Alcohols photochemical reactions

The radicals are then involved in oxidations such as formation of ketones (qv) from alcohols. Similar reactions are finding value in treatment of waste streams to reduce total oxidizable carbon and thus its chemical oxygen demand. These reactions normally are conducted in aqueous acid medium at pH 1—4 to minimize the catalytic decomposition of the hydrogen peroxide. More information on metal and metal oxide-catalyzed oxidation reactions (Milas oxidations) is available (4-7) (see also Photochemical technology, photocatalysis). 

Phosphine(s), chirality of, 314 Phosphite, DNA synthesis and, 1115 oxidation of, 1116 Phospholipid, 1066-1067 classification of, 1066 Phosphopantetheine, coenzyme A from. 817 structure of, 1127 Phosphoramidite, DNA synthesis and, 1115 Phosphoranc, 720 Phosphoric acid, pKa of, 51 Phosphoric acid anhydride, 1127 Phosphorus, hybridization of, 20 Phosphorus oxychloride, alcohol dehydration with. 620-622 Phosphorus tribromide, reaction with alcohols. 344. 618 Photochemical reaction, 1181 Photolithography, 505-506 resists for, 505-506 Photon, 419 energy- of. 420 Photosynthesis, 973-974 Phthalic acid, structure of, 753 Phthalimide, Gabriel amine synthesis and, 929... 

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. 

This study demonstrates that the addition of the 2-diazopropane with the triple bond of propargyl alcohols is regioselective, and affords new antibacterial 3H-pyrazoles. The photochemical reaction of these 3H-pyrazoles selectively leads to a- and 6-hydroxy cyclopropenes. The overall transformation constitutes a simple straightforward route to substituted cyclopropenyl alcohols without initial protection of the propargyl alcohol hydroxyl group. 

It is sometimes possible to improve detection by changing the pH of the eluent, or by the use of photochemical reactions. The common barbiturates used in therapy are weak acids that are easily separated in their acid (unionised) forms. Because the conjugate bases are much stronger chromophores than the acids, barbiturates have been detected by post-column mixing with a pH 10 borate buffer followed by uv absorption at 254 nm. An example of the second approach is the detection of cannabis derivatives in body fluids involving the conversion of cannabis alcohols to fluorescent derivatives on subjecting the column effluent to intense uv radiation. 

Metallocyclopentenes are frequently formed in photochemical reactions of the Group 14 metal alkyls or catenates in the presence of dimethylbutadiene. This class of compound also has an extensive photochemistry82. For example, photolysis of 51 (R = H or Me) produced the allylic alcohols 52 and 53 and, for R = H, 54. These alcohols could be dehydrated over AI2O3 to give the germole 55 along with other diene compounds. 

Clennan, E.L., Zhang, D. and Singleton, J. (2006). A comparison of intrazeolite and solution singlet oxygen ene reactions of allylic alcohols. Photochem. Photobiol. 82, 1226-1232... 

The proposed mechanism for the photochemical cleavage of nBn ethers (see Scheme 3) involves a n tt transition of the nitrogroup and an intramolecular, benzylic hydrogen abstraction by the excited nitro group. Rearrangement leads to a hemiacetal that decomposes to a free alcohol and to 2-nitrosobenzaldehyde that undergoes further thermal and photochemical reactions. 

HCrO ] has been shown to be the photo-active species in the photochemical reaction of dilute solutions of chromium(vi) oxyacids with alcoholic reducing agents. The association of chromate with Np , Th, and Fe" in perchlorate solution has been studied spectrophotometrically and the respective formation constants, 63.6,4.70, and 1.93, have been determined. The greater stability of the Np complex has been interpreted in terms of the limited donation of 5/-electron density from Np to the d-orbitals of chromium in the chromate ion. ... 

The photochemical reactions of l,l,4,4-tetramethyl-2,3-dioxotetralin (14) have been studied in methanol, isopropyl alcohol, cyclohexane, toluene, -butyraldehyde, methyl formate, acetic acid, dioxane, and benzene.75 In isopropyl alcohol the reduced ketone (15) is formed almost exclusively, while... 

