Beflubuitamid has two stereoisomers.[3] The substance as used in agriculture is typically a racemic mixture, a 1:1-mixture of the (S)- and (R)-form:[4][5]
Enantiomers of beflubutamid
(S)-Beflubutamid
(R)-Beflubutamid
Method of action and effects
Beflybutamid is placed in the HRAC classification group F1 based on its mode of action. Herbicides in HRAC group F1 influence the biosynthesis of carotenoids.[6] The molecular characteristic relevant to this group is the partial tetrafluorocarbon-phenyl structure.[7]
Beflubutamid inhibits the enzyme phytoene desaturase (PDS) in carotenoid biosynthesis. PDS catalyzes the dehydrogenation of phytoene in the synthesis reaction, which is necessary for the final carotenoid synthesis to take place in further reaction steps.[8]
Plants unable to complete carotenoid synthesis will die, as reactive oxygen compounds will build up in the absence of carotenoids. These reactive oxygen compounds cause the oxidation of cholorphylls and a decrease in green colorants. As such, carotenoid synthesis-inhibiting herbicides like beflubutamid are known as "bleaching herbicides".[7]
Legality
Beflubutamid has been approved in the European Union since 1 December 2007. Plant protection products containing beflubutamid are sold in Austria and Germany, but not Switzerland.[9]
Decomposition in air and soil
Beflubutamid has a low vapor pressure of 1.1·10-5 Pa at 25 °C. As such, it does not evaporate under standard conditions. The compound will decompose by photooxidation, having a half-life of 3.5 hours, and is unlikely to disperse greatly on its own in air. In soil, beflubutamid decomposes to amide and azide forms, as well as other bound residues and CO2. These degradation products are classified as harmless.[10]
Decomposition in water
Under water at standard conditions (25°C, pH=5–9), beflubutamid degrades very slowly if at all, and does not decompose via photooxidation at greater depths where light does not travel. This may have the effect of killing algae, which are attacked by beflubutamid. This destruction can have effects on organisms that feed on the algae. High levels of beflubutamid can accumulate at depths of over 200m, but at this depth algae cannot grow.[10]
↑ Paula Y. Bruice: Organische Chemie: Studieren kompakt. Pearson Studium, München 2011, ISBN 978-3-86894-102-9, S. 205.
↑ Ignaz J. Buerge, Markus D. Müller, Thomas Poiger: The Chiral Herbicide Beflubutamid (II): Enantioselective Degradation and Enantiomerization in Soil, and Formation/Degradation of Chiral Metabolites. In: Environmental Science Technology. American Chemical Society 2013, DOI:10.1021/es301877n, S. 6812–6818.
↑ Beflubutamid in the Pesticide Properties DataBase (PPDB)
1 2 Thomas Seitz, Michael G. Hoffmann, Hansjörg Krähmer: Herbizide für die Landwirtschaft: Chemische Unkrautbekämpfung. In: Chemie in unserer Zeit, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 2013, DOI:10.1002/ciuz.200300279, S. 112–126.
↑ Hans-Walter Heldt, Birgit Piechulla: Pflanzenbiochemie. Springer-Verlag Berlin Heidelberg, 2015, DOI:10.1007/978-3-662-44398-9, S. 407–411.
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