Reactions at high pressure. Part 9. The volume profile for the cycloaddition of methyl acrylate to a pyridinium betaine

Abstract

Rates of cycloaddition between N-(4,6-dimethylpyrimidin-2-yl)-3-hydroxypyridinium betaine and methyl acrylate in ethanol at 25° have been measured at pressures up to 1 000 bar. The volume of activation has been determined as –36 ± 2 cm³ mol^–1. The volume of reaction has also been measured and found to be –37 cm³ mol^–1. The characteristics of this reaction are those of a typical Diels–Alder reaction. Attempts to extend the range of dienophiles by the use of high pressure have met with only limited success.