Some furfural derivatives as nitrification inhibitors

Article abstract of DOI:10.1021/jf001318d

Three series of furfural derivatives, namely N-O-furfural oxime ethers, furfural Schiff bases (furfurylidene anilines), and furfural chalcones, have been synthesized and evaluated for nitrification inhibition activity in laboratory incubation studies in typic Ustocrept soil. Furfural oxime ethers and furfural Schiff bases showed potential activity, but furfural chalcones were only mildly active. N-O-ethyl furfural oxime among the oxime ethers, and furfurylidine-4-chloroaniline among the furfural Schiff bases, performed the best. These two compounds showed more than 50% nitrification inhibition on the 45th day at 5% dose as compared to 73% inhibition by nitrapyrin. Activity of furfural oxime ethers decreased with an increase in carbon atoms in the N-O-alkyl side chain. Introduction of a chlorine atom in the phenyl ring of furfurylidene anilines increased the persistence of their activity. N-O-Ethyl furfural oxime and furfurylidine-4-chloroaniline coated urea performed at par with their application in solution form. Ethyl and N-O-isopropyl oxime, as well as chloro- and nitro-substituted Schiff bases, did not reveal any phytotoxicity (adverse effect on germination) on chickpea seeds (Cicer arietinum) even at the highest dose (40 ppm, soil basis).

Full text of DOI:10.1021/jf001318d

4726
J. Agric. Food Chem. 2001, 49, 4726−4731
Som e F u r fu r a l Der iva tives a s Nitr ifica tion In h ibitor s
Aniruddha Datta, Suresh Walia, and Balraj S. Parmar*
Division of Agricultural Chemicals, Indian Agricultural Research Institute, New Delhi, 110012, India
Three series of furfural derivatives, namely N-O-furfural oxime ethers, furfural Schiff bases
(furfurylidene anilines), and furfural chalcones, have been synthesized and evaluated for nitrification
inhibition activity in laboratory incubation studies in typic Ustocrept soil. Furfural oxime ethers
and furfural Schiff bases showed potential activity, but furfural chalcones were only mildly active.
N-O-ethyl furfural oxime among the oxime ethers, and furfurylidine-4-chloroaniline among the
furfural Schiff bases, performed the best. These two compounds showed more than 50% nitrification
inhibition on the 45th day at 5% dose as compared to 73% inhibition by nitrapyrin. Activity of furfural
oxime ethers decreased with an increase in carbon atoms in the N-O-alkyl side chain. Introduction
of a chlorine atom in the phenyl ring of furfurylidene anilines increased the persistence of their
activity. N-O-Ethyl furfural oxime and furfurylidine-4-chloroaniline coated urea performed at par
with their application in solution form. Ethyl and N-O-isopropyl oxime, as well as chloro- and nitro-
substituted Schiff bases, did not reveal any phytotoxicity (adverse effect on germination) on chickpea
seeds (Cicer arietinum) even at the highest dose (40 ppm, soil basis).
Keyw or d s: Nitrification inhibitors; furfural oxime ethers; furfural Schiff bases; furfural chalcones;
nitrapyrin
INTRODUCTION
Sahrawat et al (8) reported that simple furan deriva-
tives such as furfural and furfural alcohol possessed
good nitrification inhibitory properties. Among the
various furan derivatives, 5-nitro-2-furfural oxime, fur-
fural oxime, and furfural semicarbazone were the most
effective (9). The nitro furan derivatives, however, led
to an accumulation of nitrite, causing toxicity to Nitro-
bacter sp.
In this study twelve furfural derivatives have been
synthesized and tested in the laboratory for their
nitrification inhibitory property (Figure 1). Both the
coating and solution applications of the inhibitors have
been assessed. The promising compounds also have been
evaluated for any adverse effect on germination of
chickpea seeds.
Nitrogen is the major nutrient limiting agricultural
production in most soils. N-fertilizers have made a major
contribution toward improving agricultural productivity
the world over. The commonly used nitrogenous fertil-
izers, especially urea, suffer from the drawbacks of a
low nitrogen use efficiency (NUE) and contributing
toward environmental pollution. The NUE hardly ex-
ceeds 50% under most situations, and it drops below
30% in the case of lowland rice culture (1, 2) The
nitrification mediated by obligate chemolithotrophic
bacteria (Family Nitrobacteraceae) seems to be the
major reason for the low NUE and high nitrogen losses.
The nitrate anion is more susceptible to leaching,
thereby causing groundwater pollution (3). As a result
of denitrification, nitrate is transformed into nitrous and
nitric oxides, which have been implicated in global
warming and depletion of the ozone layer. It has been
established that the fertilizer nitrogen contributes 1.5
Teragram (Tg ) 1012 g) N2O-N yr-1 (4) and agriculture’s
contribution to global N2O loading from the year 1986
to 2026 is likely to increase by 90% with increased
N-fertilizer consumption (5, 6). The use of nitrification
inhibitors has been suggested to minimize these ill
effects. Nitrapyrin, dicyandiamide, etridiazole, etc., are
the commonly studied commercial nitrification inhibi-
tors. The high cost of development and subsequent
registration of effective nitrification inhibitors, the
economics of their use, and the variable results obtained
with their use in field conditions are the serious
bottlenecks in their extensive use (7), underlining the
need to develop simple, economical, efficient, and safe
nitrification inhibitors.
