Methanol, irradiation

The ESR spectrum obtained for irradiated methanol solution of 1,3-butadiene or cis-... 

The natural lifetime of the solvated electron in the alcohols has not yet been determined. The half-times have been reported (28) for the electron in irradiated methanol, ethanol, 1-propanol, and 2-propanol, without any additives, as ranging from 1.5 /zsec. to 5 /xsec. However, these values are likely to be very much lower than the true natural lifetimes since the observed rate curves included reaction with the counter ion, molecular products, and trace impurities which may be present. No evidence has been obtained for the reaction ... 

In the presence of 1M trifluoroacetic acid, formation of the 2 1 adducts was totally suppressed, but no phenylsuccinimides were detected. The authors also studied the effect of the addition of methanol. It was found that upon unfiltered irradiation, methanol greatly promotes formation of the adduct resulting from initial 1,2-addition to anisole. The ratio of l,2- 2,3- 3,4-addition changed from 10 10 1 in the absence of methanol to 30 10 1 in the presence of 1M methanol and 60 10 1 with 10 M methanol. This selective effect was not observed on irradiation exclusively in the charge-transfer band. The authors conclude that the 1,2-addition favored with anisole arises from the presence of the oxygen atom, with its... 

Whereas the radical anion formed from l-methyl-2(thiomethyl)imidazole has a 7r SOMO, 4-bromo- and 4-iodo-2-methylimidazole, 5-bromo- and 5-iodo-l,2-dimethylimi-dazole and 4,5-dibromo- and 4,5-di-iodo-l,2-dimethylimidazole form cr radical anions in irradiated methanol or MeTHF solutions at 77 K251. 

The ESR spectrum obtained for irradiated methanol solution of 1,3-butadiene or cis-1,3-pentadiene is similar to that of irradiated methanol solution of allyl chloride, in which case it is known that the electron leads to reductive dehalogenation (equation 24). 

Experimental details.12 9 A solution of 457 (0.74 mmol) and triethylamine (2 mmol) in methanol was purged with nitrogen for 1 h and irradiated in a Rayonet photochemical chamber equipped with 16 low-pressure mercury discharge lamps (254nm) (Figure 3.10) for 12h. After irradiation, methanol was distilled off under reduced pressure and the product was purified by column chromatography in 90% chemical yield. 

I. A. Werner, H. Altorfer, mid X. Perlia, The effectiveness of various scavengers on the ganma-irradiated, methanolic solution of medazepam, Int. J. Pharm. 63, 155-166(1990). 

Preparation of samples for MS analysis The irradiated methanol solutions were concentrated and applied as bands to TLC plates. After development, the bands corresponding to the samples were scraped off, extracted with methanol, and taken to dryness. The residues were submitted to MS analysis. 

Fig. 4.21 EPR spectra of radicals trapped by DMPO in P25 and P25 + 0.5 % GR dispersions, (a) DMPO-O2 formed in irradiated methanol dispersions (b) DMPO- OH framed in irradiated aqueous dispersions (Reprinted with permission from Ref. [73] Copyright 2010, American Chemical Society), (c) and (d), EPR spectra of superoxide radical species trapped by DMPO in Ti02-5 % GR and Ti02-5 % CNT dispersions in BTF solvent under visible light irradiation (Reprinted with permission from Ref. [5] Copyright 2011, American Chemical Society)...

Pyridazin-3(2H)-ones rearrange to l-amino-3-pyrrolin-2-ones (29) and (30) upon irradiation in neutral methanol (Scheme 10), while photolysis of 5-amino-4-chloro-2-phenylpyridazin-3(2H)-one gives the intermediate (31) which cyclizes readily to the bis-pyridazinopyrazine derivative (32 Scheme 11). 

In some instances the solvents may react with the substrate during the irradiation. For example, 3,6-dichIoropyridazine, when irradiated in acidified methanol, gives a mixture of raonoraethylated (56), dimethylated (57) and hydroxyraethylated (58) compounds. Further transformation of the hydroxymethyl compound (58) results in the formation of y-Iactones (59) and succinates (60 Scheme 20). 

