Rate constants for the gas-phase reactions of OH radicals with β-dimethylstyrene and acetone. Mechanism of ββdimethylstyrene NOx – air photooxidation

The rate constants of gas-phase reactions of the hydroxyl radical with β-dimethylstyrene and acetone have been determined by a relative method at 298 K. The values obtained are β-dimethylstyrene (3.3 ± 0.5) × 10^?11 cm³/molecule·s and acetone (6.6 ± 0.9) × 10^?13 cm³/molecule·s. A simplified kinetic treatment of the experimental data shows that β-dimethylstyrene is stoichiometrically converted to benzaldehyde and acetone. In the photooxidation study of benzaldehyde, carbon dioxide was the only detected product. The ratio between carbon dioxide produced and benzaldehyde reacted was ≥1.     

Isomerization of unsaturated radicals. V. Unimolecular isomerization of hot α,α- and α,β-dimethallyl radicals

The 147 nm photolysis of 3,3 dimethylbut-1-ene leads mainly to the formation of very hot (?375 kJ/mol) α,α-dimethallyl radicals. On the other hand, that of 3-methyl-cis-and trans-pentene-2, as well as that of 2,3-dimethylbut-1-ene is a source of very hot α,β-dimethallyl radicals. These allylic radicals are coolled down using pressure and are allowed to combine with available methyl radicals. From the formation of various C₆H₁₂ products, it is concluded that the very hot α,α- radical isomerizes towards the α,β-structure at low pressures and vice versa. The equilibrium constant of the following process has been evaluated to be 1.72 ± 0.30.      

[3+3] Cyclization reactions of β-nitroenamines and β-enaminonitriles with α,β-unsaturated carboxylic acid chlorides

New indolizidines, quinolizidines, and octahydro-pyrido[1,2-a]azepines of lactam type were synthesized from 2-nitromethylene-pyrrolidine, -piperidine, and -hexahydroazepine, respectively, by [3+3] cyclizations with α,β-unsaturated carboxylic acid chlorides. In the case of quinolizidines, a double bond migration was observed, and explained in terms of amidity percentage. Cyanomethylene-pyrrolidine gave indolizidines of lactam type, while transformations of 1-cyanomethylene-tetrahydoisoquinoline resulted in lactams as well as ketones, when simple open-chain acid chlorides or cinnamoyl chloride were used, respectively.     

Cycloaddition reactions of sulfonylisothiocyanates with β,β-disubstituted enamines

Sulfonylisothiocyanates 1 and β,β-dimethylenamines 2 react to yield the dipoles 3. In nonpolar solvents an equilibrium exists between 3 and the thietanes 4. The free activation enthalpy for the ring closure 3→4 was obtained from the temperature dependent NMR spectra in liquid sulfur dioxide. Protonation of 3 with perchloric acid leads to the salts 8 which, as indicated by ΔG^≠-values obtained from NMR spectra, are also capable of ring closure.     

Kinetics of the reactions of cyclopropane derivatives. V. The gas-phase unimolecular reactions of 1 α-chloro-2α,3α-dimethylcyclopropane and 1α-chloro-2α,3β-dimethylcyclopropane

Thermolysis of the “all-cis” compound 1α-chloro-2α,3α-dimethylcyclopropane (A) at 550–607 K and 6–115 torr is a first-order homogeneous non-radical-chain process giving penta-1,3-diene (PD) and HCl as products. The Arrhenius parameters are log₁₀A(sec^?1) = 13.92 ± 0.08 and E = 199.6 ± 0.9 kJ/mol. The isomer with trans-methyl groups, 1α-chloro-2α,3β-dimethylcyclopropane (B) reacts by two parallel first-order processes giving as observed products trans-4-chloropent-2-ene (4CP) and PD + HCl, with log₁₀A(sec^?1) = 14.6 and 13.8, respectively, and E = 199.5 and 190.2 kJ/mol, respectively. The 4CP undergoes secondary decomposition to PD + HCl (as investigated previously). Comparison of the results for compounds (A) and (B) with those for other gas-phase and solution reactions leads to the conclusion that the gas-phase thermolyses proceed by rate-determining ring opening to form olefins which may decompose further by thermal or chemically activated reactions, and that the ring opening is a semiionic electrocyclic reaction in which alkyl groups in the 2,3-positions trans to the migrating chlorine semianion move apart, with appropriate consequences for the rate of reaction and the stereochemistry of the products.     

Tandem epoxysilane rearrangement/Wittig-type reactions using γ-phosphinoyl- and γ-phosphonio-α,β-epoxysilane

Reaction of γ-phosphinoyl- and γ-phosphonio-α,β-epoxysilane with a base followed by addition of a ketone or an aldehyde afforded dienol silyl ether derivatives via a tandem process that involves base-induced ring opening of the epoxide, Brook rearrangement, and Wittig-type reaction.     

