Thermal and photochemical reactions of biacetyl with 1,1-diethoxyethene. “Umpolung” of the reactivity of biacetyl by photochemical induced electron transfer.

The thermal and photochemical reactions of biacetyl 1 and 1,1-diethoxyethene 2 are totally complementary: 1 and 2 exclusively form the 2,2-diethoxyoxetane 4 in polar solvents at room temperature. Contrary to the literature this thermal cycloadditon proceeds uncatalyzed. 1 and 2 react photochemically under exclusive formation of the regioisomer oxetane 3 - preferably in nonpolar solvents. The inversion (“Umpolung”) of the reactivity of 1 is caused by the photoinduced electron transfer.     

Co-precipitation of metal dimethylglyoximates generated from biacetyl monoxime or biacetyl and hydroxylamine

A study has been made of some aspects of the co-precipitation of gold and platinum(II) and (IV) with palladium(II) precipitated from homogeneous solution initially containing biacetyl and hydroxylamine in 0.3M hydrochloric acid. The co-precipitation of nickel(II) with palladium(II) and vice versa from near neutral solutions initially containing biacetyl and hydroxylamine was also explored; the solid is enriched in the minor constituent in both cases. As with biacetyl monoxime-hydroxylamine systems, both nickel(II) and palladium(II) promote formation of dimethylglyoxime from such solutions between pH 7 and 8. Factors leading to this unusual behaviour in co-precipitation are discussed and a qualitative explanation tentatively advanced. The co-precipitation of nickel and palladium(II) is different when biacetyl monoxime solutions are used; the former comes out of solution faster than the latter irrespective of their concentration ratio. This disparity in the reaction rates can be used to separate nickel directly from palladium(II) by precipitation or extraction of the dimethylglyoximate into chloroform.     

Fluorometric determination of biacetyl

The fluorometric determination of biacetyl is described. 3,4-Diaminoanisole reacts with biacetyl in alkaline ethanol-water solution to give strongly fluorescing 2,3-dimethyl-6-methoxy-quinoxaline. Variables such as solvent composition, quenching by acetic and sulphuric acid, heating time and interference by other carbonyl compounds present are discussed. The method may be suitable for the determination of biacetyl in foodstuffs.     

The thermal decomposition of biacetyl

The thermal decomposition of biacetyl has been studied at small percentage conversion over the temperature range 375-417°C. For these conditions, an almost quantitative mass balance was obtained by gas-chromatographic analysis. The following equation was obtained for the overall reaction Between 240° and 277°C, the decomposition of biacetyl initiated by methyl radicals has also been studied. As source of radicals, the thermolysis of azomethane was used. Moreover, the Arrhenius parameters of the following reactions were determined: where A is in sec^?1 for reaction (1) and in cm³mole^?1 sec^?1 for reactions (3) and (4); E is in kcal/mole. Evidence is provided that the displacement reaction (4) proceeds by a two step mechanism.     

The electronic states of biacetyl

The ordering of the lower electronic states of biacetyl is discussed and the consequences for the mechanism of the radiationless S → T transitions are considered in detail.     

Photoreactions of biacetyl and tetramethylethylene. Solvent and temperature effects

The photoreaction of biacetyl and tetramethylethylene yields four products (1–4). A substantial variation in product yield and quenching kinetics with temperature and isotopic substitution is found for this photoreaction.     

Energy transfer between benzophenone and biacetyl

Energy transfer from benzophenone to biacetyl in the gas phase was studied by measuring the intensity and decay time of phosphorescence and fluorescence of both compounds as a function of pressure and composition of the mixture. We have established that benzophenone transfers energy along two parallel channels: singlet→singlet with high efficiency, k_SS? 2 ×10⁸ torr^?1s^?1, and triplet→triplet with lower efficiency, k_TT?8 × 10⁵ torr^?1s^?1.     

The stereostructure of trimers of biacetyl

Structures of two trimers of biacetyl were determined on the basis of chemical and spectroscopic evidence and the single-crystal X-ray analysis. The compounds are shown to be exo-3, endo-7-diacetyl-1- hydroxy-endo-3,5,exo-7-trimethyl-cis-2,4,6-trioxabicyclo[3.3.0]octanc (2) and 11-hydroxy-1,3,5,7,11- pentamethyl-cis-2,4,6,8-tetraoxatricyclo[3.3.3.0^3.7]undecan-9-one(3).     

Photopolymerization initiated by carbonyl compounds. VII. Solvent effects on biacetyl photoinitiation

Biacetyl is solvated by methanol or water giving an α-substituted alkanone. Irradiation of the solvated species at 300 nm in the presence of vinyl acetate or vinyl pyrrolidone, produces a significant amount of polymer. The photoprocesses leading to active free radicals are considered to be a type I photocleavage of the α-substituted alkanone.     

Ethyl radical initiated thermal decomposition of biacetyl

The thermal decomposition of mixtures of biacetyl and azoethane has been studied at low conversions in the temperature range 252–283°C. The Arrhenius parameters of some reaction steps were determined and compared with those of the corresponding reactions of methyl radicals.

