Ketones biacetyl

Disregarding inconsistencies in the natural fluorescence rate constants, it is important to note that aliphatic ketones (biacetyl and acetone) as well as several cis-azoalkanes show fluorescence in solution [81], This includes not only the examples of DBH-T [47,98] and DBO [56,103,138] (see Structnre 3.1), but also the smaller derivatives (see Structure 3.2) 2,3-diazabicyclo[2.1.1]hex-2-ene [139], diazirines, e.g., adamantyldiazirine [140], and even some sterically hindered azobenzenes [141], In contrast, DBH is not flnorescent with the exception of a report in siliceous zeohtes [66] it undergoes denitrogenation with unit quantum efficiency from the... 

Direct oxidation yields biacetyl (2,3-butanedione), a flavorant, or methyl ethyl ketone peroxide, an initiator used in polyester production. Ma.nufa.cture. MEK is predominandy produced by the dehydrogenation of 2-butanol. The reaction mechanism (11—13) and reaction equihbtium (14) have been reported, and the process is in many ways analogous to the production of acetone (qv) from isopropyl alcohol. 

Biacetyl is produced by the dehydrogenation of 2,3-butanediol with a copper catalyst (290,291). Prior to the availabiUty of 2,3-butanediol, biacetyl was prepared by the nitrosation of methyl ethyl ketone and the hydrolysis of the resultant oxime. Other commercial routes include passing vinylacetylene into a solution of mercuric sulfate in sulfuric acid and decomposing the insoluble product with dilute hydrochloric acid (292), by the reaction of acetal with formaldehyde (293), by the acid-cataly2ed condensation of 1-hydroxyacetone with formaldehyde (294), and by fermentation of lactic acid bacterium (295—297). Acetoin [513-86-0] (3-hydroxy-2-butanone) is also coproduced in lactic acid fermentation. 

The reaction of diketosulfides with 1,2-dicarbonyl compounds other than glyoxal is often not efficient for the direct preparation of thiophenes. For example, the reaction of diketothiophene 24 and benzil or biacetyl reportedly gave only glycols as products. The elimination of water from the P-hydroxy ketones was not as efficient as in the case of the glyoxal series. Fortunately, the mixture of diastereomers of compounds 25 and 26 could be converted to their corresponding thiophenes by an additional dehydration step with thionyl chloride and pyridine. 

Biacetyl monoxime has been prepared by the action of amyl nitrite on methyl ethyl ketone using sodium hydroxide1 or hydrochloric acid 2 as a condensing agent, and by melting nitroso-levulinic acid.3... 

The methyl ethyl ketone should not be allowed to stand any length of time between the addition of the hydrochloric acid and the treatment with ethyl nitrite, inasmuch as the acid causes a condensation of the ketone with itself, thereby lowering the yield of biacetyl monoxime. 

Mattay et al.5i suggested from the photoreaction of biacetyl with highly electron-rich olefins that an initial electron transfer from an electron-rich olefin to photoexcited ketone is the key step in the oxetane formation via the ion-radical pair (equation 26). 

Investigations have also examined the photochemical outcome of the inclusion of other aromatic substituents onto the norbornadienes. Examples of this are the direct and sensitized irradiation of the naphthyl-substituted derivatives 249 that brings about cyclization to 250. Sensitization of the cyclization with ketones such as benzophenone leads to a much cleaner reaction. Biacetyl has also been used as the sensitizer130,131. Cyclization also occurs with the norbornadiene 251132. 

Structures have been determined for [Fe(gmi)3](BF4)2 (gmi = MeN=CHCF[=NMe), the iron(II) tris-diazabutadiene-cage complex of (79) generated from cyclohexanedione rather than from biacetyl, and [Fe(apmi)3][Fe(CN)5(N0)] 4F[20, where apmi is the Schiff base from 2-acetylpyridine and methylamine. Rate constants for mer fac isomerization of [Fe(apmi)3] " were estimated indirectly from base hydrolysis kinetics, studied for this and other Schiff base complexes in methanol-water mixtures. The attenuation by the —CH2— spacer of substituent effects on rate constants for base hydrolysis of complexes [Fe(sb)3] has been assessed for pairs of Schiff base complexes derived from substituted benzylamines and their aniline analogues. It is generally believed that iron(II) Schiff base complexes are formed by a template mechanism on the Fe " ", but isolation of a precursor in which two molecules of Schiff base and one molecule of 2-acetylpyridine are coordinated to Fe + suggests that Schiff base formation in the presence of this ion probably occurs by attack of the amine at coordinated, and thereby activated, ketone rather than by a true template reaction. ... 

In my opinion, Noyes greatest contribution to chemistry was his elucidation of the primary process, unifying product yields with spectroscopy. Until his time no effort was made to correlate spectroscopic and chemical information, and often the primary photochemical schemes contradicted spectroscopic observations. This work started in the 1940s and continued until the end of his life. Among the molecules whose primary processes he established were acetone (his favorite molecule), other simple aliphatic ketones and aldehydes, biacetyl, and benzene. 

The ene reaction of cyclic disilene 50 with enolizable ketones such as biacetyl and acetophenone gives initially a.v-adduct 199, which gradually isomerizes to the corresponding traKi-isomer 200 104,133... 

The chiral titanocene complex 61 is an excellent catalyst for the enantioselective hydrosilyation of the ketone 131 with PMHS (133) to afford the alcohol 132 with 91 % ee [80]. Efficient asymmetric hydrosilylation of symmerical diketones is catalysed by the Rh complex coordinated by EtTRAP. Biacetyl (134) was converted to (2S,3S)-2,3-butanediol (135) with 95% ee in 69% yield [81]. 

Before the concerted vs. two-step question was further elucidated, another basic mechanistic puzzle was raised. One research group found that type II cleavage of 2-pentanone was quenched by biacetyl [6], which was known to quench excited triplets rapidly. Another group found that the reaction of 2-hexanone was not quenched under the same conditions [7]. The two groups obviously differed as to which excited state undergoes the reaction. The apparent conflict was neatly solved by the revelation that each of the two ketones reacts from both states, with 2-hexanone undergoing more unquenchable singlet reaction than 2-pentanone [8,9]. 

Diethyl ketone has been shown (Weir178) to behave similarly to acetone. The ketone decomposes from the singlet state after excitation by 2537 A. radiation and is unaffected by biacetyl. Biacetyl deactivates triplet molecules and reduces decomposition of diethyl ketone when 3130 A. radiation is used at room temperature. 

Unlike acetone, diethyl ketone cleaves well even in cumene 22>. 2-Pentanone triplet undergoes considerable a-cleavage in competition with rapid intramolecular hydrogen abstraction, as judged by the buildup of an efficient triplet quencher 23>. Biacetyl is the only likely candidate for that quencher and is the major product of a-cleavage of methyl ketones at temperatures low enough that decarbonylation of the acetyl radical is slow. Isopropyl, tert-butyl, and benzyl ketones all cleave quite efficiently and various reports have appeared on the CIDNP spectra of products derived from the radicals 24>. 

These include biacetyl, methylethyl ketone, ketene, acetaldehyde, and biacetonyl. Of these, biacetyl is the most important. 

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