Over
the last 100–120 years, due to the ever-increasing
importance of fluorine-containing compounds in modern technology and
daily life, the explosive development of the fluorochemical industry
led to an enormous increase of emission of fluoride ions into the
biosphere. This made it more and more important to understand the
biological activities, metabolism, degradation, and possible environmental
hazards of such substances. This comprehensive and critical review
focuses on the effects of fluoride ions and organofluorine compounds
(mainly pharmaceuticals and agrochemicals) on human health and the
environment. To give a better overview, various connected topics are
also discussed: reasons and trends of the advance of fluorine-containing
pharmaceuticals and agrochemicals, metabolism of fluorinated drugs,
withdrawn fluorinated drugs, natural sources of organic and inorganic
fluorine compounds in the environment (including the biosphere), sources
of fluoride intake, and finally biomarkers of fluoride exposure.
The preparation of N-methylpyrazoles is usually accomplished through reaction of a suitable 1,3-diketone with methylhydrazine in ethanol as the solvent. This strategy, however, leads to the formation of regioisomeric mixtures of N-methylpyrazoles, which sometimes are difficult to separate. We have determined that the use of fluorinated alcohols such as 2,2,2-trifluoroethanol (TFE) and 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) as solvents dramatically increases the regioselectivity in the pyrazole formation, and we have used this modification in a straightforward synthesis of fluorinated analogs of Tebufenpyrad with acaricide activity.
In previous studies, our group has shown that the use of fluorinated alcohols such as trifluoroethanol (TFE) and hexafluoroisopropanol (HFIP) as solvents dramatically increases the regioselectivity in the pyrazole formation from 1,3-diketone with methylhydrazine. We have now applied this synthetic method to the preparation of new fluorinated pyrazoles, which have then been used as synthetic intermediates in the preparation of fluorinated analogs of Tebufenpyrad, a commercial acaricide. These compounds display a strong acaricidal activity that is either comparable to or better than that of the commercial compound.
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