Kinetics and thermochemistry of the gas phase reaction of methyl ethyl ketone with iodine. I. The resonance energy of the methylacetonyl radical

The gas phase reaction of iodine (2.8–43.3 torr) with methyl ethyl ketone (MEK) (7.4–303.4 torr) has been studied over the temperature range 280–355°C in a static system. The initial rate of disappearance of I₂ is first order in MEK and half order in I₂. The rate-determining step is the abstraction of a secondary hydrogen atom by an iodine atom: where k₁ is given by and θ = 2.303RT in kcal/mole. This activation energy is equivalent to a secondary C? H bond strength of 92.3 ± 1.4 kcal/mole and ΔH of the methylacetonyl radical = -16.8 ± 1.7 kcal/mole. By comparison with 95 kcal/mole for the secondary C? H bond strength, when delocalization of the unpaired electron with a pi bond is not possible, the resonance stabilization of the methylacetonyl radical is calculated to be 2.7 ± 1.7 kcal/mole. This value is 10 kcal/mole less than the stabilization energy of the isoelectronic methylallyl radical. The difference in pi bond energies in the canonical forms of the methylacetonyl radical is shown to account for the variation in stabilization energies.     

The kinetics and thermochemistry of the gas phase reaction of cyclopentadiene and iodine. Relevance to the heat of formation of cyclopentadienyl iodide and cyclopentadienyl radical

The rate of the reaction of cyclopentadiene with iodine has been followed spectrophotometrically over the temperature range 171.7° to 276.5°C. The reaction first proceeds almost to the point of equilibrium with cyclopentadienyl iodide and HI, although the final products are fulvalene and HI. Equilibrium constants obtained are those predicted by bond additivity. A third-law value of δH⁰_{f 298} (c-C₅H₅I,g) = 49 kcal/mole is obtained. Rate studies of the reaction up to the iodide equilibrium, yield values for the rate constant . Uncertainty in the Arrhenius parameters, as well as doubts as to the applicability of the usual assumption that E₃ = 1 ± 1 kcal/mole, make difficult an evaluation of total cyclopentadienyl stabilization energy (TSE) from these data. However, the value is probably 15 < TSE < 20.     

Kinetics and hazards of thermal decomposition of methyl ethyl ketone peroxide by DSC

Differential scanning calorimetry (DSC) was applied to analyze thermal decomposition of methyl ethyl ketone peroxide (MEKPO). Thermokinetic parameters and thermal stability were evaluated. MEKPO decomposes in at least three exothermic decomposition reactions and begins to decompose at 30–32 °C. The total heat of decomposition is 1.26 ± 0.03 kJ g⁻¹. Thermal decomposition of MEKPO can be described by a model of two independent reactions: the first is decomposition of a less stable isomer of MEKPO, followed by decomposition of the main isomer, after which an exothermic reaction of the reaction products with the solvent, dimethyl phthalate. The results can be applied for emergency relief system design and for emergency rescue strategies during an upset or accident.     

Thermochemical Kinetics of Nitrogen Compounds. Part 4. The gas phase unimolecular thermal decomposition of triallylamine

The gas phase thermal decomposition of triallylamine was studied in the temperature range 531 to 620 K. The major products observed in the reaction were propylene and 3-picoline. The first order rate constants for depletion of triallylamine, obtained using the internal standard technique, are found to be independent of pressure and conversion, and fit the Arrheniusrelationship The reaction appears to be homogeneous, as a 15-fold change in thc surface-to-volume ratio of the vessel left the rate constants unchanged. The Arrhenius parameters are consistent with a molecular elimination reaction involving a six-center transition state, yielding propylene and N-allyl-prop-2-enaldimine. It is proposed that the latter product undergoes a 1,5-hydrogen transfer, followed by a ring closure reaction to yield dihydropicoline, which in turn reacts forming 3-picoline via a self-initiated decomposition reaction.     