The reactions of alkoxy radicals with O2. II. n-C3H7O radicals

n-C₃H₇ONO was photolyzed with 366 nm radiation at ?26, ?3, 23, 55, 88, and 120°C in a static system in the presence of NO, O₂, and N₂. The quantum yields of C₂H₅CHO, C₂H₅ONO, and CH₃CHO were measured as a function of reaction conditions. The primary photochemical act is and it proceeds with a quantum yield ?₁ = 0.38 ± 0.04 independent of temperature. The n-C₃H₇O radicals can react with NO by two routes The n-C₃H₇O radical can decompose via or react with O₂ via Values of k₄/k₂ ? k_4b/k₂ were determined to be (2.0 ± 0.2) × 10¹⁴, (3.1 ± 0.6) × 10¹⁴, and (1.4 ± 0.1) × 10¹⁵ molec/cm³ at 55, 88, and 120°C, respectively, at 150-torr total pressure of N₂. Values of k₆/k₂ were determined from ?26 to 88°C. They fit the Arrhenius expression: For k₂ ? 4.4 × 10^?11 cm³/s, k₆ becomes (2.9 ± 1.7) × 10^?13 exp{?(879 ± 117)/T} cm³/s. The reaction scheme also provides k_4b/k₆ = 1.58 × 10¹⁸ molec/cm³ at 120°C and k_8a/k₈ = 0.56 ± 0.24 independent of temperature, where      

Preparation of α- or β-trifluoromethylated vinylstannanes and their cross-coupling reactions

α- or β-Trifluoromethylated vinylstannanes 1, 2a, 3 and 4 were prepared form 1,1-bis(phenylthio)-2,2,3,3,3-pentafluoropropylbenzene (5) via several steps. The cross-coupling arylation reactions of 1–4 with aryl iodides bearing a bromo, methoxy, methyl, nitro or trifluoromethyl group on para- or meta-position of benzene ring afforded the corresponding coupling products in good yields. Compounds 1, 2a and 4 underwent the acylation reaction with various types of acyl chlorides to give the corresponding trifluoromethylated enone derivatives in good yields. Reduction of trifluoromethylated enone derivatives with LiAlH₄, followed by Fridel-Craft’s type of cyclization with AlCl₃ provided trifluoromethylated indene derivatives in good yields.     

Kinetics of the gas-phase reactions of OH radicals with a series of α,β-unsaturated carbonyls at 299 ± 2 K

Relative rate constants for the reaction of OH radicals with a series of α,β-unsaturated carbonyls have been determined at 299 ± 2 K, using methyl nitrite photolysis in air as a source of OH radicals. Using a rate constant for the reaction of OH radicals with propene of 2.52 × 10^?11 cm³/molec·s, the rate constants obtained are (× 10¹¹ cm³/molec·s: acrolein, 1.83 ± 0.13; crotonaldehyde, 3.50 ± 0.40; methacrolein, 2.85 ± 0.23; and methylvinylketone, 1.88 ± 0.14). These data, which are necessary input to chemical computer models of the NO_x–air photooxidations of conjugated dialkenes, are discussed and compared with literature values.     

Free radicals in γ-irradiated poly-α-methylstyrene

Electron spin resonance (ESR) spectra were observed at ?160°C and at room temperature for γ-irradiated poly-α-methylstyrene. The spectrum observed at room temperature has been attributed to the radical species while that at ?160°C results from the same radical and superposition of the spectrum due to the radical ?H₂-C(CH₃)(C₆H₅)-. The radicals which are stable at room temperature could be used to graft vinyl acetate.     

Syntheses of stereodefined β-alkylidene-γ-lactones and substituted β, γ-unsaturated δ-lactones

1-Trimethylsilyl-1,3-diyne derived trans-bis(trimethylstannyl) enynes undergo stepwise transmetallation with methyllithium to furnish the corresponding enynyllithium reagents. The application, in various orders, of a sequence of transmetallation-protonation-alkylation-hydroxyalkylation-hydroboration-oxidation reactions provides a novel approach to stereo-defined β-alkylidene γ-lactones and β, γ-unsaturated δ-lactones.     

Enantioselective synthesis of β,β-dialkyl α-hydroxy γ-butyrolactones

An ephedrine-derived morpholine dione is employed in the synthesis of chiral alkylidene morpholinones that are efficiently converted to β-substituted α,γ-dihydroxy butyramides, precursors of the corresponding butyrolactones. Enantioselective synthesis of a spiro analog of pantolactone as well as a naturally occurring pantolactone homolog is achieved with this protocol.     

1,4-addition reactions to α,β unsaturated tertiary amides

Ketones, phenylacetonitrile, ethylmalonate, cyanoethyl acetate, nitromethane and nitroethane were found to add directely to α,β-unsaturated tertiary amides in the presence of CsF/Si(OMe)₄ to give 1,4-addition products in fair to good yields.     

