Cyclohexanone, photolysis

Coyle(8) has found that the ratio of aldehyde to ester increases upon a-substitution but decreases upon 0- or y-substitution. For example, the alkenal ester ratio for cyclohexanone photolysis in methanol is 1.6, that for... 

Photolysis of pyridazine IV-oxide and alkylated pyridazine IV-oxides results in deoxygenation. When this is carried out in the presence of aromatic or methylated aromatic solvents or cyclohexane, the corresponding phenols, hydroxymethyl derivatives or cyclohexanol are formed in addition to pyridazines. In the presence of cyclohexene, cyclohexene oxide and cyclohexanone are generated. 

The reaction of vinylogous amides, or ketoaldehydes, with hydroxylamine produced 4,5,6,7-tetrahydro-l,2-benzisoxazole. A side product is the 2,1-benzisoxazole (Scheme 173) (67AHC(8)277). The ring system can also be prepared by the reaction of cyclohexanone enamines with nitrile oxides (Scheme 173) (78S43, 74KGS901). Base treatment produced ring fission products and photolysis resulted in isomerization to benzoxazoles (76JOC13). 

The cyclohexanone postulated in this scheme should also be photoactive. The series of reactions necessary to produce the acetic acid observed [11] is indeed long but currently the only reasonable explanation of this product. Previous investigators [20, 21] had not reported acetic acid from the photolysis of PET even though they isolated acetaldehyde, although Day and Wiles [25] did report it. Thus, one may reasonably assume that the presence of 1,4-cyclohexandimethanol most likely is required to produce acetic acid, at least in significant amounts. 

Cyclized polyisoprene has been used as a photoresist by being sensitized with bisazides(1-3). Recently, H.Harada et al. have reported that a partially cyclized 1,2-polybutadiene showed good properties as a practical photoresist material in reproducing submicron patterns (U ). S.Shimazu et al, have studied the photochemical cleavage of 2,6-di(h -azidobenzal)cyclohexanone in a cyclized polyisoprene rubber matrix, and have reported that the principal photoreaction is the simultaneous cleavage of the both azido groups by absorption of a single photon with a U3% quantum yield(5 ). Their result does not support the biphotonic process in the photolysis of bisazide proposed by A.Reiser et al.(6 ). 

CASRN 15457-05-3 molecular formula C13H7F3N2O5 FW 328.20 Chemical/Physical. When fluorodifen as an aqueous suspension was irradiated using UV light (A, = 300 nm), 4-nitrophenol and 4-(trifluoromethyl)-2-aminophenol formed as the major products (>90% of total product formation). In addition, 4-(trifluoromethyl)-2-nitrophenol formed as a minor product (<1%) as well as 4-hydroxy-3-nitrobenzoic acid. In methanol, photolysis of fluorodifen yielded 4-nitrophenol and 2-amino-4-(trifluoromethyl)anisole. In cyclohexanone, 4-nitrophenol and 3-(trifluoromethyl)nitrobenzene were formed (Ruzo et al., 1980). 

Photolysis of 3-cyclohexyl-anhydro-5-hydroxy-l,2,3,4-oxatriazolium hydroxide (4 R = cyclo-CaH,) in the presence of water yields cyclohexanone <70CC1591>. In the absence of water,... 

Alkyl- or aryl-dibenzothiophenes are conveniently prepared from the 2-arylthio-cyclohexanones, which are readily cyclized and dehydrogenated to yield the respective 1-, 2-, 3- or 4-substituted dibenzothiophenes (382 equation 9 Section 3.15.2.3.2). More complex polycyclic systems are available, using suitable aryenethiols, such as naph-thalenethiols, and 2-bromo-l-tetralone to synthesize the appropriate 2-arylthio ketones. Diaryl sulfides can be converted to dibenzothiophene derivatives in satisfactory yields by photolysis in the presence of iodine (equation 10) (75S532). Several alkyldibenzothiophenes with substituents in the 2- and/or 3-positions were prepared in satisfactory yield by the condensation of dichloromethyl methyl ether with substituted allylbenzo[6]thiophenes (equation 11) (74JCS(P1)1744). 