Aza-Morita-Baylis-Hillman reaction of ethyl (arylimino)acetate with methyl vinyl ketone and ethyl vinyl ketone

Aza-Morita-Baylis-Hillman (aza-MBH) reaction of ethyl (arylimino)acetate with methyl vinyl ketone and ethyl vinyl ketone has been investigated. We found that aza-MBH adducts 1 could be formed in the presence of DABCO (30 mol %) and the corresponding adducts 2 could be obtained in the presence of PPh₃ (30 mol %) in moderate to good yields in acetonitrile under mild conditions, respectively.     

Dynamics of ethyl radical decomposition. II. Applicability of classical mechanics to large-molecule unimolecular reaction dynamics

The classical trajectory method is used to investigate the unimolecular dynamics of ethyl radical dissociation. It is found that chaotic trajectories need not be backward integrable to yield accurate lifetime, and product energy and angular momenta distributions. This allows the use of large numerical integration step sizes in trajectory calculations. The product energy and angular momenta distributions are independent of the ethyl radical lifetime, and are obtained after only 50 dissociation events. Differences between classical and quantal unimolecular dynamics are discussed, and a prognosis for future trajectory studies of large-molecule unimolecular decompositions is given.     

Kinetics, mechanism, and thermochemistry of the gas phase reaction of atomic chlorine with dimethyl sulfoxide

A laser flash photolysis-resonance fluorescence technique has been employed to study the kinetics of the reaction of chlorine atoms with dimethyl sulfoxide (CH3S(O)CH3; DMSO) as a function of temperature (270-571 K) and pressure (5-500 Torr) in nitrogen bath gas. At T = 296 K and P > or = 5 Torr, measured rate coefficients increase with increasing pressure. Combining our data with literature values for low-pressure rate coefficients (0.5-3 Torr He) leads to a rate coefficient for the pressure independent H-transfer channel of k1a = 1.45 x 10(-11) cm3 molecule(-1) s(-1) and the following falloff parameters for the pressure-dependent addition channel in N2 bath gas: k(1b,0) = 2.53 x 10(-28) cm6 molecule(-2) s(-1); k(1b,infinity) = 1.17 x 10(-10) cm3 molecule(-1) s(-1), F(c) = 0.503. At the 95% confidence level, both k1a and k1b(P) have estimated accuracies of +/-30%. At T > 430 K, where adduct decomposition is fast enough that only the H-transfer pathway is important, measured rate coefficients are independent of pressure (30-100 Torr N2) and increase with increasing temperature. The following Arrhenius expression adequately describes the temperature dependence of the rate coefficients measured at over the range 438-571 K: k1a = (4.6 +/- 0.4) x 10(-11) exp[-(472 +/- 40)/T) cm3 molecule(-1) s(-1) (uncertainties are 2sigma, precision only). When our data at T > 430 K are combined with values for k1a at temperatures of 273-335 K that are obtained by correcting reported low-pressure rate coefficients from discharge flow studies to remove the contribution from the pressure-dependent channel, the following modified Arrhenius expression best describes the derived temperature dependence: k1a = 1.34 x 10(-15)T(1.40) exp(+383/T) cm3 molecule(-1) s(-1) (273 K < or = T < or = 571 K). At temperatures around 330 K, reversible addition is observed, thus allowing equilibrium constants for Cl-DMSO formation and dissociation to be determined. A third-law analysis of the equilibrium data using structural information obtained from electronic structure calculations leads to the following thermochemical parameters for the association reaction: delta(r)H(o)298 = -72.8 +/- 2.9 kJ mol(-1), deltaH(o)0 = -71.5 +/- 3.3 kJ mol(-1), and delta(r)S(o)298 = -110.6 +/- 4.0 J K(-1) mol(-1). In conjunction with standard enthalpies of formation of Cl and DMSO taken from the literature, the above values for delta(r)H(o) lead to the following values for the standard enthalpy of formation of Cl-DMSO: delta(f)H(o)298 = -102.7 +/- 4.9 kJ mol(-1) and delta(r)H(o)0 = -84.4 +/- 5.8 kJ mol(-1). Uncertainties in the above thermochemical parameters represent estimated accuracy at the 95% confidence level. In agreement with one published theoretical study, electronic structure calculations using density functional theory and G3B3 theory reproduce the experimental adduct bond strength quite well.     

