Chloroform, photolysis

Sulfonic adds have largely remained unexplored in terms of a functional group that is released from a photoremovable protecting group. One recent example has been reported by Bendig et in which methanesulfonic acid was protected as the corresponding methoxycoumarin derivative. (7-Methoxycou-marin-4-yl)methylmethanesulfonate 59 was synthesized from reaction of methanesulfonic add with 4-(diazomethyl)-7-methoxycoumarin in refluxing chloroform. Photolysis at 333 nm resulted in the release of methanesulfonic acid, as shown in Eq. (69.30). 

The following carbamates can be cleaved by photolysis. They can be prepared either from the chloroformate or from the mixed carbonate. 

Pyridinium ylide is considered to be the adduct car-bene to the lone pair of nitrogen in pyridine. The validity of this assumption was confirmed by Tozume et al. [12J. They obtained pyridinium bis-(methoxycarbonyl) meth-ylide by the photolysis of dimethyl diazomalonate in pyridine. Matsuyama et al. [13] reported that the pyridinium ylide was produced quantitatively by the transylidalion of sulfonium ylide with pyridine in the presence of some sulfides. However, in their method it was not easy to separate the end products. Kondo and his coworkers [14] noticed that this disadvantage was overcome by the use of carbon disulfide as a catalyst. Therefore, they used this reaction to prepare poly[4-vinylpyridinium bis-(methoxycarbonyl) methylide (Scheme 12) by stirring a solution of poly(4-vinylpyridine), methylphenylsulfo-nium bis-(methoxycarbonyl)methylide, and carbon disulfide in chloroform for 2 days at room temperature. 

Ried and Bopp76 have shown that the photolysis of 3,5-diphenyl-4H-thiopyran-4-one 1,1-dioxide (58) in chloroform very rapidly leads to a trimer, or to photoadducts with... 

El-Agamey, A., M. Burke, R. Edge et al. 2005. Photolysis of carotenoids in chloroform Enhanced yields of carotenoid radical cations in the presence of a tryptophan ester. Rad. Phys. Chem. 72 341-345. 

Skibsted and coworkers (Mortensen and Skibsted 1996) have shown that upon the laser flash photolysis of carotenoids in chloroform bleaching of the ground state absorption is observed and there is formation of two near infrared-absorbing species ()tmax 920 and lOOOnm for 0-CAR). The species absorbing at about lOOOnm is 0-CAR + and, as with the carotenoid/CCl302 system noted earlier, the 0-CAR,+ is formed from the other species. The nature of the other species is not defined although an adduct or a neutral carotenoid radical is proposed. 

Organic arsenic species can be rendered reactive either by photolysis with ultraviolet radiation or by oxidation with potassium permanganate or a mixture of nitric acid and sulfuric acids. Arsenic (V) can be determined separately from total inorganic arsenic after extracting arsenic (III) as its pyrrolidine dithiocarbamate into chloroform [15]. 

Clomiphene citrate is used as a mixture of E (58) and Z (60) isomers to treat infertility. Photolysis of a chloroform solution with a high-pressure mercury lamp gave the expected phenanthrenes (59) and (61), which were separated and identified by GC-MS. Study of the separate isomers (58) and (60) indicated that rapid cis-trans photoisomerization preceded ring closure so that each gave a mixture of phenanthrenes (60) and (61) (Scheme 2.2) [52],... 

The hypotensive and sedative drug reserpine (256) has long been known to decompose in daylight. The photolysis has been studied in aqueous solution under a mercury discharge tube [ 159] and in chloroform at 360-370 nm [ 160]. The conclusions were essentially the same. The derivatives detected were isoreserpine (the C-3 epimer of reserpine), 3,4-dehydroreserpine (257) and lumireserpine which was shown to be 3,4,5,6-tetradehydroreserpine (258). 

Photolysis of benzofurazan N-oxide 292 in chloroform generates the nitroxyl radical 393153 (equation 141), which is formed due to hydrogen abstraction from the solvent... 

Photolysis of an aqueous solution containing chloroform (314 pmol) and the catalyst [Pt(cohoid)/Ru(bpy) /MV/EDTA] yielded the following products after 15 h (mol detected) chloride ions (852), methane (265), ethylene (0.05), ethane (0.52), and unreacted chloroform (10.5) (Tan and Wang, 1987). In the troposphere, photolysis of chloroform via OH radicals may yield formyl chloride, carbon monoxide, hydrogen chloride, and phosgene as the principal products (Spence et al., 1976). Phosgene is hydrolyzed readily to hydrogen chloride and carbon dioxide (Morrison and Boyd, 1971). 

In a similar way, 46 released its alcohol moiety and formed 50 in argon-saturated solvents (Scheme 29). In comparison, 47 was unreactive in solvents that do not have easily abstractable H-atoms, such as benzene and chloroform. However, photolysis of 47 in solvents such as methanol, ethanol, and toluene, which have H-atoms that can easily be abstracted, released the alcohol moiety of 47 and yielded lactone 51 (Scheme 30). The quantum yield for forming 51 was 0.02 in 2-propanol. Lactone 51 must come from intermolecular H-atom abstraction of 47 from the solvent rather than intramolecular H-atom abstraction to form photoenols. 

Aminoquinoxaline-3-thione (166) reacts with cr-chloroesters under alkaline conditions, and (2-aminoquinoxaline)thioglycollic acids (167) are obtained. With et-haloketones in the presence of alkali, ring closure takes place and quinoxalino]2,3-6] [ l,4]thiazines, such as 168 are isolated.174 Photolysis of 3-methylquinoxaline-2-thione in ethanol or chloroform yields 3-methyl-2-quinoxalyl disulfide.175... 

Photolysis of Pt02(PPh3)2 in a nitrogen-saturated chloroform solution results in dissociation of singlet oxygen (equation 452).1548... 

Large (20-85 mg) single crystals of diester 1 were grown by slow evaporation and were photolyzed by the output from a Molectron UV-22 nitrogen laser (337 nm, 330 mW). The optical activity produced in each photolysis was determined by dissolving the sample in chloroform and measuring its [a]D values. 

Kormann, C., Bahnemann, D.W., and Hoffmann, M.R., Photolysis of chloroform and other organic molecules in aqueous TiOz suspensions, Environ. Sci. Technol., 25, 494, 1991. 

---