Rate Constants for the Addition of 2-Hydroxy-2-propyl Radicals to Alkenes in Solution studied by laser flash photolysis

Absolute rate constants for the addition of the highly nucleophilic 2-hydroxy-2-propyl radical to eight fast-reacting 1- and 1,1-disubstituted alkenes in MeOH at room temperature have been determined by laser flash photolysis. Also the absorption spectra of the 2-hydroxy-2-propyl and the benzylic and alkyl-type adduct radicals are presented. The rate constants were obtained using various methods for the analysis of the kinetic traces and support earlier findings.     

Absolute Rate Constants for the Addition of the 2‐(Methoxycarbonyl)propan‐2‐yl and the 3,3,3‐Trifluoracetonyl Radicals to Alkenes in Solution

Absolute rate constants and some of their Arrhenius parameters were obtained by time‐resolved electron spin resonance (ESR) spectroscopy for the addition of the 2‐(alkoxycarbonyl)propan‐2‐yl and 3,3,3‐trifluoroacetonyl (=3,3,3‐trifluoro‐2‐oxopropyl) radicals to a variety of mono‐ and 1,1‐disubstituted alkenes. Their analysis shows that the addition of 2‐(alkoxycarbonyl)propan‐2‐yl is mainly governed by the exothermicity of the reaction with slight modifications by nucleophilic and electrophilic effects giving rise to an overall ambiphilic behavior. In contrast, large electrophilic polar effects dominate the addition of the 3,3,3‐trifluoroacetonyl (=3,3,3‐trifluoro‐2‐oxopropan‐2‐yl) radical, as it is expected from its large electron affinity. For both radicals, the activation energies are well‐predicted by analytic equations for the enthalpic and polar terms. A comparison of the rate data of 2‐(alkoxycarbonyl)propan‐2‐yl with the homo‐ and copolymerization rate constants of the propagating radical of methyl methacrylate shows that the additions of these structurally related low‐ and high‐molecular‐weight radicals to alkenes are governed by very similar effects.     

Absolute Rate Constants for the Addition of the 1‐(tert‐Butoxy)carbonylethyl Radical to Alkenes in Solution

Absolute rate constants and some of their Arrhenius parameters are reported for the addition of the 1‐[(tert‐butoxy)carbonyl]ethyl radical (MeC . HCO₂Me₃) to several mono‐ or 1,1‐disubstituted alkenes in acetonitrile as obtained by time‐resolved electron spin resonance spectroscopy. At 295 K, the rate constants range from 470 M ⁻¹ s⁻¹ (but‐1‐ene) to 2.4⋅10⁵ M ⁻¹ s⁻¹ (1,1‐diphenylethene), the experimental activation energies range from 26.8 kJ/mol (but‐1‐ene) to 14.7 kJ/mol (styrene), and the frequency factors obey on the average log (A/M ⁻¹ s⁻¹)=7.9±0.5. The rate constants of the secondary 1‐[(tert‐butoxy)carbonyl]ethyl radical are close to the geometric mean of those of the related primary [(tert‐butoxy)carbonyl]methyl and the tertiary 2‐(methoxycarbonyl)propan‐2‐yl radicals. The activation energies for addition of these three carboxy‐substituted alkyl radicals are mainly governed by the addition enthalpy but are also substantially lowered by ambiphilic polar effects. The results support a previously derived predictive analysis, and relations to rate constants of acrylate polymerizations are discussed.     

Absolute Rate Constants for the Addition of the 1‐(tert‐Butoxy)carbonylethyl Radical onto Cyclic Alkenes in Solution

Absolute rate constants are reported for the addition of the 1‐[(tert‐butoxy)carbonyl]ethyl (= 2‐(1,1‐dimethylethoxy)‐1‐methyl‐2‐oxoethyl) radical ^.CHMeCO₂(t‐Bu) to several cyclic and monosubstituted alkenes in MeCN as obtained by time‐resolved electron paramagnetic resonance (EPR). The activation energies for the addition of this alkyl radical are mainly governed by the addition enthalpy but are also substantially lowered by the ambiphilic effect and by relief of cyclic strain.     