MATERIALS AND METHODS
Ch em ica ls a n d Rea gen ts. These were procured from s.
d. fiNE CHEM Ltd., Mumbai, India and used without further
purification except furfural, which was freshly distilled each
time before use. Nitrapyrin (90% purity) was obtained from
Dow Elanco (Indianapolis, IN). Commercial-grade organic
solvents were distilled before use.
Ch r om a togr a p h y a n d Sp ectr oscop y. Thin-layer chro-
matography (TLC) was performed on silica gel G plates,
preactivated at 100 °C for 2 h. The 1H NMR spectra were
recorded on a Varian EM-360, 60-MHz instrument. Samples
were dissolved in CDCl3, and tetramethylsilane (TMS) was
used as an internal standard. Chemical shifts are reported in
δ values relative to TMS, and J values are expressed in Hertz.
For colorimetric estimation, a Varian series 634 UV-Vis
double-beam spectrophotometer was used.
Syn th esis of F u r fu r a l Oxim es. A mixture of freshly
distilled furfural (0.2 mol, 19.2 g), hydroxylamine hydrochlo-
ride (0.1 mol, 13.9 g), and pyridine (20 mL) was refluxed in
ethanol (100 mL) for 1 h on a water bath. Completion of the
reaction was checked by TLC (hexane/acetone, 3:1). At the end
of the reaction, ethanol was distilled off, and ice-cooled water
(100 mL) was added. The precipitated furfural oxime (I) was
* To whom correspondence should be addressed. Phone: 91-
11-578-3272. Fax. 91-11-576-6420. E-mail: bsparmar@
yahoo.com.
10.1021/jf001318d CCC: $20.00 © 2001 American Chemical Society
Published on Web 09/14/2001

Furfural Derivatives as Nitrification Inhibitors
J. Agric. Food Chem., Vol. 49, No. 10, 2001 4727
1H, Hb, ortho and meta coupled, J ) 4 Hz), 6.9 (d, 1H, Ha,
ortho coupled, 4 Hz), 7.8 (d, 1H, Hc), 7.9 (s, 1H, -CHdN-).
Yield, 3.4 g (76%).
Syn th esis of F u r fu r a l Ch a lcon es. Three furfural chal-
cones, namely 3-(furan-1-yl)-1-phenyl-prop-2-en-1-one (VII),
3-(furan-1-yl)-1-4-hydroxyphenyl-prop-2-en-1-one (VIII), and
4-(furan-1-yl)-but-3-en-2-one (furfurylideneacetone, IX), were
synthesized following the Claisen-Schmidt reaction (10). A
methanolic solution of freshly distilled furfural was reacted
with acetophenone, 4-hydroxyacetophenone ,and acetone in the
presence of methanolic NaOH solution to obtain the desired
compounds.
3-(Furan-1-yl)-1-phenyl-prop-2-en-1-one (VII. mp, 45-46 °C.
1
Rf: 0.65 (hexane/acetone, 75:25); H NMR (CDCl3): δ 6.6 (dd,
1H, Hb, J ) 4 Hz), 6.9 (d, 1H, -CHdCH-CO, 4 Hz), 7.7 (m,
6H, 3 Ar-H, Ha, Hc, -CHdCH-CO), 8.3 (m, 2H, Ar-H).
Yield, 15.8 g (80%).
3-(Furan-1-yl)-1-(4-hydroxy-phenyl)-prop-2-en-1-one (VIII),
1
mp, 160 °. Rf: 0.32 (hexane/acetone, 75:25). H NMR (CDCl3/
Acetone D6): δ 6.6 (dd, 1H, Hb, J ) 4 Hz), 6.8 (d, 1H, -CHd
CH-CO, 4 Hz), 7.1 (m, 2H, Ar-H), 7.5 (s, 1H, Ha), 7.7 (m,
2H, CHdCH-CO, Hc), 8.1(m, 2H, Ar-H), 9.0 (s, 1H, -OH,
broad, D2O exchangeable). Yield, 16.6 g (77%).
F igu r e 1. Generic structures of furfural derivatives.
4-(Furan-1-yl)-but-3-en-2-one (furfurylideneacetone, IX). mp,
39 °C. Rf: 0.61 (hexane/acetone, 75:25). 1H NMR (CDCl3): δ
2.5 (s, 3H, -CO-CH3), 6.6 (dd, 1H, Hb, ortho and meta coupled,
J ) 4 Hz), 6.9 (d, 1H, CHdCHCO, J ) 4 Hz), 7.4 (s, 1H, Ha),
7.5-8.0 (m, 2H, -CHdCHCO, Hc). Yield 8.2 g (60%).
Syn th esis of F u r fu r a l-Sch iff Ba ses. Furfural (0.1 mol,
9.6 g), substituted aniline (0.1 mol), and methanol (50 mL)
were put in a beaker and heated gently on a water bath. The
solution was then cooled in an ice bath. The solid that
separated was filtered and recrystallized from methanol. Four
Schiff bases, namely furfurylideneaniline (X), furfurylidene-
4-chloroaniline (XI), furfurylidene-3,4-dichloroaniline (XII),
and furfurylidene-3-nitro aniline (XIII) were synthesized,
crystallized from methanol, and characterized spectroscopi-
cally.
filtered, dried, and recrystallized from ethanol as fluffy,
1
colorless needles; mp. 86-87 °C; H NMR (CDCl3): δ 6.6 (m,
Hb), 7.6 (m, 2H, Ha, Hc), 8.2 (s, 1H, -CH)N-), 10.0 (s, 1H,
broad, D2O exchangeable OH); yield: 19 g (86%).
