Hydrogen yields from cyclohexane solutions

Figure 4. Hydrogen, cyclohexene, bicyclohexyl yields from molar solutions of benzene in cyclohexane...

Will the solvent react with the excited state to yield undesirable side-products Often there is a real possibility that the solvent will enter into the picture through reaction with the excited solute. A common example of this is the abstraction of hydrogen atoms from solvents by excited ketones. Several solvents often used for a preliminary examination due to their relative inertness are benzene, /-butanol, carbon disulfide, carbon tetrachloride, and cyclohexane. 

Excited molecules produced by the radiation may also transfer their energy to other substrates. The yield of hydrogen in the radiolysis of cyclohexane-benzene solutions is considerably lower than would be expected from the electron fraction of each component and the known hydrogen yields for the pure compounds125. 

The yields of hydrogen, cyclohexene, and bicyclohexyl decrease markedly on adding C02 or SF6 to cyclohexane (56, 57), and these decreases can be qualitatively accounted for in this way. The energy taken up by XY in Reaction 7 may result in formation of products derived from the solute. 

Hydrogen Halides. In an initial study of solutions of HI in cyclohexane the hydrogen yield was greater than that from the pure solvent... 

DC1 solutions in cyclohexane have recently been studied (44, 52). Data similar to those from DI solutions have been obtained but can be more easily interpreted, at least in the low concentration region, since DC1 is a relatively poor hydrogen-atom scavenger. Here too, however, the total hydrogen yield increases upon adding DC1 [as noted earlier (II, 29)]. Allowing for a contribution of this excess to the HD yield, a value of aDci -— 10 can be estimated. 

The yields of CH3 radicals from CH3Cl-cyclohexane solutions together with the corresponding hydrogen yields are shown in Table IV. In the last column, the quantity [(G(H2)0 — G(H2)Ch3ci)/G(CH3)] is evaluated and is close to unity at all concentrations. If one assumes that no more than one molecule of H2 can be produced by Reaction 16, then /" must be close to zero. Conversely, the concern expressed earlier, that f might be considerably smaller than 1, does not seem to be borne out by experimental observations for cyclohexane. 

Typical procedure. 6-N-Phthaloyl-2 -0-(9-phenylxanthen-9-yl)-5 -0-(fluoren-9-yl-metln-oxycarbonyl)adenosine 865 [628] To a solution of 864 (635 mg, 1 mmol) in dry pyridine (10 mL) was added dropwise a solution of Fmoc-Cl (336 mg, 1.3 mmol) in dry acetonitrile (5 mL). The reaction mixture was stirred for 4.5 h at room temperature and was then poured into cold, saturated sodium hydrogen carbonate solution (100 mL). The resulting mixture was extracted with chloroform (2 x 50 mL), the combined organic layers were concentrated in vacuo, and the residue was dried by co-evaporation with toluene (4 x 25 mL). It was then dissolved in dichloro-methane, and precipitation from cyclohexane gave 865 yield (717 mg, 82%) ... 

The photochemical reactions of substituted 1,2-cyclononadiene, 1-methyl-1,2-cyclononadiene 84, were also reported by Stierman and co-workers. Direct irradiation > 220 nm) of 84 in pentane solution affords seven isomers 85-91 as the primary products, along with the secondary product 92. Methyl derivative 84 seems to favor vinylcarbene intermediates, in contrast to the concerted reaction of 72. Benzene-sensitized irradiation of strained l-t-butyl-l,2-cyclooctadiene 93 affords the spiro compound 94 in the vapor phase, and irradiation (254 nm) of a dilute benzene solution of 93 yields 3-7-butylbicyclo[3.3.0]oct-2-ene 95 and 2-7-butyl-l,3-cyclooctadiene 96 in a 1 1 ratio.The difference in reactivity between the vapor phase and the solution is explained as follows the vapor-phase reaction proceeds through biradical 97, whereas selective hydrogen abstraction from C7 yields biradical 98 in solution. On the other hand, direct irradiation (254 nm) of 93 in cyclohexane solution affords five photoproducts 95, 96, and 99-101. 

Hydrogen absorption being completed, the solution was filtered and evaporated to one-fifth of its volume and cooled in a refrigerator. The precipitate was filtered, washed with water, and then crystallized from ligroin, thus yielding 4 g of 2-cyclohexyl-2-hydroxy-cyclohexane-... 

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