Fast Reaction Rate

Kinetics and Mechanisms. Early researchers misunderstood the fast reaction rates and high molecular weights of emulsion polymerization (11). In 1945 the first recognized quaHtative theory of emulsion polymerization was presented (12). This mechanism for classic emulsion preparation was quantified (13) and the polymerization separated into three stages. 

A fast reaction rate using the catalyzed product... 

In its catalyzed form [catalyzed with hydroquinone (HQ), benzo-quinone, or copper], DEHA has a very fast reaction rate, almost as fast as catalyzed sulfite. Hydroquinone is the most popular catalyst for DEHA, and it is likely that the rapid reaction rate is, in part at least, due to the catalyst simply acting as an oxygen scavenger in its own right. 

Among methylene chloride, chloroform, carbon tetrachloride, and hexane, fast reaction rate was observed in methylene chloride or chloroform solvents, but slow... 

Due to excellent yields, mild reaction conditions, and a fast reaction rate, the azolide method is well suited to the synthesis of isotopically labeled esters, even ones with very short half-lives, just as it is always useful for the esterification of sensitive carboxylic acids, alcohols, and phenols under mild conditions. An example is provided by the synthesis of [nC]-quinuclidinyl benzilate prepared from benzilic acid, CDI, and nC-labeled quinuclidinol.[147]... 

Example Procedures. Due to the fast reaction rate of Ti-isop, two different procedures were employed for TEOS-PTMO and Ti-containing systems. 

Since each semiconductor particle can be considered as a microphotocell, fast reaction rates can be expected because of the extremely large surface area of the semiconductor on which the reactions take place. 

Of the three catalytic systems so far recognized as being capable of giving fast reaction rates for methanol carbonylation—namely, iodide-promoted cobalt, rhodium, and iridium—two are operated commercially on a large scale. The cobalt and rhodium processes manifest some marked differences in the reaction area (4) (see Table I). The lower reactivity of the cobalt system requires high reaction temperatures. Very high partial pressures of carbon monoxide are then required in the cobalt system to... 

Spherical diffusion has peculiar properties, which can be utilized to measure fast reaction rates. The diffusion current density of a species i to a spherical electrode of radius ro is given by ... 

The thermal plasma is a source of high energy density with temperature of a few thousand degrees and high ultraviolet radiation. These result in fast reaction rates, high throughput in smaller reactors, heat generation independent of the chemical composition, avoidance of dioxins and furans... 

In contrast, a fast reaction rate will result in steep concentration gradients for the reactants and a higher reaction rate near the solvent interface. This concept is represented diagrammatically in Figure 2.13b, where the concentration of reactant A is almost as high as that in phase 1 at the solvent interface, but plummets as it is rapidly consumed by the reaction. Thus, for a fast reaction, the majority of reactant is converted to product near the phase boundary layer and the rate of the reaction is limited by the rate of phase transfer and diffusion. 

All primary amines react with fluorescamine under alkaline conditions (pH 9-11) to form a fluorescent product (Figure 10.12) (excitation maximum, 390 nm emission maximum, 475 nm). The fluorescence is unstable in aqueous solution and the reagent must be prepared in acetone. The secondary amines, proline and hydroxyproline, do not react unless they are first converted to primary amines, which can be done using A-chlorosuccinimide. Although the reagent is of interest because of its fast reaction rate with amino acids at room temperature, it does not offer any greater sensitivity than the ninhydrin reaction. 

A model for the SSP of PET under typical industrial processing conditions has been developed by Ravindrath and Mashelkar [15]. Their calculations are also based on experimental data reported in the literature. The results allow the rough conclusion that the reaction rate decreases by a factor of 6 for the temperature range between 285 and 220 °C, accompanied by a decrease of the thermal degradation by a factor of 40. The fact that suitable SSP conditions can be found to warrant a fast reaction rate and minimal degradation makes this process industrially important. These same authors also state that at an early stage of the reaction the kinetics have a predominant influence, whereas diffusivity plays a major part at a later stage of the reaction. 

The high solvolytic stereospecificity of the tosylate 91 together with the unexpectedly fast reaction rates was tentatively interpreted by Cram 88b> in terms of /8-phenyl participation in the ionization step to produce a highly strained bridged carbonium ion 96 which is opened in a second reaction step to give the final product. Both the formation of 96 and its opening must involve complete inversion in order to ensure retention of stereospecificity in the overall solvolytic process. 

Polyesterifications, like many step polymerizations, are carried out at moderate to high temperatures not only to achieve fast reaction rates but also to aid in removal of the small molecule by-product (often H2Q). The polymerization is an equilibrium reaction and the... 

A supercritical fluid (SCF) is a substance above its critical temperature and critical pressure. The critical temperature is the highest temperature at which a substance can exist as a gas. The critical pressure is the pressure needed at the critical temperature to liquify a gas. Above the critical temperature and critical pressure, a substance has a density characteristic of a liquid but the flow properties of a gas, and this combination offers advantages as a reaction solvent. The liquidlike density allows the supercritical fluid to dissolve substances, while the gaslike flow properties offer the potential for fast reaction rates. Supercritical carbon dioxide (scC02) has a critical temperature of 31°C and critical pressure of 73 atm. 

