Reaction mixing mechanisms

A solution containing botli reactants and a catalyst may be mixed mechanically to bring tire constituents into efficient contact—otlierwise, tire rate of tire catalytic reaction would be affected by mass transport (e.g., diffusion)... 

Reactor Design. The continuous polymerization reactions in this investigation were performed in a 50 ml pyrex glass reactor. The mixing mechanism utilized two mixing impellers and a Chemco magnet-drive mechanism. 

A simple, high-yield procedure for the conversion of ArTlXj into ArjTlX compounds has recently been described 90). This symmetrization reaction, the mechanism of which is not known, can be effected by treatment of the ArTlX2 compound either with triethyl phosphite or with hot aqueous acetone. As a wide variety of ArTlXj compounds can now be easily prepared by electrophilic thallation of aromatic substrates with thallium(III) trifluoroacetate (q. v.), symmetrization represents the method of choice for the preparation of the majority of ArjTlX compounds. Only about twenty mixed compounds, RR TIX, have been prepared so far, and the only general synthetic procedure available consists of a disproportionation reaction between an RTIX2 species and another organometallic reagent [e.g., Eqs. (5)-(7)]. 

Considerations of mixed mechanisms and mixed reactive states might apply to these cases also, but there is no direct evidence that cyclo-hexenone itself reacts from other than the lowest zn-n state. Both cis and trans products are produced, except possibly in the acrylonitrile reaction 97>, and cis and trans-2-butene give the same mixture of products. A predominant biradical mechanism would seem the logical choice. 

The above considerations should bear some relationship with the stereochemistry of the reaction. As indicated earlier (8ection 2 Hebert et ai, 1985), in the reaction of anthracene anion radicals with optically active 2-octyl bromide, racemization is mostly observed together with a small but distinct amount (ca. 10%) of inversion. In the context of the ET-8n2 mixed mechanism sketched above, this can be rationalized in terms of a minor contribution of the latter pathway that would not detectably affect the overall rate constant of the reaction. The weakness of the bonded interactions in the transition state derives from the relatively poor affinity of the alkyl radical for the aromatic hydrocarbon. This is consistent with the fact that in those of the radical-anthracene pairs that were not favourably oriented for the 8, 2 reaction to occur, the alkyl radical escapes from the... 

Rule 3 applies to heterogeneous reactions with mixed mechanisms i. e. radical and ionic. These will have their radical component enhanced by sonication although the general mechanical effect from Rule 2 may still apply. Two situations which may occur in heterogeneous systems involving two mechan-... 

We have discussed above the influence of reagent mobility on the kinetics of the electron tunneling reaction in two extreme situations, a < a and A > Rz. In the intermediate case, a a 4, i r(the mixed mechanism of reagent mobility), the equations for the kinetics of electron tunneling reactions also have a sufficiently simple form only in two extreme situations small, t r = Rz/D, and large, t > r, observation times [32], If the initial spatial distribution of reagents is random and n(0) N, the kinetics of electron tunneling reactions is described by eqn. (35) at l z, and by the equation... 

Place 92.5 g (115 ml, 1.25 mol) of isobutyl alcohol (2-methylpropan-l-ol) and 8.55 g (0.275 mol) of purified red phosphorus (Section 4.2.59, p. 458) in a 500-ml three-necked flask fitted with a sealed mechanical stirrer, a reflux condenser and a dropping funnel containing 100 g (32 ml, 0.62 mol) of bromine (for precautions in the use of bromine, see Section 4.2.9, p. 422). Start the stirrer, heat the flask (e.g., in an oil bath) so that the contents reflux gently, and introduce the bromine at such a rate that it appears to react completely so that there is little bromine vapour above the surface of the reaction mix-... 

The methods of mechanical micromachining and micro EDM have been extensively applied to the fabrication of components such as micro heat exchangers, mixers, and reaction channels as well as chemical microsystems with integrated heat exchange, reaction, mixing, and distribution elements (Figure 10). 

Since mixing and good heat transfer are of vital importance in viscous polymerization reactions, a mechanically agitated continuous stirred-tank reactor is widely used in polymerization processes. Solution polymerization, emulsion polymerization, and solid-catalyzed olefin polymerization are all carried out in a mechanically agitated slurry reactor. 

A good agreement was obtained between experimental rate coefficients and those calculated assuming a complex/direct mixed mechanism, including TS intramolecular interactions (Table 12.5). The largest discrepancies were of 15%, 52% and 24% for propanone, 2-pentanone and methyl butanone, respectively. This agreement supports the used theoretical approach and validates the relevance of reactant complexes and hydrogen-bond like interactions on ketones + OH reactions. 

The role of a surface in initiating chain carriers which propagate primarily in the homogeneous phase has already been discussed it is a relatively minor branch of catalytic behavior. Reactions which proceed entirely at the surface of a catalyst appear to be much more common. This latter class is distinguished from the former in showing a direct proportionality between rate of reaction and amount of catalyst, other parameters being held constant. When such a relation docs not obtain experimentally, one is faced with either a mixed mechanism or a diffusion-controlled rate, and the mechanistic interpretation of the rate data becomes extremely difficult. 

A reaction with mechanism (99) should show general base catalysis but under some conditions this catalysis is difficult to detect and the rate may be dominated by hydroxide ion catalysis. However, recent work has now been carried out on the detritiation of chloroform in which general base catalysis by amines was observed [171(a)]. In the work with chloroform in which general base catalysis was not detected [114], since it was not possible to obtain a Bronsted exponent by measuring catalytic coefficients for a series of bases, an alternative procedure first suggested by Bell and Cox [172] was used. The rate of detritiation of chloroform was measured in a mixed solvent of water with varying amounts of dimethylsulphoxide and a constant concentration of hydroxide ion. As discussed briefly in Sect. 4.4 an acidity function (H ) has been determined for these solvent... 

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