Supercritical Carbon Dioxide. 5. Carboxyinversion Reactions of Diacyl Peroxides. Alkyl Group Rearrangement and CO2 Exchange

Article abstract of DOI:10.1021/jo00385a020

The decomposition of bis(isobutyryl) peroxide in supercritical Co2, CCl4, and CHCl3 gives both radical and ion pair-derived products in all three media.The rate constant in supercritical CO2 at 40 deg C, ?^* -0.05, and density 0.93 is 3.6 * 10E-5 s^-1.The rate constants in CCl4 and in CHCl3 at the same temperature are 7.72 * 10E-5 and 42.5 * 10E-5, respectively.The rate constant in CO2 fits a relationship with ?^* observed for aromatic solvents.The products in CO2 include isopropyl isobutyryl carbonate (the carboxyinversion compound), 17percent yield, isopropyl isobutyrate, 5percent or less, and isobutyric acid, 17percent yield.There is no exchange of the inverted CO2 moiety of isopropyl isobutyryl carbonate for CO2 from the medium.The decomposition of cyclobutanecarbonyl m-chlorobenzoyl peroxide in CO2 is compared with the results reported by Taylor et al. (Taylor, K.G.; Govindan, C.K.; Kaelin, M.S.J.Am.Chem.Soc. 1979, 101, 2091) in conventional solvents.The rate constant for the decomposition of this peroxide in CO2 at 55 deg C at a density of 0.81 is 2.2 * 10E-5 s^-1, in CCl4 it is 2.93 * 10E-5 s^-1, and in CHCl3 it is 27.2 * 10E-5 s^-1.The alkyl groups in the alkyl m-chlorobenzoate esters and alkyl m-chlorobenzoyl carbonates (carboxyinversion products) from this peroxide are rearranged in part to cyclopropylmethyl and 3-butenyl groups.The 13C of the carbonate carbonyl in the cyclopropylmethyl m-chlorobenzyl carbonate is about 12percent exchanged, but that from the carboxyinversion product with the unrearranged alkyl group is not exchanged.The effects of medium changes on the product are as follows: the change from CO2 to CCl4 increased the total yield of carboxyinversion compounds, but did not change the relative yields of the isomers appreciably.The further change in medium to CHCl3 drastically lowered the total yield of carboxyinversion compounds, again without changing the ratios of the isomers very much, and at the same time caused a large increase in the total yield of the esters.Both the ester yields and the rate appear to depend more on the hydrogen-bond-donor properties of the medium than on ?^*.