Syn th esis of F u r fu r a l Oxim e Eth er s. A solution of
furfural oxime (0.03 mol) and alkyl bromide (0.04 mol) in dry
acetone (200 mL) was refluxed in the presence of dry potas-
sium carbonate (10 g) for 48 h on a water bath. Completion of
the reaction was checked by TLC (hexane/acetone, 3:1, visual-
izing reagent 2,4-diphenyl hydrazine). On completion of the
reaction two pink spots were observed for the syn and anti
isomers. The pink spots emerged fully after 15-20 min of the
spray. After completion of the reaction, the solid potassium
carbonate was filtered out, and the solvent was distilled off
under reduced pressure. Ice-cooled water (100 mL) was then
added, and the mixture was extracted with diethyl ether three
times with 50 mL each of the solvent. The organic phase was
dried over anhydrous sodium sulfate, and the solvent was
distilled off to obtain a yellowish viscous liquid. This liquid
was subjected to column chromatography over silica gel (60-
120 mesh) using hexane/acetone (80:20) mixture as the eluant
to yield yellowish viscous furfural oxime ethers. The test
samples consisted of a mixture of two isomers.
Furfurylideneaniline (X). mp, 57 °C. Rf: 0.56 (hexane/
acetone, 75:25). 1H NMR (CDCl3): δ 6.8 (dd, 1H, Hb, ortho and
meta coupled, J ) 4 Hz.), 7.2 (d, 2H, Ar-H, ortho coupled, J )
8 Hz), 7.4-7.8 (m, 4H, 3Ar-H, Ha), 7.9 (s, 1H, Hc), 8.5 (s, 1H,
-CHdN-). Yield 13.6 g (79.53%).
Furfurylidene-4-chloroaniline (XI). mp, 58 °C. Rf: 0.57
1
(hexane/acetone, 75:25). H NMR (CDCl3): δ 6.8 (dd, 1H, Hb,
ortho and meta coupled, J ) 4 Hz), 7.2-7.8 (m, 5H, 4 Ar-H,
Ha), 7.9 (s, 1H, Hc), 8.5 (s, 1H, -CHdN-). Yield 16.4 g
(79.84%).
N-O-Ethyl furfural oxime (II). Rf: 0.35, 0.78 (hexane/acetone,
Furfurylidene-3,4-dichloroaniline (XII). mp, 43 °C. Rf: 0.57
1
1
75:25). H NMR (CDCl3): δ 1.6 (t, 3H, -CH2CH3, J ) 7 Hz),
(hexane/acetone, 75:25). H NMR (CDCl3): δ 6.8 (dd, 1H, Hb,
4.1 (q, 2H, -CH2CH3), 6.8 (dd, 1H, Hb, ortho and meta coupled,
J ) 4 Hz), 7.7 (d, 1H, Ha ortho coupled, J ) 4 Hz), 7.9 (s, 1H,
-CHdN-), 8.0 (d, 1H, Hc, ortho coupled, J ) 3 Hz). Yield, 3.1
g (75%).
ortho and meta coupled, J ) 4 Hz), 7.3 (m, 1H, Ar-H, ortho
and meta coupled), 7.5 (m, 2H, 1Ar-H, Ha), 7.9 (m, 2H, 1Ar-H,
Hc), 8.5 (s, 1H, -CHdN-). Yield 18.96 g (79%).
Furfurylidene-3-nitroaniline (XIII). mp, 56 °C. Rf: 0.45
1
N-O-Isopropyl furfural oxime (III). Rf: 0.38, 0.80 (hexane/
(hexane/acetone, 75:25). H NMR (CDCl3): δ 6.8 (dd, 1H, Hb,
1
acetone, 75:25). H NMR (CDCl3): δ 1.6 (d, 6H, -CH-(CH3)2,
J ) 4 Hz, ortho and meta coupled), 7.3 (d, Ha, J ) 3 Hz, ortho
coupled), 7.8-6.5 (m, 5H, 4Ar-H, Hc), 8.6 (s, 1H, -CHdN-).
Yield 17.32 g (80.18%).
J ) 6 Hz), 4.4 (heptet, 1H, -CH-(CH3)2), 6.8 (dd, 1H, Hb, ortho
and meta coupled, J ) 4 Hz), 7.8 (d, 1H, Ha, ortho coupled, J
) 4 Hz), 7.9 (s, 1H, -CHdN), 8.0 (d, 1H, Hc, ortho coupled, J
) 3 Hz). Yield, 3.4 g (75%).
Nitr ifica tion In h ibition Stu d y. Test Soil. The institute
farm soil [sand 60.8%, clay 20.5%, silt 18.7%, organic carbon
0.5%; pH (soil/water, 1:2.5) 7.9; EC at 25 °C 0.35 dSm-1
;
N-O-Butyl furfural oxime (IV). Rf: 0.38, 0.83 (hexane/
acetone, 75:25). 1H NMR (CDCl3): δ 1.2 (m, 3H, -CH2-
(CH2)2CH3), 1.6 (m, 2H, -CH2CH2CH2CH3), 2.0 (m, 2H,
-CH2CH2CH2CH3), 4.0 (t, 2H, -OCH2(CH2)2CH3, J ) 6 Hz),
6.7 (dd, 1H, Hb, ortho and meta coupled, 1 Hz), 7.7 (d, 1H, Ha,
ortho coupled, J ) 4 Hz), 7.8 (s, 1H, -CHdN-), 7.9 (d, 1 H,
Hc ortho coupled, J ) 3 Hz). Yield, 3.8 g (76%).
available N 55.72 kg ha-1, nitrate-N 8.54 mg kg-1, nitrite-N
(traces), ammonium-N 3.20 mg kg-1] was used for in vitro
incubation studies.
