13C-NMR spectroscopy was applied to the evaluation
of soil-bound residues of the fungicide cyprodinil (4-cyclopropyl-
6-methyl-2-phenylaminopyrimidine). A mixture of the
13C-
and 14C-labeled fungicide was used to obtain
structural
information as well as information on the quantitative
distribution in the various fractions. Bound residues
were
accumulated by a 6-month incubation of the labeled
compound with a clay loamy soil. Depending on the
concentration of [13C]cyprodinil (500, 250, 80, and
3 mg/kg),
binding ranged from 18% to 54% of the initial
radioactivity.
After methanol extraction of soil (10 g dry weight) treated
with
500 mg/kg (5.0 mg) of the fungicide, the amount of unextracted bound material was equivalent to 0.9 mg of
13C-labeled cyprodinil. Upon fractionation, 0.21 mg of
the
bound fungicide was found in the dialyzed humic acid,
0.13 mg in fulvic acid (after extraction with
CH2Cl2), and 0.24
mg in humin. The methylene chloride extract from
fulvic
acid mainly contained unchanged cyprodinil (0.21 mg) that
was apparently sequestered in soil by physical forces.
The humic acid fraction was dissolved in a 1% solution
of
NaOD and examined by 13C-NMR. The NMR
spectrum
of the material from the control sample exhibited all the
characteristic features of a typical humic acid. When
the
control humic acid was spiked with cyprodinil labeled
uniformly with 13C at the phenyl ring, four additional
signals
at 121.9, 124.4, 131.8, and 143.4 ppm could be
distinguished
in the NMR spectrum. However, when humic acid
originated from the soil that was incubated with the
phenyl-labeled fungicide, only two strong NMR signals, at 122.5
and 131.8 ppm, and two less significant signals around 142
and 162 ppm were observed. The difference in the
signal
pattern indicated cleavage of the cyprodinil molecule
between
the aromatic rings and independent binding of the phenyl
and pyrimidyl moieties to humic acid.
Nach der Umsetzung von p-Hydroxyphenylzimtsaure 7 mit HNO, wurden die Verbindungen 10 bis 15 isoliert und spektroskopisch charakterisiert. Das in der Literatur vermeintlich als 1,2,3-Oxadiazol-3-oxid 5 beschriebene Produkt ist nach der Rontgenstrukturanalyse das Furoxan 10.Es kristallisiert in der Raumgruppe E , / c [a = 6.894, b = 9.000, c = 12.675 A und B = 102.59"' (2 = 4); R = 0.066 fur 1272 symmetrieunabhangige Reflexe mit I 5 2 a (I)]. Bei der um einen Sauerstoff armeren Verbindung 11 handelt es sich urn das entsprechende Furazan. Der alkalische Abbau der beiden Hauptprodukte 10 und 12 fuhrt zu 13 und 25 -27 bzw. zu 28.
Structure Determinations of Oxadiazole Ring SystemsThe compounds 10 -15 generated in the reaction ofp-hydroxyphenylcinnamic acid 7 with HNO,, were isolated and spectroscopically characterized, 10 is supposed in the literature to be a 1,2,3-oxadiazole %oxide 5; it actually has the constitution of a furoxan, and crystallizes in the space group E , / c [a = 6.894, b = 9.000, c = 12.675 A andB = 102.59" (2 = 4); R = 0.066 for 1272 symmetrically independent reflections with I 2 2 a (I)]. The compound with one oxygen less is the corresponding furazan 11. Alkaline degradation of the main products 10 and 12 leads to 13 and 25 -27 and to 28, respectively.
Einleitung
Abstract A final decision between the 2-and 3-oxide structure of the thermally or photo-chemically accessible monoxides of 1,2,3-thiadiazoles is given with the aid of an X-ray analysis of 4-phenyl-1,2,3-thiadiazole-3-oxide. The compound crystallizes in the ortho-rhombic space group Pbca, Z = 8, with a = 7.598(6), b= 18.865(5) and c= 11.225(6) Å. The structure was solved by the heavy atom method and refined to R = 0.042 for 1643 independent reflections. The heterocyclic ring is planar within experimental error and the bond distances S-C and S-N are rather short. In the crystal the molecules are linked by an unusual short contact distance between sulphur and oxygen (2.75 Å).
Protonation of the bases 6, 7 and 8 with trifluoroacetic acid was investigated on the basis of 1–3C‐nmr measurements. Two models for the generated ions 1–3 are discussed. A decision is possible in favour of carbenium ions, which are stabilized by adjacent heteroatoms.
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