2-Propanol, photochemical reaction with

The dimerization of ketones to 1,2-diols can also be accomplished photochemi-cally indeed, this is one of the most common photochemical reactions. The substrate, which is usually a diaryl or aryl alkyl ketone (though a few aromatic aldehydes and dialkyl ketones have been dimerized), is irradiated with UV light in the presence of a hydrogen donor such as isopropyl alcohol, toluene, or an amine. In the case of benzophenone, irradiated in the presence of 2-propanol, the ketone molecule initially undergoes n — k excitation, and the singlet species thus formed crosses to the T, state with a very high efficiency. 

Arylpropanediones (except o-tolyl) were photochemically inert in benzene solution but underwent photopinacolization and photoaddition in 2-propanol n4>. Reactions occurred at the carbonyl group adjacent to the aromatic ring as has also been observed with 1,2-indanediones 115). 

There are some differences in the photochemical reactions of 91a and 91b and alkenes when the acetonitrile solvent is replaced by other solvents such as alcohols, ethyl acetate and chlorinated hydrocarbons. These include (1) a change in the product ratio, (2) a change in the reaction quantum yield and (3) the formation of new products by trapping solvent molecules. For example, irradiation of 91b with 1-hexene in methanol gives the methoxyalkyl)anilines 104 and 105 (equation 37) rather than 100b and 101b. It should be noted that with all of the alcohols tested (i.e. methanol, 2-propanol, terf-butyl alcohol and TFE) the alkoxyaniline 106 is formed at most in trace amounts. 

The photoreductive dimerization of aromatic ketones with i-propanol acting as reducing agent (whereby it is oxidized to acetone) is an example of the involvement of a reactive ground state produced by a photochemical reaction ... 

In the literature, only a few examples of a univariate calibration and analysis applied to a microreaction process can be found. For example, Lu et al. described the UV spectroscopic monitoring of the photochemical reaction of benzophenone with 2-propanol to form benzopinacol [18]. In this case, the analytical system was calibrated using an external non-reactive standard. A peak decrease between 320... 

Maleimide. Maleimide and maleic anhydride are simple olefins and very useful molecules in organic syntheses for introducing various substituents. Addition reactions, cyclodimerization, Diels-Alder reactions and polymerization reactions are as well-known as their photochemical reactions. They are also known as electron acceptors in photoinduced electron-transfer reactions. The photosensitized reaction of maleimide with xanthone in 2-propanol has been investigated by TR EPR. The emissive CIDEP spectrum observed in 2-propanol is predominantly assigned to two kinds of maleimide alkyl-type radicals. On the other hand, the absorptive spectrum of the maleimide radical-anion was observed in 2-propanol in the presence of hydrochloric acid. The hydrochloric acid addition effect on the CIDEP patterns indicates the existence of two mechanisms for the photosensitization of maleimide by xanthone. One is a T-T energy transfer to maleimide followed by hydrogen abstraction by maleimide... 

The photochemical reaction of a-iodocycloalkanones 1 to 7 in methanol, brought about by irradiation with a high-pressure mercury lamp at room temperature, afforded predominantly photocleavage products, methyl CO,CO-dimethoxyalkanoates Ic to 10c, in good yields. These reactions did not occur under the same conditions in the absence of light. Similarly, the reaction of a-iodocyclododecanone 6 in ethanol, 1-propanol, and 2-propanol yielded the corresponding (0,(B-dialkoxyalkanoates. These results are summarized in Scheme 2 and Table 56.1. 

The photochemical and y-ray-induced reactions of purines and purine nucleosides with 2-propanol lead to substitution of C(CH3).20H... 

Steenken S, Jovanovic SV, Candeias LP, Reynisson J (2001) Is frank" DNA-stand breakage via the guanine radical thermodynamically and sterically possible Chem Eur J 7 2829-2833 Steinmaus H, Rosenthal I, Elad D (1969) Photochemical and y-ray-induced reactions of purines and purine nucleosides with 2-propanol. J Am Chem Soc 91 4921-4923 Steinmaus H, Rosenthal I, Elad D (1971) Light- and y-ray-induced reactions of purines and purine nucleosides with alcohols. J Org Chem 36 3594-3598 Stelter L, von Sonntag C, Schulte-Frohlinde D (1974) Radiation chemistry of DNA-model compounds, V. Phosphate elimination from ribose-5-phosphate after OH radical attack at C-4. Int J Radiat Biol 25 515-519... 