Alcohols and ethers absorb only in the short-wavelength ultraviolet region 200 nm). This makes them very useful solvents for many photochemical reactions on account of their transparency to longer-wavelength radiation, but they are reactive towards the excited states of some classes of compound such as ketones. Where such reactivity does compete with the desired processes, the choice of t-butanol, which does not contain a readily abstracted alpha-... 

Photochemical reactions of carbohydrates have been discussed.279 Therefore, only examples applicable to the synthesis of branched sugars are briefly described here. Although non-stereoselectivity and low yield are general defects of photoreactions, photoaddition of an alcohol to the enones 125 and 122a proceeded with the same stereo- and regio-selec-tivities as ionic addition ( see Section II,4,c), and in rather better yields,... 

A photochemical process consisting in the esterification, with pyru-voyl chloride,45 of the alcohol to be oxidized, followed by photochemical reaction of the ester obtained, has been applied to some thymine nucleosides.43 Derivatives (33a and 33b) of 3 -ketothymidine were prepared43 by this method. 

Photochemical reactions of alkynic ketones, e.g. l-phenylprop-2-yn-l-one (111) in alcohols gave 2,5-disubstituted furans, postulated as arising from a 1 1 adduct whose... 

Photoreduction occurs by hydrogen atom abstraction or by electron transfer. The first process is a common photochemical reaction of carbonyl derivatives and other unsaturated molecules in the presence of suitable hydrogen atom donors (which can be alcohols, paraffins, ethers, etc., that is, almost any molecule with a not-too-strong C—H bond). 

Diaryl ketones do not undergo photodissociation in the same way as alkyl ketones, probably because cleavage to phenyl and other aryl radicals is unfavorable (Table 4-6). Nevertheless, aromatic ketones are photochemically reactive in the presence of compounds that can donate a hydrogen atom, with the result that the carbonyl group is reduced. Indeed, one of the classic photochemical reactions of organic chemistry is the formation of 1,1,2,2-tetraphenyl-1,2-ethanediol (3, benzopinacol) by the action of light on a solution of diphenyl-methanone (2, benzophenone) in isopropyl alcohol. The yield is quantitative. 

The stereospecificity of methanol addition to neopentylsilenes has been investigated by Jones and Bates68. The mild thermal retro-Diels-Alder reaction (at ca 200 °C) of E and Z anthracene [4 + 2] cycloadducts 110 liberates stereospecifically the corresponding silenes 111, which are trapped by methanol. The ratio of the diastereomeric products 396a/396b coincides with the E/Z ratio of the precursors 110 (equation 117). In photochemical reactions of similar silene precursors, alcohols were used also to probe the decomposition mechanism69. 

Ekpenyong Kl, Shetlar MD (1979) Photochemical reactions of cytosine N-methyl analogs in alcoholic solutions. Photochem Photobiol 30 455-461 Elad D (1976) Photoproducts of purines. In Wang SY (ed) Photochemistry and photobiology of nucleic acids. Academic Press, New York, pp 357-380 Elad D, Rosenthal I (1969) Photochemical alkylation of caffeine with amino-acids. Chem Commun 905-906... 

Salomon J, Elad D (1973) Photochemical reactions of nucleic acid constituents. Peroxide-initiated reactions of purines with alcohols. J Org Chem 38 3420-3421 Salomon J, Elad D (1974) Ultraviolet and y-ray-induced reactions of nucleic acid constituents. Reactions of purines with amines. Photochem Photobiol 19 21-27 Samuni A, Neta P (1973) Hydroxyl radical reaction with phosphate esters and the mechanism of phosphate cleavage. J Phys Chem 77 2425-2429... 

Shaw AA, Voituriez L, Cadet J, Gregoli S, Symons MCR (1988) Identification of the products from the direct effect of y-radiation of thymidine. J Chem Soc Perkin Trans 2 1303-1307 Shetlar MD (1976) The photoreactions and free radical induced reactions of 1,3-dimethyluracil in methanol and other alcohols. Photochem Photobiol 24 315-319 Shetlar MD (1979) Photochemical and free radical initiated reactions of 1,3-dimethylthymine with isopropanol. Photochem Photobiol 29 253-259... 

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