Singlet-oxygen generation in the catalytic reaction of dioxiranes with nucleophilic anions.
Nucleophilic anions such as Cl(-), I(-), Br(-), t-BuO(-), O(2)(-) and OH(-) efficiently catalyze the decomposition of dimethyldioxirane (DMD) and methyl(trifluoromethyl)dioxirane (TFD). Singlet oxygen ((1)O(2)) is formed in these catalytic reactions, as demonstrated by the characteristic infrared chemiluminescence (IR-CL) at 1268 nm. The yield of (1)O(2) generation, measured by the IR-CL method, lies in the range between 2 and 98%, which depends on the particular anion employed. For the bromide ion, the catalytic decomposition of the dioxirane is in competition with the oxidation of Br(-) to elemental bromine.
Kinetics and mechanism of the highly efficient generation of singlet oxygen in dimethyldioxirane decomposition induced by the chloride ion
The decomposition of dimethyldioxirane induced by the chloride anion has been investigated by methods of infrared chemiluminescence and quantum chemistry. The reaction leads to efficient generation of singlet excited molecular oxygen 1O2 (the excitation yield in acetone is 61%). A mechanism of peroxide decomposition is proposed in which the key reactions are the addition of the chloride ion to an oxygen atom of dioxirane, resulting in dioxirane ring opening and the formation of the 2-chlorooxy-2-hydroxy propane alcoholate (k1), and the interaction of the latter with another dimethyldioxirane molecule. This interaction results either in the formation of an adduct, which further decomposes to evolve 1O2, and catalyst regeneration (k2) or in the formation of the 2-chloroxyisopropyl radical, which leads to the irreversible consumption of the chloride ion catalyst (k3). The decay kinetics of the infrared chemiluminescence of 1O2 has been studied in a wide range of reactant concentrations. The temperature dependence of the rate constant of the reaction of dimethyldioxirane with the chloride ion has been determined by a kinetic analysis of the mechanism proposed: log(2k1) = (11.1 ± 0.7) − (46 ± 4)/Θ, where Θ = 2.3RT kJ/mol. Estimation of the ratio of the rates of the reaction of the 2-chlorooxy-2-hydroxy propane alcoholate with dimethyldioxirane via two pathways (k3/k2) has demonstrated that the fraction of the process involving electron transfer does not exceed 1.5% under the experimental conditions examined. Nevertheless, the latter reaction, which withdraws the chloride ion from the catalytic cycle of dimethyldioxirane decomposition yielding singlet oxygen, has a marked effect on the overall kinetics of the process.
The development of a liquid antihistaminic preparation with sustained release properties.
The relative capacity of several cation exchange resins to adsorb methapyrilene has been determined by an in vitro method. It was demonstrated that methapyrilene adsorbed on sulfonic acid cation exchange resin possessed pharmacological activity approximating that of a solution of methapyrilene hydrochloride as measured by the protection against histamine-induced asthma in the intact guinea pig. It is suggested that the use of ion exchange resins as carriers of drugs in liquid dosage forms may be useful in sustained release preparations.