Acetone photochemical decomposition

Branching. Photochemical decomposition of D6-acetone yields CD3, which can then react with acetone or with an added hydrocarbon 43... 

Thiophenols may also be synthesized via the photochemical decomposition route 156). Thus, treatment of arylthallium ditrifluoroacetates with an aqueous solution of potassium Ar,AT-dimethyldithiocarbamate led in quantitative yields to the formation of the corresponding aryl AT,A -dimethyl-dithiocarbamates. Subsequent photolysis in aqueous acetone then led to disulfides which were reduced to the thiophenols. A small amount of aryldithiocarbamate formed as a by-product in the photolysis was converted to the same thiophenol by hydrolysis. The overall reaction sequence is illustrated in Eq. (18). 

Colorless or white cubic crystals or granules becomes yellowish when exposed to bright light due to photochemical decomposition liberating traces of free iodine density 3.13 g/cm melts at 681°C vaporizes at 1,330°C highly soluble in water, 140 g/lOOmL at 20°C aqueous solution readily dissolves iodine sparingly soluble in ethanol (about 2 g/lOOmL at 25°C) and acetone slightly soluble in ether and ammonia. 

In these experiments hydroxyl was obtained by photochemical decomposition of H202. Analysis of reaction products was also made. Hydroxyl concentrations were too low to be measured by the spectroscopic method, but were sufficient for detecting the reaction products such as acetone, which was apparently formed by the reaction of the iso-C3H7 radical with the O2 molecule. 

However, if the photochemical reaction is run in the presence of oxygen, then of course, the methyl radicals are oxidized, and one obtains instead methanol, formaldehyde, and their decomposition products. Now, if the vessel is pumped out after a photo-oxidation and once again a normal photolysis of acetone is run, the products in the first 10 or 15 minutes are still oxidation products rather than hydrocarbon products. It takes from 15 to 30 minutes to remove whatever it is that is attached to the wall before the normal photochemical decomposition of pure acetone products are produced. These results should remind us that oxidation system do produce species, some of which are not known or understood. 

The body of literature on the photochemical decomposition of acetone is by now quite imposing, and excellent critiques of the %work are available. " This particular photolysis owes its importance to the fact that it has been one of the chief sources of quantitative data on the behavior of methyl radicals. It is therefore of some consequence to examine the principal features of the reaction. 

We have omitted the decompositions of secondary species and products caused by light absorption. This is a reasonable approximation so long as the absorption coefficients of these species are of the same order of magnitude as acetone itself, or a smaller order of magnitude, since the photolysis reactions seldom proceed to more than a few per cent completion. When, however, reactions are permitted to go to completion or intermediates or products have absorption coefficients much larger than the parent species, there may well be appreciable photochemical decomposition of these products. 

The photochemical decomposition of heptachlor (44) yields through the excited singlet state the mono-dechlorination isomer pair 48 and 49, while triplet-sensitisers (e.g. acetone) give rise through the triplet state to the formation of 2,3,4,4,5,... 

The vapor-phase photochemical decomposition of acetone proceeds in the presence of iodine vapor but the amount of carbon monoxide formed becomes very small. Explain how this result argues against the one-step process, acetone... 

Scheme II-A. A representation of the photochemical decomposition of propanone (acetone [CH3COCH3]) to carbon monoxide (CO) and the methyl radical (CHs ). The species in brackets represents a photochemically excited molecule in which an antibonding orbital is occupied.

Scheme 9. A representation of the pathway by which 2-hexanone undergoes photochemical decomposition to propanone (acetone, CH3COCH3) and propene (CH3CHAH2) by internal abstraction of a y-hydrogen and cleavage of the P-y-carbon-carbon bond.

Yields of excited states from 1,2-dioxetane decomposition have been determined by two methods. Using a photochemical method (17,18) excited acetone from TMD is trapped with /n j -l,2-dicyanoethylene (DCE). Triplet acetone gives i7j -l,2-dicyanoethylene with DCE, whereas singlet acetone gives 2,2-dimethyl-3,4-dicyanooxetane. By measuring the yields of these two products the yields of the two acetone excited states could be determined. The yields of triplet ketone (6) from dioxetanes are determined with a similar technique. 

Hoare and Wellington (22) produced CH3O radicals from the photochemical (50° and 100°C.) and thermal (135°C.) decompositions of di-terf-butyl peroxide in the presence of 02. The initially formed tert-butoxy radicals decomposed to acetone plus methyl radicals, and the methyl radicals oxidized to methoxy radicals. Formaldehyde and CH3OH were products of the reaction the formation of the former was inhibited, and the latter was enhanced as the reaction proceeded. If the sole fate of CH3O were either... 

The photochemically produced PtCPEt fragment, stabilized as the cis- and trans-PtH (PEt- )2 complexes, has proved (54,55,56) to be an efficient and long lived homogeneous catalyst for H2/D2 exchange (Equation 17), deuteration of acetone or acetontrile (Equations 18 and 19), decomposition of formic acid (Equation 20), and hydrolysis of acetonitrile (Equation 21). Because of the catalytic promise... 

In addition to the thermal decomposition the photochemical reaction of geminal diazide 62 was also studied. Irradiation of an acetone solution of 62 under an inert gas atmosphere afforded a complex mixture of products which could not be separated or identified. However, if the reaction was carried out in the presence of oxygen the uracil derivative 66 was obtained in 48 % yield. Surprisingly, in addition to the oxidation of the CH2 group, the 6-diazidomethyl function was completely lost during the reation [91JCS(P1)1342]. At the present time no mechanistic explanation for this unusual behavior can be presented. On the other hand, photooxidation of compound 63 leads straightforward to compound 67 [91 JCS(P1)1342],... 

R CHORj. Such radicals have been formed by hydrogen atom abstraction from the ether by radicals produced from thermal decomposition of peroxides (67, 75, 76). Similar radicals may be produced in photochemical processes, either by direct irradiation (29, 54), or by the use of a photosensitizer or a photoinitiator, such as acetone or benzophenone (21, 64, 66). The ether radicals once produced, participate in a variety of chemical reactions. It might be noted that resonance forms as illustrated... 

The photochemical dissociation of di-(-butyl peroxide appears to proceed in a very similar way to the thermal decomposition. Dorfman and Salsburg47 photolyzed di-(-butyl peroxide using 2537 and 2650 A. radiation between 25 and 75°C. They found that the main products were ethane and acetone in relative yields of 1 2. With low intensity radiation, some methane was obtained and, even though acetone was removed to prevent its reactions becoming appreciable, (-butanol was produced. The evidence is therefore very strong that di-f-butyl peroxide decomposes by the usual breaking of the peroxide 0—0 bond and the (-butyl radicals then rapidly decompose to give acetone and methyl radicals, i.e.,... 

The 24 hour photolysis of chlorendic anhydride (III) in acetone in the presence of diethoxyacetophene (IV) yielded at least twelve measurable products as observed by the GC/MS procedure (Table I). Some of the products observed, i.e. 4-methyl-4-hydroxy-2-pentanone, biacetal, 4-methyl-3-pentene-2-one, ethyl acetate, 3-methyl-3-hy-droxy-2-butanone, 4-methyl-2-pentanone, and 2,4-pentane-dlone, are clearly derived from the photochemically induced decomposition of acetone and/or dlethoxyacetophe-none. 

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