The Mercury Photosensitized Reactions of 1-Butene and 2-Butene

Abstract

An investigation has been made of the reactions of 1‐butene and 2‐butene with mercury (³P₁) atoms at 30°C in a static system. The main products of the 1‐butene reaction are 2‐butene and liquid polymer. A large number of other products are also formed especially at low pressures. The rate of isomerization increases rapidly with pressure in the region of complete quenching, while the rate of polymerization falls off rapidly. The over‐all rate of consumption of 1‐butene increases very slightly with increasing pressure. The over‐all quantum yield of 1‐butene consumption is 0.32 at 20‐mm pressure. The principal steps in the mechanism proposed for the reaction are: $$\begin{array}{c}\text{1−}{\mathrm{C}}_4{\mathrm{H}}_8+\mathrm{Hg}{(}^3{\mathrm{P}}_1\text{)→1−}{\mathrm{C}}_4{\mathrm{H}}_8^{*}+\mathrm{Hg}{(}^1\mathrm{So}\mathrm{),}\\ \text{1−}{\mathrm{C}}_4{\mathrm{H}}_8^{*}\text{+1−}{\mathrm{C}}_4{\mathrm{H}}_8\text{→2−}{\mathrm{C}}_4{\mathrm{H}}_8\text{+1−}{\mathrm{C}}_4{\mathrm{H}}_8,\\ \text{1−}{\mathrm{C}}_4{\mathrm{H}}_8^{*}\to {\mathrm{C}}_4{\mathrm{H}}_7+\mathrm{H},\end{array}$$ followed by polymerization reactions of the type $$\text{1−}{\mathrm{C}}_4{\mathrm{H}}_8+{\mathrm{C}}_4{\mathrm{H}}_7\to {\mathrm{C}}_8{\mathrm{H}}_{15},\mathrm{etc}.$$ It is therefore possible for the first time, to obtain a direct measurement of the rate of collisional deactivation merely by determining the rate of formation of 2‐butene. 2‐butene is much less reactive than 1‐butene. The over‐all quantum yield of 2‐butene consumption has a maximum value of 0.11 at an initial pressure of 1–2 mm. Above this pressure the rate of 2‐butene consumption falls off rapidly. The main product of the reaction is a liquid polymer. Smaller amounts of hydrogen and methane are also formed. An activated molecule mechanism is proposed which accounts for the essential aspects of the reaction.