l EFFECT OF HYDROCARBON STRUCTURE ON REACTION PROCESSES LEADING TO SPONTANEOUS IGNITION

Previous work show- that heptane and isooctane not only cliffered greatly in respect to their susceptibilities to vapor-phase oxidation but that the nature of the oxidation products was also clifferent. These facts were interpreted on the basis of the temperature reqtired for OXL dative attack and on the thermal stability of the alkyl and pero ~ rtii-. cals obtained. This work has been extended to other aliphatic hydro-carbons in the present investigateion. d Experiments with 2,2,~-trimethy~exane, which cliffers from isooctane in having one more methylene group, show that this compound occupies an intermediary positim between isooctane and n-heptane in susceptibility to oxidation. The addition of a methylene group reduces the resistivity of a hydrocarbon to oxidation. ‘The2,2-dimethylbutane, which contafis two secondary C-H bonds, is more easily oxidized than its isomer, 2,S-dtiethylbutsae, which contains two tertiary C-H bonds. This appsrent anomaly may be due to the fact that tertiary C-H bonds in 2,3-dimethylbutme are sterically shielded from oxygen attack by the adjacent methyl groups. ~ the temperature range from 35U0 to 450 ° C 3-heptene gave oxida-tion products similar to those from n-heptane but showed greater resist-ance to oxidative attack. At temperatures of ~ “ to 5500 C!, isobutene appeared slightly more susceptible to oxidation than isobutane. Possible emanations for these observations are suggested. When a reaction ttie with l/&inch inside diameter was used, iso-octane gave oxidaticm prducts similar to those previously reported with the l/16-inch tube. However, for a given contact time the etient of reaction and the danger of explosion were much greater in the larger diameter tube. These results i,~ustrate the importance of a high surface-to-volmne ratio in controlling vapor-phase oxidation processes