Treatments. The test chemicals were evaluated for the
nitrification inhibitory effect in laboratory incubation studies
at 5, 10, 15, and 20% of applied urea-N along with the urea
alone as control. The experiments were laid following random-
ized complete block design. A 200-g portion of soil was mixed
thoroughly with the calculated amount of test chemical (2, 4,
6, 8 mg of test chemical, making respectively 5, 10, 15, and
20% of the applied 200 mg urea-N L-1 dose) followed by
addition of 40 mg of urea-N in aqueous solution to provide 200
ppm urea-N in each treatment. Nitrapyrin (N-Serve) at 5% of
applied urea-N was used as a standard. A control (200 ppm
N-O-Hexyl furfural oxime (V). Rf: 0.39, 0.84 (hexane/acetone,
75:25). 1H NMR (CDCl3): δ 1.0 (m, 3H, -CH2(CH2)4-CH3), 1.4
(m, 8H, -CH2(CH2)4CH3), 4.2 (m, 2H, -CH2(CH2)4CH3), 6.7
(dd, 1H, Hb), 7.4 (d, 1H, Ha, ortho coupled, J ) 4 Hz), 7.9-7.7
(m, 2H, Hc, -CHdN). Yield, 4.3 g (74%).
N-O-Allyl furfural oxime (VI). Rf: 0.25, 0.76 (hexane/acetone,
1
75:25). H NMR (CDCl3): δ 4.8 (d, 2H, -OCH2, J ) 4 Hz), 5.5
(m, 2H, -CH2CHdCH2), 6.3 (m, 1H, -CH2CHdCH2), 6.8 (dd,

4728 J. Agric. Food Chem., Vol. 49, No. 10, 2001
Datta et al.
Ta ble 1. Effect of F u r fu r a l Der iva tives on Nitr ifica tion
In h ibition
urea-N alone) was simultaneously run. Distilled water was
added to bring the soil moisture to one-third of the water-
holding capacity of the soil. The treated soils were incubated
in 500-mL beakers covered with muslin cloth at 28 °C and 98%
RH in a BOD incubator. The moisture content of the incubated
beakers was maintained by adding the required amount of
distilled water every alternate day.
Sampling and Estimation of Ammonium, Nitrite, and
Nitrate. Samples from the incubated soils were drawn after
15, 30, 45, and 60 days of incubation. For estimation of nitrate,
a soil sample equivalent to 20 g of dry soil was withdrawn
and extracted with 50 mL of distilled water (11), and for
estimation of nitrite and ammonium a soil sample equivalent
to 5 g of dry soil was withdrawn and extracted with 50 mL of
KCl (12).
Ammonium and nitrite were estimated by following the
indophenol blue method and modified Greiss-Ilosvay method
(12), respectively. Nitrate was estimated by following the
phenol disulfonic acid method (11).
The ammonium, nitrate, and nitrite contents were obtained
from the standard curves and expressed in mg kg-1. The
nitrification rate and percent nitrification inhibition were
calculated as per Sahrawat et al. (13) as follows:
nitrification inhibition (%)a
dose
compd (% urea-N)
15th d
30th d
45th d
60th d
NS
I
5
5
10
15
20
5
10
15
20
5
10
15
20
5
10
15
20
5
10
15
20
5
10
15
20
5
10
15
20
5
10
15
20
5
10
15
20
5
10
15
20
5
10
15
20
5
10
15
20
5
10
15
20
83.14a
76.55ab
49.44vwx
55.06rs
72.81a
32.61uv
37.92st
54.55a
61.74qr
65.31op
71.61ijkl
18.13w
20.76uv
25.60opqr
26.42nopq
27.78mno
33.07hi
60.04mnop 42.71pq
73.76fghi 62.17jkl
67.04mno 60.64lmno
72.98ghijk 68.88cdef
76.05cdef 70.79c
44.74op
53.58l
II
III
IV
59.15jk
65.76def 37.27fg
79.67b
74.54b
69.20bc
41.80d
66.90mno 59.23mnopq 51.45lm
69.85klm 64.44ij 58.02k
23.75qrs
32.12hij
74.97defgh 69.32cdef
62.88fgh 36.51fg
66.41cde 39.24def
49.41mn 24.40pqrs
79.16b
71.47c
65.08op
69.28lmn
58.18nopq
65.02hi
54.00l
29.49jklm
73.80fghi 67.29fgh
76.99bcde 70.18cde
59.59ijk 33.32hi
62.41ghi 36.57fg
V
53.06tu
59.55rs
64.43opq
69.15lmn
48.83wx
52.04tuv
57.19pqr
65.82ghi
37.21t
20.91tuv
41.11qrs 26.11opqr
50.86lm
59.00k
32.18hij
34.70gh
(NO3- + NO2-) - N
(NH4+ + NO3- + NO2-) - N
VI
67.18mno 60.65lmno
72.83ghijk 64.19ij
75.47defg 68.93cdef
38.37rst 18.83vw
40.85qrs 20.78uv
nitrification rate )
% nitrification )
× 100
47.66no
22.62stu
77.18bcd
65.27op
70.41jkl
71.00c
49.88mn 27.13mnop
30.42vw 15.62xy
VII
VIII
IX
47.00x
50.49uvw
33.68u
41.28qr
47.71no
26.83x
33.45uv
22.21stu
29.03klmn
32.80hi
9.73z
nitrification rate in control - nitrification rate in sample
nitrification rate in control
74.99defgh 58.90nopq
77.64bcd
50.12u
62.02kjlm
36.91z
× 100
54.20t
41.59y
13.73y
Coa tin g ver su s Solu tion Ap p lica tion of Nitr ifica tion
In h ibitor s. N-O-Ethyl furfural oxime (II) and furylidine-4-
chloroaniline (XI), the two most active furfural derivatives,
were evaluated as coating on urea and as solution application.
