Propyl photolysis

As mentioned briefly in Chapter 5, the photodimerization of acenaphthylene is subject to a very interesting heavy-atom solvent effect. The results of the photolysis of acenaphthylene in some heavy-atom solvents are given in Table 10.6.<4a) The data in Table 10.6 show that the heavy-atom solvents n-propyl bromide and ethyl iodide yield product ratios similar to that obtained in the sensitized photolysis, indicating a greater role of the triplet state in... 

In order to determine the sensitivity of coumarin dimerization to heavy-atom perturbation, the direct photolysis was carried out in butyl chloride, propyl bromide, and ethyl iodide. Comparison of these results with those obtained in nonpolar solvents indicated that there was no significant change in the amount of the triplet-derived product (80) formed in the heavy-atom solvents as would be expected if heavy-atom perturbation were important.<90) More recent investigations,<93W however, of the formation of (79) in carbon tetrachloride indicate that halocarbon enhancement of the formation of this isomer exists. A direct measure of the intersystem quantum... 

UV Spectra Observations for Photolysis of Propyl N-o-Tolyl Carbamate (2a)a... 

A series of symmetrically 1,3-disubstituted 2-propyl radicals was generated by photolysis of a mixture of a Group 14 substituted olefin and the corresponding Group 14 hydride, as illustrated in reaction 18. The structures of these radicals were then investigated using E.S.R. measurements. 

Preparative Photolysis. The preparative photolysis of an aqueous solution (pH=8.5) of AETSAPPE (2.5 M) was conducted in a 1-inch diameter quartz test tube in a Rayonet Reactor (Southern New England Radiation Co.) fitted with 254 nm lamps. Within two hours the solution gelled and the reaction was terminated. Upon acidification the solution cleared, and the product could be re-precipitated by addition of base. This indicates loss of the thiosulfate functionality. The product was dissolved in dilute HC1, precipitated with acetone, and filtered. This process was repeated three times, and the final precipitate was washed with water. The product (20 to 30 mg) was dried in vacuo for 24 hours and stored in a dessicator until use. Comparison of the13 C NMR spectrum of the product with the starting AETSAPPE 13C NMR spectrum clearly shows that the thiosulfate methylene peak shifted upfield, from 39 ppm to 35 ppm. The complete 13 C NMR and IR analysis of the product were consistent with the disulfide product. Further, elemental analysis of the product confirmed that the product was the desired disulfide product 2-amino (2-hydroxy 3-(phenyl ether) propyl) ethyl disulfide (AHPEPED) Expected C 58.39, H 7.08, N 6.20, S 14.18 actual C 58.26, H 7.22, N 6.06, S 14.28. 

Photolysis of Hvdroxy-3-faminoethane thiosulfuric add) propyl phenyl ether (AETSAPPEt. AETSAPPE possesses identical functionality to the thiosulfate group in PATE, but being only monofunctional, AETSAPPE is incapable of forming insoluble polymer upon photolysis. As a result, the reaction products should remain soluble in typical organic solvents, making separation and identification of products possible. 

Preparative photolysis of AETSAPPE (0.25 M aqueous solution) at 254 nm (Rayonet reactor) resulted in the formation of the disulfide product 2-amino(2-hydroxy-3-(phenyl ether) propyl) ether disulfide (AHPEPED) as the primary photoproduct Photolysis of AETSAPPE at 254 nm (isolated line of medium pressure mercury lamp) resulted in rapid initial loss of starting material accompanied by formation (analyzed by HPLC) of AHPEPED (Figure 12a and 12b) (Scheme IV). Similar results were obtained for photolysis- at 280 nm. Quantum yields for disappearance of AETSAPPE and formation of AHPEPED at 254 nm and 280 nm are given in Table I. The photolytic decomposition of AETSAPPE in water was also accomplished by sensitization ( x =366 nm) with (4-benzoylbenzyl) trimethylammonium chloride (BTC), a water soluble benzophenone type triplet sensitizer. The quantum yield for the sensitized disappearance (Table I) is comparable to the results for direct photolysis (unfortunately, due to experimental complications we did not measure the quantum yield for AHPEPED formation). These results indicate that direct photolysis of AETSAPPE probably proceeds from a triplet state. 

When trifluralin was released in the atmosphere on a sunny day, it was rapidly converted to the photochemical 2,6-dinitro-7V-propyl-a,a,a-trifluoro-/ -toluidine. The estimated half-life is 20 min (Woodrow et ah, 1978). The vapor-phase photolysis of trifluralin was studied in the laboratory using a photoreactor, which simulated sunlight conditions (Soderquist et al., 1975). Vapor-phase photoproducts of trifluralin were identified as 2,6-dinitro-Wpropyl-a,a,a-trifluoro-p-toluidine, 2,6 dinitro-a,a,a-trifluoro-jo toluidine, 2-ethyT7-nitro-l-propyl-5-(trifluoromethyl)benzimidaz-ole, 2 ethyT7-nitro-5-(trifluoromethyl)benzimidazole, and four benzimidazole precursors, reported by Leitis and Crosby (1974). Similar photoproducts were also identified in air above both bare surface treated soil and soil incorporated fields (Soderquist et al., 1975). 

