Acetone photochemical reaction

A simple aliphatic ketone such as acetone, when promoted to its n,n excited state, undergoes a single unimolecular photochemical reaction in high quantum yield namely a-cleavage giving a methyl and acetyl radical which react further in secondary dark processes. In general, competition... 

The reaction of (fluoroalkenyl)carboranes with potassium permanganate in acetone leads to formation of a-diketones [119. These compounds react by photochemical reaction in which the radical formation at boron is followed by addition to the double bond [120] (equation 92). 

Norbornadiene derivative 123, on either direct or sensitized irradiation in solution, gives quadricyclene 124 (Equation 9). On the other hand, photochemical reaction of 125 in acetone at room temperature is very rapid and the product 126 is obtained in high yield (Equation 10) <1998HCA828>. 

The photochemical reaction of azathymine derivative 556 with acetone afforded 557 (89MI2). The proposed reaction mechanism involved a biradical intermediate, which was trapped with a second mole of acetone. 

SN NMR has been used to study the mechanism of the photochemical reaction of 5-phenyl-l,2,4-thiadiazole (see Section 5.08.5.2). 5-Phenyl-l,2,4-thiadiazole-4-1SN and 3-phenyl-l,2,4-thiadiazole-2-1SN were synthesized. The 15N NMR chemical shifts reported for the 4-position derivative was +302.2 ppm (acetone- ) and for the 2-position derivative +258.4 ppm (CDCI3) relative to a reference of ammonia <2003JOC4855>. 

We can illustrate the application of PAC to a simple photochemical reaction. Acetone is readily excited to its singlet excited state which rapidly undergoes efficient intersystem crossing to its triplet state. The triplet state decays in solution primarily by radiationless decay. The PAC experimental waveforms obtained from the photoexcitation of acetone in air and argon-saturated cyclohexane are shown in Fig. 1. In addition, the waveform obtained from the calibration compound 2-hydroxybenzophenone is also shown. 

Scheme 14.—Proposed Mechanism for Photochemical Reaction of Methyl 3,4-0 Ethylidene-/3-L-arabinopyranoside (35) with Excited Acetone.

Full papers have appeared on the friedelanes from Hydnocarpus octandra and Trichadenia zeylanica, the mechanism of the photochemical reaction of friedelin with acetone, and the rearrangement of 3/8,4/3-epoxyfriedelane (195) to... 

Two examples of the chain reaction involving the a-methylene radical are the irradiation of acetone in the presence of norbornene,107 and that of cyclohexanone in the presence of cyclohexene.108 106 These reactions predominate so that the other products derived from the photochemical reactions were not initially characterized. 

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. 

Following a newly discovered indole synthesis, it has been shown that photochemical reaction of acetone anion with 3-amino-2-chloropyridine in liquid ammonia gives 2-methylpyrrolo[3,2-6]pyridine in 45% yield (80JOC1546). 

Propanone (acetone) vapor undergoes a photodissociation reaction with 313-nm light with somewhat less than unity. Absorption of light by 2-propanone results in the formation of an excited state that has sufficient energy to undergo cleavage of a C-C bond (the weakest bond in the molecule) and form a methyl radical and an ethanoyl radical. This is a primary photochemical reaction ... 

The photochemical reaction of non-K-region oxides like dideuterated benzene oxide (303) and naphthalene 1,2-oxide has been studied at room temperature and at 77 K in acetone. When D-(303) is irradiated in acetone at room temperature, products corresponding to migration of the oxirane ring to the next position are obtained. 

Laroff GP, Fischer H (1973) The enol of acetone during photochemical reaction of 3-hydroxy-4-methyl-2-butanone and of acetone. Helv Chim Acta 56 2011 -2020 Lehni M, Fischer H (1983) Effects of diffusion on the self-termination kinetics of isopropylol radicals in solution. Int J Chem Kinet 15 733-757... 