II was tested at 5 and 10% and XI at 2.5, 5, and 7.5% of the
applied urea-N. For coating, urea was first sprayed with 2%
coal tar in hexane as a binder, followed by spraying of the
calculated amount of II and XI in dichloromethane. Upto 7.5%
of XI could be coated on urea without any adverse effect on
its physical form. Being more viscous, II could be coated up to
10% concentration by using 2% coal tar as binder, without any
significant deterioration in its physical form though coating
at 5% level of the inhibitor was the optimum.
For application as solution, 1 kg of air-dried soil was mixed
with the calculated quantity of the test chemical in a volume
of dichloromethane sufficient to ensure thorough mixing. After
mixing, 200 mg of urea-N prills was added and mixed
thoroughly. From the treated soil, twelve lots of 25 g each were
taken in 50-mL beakers, water was maintained at one-third
of the water-holding capacity, and the soil was incubated as
before. Samples were periodically withdrawn and analyzed as
described earlier.
Effect on Ger m in a tion of Ch ick p ea Seed s. Oxime
ethers (II and VI) and furfural Schiff bases (XI and XIII) were
evaluated for effects on the germination of chickpea seeds
(Cicer arietinum) at 10 and 40 ppm levels (soil basis, equiva-
lent to 5 and 20% of applied urea-N). The evaluation was done
at room temperature in five replicates.
Sta tistica l Tr ea tm en t. The nitrification inhibition per-
centage data were statistically analyzed following the proce-
dure laid out by Gomez and Gomez (14). The analysis of
variance was computed and treatment means were compared
by Duncan’s multiple range test (DMRT) at 5% level.
59.68rs
62.27pqr
57.52s
46.83x
39.48qrst 17.41wx
52.65stu
43.09y
41.64qr
28.73wx 13.59y
32.68uv 19.41vw
39.49qrst 24.20qrs
26.09opqr
63.27pq
66.50no
70.91ijkl
69.22lmn
70.97ijkl
50.30uvw
58.11opq
61.11klmn
51.66tuvw
56.92qr
45.22op
30.52ijkl
X
30.61vw 22.01stu
38.53rst 28.89klmn
74.03efghi 67.56efgh
76.01cdef 69.33cdef
72.80ghijk 67.74defg
52.13lm
36.97fg
64.57defg 39.45def
59.37ijk 32.06hij
63.36efgh 37.03fg
XI
78.62bc
82.89a
70.38cd
75.52ab
77.36a
66.95cd
70.04b
51.21lm
47.87bc
49.22b
32.36hij
84.59a
XII
XIII
70.03klm
60.38lmno
73.19fghij 63.68ijk
60.35hijk 38.62ef
62.25ghij 45.10c
66.38cde 47.09bc
31.55uvw 23.50rst
38.59rst 30.69ijk
77.21bcd
79.18b
68.89cdef
71.17c
72.00hijkl 53.83st
73.39fghij 58.44nopq
74.81defgh 68.76cdef
57.17k
39.62def
79.28b
70.84c
65.02defg 41.39de
a
The means are average of three replicates. Those followed by
common letter show insignificant difference. Standard deviation
(() with mean of three replicates ranged from (0.2 to (1.3.
was the most active. At 5 and 20% doses, it showed 67
and 80% nitrification inhibition (NI), respectively, on
the 15th day. The corresponding NI values on the 45th
day were 54 and 69%, respectively. When its dose was
increased from 5 to 20%, the NI effect did not increase
proportionately. As evident from the DMRT results, on
all the four sampling days, each dose of II differed
significantly from the other. The remaining ethers also
showed a similar trend.
RESULTS AND DISCUSSION
Nit r ifica t ion In h ibit or y Act ivit y of F u r fu r a l
Oxim e Eth er s. Results obtained in the in vitro soil
incubation study are reported in Table 1. The oxime
ethers in general have been found to be effective
nitrification inhibitors. N-O-ethyl furfural oxime (II)
Nitrification inhibitory activity of II fell gradually
with time up to 45th day. On the 15th day at 20% dose,
80% inhibition was observed; whereas on the 30th and
45th days, NI activity was 75 and 69%, respectively.
After the 45th day, the activity fell sharply, and it

Furfural Derivatives as Nitrification Inhibitors
J. Agric. Food Chem., Vol. 49, No. 10, 2001 4729
reached 42% on the 60th day. All the other doses of II
as well as all the doses of III and IV behaved similarly.