Most photodecarbonylation reactions of cyclic ketones, especially in the vapor phase, have been postulated to proceed from various vibrational levels of excited singlet states.321 However, the elimination reaction leading to unsaturated aldehydes has now been shown to occur largely via excited triplet states. In solution, where the lowest vibrational levels of the excited states are rapidly reached, to-alkenals are the major products observed in both photolysis and radiolysis of cyclopentanone and cyclohexanone. The reaction is quenched by oxygen and dienes,322-324 as well as by the alkenal produced in the reaction.325 The reaction is also sensitized by benzene triplets.322,323 With cyclopentanone, quenching by 1M piperylene occurs some 20 times as fast... 

Photolysis of cyclohexanone gives rise to carbon monoxide, ethylene, propylene (1), cyclopentane, 1-pentene (3), and 5-hexenal (29). Cyclo-hexenyl cyclohexanone, water, and a polymer have also been reported as products, especially when the photolysis is conducted in the temperature range from 100°-300° in the presence of short wavelength radiation (3). At 3130 A. and over the temperature range of 100°-300° the ketone that is decomposed is almost fully accounted for in the products (5) and the stoichiometry of the products fits the eq. 15-18 (3,27) ... 

The diradical mechanism as applied to this system is as hypothetical as in the cases of cyclopentanone and cyclohexanone. The only data on the use of radical scavengers is a report on the photolysis of cycloheptanone in the presence of 3.2 mm. of oxygen. In this case, both of the C hydrocarbons and 6-heptenal was observed to be formed. It is quite likely that the reactions 30-33 are concerted processes. 

The photolysis of cyclohexanone has been studied by several workers. The formation of 5-hexenal, presumably by an intramolecular rearrangement as in the vapor phase by eq. 18, has been observed in the pure liquid (36) and in 1-octene solution (21). 

Photolysis of cyclohexanone also gives rise to a small amount of carbon monoxide, the quantum yield for the process at 3130 A. being 0.02. Photolysis at shorter wavelengths gives rise to high boiling products which are formed by a reaction between the ketone and the substrate. In cyclohexanol solution, cyclohexanone pinacol is formed (40). 

In 1-octene solution, the following products are observed (21) a mixture of cis and trans 2-octene, a hydrocarbon of the formula C16H34, 2-octyl cyclohexanone, a compound of the formula C22H42O believed to be formed by the addition of 2 molecules of 1-octene to 1 molecule of the ketone, and a compound of formula C3oH6S0 believed to be formed by the addition of 3 molecules of 1-octene to 1 molecule of cyclohexanone. In addition, a considerable amount of a polymer is also formed. The complex mixture of products clearly indicates the difficulties in the study of photolysis in the condensed phase, particularly if it is necessary to determine the mechanism of the formation of the various products. 

The asymmetric addition of ethyl azidoformate (N3C02Et) to an optically active enam-ine, prepared from cyclohexanone and (S )-2-pyrrolidinemethyl methyl ether, followed by photolysis produces 2-(ethoxycarbonylamino)cyclohexanone with modest enantiomeric excess (18 %ee) in 40% yield159. Use of (S -pyrrolidinemethyl trimethylsilyl ether as a chiral auxiliary increases the steric hindrance and provides the same product with the highest value of %ee (35%) in 51% yield. 

Photolysis of (102) in the presence of water yielded cyclohexanone (27%) which was suggested to be formed via cyclohexyl azide and the antiaromatic, unknown triazirine... 

Using 2,2-dimethylcyclobutanone [26a], as a specific example, initial excitation to produce an excited state species followed by a-cleavage would produce the acyl alkyl biradical [30]. Subsequent decomposition of [30] would then afford ester [27a] (via ketene), cyclopropane [28a], and acetal [29a], the observed photoproducts. The intermediacy of biradical [30] was supported by (a) the nearly exclusive formation of methyl acetate (as opposed to methyl isobutyrate), (b) the exclusive formation of the 5,5-dimethyl substituted acetal [29a] (as opposed to its 3,3-dimethyl substituted isomer), (c) its role as a common intermediate for all products, and (d) analogy to the photochemistry of cyclopentanones and cyclohexanones. Recently, Wasacz and Joullie have reported that photolysis of oxacyclohexanone [32] affords a 3% yield of acetal [29a] (18). It is conceivable that the formation of [29a]... 

