Acetone sensitivity

Not all air-inhibited surfaces can be detected by the Barcol hardness tests. It is recommended that the acetone sensitivity test should also be used, where appropriate. This involves application of a small amount of acetone to the resin surface. The wetted surface is then rubbed lightly with the finger until the acetone has evaporated. If the surface softens or becomes tacky, the resin has not fully cured. 

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Acetone sensitization provided semibullvalene (38) while direct photolysis gave cyclooctatetraene (39). Several structural representations of semibullvalene are shown below ... 

Thus Saltiel has concluded that the small increase in [T]S/[C], in going from benzene to acetone indicates that a mixed mechanism is operative for acetone-sensitized isomerization, that is, both triplet energy transfer and, to a minor extent, Schenck intermediates are involved. When acetophenone or benzophenone is used as a sensitizer the pss is close to the thermodynamic... 

The acetone-sensitized photodehydrochlorination of 1,4-dichlorobutane is not suppressed by triplet quenchers (20), but the fluorescence of the sensitizer is quenched by the alkyl chloride (13). These observations imply the operation of a mechanism involving collisional deactivation, by the substrate, of the acetone excited singlet state (13,21). This type of mechanism has received strong support from another study in which the fluorescence of acetone and 2-butanone was found to be quenched by several alkyl and benzyl chlorides (24). The detailed mechanism for alkanone sensitization proposed on the basis of the latter work invokes a charge-transfer (singlet ketone)-substrate exciplex (24) and is similar to one of the mechanisms that has been suggested (15) for sensitization by ketone triplets (cf. Equations 4 and 5). 

Reports of [ 2 + 2] cycloaddition of nitrogen containing heterocycles to alkenes are so numerous that attention can be drawn here to only a few. Recent examples include the acetone-sensitized photoaddition of 4-oxazolin-2-one (248) to ethylene to give the cis-adduct 249,203 the photocycloadditions of N-substituted imidazoles to acrylonitrile204 and of N-methyl-4-hydroxy-quinol-2-one to cyclohexene,205 and the photoaddition of pentafluoro-pyridine to ethylene to give the 1 1- and 1 2-adducts 250 and 251,... 

Choudhry, G.G. and Hutzinger, 0. Acetone-sensitized andnonsensitizedphotolysesoftetra-, penta-, and hexachlorobenzenes in acetonitrile-water mixtures photoisomerization and formation of several products including polychlorobiphenyls, Environ. Sci. Technol, 18(4) 235-241, 1984. 

Acetone-sensitized [2+2]-photocycloaddition of 2(3//)-oxazolones 247a to maleic anhydride and dimethylmaleic anhydride gives the corresponding anti-cyclobutane cycloadducts 253 as the major products. Similar photoreaction of 2(37/)-oxazolones with 1,6-anhydro-4-(9-benzyl-2,3-dideoxy- 3-D-e 7t/ira-2-hex-enopyranose 254 results in the exclusive formation of the anh-cyclobutane-type adduct 255 (Fig. 5.61). ... 

Direct flash excitation (>400 nm) or the triplet-acetone-sensitization of nitrosamide X in degassed water or benzene solutions gives the amidyl radical transient exhibiting lax 335-350 nm. This transient is not observed with undegassed solution of X, indicating that oxygen has intercepted the precursor of the amidyl radical at least, with the diffusion controlled rate... 

Other systems for which the results cannot be explained by energy transfer include the ketone sensitized isomerization of / -methylstyrene, 1,2-dichloro-ethylene and 2-butene studied by Caldwell,147,148 deuterium exchange between acetone-d8 and tetramethylethylene reported by Japar, Pomerantz, and Abrahamson,149 and the acetone sensitized isomerization of 1-methoxy-l-butene examined by Turro and Wriede.71... 

Acetone sensitized irradiation of the. y ,st>/-biscyc opentadienequinonc adduct 11 affords the cage compound 12 (a heptacyclic dione) in 60% yield which was further converted to 1,4-... 

Similarly, acetone sensitized irradiation of the epoxy tetraene 13 resulted in ring closure to the caged epoxide M.171... 

Photocyclodimerizations have also been applied to the synthesis of cage compounds.47 Thus, acetone sensitized irradiation of pentacyclo[6.6.0.02 12.03 6.07-11]tetradeca-4,9,13-triene (24) affords heptacyclo[6.6.0.02 7.03,6.04,14.05 9.010,13]tetradec-l l-ene (25)48 and direct irradiation of l,4,5,8-tetrahydronaphthalene-2,3-dicarboxylic anhydride in dioxane yields four isomeric double tetraasteranes (nonacyclo[10.8.0.02 11.04,9.04 19.06-17.07,1< 0914.014 19]eicosan).49... 

Photodimerization of thymin to butane type dimers is one of the important causes of UV radiation damage to genetic material DNA in its native double helix form. The reaction occur from the triplet state as confirmed by acetone sensitized photodimerization of thymine. These dimers can be monomerized when irradiated by short wavelength radiations. which are absorbed by the dimer only. 