Kinetics of the gas-phase reactions of NO3 radicals with a series of alkynes,haloalkenes, and α,β-unsaturated aldehydes

Rate constants for the gas-phase reactions of NO₃ radicals with a series of alkynes, haloalkenes, and α,β-unsaturated aldehydes have been determined at 298 ± 2 K using a relative rate technique. Using rate constants for the reactions of NO₃ radicals with ethene and propene of (1.1 ± 0.5) × 10^?16 cm³ molecule^?1 s^?1 and (7.5 ± 1.6) × 10^?15 cm³ molecule^?1 s^?1, respectively, the following rate constants (in units of 10^?16 cm³ molecule^?1 s^?1) were obtained: acetylene, ≤0.23; propyne, 0.94 ± 0.44; vinyl chloride, 2.3 ± 1.1; 1,1-dichloroethene, 6.6 ± 3.1; cis-1,2-dichloroethene, 0.75 ± 0.35; trans-1,2-dichloroethene, 0.57 ± 0.27; trichloroethene, 1.5 ± 0.7; tetrachloroethene, <0.4; allyl chloride, 2.9 ± 1.3; acrolein, 5.9 ± 2.8; and crotonaldehyde, 41 ± 9. The atmospheric implications of these data are discussed.     

Synthese von diastereo- und enantio-selektiv deuterierten β,ε-, β,β-, β,γ- und γ,γ-Carotinen

Synthesis of Diastereo- and Enantioselectively Deuterated β,ε-, β,β-, β,γ- and γ,γ-Carotenes We describe the synthesis of (1′R, 6′S)-[16′, 16′, 16′-²H₃]-β, εcarotene, (1R, 1′R)-[16, 16, 16, 16′, 16′, 16′-²H₆]-β, β-carotene, (1′R, 6′S)-[16′, 16′, 16′-²H₃]-γ, γ-carotene and (1R, 1′R, 6S, 6′S)-[16, 16, 16, 16′, 16′, 16′-²H₆]-γ, γ-carotene by a multistep degradation of (4R, 5S, 10S)-[18, 18, 18-²H₃]-didehydroabietane to optically active deuterated β-, ε- and γ-C₁₁-endgroups and subsequent building up according to schemes \documentclass{article}\pagestyle{empty}\begin{document}${\rm C}_{11} \to {\rm C}_{14}^{C_{\mathop {26}\limits_ \to }} \to {\rm C}_{40} $\end{document} and C₁₁ → C₁₄; C₁₄+C₁₂+C₁₄→C₄₀. NMR.- and chiroptical data allow the identification of the geminal methyl groups in all these compounds. The optical activity of all-(E)-[²H₆]-β,β-carotene, which is solely due to the isotopically different substituent not directly attached to the chiral centres, is demonstrated by a significant CD.-effect at low temperature. Therefore, if an enzymatic cyclization of [17, 17, 17, 17′, 17′, 17′-²H₆]lycopine can be achieved, the steric course of the cyclization step would be derivable from NMR.- and CD.-spectra with very small samples of the isolated cyclic carotenes. A general scheme for the possible course of the cyclization steps is presented.     

Photochemical reactions of β-aminovinyl aryl thioketones

Irradiation of β-aminovinyl aryl thioketones ( 1a-b ) afforded β-aminovinyl aryl ketones ( 2a-b ). 2H-Thiopyran derivatives ( 4a-b ) were obtained when β-aminovinyl phenyl thioketone ( 1a ) was irradiated with methyl acrylate and acrylonitrile. 4H-Thiopyran derivatives ( 6,8 ) were also obtained thermally in the reaction of β-aminovinyl phenyl thioketone ( 1a ) and methyl propiolate and maleic anhydride.     

Kinetics of the gas-phase reactions of β-phellandrene with OH and NO3 radicals and O3 at 297 ± 2 K

Rate constants for the gas-phase reactions of the biogenically emitted monoterpene β-phellandrene with OH and NO₃ radicals and O₃ have been measured at 297 ± 2 K and atmospheric pressure of air using relative rate methods. The rate constants obtained were (in cm³ molecule^?1 s^?1 units): for reaction with the OH radical, (1.68 ± 0.41) × 10^?10; for reaction with the NO₃ radical, (7.96 ± 2.82) × 10^?12; and for reaction with O₃, (4.77 ± 1.23) × 10^?17, where the error limits include the estimated uncertainties in the reference reaction rate constants. Using these rate constants, the lifetime of β-phellandrene in the lower troposphere due to reaction with these species is calculated to be in the range of ca. 1–8 h, with the OH radical reaction being expected to dominate over the O₃ reaction as a loss process for β-phellandrene during daylight hours.     

13‐cis‐β,β‐Carotene and 15‐cis‐β,β‐carotene

13‐cis‐β,β‐Carotene, C₄₀H₅₆, crystallizes with a complete molecule in the asymmetric unit, whereas 15‐cis‐β,β‐carotene, also C₄₀H₅₆, has twofold symmetry about an axis through the central bond of the polyene chain. The polyene methyl groups are arranged on one side of the polyene chains for each molecule and the 6‐s‐cisβ end groups, with the cyclohexene rings in half‐chair conformations, are twisted out of the planes of the polyene chains by angles ranging from 41.37 (17) to 52.2 (4)°. The molecules in each structure pack so that the arms of one occupy the cleft of the next, and there is significant π–π stacking of the almost‐parallel polyene chains of the 15‐cis isomer, which approach at distances of 3.319 (1)–3.591 (1) Å.