Quantum chemical calculations on the catalytic dehydration of 2-propanol

The charge on atoms and the bond strengths in CH₃CHOHCH₃, CH₃ CH₃, CH₃CHOHCH ₂ ^– , CH₃ CH ₂ ^– and CH₃ CH₃...O(H)CH(CH₃)₂ have been calculated by the CNDO/2 method. The results are in agreement with published experimental observations on catalytic dehydration. A modified mechanism of anti-elimination on solid catalysts is proposed.

---

CH₃CHOHCH₃, CH₃ CH₃, CH₃CHOHCH ₂ ^– , CH₃ CH ₂ ^– CH₃ CH₃...O(H)CH(CH₃)₂, CNDO/2. . .

     

Kinetics of the dehydration of 2-propanol on modified activated charcoal containing acid sites

A study was carried out on the kinetics of the dehydration of 2-propanol on activated bone charcoal (ABC) with supported acid sites. The rate-limiting step is the loss of water from the alcohol molecule adsorbed on the acid site. The sites containing the minimum amount of water are the most active. The reaction on these sites presumably proceeds through a concerted mechanism, which is possible at sufficiently high temperatures (above 120 °C). Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 44, No. 5, pp. 321–327, September–October, 2008.     

The photoinitiated substitution reactions of 2-pyridinecarbonitrile with benzophenone in aqueous 2-propanol

The photoinitiated reaction of 2-pyridinecarbonitrile and benzophenone in acidic 4:1 2-propanol-water yields substitution product 3 and bicyclic product 4 . In nonacidic solution 3 is the principal product in addition to small amounts of a bipyridyl compound 5 .     

Catalytic dehydration of 2-propanol on (WO3)3 clusters on TiO2(110)

Our study of a (WO3)3/TiO2(110) model mixed oxide catalyst shows that this system is an extremely efficient for dehydration of alcohols, effectively lowering the energy barrier as much as possible for an endothermic reaction without yielding a significant concentration of other side products.     

The SRN2 mechanism of nucleophilic substitution

1-Alkylpyridiniums react with nitroalkane and ethylmalonate anions by a radical nucleophilic substitution mechanism not involving radical chains.     

Evaluation of the dehydration performance of zeolite NaA membrane on porous alumina tube by the alumina X-ray diffraction intensity.

A zeolite NaA (A-type zeolite of ca. 0.4 nm pore size; Linde Type A, LTA) membrane for the dehydration of alcohol was characterized by X-ray diffraction analysis (XRD). Also, the relationship between the X-ray absorption and the EtOH/H2O pervaporation (PV) dehydration performance (water selectivity and permeation flux) of the LTA membrane was first investigated. The LTA membranes used here were gel-synthesized hydrothermally on an alumina porous support tube. Since diffraction lines from the alumina generate from a deeper layer than those of the LTA crystal, and are absorbed by both the surface LTA crystal and materials embedded in the alumina porous support, the alumina (113) diffraction line was intensively monitored to estimate the overall X-ray absorption by the LTA membrane. The intensity of the alumina (113) diffraction line showed a good correlation with the PV dehydration performance of the LTA membrane, that is, lower values with the water selectivity and higher values with the permeation flux. The lower diffraction intensity means stronger X-ray absorption by the LTA membrane. The major factor causing the difference in the X-ray absorption is the thickness or quantity of materials embedded in an alumina porous support, rather than those of the surface LTA crystal. These phenomena can be used conveniently (without real PV experiments) to determine the EtOH/H2O PV dehydration performance of the LTA membrane.     

Novel efficient mesoporous solid acid catalyst UDCaT-4: dehydration of 2-propanol and alkylation of mesitylene

A novel mesoporous solid acid catalyst named UDCaT-4 was synthesized by incorporating superacidic centers of persulfated alumina and zirconia into highly ordered and well-defined hexagonal mesoporous silica. The catalyst is well characterized, and its properties are compared with those of bulk persulfated alumina and zirconia (PAZ) by FTIR spectroscopy, X-ray diffraction, Brunauer-Emmett-Teller surface area, pore size analysis, scanning electron microscopy, energy dispersive X-ray spectroscopy, and ammonia temperature-programmed desorption. UDCaT-4 is more acidic than PAZ. The dehydration processes of 2-propanol, diisopropyl ether, and n-propanol were studied independently including a mixture of n-propanol and 2-propanol to throw light on kinetics and mechanism. For alkylation of mesitylene with 2-propanol, UDCaT-4 exhibits superior catalytic activity in comparison with PAZ and also it shows remarkable stability toward coke formation. Kinetic interpretations of the observed rate data are presented for all reactions, and mechanistic models are developed. The results are novel.     

