Alkylating agents activation, deactivation

When olefins are used as alkylating agents, the catalytic activity of Nafion-H slowly decreases, most probably due to some polymerization on the surface, which deactivates the catalytic sites. The activity decreases faster when more reactive branched alkenes are used. The use of alcohols instead of olefins as the alkylating agents improves the lifetime of the catalyst. With alcohols, no ready polymerization takes place, since water formed as byproduct inhibits polymerization of any olefin formed (by dehydration) but does not affect the acidity of the catalyst at the reaction temperatures. 

Catalysts which have been found to promote dimerization of phenyl isocyanate include pyridine (11), methylpyridine (12), triethylamine (13), X-methyl- (or ethyl-)morpholine, triethylphosphine, and other alkyl or alkyl-arylphosphines (14, 15). Alkylphosphines bring about a very violent polymerization since they act as active catalysts and the polymerization is quite exothermic. Triphenylphosphine is inactive. Alkyl-arylphosphines are not as active as alkylphosphines and permit better control of the reaction. Another convenient method (14, 16) for control of phosphine-catalyzed dimerization involves the addition of an alkylating agent such as benzyl chloride in an amount stoichioraetrically equivalent to the substituted phosphine present. Complete deactivation of the catalyst results. By this means the reaction may be mitigated or even quenched and then activated by the addition of more catalyst. 

Hopeful of designing an alkylating agent towards the haem-site of AR, 17 6-hydroxy-10-methylthioestra-l,4-dien-3-one (79) was synthesized and had better affinity (apparent AT = 45 nM) for the binding site than testosterone = 610 nM). The inhibition by this compound was not entirely enzyme-activated, as it was irreversibly deactivated in the absence of NADPH, although interestingly it was shown that the half-life for AR was decreased when NADPH was included in the incubation medium [207]. 

The function of the excess TMA is the focus of considerable controversy. To it have been ascribed the roles of alkylating agent, ionizing agent, chain-transfer agent, and deactivator. TMA can be removed, at least partially, by vacuum distillation, leaving a toluene-soluble material, which remains a competent activator for metallocene polymerization. 

The trend in relative effectiveness of RAFT agents with varying Z is rationalized in terms of interaction of Z with the C=S double bond to activate or deactivate that group towards free radical addition. Substituents that facilitate addition generally retard fragmentation. O-Alkyl xanthates (Z=0-alkyl, Table... 

Zeolite catalysts due to their shape selectivity, thermostability, the easy separation from the products and the possibility of regeneration of the deactivated catalysts, have been widely used in the field of petrochemistry [2,3]. However, their use in fine organic synthesis has been limited. Recently, zeolite catalysts were found to be active in the alkylation of aromatics, however, there is no report to date on the benzylation of naphthalene. In this paper, we disclose a new catalytic method for the benzylation of naphthalene using zeolite H-beta as the catalyst and benzyl chloride as the benzylating agent. The optimum reaction conditions for the production of more 2-benzylnaphthalene are also examined in this study. The results obtained over H-beta catalyst are compared with zeolite H-Y and the conventional catalyst, AICI3. 

Next the activity of the catalyst has to be related to the amount of deactivating agent. This is done by means of exponential deactivation functions. Three deactivating functions were selected one for the effect of alkylation, one for the monomolecular steps and one for the bimolecular steps, as illustrated in Fig. 5.3.3.D-2. The deactivation parameter in the exponentials was derived from the experimental data. The evolution of the deactivating functions with the coke content is also shown. 

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