共查询到20条相似文献,搜索用时 31 毫秒
1.
3-Methyl-3-(o-tolyl)-1,2-dioxetane 1 and 3-methyl-4-(o-bromophenyl)-1,2-dioxetane 2 were synthesized in low yield by the β-bromo hydroperoxide method. The activation parameters were determined by the chemilumin-escence method (for 1 ΔG? = 24.7 ± 0.3 kcal/mol, ΔH? = 25.4, ΔS? = + 1.9 e.u., k60 = 3.4 × 10?4s?1; for 2 ΔG? = 24.7 ± 0.4 kcal/mol, ΔH? = 24.7, ΔS? = 0.0 e.u., k60 = 4.1 × 10?4s?1). Thermolysis of 1–2 directly produced high yields of excited triplets as expected for this type of dioxetane [triplet chemiexcitation yields (?7) for 1 0.03; for 2 0.02; the ?T/?S ratios were estimated to be approximately 200 for both compounds]. The effect of ortho-aryl substituents was inconsistent with electronic effects. The ortho substitution in 1–2 resulted in a marked increase in stability of the dioxetanes. The results are discussed in relation to a diradical-like mechanism. 相似文献
2.
trans-3-Methyl-4-(p-anisyl)-1,2-dioxetane 1, trans-3-methyl-4-(o-anisyl)-1,2-dioxetane 2 , 3-methyl-3-benzyl-1,2-dioxetane 3 , and 3-methyl-3-p-methoxybenzyl-1,2-dioxetane 4 were synthesized in low yield by the β-bromo hydroperoxide method. The activation parameters were determined by the chemiluminescence method (for 1 ΔG≠ = 22.8 ± 0.3 kcal/mol, Δ≠ = 22.2, ΔS≠ = −1.7 e.u., k60 = 7.6 × 10−3s−1; for 2 ΔG≠ + 23.6 ± 0.3 kcal/mol, ΔH≠ = 22.8, ΔS≠ = −2.2 e.u., k60 = 2.5 × 10−3S−1; for 3 ΔG≠ = 24.0 ± 0.4 kcal/mol, ΔH≠ = 23.1, ΔS≠ = −2.7 e.u., k60 = 1.2 × 10−3S−1; for 4 ΔG≠ = 24.0 ± 0.2 kcal/mol, ΔH≠, = 23.2, ΔS≠, = −2.4 e.u., k60 = 1.2 × 10−3s−1). Thermolysis of 1–4 produced excited carbonyl fragments (direct production of high yields of triplets relative to excited singlets) [chemiexcitation yields ϕT, ϕS, respectively: for 1 0.02, 0.0001; for 2 0.02, 0.0001; for 3 0.03, 0.0002; for 4 0.02, 0.0001]. The effect of paramethoxyaryl substitution was consistent with electronic effects. The ortho substitution in 2 resulted in an increase in stability of the dioxetane, opposite that observed for an electronic effect. The results are discussed in relation to a diradical-like mechanism. 相似文献
3.
Alfons L. Baumstark Sean L. Anderson Chariety J. Sapp Pedro C. Vasquez 《Heteroatom Chemistry》2001,12(3):176-179
3‐Methyl‐3‐(3‐pentyl)‐1,2‐dioxetane 1 and 3‐methyl‐3‐(2,2‐dimethyl‐1‐propyl)‐1,2‐dioxetane 2 were synthesized in low yield by the α‐bromohydroperoxide method. The activation parameters were determined by the chemiluminescence method (for 1 ΔH‡ = 25.0 ± 0.3 kcal/mol, ΔS‡ = −1.0 entropy unit (e.u.), ΔG‡ = 25.3 kcal/mol, k1 (60°C) = 4.6 × 10−4s−1; for 2 ΔH‡ = 24.2 ± 0.2 kcal/mol, ΔS‡ = −2.0 e.u., ΔG‡ = 24.9 kcal/mol, k1 (60°C) = 9.2 × 10−4s−1. Thermolysis of 1–2 produced excited carbonyl fragments (direct production of high yields of triplets relative to excited singlets) (chemiexcitation yields for 1: ϕT = 0.02, ϕS ≤ 0.0005; for 2: ϕT = 0.02, ϕS ≤ 0.0004). The results are discussed in relation to a diradical‐like mechanism. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:176–179, 2001 相似文献
4.