Nucleophilic substitution reactions of N-chloramines: evidence for a change in mechanism with increasing nucleophile reactivity

Third-order rate constants (kNu)H (M-2 s-1) for the hydronium ion catalyzed reactions of a range of nucleophiles with N-chlorotaurine (1) in water at 25 degrees C and I=0.5 (NaClO4) are reported. The solvent deuterium isotope effects on hydronium ion catalysis of the reaction with 1 of bromide and iodide ion are (kBr)H/(kBr)D=0.30 and (kI)H/(kI)D=0.54, respectively. The inverse nature of these isotope effects and the absence of general acid catalysis are consistent with a stepwise mechanism involving protonation of 1 in a fast preequilibrium step. The appearance of strong catalysis by general acids for the reaction of the more nucleophilic SO(3)2- and HOCH2CH2S- with the chloramine indicates a change to a concerted mechanism, with protonation of the chloramine at nitrogen and chlorine transfer to the nucleophile occurring in a single step. A rough estimate of the lifetime of the protonated chloramine in the presence of the thiolate anion suggests that the concerted mechanism is enforced by the absence of a significant lifetime of the protonated substrate in contact with the nucleophile. Theoretical calculations provide evidence against an electron-transfer mechanism for chlorination of the nucleophiles by protonated 1.     

Computational study of the substitution effect on the mechanism for phospha-Wittig reaction

The phospha-Wittig reaction HP=PH₃ + O=CHX → HP=CHX + O=PH₃ (X = H, F, Cl, Me, OMe, NMe₂, CMe₃) was examined using the density functional theory calculations. All of the structures were completely optimized at the B3LYP/6-311++G** level of theory. The reactivities of various O=CHX were examined by estimating their activation energies. The main finding of this work is that the configuration mixing model can successfully predict the relative ordering of the activation energy and reaction enthalpies of the phospha-Wittig reaction. It was demonstrated that O=CHX with more electro-releasing substituents will possess a smaller singlet–triplet splitting. This will facilitate the phospha-Wittig reaction and will result in a larger exothermicity.     

Kinetics and mechanism of photochemical reactions of peroxomonosulfate in the presence and absence of 2-propanol

The photochemical decomposition of peroxomonosulfate (PMS) in the presence and absence of 2-propanol at 25°C was found to obey an overall first-order rate – d[PMS]/dt = k_?[PMS]. In the absence of 2-propanol, the quantum yield ≤ for the decomposition of PMS was found to depend upon the concentration of PMS at [PMS] > 2 × 10^?M, and is independent of concentration at [PMS] > 2 × 10^?2M. The quantum yield in the presence of 2-propanol was found to be 3.03 at [PMS] = 1 × 10^?2M and 4.45 at higher concentrations of PMS. In the pH range of 2–9.0 the quantum yield was found to be independent of pH, and the overall rate constant k_? was found to be 6.49 × 10^?3 s^?1 and 1.68 × 10^?3 s^?1, respectively, in the presence and absence of isopropanol. A suitable chain mechanism is proposed and explained.     

Further tests of the approximate double substitution coupled-cluster method

Comparisons are made between the approximate form (ACCD ) of double substitution coupled-cluster theory and the complete form (CCD) in the evaluation of total correlation energies, molecular structures, vibrational frequencies, bond lengths, dissociation energies, permanent electrical moments, and electric field gradients. Though ACCD may recover as little as half of the higher-order correlation energy when that energy is small, it does recover a very high percentage when that energy is large. ACCD and CCD potential surfaces tend to have similar shape, and for many molecular properties, the results show ACCD to be very nearly equivalent to CCD.     

Effect of structure on the mechanism of dehydration of clay minerals

The kinetics of the isothermal dehydration of two clay minerals, attapulgite and powdered vermiculite were studied both in vacuo and in the presence of constant water vapour pressure. The mechanism of dehydration was found to be interfacial where diffusion plays a dominant role and it is called “activated diffusion”. A comparison is made with some layered structure clay minerals.     

Decomposition of 2-propanol on an intermetallic compound for hydrogen storage

Decompositon of 2-propanol has been carried out on the hydrogen storage material Mg₂Cu and its modified form (OH–Mg₂Cu) to study their catalytic behavior. The reaction was carried out in a continuous flow type reactor in the temperature range of 403–513 K at various flow rates. Mg₂Cu showed good catalytic activity with large amounts of condensation products. Its modified form gave acetone as the only products. The reason for these differences is explained in terms of differences in the structure of the catalyst as determined by XRD and XPS, as well as by surface area measurements. The reason for the formation of condensation products is discussed.     

Isomerization of thiocarboxylic esters of 1-bromo-2-propanol and 2-bromo-1-propanol

Conclusions The rate constant for the isomerization of the thioacetates and thiobenzoates of l-bromo-2-propanol and 2-bromo-1-propanol in aprotic solvents, in contrast to the case for the esters of the corresponding carboxylic acids, is independent of the nature of the group adjacent to the thiocarboxylic group.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1418–1420, June, 1988.     

23Na NMR study of the mechanism for the dehydration of zeolite NaA

Conclusions Water molecules in partially dehydrated zeolite directly interact with Na⁺ cations. The final three or four water molecules per unit cell removed upon the dehydration of zeolite are apparently bound to Na⁺ cations of the eight-membered windows, while the previous 10 molecules are bound to Na⁺ cations of six-membered windows.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1160–1162, May, 1988.