82)... 

Photolysis studies of SiH have iavolved a sensitizer, eg, mercury vapor, because SiH does not absorb uv-radiation at wavelengths above 185 nm (49). The mercury-sensitized photolysis of SiH leads to the formation of H2, Si2H, Si Hg [7783-26-8] and polymeric solid silanes the quantum yields of H2 and Si2Hjj are ca 1.6 and 0.6, respectively (50,51). The photolysis of SiH in the presence of GeH or CH I produces SiH GeH or CH SiH, respectively... 

Fehlner and Strong produced oxygen atoms at 25 and 100 °C from the mercury-sensitized photolysis of N2O. The oxygen atoms reacted with B2H6 to produce H2, B4H10, B5H9, and a white solid of empirical formula HBO. The proposed reaction steps included... 

The first publications dealt with simple alkyloxiranes, The photochemical behavior of oxirane, methyloxirane, and ethyloxirane has been investigated by direct irradiation or mercury-sensitized photolysis. The products formed by cleavage have been analyzed, but the nature of the primary processes has not been touched on. A free-radical mechanism has been proposed. A free-radical chain mechanism has been established on the basis of the products obtained on direct irradiation (254 nm) of pure methyloxirane. Experiments with the aim of clarifying the primary photochemical processes were published recently, with irradiation of methyloxirane in the gas phase at 185 nm. Mainly propanal was obtained with a little acetone and traces of ethanol and propanol. An outline of the reaction mechanism is presented in Eq. 325. 

Thietanes are photochemically unstable and should be protected from light if they are to be stored for any length of time. Short-lived (hot) biradical intermediates, for example, 98a, appear to be formed and can undergo a variety of reactions, as shown for thietane. " Mercury-sensitized photolysis gives triplet biradicals that are longer lived than the singlet biradicals formed on direct excita-tion. " Some cyclopropane product is produced in the sensitized photolysis. The second excited singlet state of thietane decomposes either to ethylene and thio-formaldehyde via a 1,4-biradical or to elemental sulfur and cyclopropane. ... 

First attempts made by the Paneth technique to detect free radicals failed due to experimental diflSculties. However, upon reinvestigation, the occurrence of free radicals was proved in the mercury-sensitized photolysis , as well as in the direct photolysis at several wavelengths. Using the para-ortho hydrogen method, Patat came to a similar conclusion. He found the para-ortho conversion to be negligible below 200 °C, however, at higher temperatures the hydrogen atom and free radical concentrations became measurable. 

According to Lossing °, free radical formation amounts to at least 95 % of the dissociation in the mercury-sensitized photolysis of mixtures of CD3CDO and CH3CHO. Blacet and Brinton, as well as Ausloos andSteacie have investigated the photolysis of CH3CDO. Their results are in accordance with a free radical mechanism. 

The products of the mercury-sensitized photolysis are similar to those found in the direct photolysis In contradiction to earlier findings , C2H4 was proved to be a product of the reaction , found only in small amounts due to its being consumed by secondary reactions. 

As regards the primary processes, there seems to be no essential difference between the mercury-sensitized photolysis and the direct photolysis at 2537 A (refs. 20, 154, 155). The value of a is smaller in the sensitized reaction than in the direct photolysis at 2537 A this is presumably due to the fact that in the former case a significant fraction of the excess energy appears as the kinetic energy of the mercury atom. 

Considerable amounts of hydrogen and ketene were observed by Lossing among the products of the mercury-sensitized photolysis at 55 °C. He concluded that these were formed as the result of the mercury-sensitized decomposition of the acetyl radicals rather than in primary processes analogous to IV and V. 

The quantum yields of acetone consumption and ethane formation decrease with increasing intensity. The dependence of the C2H6/CO ratio on light intensity can be demonstrated in a very wide intensity range if the results of the mercury-sensitized photolysis are also taken into consideration (Table 16). An increase in the quantmn yield of biacetyl formation with increasing intensity is apparent from the results of Herr and Noyes, and has also been confirmed by the direct measurements of Howland and Noyes. 

The products of the mercury-sensitized photolysis differ only slightly from those found in the direct photolysis at 2537 A hence, the mechanisms of the secondary reactions are probably also similar . The only significant difference appears to be the formation of ketene and hydrogen in the sensitized reaction at 55 °C. These products are probably the results of the reaction ... 

Mercury-sensitized photolysis (A = 253.7nm) of H2 with N-trimethylborazine produces the new derivative l,2-di-(3, 5 -dimethylborazinyl)ethane (56). ... 

The mercury-sensitized photolysis of tricyclo[4.1.0.0 ]heptane (67)—cf. Table 9 entry 3c—probably proceeds by primary cleavage of a lateral C—C bond (equation 39). 

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