David J. Waddington

Self-reactions of isopropylperoxy radicals in the gas phase

The photo-oxidation of 2,2′-azopropane has been studied in order to determine the overall rate constant for the second-order removal of isopropylperoxy radicals. Arrhenius parameters of log10(Aobs/dm3 mol–1 s–1)= 9.15 ± 0.03 and Eobs= 18.65 ± 0.50 kJ mol–1 have been determined over a temperature range 300–373 K. These values are compared with those obtained for the self-reactions of primary and tertiary alkylperoxyradicals, and the corresponding reactions in solution.

Reactions of oxygenated radicals in the gas phase. Part 10.—Self-reactions of ethylperoxy radicals

The photo-oxidation of azoethane has been studied by molecular modulation spectroscopy in order to determine the overall rate constant for the second-order removal of ethylperoxy radicals between 303 and 457 K. The principal molecular products of the reaction between 302 and 373 K are acetaldehyde, ethanol and ethyl hydroperoxide. From the reaction rate data and analytical results, the following results have been obtained for the reactions 2C2H5O2˙→ CH2CHO + C2H5OH + O2. (3a) 2C2H5O2˙→ 2C2H5O˙+ O2. (3b)k3b/k3a increases with temperature from 1.75 ± 0.05 at 302 K to 2.45 ± 0.15 at 373 K. Arrhenius expressions for reactions (3a) and (3b) have been estimated.

Gas-phase oxidation of butene-2: The role of acetaldehyde in the reaction

The gas-phase oxidation of butene-2 has been studied under two different sets of conditions. At 184°C, the principal products, when butene-2 is co-oxidized with acetaldehyde, are the isomeric epoxybutanes. Between 277° and 400°C, butene-2-molecular oxygen mixtures yield acetaldehyde and oxides of carbon as the main products, although the eposides are still formed in significant yield. The proportion of acetaldehyde to epoxides does not change on increasing the temperature, while the proportion of carbon monoxide to carbon dioxide increases significantly. The results are explained in terms of addition reactions of oxygenated radicals to the alkene. Acetaldehyde is considered to be formed by addition of hydroxy, followed by oxygen, while, below 300°C, the principal source of epoxide is thought to be peracetyl attack on the alkene. Rate data for the addition of peracetyl to butene-2 at 184°C suggests that this reaction is as facile as the abstraction reaction between peracetyl and acetaldehyde.

Reactions of oxygenated radicals in the gas phase. Part 9.—Self-reactions of isopropylperoxy radicals

The principal products of the photo-oxidation of trans-2,2′-azopropane between 333 and 373 K are acetone, isopropyl alcohol, isopropyl hydroperoxide, acetaldehyde, formaldehyde, methyl alcohol and cis-2,2′-azopropane. The reaction mechanism has been simulated in detail, and, in conjunction with results obtained earlier for the overall self-reaction of isopropylperoxy radicals, the following rate data have been obtained for the reactions 2(CH3)2CHO2·→(CH3)2CHOH +(CH3)2CO + O2(3a), 2(CH3)2CHO2·→ 2(CH3)2CHO·+ O2(3b)k3b/k3a increases with temperature, from 1.39 ± 0.04 at 302 K to 1.83 ± 0.04 at 333 K and 2.80 ± 0.08 at 373 K. Values of A3a and A3b of 2.44 ± 0.31 × 107 and 1.38 ± 0.26 × 109 dm3 mol–1 s–1 and E3a and E3b of 12.0 ± 1.0 and 21.3 ± 1.5 kJ mol–1 were determined.