The quantum yields and G values of H2 elimination for a larger group of alkanes are eolleeted in Table 4 the values were mostly determined by using Eq. (10). Because in the photolysis and radiolysis of the -alkanes shown in the table various kinds of radicals are produced simultaneously (e.g., -propyl and ec-propyl from propane), the weighted averages of several k /kc values were used in Eq. (10). The ratios can be determined by suppressing the radiolytic alkene and dimer yields in the presence of radical scavenger (e.g., I2) ... 

While the relative importance of the various paths is not well established, it is expected that dissociation to the alkoxy radical, RO, and N02 will predominate. Luke et al. (1989) experimentally measured rates of photolysis of simple alkyl nitrates and compared them to rates calculated using the procedures outlined in Chapter 3.C.2. Figure 4.22 compares the experimentally determined values of the photolysis rate constants (kp) for ethyl and n-propyl nitrate with the values calculated assuming a quantum yield for photodissociation of unity. The good agreement suggests that the quantum yield for photodissociation of the alkyl nitrates indeed approaches 1.0. 

FIGURE 4.22 Experimental values of the photolysis rate constant, kp, for (a) ethyl nitrate and (b) n-propyl nitrate as a function of zenith angle compared to calculated values shown by the solid lines. Different symbols represent different measurement days (adapted from Luke et al., 1989). 

Photolysis of JV-aryl amides of /3-ketocarboxylic acids 135 proceeds in a different way.93 Thus, phenylisocyanate 136 is formed in 60% yield when in 135 R = phenyl. When R = methyl or propyl, the yield decreases to 18%. Consequently, this reaction belongs only formally to the scope of the discussed rearrangements. It seems that this is a special example of Norrish Type II reaction.324 This assumption is supported by the yield dependence of... 

Intramolecular abstraction of hydrogen by the intermediate alkoxy radical B to furnish the alkyl radical C always takes place through a six-membered transition state. In the photolysis of organic nitrites, no exception to this rule of six has been recorded to date. Thus, photolysis of 3-phenyl-l-propyl nitrite does not yield any product corresponding to attack on the a-carbon through a five-membered transition state (90), although abstraction of such a hydrogen should be exothermic to the extent of ca. 25 kcal./mole. 3 Also, irradiation of 5-phenyl-l-pentyl... 

Photolysis of 1 -benzyl- 1-methylsilacyclobutane, which proceeds via rearrangement to an isotoluene intermediate followed by ring opening, produces l-propyl-l-methyl-2,3-benzosilacyclobutene in quantitative yield <2000CJC1459>. 

An improved synthesis7 of aldosterone acetate lb was based on the readily available dienone 30. Conversion to the nitrite and photolysis affords the oxime 31 with no attack on C19. On warming in iso-propyl alcohol this oxime 31, cyclized smoothly to the nitrone 32 with the loss of water. This nitrone is at the right oxidation level to rearrange to the 21-acetoxyimine. The overall yield of nitrone from 30 was 55%. 

Thermal decomposition of butane involves the unimolecular decomposition of sec- and n-butyl radicals as chain carrier steps, but little quantitative information can be obtained from the work. The best estimation of the A factor for the thermal decomposition of butyl radical is based on the high-temperature photolysis of 2-methylbutanal and has the value, log A — 15.32.64 Corresponding values for w-propyl radicals2 were 15.3655 and 13.9.62 In view of the complexity of these experimental systems, these compare reasonably with the value of 14.35 in Table XX. 

In an attempt to detect alkyl radicals spectroscopically, Thrush168 carried out the flash photolysis of ethyl, propyl, and isopropyl iodides... 

A study of chemically induced dynamic electron polarization, CIDEP (see Section 12.3.3) on F and G pairs of radicals formed under photolysis of a common termo- and photoinitiator 2,2 -azobis(2-methylpropionitrile) (AIBN) led to a tentative conclusion that initial spatial separation of 2-cyano-2-propyl radicals does not depend upon viscosity However, it is plausible that the diamagnetic dinitrogen molecule formed under photolysis of AIBN (and is invisible by ESR) separates further from a contact RP under photolysis in solvents of lower viscosity. The problem of initial spatial separation and mutual orientation ofradicals under photolysis still waits experimental elucidation. 

The data shown in Scheme 12.7 confirm that addition of (substituted) benzoyl radicals is slower than that of counter radicals (Scheme 12.7b), and therefore the benzoyl adducts have weak signals in the TR ESR spectra. A similar conclusion was obtained by FT TR ESR study of the photolysis of IRG2959 in the presence of NBA (Schemes 12.1 and 12.3)." ° ESR signals of two products of photolysis of IRG2959, namely, 2-hydroxy-2-propyl radical and substimted benzoyl radical, demonstrate quite different time dependences in the presence of acrylate. The signal of 2-hydroxy-2-propyl radical disappears faster with an increase in acrylate concentration, whereas benzoyl radical is practically unaffected by the presence of acrylate in concentrations up to 0.1 M." ° However, one can obtain only estimations of kinetic rate constants A add... 

The same question arises in photolysis of benzo-bicyclo[2.2.2]octadienediones (77) which are summarized in Table 5. In all cases where long wavelength light was used at room temperature, a new maximum at about 500 nm was observed. As with 73, intensity of this maximum built up to a low level at the beginning of irradiation, remained constant, and finally decreased. The simplest explanation for the results is that isomerization of 77 to cyclobutanedione 78 competes with direct bisdecarbonyla-tion to naphthalene (79). This is supported by an nmr-study 61> in which it was shown that, within the limits of sensitivity of the method, naphthalene (R = n-propyl) was... 

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