Absolute Rate Constants for the Reactions of Primary Alkyl Radicals with Aromatic Amines(1)

Hydrogen abstraction from diarylamines (4-X-C(6)H(4))(2)NH [X = H, CH(3), C(8)H(17), CH(3)O, and Br] by the 2-methyl-2-phenylpropyl radical in n-dodecane solution was investigated by thermolysis of 3-methyl-3-phenylbutanoyl peroxide in the presence of various concentrations of the amines. The reaction is a non-chain process in which the 2-methyl-2-phenylpropyl radical and its rearrangement product, the 2-benzylpropan-2-yl radical, abstract hydrogen from both the solvent and the amine. Cross-disproportionation reactions of the rearranged radical led to the formation of significant amounts of beta,beta-dimethylstyrene. Rate constants for hydrogen abstraction by the unrearranged, primary alkyl radical from n-dodecane (k(373K) = 3.5 x 10(3) M(-)(1) s(-)(1)), diphenylamine (k(373K) = 1.3 x 10(6) M(-)(1) s(-)(1)), and the substituted diarylamines were determined from the product yields and the known rate constant for the radical rearrangement. From kinetic experiments with N-deuteriodiphenylamine the deuterium kinetic isotope effect,k(NH)/k(ND), was found to be 2.3 at 373 K.     

The Addition of tert-Butyl (Me3Ċ) and (tert-Butoxy)carbonylmethyl (Me3CO2CĊH2) radicals to alkynes in solution studied by ESR spectroscopy

Absolute rate constants and their temperature dependence are determined by time-resolved electron spin resonance for the addition of Me₃? to 20 and of Me₃CO₂C?H₂ to six mono- and disubstituted alkynes in solution. For Me₃? the rate constants show polar alkyne-substituent effects which are, however, weaker than for the corresponding alkenes. For Me₃CO₂?H₂, the rate constants do not vary strongly with alkyne substitution and probably increase with increasing reaction exothermicity. Both radicals react generally slower with alkynes than with alkenes which is discussed in terms of the state correlations. Several vinyl-type radical adducts of Me₃? to alkenes are characterized by electron spin resonance, and their spectral data indicate linear or bent configurations of the radical carbon depending on the substitution.     

Absolute Rate Constants for the Addition of Cyanomethyl (·CH2CN) and (tert-Butoxy)carbonylmethyl (·CH2CO2C(CH3)3) radicals to alkenes in solution

Absolute rate constants and their temperature dependence were determined by time-resolved electron spin resonance for the addition of the radicals ·CH₂CN and ·CH₂CO₂C(CH₃)₃ to a variety of mono- and 1,1-disubstituted and to selected 1,2- and trisubstituted alkenes in acetonitrile solution. To alkenes CH₂?CXY, ·CH₂CN adds at the unsubstituted C-atom with rate constants ranging from 3.3·10³ M ^?1S ^?1 (ethene) to 2.4·10⁶ M ^?1S ^?1 (1,1-diphenylethene) at 278 K, and the frequency factors are in the narrow range of log (A/M ^?1S ^?1) = 8.7 ± 0.3. ·CH₂CO₂C(CH₃)₃ shows a very similar reactivity with rate constants at 296 K ranging from 1.1·10⁴ M ^?1S ^?1 (ethene) to 10⁷ M ^?1S ^?1 (1,1-diphenylethene) and frequency factors log (A/M ^?1S ^?1) = 8.4 ± 0.1. For both radicals, the rate constants and the activation energies for addition to CH₂?CXY correlate well with the overall reaction enthalpy. In contrast to the expectation of an electro- or ambiphilic behavior, polar alkene-substituent effects are not clearly expressed, but some deviations from the enthalpy correlations point to a weak electrophilicity of the radicals. The rate constants for the addition to 1,2- and to trisubstituted alkenes reveal additional steric substituent effects. Self-termination rate data for the title radicals and spectral properties of their adducts to the alkenes are also given.     