In the thermolysis of cyclohexanone virtually all of the products arise from the (8-cleaved structure 5.23) Jwo effects are important here. In the ion the a-cleavage structure is specifically stabilized (see below) and the jff-cleavage structure 9, would be specifically destabilized by the heteroatom which is at an active site in the odd alternant n system associated with the carbonyl. The primary photolysis products of cyclohexanone 24) are much more closely correlated to its mass spectrum than the thermolysis products are. This is because n- n excitation can be relaxed by an a-cleavage (Norrish type I) analogous to 7. The analogy for the photochemical reactions is, however, far from perfect because of the stabilizing effect of the oxygen atom on the even alternant even electron ions, e.g. 10. The photolysis of... 

A single example of the formation of an oxaziridine by nitrene addition to a carbonyl group was found in the photolysis of ethyl azidoformate in the presence of excess acetone (for about 40 hr), producing oxaziridine 13. The reaction failed to give the corresponding oxaziridine when acetone was substituted by cyclohexanone. ... 

The first photochemical Beckmann rearrangement of aromatic aldoximes was reported in 1963. Subsequently, cyclohexanone oxime was shown to rearrange, upon photolysis, to caprolactam. Although the presence of oxaziridines in the solutions of photolyzed oximes was demonstrated, no oxaziridines have been isolated from these reaction mixtures presumably because of the general instability of oxaziridines that have no substituents on the ring nitrogen. The qualitative results are consistent with the intermediacy of oxaziridines in the photolysis of oximes to amides, yet the possibility of the reactions following other pathways cannot be ruled out. ... 

Bamford and Norrish observed that the free radical formation is the sole primary process in the photolysis of cyclohexanone, while step II is the major reaction occurring in the photolysis of 1-menthone. These results are rather difficult to interpret if reaction II occurs through a four-centred ring complex however, if a six-centred complex is involved, the consideration of the steric factors leads to a conclusion which is reconcilable with the results of Bamford andNorrish. The significance of steric factors (stereoelectronic requirements) appears from the fact that type II elimination is the major intramolecular path in the photolysis of ciy-2- -propyl-4-t-butyl cyclohexanone, while the photolysis of the tram compound yields the cis isomer as the major product The difference has been explained... 

The products of the photolysis of cyclohexanone are CO, C2H4, C3H6, cyclo-C5H10, as well as 5-hexenal . Cyclohexenyl cyclo-... 

Reaction I (in a peculiar form), as well as reactions II, III and IV all occur in the photolysis of cyclobutanone, though the quantum yield of step IV is very low. The occurrence of reaction III in the photolysis of cyclopentanone was not reported however, in that of cyclohexanone and cycloheptanone again all four reactions seemed to take place. 

A pressure increase, brought about by an increase in the concentration of the ketone or by the addition of an inert gas, enhances the formation of the unsaturated aldehyde as compared to that of CO. The value of awehyde increases at the expense of 0co> thus, the ketone consumption yield is independent of pressure. This seems to be generally valid in the photolysis of the cyclic ketones it was confirmed, for instance, for cyclopentanone °, cyclohexanone 2-methyl cyclohexanone and 2,6-dimethyl cyclohexanone . An increase in wavelength also favours the formation of the aldehyde as compared to decarbonylation in the photolysis of cyclobutanone , cyclopentanone and cyclohexanone . At 3130 A, the decrease in temperature has a similar effect on the product distribution in the photolysis of cyclopentanone , cyclohexanone , 2-methyl cyclohexanone , and 2,6-dimethyl cyclohexanone to that caused by the increase in wavelength or pressure. However, at shorter wavelengths, the quantum yields seem to be independent of temperature . ... 

The reactions taking place in the vapour phase also occur in the condensed phase, and their mechanisms are probably similar. However, as may be expected on the basis of the results obtained for the gas phase photolysis, the formation of olefins, cycloparaffins, and CO is of less importance, while that of the saturated aldehydes is more important in the liquid phase or solution, where energy dissipation by collision is more efficient. The decarbonylation products were shown to be only of minor importance in the photolysis of liquid cyclopentanone and cyclohexanone . The unsaturated aldehyde was found to be the main product in the liquid-phase photolysis of cyclopentanone (methyl cyclohexanone . Unsaturated aldehydes were also identified in the photolysis products of other cyclic ketones in the liquid phase as well as in solution . ... 

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