The reduction in the activity of these chemicals with
passage of time was attributed to their loss, probably
due to their metabolism by soil microorganisms, and is
associated with the reestablishment of the population
of the nitrifying bacteria.
N-O-Ethyl furfural oxime (II) was found to be the
most effective, though statistically it was equal to the
corresponding N-O-isopropyl derivative (III) at different
doses and times. Among the five oxime ethers, N-O-
hexyl furfural oxime (V) was least active. At lower doses
(5 and 10%) the nitrification inhibitory effect of V
started diminishing after the 30th day, whereas at
higher doses (15 and 20%), the activity fell rapidly after
the 45th day. Unlike the other compounds, the lower
activity of V did not persist for longer time.
N-O-allyl furfural oxime (VI) showed considerable NI
activity initially (15th day) but the activity decreased
rapidly after the 30th day at all four doses. On the 15th,
30th, and 45th days, the NI activities at 5% dose were
67, 61, and 38%, respectively. The corresponding values
for II were 67, 61, and 54%. Thus, initially there was
no statistically significant difference between II and VI
at the 15th and 30th days, but on the 45th day the
difference was pronounced. VI did not show persistent
activity, and this can be attributed to the allyl group
which is more susceptible to degradation.
As compared to furfural oxime, the activity of oxime
ethers was significantly higher at all the doses. Initially,
the difference was less pronounced, but after the 15th
day, it became pronounced. Thus, the greatest advan-
tage of oxime ethers as compared to the parent oxime
is the increased persistence of activity in soil.
The activity of II did not differ substantially with
nitrapyrin at the initial stages, but with the passage of
time, the difference increased. Though the activity was
less compared to that of nitrapyrin, the inhibition of
nitrification was still to the extent of over 50% at 5%
dose on the 45th day. Similarly, the NI activity at higher
doses (15 and 20%) of the corresponding isopropyl and
butyl derivatives was comparable to that of the standard
nitrification inhibitor nitrapyrin. Unlike these test
chemicals, the activity of nitrapyrin persisted even after
the 45th day. N-O-Allyl furfural oxime ether (VI)
initially showed activity comparable with that of ni-
trapyrin, but with passage of time the activity de-
creased.
The structure activity relationships (SAR) study
showed that NI activity of the furfural oxime ethers
decreased with an increase in chain length of the alkyl
group. Introduction of a double bond in the side chain
showed high activity initially but it did not persist for
long.
ence widened with passage of time. The remaining two
chalcones, VIII and IX, were, however, less active.
Activity of all the three chalcones decreased quickly with
time. Starting from the 15th day, the activity of the
compounds showed substantial difference with nitrapy-
rin even at the highest dose (20%) of application. The
same dose of the chalcones showed significant difference
in activity on the 15th, 30th, and 60th days, whereas
the difference in activity on the 45th day was not
significant. Introduction of a hydroxy group in the
phenyl ring significantly reduced the activity of these
compounds. The chalcones as a class failed to show
significant NI property.
Nit r ifica t ion In h ib it or y Act ivit y of F u r fu r a l
Sch iff Ba ses. Among the Schiff bases, furfurylidine-
4-chloroaniline (XI) outperformed all the other com-
pounds, and it was followed closely by XII. At 5 and
20% doses, it showed 73 and 85% NI activity respec-
tively on the 15th day. The activity at higher doses (15
and 20%) did not differ significantly from that of
nitrapyrin (5%) on the 15th and 30th days and was
comparable even up to the 60th day. The lower doses
(5 and 10%) showed comparable activity with nitrapyrin
up to 30th day. These doses inhibited 60% nitrification
as compared to the control up to the 45th day. Like
nitrapyrin, its activity decreased gradually up to the
45th day but decreased rapidly after 45 days. All the
doses of XI followed this pattern. Furfurylidine-3,4-
dichloroaniline (XII) at 15 and 20% doses showed
excellent NI activity. On the 15th day, it showed 70%
NI at 5% and 79% NI at 20% dose. This compound
inhibited more than 50% nitrification up to the 45th day.
Its 15 and 20% doses showed marginally inferior activity
as compared to that of nitrapyrin. As with XI, there was
no significant difference between the 15 and 20% doses
on the 45th day. The 15% dose can thus be considered
optimum for both monochloro- and dichloro-substituted
Schiff bases. Furfurylidine aniline (X) and furfurylidine-
3-nitroaniline (XIII) showed considerable nitrification
inhibition property up to the 30th day, but with the
passage of time the activity decreased gradually. The
NI activity at the 5 and 20% doses of XIII on the 15th
day was 72 and 79% and on 45th day was 32 and 65%,
respectively. In case of X, on the 15th day NI activity
for the 5 and 20% doses was 69 and 76%, respectively,
whereas on the 45th day the values were 31 and 65%.
Thus, the 20% dose of both the compounds showed
greater persistence of activity up to the 45th day
followed by the 15% dose. In the case of the 5 and 10%
doses, the activity started diminishing rapidly from the
15th day onward. On the 15th day the difference of
activity between these was insignificant, but with the
passage of time it became significant.