The chlorine atom in 4-chloropyridine can be replaced photochemically by the dimethyl ketyl radical755. Irradiation of 4-chloropyridine in a 4 1 mixture of 2-propanol and water gives a low yield (2%) of 2-(4 -pyridyl)-2-propanol. Sensitization by benzophenone increases the yield to 25%, but the product is now accompanied by 6% of diphenyl-(4-pyridyl)methanol. The major product is believed to be formed via hydrogen abstraction from 2-propanol by photoexcited pyridine. Protonated pyridines do not undergo this abstraction process, and accordingly the product yield decreases under acidic conditions. The radical (259) formed from the pyridine will combine (at position 4) with the dimethyl ketyl radical (260) and elimination of HC1 from the adduct (261) completes the reaction (equation 194). 

In the case of photolysis of acidic aqueous solutions of Eu2+ ion at 366 nm, the excited state results from 4f —> 5d transitions localized on the metal centre. These excited states have also considerable MLCT character because of strong mixing of metal 5d orbitals with ligand orbitals. In the case of the reaction of Eu3+ with H2 which occurs on photolysis at 254 nm, the photo reaction is due to the formation of an LMCT excited state. This process has been successfully used in the photochemical separation of Eu from other members of the lanthanides because Eu2+ is the only member of the lanthanide series which is at suitably low energy that an LMCT state is accessible [98]. Yb3+ and Sm3+ ions behave in a similar fashion to Eu3+ as far as their photochemical behaviour is concerned. Aqueous solutions of Sm3+ or Yb3+ containing 2-propanol on photolysis at 185 nm give hydrogen and acetone as products probably by a mechanism similar to Eu3+ ion. 

Other approaches for insolubilization have been proposed by Francotte more stable CSPs could be obtained by cross-linking polysaccharide derivatives photochemical I y initiated ] 163] or thermally initiated ] 164] (Tables 9.5 and 9.6) using a radical reaction. The new CSPs exhibited improved separations for many racemates, predominantly through the ability to use chloroform and other co-solvents. Further, compounds that were insoluble in the commonly used /)-heptane-2-propanol eluents could be easily separated into individual enantiomers, and for many enantioseparations run times can be reduced with chloroform, ethyl acetate or THF containing mobile phases. These improved CSPs are about to be commercialized. 

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. 

Photoinduced electron transfer is a subject characterised, particularly at the present time, by papers with a strongly theoretical content. Solvent relaxation and electron back transfer following photoinduced electron transfer in an ensemble of randomly distributed donors and acceptors, germinate recombination and spatial diffusion a comparison of theoretical models for forward and back electron transfer, rate of translational modes on dynamic solvent effects, forward and reverse transfer in nonadiabatic systems, and a theory of photoinduced twisting dynamics in polar solvents has been applied to the archetypal dimethylaminobenzonitrile in propanol at low temperatures have all been subjects of very detailed study. The last system cited provides an extended model for dual fluorescence in which the effect of the time dependence of the solvent response is taken into account. The mechanism photochemical initiation of reactions involving electron transfer, with particular reference to biological systems, has been discussed by Cusanovich. ... 

Jensen and coworkers [25] demonstrated the photochemical synthesis of benzo-pinacol (Scheme 6.9) within a sUicon/quartz microreactor (channel dimensions 500 pm wide x 250 pm deep), which enabled UV light to pass through the quartz layer and irradiate the reaction mixture contained within the microchannel network. Employing on-line UV analysis, they were able to assess the reaction progress rapidly and with ease. Preliminary investigations conducted at flow rates of >10.0 pi min showed no benzopinacol formation. Only recovery of the unreacted starting materials benzophenone and 2-propanol was observed. By reducing the flow rate to... 

These osmium(VI) complexes, along with the ruthenium(VI) complex trans-[Ru02(L)] (L = m t>-l,2,6,10,ll-pentamethyl-2,6,10-triaza[ll]-(2,6)-pyridino-phane) can be used for the photochemical oxidation of hydrocarbons. The reaction has been used for the oxidation of 2-propanol to acetone, of both benzyl alcohol and toluene to benzaldehyde, of cyclohexane to both cyclohexanol and cyclohexanone, and of the epoxidation of cyclohexene, fran -stilbene, and norbomene. 

---