Bimolecular quenching of the excited states of metal complexes generally involves electron transfer or energy transfer processes ( 1). Recently, however, Pt2(pop)4 " has been found to undergo a photochemical reaction involving atom abstraction as a primary photoprocess (.26). The reaction involves the catalytic conversion of isopropanol to acetone ... 

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],... 

Estimates of the triplet energy level of a molecule may be made by observing whether it can accept or transfer energy to several other molecules. Hammond and co-workers42 have shown that ds-trans interconversions of piperylene, 2-pentene, and 1 2 dichloroethylene may be affected by many photosensitizers. The stationary states of the sensitized ds-trans ratios of piperylene with various donors were found to form a coherent pattern if triplet energy transfer was assumed as the key step in the photochemical reaction. From these results they were able to infer the presence and the energies of the triplet states of acetone, phenanthrenequinone, and fluorenone, for which phosphorescence data are not available. The triplet levels were estimated as >70, 65, and 62 kcal./mole, respectively. 

Direct observation of transient radicals in liquid photolysis has added a new dimension to mechanistic organic photochemistry. While the nature of the primary process in the photolysis of gaseous acetone is well known (364), the mechanism of the photochemical reaction in pure liquid acetone or in hydrocarbon solvent has not been established in detail. Zeldes and Livingston (216) have observed (CH3)2COH, C COCH, and some CH3 radicals when pure liquid acetone is photolysed and have suggested the following mechanism ... 

Photochemical reactions of PCDEs have been studied in different solvents, but no difference in the amount of PCDFs has been observed [72,73], In the case of PCBs, the rate of dechlorination is faster in polar solvents than in hydrocarbon solvents [3]. Dehalogenated PCDEs have dominated in photolysis in -hexane [72], but photolysis of PCDEs in acetone solution inhibits dechlorination and favors photocyclization [73]. Therefore, it has been suggested that reactions in the environment in conditions near to acetone solution could have significance in the formation of PCDFs from PCDEs [73]. Photolysis in acetone solution can be used to synthesize PCDF congeners [74]. Carbonium ion is a possible intermediate in ring closure of PCDEs to PCDFs [75]. PCDFs can be synthesized from PCDEs... 

There is continued interest in micellar and surface effects, and Leigh and Scaiano have reported the results of a study of the photochemical activity of acetone in micelles. The micellar photoreactivity of the keto-acid (1) has also been studied. Two publications have dealt with a theoretical treatment of the photochemical reaction of dibenzyl ketone. ... 

An ET mechanism is involved in the photochemical reaction of 2- and 4-cyanopiridine and other cyanoazines with alcohols, alkenes, or amines substitution products are usually obtained. As an example, allylpyridines (and quinolines) are obtained from the acetone-sensitized reaction of the corresponding cyanohetero-cycles in the presence of alkenes (Scheme 53). The reactions of various dicyano-pyridines have also been studied in detail and the distribution of the products obtained is well rationalized with an ET mechanism [168]. 

Two additional complications may be present in photochemical reactions, the presence of hot molecules and hot radicals referred to earlier in thermal systems, and the possible physical and chemical primary processes that may occur. Compounds such as biacetyl, O2, NO and olefins are particularly efficient quenchers of electronically excited species. In accordance with the Wigner spin conservation rule that the total spin in a quenching process is conserved, triplet state acetone ( A) is quenched very efficiently to the ground state ( A) by olefins (O) . 

Intramolecular Additions - The predominant photochemical reaction of the allene derivatives (65) is (2 + 2)-cycloaddition yielding the housanes (66). The reaction occurs in a variety of solvents (e.g. hexane, acetonitrile or acetone) and the triplet excited state of (65) is implicated. In hexane and... 

Photoreactions of Pyridones - The pyridone derivative (122) undergoes ready (2 + 2) head-to-head photochemical addition when irradiated in acetone. The reaction appears to be very facile and requires only 16 minutes irradiation at 5°C to give a 79% yield of the adduct (123) which has been used as the starting material in a total synthesis of (-)-perhydrohistrionico-toxin (124). 

---