Reactive processing chain modification reactions

Substitution Reactions on Side Chains. Because the benzyl carbon is the most reactive site on the propanoid side chain, many substitution reactions occur at this position. Typically, substitution reactions occur by attack of a nucleophilic reagent on a benzyl carbon present in the form of a carbonium ion or a methine group in a quinonemethide stmeture. In a reversal of the ether cleavage reactions described, benzyl alcohols and ethers may be transformed to alkyl or aryl ethers by acid-catalyzed etherifications or transetherifications with alcohol or phenol. The conversion of a benzyl alcohol or ether to a sulfonic acid group is among the most important side chain modification reactions because it is essential to the solubilization of lignin in the sulfite pulping process (17). 

Classes of Polymer Chain Modification Reactions, Carried out in Reactive Polymer Processing Equipment, 604... 

CLASSES OF POLYMER CHAIN MODIFICATION REACTIONS, CARRIED OUT IN REACTIVE POLYMER PROCESSING EQUIPMENT... 

There are many polymer chain modification reactions of different types that have been carried out on polymer melts processed in single and twin rotor extruders. This activity, (4-6) in the analysis of polymerization reactors, driven by market forces seeking to create value-added polymers from commodity resins, started in the mid-1960s in industrial research laboratories (7). Indeed much of the early work is to be found in the patent literature.1 Although in recent times more publications, both industrial and academic can be found in the open literature, there is still a good deal of industrial secrecy, because the products of reactive polymer processing are of significant commercial value to industry. Below we will deal briefly with two important examples of such reactions. 

Oxidative amino acid side-chain modifications do not result in a stable end product of the oxidation process, but very often highly reactive intermediates are formed. These include chemically reactive groups, like ketones and aldehydes, or the formation of protein hydroperoxides. The presence of such protein hydroperoxides leads to a process called protein peroxidation. Here secondary reactions occur if the protein hydroperoxide decomposes and initiates further oxidative reactions, again forming oxidized protein forms. 

The modification of a radical by reacting with a certain point of its own chain (also indicated as bite back ) and elimination of a cyclic compound is a common type of propagation reaction. It takes place in many pyrolytic processes when the steric structure of the molecule allows the reaction, when the eliminated molecule is favored energetically (e.g. aromatic rings), and when the reactivities of specific centers in the molecule are active. The kinetic factors are in general more difficult to estimate, but the probability of a efficient collision with another large molecule may be lower than that with the own chain of the radical, which also favors the bite back reactions. 

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