Thus, in case of the Schiff bases, the nitrification
inhibitory activity persisted for longer periods with an
increase in the dose of the compound. However, the
increase in NI activity, though statistically significant,
was not of a high order. The introduction of a chlorine
atom in the phenyl ring apparently increased the
persistence as well as the activity. However, introduc-
tion of more than one chlorine reduced the activity. The
activity of dichlorosubstituted Schiff base was signifi-
cantly inferior to that of the monochloro derivative at
most doses and sampling days except on the 60th day.
It has been reported previously (15) that the NI activity
increased with the number of chlorine substituents in
Nit r ifica t ion In h ib it or y Act ivit y of F u r fu r a l
Ch a lcon es. Among the three test chalcones, 3-(furan-
1-yl)-1-phenylprop-2-en-1-one (VII) showed the best
performance (Table 1). On the 15th day it showed 67%
NI activity at 5% dose and 78% activity at 20% dose.
The corresponding values on the 45th day were 30 and
48%, respectively. Thus, VII showed initially good
activity which could not be sustained for long. All the
doses exhibited the same trend. Higher doses showed
better activity but not a long lasting effect. All the four
doses showed significant differences among themselves.
At the highest dose (20%), VII showed less activity
(78%) as compared to nitrapyrin (83%) and the differ-

4730 J. Agric. Food Chem., Vol. 49, No. 10, 2001
Datta et al.
Ta ble 3. Effect of Oxim e Eth er s (II a n d III) a n d Sch iff
Ba ses (XI a n d XIII) on th e Ger m in a tion of Ch ick p ea
Seed s
Ta ble 2. Effect of Coa ted vs Solu tion Ap p lica tion of
N-O-Eth yl F u r fu r a l Oxim e (II) a n d
F u r fu r ylid in e-4-Ch lor oa n ilin e (XI) on Nitr ifica tion
In h ibition
dose
(ppm, soil basis)
germination
nitrification inhibition (%)a
compd
(%)a ( SD
dose
appl.
compd
(% urea-N) method 15th d 30th d 45th d 60th d
control
II
-
10
40
10
40
10
40
10
40
82 ( 2.1
79 ( 1.3
82 ( 2.5
81 ( 1.5
82 ( 2.5
81 ( 2.4
80 ( 0.9
83 ( 2.4
81 ( 1.8
II
5.0
10.0
2.5
coating 67.90d 61.24c 56.51c 29.16d
solution 65.13d 60.86c 56.74c 29.25d
coating 74.05bc 68.84b 59.97bc 36.16bc
solution 72.43c 68.51b 59.56bc 34.97bc
coating 55.63e 41.40d 30.97d 21.64e
solution 53.22e 39.03d 31.34d 21.85e
coating 73.60bc 65.78b 60.35bc 34.47c
solution 72.43c 67.78b 59.77bc 35.31bc
coating 75.61b 67.61b 62.39b 38.45b
solution 76.43b 68.98b 62.13b 37.45bc
solution 82.13a 75.59a 67.55a 53.37a
III
XI
XI
5.0
XIII
7.5
a
The means are averages of five replicates.
nitrapyrin
5.0
Ger m in a tion of Ch ick p ea Seed s. The most active
products, namely II, III, XI, and XIII, did not adversely
affect the germination of chickpea seeds, even at the
highest dose (40 ppm, soil basis; Table 3). The test
compounds, as well as the control, showed around 80%
germination. The vigor of the seedlings was also similar.
a
The means are averages of three replicates. Those followed
by a common letter show insignificant difference.
the aniline ring. The present results do not corroborate
this finding.
There was no significant difference in activity be-
tween furfurylidineaniline (X) and its nitro derivative
XIII at most of the doses and periods, though in some
cases (such as the 20% dose on 15th day) significantly
better activity was recorded with XIII. The nitro group
failed to improve the activity of the substituted Schiff
base. The NI activity of nonchlorinated Schiff bases,
though initially higher, did not persist for longer
periods. Initially, all the Schiff bases showed similar
activity at a given dose and time, but with the passage
of time the difference in activity between the chlorinated
and the nonchlorinated Schiff bases widened.
Gen er a l Com p a r ison of Activity of F u r fu r a l
Der iva tives. An appraisal of the NI values indicated
that on the 15th day all the four Schiff bases, oxime
ethers except N-O-hexyl furfuraloxime (V) and the
chalcone, 3-(furan-1-yl)-1-phenylprop-2-en-1-one (VII),
revealed similar activity. In general, the Schiff bases
performed slightly better than the oxime ethers. On the
15th day, the Schiff bases were undoubtedly the best,
followed closely by the oxime ethers. The chalcones,
except VII, were the poor third. With the passage of
time, the difference in activity at 5% dose of the
chalcones, Schiff bases, and the oxime ethers widened.
Overall, chlorosubstituted Schiff bases were the best
among the test compounds followed by N-O-ethyl,
isopropyl, and butyl oxime ethers.
When NI activity of the test compounds was compared
at the 20% dose, it was observed that, except V, VII,
and IX, the remaining compounds performed distinctly
better and were comparable on the 15th day. The
observations on the 45th day revealed that the chalcones
did not have a long-lasting effect, whereas the Schiff
bases showed generally persistent activity. The differ-
ence in NI activity of the Schiff bases and N-O-ethyl
furfural oxime started widening from the 60th day, but
up to the 45th day they were comparable. None of the
treatments led to an accumulation of nitrite nitrogen.
