Aromatic hydrocarbons, telomerization

An initiator system has been found independently in the laboratories of Esso and Sun Oil (3, 4). This system promotes transmetalation and chain propagation reactions at comparable rates so that a telomerization reaction of ethylene with aromatic hydrocarbons is realized under relatively mild operating conditions. 

Ethylenation of n-butyllithium, phenyllithium, and benzylic lithium compounds does not occur at low temperature and ordinary pressure (9). Under more rigorous conditions, telomerization of ethylene in aromatic hydrocarbons proceeds vigorously in the presence of an organolithium compound and an amine. Although n-butyllithium is introduced initially, rapid transmetalation occurs to the more acidic aromatic hydrocarbon (telogen) which subsequently adds to ethylene (taxogen) and initiates the carbanionic polymerization of ethylene. This polymerization proceeds to modest molecular weight, but it is terminated by transmetalation back to the aromatic hydrocarbon which initiates another chain to complete the catalytic cycle. 

Much of the early work with N-chelated organolithium compounds was concerned with polymeric reactions—in particular the telomerization of ethylene onto aromatic hydrocarbons such as benzene and toluene to produce long-chain alkylbenzenes (6,7, 8, 9). 

All the above reactions involve hydrogen—lithium interconversion (metalation). There are a limited amount of data available indicating that N-chelated organolithium intermediates also undergo nucleophilic addition to carbon-carbon double and triple bonds much more readily than does the organolithium reagent alone. Indeed, this enhanced reactivity toward addition reactions is a key factor in the telomerization of ethylene onto aromatic hydrocarbons (6, 7,8,9). 

This report covers the use of chelated organosodium compounds as novel catalysts for telomerizing conjugated diolefins with weak hydrocarbon acids such as aromatics and olefins (7). The factors affecting the chain-transfer reaction were of particular interest because one of our objectives was to increase selectivity to low-molecular-weight species. The products are useful in synthesizing plasticizer alcohols, flame retardants, and surface coatings. 

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