Rate constant terminal double bond

The parameter K shown in the figure represents the reactivity of the terminal double bonds, defined by K=k lk, and k is the rate constant of TDBP. The... 

As a first approach, we studied the epoxidation of the exocychc double bond of 1 by weto-chloroperbenzoic acid (mCPBA) in dichloromethane. IR spectra provided evidence for a fluorescent epoxide [94]. Eater on, surface-catalyzed epoxidation was ascribed to the formation of further fluorescent BODIPY derivatives [54]. The bimolecular rate constant had been determined beforehand, and pointed to the concentration range of mCPBA for maintaining useful pseudo-first-order kinetics. Immobilization turned out to be a major issue because, while the oxidizing species should have free access to the double bond, the translational mobility of the substrate must be widely suppressed. Introduction of a further terminal double bond permitted subsequent immobilization on polymeric sihcone [102-104]. 

Butyllithium initiation of methylmethacrylate has been studied by Korotkov (55) and by Wiles and Bywater (118). Korotkov s scheme involves four reactions 1) attack of butyllithium on the vinyl double bond to produce an active centre, 2) attack of butyllithium at the ester group of the monomer to give inactive products, 3) chain propagation, and 4) chain termination by attack of the polymer anion on the monomer ester function. On the basis of this reaction scheme an expression could be derived for the rate of monomer consumption which is unfortunately too complex for use directly and requires drastic simplification. The final expression derived is therefore only valid for low conversions and slow termination, and if propagation is rapid compared to initiation. The mechanism does not explain the initial rapid uptake of monomer observed, nor the period of anomalous propagation often observed with this initiator. The assumption that kv > kt is hardly likely to be true even after allowance is made for the fact that the concentration of active species is much smaller than that of the added initiator. Butyllithium disappears almost instantaneously but propagation proceeds over periods from tens to hundreds of minutes. The rate constants finally derived therefore cannot be taken seriously (the estimated A is 2 x 105 that of k ) nor can the mechanism be regarded as confirmed. 

The industrial Wacker process is carried out in aqueous hydrochloric acid using PdClj/CuCh as the catalyst under oxygen pressure. The oxidation of higher terminal alkenes under the same conditions is slow and sometimes accompanied by undesired by-products formed by the chlorination of carbonyl com-poimds by CuCh, and isomerization of double bonds. Earlier examples of oxidation of various alkenes, mainly in aqueous solutions, have been tabulated.The pseudo-first-order rate constants for oxidation of various alkenes, relative to the value for cycloheptene, with PdCb in the presence of benzoquinone in aqueous solution have been rqwrted. An accelerating effect of surfactants such as sodium lauryl sulfate on the stoichiometric oxidation of higher alkenes in an aqueous solution has been reported. 

The majority of radical reactions of interest to synthetic chemists are chain processes [3,4]. For those readers who are not familiar with this chemistry, some general aspects of radical chain reactions are discussed here. Scheme 1 represents the simple addition of a thiol to a carbon-carbon double bond as an example of a chain process. Thus, RS radicals, generated by some initiation processes, undergo a series of propagation steps generating fresh radicals. The chain reactions are terminated by radical combination or disproportionation. In order to have an efficient chain process, the rate of chain transfer steps must be greater than that of chain termination steps. Since the termination rate constants in the liquid phase are controlled by diffusion (i.e. 10 M s ) and radical... 

The term 1-alkyne polymerization refers to a process in which a terminal alkyne undergoes, similar to the ROMP process of a cyclic olefin, a [2 + 2] cycloaddition to a metal carbene (alkylidene). This can proceed via a- or p-insertion of the alkyne into the metal-carbon double bond (Scheme 4). Both insertion mechanisms lead to conjugated polymers. With a few exceptions, polymerizations based on a-insertion are the preferred ones, since they offer better control over molecular weights due to favorable values of fei/fep k and kp are the rate constants of initiation and propagation, respectively). 

LFsing the assumptions that (1) any carbon double bond in the unsaturated polyester and styrene monomer has the same rate constant for reaction with an initiator radical [/ ], (2) the rate of initiation can be lumped with the rate of conversion to give a rate expression of the total radical concentration [/ ], (3) the propagation reactions can be expressed by a single average rate constant, and (4) all termination reactions can be combined in a single effective termination constant, the following rate... 

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