Coa tin g Com p a r ed to Solu tion Ap p lica tion . The
nitrification inhibition data reported in Table 2 revealed
that the coated products, on most of the sampling days
and doses, showed activity statistically similar with that
of their application as solution. Thus, under laboratory
conditions, any of the methods can be used to apply the
inhibitor. However, the coated products would be pref-
erable for field applications because of the convenience
in handling.
CONCLUSION
Furfural oxime ethers and furfural Schiff bases have
been found to possess potential as nitrification inhibi-
tors, but the chalcones in general showed poor activity.
Excellent activity of oxime ethers and Schiff bases has
been attributed to the aldoximino moiety attached to
the furan ring. Among the furfural oxime ethers, the
N-O-ethyl derivative was the most active, followed by
N-O-isopropyl, butyl, n-hexyl, and allyl furfural oxime.
Activity of oxime ethers increased with an increase in
dose but not proportionately. At the lower dose of 5%,
the activity of these compounds, though considerable,
was lower than that of nitrapyrin. Apparently, an
increase in the number of carbon atoms in the alkyl
chain of the oxime ethers reduced the nitrification
activity of the compounds. Activity decreased with the
introduction of a double bond in the alkyl group.
Furfural oxime, an intermediate used in the synthesis
of furfural oxime ethers, itself possessed good activity,
but the activity was not long lasting. Among the Schiff
bases, the chlorinated products showed considerable
activity up to 45 days. At the 20% dose, monochloro-
substituted Schiff base was more active than nitrapyrin
up to the 30th day and was comparable to nitrapyrin
up to the 60th day. Application of oxime ether and Schiff
base coated urea failed to show improvement when
compared with their application in solution form. These
products also did not show any adverse effect on the
germination of chickpea seeds. It can thus be concluded
that there exists a potential for improving the nitrogen
use efficiency of urea fertilizer and minimizing envi-
ronmental pollution from nitrogenous fertilizers by
developing nitrification inhibitory compounds from in-
dustrially cheap raw materials such as furfural. On the
basis of SAR leads, more derivatives can be synthesized
and tested. However, nitrapyrin is still by far the most
active nitrification inhibitor.
LITERATURE CITED
(1) DeDatta, S. K.; Buresh, R. J . Integrated nitrogen
management in irrigated rice. Adv. Soil Sci. 1989, 10,
143-169.
(2) Raun, W. R.; J ohnson, G. V. Improving nitrogen use
efficiency for cereal production. Agron. J . 1999, 9, 357-
363.

Furfural Derivatives as Nitrification Inhibitors
J. Agric. Food Chem., Vol. 49, No. 10, 2001 4731
(3) Eichner, M. Nitrous oxide emissions from fertilized soils.
Summary of available data. J . Environ. Qual. 1990, 19,
272-280.
(4) Mosier, A. R.; Duxbury, J . M.; Freney, J . R.; Heinem-
eyer; Minami, K. Nitrous oxide emissions from agricul-
tural fields: assessment, measurement and mitigation.
Plant Soil 1996, 181, 95-108.
(5) Prasad, R. Fertilizer urea, food security, health and the
environment. Curr. Sci. 1998, 75, 677-683.
(6) Iserman, K. Agriculture’s share in the emission of trace
gases affecting the climate and some proposals for
reducing this share. Environ. Pollut. 1994, 83, 95-111.
(7) Sahrawat, K. L.; Keeney, D. R. Perspectives for research
on development of nitrification inhibitors. Commun.
Soil. Sci. Plant Anal. 1985, 16, 517-524.
(8) Sahrawat, K. L.; Mukherjee, S. K. Nitrification inhibi-
tors. 1. Studies with furano compounds. Plant Soil 1977,
47, 687-691.
(9) Kuzvinzwa, S. M.; Devakumar, C.; Mukherjee, S. K.
Evaluation of furano compounds as nitrification inhibi-
tors. Bull. Indian Soc. Soil Sci. 1984, 13, 165-172.
(10) Furniss, B. S.; Hannaford, A. S.; Smith, P. W. G.;
Tatchell, A. R. Vogel’s Textbook of Practical Organic
Chemistry. 5th ed.; Longman Scientific and Technical:
Essex, England, 1989; pp 1032-1036.
(11) Ghosh, A. B.; Bajaj, J . C.; Hasan, R.; Singh, D. Deter-
mination of nitrate nitrogen. In Soil and Water Testing
Methods. A Laboratory Manual; Division of Soil Science
and Agricultural Chemistry, Indian Agricultural Re-
search Institute: New Delhi; 1983; pp 14-16.
(12) Keeney, D. R.; Nelson, D, W. Nitrogen inorganic forms.
In Methods of Soil Analysis. Part 2: Chemical and
Microbiological Properties, 2nd ed.; Page, A. L., Ed.;
American Society of Agronomy, Soil Science Society of
America: Madison, WI, 1989; pp 643-698.
(13) Sahrawat, K. L. On the criteria for comparing the ability
of compounds for retardation of nitrification in soil.
Plant Soil 1980, 55, 487-490.
(14) Gomez, K. A.; Gomez, A. A. Statistical Procedures for
Agricultural Research. J ohn Wiley and Sons Inc.: New
York, 1984.
(15) Thompson, F. R.; Corke, C. F. Persistence and effects
of some chlorinated anilines on nitrification in soil. Can.
J . Microbiol. 1969, 15, 791-796.
Received for review November 2, 2000. Revised manuscript
received J uly 15, 2001. Accepted August 1, 2001.
J F001318D