Decomposition of organic hydroperoxides on cation exchangers XV. The kinetics of the decomposition process of p-isopropylcumene hydroperoxide on a catalyst of montmorillonite type

The decomposition of p-isopropylcumene hydroperoxide on a catalyst of montmorillonite type containing Sn²⁺ ions, Sn²⁺-K10 showed first order kinetics in the range of 45-55°C. The activation energy, the enthalpy of activation, the entropy as well as the Gibbs free energy of activation were calculated for the investigated temperature region. Acetone and p-isopropylphenol were produced by this chemical decomposition; both compounds are important intermediates in the chemical industry. This revised version was published online in June 2006 with corrections to the Cover Date.     

Reasons for and Consequences of the Mysterious Behaviour of Newly Prepared Hemipyridine Solvate of Bis(pyridine)silver(I) Permanganate,Agpy<Subscript>2</Subscript>MnO<Subscript>4</Subscript>*0.5py

Compositions and chemical identities of compounds formed in silver–permanganate–pyridine–water systems, as well as of their recrystallization products obtained from benzene–acetone solutions, have been elucidated. Three compounds: Agpy₂MnO₄ (1), 7Agpy₂MnO₄*Agpy₄MnO₄ (Agpy_2.25MnO₄) (2) and Agpy₂MnO₄ * 0.5py (Agpy_2.5MnO₄) (3) were isolated. The compositions of the products obtained by a method described previously [1] for the preparation of ‘Agpy₂MnO₄’ (1*) and ‘Agpy_2.5MnO₄’ (2*) were determined and the constituent compounds identified. It has been established that the instability of compound (3) is due to the presence of the benzene, substituting for pyridine at the solvate sites. The benzene, however, is released at room temperature, disrupting the crystal lattice of (3), and the whole process leads to the loss of the solvate pyridine and to the formation of (1).     

A select and insert sorting algorithm

A general sorting algorithm, having the well knownO(n ²) algorithmsStraight Insertion Sort andSelection Sort as special cases, is described. This algorithm is analyzed in the case that certain choices in the algorithm are done randomly, and this yields an algorithm that has an average complexity ofO(n ^1.5) and a worst case complexity ofO(n ²). However, making random choices (by some random number generator) is time consuming, and a simple quasi-random scheme is therefore implemented. Test runs indicate that also this version has average complexity ofO(n ^1.5), and it even seems to perform better than the version using real random choices (even if we disregard the time used for the random choices). This version also needs very little administrative overhead, and it therefore compares favourably to many other sorting algorithms for small and medium sized arrays.     

The gas-phase molecular structure of 1-fluorosilatrane from electron diffraction

The molecular geometry of 1-fluorosilatrane has been determined by gas-phase electron diffraction. The distance between the nitrogen and silicon atoms is much longer in the gas phase, viz., 2.324±0.014 Å, than in the crystal, 2.042 (1) Å [5]. This indicates a weakened donor-acceptor interaction possibly as a consequence of the absence of intermolecular interactions in the gas phase. The five-membered rings take envelope conformations with the carbon atoms adjacent to nitrogen at the envelope tips. The following bond distances ( _g , Å) and bond angles (°) were obtained with their estimated total errors: N-C, 1.481±0.008; C-C, 1.514±0.011; O-C, 1.392±0.004; Si-O, 1.652±0.003; Si-F, 1.568±0.006; C-H, 1.118±0.005; N-C-C, 104.5±0.6; C-C-O, 117.0±0.7;C-O-Si, 123.7±0.6; O-Si-F, 98.7±0.3; O-Si-O, 117.8±0.1; C-N-C, 115.0±0.3.     

Local and global uncertainty analyses of a methane flame model

Local and global uncertainty analyses of a flat, premixed, stationary, laminar methane flame model were carried out using the Leeds methane oxidation mechanism at lean (phi = 0.70), stoichiometric (phi = 1.00), and rich (phi = 1.20) equivalence ratios. Uncertainties of laminar flame velocity, maximal flame temperature, and maximal concentrations of radicals H, O, OH, CH, and CH(2) were investigated. Global uncertainty analysis methods included the Morris method, the Monte Carlo analysis with Latin hypercube sampling, and an improved version of the Sobol' method. Assumed probability density functions (pdf's) were assigned to the rate coefficients of all the 175 reactions and to the enthalpies of formation of the 37 species. The analyses provided the following answers: approximate pdf's and standard deviations of the model results, minimum and maximum values of the results at any physically realistic parameter combination, and the contribution of the uncertainty of each parameter to the uncertainty of the model result. The uncertainty of a few rate parameters and a few enthalpies of formation causes most of the uncertainty of the model results. Most uncertainty comes from the inappropriate knowledge of kinetic data, but the uncertainty caused by thermodynamic data is also significant.     