Gerard W. Liesegang Michael M. Farrow Licesio J. Rodriguez Roger K. Burnham Edward M. Eyring Neil Purdie 《国际化学动力学杂志》1978,10(5):471-487
A temperature dependence study of the ultrasonic amplitudes, velocities, and relaxation times for a presumed conformational transition of noncomplexed aqueous 18-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane) is discussed. At all temperatures a single relaxation was observed within a 15–255-MHz frequency range. The equilibrium constant for the presumed conformational transition \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CR}_1 \mathop \rightleftarrows\limits^{K_{12} } {\rm CR}_2 $\end{document} was determined to be K21 = (2 ± 2) × 10?2. The activation parameters are ΔH21≠ = 10.2 ± 1.0 kcal/mol, ΔS21≠ = 7.7 ± 0.2 cal/(mol·deg), ΔH12≠ = 7.4 ± 1.0 kcal/mol, and ΔS12≠ = 7.7 ± 0.2 cal/(mol·deg), while the thermodynamic enthalpy and entropy were found to be ?2.6 ± 1.0 kcal/mol and 0 ± 0.2 cal/(mol·deg), respectively. The rate constants at 25.0°C for the presumed conformational transition are k21 = (1.0 ± 0.3) × 107 sec?1 and k12 = (6.2 ± 0.2) × 108 sec?1. 相似文献
5.
《Electroanalysis》2005,17(11):1003-1007
A novel PVC membrane ion‐selective electrode based on tribenzyltin(IV) dithiocarbamate [Sn(IV)–TBDTB] as neutral carrier was developed for thiocyanate (SCN?) determination. The electrode exhibits a near‐Nernstian response for SCN? with a slope of 62.8±2.0 mV per decade over a wide concentration range 1.0×10?1–2.0×10?6 mol L?1 and a detection limit of 1.0×10?6 mol L?1 in MES–NaOH buffer, pH 6.0, at 25 °C. The electrode prepared with 1.5 wt.% Sn(IV)–TBDTB, 32.5 wt.% PVC and 66.0 wt.% 2‐nitrophenyloctyl ether (o‐NPOE) shows optimal response characteristics. Anti‐Hofmeister selectivity sequence for a series of anions shown by the electrode was as follows: SCN?>Sal?>I?>ClO >phCOO?>CH3COO?>Br?>Cl?>NO >NO >Citrate>SO42?. The useful pH range for the electrode was found to be 3–7 with a response time 30–40 s. The electrode has been used for direct determination of thiocyanate in wastewater with satisfactory results. 相似文献
6.
《Journal of Coordination Chemistry》2012,65(1-3):61-69
The influence of placing thioether linkages trans to a site of nitrito substitution and spontaneous nitrito-tonitro isomerization is reported for the [CoQS(H2O)]3+ cation where QS is 1,11-diamino-3,6,9-trithiaundecane. Preparation and characterization is described for the aqua and nitrito complexes. Rate data for the substitution process is presented at 17.7, 25.0 and 35.0°C. It is consistent with the mechanism first proposed by Basolo and Pearson in which N2O3 is the nitrosation agent. [CoQS(H2O)]3+ is three hundred times more reactive than [Co(NH3)5H2O]3+ under identical conditions. Isomerization is dramatically slower than the conversion of [CoQS(H2O)3+ to [CoQS(ONO)]2+. The isomerization process was studied at 5 wavelengths, 3 temperatures and various conditions of acid and nitrite ion at an ionic strength of 0.11–0.60 M. Studies at 25°C give kisom = 1.21 ± 0.12 × 10?4 sec ?1. Similar determinations at 17.7 and 35.0°C give kisom = 3.84 ± 0.65 × 10?5 sec?1 and 3.59 ± 0.13 × 10?4 sec?1 respectively. The thermodynamic activation parameters ΔH≠, ΔG≠, and ΔS≠ obtained from an Eyring plot gives ΔH≠ = 111.3 kJ/mol, ΔS≠ = + 53 J/molK and ΔG≠ = 95.4 kJ/mol. These results are discussed in the context of present knowledge and experience with other cobalt(III) ligand systems. 相似文献
7.
