Condensibility influence

Kozlov, G. V. Musaev, Yu. 1. Shustov, G. B. Burmistr, M. V. Korenyako, V. A. Kinetics of high-temperature poly condensation influence of synthesis temperature and solvent thermodynamical quality. Problems of Chemistry and Chemical Technology, 2001, (2), 106-109. 

Cannizzaro reaction Two molecules of many aldehydes, under the influence of dilute alkalis, will interact, so that one is reduced to the corresponding alcohol, while the other is oxidized to the acid. Benzaldehyde gives benzyl alcohol and benzoic acid. Compare the aldol condensation. 

In the sections below a brief overview of static solvent influences is given in A3.6.2, while in A3.6.3 the focus is on the effect of transport phenomena on reaction rates, i.e. diflfiision control and the influence of friction on intramolecular motion. In A3.6.4 some special topics are addressed that involve the superposition of static and transport contributions as well as some aspects of dynamic solvent effects that seem relevant to understanding the solvent influence on reaction rate coefficients observed in homologous solvent series and compressed solution. More comprehensive accounts of dynamics of condensed-phase reactions can be found in chapter A3.8. chapter A3.13. chapter B3.3. chapter C3.1. chapter C3.2 and chapter C3.5. 

Kramers solution of the barrier crossing problem [45] is discussed at length in chapter A3.8 dealing with condensed-phase reaction dynamics. As the starting point to derive its simplest version one may use the Langevin equation, a stochastic differential equation for the time evolution of a slow variable, the reaction coordinate r, subject to a rapidly statistically fluctuating force F caused by microscopic solute-solvent interactions under the influence of an external force field generated by the PES F for the reaction... 

Because of the general difficulty encountered in generating reliable potentials energy surfaces and estimating reasonable friction kernels, it still remains an open question whether by analysis of experimental rate constants one can decide whether non-Markovian bath effects or other influences cause a particular solvent or pressure dependence of reaction rate coefficients in condensed phase. From that point of view, a purely... 

Leitner D M 1999 influence of quantum energy flow and localization on molecular isomerization in gas and condensed phases Int. J. Quant. Chem. 75 523-31... 

Much of chemistry occurs in the condensed phase solution phase ET reactions have been a major focus for theory and experiment for the last 50 years. Experiments, and quantitative theories, have probed how reaction-free energy, solvent polarity, donor-acceptor distance, bridging stmctures, solvent relaxation, and vibronic coupling influence ET kinetics. Important connections have also been drawn between optical charge transfer transitions and thennal ET. 

This Reaction should be carefully distinguished from the Claisen Conden-tation, which is the condensation of an ester, under the influence of sodium ethoxide, with (i) another ester, (ii) a ketone, or (iii) a nitrile, with the elimination of alcohol. For details of this condensation, see Ethyl Acetoacetate, p. 264. 

It is readily prepared by the action of metallic sodium on dry ethyl acetate. The reaction, which occurs only in the presence of a trace of ethanol, is complex, but may be considered (in effect) as a condensation of two molecules of ethyl acetate under the influence of sodium ethoxide, the sodium derivative of the enol form being thus obtained. Clearly, only a trace of ethanol is thus initially... 

For the preparation of 4-substituted coumarins, a phenol may be condensed with ethyl acetoacetate under the influence of sulphuric acid. Thus resorcinol (II) readily undergoes this condensation (which is represented diagrammatically above) to give 7-hydroxy-4-methyl-coumarin (III). Note that the coumarins, like all 2 pyrones, are systematically lactones. 

In molecular distillation, the permanent gas pressure is so low (less than 0 001 mm. of mercury) that it has very little influence upon the speed of the distillation. The distillation velocity at such low pressures is determined by the speed at which the vapour from the liquid being distilled can flow through the enclosed space connecting the still and condenser under the driving force of its own saturation pressure. If the distance from the surface of the evaporating liquid to the condenser is less than (or of the order of) the mean free path of a molecule of distillate vapour in the residual gas at the same density and pressure, most of the molecules which leave the surface will not return. The mean free path of air at various pressures is as follows —... 

The aniline then reacts with the ap-unsaturated aldehyde by 1 4-addition the addition product, under the influence of strong acid, cyclises to form 1 2-dihydroquinaldine. The latter is dehydrogenated by the condensation products of aniline with acetaldehyde and with crotonaldehyde simultaneously produced ( .c., ethylideneaniline and crotonylideneaniline) these anils act as hydrogen acceptors and are thereby converted into ethylaniline and n-butyl-aniline respectively. 

Furfural undergoes condensation to furoin under the catal3rtic influence of cyanide ions in aqueous alcohol solution (compare Benzoin, Section IV,125) ... 

If the condensation is done with /S-aminocrotonic ester or (2-aminopent-2-en-4-one)enamine, intermediates 245b are also obtained then they are cyclized either to 2--aininothiazoles (243b) under the influence of alkalis or to A-4-thiazol-2-ones by acids (Scheme 125b) (728). 

The pores in question can represent only a small fraction of the pore system since the amount of enhanced adsorption is invariably small. Plausible models are solids composed of packed spheres, or of plate-like particles. In the former model, pendulate rings of liquid remain around points of contact of the spheres after evaporation of the majority of the condensate if the spheres are small enough this liquid will lie wholly within the range of the surface forces of the solid. In wedge-shaped pores, which are associated with plate-like particles, the residual liquid held in the apex of the wedge will also be under the influence of surface forces. 

Numerous studies have probed how novolac microstmcture influences resist hthographic properties. In one example, a series of resists were formulated from novolacs prepared with varying feed ratios ofpara-jmeta-cmso. These researchers found that the dissolution rate decreased, and the resist contrast increased, as thepara-jmeta-cmso feed ratio increased (33). Condensation can only occur at the ortho position ofpara-cmso but can occur at both the ortho- and i ra-positions of meta-cmso. It is beheved that increased steric factors and chain rigidity that accompany increasedpara-cmso content modify the polymer solubihty. 

The Beckstead-Derr-Price model (Fig. 1) considers both the gas-phase and condensed-phase reactions. It assumes heat release from the condensed phase, an oxidizer flame, a primary diffusion flame between the fuel and oxidizer decomposition products, and a final diffusion flame between the fuel decomposition products and the products of the oxidizer flame. Examination of the physical phenomena reveals an irregular surface on top of the unheated bulk of the propellant that consists of the binder undergoing pyrolysis, decomposing oxidizer particles, and an agglomeration of metallic particles. The oxidizer and fuel decomposition products mix and react exothermically in the three-dimensional zone above the surface for a distance that depends on the propellant composition, its microstmcture, and the ambient pressure and gas velocity. If aluminum is present, additional heat is subsequently produced at a comparatively large distance from the surface. Only small aluminum particles ignite and bum close enough to the surface to influence the propellant bum rate. The temperature of the surface is ca 500 to 1000°C compared to ca 300°C for double-base propellants. 

The thermal conductivity of most materials decreases with temperature. When the foam stmcture and gas composition are not influenced by temperature, the k of the cellular material decreases with decreasing temperature. When the composition of the gas phase may change (ie, condensation of a vapor), then the relationship of k to temperature is much more complex (143,191,198). 

Fig. 1. Influence of pH on A, the addition reaction of urea and formaldehyde (1 1) and B, the condensation of methylolurea with the amino hydrogen of a...

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