Über die Produkte der Reaktion von Ethylbromid mit Kaliumhydroxid in wäßrig‐alkoholischen Lösungen und den Verlauf dieser SN2‐Reaktion

Abstract

About the Products of the Reaction of Ethyl Bromide and Potassium Hydroxide in Aqueous Alcoholic Solutions and the Progress of this SN2 ReactionIn the textbooks of organic and general chemistry the reactions of ethyl bromide or methyl bromide with hydroxide ions in alcoholic or aqueous‐alcoholic solutions are the main examples for the SN2 reaction mechanism first established by INGOLD and HUGHES in 1933–1935.It seems clear that the main product of the reaction between ethyl bromide and potassium hydroxide is ethanol apart from a small proportion of ethene in the competing elimination reaction. But the main product of this reaction in ethanolic or aqueous ethanolic solution is diethyl ether or in methanolic or aqueous methanolic solution methyl ethyl ether. Even in the case of using only water, potassium hydroxide and ethyl bromide one can gain 17% of diethyl ether. Kinetic investigations demonstrate that there is a real equilibrium between ethoxide and hydroxide ions in aqueous ethanolic solution. The equilibrium constant is near 0.5, that means that a mixture of ethanol and water contains a rather high amount of ethoxide ions if potassium hydroxide is dissolved in the solution. On the other hand, in the substitution reaction ethoxide ions react 2.5 times faster than OH⊖ at 20°C and 4.5 times faster at 100°C. Therefore, the main substitution reaction in aqueous ethanolic solution after formation of ethoxide ions according to the equilibrium equation image is the reaction to diethyl ether according to equation image