Studies On The Photochemical Degradation Of Scopoletin

In order to use scopoletin as botanical acaricide effectively, assess its environmental safety accurately and provide information about its photodegradation for pesticide registration, this paper studied the photochemical degradation of scopoletin in different solvents and water, and identified the photolysis products of scopoletin.1. Photochemical degradation of scopoletin in different solventsThe photolysis of scopoletin in water, acetone, methanol and ethyl acetate has been studied. The result indicated that the photodegradation of scopoletin in four solvents under 500 W xenon lamp followed first-order kinetics. When the mass concentration of scopoletin was 10 mg/L, the photolysis rates showed as following sequence:water> acetone> ethyl acetate> methanol, and the half-lives were 5.41 h,9.89 h,35.70 h and 45.30 h, respectively.2. Photochemical degradation of scopoletin in waterThe photolytic characteristics of scopoletin in different light, initial concentration, temperatures, pH values, water, surfactants, NO3-/NO2- and H2O2 were investigated by HPLC. The results showed as following:(1) The photolysis of scopoletin in pure water, under the six selected light sources, followed first-order kinetics, and the degradation rates changed in the order of 500 W mercury lamp>sunlight>18 W UV lamp>500 W xenon lamp>300 W xenon lamp>100 W xenon lamp. (2) The photolysis half-lives of scopoletin were 3.22 h,5.41 h,9.90 h and 19.58 h under the initial concentration of 5 mg/L, 10 mg/L,20 mg/L and 40 mg/L, respectively; the trend of photolysis rate of scopoletin under the same initial concentration leveled off with time passing by. (3) In the range from 5 ℃ to 65 ℃, the degradation rate of scopoletin increased from 5 ℃ to 15 ℃, reached a maximum at 15℃ at which temperature the half-life was 5.12 h, and then decreased from 15 ℃ to 65 ℃. (4) The photolysis rate of scopoletin increased with pH values raising, and showed a trend of pH9.0> pH8.0> pH7.0> pH6.0> pH5.0. It indicated that scopoletin is relatively stable under acidic condition, while alkaline condition facilitates degradation. (5) The photolysis rates of scopoletin in five types of water showed an order of pure water> river water>stream water> lake water> tap water> ocean water. The photolysis rate of scopoletin in pure water was fastest, and the photolysis half-life was 5.41 h. (6) By adding different surfactants (Nongru 600#, Nongru 500#, Tween-80, SDS and CTAB), the results indicated that the five surfactants had shown inhibiting effect in a certain extent. The inhibiting effect of Nongru 600#, Nongru 500# and SDS increased with the concentration of surfactants raising while the trend of Tween-80 was opposite, and CTAB increased with the concentration increasing, and then decreased. (7) NO3- and NO2- could restrain the photolysis rate of scopoletin in aqueous solution; however, NO2- had a stronger effect than NO3-. The photolysis half-life of scopoletin increased with the increasing concentrations of NO3- and NO2-. When fortified level was 50 mg/L, the inhibiting ratios of NO3- and NO2- were 18.10% and 28.16%. (8) The photolysis rate of scopoletin by adding H2O2 increased with the concentration raising. Its promoting ratio in the experiment was up to 9.13%.3. Preliminary identification of three photolysis products of scopoletinAfter 10 d illumination under 500W xenon lamp in pure water, three kinds of photolysis products of scopoletin were identified, which were 6,7-Dihydroxy-chromen-2-one,3,4,6-Trihydroxy-2-methyl-benzaldehyde and 2,4,5-Trihydroxy-benzaldehyde. The molecular weights of the products were 178,168 and 154, and the formula were C9H6O4, C8H8O4 and C7H6O4, respectively. According to the proposed photodegradation pathways, scopoletin might have three types of reactions, which were molecular rearrangement, photo-hydrolysis and photo-oxidation.