The mechanism of epoxide reactions. Part XII. Reactions of ethylene oxide with alcohols in the presence of sodium alkoxides and of tertiary amines

Abstract

The kinetics of the base-catalysed solvolyses of ethylene oxide in a series of alcohols have been studied and comparisons made between reactions catalysed by sodium alkoxides and reactions catalysed by tertiary amines. In the former case the reactions take place in a single step and the effects of substituent groups on reactivity tend to cancel, so that in the temperature range 60-70" the rates in nine alcohol-alkoxide combinations are all very si m i I a r.The amine-catalysed reactions take place in several stages, the active catalyst in the case of triethylamine a t temperatures below 50" being triethyl-2-hydroxyethylammonium alkoxide. formed by an initial relatively slow reaction between triethylamine and ethylene oxide and subsequent rapid equilibration of the resulting zwitterion with solvent. With a series of nuclear-substituted NN-dimethylanilines nucleophilic catalysis was also demonstrated and a t higher temperatures this probably constitutes the major reaction route for reactions catalysed by tertiary amines. General base catalysis by tertiary amines was shown to be negligible in all the solvents studied. THE solvolysis2 of ethylene oxide in an alcohol ROH in the presence of the alkoxide ion ROmay be thought of as a special case of the base-catalysed polymerisation of ethylene oxide (equation l ) , 3 in which the composition of the reaction medium remains constant and in which only the first addition step (n = 1) takes place. A similar mechanism has been suggested for the curing /*\ CH,-CH, + RIO(CH,*CH,*O)-, -R1O (CH,*CH,*O) -n (1)

Cure mechanisms of diglycidyl ether of bisphenol A (DGEBA) epoxy with diethanolamine

“…This is in good agreement with the ring opening of ethylene oxide, and shows a remarkable insensitivity to curing agent and molecular environment [8]. The activation energy, on the other hand, is quite sensitive to such details [10].…”

“…The chemical details of this reaction are less understood than that of the adduct-forming reaction, but it is clear that the reaction rate is not a simple function of temperature and epoxide reaction extent [6]. The complex kinetics is thought to result from the formation of a temperature sensitive transition state (or "activated") complex [7][8][9][10] as well as a diverse mixture of hydrogen bonded complexes that can either accelerate or inhibit the reaction [11]. The purpose of the present paper is to review the existing literature and to provide additional quantification of the gelation reaction that will increase the understanding of the polymerization mechanism as well as aid the prediction and optimization of the cure process as part of a comprehensive modeling effort of DGEBA/DEA.…”

Catalytic effect of amines on the ethoxylation of dodecyl alcohol

“…This probably is due to the thermal instability of the quaternary ammonium ion. (According to Laird and Parker (7), the quaternary ammonium hydroxide is stable below 60 C). Hence, the two steps of ethoxylation consist of two processes which depend differently on the temperature of the reaction.…”

“…In some cases primary or secondary amines are used (3), and the amine is also ethoxylated. However, tertiary amines generally are used as catalysts (4,5,6,7).…”

“…The reaction of more reactive alcohols (e.g., methyl alcohol) with ethylene oxide, however, has been catalyzed with dimethyl aniline (7). In the case of triethyl amine the low boiling point of the catalyst results in a high loss during the reaction.…”