Methanol kinetics

A more direct method of cleavage has been developed which consists of heating 502 overnight in toluene with a dispersion of sodium and chlorotrimethylsi-lane.352 418 This procedure led efficiently to 506 whose hydrolysis with dry methanol (kinetic quenching) resulted in the production of a mixture of dihydro diesters rich in 507 (77 %). The structurally rigid 508 and related a-diketones have subsequently been elaborated from this diester as starting material.418) Related endo.endo diesters bearing external methyl and methylthio substituents (509) have also been synthesized.419 ... 

Catalytic tests in the Oxydative Dehydrogenation (ODH) of methanol Kinetic runs were performed in a stainless steel tubular reactor with an internal diameter of 1cm, kept isothermal with a fluidized bed of sand. Liquid methanol was fed, by a syringe pump, into a vaporizer chamber kept at 200 °C and was then sent, after the addition of a stream of oxygen and helium, into a stainless steel coil kept at the same temperature of the reactor. 

Figure 8.4. Occupation numbers of the methanol kinetics (0, left, right, Oj, number of empty sites, markers 0.1 mol/1, lines 0.8mol/l).

Cole EB, Lakkaraju PS, Rampulla DM, Morris AJ, Abelev E, Bocarsly AB (2010) Using a one-electron shuttle for the multielectron reduction of CO2 to methanol kinetic, mechanistic, and structural insights. J Am Chem Soc 132(33) 11539-11551... 

Figure 5.1 Initial state (is) and transition state (ts) transfer chemical potential variations for solvolysis of trans- Coipy)4,C in aqueous methanol. Kinetic data are from Ref. 209, solubility data from Ref. 210 (is) values were obtained by using 8 , x°(Cl") values interpolated from Ref. 202. Transfer chemical potentials for Rb" and for Ba " (also from Ref. 202) are shown for comparison. All values are on the molar scale, at 298.2 K.

Anhydrous, monomeric formaldehyde is not available commercially. The pure, dry gas is relatively stable at 80—100°C but slowly polymerizes at lower temperatures. Traces of polar impurities such as acids, alkahes, and water greatly accelerate the polymerization. When Hquid formaldehyde is warmed to room temperature in a sealed ampul, it polymerizes rapidly with evolution of heat (63 kj /mol or 15.05 kcal/mol). Uncatalyzed decomposition is very slow below 300°C extrapolation of kinetic data (32) to 400°C indicates that the rate of decomposition is ca 0.44%/min at 101 kPa (1 atm). The main products ate CO and H2. Metals such as platinum (33), copper (34), and chromia and alumina (35) also catalyze the formation of methanol, methyl formate, formic acid, carbon dioxide, and methane. Trace levels of formaldehyde found in urban atmospheres are readily photo-oxidized to carbon dioxide the half-life ranges from 35—50 minutes (36). 

Methanol carbonylation is one of only a few industrially important catalytic reactions for which the quantitative reaction kinetics is known (21). 

The kinetics of formation and hydrolysis of /-C H OCl have been investigated (262). The chemistry of alkyl hypochlorites, /-C H OCl in particular, has been extensively explored (247). /-Butyl hypochlorite reacts with a variety of olefins via a photoinduced radical chain process to give good yields of aUyflc chlorides (263). Steroid alcohols can be oxidized and chlorinated with /-C H OCl to give good yields of ketosteroids and chlorosteroids (264) (see Steroids). /-Butyl hypochlorite is a more satisfactory reagent than HOCl for /V-chlorination of amines (265). Sulfides are oxidized in excellent yields to sulfoxides without concomitant formation of sulfones (266). 2-Amino-1, 4-quinones are rapidly chlorinated at room temperature chlorination occurs specifically at the position adjacent to the amino group (267). Anhydropenicillin is converted almost quantitatively to its 6-methoxy derivative by /-C H OCl in methanol (268). Reaction of unsaturated hydroperoxides with /-C H OCl provides monocyclic and bicycHc chloroalkyl 1,2-dioxolanes. 

Dente and Ranzi (in Albright et al., eds.. Pyrolysis Theory and Industrial Practice, Academic Press, 1983, pp. 133-175) Mathematical modehng of hydrocarbon pyrolysis reactions Shah and Sharma (in Carberry and Varma, eds.. Chemical Reaction and Reaction Engineering Handbook, Dekker, 1987, pp. 713-721) Hydroxylamine phosphate manufacture in a slurry reactor Some aspects of a kinetic model of methanol synthesis are described in the first example, which is followed by a second example that describes coping with the multiphcity of reactants and reactions of some petroleum conversion processes. Then two somewhat simph-fied industrial examples are worked out in detail mild thermal cracking and production of styrene. Even these calculations are impractical without a computer. The basic data and mathematics and some of the results are presented. 

Methanol synthesis served as the model for the true mechanism. Stoichiometry, thermodynamics, physical properties, and industrial production rates were all taken from the methanol literature. Only the reaction mechanism and the kinetics of methanol synthesis were discarded. For the mechanism a four step scheme was assumed and from this the... 