Reactions of oxygenated radicals in the gas phase. Part 6.—Reactions of isopropylperoxy and isopropoxy radicals

The principal products of the photo-oxidation of trans-2,2′-azopropane are acetone, isopropanol, isopropyl hydroperoxide and cis-2,2′-azopropane. The reaction mechanism has been simulated in detail. From the analytical results recorded in this paper and results from the self-reaction of isopropylperoxy radicals, the following rate data have been obtained for these reactions at 302 K. 2(CH3)2CHO2·→(CH3)2CHOH +(CH3)2CO + O2(3a), 2(CH3)2CHO2·→ 2(CH3)2CHO2·+ O2, (3b)(CH3)2CHO·+ O2→(CH3)2CO + HO2·, (5)(CH3)2CHO2H +(CH3)2CHO·→(CH3)2CHOH +(CH3)2CHO2·; (8), k3a= 2.15 ± 0.10 × 105 dm3 mol–1 s–1; k3b= 2.99 ± 0.20 × 105 dm3 mol–1 s–1; k8/k5= 166 ± 5. Further, a value of kd/kc= 0.60 ± 0.01 at 302 K has been found: 2(CH3)2ĊH → CH3CH2CH3+ CH3CHCH2(d), 2(CH3)2ĊH →(CH3)2CH—CH(CH3)2(c)

Anomalous electric polarizations and the sub-millimetre spectra in solution of some metal acetylacetonates

The molar electric polarizations at 29.7 cm–1 are reported for beryllium (II) bisacetylacetonate (2,4-pentanedionate) for the tris-acetylacetonates of AlIII, CoIII, CrIII, FeIII and MnIII and for ThIV-tetrakisacetylacetonate in benzene solution. The values are all intermediate between those at radio and visible frequencies, showing that there is absorption above, at and below 29.7 cm–1.The spectra between 5 and 25 cm–1 for benzene solutions of the trisacetylacetonates of AlIII and FeIII and for FeIII trisdipivalylmethanate (hexamethylacetylacetonate) are reported. The first two of these show a steady rise in absorption with increasing frequency, the third shows much less absorption rising slowly. Spectra in benzene solutions between 30 and 200 cm–1 are reported for Be(acac)2, for the trisacetylacetonates of AlIII, CoIII, CrIII, FeIII and MnIII. All these show very broad absorption bands divided into two regions by a window at 100–130 cm–1. The lower band is centred around 60–80 cm–1.Solution spectra for CeIV- and ThIV-tetrakisacetylacetonates show little absorption below 130 cm–1 but above this it rises rapidly. The spectra for FeIII-trishexafluoroacetylacetonate and FeIII-trisdipivalylmethanate show respectively a blue shift of the lower peak to ∼106 cm–1 and very little absorption below 160 cm–1.These spectra, together with those observed by Larsson and Eskilsson at 300–1600 cm–1 explain ∼50–60 % of the observed differences of polarization between radio and visible frequencies (PRF–PVF). For the AlIII and CrIII compounds most of the remaining differences are explained by the absorption in the microwave region observed by Dasgupta and Smyth and by DiCarlo et al. The unusually large PRF–PVF values are due to almost continuous absorption over a very wide range of frequency.The origin of the very broad absorption peaks below 100 cm–1 is discussed. For various reasons, including comparisons with the spectra observed for the crystalline substances, it is concluded that they arise from intramolecular vibrations which are very heavily damped by collisions with solvent. The low absorption by FeIII trisdipivalylmethanate and by the CeIV- and ThIV-tetrakisacetylacetonates below 130 cm–1 is probably due to steric interference.The possible nature of these vibrations is considered in the light of spectroscopic and dielectric observations and further evidence from crystallographic calculations made by Prof. C. E. Pfluger, from neutron scattering spectra for the trisacetylacetonates of AlIII, CrIII and FeIII, the trishexadeutero- and trishexafluoro-acetylacetonates of FeIII, FeIII-trisdipivalylmethanate and the tris-3-bromo- and tris-3-nitroacetylacetonates of CrIII together with the sub-millimetre spectra of the last two compounds. It seems probable that they involve bending of the chelate rings about the O … O vectors, with some ring flexing, thus causing large movements of the peripheral atoms.