Looking Back and Ahead: Gas-Phase Electron Diffraction at 75

At 75, gas-phase electron diffraction is still the method of choice for selected problems in molecular structure determination. It works best when being applied with other techniques in a concerted way.     

1,3- And 1,5-migrations involving chlorine

Rearrangement processes involving chlorine have been observed in the reaction of l,l,l-trichloro-2-hydroxy-4-miethyl- petene-3($\text{1}$) with inorganic acid chlorides. Conversion of compound $\text{2}$ to $\text{3}$ represent a new example of a 1,3-chlorine shift. Formation of compound $\text{4}$ from $\text{6}$ is a new type of rearrangement involving 1,5-chlorine migration, and at the same time, is a good example of the role of kinetic vs. thermodinamic control in chemical processes. The transformations were found to proceed via radical intermediates.     

Enantioefficient synthesis of alpha-ergocryptine: first direct synthesis of (+)-lysergic acid

The first direct synthesis of (+)-lysergic acid (2a) suitable for scale-up has been achieved by the following reaction sequence. Bromoketones 4d or 4g were allowed to react with amine 5 followed by deprotection, and the resulting diketone 6c was transformed into the unsaturated ketone (+/-)-7 by the LiBr/Et(3)N system. Resolution afforded (+)-7, which was further transformed by Sch?llkopf's method into the mixture of esters 2e and 2f. Upon hydrolysis the latter mixture afforded (+)-2a. The peptide part of alpha-ergocryptine (1) was prepared according to the Sandoz method; the stereoefficiency, however, has been significantly improved by applying a new resolution method and recycling the undesired enantiomer. Coupling the peptide part with lysergic acid afforded 1. Having synthetic (+)-7 in hand, we can claim the total synthesis of all the alkaloids which were prepared earlier from (+)-7 that had been obtained through degradation of natural lysergic acid.     

Synthesis of Vinca Alkaloids and Related Compounds. 79. An Intriguing Retro Diels-Alder Reaction(1)

The dimerization products of criocerine (1) are different (2 or 3) depending on whether the reaction is carried out in acetic acid or trifluoroacetic acid. The highly strained product 3 rearranges spontaneously through a retro Diels-Alder reaction. All structures involved were thoroughly investigated by NMR spectroscopic methods.     

Donor-acceptor properties of isonitriles studied by photoelectron spectroscopy and electron transmission spectroscopy

Some alkyl and aryl isonitriles, considered as CO analogue sigma-donor and pi-acceptor ligands in transition metal chemistry, were studied by means of HeI photoelectron spectroscopy and electron transmission spectroscopy, in order to evaluate their donor-acceptor properties from the measured ionization energies (IE) and vertical electron attachment energies (VAE). The investigated molecules were 2-propyl, 1-butyl, tert-butyl, 1-pentyl, cyclohexyl, 2,6-dimethylphenyl, 4-methoxyphenyl and 4-chorophenyl isonitrile. By interpreting the spectra on the basis of literature data and quantum chemical calculations, the spectral features associated with the molecular orbitals mainly involved in coordination and back-donation were identified. The results show that the IE (10.62-10.95 eV) of the sigma electron pair (n(c)) responsible for the sigma-donor capability is substantially lower than that of CO. The VAEs of the empty pi* orbitals involved in the d/pi* back-donation indicate that aryl isonitriles are better acceptors (VAE <0.3 eV) than their aliphatic counterparts (VAE >2.7 eV). In the case of aryl derivatives, the pi-donor ability could also play some role in metal-ligand bonding (IE 8.74-9.34 eV). Isonitrile coordination characteristics are also compared with those of CO, N(2) and CH(3)CN.