In the original announcement of the workshop the participants were told that everything was to be taken from methanol synthesis except the kinetics. Some may have interpreted this to mean that the known thermodynamic equilibrium information of the methanol synthesis is not valid when taken together with the kinetics. This was not intended, but... 

Parekh, V.J., 1980, Preliminary Kinetic Study of the Low-Pressure Methanol, MS. Thesis, University of Akron, OH. 

Here a four-step mechanism is described on the framework of methanol synthesis without any claim to represent the real methanol mechanism. The aim here was to create a mechanism, and the kinetics derived from it, that has an exact mathematical solution. This was needed to perform kinetic studies with the true, or exact solution and compare the results with various kinetic model predictions developed by statistical or other mehods. The final aim was to find out how good or approximate our modeling skill was. 

Remarks The aim here was not the description of the mechanism of the real methanol synthesis, where CO2 may have a significant role. Here we created the simplest mechanistic scheme requiring only that it should represent the known laws of thermodynamics, kinetics in general, and mathematics in exact form without approximations. This was done for the purpose of testing our own skills in kinetic modeling and reactor design on an exact mathematical description of a reaction rate that does not even invoke the rate-limiting step assumption. 

To facilitate the use of methanol synthesis in examples, the UCKRON and VEKRON test problems (Berty et al 1989, Arva and Szeifert 1989) will be applied. In the development of the test problem, methanol synthesis served as an example. The physical properties, thermodynamic conditions, technology and average rate of reaction were taken from the literature of methanol synthesis. For the kinetics, however, an artificial mechanism was created that had a known and rigorous mathematical solution. It was fundamentally important to create a fixed basis of comparison with various approximate mathematical models for kinetics. These were derived by simulated experiments from the test problems with added random error. See Appendix A and B, Berty et al, 1989. 

The UCKRON AND VEKRON kinetics are not models for methanol synthesis. These test problems represent assumed four and six elementary step mechanisms, which are thermodynamically consistent and for which the rate expression could be expressed by rigorous analytical solution and without the assumption of rate limiting steps. The exact solution was more important for the test problems in engineering, than it was to match the presently preferred theory on mechanism. 

Surface SHG [4.307] produces frequency-doubled radiation from a single pulsed laser beam. Intensity, polarization dependence, and rotational anisotropy of the SHG provide information about the surface concentration and orientation of adsorbed molecules and on the symmetry of surface structures. SHG has been successfully used for analysis of adsorption kinetics and ordering effects at surfaces and interfaces, reconstruction of solid surfaces and other surface phase transitions, and potential-induced phenomena at electrode surfaces. For example, orientation measurements were used to probe the intermolecular structure at air-methanol, air-water, and alkane-water interfaces and within mono- and multilayer molecular films. Time-resolved investigations have revealed the orientational dynamics at liquid-liquid, liquid-solid, liquid-air, and air-solid interfaces [4.307]. 

The following table gives exchange rates in methanolic sodium methoxide for a number of hydrocarbons and equilibrium acidities for some. Determine whether there is a correlation between kinetic and thermodynamic acidity in this series of compounds. If so, predict the thermodynamic acidity of the hydrocarbons for which no values are listed. 

The importance of the solvent, in many cases an excess of the quatemizing reagent, in the formation of heterocyclic salts was recognized early. The function of dielectric constants and other more detailed influences on quatemization are dealt with in Section VI, but a consideration of the subject from a preparative standpoint is presented here. Methanol and ethanol are used frequently as solvents, and acetone,chloroform, acetonitrile, nitrobenzene, and dimethyl-formamide have been used successfully. The last two solvents were among those considered by Coleman and Fuoss in their search for a suitable solvent for kinetic experiments both solvents gave rise to side reactions when used for the reaction of pyridine with i-butyl bromide. Their observation with nitrobenzene is unexpected, and no other workers have reported difficulties. However, tetramethylene sulfone, 2,4-dimethylsulfolane, ethylene and propylene carbonates, and salicylaldehyde were satisfactory, giving relatively rapid reactions and clean products. Ethylene dichloride, used quite frequently for Friedel-Crafts reactions, would be expected to be a useful solvent but has only recently been used for quatemization reactions. ... 

Het = heteroaryl residue] follow second-order kinetics, first order with respect to each reactant. Regular kinetics of this kind are also observed in the reaction of sodium arylsulfide in methanol provided that no free thiol is present (see Section II,D, l,c). As to other heterocyclic systems, A -oxides and bromofuran derivatives show similar kinetic behavior. 

Kinetic studies on 2-, 3-, and 4-chloro-l-methylpyridinium salts showed a 30 10 ratio of the reaction rates at 50° with 4-nitro-phenoxide ion in methanol. The activation energy for reaction at the 4-position is one kilocalorie lower ( 8-fold higher rate) than for reaction at the 2-position. The reversal in rates relative to the corresponding halopyridines is the result of a much higher entropy of activation for the 2-chloro compound. The 3-chloro compound has a favorable entropy of activation also, but the energy of activation is about 13 kcal higher than that of the isomers (cf. Table II and Section III, A, 2). 

---