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.     

Lipophilic Functionalized Cobyrinic-Acid Derivatives. Part 1. Cobester α-monoacids (α,α,α,β,β,β-hexamethyl α-hydrogen Coα, Coβ-dicyanocobyrinates)

The four α,α,α, β,β,β,-hexamethyl α-hydrogen Coα, Coβ-dicyanocobyrinates 2b, d–f , with a free b-, d-, e-, and f-propionic-acid function, respectively, were prepared by partial hydrolysis of heptamethyl Coα, Coβ-dicyanocobyrinate (cobester; 1 ) in aqueous sulfuric acid. The cobester monoacids 2b, d–f were obtained as a ca. 1:1:1:1 mixture which was separated. The monoacids were purified by chromatography and isolated in crystalline form. The position of the free propionic-acid function was determined by an extensive analysis of 2b, d–f using 2D-NMR techniques; an analysis of the C,H-coupling network topology resulted in an alternative assignment strategy for cobyrinic-acid derivatives, based on pattern recognition. Additional information on the structure of the most polar of the four hexamethyl cobyrinates, of the b-isomer 2b , was also obtained in the solid state from a single-crystal X-ray analysis. Earlier structural assignments based on 1D-NMR spectra of the corresponding regioisomeric monoamides 3b, d–f (obtained from crystalline samples of the monoacids 2b, d–f ) were confirmed by the present investigations.     

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.     

The reactions of perfluoro- and α,α-dichloropolyfluoroalkanesulfinates

Sodium perfluoroalkanesulfinate, R_FSO₂Na [R_F?Cl(CF₂)₄, 1a; CF₃(CF₂)₅, 1b; Cl(CF₃)₆, 1c] reacted with bromine in aqueous solution to give the corresponding sulfonyl bromide R_FSO₂Br (2a-2c) and in acetonitrile or acetic acid, to form perfluoroalkyl bromide R_FBr (3a-3c). Heating in acetonitrile at 80°C, 2a-2c were converted smoothly into 3a-3c. However, reaction of sodium α,α-dichloropolyfluoroalkanesulfinate RCCl₂SO₂Na (R?CF₃, Cl(CF₂)n, n=2, 4, 6, 5a-5d) with bromine in aqueous solution gave directly the corresponding bromoalkanes 1-bromo-1,1-dichloropolyfluoroalkane RCCl₂Br (6a-6d). In aqueous potassium iodide solution, 1a-1c, 5a and 5b also reacted with iodine to form the corresponding iodo-polyfluoroalkane 4a-4c, 7a and 7b directly. 6a and 7a underwent free radical addition to alkene readily in the presence of free radical initiator and reacted with Na₂S₂O₄ in the usual way to form α,α-dichloropolyfluoroethane sulfinate (5a). 5a was stable in strong acid, but reacted with strong base to yield 10. 5a was oxidised by hydrogen peroxide to the sulfonate 11 and reduced by zinc in dilute acid to from the α-chloro sulfinate 12.     

Carbon Magnetic Resonance Spectra of α, β, γ, δ- and α, β, α′, β′- Unsaturated Ketones

Carbon-13 spectra of a series of 26 unsaturated ketones (ortho- and para-cyclo-hexadienones and corresponding open-chain analogues) have been measured by Fourier-transform. Pulse spectroscopy. A complete analysis has been achieved by means of double resonance experiments using noise-modulated and coherent off-resonance proton irradiation and with the aid of non-decoupled spectra. Chemical shifts are interpreted in terms of charge distribution in the dienone system and of methyl substituent effects. Carbon chemical shifts were also obtained for O-protonated ortho- and para-cyclohexadienones. One-bond and long-range carbon-proton and carbon-fluorine spin coupling constants are reported for several compounds.     

Applications of 1,4-addition of grignard reagents to α,β-unsaturated acid derivatives. III—configuration studies of α,β-diaryl-α,β-dialkylpropionitriles

The configuration of twenty-four different α,β-diaryl-α,β-dialkylpropionitriles has been determined using nuclear magnetic resonance spectra. The erythro form showed greater deshielding of the methine hydrogen and alkyl groups in its spectra than the corresponding threo isomer. The former, however, showed less deshielding of the aryl groups than the threo isomer. Infrared spectra were not suitable for assignments of configuration.     

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.      

Kinetics of the reactions of cyclopropane derivatives,part II. The gas-phase pyrolysis of cyclopropylamine

At temperatures of 356-425°C and pressures of 15–60 Torr, cyclopropylamine reacts to give an equimolar mixture of ammonia and N-propylidenecyclopropylamine as the initial product. The reaction is first order, homogeneous, and unaffected by the presence of radical inhibitors, and thus proceeds by an initial rate-determining unimolecular isomerization to give a reactive intermediate, which then reacts with a further molecule of cyclopropylamine to give the observed products. Reaction in the presence of added aliphatic amines gives other imines in addition, and the nature of these indicates that the intermediate is propenylamine or its tautomer propylideneamine:      

The synthesis of β-heteroarylamino-α,β-dehydro-α-amino acid derivatives via thiazolones

2-Alkoxy-4-heteroarylaminomethylene-5(4H)-thiazolones 4 were converted with various nucleophiles into β-heteroarylamino-α,β-dehydro-α-amino acid derivatives 11, 14, 15, 16, 17, 18 , and 19 . Reduction of 4 with sodium borohydride in ethanol saturated with gaseous ammonia afforded the corresponding β-heteroaryl-amino substituted alanyl amides 20 . Thiazoledione derivative 7a was transformed with sodium methoxide in methanol into 1-(4,6-dimethylpyrimidinyl-2)-4-mercaptocarbonylimidazol-2(3H)-one ( 8a ).     

The synthesis of β-heteroarylamino-α,β-dehydro-α-amino acid and β-heteroarylamino-α-amino acid derivatives

From heteroarylaminomethyleneoxazolones 4 , obtained from N-heteroarylformamidines 2 and 2-phenyl-5-oxo-4,5-dihydro-1,3-oxazole ( 3 ), the following β-heteroarylamino-α,β-dehydro-α-amino acid derivatives were prepared: methyl 8 and ethyl esters 9 , amides 10 and 11 , hydrazides 12 , and azides 15 . By catalytic hydrogenation the compounds 4 were converted into β-heteroarylamino substituted amides 18 and β-heteroarylamino-α-amino acids 20 .     

Synthesis of novel α,α′,β-trisubstituted β-lactones

A concise and efficient synthesis of α,α′,β-trisubstituted β-lactones is presented. These novel lactones are easily obtained in five steps and will be dedicated to anionic ring opening polymerization.     

The photochemistry of α,β-acetylenic ketones. II. Formation of furan derivatives

The photochemical reactions of α,β-acetylenic ketones have been examined. Irradiation of 1-p-substituted phenyl-2-propyn-1-ones 2–4 in primary alcohols gave 2,5-disubstituted furans 2a–4c. The formation of furans can be explained in terms of cyclization, followed by dehydration of the 1:1-adduct of acetylenic ketone and alcohol, which was formed initially by hydrogen atom abstraction from alcohol by the excited acetylenic ketone. Irradiation of 1-p-tolyl-2-propyn-1-one ( 2 ) in ethanol-d₁ yielded 2-methyl-5-p-tolylfuran ( 2b ) containing no deuterium. This result was consistent with a mechanism that involves hydrogen atom abstraction from alcohol by the carbon of triple bond rather than abstraction by carbonyl oxygen.