Kinetics of the gas phase reaction of methyl benzoate with bromine and iodine: The methoxyl C?H bond strength of methyl esters

The gas phase reactions of PhCOOCH₃ with I₂ and Br₂ were studied spectrophotometrically in a static system over the temperature ranges 344–359° and 246–303°, respectively. For each system the initial rate was first order in PhCOOCH₃ and half order in halogen as the concentration of PhCOOCH₃ was varied from 1.4 to 15.2 torr, that of I₂ from 6.2 to 26.4 torr, and that of Br₂ from 3.0 to 13.6 torr. The rate-determining step is the extraction of a methoxyl hydrogen atom: Empirical assignment of A-factors for k₁ lead to for the I₂ system, and to for the Br₂ system, where ? = 2.303RT in kcal/mole. Combined with the assumption that E_–1 = 1 ± 1 kcal/mole and 2 ± 1 kcal/mole for HI and HBr, respectively, DH (PhCOOCH₂? H) calculated from the two systems shows excellent agreement at 100.2 ± 1.3 kcal/mole and 100.1 ± 1.3 kcal/mole. Using a value of δH (PhCOOMe) = –65.6 ± 1.5 kcal/mole obtained from group additivity estimates, δH_f,298⁰ (PhCOOCH₂) is calculated to be –16.7 ± 2.0 kcal/mole. Unimolecular decomposition of the Ph(CO)O°CH₂ radical was also observed: with a rate constant equal to The abnormally high methoxyl C? H bond strength is discussed in relation to the bonding in ethers, alkanes, and esters.     

Kinetics and thermochemistry of the methyl radical: Study of the CH3 + HCl reaction

The kinetics of the reaction between CH₃ and HCl was studied in a tubular reactor coupled to a photoionization mass spectrometer. Rate constants were measured as a function of temperature (296–495 K) and were fitted to an Arrhenius expression: k₁ = 5.0(±0.7) × 10^?13 exp{?1.4(±0.3) kcal mol^?1/RT} cm³ molecule^?1 s^?1. This information was combined with known kinetic parameters of the reverse reaction to obtain Second Law determinations of the methyl radical heat of formation {34.7(±0.6) kcal mol^?1} and entropy {46(±2) cal mol^?1 K^?1} at 298 K. Using the known entropy of CH₃, a more accurate Third Law determination of the CH₃ heat of formation at this temperature was also obtained {34.8(±0.3) kcal mol^?1}. The values of k₁ obtained in this study are between those reported in prior investigations. The results were also used to test the accuracy of the thermochemical information which can be obtained from kinetic studies of R + HX (X = Cl, Br, I) reactions of the type described here.     

MP2 study of substituent effects of 2-substituted alkyl ethyl methylcarbamates in homogeneous, unimolecular gas phase elimination reaction

Møller-Plesset MP2/6-31G method was used to examine the gas-phase elimination of 2-substituted alkyl ethyl N,N-dimethylcarbamates. The results of these calculations support a concerted non-synchronous six-membered cyclic transition state mechanism for carbamates containing a C_β–H bond at the alkyl side of the ester. These substrates produce the N,N-dimethylcarbamic acid and the corresponding olefin. The unstable intermediate, N,N-dimethylcarbamic acid, rapidly decomposes through a four-membered cyclic transition state to dimethylamine and CO₂ gas. Correlation of the logarithm of theoretical rate coefficients against original Taft's σ* values gave an approximate straight line (ρ*=−1.39, r=0.9558 at 360 °C). In addition to this fact, when log k_rel is plotted against the theoretical log k_rel for 2-substituted ethyl N,N-dimethylcarbamates a reasonable straight line (r=0.9919 at 360 °C) is obtained, suggesting similar mechanism.     

Kinetics of the gas-phase reaction of allyl alcohol with iodine. The heat of formation and stabilization energy of the hydroxyallyl radical

The reaction of iodine with allyl alcohol has been studied in a static system, following the absorption of visible light by iodine, in the temperature range 150-190°C and in the pressure range 10-200 torr. The rate-determining step has been found to be and k₃ is consistent with the equation From the activation energy and the assumption E_-3 = 1 ± 1 kcal mol^?1, it has been calculated that kcal mol^?1. The stabilization energy of the hydroxyallyl radical has been found to be 11.4 ± 2.2 kcal mol^?1.     