Cundall has done extensive work on benzene231,237 and acetone243 sensitized isomerizations of the 2-butenes, and in every case reported a photostationary or radiostationary trans/cis ratio of 1.27-1.37. Sato, however, has measured a value of unity for the benzene photosensitized isomerization.510 With higher homologs, from 2-pentene to 2-octene, benzene-sensitized isomerizations yield trans/cis ratios of 1.0,238 while acetone-sensitized isomerization of the 2-pentenes in solution yields a ratio of 1.65.244 At present no explanation is possible for the differences between 2-butene and 2-pentene. Until much more information is gathered relating to rates of triplet energy transfer as functions of olefin structure, sensitizer, and medium, the natural decay ratios of each olefin s common triplet cannot be deduced from photostationary trans/cis ratios. 

The acetone-sensitized photolysis of Thy in the presence of l-cysteine (R = cys-teinyl), yields mainly 5-S-L-cysteinyl-5,6-dihydrothymine (see above), but also minor amounts of 5-S-L-cysteinylmethyluracil and 5-S-L-cysteinylmethyl-5,6-dihydrouracil are formed (Shetlar and Horn 1987 for an earlier study see Var-ghese 1973). 

Gorner H (1993) Acetone-sensitized photolysis of 5-iodouracil and 5-iodouridine in aqueous solution in the presence of alcohols free radical chain mechanism. J Photochem Photobiol A Chem 72 197-208... 

Shetlar MD, Horn K (1987) Mixed products of thymine and cysteine produced by direct and acetone-sensitized photoreactions. Photochem Photobiol 45 703-712 Sheu C, Foote CS (1995a) Reactivity toward singlet oxygen of a 7,8-dihydro-8-oxoguanosine ( 8-hydroxyguanosine ) formed by photooxidation of a guanosine derivative. J Am Chem Soc 117 6439-6442... 

To prevent the meta photocycloaddition, the use of rigid face-to-face skeletons is also an effective strategy. Acetone-sensitized excitation of 208 gave only 209 reversibly [262-264] reactions of 210 and 211 gave similar results [265,266] (Scheme 61). X-ray analysis of 210 showed the distance of the aromatic carbons which react is 3.04 A [263],... 

Prinzbach and co-workers studied the photocycloaddition of a rigid compound in which naphthalene and alkene were placed [294], Distances between naphthyl (3-carbons and olefinic carbons of 272 are 2.911 and 2.944 A. Direct or acetone-sensitized photoexcitation induced an efficient meta addition to the naphthalene ring to give 273, the ortho addition did not occur, although it is not clear whether the ortho process occurred (Scheme 76). 

Solubility in water, 4 g/100 mL. Slightly soluble in alcohol, benzene, ethylene glycol, carbon tetrachloride, and dioxane sparingly soluble in ether and acetone. Sensitive to oxidation, moisture, and light liquefies upon loss of water of crystallization.2... 

Diazenedioxylene 91 underwent acetone-sensitized phototransformation to give an inseparable mixture of five to eight products and no compound could be assigned the expected stmcture 93 by any spectroscopic means. 

Swenton and co-workers have shown that both 6-azauracil and 6-azathymine photocycloadd with acetone sensitization to olefins to give (2 + 2)-photocycloadducts in high yield and with high regiospecificity69. 6-Azauracil has been shown to cycloadd to ethylene, tetramethylethylene, isobutylene, cyclohexene, cis- and trans-cyclooctene, ethyl vinyl ether, vinyl acetate, and isopropenyl acetate. Cis- and trans-cyclooctene give the same epimeric mixture of cycloadducts in approximately the... 

Acetone sensitized photolysis. Labeled residues identified (Havron and Sperling. 1977). 

Substituted sultams 21 undergo DPM rearrangement by acetone sensitization to give 22 in moderate yields (Scheme 4.11) [15],... 

Direct photolysis of l,l-dicyano-3,3-dimethyl-l,4,5-hexatriene 29 gives an allenyl-cyclopropane 30 via DPM rearrangement in 57% yield, while acetone-sensitization yields a hausan 31 via an intramolecular [2 + 2] cycloaddition (Scheme 4.15) [20]. 

Under acetone-sensitized conditions, an intermolecular electron transfer from the sulfur to triplet acetone has been postulated in thioalkyl-N-substituted phthalimides. Proton transfer from the terminal a-position of the sulfur, followed by C—C bond formation, efficiently leads to macrocyclization with long and flexible chains as linkers (Scheme 9.7) [9]. 

The synthesis of a variety of dihydrobenzofuranes can be accomplished via the Aryl SN1 mechanism. The acetone-sensitized irradiation of various o-chlorophenyl allyl ethers in polar solvents affords the aryl cation, which adds onto the tethered double bond following the 5-exo-trig mode leading to (dihydro)benzofurans. The reaction is solvent-dependent, and byproducts are also generally obtained. The best results are found when ethyl acetate is used. Depending on the substrate employed, the cation intermediate can yield products as a result of proton elimination or trapping by chloride ions (Scheme 10.54) [70],... 

Acetone-sensitized and unsensitized reductive dechlorination of tetra-, penta- and hexa-chlorobenzenes have been studied373,374, 1,2,4-Trichlorobenzene 125 is the major photoproduct from 1,2,3,5-tetrachlorobenzene 122 in the unsensitized process, whereas the... 

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