Diacetyl, photolysis

Photolysis of acetone forms methyl radicals, isolated as dimethyl-mercury, and acetyl radicals isolated as diacetyl. Photolysis of benzo-phenone forms phenyl radicals which remove a tellurium mirror to give diphenyltellurium. 

Pyrrole, 2-cyano-l-(2-hydroxyethyl)-5-nitro-ipso substitution, 4, 243 Pyrrole, 2-cyano-l-methyl-photochemical rearrangement, 4, 42 photolysis, 4, 203 Pyrrole, 2-cyano-3-methyl-photochemical rearrangement, 4, 202 Pyrrole, 2-cyano-4-methyl-photochemical rearrangement, 4, 202 Pyrrole, 2-cyano-5-methyl-photochemical rearrangement, 4, 202 Pyrrole, diacetoxymethyl-synthesis, 4, 274 Pyrrole, 2,4-diacetyl-synthesis, 4, 218 Pyrrole, 2,5-diacetyl-synthesis, 4, 218, 219 Pyrrole, 2,4-dialkyl-... 

Despite this fact and the low (CH3-CO) bond dissociation energy in the acetyl radical, the products of photolysis of acetone with light of wavelength 3130 A. have been shown to contain substantial amounts of diacetyl, which could only arise from the combination of acetyl radicals. 

The suppression of polymerisation by 02 and benzoquinone was due to the fact that these species captured a significant fraction of the secondary electrons produced and not to their ability to scavenge free radicals. The negative ions thus produced underwent charge neutralisation with (CH3)3C+ thus reducing the yield of polymerisation initiators. In confirmation of the fact that ionic rather than free radical processes were important was the observation that the production of free radicals within the solution by the photolysis of diacetyl failed to initiate polymerisation. Spectroscopic evidence for the existence of (CH3)3C+ in the pulse radiolysis of isobutene was obtained subsequently31. 

At 3130 A., (87) is the dominant process while, at 2537 A., dissociation is almost entirely by reaction (88)." Process (89) has been shown to occur in flash photolysis,74 but this was unimportant at low intensities. The photooxidation was first studied by Bowen and Tietz,26 who found peracetic acid and diacetyl peroxide as products. The rate of reaction... 

The photooxidation of mono-ketones appears to proceed at all wavelengths as if one were studying the oxidation of the radicals produced by photolysis. This appears to be true also for dialkyl peroxides, aldehydes, and azoalkanes. In the photooxidation of diacetyl there is evidence that at longer wavelengths reaction occurs between excited molecules and oxygen, whereas with ketene under similar conditions deactivation of the excited molecule appears to be the chief reaction. 

Reactions of piperazine-2,5-diones with phosphorus pentachloride and phosphorus pentabromide have been described in Sections V.ID and V.IF, respectively. Aromatic aldehydes condense with 3-methylpiperazine-2,5-dione in the presence of acetic anhydride to form mainly mono-A -acetyl derivatives of trans-3-arylidene-6-methylpiperazine-2,5-diones (e.g., 96, R = Ac) (1066). In these products the acetyl group was shown to be attached to position 1 and the 4,5-amide group was found to be sterically hindered. Photolysis formed the cis isomers. Both isomers were deacetylated with methanolic potassium hydroxide (1066). Condensation of 1,4-diacetylpiperazine-2,5-diones with aldehydes has been applied to the synthesis of unsymmetrical 3,6-diarylidenepiperazine-2,5-diones and the reaction has been extended to l,4-diacetyl-3,6-dimethylpiperazine-2,5-diones (1624). Treatment of (96, R = H) with triethyloxonium tetrafluoroborate in dichloromethane gave the monoimino ether, 5-benzylidene-6-ethoxy-3-hydroxy-2-methyl-2,5-dihydropyrazine (97) (1066). l-Methylpiperazine-2,5-dione similarly treated gave 5-ethoxy-l-methyl-2-oxo-l,2,3,6-tetrahydropyrazine (which was condensed with anthranilic acid at 150° to 2-methyl-l,2-dihydropyrazino[2,l-fi]quinazoline-3(4/0.6-dione (98) (1625), and l,4-dimethylpiperazine-2,5-dione gave 5-ethoxy-l,4-dimethyl-2-oxo-1,2,3,4-tetrahydropyrazine and 5,5-diethoxy-l,4-dimethylpiperazin-2-one (1626). 

Acyl radicals are prduced in photolysis of diacetyl, when hydrogen is abstracted from aldehyde, or when an oxvgen atom or an ozone molecule reacts with olefin. 

Photolysis of Compound X, Butyl Nitrite, and Diacetyl. A relatively pure sample of compound X was prepared from diacetyl and nitrogen dioxide by means of the photolysis and cold trap collection technique described previously. This sample was then vaporized back into the long-path cell, mixed with 1 atm. of oxygen, and photolyzed with the AH-6 arc. The exact partial pressure of compound X could not be measured because of the presence of an unknown percentage of water vapor. However, if the compound X infrared bands are comparable in strength to those of nitrites and nitrates, its partial pressure was in the part per million range. Ozone was quickly formed in the photolysis. This is shown in Figure 22. 

Pure diacetyl, dibutyryl, and p Tuvic acid have all been reported to produce ozone on photolysis in oxygen. First attempts to verify this result with use of the long-path infrared technique were frustrated by appearance in the spectrum of a band of methanol which masked the absorption resulting from ozone. This difficulty was overcome by the use of the following technique ... 

The most frequently encountered examples of the first type are the addition of diazoalkanes to 3//-pyrazoles (or addition of two moles of diazoalkane to an acetylene). For example, in the reaction of 2-diazopropane with dimethyl butynedioate, addition of one mole of 2-diazo-propane generated dimethyl 3,3-dimethyl-3/f-pyrazole-4,5-dicarboxylate (1), and addition of a second mole of 2-diazopropane gave dimethyl 4,4,8,8-tetramethyl-2,3,6,7-tetraazabicy-clo[3.3.0]octa-2,6-diene-l,5-dicarboxylate (2) which on photolysis (not thermolysis or sensitized photolysis ) gave a 41% yield of dimethyl 2,2,4,4-tetramethylbicyclo[1.1.0]bu-tane-l,3-dicarboxylate (3). Similar bis-additions are known for dicyano-, diacetyl-, and diben-zoylacetylene, but only the dicyano system gives the bicyclobutane on thermal deazetization. ... 

Zeldes, H., and if. Livingston Magnetic Resonance Studies of Liquids during Photolysis, IV Free Radicals from Acetaldehyde, Diacetyl and Acetoin. J. Chem. Phys. 47, 1465 (1967). 

The energy transfer is a triplet-triplet process (p. 197) and because ketones provide high yields of the triplet state, compounds such as acetone, benzophenone, and diacetyl have been used in the study of these reactions. Sensitized reactions often result in a higher reaction quantum yield than observed in direct photolysis. The reaction quantum yield for the direct photolysis of ethyl pyruvate at 313 nm in benzene... 

Suginome, H., Sato, N., and Masamune, T., Photolysis of nitrites of 3-0, N-diacetyl-22,27-imino-17,23-oxidojervan-5-ene-3-ll- and 3,11-diols, Tetrahedron Lett., 1557,1967 Suginome, H., Sato, N., and Masamune, T, Some observation on photolysis of fused cyclopentyl nitrites. Bull. Chem. Soc. Ipn., 42, 215, 1969. 

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