The two primary hydroxyl groups provide fast reaction rates with diisocyanates, which makes this diol attractive for use as a curative in foams. It provides latitude in improving physical properties of the foam, in particular the load-bearing properties. Generally, the ability to carry a load increases with the amount of 1,4-cydohexanedimethanol used in producing the high resilience foam (95). Other polyurethane derivatives of 1,4-cyclohexanedimethanol indude elastomers useful for synthetic rubber products with a wide range of hardness and elasticity (96). 

The observed rate constants in the pH range 6 < pH < 7 may not be determined precisely because of the short time intervals. Probably, our values reflect only the lower limits of the fast reaction rates at neutral pH. 

The rather fast reaction rate of halomethanes with Cl atoms suggests that this process may play a primary role in the removal of halomethanes from the troposphere and results in the formation of HC1 or 1C1 molecules. These degradation pathways do not lead to bromine or iodine atoms but to relatively stable molecules, which may initiate a different bromine and iodine cycles in the marine boundary layer. The atmospheric lifetime of IC1 is probably controlled by its sunlight photodissociation to iodine and chlorine atoms. Another possible degradation pathway of IC1 may be the hydrolysis to hypoiodous acid IOH, which may further be dissolved in seawater. 

Electronic spectra may be used (as in organic chemistry) as fingerprints, and they are very important in kinetic studies. The change in the electronic spectrum of a reaction mixture as the reaction proceeds is often the best way of following its rate, and quite elaborate methods are available for measuring very fast reaction rates. However, the application which the reader is most likely to encounter in more advanced texts is in the area of coordination compounds of the transition elements, whose electronic spectra may yield information about structure and bonding. 

Obviously, these equations are only valid for a fast reaction rate compared to the feed rate. In fact, the reaction rate is implicitly taken to equal the feed rate. 

Enzymes induce fast reaction rates under mild conditions. 

We think that judicious application of molecular simulation tools for the calculation of thermophysical and mechanical properties is a viable strategy for obtaining some of the information required as input to mesoscale equations of state. Given a validated potential-energy surface, simulations can serve as a complement to experimental data by extending intervals in pressure and temperature for which information is available. Furthermore, in many cases, simulations provide the only realistic means to obtain key properties e.g., for explosives that decompose upon melting, measurement of liquid-state properties is extremely difficult, if not impossible, due to extremely fast reaction rates, which nevertheless correspond to time scales that must be resolved in mesoscale simulations of explosive shock initiation. By contrast, molecular dynamics simulations can provide converged values for those properties on time scales below the chemical reaction induction times. Finally,... 

There are several demands that must be more or less fulfilled by the mediator before a successfull amperometric detection of NADH with CMEs can be realized. Despite having a E° lower or comparable with the optimal working potential range for amperometric detection, the mediator should exhibit fast reaction rates both with the electrode proper and NADH, and also be chemically stable at any redox state. Furthermore, the redox reaction of the mediator should involve two electrons and at least one proton making possible, at least theoretically, a fast inner sphere hydride transfer in the homogeneous reaction with NADH. 

The process flowsheet inside the battery limits (IBL) is at this stage unknown. However, the recycle of reactant may be examined. The patent reveals that the catalyst ensures very fast reaction rate. Conversion above 98% may be achieved in a fluid-bed reactor for residence time of seconds. Thus, recycling propylene is not economical. The same conclusion results for ammonia. The small ammonia excess used is to be neutralized with sulfuric acid (30% solution) giving ammonium sulfate. Oxygen supplied as air is consumed in the main reaction, as well as in the other undesired combustion reactions. 

Thermoset polyurethanes are cross-linked polymers, which are produced by casting or reaction injection molding (RIM). For cast elastomers, TDI in combination with 3,3,-dichloro-4,4,-diphen5lmethanediamine (MOCA) are often used. In the RIM technology, aromatic diamine chain extenders, such as diethyltoluenediamine (DETDA), are used to produce poly(urethane ureas) (47), and replacement of the polyether polyols with amine-terminated polyols produces polyureas (48). The aromatic diamines are soluble in the polyol and provide fast reaction rates. In 1985, internal mold release agents based on zinc stearate compatibilized with primary amines were introduced to the RIM process to minimize mold preparation and scrap from parts tom at demold. Some physical properties of RIM systems are listed in Table 7. 

Dimethylformamide, as other amides, offers some unique features as a halogenation solvent. Fast reaction rates and high selectivities are repeatedly noticed. This is attributed to the in situ formation of remarkable intermediates, several of which have been isolated and characterized. 

NHCs are also efficient ligands for the palladium-catalyzed coupling of primary alkyl chlorides with aryl Grignard reagents [99]. Functionalization on both coupling partners is also tolerated in this case. This was due to the mild reaction conditions and fast reaction rates (1 hour of reaction at room temperature). 

It can be seen immediately that a decrease of the concentration of the species E] and E2 results in an increase of x in the same proportions. R. Guillaumont and J.P. Adloff [4] have shown, for 100 atoms of plutonium, assuming a very fast reaction rate (k = 1011 M s 1), the half-time x is equal to 50 ps and 1.6 y in a volume of 1 pi and 1 cm3 respectively. Obviously, a decrease in the rate constant would yield much higher reaction times (exponential). Diffusion phenomena have negligible effects since for a typical coefficient... 

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