Orientation of addition of hydrogen atoms to propylene, butene‐1, and isobutene

Abstract

The orientation of addition of H atoms to the asymmetric olefins propylene, butene-I, and isobutene has been determined as a function of atom concentration, olefin concentration, hydrogen pressure, total pressure, and olefin conversion. Conditions have been determined for which complicating secondary processes are believed to be unimportant. The percentage of nonterminal addition is 5.7, 5.7, and 0.48 for propylene, butene-I, and isobutene, respectively. From these data activation energy differences between nonterminal and terminal addition of 1.7 and 3.2 kcal/mole for the linear olefins and isobutene, respectively, may be calculated. For D atom addition to propylene, a small isotope effect was observed, nonterminal addition being 5.4%. These observations are consistent with a predominantly free radical or electroneutral character for H atoms.

Reaction of H and D atoms with deuterated propylenes

“…The relative amount of nonterminal addition is independent of total pressure, apart from a slight faII-off at low pressures because of reduced stabilization of chemically activated n-propyl radicals [4,12]. The data are also independent of light intensity between 5X 10" and 5 X IOl4 quanta cm-2 sec-l, and of olefin concentration over the range studied.…”

“…Because deuterium substitution often serves as a useful guide in understanding the factors which control the rates of chemical reactions, an experimental study was undertaken to compare these two kinetic effects for four deuterium-substituted propylenes, CH3CDCH2, CHsCHCD2, CD.$CHCH2, and C3Ds, with the known behavior for C3H6 [1,4]. The experimental techniques used for this study are described in detail elsewhere [1, 4,5].…”

“…The percentage of nonterminal addition was calculated [4] for fully protonated n-propyl-n-propyl, n-propyl-isopropyl, and isopropyl-isopropyl pairs, respectively, using the k d / k , data of Terry and Futrell [S]. In calculating the percentage of nonterminal addition to the various substituted propylenes, it has been assumed that these same k d / k , ratios apply.…”

“…The experimental techniques used for this study are described in detail elsewhere [1, 4,5]. Briefly, mixtures of 0.3-10 torr olefin in 100-700 torr Hz(D2), saturated with mercury vapor, are irradiated at 25 f 2°C with a low-pressure mercury arc.…”

“…Briefly, mixtures of 0.3-10 torr olefin in 100-700 torr Hz(D2), saturated with mercury vapor, are irradiated at 25 f 2°C with a low-pressure mercury arc. The H(D) atoms generated by mercuryphotosensitized decomposition of H2(D2) either add to the propylene double bond to form n-propyl or isopropyl radicals [4] or abstract from the /?-position to form ally1 radicals [ 11. Gas-chromatographic analysis using three 50-ft SCOT squalane columns at 0°C and one 50-ft SCOT didecyl phthalate column at room temperature in series was used for quantitative analysis of the four observable c 6 products, 4-methylpentene-1, 2,3-dimethylbutane, 2-methylpentane, and n-hexane [ 1 1.…”