The thermal unimolecular decomposition of three vinylethers has been studied in a VLPP apparatus. The high-pressure rate constant for the retro-ene reaction of ethylvinylether was fit by log k (sec?1) = (11.47 + 0.25) - (43.4 ± 1.0)/2.303 RT at <T> = 900 K and that of t - butylvinylether by log k (sec?1) = (12.00 ± 0.27) - (38.4 ± 1.0)/2.303 RT at <T> = 800 K. No evidence for the competition of the higher energy homolytic bond-fission process could be obtained from the experimental data. The rate constant compatible with the C? O bond scission reaction in the case of benzylvinylether was log k (sec?1) = (16.63 ± 0.30) - (53.74 ± 1.0)/2.303 RT at <T> = 750 K. Together with ΔHf,3000(benzyl·) = 47.0 kcal/mol, the activation energy for this reaction results in ΔHf,3000(CH2CHO) = +3.0 ± 2.0 kcal/mol and a corresponding resonance stabilization energy of 3.2 ± 2.0 kcal/mol for 2-ethanalyl radical. 相似文献
8.
Jonathan F. Ojo Jide Ige Grace O. Ogunlusi Olanrewaju Owoyomi Esan S. Olaseni 《Transition Metal Chemistry》2006,31(6):782-785
The kinetics of the reactions between Fe(phen)
3
2+
[phen = tris–(1,10) phenanthroline] and
Co(CN)5X3− (X = Cl, Br or I) have been investigated in aqueous acidic solutions at I = 0.1 mol dm−3 (NaCl/HCl). The reactions were carried out at a fixed acid concentration ([H+] = 0.01 mol dm−3) and the second-order rate constants for the reactions at 25 °C were within the range of (0.151–1.117) dm3 mol−1 s−1. Ion-pair constants K
ip for these reactions, taking into consideration the protonation of the cobalt complexes, were 5.19 × 104, 3.00 × 102 and 4.02 × 104 mol−1 dm−3 for X = Cl, Br and I, respectively. Activation parameters measured for these systems were as follows: ΔH* (kJ K−1 mol−1) = 94.3 ± 0.6, 97.3 ± 1.0 and 109.1 ± 0.4; ΔS* (J K−1) = 69.1 ± 1.9, 74.9 ± 3.2 and 112.3 ± 1.3; ΔG* (kJ) = 73.7 ± 0.6, 75.0 ± 1.0 and 75.7 ± 0.4; E
a
(kJ) = 96.9 ± 0.3, 99.8 ± 0.4, and 122.9 ± 0.3; A (dm3 mol−1 s−1) = (7.079 ± 0.035) × 1016, (1.413 ± 0.011) × 1017, and (9.772 ± 0.027) × 1020 for X = Cl, Br, and I respectively. An outer – sphere mechanism is proposed for all the reactions. 相似文献
9.
Harald Günther Oswald Eppers Heike Hausmann Dietmar Hüls Hans-Egbert Mons Klaus-Dieter Klein Adalbert Maercker 《Helvetica chimica acta》1995,78(8):1913-1932
The solution structure and the aggregation behavior of (E)-2-lithio-1-(2-lithiophenyl)-1-phenylpent-1-ene ( 1 ) and (Z)-2-lithio-1-(2-lithiophenyl)ethene ( 2 ) were investigated by one- and two-dimensional 1H-, 13C-, and 6Li-NMR spectroscopy. In Et2O, both systems form dimers which show homonuclear scalar 6Li,6Li spin-spin coupling. In the case of 2 , extensive 6Li,1H coupling is observed. In tetrahdrofuran and in the presence of 2 mol of N,N,N′,N′-tetramethylethylylenediamine (tmeda), the dimeric structure of 1 coexists with a monomer. The activation parameters for intra-aggregate exchange in the dimers of 1 and 2 ( 1 (Et2O): ΔH≠ = 62.6 ± 13.9 kJ/mol, ΔS≠ = 5.8 ± 14.0 J/mol K, ΔG≠(263) = 61.1 kJ/mol; 2 (dimethoxyethane): ΔH≠ = 36.9 ± 6.5 kJ/mol, ΔS≠ = ?61 ± 25 J/mol K, ΔG≠(263) = 54.0 kJ/mol) and the thermodynamic parameters for the dimer-monomer equilibrium for 1 (ΔH°; = 26.7 ± 5.5 kJ/mol, ΔS° = 63 ± 27 J/mol K), where the monomer is favored at low temperature, were determined by dynamic NMR studies. 相似文献
10.
