Acetone photodecomposition

Figure IX-D-3. Experimental determinations of the quantum yields of acetone photodecomposition (01 4- 0ii) as a function of wavelength for photolyses in air at 760Torr and 298 K. The dashed gray curves define an envelope that describes the range of possible values. Values from the two dashed curves were used in estimating the possible range of photolysis constants shown in figure IX-D-6. Authors of the current study recommend use of the values given by the short-dashed line. The maximum values are also given in table IX-D-2.

Hi) Minor processes in acetone photodecomposition Primary process (III), H-atom formation, has been observed by Takahashi et al. (2004) and Lightfoot et al. (1988) in photolysis of acetone at 193 nm. Lightfoot et al. (1988) reported that 3% of acetone... 

Table IX-D-3. Quantum yields for acetone photodecomposition by process (II) CH3C(0)CH3 +hv (CH3CO + CH3) 2CH3 -P CO(II), in air (760Torr) as a function of wavelength. The minimum values shown are recommended for use in tropospheric modeling...

The quantum yield data (maximum and minimum) given in table IX-D-2 apppear to be the best current choices for modeling acetone photodecomposition within the... 

Figure IX-D-7. Plot of the estimated photolysis frequencies for acetone photodecomposition for a cloudless day within the lower troposphere at 760Torr and 298 K. The black solid and dashed curves represent the maximum and minimum / -values, respectively, for the total photodecomposition [process (I) 4- process (II)] as estimated from the quantum yield data of table IX-D-2. The gray curve is the estimated maximum value for photodissociation by process (II) in the lower troposphere as estimated using the maximum quantum yield given in table IX-D-3. If the more probable, minimum estimates for lower tropospheric pressures are used in the calculation, the / -values for process (II) in acetone are very near zero.

Studies in the photoinitiation of polymerization by transition metal chelates probably stem from the original observations of Bamford and Ferrar [33]. These workers have shown that Mn(III) tris-(acety]acetonate) (Mn(a-cac)3) and Mn (III) tris-(l,l,l-trifluoroacetyl acetonate) (Mn(facac)3) can photosensitize the free radical polymerization of MMA and styrene (in bulk and in solution) when irradiated with light of A = 365 at 25°C and also abstract hydrogen atom from hydrocarbon solvents in the absence of monomer. The initiation of polymerization is not dependant on the nature of the monomer and the rate of photodecomposition of Mn(acac)3 exceeds the rate of initiation and the initiation species is the acac radical. The mechanism shown in Scheme (14) is proposed according to the kinetics and spectral observations ... 

Quenching of Singlets of Carbonyl-Containing Compounds, a. Acetone. Recent reports have shown that singlet complications are not restricted to hydrocarbons for example, the photodecomposition of 1,4-dichlorobutane (52) to free radicals is sensitized by the (n, n) singlet state of acetone.216 Besides the observations that 52 quenches acetone fluorescence and that... 

The (CH3CO-CH3) bond dissociation energy has been measured by the kinetic, and more recently by the electron impact, methods, and concordant values40 41 of 71 kcal. mol.-1 were obtained so that when acetone suffers a photodecomposition of type A, the fragments still carry excess energy. 

The energy required to dissociate the acetone molecule into two methyl radicals and a molecule of carbon monoxide may be calculated from thermocheinical data and amounts to 89 kcal. mol.-1. It would be energetically possible, therefore, for a photodecomposition of type B to occur,... 

The simplest change which may be made in the acetone molecule is the substitution of a hydrogen atom by chlorine, yet this slight alteration leads to a very profound change in the pattern of photodecomposition. 

With the exception of the photolysis of acetone itself, no other photodecomposition of a ketone has been studied so extensively as that of hexafiuoroacetone. 

Surely, many such common reactions could be utilized for the intentional destruction of unwanted herbicides and their residues (41). Metham might be caused to react simply with aqueous ammonia to form harmless methylthiourea many herbicides including prometryne and metribuzin (Sencor) might be degraded by dilute hypochlorite ("chlorinated lime") of the type used to purify swimming pools, and the photodecomposition of others (such as 2,4,5-T) might be accelerated by cheap nontoxic photosensitizers such as acetone (Table III) (42). The variations of environmental chemistry applications to control and direct herbicide persistence and effectiveness now appear endless. 

It is obvious that the whole process is catalytic in both Eu2+ and H+ ions and the net reaction is the photodecomposition of 2-propanol into acetone and hydrogen. 

Photodecomposition. Owing to its simple structure and great importance as a model compound, there have been many studies of acetone photochemistry. The bulk of this work has been reviewed earlier (148,175). The photodecomposition of acetone has shown the major products to be carbon monoxide, ethane, and methane. Under proper conditions, other minor products are produced. 

Photodecomposition. Since the last review of photochemistry of HFA (61), there has been a great deal of effort expended in the study of the primary processes and decomposition modes of HFA. The photodecomposition products observed appear to be carbon monoxide and hexafluoroethane exclusively. The trifluoroacetyl radical, CF3CO, must be very unstable. As in acetone, it has been proposed that the decomposition processes must overcome an energy barrier, as temperature-dependent quantum yields were observed (252). A detailed mechanism that takes into account a vibrational deactivation cascade has been proposed by several authors (34,35,97,252). 

The very small photodecomposition yields at low temperatures are to be expected in this region, as the photon energy available at 365.0 nm [78.5 kcal/mol is less than that required for dissociation by process 93 and is marginal for process 92 (AH92 = 69.5 kcal/mol, AHg = 89.3 kcal/mol)]. The temperature dependence of these yields has been best explained as a unimolec-ular decomposition of T- with an activation energy of 15 kcal/ mol (176), a value comparable to Ea values found for acetone and hexafluoroace tone. 

The conversion of the benzohydroxamic acid (191) into the amide (192) is the result of nitrogen-oxygen bond homolysis.Photodecomposition of aminophenazone (193) in aqueous solution gave N-acetyl-N-methyl-N -phenylhydrazine (194), whereas on irradiation in acetone products arising by... 

Photodecomposition of carbohydrate-derived geminal diazides appears to proceed via intermediate carbenes, ° whereas irradiation of the diazidomethylpyrimidine (70) in acetone affords the uracil carboxylate (71), but only in the presence of oxygen. 

SCHEME 13.17 Photodecomposition and self-initiation mechanism of acetone. 

Upper-limit lifetimes, inasmuch as aldehydes and ketones also are subject to photodecomposition this applies specifically to formaldehyde and acetone. 

Gardner, E. P., R. D. Wijayaratne, and J. G. Calvert (1984). Primary quantum yields of the photodecomposition of acetone in air under tropospheric conditions. J. Phys. Chem. 88, 5069-5676. 

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