POLYHALOGENOALLENSE .6. SOME ADDITION REACTIONS OF PERFLUOROPENTA-1,2-DIENE

Perfluoropenta-1,2-diene is inert towards chlorine, hydrogen chloride, and hydrogen bromide at room temperature in the dark, but combines quantitatively with anhydrous hydrogen fluoride under these conditions to give cis- and trans-2H-nonafluoropent-2-ene. The latter is also obtained by treatment of perfluoropenta-1,2-diene with caesium fluoride in formamide; reaction of the diene with caesium fluoride alone provides perfluoropent-2-yne. Anhydrous methanol readily attacks perfluoropenta-1,2-diene to give trans-2H-octafluoro-1- methoxypent-2-ene and heptafluoro-1-methoxypent-2-yne. Photochemical hydrobromination of perfluoropenta-1,2-diene gives 3H-2-bromo-octafluoropent-1- ene and 1H-2-bromo-octafluoropent-2-ene (probably both as cis- and trans-isomers), while photochemical chlorination with an excess of chlorine gives 1,2,2,3-tetrachloro-octafluoro-n-pentane. The n.m.r. spectra of the reaction products are presented, and possible reaction mechanisms are discussed.