Alfons L. Baumstark Sean L. Anderson Chariety J. Sapp Pedro C. Vasquez 《Heteroatom Chemistry》2001,12(6):459-462
3‐Methyl‐3‐(3‐pentyl)‐1,2‐dioxetane 1 and 3‐methyl‐3‐(2,2‐dimethyl‐1‐propyl)‐1,2‐dioxetane 2 were synthesized in low yield by the α‐bromohydroperoxide method. The activation parameters were determined by the chemiluminescence method (for 1 ΔH‡ = 25.0 ± 0.3 kcal/mol, ΔS‡ = −1.0 entropy unit (e.u.), ΔG‡ = 25.3 kcal/mol, k1 (60°C) = 4.6 × 10−4s−1; for 2 ΔH‡ = 24.2 ± 0.2 kcal/mol, ΔS‡ = −2.0 e.u., ΔG‡ = 24.9 kcal/mol, k1 (60°C) = 9.2 × 10−4s−1. Thermolysis of 1–2 produced excited carbonyl fragments (direct production of high yields of triplets relative to excited singlets) (chemiexcitation yields for 1: ϕT = 0.02, ϕ ≤ 0.0005; for 2: ϕT = 0.02, ϕS ≤ 0.0004). The results are discussed in relation to a diradical‐like mechanism. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:459–462, 2001 相似文献
11.
Pd-catalyzed double carbomethoxylation of the Diels-Alder adduct of cyclo-pentadiene and maleic anhydride yielded the methyl norbornane-2,3-endo-5, 6-exo-tetracarboxylate ( 4 ) which was transformed in three steps into 2,3,5,6-tetramethyl-idenenorbornane ( 1 ). The cycloaddition of tetracyanoethylene (TCNE) to 1 giving the corresponding monoadduct 7 was 364 times faster (toluene, 25°) than the addition of TCNE to 7 yielding the bis-adduct 9 . Similar reactivity trends were observed for the additions of TCNE to the less reactive 2,3,5,6-tetramethylidene-7-oxanorbornane ( 2 ). The following second order rate constants (toluene, 25°) and activation parameters were obtained for: 1 + TCNE → 7 : k1 = (255 + 5) 10?4 mol?1 · s?1, ΔH≠ = (12.2 ± 0.5) kcal/mol, ΔS≠ = (?24.8 ± 1.6) eu.; 7 + TCNE → 9 , k2 = (0.7 ± 0.02) 10?4 mol?1 · s?1, ΔH≠ = (14.1 ± 1.0) kcal/mol, ΔS≠ = ( ?30 ± 3.5) eu.; 2 + TCNE → 8 : k1 = (1.5 ± 0.03) 10?4 mol?1 · s?1, ΔH≠ = (14.8 ± 0.7) kcal/mol, ΔS≠ = (?26.4 ± 2.3) eu.; 8 + TCNE → 10 ; k2 = (0.004 ± 0.0002) 10?4 mol?1 · s?1, ΔH≠ = (17 ± 1.5) kcal/mol, ΔS≠ = (?30 ± 4) eu. The possible origins of the relatively large rate ratios k1/k2 are discussed briefly. 相似文献
12.