Evaluation of adiabatic runaway reaction of methyl ethyl ketone peroxide by DSC and VSP2

Methyl ethyl ketone peroxide (MEKPO) is generally applied to manufacturing in the polymerization processes. Due to thermal instability and high exothermic behaviors of MEKPO, if any operation is undertaken recklessly or some environmental effect is produced suddenly during the processes, fires and explosions may inevitably occur. In this study, thermal analysis was evaluated for MEKPO by differential scanning calorimetry (DSC) test. Vent sizing package 2 (VSP2) was used to analyze the thermal hazard of MEKPO under various stirring rates in a batch reactor. Thermokinetic and safety parameters, including exothermic onset temperature (T ₀), maximum temperature (T _max), maximum pressure (P _max), self-heating rate (dT dt ⁻¹), pressure rise rate (dP dt ⁻¹), and so on, were discovered to identify the safe handling situation. The stirring rates of reactor were confirmed to affect runaway and thermal hazard characteristics in the batch reactor. If the stirring rate was out of control, it could soon cause a thermal hazard in the reactor.     

Mass spectrometry—II: The unimolecular decomposition of benzaldehyde azine in the gas phase induced by electron-impact

The mass spectra of benzaldehyde azine-α, αA-d² (III) and benzaldehyde azine-d¹⁰ (IV) reveal that both ring and α hydrogen are lost from the molecular ion of benzaldehyde azine (II) in forming the [M –1] ion. Data from the spectra of III and IV at 70 eV and reduced ionizing voltages are consistent with the existence of two competing pathways producing [M –1] ions. Rearrangement ions are observed in the spectra of II. Randomization is unimportant in the electron-impact-induced fragmentation reactions of II. The rearrangement-fragmentation reactions for II in general parallel those previously observed for acetophenone azine (I).     

Thermochemical kinetics of nitrogen compounds. V. The unimolecular thermal decomposition of diallylamine in the gas phase

The kinetics of the thermal decomposition of diallylamine to propylene and prop-2-enaldimine have been studied in the gas phase in presence of an excess of methylamine over the temperature range of 532.7 to 615.6°K, using a static reaction system. Methylamine reacted with the unstable primary product prop-2-enaldimine, forming the thermally stable N-methyl prop-2-enaldimine. First-order rate constants, based on the internal standard technique, fit the Arrhenius relationship log k(s^?1) = (11.04 ± 0.13) ? (37.11 ± 0.33 kcal/mole)/2.303 RT. They were independent on the initial total pressure (46–340 torr), the initial pressure of diallylamine (9.2–65 torr), or methylamine as well as the conversion attained. Despite an apparent surface sensitivity, the reaction is essentially homogeneous in nature as demonstrated by experiments carried out in a packed reaction vessel. The observed activation parameters for the title reaction together with those observed earlier for triallylamine and allylcyclohexylamine are consistent with the proposed concerted reaction mechanism involving a cyclic 6-center transition state. The observed substituent effects suggest a nonsynchronous mode of bond breaking and bond formation.     

Kinetics and mechanism of oxidation of acetone,ethyl methyl ketone and diethyl ketone with chloramine-T in hydrochloric acid medium

The kinetics of oxidation of aliphatic ketones (acetone, ethyl methyl ketone and diethyl ketone) by chloramine-T in presence of hydrochloric acid (0.1 to 0.3M) have been investigated at 30 °C. The rate of disappearance of chloramine-T has been found to be first order each with respect to oxidant, ketone and [H⁺], in the range of the acid concentrations studied. The thermodynamic and kinetic parameters have been evaluated by determining the rate constants at different temperatures. The products of the reaction have been identified as chloroketones by their NMR spectra. The solvent isotope effect has been studied in the case of the oxidation of acetone and ethyl methyl ketone. A mechanism has been proposed.     

