Dichloroethane photolysis

The photolysis of chlorodiazirine was investigated in several cases. From chloromethyl-diazirine (232) vinyl chloride was formed as the stable primary product of stabilization of chloromethylcarbene, with acetylene and hydrogen chloride as secondary products. Some 1,1-dichloroethane was assumed to have been formed through a linear diazo compound by reaction with HCl. Added HBr yielded 1-bromo-l-chloroethane (76MI5Q800). 

The results of low-temperature matrix-isolation studies with 6 [41a] are quite consistent with the photochemical formation of cyclo-Cif, via 1,2-diketene intermediates [59] and subsequent loss of six CO molecules. When 6 was irradiated at A > 338 nm in a glass of 1,2-dichloroethane at 15 K, the strong cyclobut-3-ene-1,2-dione C=0 band at 1792 cm in the FT-IR spectrum disappeared quickly and a strong new band at 2115 cm appeared, which was assigned to 1,2-diketene substructures. Irradiation at A > 280 nm led to a gradual decrease in the intensity of the ketene absorption at 2115 cm and to the appearance of a weak new band at 2138 cm which was assigned to the CO molecules extruded photo-chemically from the 1,2-diketene intermediates. Attempts to isolate cyclo-Cig preparatively by flash vacuum pyrolysis of 6 or low-temperature photolysis of 6 in 2-methyltetrahydrofuran in NMR tubes at liquid-nitrogen temperature have not been successful. 

Photolytic. Dalapon (free acid) is subject to photodegradation. When an aqueous solution (0.25 M) was irradiated with UV light at 253.7 nm at 49 °C, 70% degraded in 7 h. Pyruvic acid is formed which is subsequently decarboxylated to acetaldehyde, carbon dioxide, and small quantities of 1,1-dichloroethane (2-4%) and a water-insoluble polymer (Kenaga, 1974). The photolysis of an aqueous solution of dalapon (free acid) by UV light (X = 2537 A) yielded chloride ions, carbon dioxide, carbon monoxide, and methyl chloride at quantum yields of 0.29, 0.10, 0.02, and 0.02, respectively (Baxter and Johnston, 1968). 

Benzene and some halogenated compounds including carbon tetrachloride, trichlorotriflu-oroethane (Freon 113), and dichloroethane absorb light weakly and thus photolyze relatively slowly. Therefore even shorter wavelengths than those available from the current technology are needed to create a commercially viable, direct photolysis process for these compounds. 

In the above measurement, the pulse duration is longer than the rates of the cyclization and ring-opening reactions. To determine the rates precisely, it is desirable to employ a shorter laser pulse. We measured the response time of the following dithienylethene in 1,2-dichloroethane by using a femto laser (180 fs) photolysis apparatus.20... 

The dynamics of reversible onium ion formation has been studied by generating carbenium ions in the presence of nucleophiles using pulse radiolysis or flash photolysis, and following the rate of disappearance of the carbenium ions by UV. As discussed in Chapter 2, the kinetics of reaction of various electrophiles with nucleophiles obey a general reactiv-ity/selectivity relationship. The rates of reaction of various nucleophiles with carbenium ions are summarized in Table 9. These rates often approach diffusion controlled limits (k 10 ° mol-,-L-sec l). The rates are slower for less nucleophilic and less electrophilic compounds, and are particularly slow with sterically hindered amines such as lutidine (2,6-dimethylpyridine) [63]. Solvent effects are minimal when the reactions are diffusion controlled, although tributyl amines react slower with carbenium ions in more nucleophilic dichloroethane than in methylene chloride. 

As discussed earlier, organic compounds with double bonds, especially with chlorine, react quickly with hydroxyl radical. On the other hand, saturated organic compounds such as 1,1-dichloroethane and chloroform, are better removed by UV photolysis. Depending on the type of organic compound, initial contaminant concentration will affect the performance of the process. For high contaminant level, multiple AOPs can be used. For example, for a COD > 5000 mg/L, sequential treatment using Fenton s reagent followed by UV oxidation may be chosen. 

Figure 2.5. Kinetic traces of AO.D.480 during the pulse radiolysis-laser flash photolysis experiment of t-St (5 x 10-3 M) in the absence (a) and presence (b) of ANS (1.0 M) in Ar-saturated 1,2-dichloroethane.

Figure 2.7. Transient absorption spectra observed at Ons, 100 ns, and 1 ps after the 8-ns electron pulse, and transient fluorescence spectrum of TMB + observed at 300 ns after the electron pulse during pulse radiolysis-laser flash photolysis of TMB (lx 10-2M) in Ar-saturated 1,2-dichloroethane. Excitation wavelength, 532 nm. Laser pulse energy, 140 mJ pulse-1.

The photolysis of phosgene in the presence of ethene gives results which are quite different from those obtained by the photochlorination of ethene with molecular chlorine, in which the main reaction product is 1,2-dichloroethane. The proposed mechanism for the phosgene reaction is given below [2185] ... 

Stiles4 found that flash photolysis of benzenediazonium-2-carboxylate led to the formation of N2, C02. biphenylene. and triphenylene. Biphenylene predominated over triphenylene. Yields were low. Fricdmans obtained biphenylene in yields as high as 30% by heating benzenediazonium-2-carboxylate in gently boiling, stirred 1,2-dichloroethane (b.p. 83-84°). 

Diphenyl sulfide radical cation has been reported [116] to absorb in the visible with = 780 nm for the species formed by gamma radiolysis of Ph2S in 1,2-dichloroethane at 77 K. Laser flash photolysis of 46 in acetonitrile provides Ph2Ss which shows absorption bands at 330 and 750 nm [117]. 

Figure 2. Photolysis of polyisoprene hydroperoxide in 1,2-dichloroethane solution, 30°C,X = 365 nm...

Figure 3. Photolysis of cis-polyisoprene hydroperoxide (0.06% -00H) in 1,2-dichloroethane at 30°C determination of quantum yields at various wavelengths...

The same reaction pathway is involved in photolysis of (144). When the reaction is performed in dichloroethane, (145) is obtained in 40% yield. In methanol, two products (147) and (148) are formed, both derived from common intermediate (146) (Scheme 22) <84JOC587>. 

Generation of [(i7 -S S)W(CO)4(CB)] by flash photolysis in chlorobenzene (CB) enabled rates of ring closure to be obtained and the activation parameters are shown in Table 10.3. For x = 1 (in dichloroethane) and 2, ring closure is probably associative but for x = 3-5 the values of correspond to those expected for dissociative loss of CB and the values of A5 are probably related to entropy changes imposed by freezing of internal rotations when the transition state is formed. 

Dry state absorbtion conditions, microwave irradtion, and photolysis have all been used to accelerate the DBR. Recently Kerr has described simple conditions that promote the DBR at near ambient conditions His optimized procedure used dichloroethane as the solvent with heating at 30 C for 18 h with no additives. Dichloroethane and gentle heating were both critical for high yields. It is interesting that ambient laboratory temperature, measured as 14-17 °C, was insufficient and resulted in sluggish reactions. 

Evidence for a 14-electron [(phen)Mo(CO)2] intermediate was obtained from a study of CO isotopic enrichment of /ac-[(MeCN)-(phen)Mo(CO)3]. Pulsed laser flash photolysis of (2) (M = Cr or Mo) in 1,2-dichloroethane or chlorobenzene produces the five-coordinate (3) which... 

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