A New Chemical Actinometer for UVB Radiation – p-Hydroxyphenacyl Phenylacetate (pHPPA)

            Vít Ladányi*, Jamaludin Al Anshori, Pavel Dvořák, Joggi Wirz, Dominik Heger

  RECETOX and Department of Chemistry, Faculty of Science, Masaryk University, Kamenice 5, 625 00
                                       Brno, Czech Republic

                                       *ladanyi@mail.muni.cz



Chemical actinometry is used to access the number of incident photons, which is often an important
characteristics. There is a plenty of chemical actinometers summarized in IUPAC recommendation [1],
but we found only a few of them correctly characterized, well performing and reliable. We want to
introduce a new standard chemical actinometer for UVB radiation, which would be not sensitive to
daylight (like ferrioxalate, uranyl oxalate, azobenzene and others [1]) and would be easily
evaluated from UV-vis spectrophotometric measurements. The p-hydroxyphenacyl phenylacetate
actinometer is based on the photo-Favorskii rearrangement to p-hydroxyphenylacetic acid and
phenylacetic acid. The photoproducts absorb only below 290 nm (p-hydroxyphenylacetic acid) and 280
nm (phenylacetic acid), what make pHPPA potentially usable without correction on photoproducts at
low conversions. The quantum yields were found to be independent of the temperature (at 15 – 35 °C
range) and irradiation wavelength. As the photo-Favorskii reaction is pH dependent we recommend
using pHPPA at pH 2 (0.01 M HCl) where the QY = 0.45. The great advantage of this newly proposed
actinometer in comparison to previously recommended is the simplicity and precision of
spectrophotometric detection of reaction progress without the need of further chemical workup or
other analytical tools. We also developed the script for the evaluation of photon fluxes from
measured UV-vis spectra.


 [1] H. J. Kuhn, Chemical Actinometry (IUPAC Technical Report), Pure and Applied Chemistry 2004,
76, No. 12, p. 2105 - 2146