The equilibrium I2(g) + 2NO(g) = 2INO(g) has been studied at room temperature by ultraviolet absorption spectroscopy. The equilibrium constant has been measured as Kp = (2.7 ± 0.3) × 10?6 atm?1 at 298 K. Third-law calculations lead to ΔH°f,298 (INO) = 120.0 ± 0.3 kJ/mol. The relative absorption spectrum of INO has been measured between 225 and 300 nm. Quantitative measurements gave ?(λmax = 238 nm) = (1.79 ± 0.5) × 104 L/mol·cm and ?(410 nm) = 234.7 ± 21 L/mol·cm. 相似文献
13.
Pedro C. Vasquez Derrick C. Bennett Kishia K. Towns G. Davon Kennedy A. L. Baumstark 《Heteroatom Chemistry》2000,11(4):299-302
A kinetics study of the thermolysis of a series of hexasubstituted‐4,5‐dihydro‐3H‐pyrazoles (pyrazolines 1a: 3,3,4,4‐tetramethyl‐5‐phenyl‐5‐acetoxy; 1b: cis‐3,5‐diphenyl‐3,3,4‐trimethyl‐5‐acetoxy; 1c: cis‐3,5‐diphenyl‐3,4,4‐trimethyl‐5‐methoxy; 1d: 3,3,5‐triphenyl‐4,4‐dimethyl‐5‐acetoxy), which produced the corresponding hexasubstituted cyclopropanes 2a–d in quantitative yields was carried out. The first order rate constants (k1) for thermal decomposition and activation parameters were determined. The relative reactivity series was found to be 1d >> 1b ∼ 1c > 1a. The activation parameters for thermolysis were found to be: for 1a ΔH‡ = 39.8 kcal/mol, ΔS‡ = 14 eu, k150° = 6.8 × 10−5 s−1; for 1b ΔH‡ = 33.5 kcal/mol, ΔS ‡ = 0.2 eu, k150° = 1.7 × 10−4s−1; for 1c ΔH‡ = 32.7 kcal/mol, ΔS‡ = −1.8 eu, k150° = 1.2 × 10−4s−1; for 1d ΔH‡ = 30.1 kcal/mol, ΔS‡ = −1.6 eu, k150° = 8.8 × 10−3s−1. The effect of variation of C3 substituents on the activation parameters for thermolysis paralleled the trend reported for acyclic analogs. The results are consistent with the formation of a (singlet) 1,3‐diradical intermediate with subsequent closure to yield the cyclopropanes. The mechanism of diradical formation appears to involve N2‐C3 bond cleavage as the rate determining step rather than simultaneous two bond scission. © 2000 John Wiley & Sons, Inc. Heteroatom Chem 11:299–302, 2000 相似文献
14.
《Tetrahedron》1988,44(2):405-416
The synthesis, crystal structure (7,8), conformation and dynamics of pentaspiro[2.0.2.0.2.0.2.0.2.1] hexadecane 6, pentaspiro [3.0.2.0.3.0.2.0.3.1] nonadecane 7 and pentaspiro [3.0.3.0.3.0.3.0.3.1] heneicosane 8 are described. Chair conformations have been found in the solid state (7,8) and in solution (6,7,8). The activation parameters of the chair-to-chair interconversion have been determined from bandshape analyses of exchange broadened 1H-NMR (6,7) and13 C-NMR spectra (8), respectively. The results were as follows: 6: ΔH3 = 48.9 ± 0.8 kJ/mol, ΔS3 = -20.7 ± 2.8 J/mol, grd, ΔG3298 = 55.0 ± 0.1 kJ/mol; 7: ΔH3=51.2±0.7 kJ/mol, ΔS3 = -12.0±2.4 J/mol, grd, ΔG3298 = 54.8±0.1 kJ/mol; 8: ΔH3 - 74.2±0.6 kJ/mol, ΔS3 =-21.9 ± 1.5 J/mol, grd, ΔG3298 = 80.7 ± 0.2 kJ/mol. On the basis of these values the barrier of inversion of the still unknown hexaspirane 5 is predicted to exceed 160 kJ/mol. 相似文献
15.
