Effect of Alcohols on the Stability of Iprodione in Solution
J. Agric. Food Chem., Vol. 56, No. 2, 2008 505
Scheme 1. Mechanism of degradation of iprodione
+
°
C and an ESI-MS ion at m/z 330.05 [M] . Anal. Calcd for
(9) or by its chemical transformation in a sterile mineral medium
(10). The cyclization of 3-(isopropylcarbamoyl)-5-(3,5-dichlo-
rophenyl) hydantoic acid (2), the metabolism of iprodione in
rats (11), the metabolism of iprodione in plants (8), or the
reaction of 3-isopropylimidazolidine-2,4-dione with 3,5-dichlo-
rophenylisocyanate (9) also produces 6.
C13H13Cl2N3O3: C, 47.29; H, 3.97; Cl, 21.48; N, 12.73. Found:
C, 47.40; H, 3.97; Cl, 21.48; N, 12.70.
Structures of the Product from Methanol. Insightful
information regarding the structure of the product was derived
from mass spectral and NMR data. Elemental analyses and ESI-
+
MS-generated [M] ion peak at m/z 330.05 established that the
Additional Degradation Study. In addition to the methanol-
product is an isomer of iprodione.
related study, the solutions of iprodione in benzyl alcohol,
1
-butanol, 2-butanol, tert-butanol, ethanol, 1-hexanol, 2-methyl-
Gas Chromatography–Mass Spectrometry. The GC-MS
analysis was performed under electron impact (EI) mode. The
mass spectrum (Figure 2) produced ions at m/z 99, 127, 142,
and 188 that were consistent with the theoretical values for the
partial structures 2, 3, 4, and 5 (Figure 3), respectively. The
1-propanol, 1-propanol, 2-propanol, and 1-octanol were analyzed
to determine its stability. The results of these analyses are
summarized in Table 1. This table’s data clearly indicate that,
except for benzyl alcohol, all primary alcohols degrade iprodione
quite rapidly. A much slower degradation was observed with
benzyl alcohol. The presence of 1% water in methanol or ethanol
did not slow down the degradation of iprodione. However,
somewhat slower rates of reaction are observed if 1% water is
present in 1-propanol, 1-butanol, 1-hexanol, 2-methyl-1-pro-
panol, or 1-octanol. By comparison with the primary alcohols,
the degradation by a secondary alcohol was found to be
extremely slow, and no degradation occurred if 1% water is
present in 2-propanol. tert-Butanol, the only tertiary alcohol
available for the present study, did not show any adverse effect
on the stability of iprodione. The lack of reaction of tert-butanol
or very slow degradation by secondary alcohols is most likely
due to the crowding or steric effects created by substituents on
the hydroxyl group bearing a carbon atom.
Identification of Products. The identification of the products
arising from iprodione’s reaction with various alcohols was
achieved by the comparison of their GC-ECD chromatograms
and mass spectral information with the respective data of the
product from methanol. Also, the melting points of the isolated
products, as well as those of products’ mixtures with the product
from methanol, were considered for determining a product’s
identity. These comparisons did not show any discrepancy
between the compared data, thereby proving that 6 is the
common structure for all products, including the one from
methanol.
+
appearance of these ions and another at m/z 329, due to [M-1] ,
lends conclusive support for the product to have structure 6
(
Figure 3).
Nuclear Magnetic Resonance Spectrometry. Tables 2 and
1
13
3
, respectively, show the H NMR and C NMR data for the
methanol-assisted decomposition product of iprodione. The
assignment of chemical shift values for various hydrogen and
1
carbon atoms was made on the basis of H NMR spectrum,
1
3
C NMR spectrum, heteronuclear single quantum correlation
(
(
HSQC) experiment, heteronuclear multiple bond correlation
HMBC) experiment, and software-generated calculated values.
Similar to the GC-MS data, the NMR data were consistent with
the assignment of structure 6 for the product. As expected, the
proton (Figure 4; Table 2) and carbon (Figure 5; Table 3)
spectra showed signals for 13 hydrogen and 13 carbon atoms.
The two methyl groups had identical proton and carbon
resonances, indicating the magnetic equivalence of these two
groups. Some other data (Table 2, Table 3) indicate that an
identical NMR-related relationship also exists either between
2
′ and 6′ or between 3′ and 5′ positions. The molecular model
(
Figure 6) of product 6 also predicts these three equivalences.
1
The H NMR signal due to the -NH- group of the product
appeared as a singlet at δ 10.0, whereas the signal of iprodione,
recorded under identical conditions, gives a doublet at δ 7.6.
This downfield shift of the product’s -NH- signal and its lack
of coupling are in conformity with structure 6 for the product.
Reaction Mechanism. The formation of a common product
(6) from all of the reacting alcohols, the faster reaction rate
of primary alcohols, except benzyl alcohol, the slower
reaction rate of secondary alcohols, and the complete lack
of reaction of tert-butanol point to a common reaction
mechanism. The most likely mechanism of the transformation
Thus, it is evident from the above that N-(3,5-dichlorophenyl)-
3-(1-methylethyl)-2,4-dioxo-1-imidazolidine carboxamide (6) is
the product from the reaction of iprodione with methanol. The
same compound (6) was also reported to have been obtained
from iprodione by its rearrangement in an ethanolic solution