Ether linkages, epoxide reactions

Theoretically, the hydroxyl groups generated in the above reaction sequence are capable of reacting with other epoxide groups, thus forming an ether linkage. This reaction can be catalyzed by tertiary amines. 

The reaction of the epoxide with a thiol group yields a thioether linkage, whereas reaction with a hydroxyl gives an ether and reaction with an amine results in a secondary amine bond. The relative reactivity of an epoxy group is thiol > amine > hydroxyl, and this is reflected by... 

Porath, 1974). B/s-oxirane compounds also can be used to introduce epoxide groups into soluble dextran polymers in much the same manner (Boldicke et al., 1988 Bocher et al., 1992). The epoxide group reacts with nucleophiles in a ring-opening process to form a stable covalent linkage. The reaction can take place with primary amines, sulfhydryls, or hydroxyl groups to create secondary amine, thioether, or ether bonds, respectively (Chapter 2, Section 1.7). 

In order that an alternating copolymer is produced, the metal alkoxide must undergo faster insertion of carbon dioxide than reaction with a second equivalent of epoxide. If the metal alkoxide reacts with a second epoxide or undergoes decarboxylation reactions, ether linkage(s) may be formed. Ether linkages are undesirable as they compromise the properties of the polymer and reduce the carbon dioxide uptake. 

Lignin condensation reactions include the formation of diphenylmethanes (57) and (52) and a-carbohydrate ether linkage (55) that may be derived from the quinonemethide (42) [32,277,336-340] or the epoxide (49) [342,343] intermediate. Coniferyl alcohol may be involved in the formation of p-7-linked condensed unit (54) [338,339]. 

In 2006 Fukuyama published a total synthesis of racemic morphine starting from isovanillin and a cyclohexene-epoxide [16, 17]. The key features in their synthesis are (1) a construction of the ether linkage between A and C rings by Tsuji-Trost coupling, (2) an intramolecular Heck reaction to construct A-C-E tricyclic system, and (3) an intramolecular Mannich-type reaction of a ketone with an aminal to provide the pentacyclic structure of morphine in a one-step reaction by double cyclization. 

The photoinitiated cationic polymerization of liquid epoxidized polyisoprene is an efficient method to generate rapidly crosslinked elastomers. In the presence of a triarylsulfonium salt, the reaction develops readily upon UV exposure, with formation of both inter and intramolecular ether linkages. The formulation reactivity can be substantially enhanced by the addition of a difunctional vinyl ether or acrylate monomer, which acts as a reactive diluent and leads to the formation of an... 

III) Reaction of epoxide groups with —OH groups to give ether linkages and new —OH groups ... 

The reaction of fiber with an epoxide leads to the formation of an ether linkage and a new OH group. Therefore graft-polymerization reactions are possible [38]... 

Owing to their low reactivity, it is usual to incorporate accelerators such as tertiary amines or imidazoles. Even so, the reaction mechanism is complex, as three competing reactions take place. The anhydride reacts with the epoxy hydroxyls to form half esters. The half ester containing the free carboxyl group is then available to react with an epoxide ring, which generates another hydroxyl. The newly formed hydroxyl can react with another anhydride or, in the presence of the free acid, it can react with another epoxy to form an ether linkage. 

Epoxide ring opening usually takes place at the least hindered C-0 bond, but cleavage is also observed at the other carbon. This results in regio-irregular polymers. Also, if instead of alternate epoxide and CO insertion, consecutive epoxide insertion takes place, then ether linkages rather than carbonate linkages are formed. Consecutive CO insertion has an unfavorable reaction enthalpy and has never been observed. 

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