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252–283°C. , .

     

Radiationless transitions between excited singlet states of biacetyl

Emission processes from lower excited states S₁ (fluorescence) and T₁ (phosphorescence) have been studied in the gas and liquid phases when biacetyl is excited into the second singlet state S₂. (In agreement with Kasha's rule no fluorescence is observed from the S₂ state.) In the liquid phase, when biacetyl is excited into the singlet states S₁ and S₂, no difference is observed between these emission processes. This phenomenon certainly results from an efficient nonradiative transition between the second excited singlet state S₂ and the first excited state S₁ with practically no excess vibrational energy. The quantum yield of this transition is almost unity and does not depend on the nature of the solvent. In the gas phase no emission processes are observed when biacetyl is excited into the S₂ state at low pressure (less than 10 mm Hg). High pressure of inert gas is necessary in order to observe these processes. As for excitation into the S₁ state with vibrational energy, loss of vibrational energy through collisions occurs from the S₂ state. The quantum yield of the S₂ → S₁ transition by excitation at 290 nm is estimated around 0.5–0.6 at 6 atm of inert gas (ethane, ethylene, or carbon dioxide).     

Spectrophotometric determination of nickel with biacetyl bis(4-phenyl-3-thiosemicarbazone)

A simple method is described for the rapid spectrophotometric determination of nickel with biacetyl bis(4-phenyl-3-thiosemicarbazone). The yellow color is measured at 460 nm (? = 22,800 liters mol^?1 cm^?1) against a reagent blank at pH 2.5 in a solution containing 60% ($\text{v}\text{v}$) dimethylformamide. Beer's law is obeyed over the range 0.2–2 ppm of nickel.     

The electronic relaxation of biacetyl in the vapor phase

The emissions of biacetyl after pulsed dye-laser excitation were studied at pressures down to 0.05 mtorr. At all energies the time-resolved fluorescence was composed of a nanosecond and a microsecond component. At “zero” pressure the long lived phosphorescence was absent while the “hot” phosphorescence has the same time characteristics as the slow fluorescence. By increasing the pressure the slow fluorescence was quenched while the milisecond phosphorescence was induced. We determined the low-pressure emission characteristics and the pressure effects as a function of excitation energy.From our data we obtained the parameters describing the intermediate type singlet-triplet coupling, the radiative and non-radiative relaxation rates from the singlet and triplet levels and the cross sections for the slow fluorescence quenching, all as a function of energy. Strong evidence is obtained for the participation of rotational states in the intra-molecular relaxation. The important difference between the situation where the singlet levels are isolated (low energy) and where the singlet level widths overlap (at higher energies) is demonstrated. In the former situation very large fluorescence quenching cross sectios were found. It is further shown that for high energies at least two effective collisions are needed to obtain a thermalized triplet; the mean energy removed per effective collision is 2200 cm^?1.     

Studies on pyridylhydrazones derived from biacetyl as analytical reagents

The synthesis, spectral characteristics (ir, uv), hydrolysis, and acid—base properties of biacetyl bis(2-pyridyl)hydrazone (BBPH), biacetylmonoxime-(2-pyridyl)hydrazone (BMPH), and biacetyl mono(2-pyridyl)hydrazone (BPH) have been reported. The behavior of BPH with a variety of metal ions has now been studied by spectrophotometry.     

Thermal energy charge transfer reactions of acetone and biacetyl

Rate coefficients up to a factor of 2.5 times larger than the capture collision rate are reported for a series of thermal energy, positive ion-molecule reactions of acetone and biacetyl. These rapid rates are interpreted in tems of a dissociative charge transfer process in which an electron is transferred in a non-spiralling collision from outside the classical capture limit. The factor which lead to this type of mechanism are discussed briefly.     

On the lower excited electronic states of biacetyl

An ab initio SCF and CI study has been carried out for the ground and electronically excited states of biacetyl (CH₃COCOCH₃). The second absorption band in the 4.40 eV region has been assigned to a ¹A_g → ¹B_g nπ^* transition The character of the lower-lying states has been analyzed in terms of the CI wavefunctions.     

Electronic relaxation of biacetyl in a supersonic jet

Emission spectra have been recorded and decay times measured for biacetyl selectively excited in the 0⁰₀ band of the S₁S₀ (¹A_u¹A_g) transition. The spectrum of the “long emission” corresponds to a superposition of the fluorescence and of the “hot” phosphorescence. The results may be treated in terms of a uniform distribution of the singlet oscillator strength among the quasi-stationary levels, in the absence of vibrational redistribution on a microsecond scale.     

Penta- and tetracoordinated phosphorous in reactions of biacetyl with diethylacetylphosphite and diethyl chlorophosphite

Conclusions Diethylacetyl phosphite and diethyl chlorophosphite react with biacetyl, intermediately forming, as do other derivatives of phosphorous acid, 1,3,2-dioxaphospholenes with a pentacoordinated phosphorous atom; the latter are rapidly transformed to noncyclic or cyclic derivatives of tetracoordinated phosphorous.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2609–2611, November, 1968.Deceased.