Collect. Czech. Chem. Commun. 1986, 51, 368-374

Chemical actinometry in the UV range based on the photohydrolysis of 3,4-dimethoxynitrobenzene

Libuše Pavlíčková, Petr Kuzmič and Milan Souček

Institute of Organic Chemistry and Biochemistry, Czechoslovak Academy of Sciences, 166 10 Prague


Photochemical hydrolysis of 3,4-dimethoxynitrobenzene in aqueous potassium hydroxide leading to the formation of 2-methoxy-5-nitrophenolate anion is routinely used for the determination of UV light intensity. The quantum efficiency of the actinometric system is independent on the excitation wavelength ( 254, 313, 365 nm) and reaches the value of 0.116 ± 0.002 in 0.5 M-KOH. The light intensity determination is based purely on UV/VIS spectral absorption data. A photokinetic model is presented for the reaction which is generally applicable for any photochemical system with the involvement of inner filtration due to products and partial light absorption. The evaluation of primary spectral data is performed by numerical integration of the photokinetic equation.