Rhenium(I)‐Catalyzed ortho‐C−H Addition to Bicyclic Alkenes

Hydroarylation of bicyclic alkenes has been developed using a low‐valent Re^I‐catalyzed, directing group‐assisted C?H bond activation strategy. The addition of sodium acetate significantly improves the reaction efficiency; moreover, bicyclic alkenes such as 7‐oxa and aza benzonorbornadienes worked efficiently under this reaction condition. Preliminary mechanistic studies suggest that, after the alkene insertion, the rhenacycle preferentially undergoes protonolysis rather than reductive elimination.     

Photocycloaddition of Quinoxaline-2(1H)-thiones to Alkenes

A synthetically useful C? C bond formation involving the photochemical addition of quinoxaline-2(1H)-thiones to alkenes is described. Irradiation of the quinoxaline-2(1H)-thiones 1–4 in the presence of the alkenes 7 gave the 2-(2′-mercaptoalkyl)quinoxalines 8–11 in moderate-to-good yields via ring cleavage of an intermediate aminothietane with aromatization of the quinoxaline ring. The latter was formed by [2+2] photocycloaddition of the C?S bond of the quinoxaline-2(1H)-thione and the C?C bond of the alkene.     

Absolute Rate Constants in Free-Radical Polymerization. III. Determination of Propagation and Termination Rate Constants for Styrene and Methyl Methacrylate

A spatially intermittent polymerization (SIP) reactor has been used for determination of absolute rate constants in photo-initiated, free-radical polymerization of styrene (STY) and methyl methacrylate (MMA). Experimental data are reported in the temperature range 15-30°C and in the high molecular weight region for MMA and STY. Additional experimental data are reported at 30° C and various lower molecular weights for STY which indicate that the propagation rate constant K is independent of polymer molecular weight, and K is dependent on molecular weight, especially at low molecular weight, approaching an approximately constant value at high molecular weight.     

Darstellung von Organylquecksilber(II)‐di(methansulfonyl)amiden und Kristallstruktur von Ph–Hg–N(SO2Me)2

Polysulfonylamines. CXXIV. Preparation of Organylmercury(II) Di(methanesulfonyl)amides and Crystal Structure of Ph–Hg–N(SO₂Me)₂ Four N,N‐disulfonylated organylmercury(II) amides R–Hg–N(SO₂Me)₂, where R is Me, ⁱPr, Me₃SiCH₂ or Ph, were obtained on treating the appropriate chlorides RHgCl with AgN(SO₂Me)₂, and characterized by ¹H and ¹³C NMR spectra. In the crystal structure of the phenyl compound (orthorhombic, space group Pbca, Z = 8, X‐ray diffraction at –95 °C), the molecule exhibits a covalent and significantly bent C–Hg–N grouping [bond angle 172.7(3)°; Hg–C 204.0(8), Hg–N 209.1(7) pm]. One sulfonyl oxygen atom forms a short intramolecular Hg…O contact [296.1(5) pm] and simultaneously catenates glide‐plane related molecules via a second Hg…O interaction 297.6(5) pm], thus conferring upon Hg^II the effective coordination number 4 and a geometrically irregular coordination polyhedron (bond angles from 173 to 54°).     

Rate Constants for the Reactions of NO3 and SO4 Radicals with Oxalic Acid and Oxalate Anions in Aqueous Solution

Rate constants for the reactions of NO3 and SO4 radicals with oxalic acid and oxalate anions in aqueous solution have been measured using pulse radiolysis and laser flash photolysis.     

Benzyl(triphenyl)phosphonium Dichloroiodate: A New Reagent for Coiodination of Alkenes

A mild, efficient, and regio‐ and stereoselective method for iodoalkoxylation and iodohydroxylation of olefins has been developed using benzyl(triphenyl)phosphonium dichloroiodate as iodine source. This procedure led to the corresponding iodoalkoxylated and iodohydroxylated products in moderate to excellent yields.