There is a scattered body of data in the literature on ordinary photochemical reactions in the pyrimidine and quinazoline series in most cases the mechanisms are unclear. For example, UV irradiation of 4-aminopyrimidine-5-carbonitrile (109 R=H) in methanolic hydrogen chloride gives the 2,6-dimethyl derivative (109 R = Me) in good yield the 5-aminomethyl analogue is made similarly (68T5861). Another random example is the irradiation of 4,6-diphenylpyrimidine 1-oxide in methanol to give 2-methoxy-4,6-diphenyl-pyrimidine, probably by addition of methanol to an intermediate oxaziridine (110) followed by dehydration (76JCS(P1)1202). 

A -Bridgehead compounds have been obtained from the photochemical cyclization of cfi-1-styrylimidazoles. For example, irradiation of the imidazole (532) in methanol in the presence of I2 resulted in cyclization at the 2-position of the imidazole ring with the formation of an imidazo[2,l-a]isoquinoline (533) (76JCS(Pl)75). Isomerization of the trans-to the c/i-styrylimidazole was followed by photodehydrocyclization, trans- 1-Styrylbenzimidazole (534) was isomerized under Pyrex-filtered light in the presence of one molar equivalent of I2. The resulting cis isomer on irradiation through quartz gave the benzimidazo[2,l-a]isoquinoline (535) in 53% yield. 

The photolysis of 4-substituted 2,3-dimethyl-3-isoxazolin-5-ones has been studied. Irradiation in methanol or ethanol with a 100 W high-pressure mercury lamp through a Pyrex filter of a 4-phenylthio compound produced a semithioacetal (Scheme 5). In contrast, an H, Cl or OPh moiety gave no reaction. The use of alkylthio substitution gave similar products. Cyclic compounds yielded cyclic products (Scheme 5), and the photolysis of (29) in benzene... 

Certain substituted o-nitrotoluenes can be induced to cyclize, forming 2,1-benzisoxazoles. Bis(2-nitrophenyl)methane when irradiated gave 3-(o-nitrophenyl)-2,l-benzisoxazole. The possible intermediates including a biradical were discussed (74TL4359). 3-(o-Nitrophenyl)-2,1-benzisoxazole was prepared by the acid cyclization of bis(2-nitrophenyl)methanol (Scheme 178) (65RRC1035>. 

In contrast to the behavior observed for (99), irradiation of a methanol solution of l-(2,4,6-trinitrophenyl)-2,3-diphenylaziridine (101) affords 1-hydroxy-4,6-dinitrobenz-imidazole (102) and benzaldehyde (68TL4801). 

The dlenophlle, 3-acetyl-2(3H)-oxazolane, Is an attractive Intermediate for the synthesis of vicinal aminoalcohols with cIs configurations. It reacts with 1,3-dienes, even under quite mild conditions, to form (4+2) cycloadducts. Its high reactivity with deactivated 1,3-dienes Is noteworthy. This property is present also in 2(3H)-oxa201one which can be obtained easily through solvolysis of 3-acetyl-2(3H)-oxa2olone In methanol. 3-Acetyl-2(3H)-oxazolone, on UV irradiation In the presence of a sensitizer, combines easily with olefins to form (2+2) cycloadducts, the hydrolysis of which leads to the class of cis-2-aminocyclobutanols. 

Depending on the electronic state of azafulvalene and the reaction conditions, simple nucleophiles such as amines or alcohols show a different behavior. Upon heating methanol reacted with azafulvalenes as electron-rich olefins by addition to the central double bond (64BSF2857 67LA155). Using the TAF 77 (Ar = Ph), the addition reaction in a neutral benzene-ethanol solution required several days to obtain a minor amount of 147, while the reaction proceeded rapidly in the presence of a catalytic amount of potassium hydroxide (79JOC1241). Tlie yellow-colored adduct 147 can be reconverted to the quinoid starting material by irradiation (Scheme 58). 

Irradiation of a methanolic solution of 3-acylaminofurazans 185 at X = 310 nm in the presence of ammonia or primary or secondary amines produced excellent yields (70-95%) of 3-(R-amino)-5-R -l,2,4-oxadiazoles 186 (Scheme 117) (95S917). Similar results were obtained by irradiation of 3-aroylaminofurazans in the presence of pyrrolidine at X = 254 nm (92AP151). 

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