Kinetics of the reaction of methyl radical with hydroxyl radical and methanol decomposition

The CH3 + OH bimolecular reaction and the dissociation of methanol are studied theoretically at conditions relevant to combustion chemistry. Kinetics for the CH3 + OH barrierless association reaction and for the H + CH2OH and H + CH3O product channels are determined in the high-pressure limit using variable reaction coordinate transition state theory and multireference electronic structure calculations to evaluate the fragment interaction energies. The CH3 + OH --> 3CH2 + H2O abstraction reaction and the H2 + HCOH and H2 + H2CO product channels feature localized dynamical bottlenecks and are treated using variational transition state theory and QCISD(T) energies extrapolated to the complete basis set limit. The 1CH2 + H2O product channel has two dynamical regimes, featuring both an inner saddle point and an outer barrierless region, and it is shown that a microcanonical two-state model is necessary to properly describe the association rate for this reaction over a broad temperature range. Experimental channel energies for the methanol system are reevaluated using the Active Thermochemical Tables (ATcT) approach. Pressure dependent, phenomenological rate coefficients for the CH3 + OH bimolecular reaction and for methanol decomposition are determined via master equation simulations. The predicted results agree well with experimental results, including those from a companion high-temperature shock tube determination for the decomposition of methanol.     

the extraction of some metallic bromides from aqueous solutions with methyl ethyl ketone and methyl iso-butyl ketone

The extraction of the following metals from aqueous solutions containing excess bromide with methyl ethyl ketone (MEK), and methyl isobutyl ketone MIBK has been investigated:—Cu(I), Cu(II), Zn(II), Ni(II), Co(II), Fe(II), Fe(III), Al(III), Mn(II), Sn(II) and Sn(IV). The use of MEK was found to be strictly limited by its solubility in acidic aqueous solutions. Determinations of the formulae of the extracted compounds were attempted in two cases but were found to be not wholly satisfactory and were discontinued. An interesting reaction between the cupric bromide complex and the solvents was noticed. Separations of Fe(IIl) from Mn(II), Fe(III) from Al(III), Fe(III) from Co(Il) and Fe(III) from Ni(II) could be achieved under suitable conditions.     

Kinetics and mechanism of the thermal decomposition reaction of acetone cyclic diperoxide in the gas phase

The kinetics of the thermal decomposition reaction of gaseous 3,3,6,6-tetramethyl-1,2,4,5-tetroxane (ACDP) in the presence of n-octane was studied in the 403.2–523.2 K temperature range. This reaction yields acetone as the organic product. Under optimum conditions, first-order kinetics were observed, included when the S/V ratio of the Pyrex reaction vessel was increased by a nearly six-fold factor. In the range 443.2–488.2 K the temperature dependence of the rate constants for the unimolecular reaction in conditioned vessels is given by In k₁/(s^?1) = (31.8 ± 2.5) ? [(39.0 ± 2.5)/RT]. The value of the energy of activation in kcal/mol correspond to one O? O bond homolysis of the ACDP molecule in a stepwise biradical initiated decomposition mechanism. At the lower reaction temperatures as well in preliminary experiments participation of a surface catalyzed ACDP decomposition process could be detected. © 1994 John Wiley & Sons, Inc.     

The photochemistry of methyl cyclobutyl ketone. Part 2. Temperature dependence and the acetyl radical decomposition

Following earlier room-temperature studies, gaseous mixtures of methyl cyclobutyl ketone (MCK) diluted in argon have been photolyzed at temperatures up to 205°C. Experiments have been carried out at a variety of pressures (up to ca. 2 atm) at wavelengths of 313 nm (steady state conditions) and 308 nm (pulsed photolysis). The results are consistent with a mechanism dominated by radical-radical reactions involving acetyl, methyl, and cyclobutyl radicals. Acetyl radical processes predominate at lower temperatures while methyl radical reactions are more important at high temperatures. The results are interpreted via kinetic modelling of a mechanism in which a key role is played by the acetyl radical decomposition reaction Values for k₃ have been obtained and its temperature and pressure dependence are fitted by RRKM theory and a weak-collisional activation model to yield This high-pressure limiting Arrhenius equation is consistent with other studies in the same temperature range, but is difficult to reconcile with higher temperature investigations.