The mutual combination reaction is proposed as the rate-limiting step in the removal of ClO radicals at moderate pressures. The third--order rate constants measured at room temperature were k1(Ar) = 3.51 ± 0.14 × 109 l2/mol2·ec; k1(He) ≈ 2.8 × 109 l2/mol2·sec, and k1(O2) ≈ 7.9 × 109 l2/mol2·sec. There is also an independent second-order reaction for which k3 ≈ 8 × 106 l/mol·sec. A new absorption spectrum has been observed in the ultraviolet and attributed to Cl2O2. The extinction coefficient for Cl2O2 has been measured at six wavelengths, and, between 292 and 232 nm, it increases from 0.4 × 103 to 2.9 × 103 l/mol·cm. In the presence of the chlorine atom scavengers OClO or Cl2O, Cl2O2 exists in equilibrium with ClO. The equilibrium constant Ke1 = 3.1 ± 0.1 × 106 l/mol at 298 K, and, with ΔS10 estimated to be ?133 ± 11 J/K·mol, ΔH10 = ?69 ± 3 kJ/mol and ΔHf0(Cl2O2) = 136 ± 3 kJ/mol. 相似文献
16.
Base hydrolysis reactions of [Cr(tmpa)(NCSe)]2O2+, [Cr(tmpa)(N3)]2O2+, [Cr2(tmpa)2(μ−O)(μ−PhPO4)]4+ and [Cr2(tmpa)2(μ−O)(μ−CO3)]2+ follow the pseudo‐first‐order relationship (excess OH−): kobsd=ko+kbQp[OH−]/(1+Qp[OH−]). For the CO32− complex, kb(60°C)=(1.50±0.03)×10−2 s−1; ΔH‡=61±2 kJ/mol, ΔS‡=−99±7 J/mol K; Qp(60°C)=(3.8±0.3)×101 M−1; ΔH°=67±2 kJ/mol, ΔS°=230±7 J/mol K (I=1.0 M). An isokinetic relationship among kOH(=kbQp) activation parameters for five (tmpa)CrOCr(tmpa) complexes shows that all follow essentially the same pathway. Activated complex formation is thought to require nucleophilic attack of coordinated OH− at the chromium‐leaving group bond in the kb step, accompanied by reattachment of a tmpa pyridyl arm displaced by OH− in the Qp preequilibrium. Abstraction of both thiocyanate ligands was observed upon mixing [Cr(tmpa)(NCS)]2O2+ with [Pd(CH3CN)4]2+ in CH3CN solution. The proposed mechanism requires rapid complexation of both reactant thiocyanate ligands by Pd(II) (Kp(25°C)=(4.5±0.2)×108 M−2; ΔH°=−32±6 kJ/mol, ΔS°=59±19 J/mol K) prior to rate‐limiting Cr NCS bond‐breaking (k2(25°C)=(1.17±0.02)×10−3 s−1; ΔH‡=98±2 kJ/mol, ΔS‡=27±5 J/mol K). Pd(II)‐assisted NCS− abstraction is not driven by weakening of the Cr( )NCS− bond through ligation of the sulfur atom to palladium, but rather by a favorable ΔS‡ resulting from the release of Pd(NCS)+ fragments and weak solvation of the activated complex in CH3CN solution. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 351–356, 1999 相似文献
17.
Alexandre E. Rachkov Soo-Hwan Cheong Anna V. Elskaya Kazuyoshi Yano Isao Karube 《先进技术聚合物》1998,9(8):511-519
The polymers selective to six different steroids (testosterone, Δ4-androstene-3,17-dione, 1,4-androstadiene-3,17-dione, β-estradiol, progesterone, testosterone propionate) have been synthesized using molecular imprinting based on noncovalent interactions. Analysis of the influence of structural features of the steroids under study has shown that molecules with a relatively rigid structure and the OH group at C-17 position are the most efficient templates for methacrylic acid-containing imprinted polymers. The chromatographic study of the polymers synthesized has demonstrated a strong dependence of the selectivity and intensity of interaction with analytes on the composition of solvents used both as porogen and chromatographic mobile phase. To obtain polymers with highly selective recognition sites and to create the optimal conditions for molecular recognition, all possible interactions (between template and functional monomer, template and solvent, solvent and functional monomer) should be taken into account. <?TF="palat-i"> The batch rebinding study of testosterone by the imprinted polymer in acetonitrile has revealed some heterogeneity of recognition sites, and permitted determination of Kass = 1.05 × 104 M −1, ΔG° = −5.4 kcal/mol and N = 1.2 μmol/g for high-affinity sites and Kass = 0.33 × 104 M −1, ΔG° = −4.8 kcal/mol and N = 2.2 μmol/g for low-affinity sites. <?TF="palat-i"> The results obtained show how it is possible to regulate in different modes the molecular recognition by imprinted polymers as well as to fabricate polymers possessing the necessary properties depending on their practical application.© 1998 John Wiley & Sons, Ltd. 相似文献
18.
Laura C. Leiva Nelly L. Jorge Jorge M. Romero Lzaro F. R. Cafferata Manuel E. Gmez Vara 《国际化学动力学杂志》2004,36(5):302-307
The thermal decomposition reaction of acetone cyclic diperoxide (3,3,6,6‐tetramethyl‐1,2,4,5‐tetroxane, ACDP), in the temperature range of 130.0–166.0°C and initial concentrations range of 0.4–3.1 × 10?2 mol kg?1 has been studied in methyl t‐butyl ether solution. The thermolysis follows first‐order kinetic laws up to at least ca 60% ACDP conversion. Under the experimental conditions, the activation parameters of the initial step of the reaction (ΔH# = 33.6 ± 1.1 kcal mol?1; ΔS# = ?4.1 ± 0.7 cal mol?1 K?1; ΔG# = 35.0 ± 1.1 kcal mol?1) and acetone, as the only organic product, support a stepwise reaction mechanism with the homolytic rupture of one of its peroxidic bond. Also, participation of solvent molecules in the reaction is postulated given an intermediate diradical, which further decomposes by C? O bond ruptures, yielding a stoichiometric amount of acetone (2 mol per mole of ACDP decomposed). The results are compared with those obtained for the above diperoxide thermolysis in other solvents. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 302–307, 2004 相似文献
19.
The flash photolysis of azo?n?propane and of azoisopropane has been studied by kinetic spectroscopy. Transient absorption spectra in theregion of 220–260 nm have been assigned to the n-propyl and isopropyl radicals. For the n-propyl radical, ?max = 744 ± 39 l/mol cm at 245 nm and the rate constants for the mutual reactions were measured to be kc = (1.0 ± 0.1) × 1010 l/mol sec (combination) and kd = (1.9 ± 0.2) × 109 l/mol sec (disproportionation). For the isopropyl radical, ?max = 1280 ± 110 l/mol cm at 238 nm, with kc = (7.7 ± 1.6) × 109 l/mol sec and kd = (5.0 ± 1.2) × 109 l/mol sec The rate constant for the dissociation of the vibrationally excited triplet state of the azopropanes into radicals was measured from the variation in the quantum yield of radicals with pressure. For azo-n-propane k = (6.6 ± 1.3) × 107 sec?1, and for azoisopropane k = (1.6 ± 0.4) × 108 sec?1. Collisional deactivation of the vibrationally excited singlet and triplet states was found to occur on every collision for n-pentane; but nitrogen and argon were inefficient with a rate constant of 1.1 × 1010 l/mol sec. Spectra observed in the region of 220–260 and 370–400 nm areattributed to the cis isomers of the parent trans-azopropanes. These are formed, as permanent products, in increasing amounts as the pressure is increased. 相似文献
20.
Constantinos G. Screttas Georgios A. Heropoulos Miltiades I. Karayannis 《Tetrahedron》1984,40(24):5275-5279
Galvinoxyl (G*) reacts with a series of substituted acetic acids and forms hydrogalvinoxyl (GH) as the sole product. The kinetic data conform with a Bronsted type analysis. Hydrogalvinoxyl may dissociate to the relevant cation G+, in a process which appears to be a thermal hydride ejection. In addition GH exhibits thermochromism with the following parameters: ΔH = -17.0 ±0.8 kcal mol-1 and at 298 K, Ke = 1.16 (±0.28) × 10-5 M-1, ΔS = -79.0±8.0 cal Kcal mol-1. The behaviour of G* at various acidities is described. 相似文献