Ionic liquids as herbicides and plant growth regulators

Article abstract of DOI:10.1016/j.tet.2013.03.097

New ILs containing the (2,4-dichlorophenoxy)acetate anion have been synthesized and characterized (properties, chemical and thermal stability, surface activity). Next, the possibility to use them as herbicides and plant growth regulators has been studied.

Full text of DOI:10.1016/j.tet.2013.03.097

Tetrahedron xxx (2013) 1e5
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Tetrahedron
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Ionic liquids as herbicides and plant growth regulators
,
a
a
b
Juliusz Pernak a , Micha1 Niemczak , Katarzyna Materna , Katarzyna Marcinkowska ,
*
Tadeusz Praczyk b
a Department of Chemical Technology, Poznan University of Technology, Poznan 60-965, Poland
b Institute of Plant Protection, National Research Institute, Poznan 60-318, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
New ILs containing the (2,4-dichlorophenoxy)acetate anion have been synthesized and characterized
(properties, chemical and thermal stability, surface activity). Next, the possibility to use them as her-
bicides and plant growth regulators has been studied. The obtained ILs exhibited higher biological
activity than the currently used herbicide (2,4-D salt) and plant growth regulator (CCC).
Ó 2013 Elsevier Ltd. All rights reserved.
Received 21 December 2012
Received in revised form 12 March 2013
Accepted 26 March 2013
Available online xxx
Keywords:
Ionic liquids
Herbicidal ionic liquids
Plant growth regulator
2,4-D
1. Introduction
potato tuber diseases are also proposed in the agrochemistry
field.14 Enhanced stabilization of the tobacco mosaic virus using
Ionic liquids (ILs), due to their properties and enormous po-
tential application still enjoy a great interest in both academia and
industry. They are substances composed exclusively of ions, which
form phases that are liquids below 100 ꢀC.1e6 ILs, from dependence
on the cation, are divided into: imidazolium, ammonium, pyr-
idinium, phosphonium, piperidinium, morpholinium, sulfonium,
and lately pyrylium.7 They have negligible vapor pressure under
ambient conditions and are usually non-flammable. By modifica-
tion of the cation and/or anion an enormous range of potential ILs is
possible. The evaluation of these compounds proceeds very quickly
from the first generation (ILs with unique tunable physical prop-
erties) to the second generation (ILs with targeted chemical prop-
erties combined with selected physical properties), to the third
generation (ILs with targeted biological properties combined with
physical and chemical properties).8,9
protic ILs has recently been described.15
Chlormequat
chlorided2-chloroethyltrimethylammonium
chloride (CCC), was prepared in 191016 and described as a plant
growth regulator by Tolbert in 1960.17,18 It is used to prevent
lodging and to increase yields in wheat, rye, oats, and triticale.
Moreover, CCC is also applied to increase lateral branching and
flowering in some ornamental plants and to increase fruit setting in
pears, olives, vines, and tomatoes.19
(2,4-Dichlorophenoxy)acetic acid (2,4-D) was first described by
Zimmerman and Hitchcock.20 This phenoxy acid is a systemic
herbicide used in the control of broadleaf weeds and is also a syn-
thetic auxin often used in laboratories for plant research.
Due to the toxicity and side effects of 2,4-D and CCC, their use is
heavily criticized. However, these are cheap and widely used, es-
pecially 2,4-D. Additionally, both have an ionic structure. For this
reason we have decided to use them as substrates in the synthesis
of the third generation ILs.
The aim of our work was the synthesis of new salts and the
study of the possibility to use them as herbicides and plant growth
regulators. In our study we have looked for answers to two basic
questions. First, whether these compounds are ionic liquids? Sec-
ond, whether the activities of the cation and anion are maintained?
To answer these questions the chemical and thermal stability,
surface and biological activity of 2-chloroethyltrimethylammonium
and trimethylvinylammonium (2,4-dichlorophenoxy)acetates have
been tested.
ILs might be easily adapted toward ‘designer drugs’, since the
physical, chemical, and biological properties of a drug can be tuned
by choice of the counterion.10 Recently the third generation phy-
topharmaceuticalsdherbicidal ionic liquids were published.11e13
The novel hydrophobic fungicide with thiabendazole and imidaz-
ole as ILs, with increased rain persistence and activity against
* Corresponding author. Tel.: þ48 61 665 3682; fax: þ48 61 665 3649; e-mail
address: juliusz.pernak@put.poznan.pl (J. Pernak).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.03.097
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2
J. Pernak et al. / Tetrahedron xxx (2013) 1e5
2. Results and discussion
The product of dehydrochlorination of CCC or [CC][2,4-D] via
elimination was a vinyl group attached to the nitrogen atom
(Scheme 3). The reactions order (n) was calculated by the Ost-
waldeZawicki method. It has been found that it is an E2 elimination
reaction.
The reaction of sodium (2,4-dichlorophenoxy)acetate with
2-chloroethyltrimethylammonium chloride in water gave 2-
chloroethyltrimethylammonium (2,4-dichlorophenoxy)acetated
[CC][2,4-D] in 95% yield (Scheme 1).
CH3
N
CH3
N
H3C
X
Cl
H3C
X
KOH
-KCl
O
O
CH3
N
O
O
CH3
N
H3C
Cl
Cl
O
O
H3C
Cl
CH3
CH3
-NaCl
Na
CH3
Cl
Cl
Cl
Cl
CH3
Scheme 3. Elimination reaction in 2-chloroethyltrimethylammonium cation, when
X¼Cl or 2,4-D anion.
Scheme 1. Synthesis of 2-chloroethyltrimethylammonium (2,4-dichlorophenoxy)
acetated[CC][2,4-D], 95% yield.
The change in concentration as time function during the re-
action between CCC or [CC][2,4-D] and potassium hydroxide in
water at 30 ꢀC, with 0.100 mol Lꢁ1 initial concentration of both
reactants, is shown in Fig. 1.
Exchange of the chloride anion in the quaternary ammonium
chlorides was effective. Many quaternary ammonium salts are
highly hygroscopic, so water should be avoided as a solvent. Very
good results were obtained by using anhydrous methanol as a sol-
vent and a stoichiometric amount of a base (e.g., KOH). In this
case, KCl came out of reaction mixture and anhydrous product was
obtained after evaporation of the solvent under mild conditions.
For [CC][2,4-D] the exchange reaction could not be carried out in
methanol with a base because elimination occurred. [CC][2,4-D]
has proved to be unstable in an alkaline medium. In contact with
base trimethylvinylammonium (2,4-dichlorophenoxy)acetate was
formedd[TMVA][2,4-D] as shown in Scheme 2. The yield was 97%.
O
O
O
CH3
N
O
CH3
N
KOH
-KCl
O
H3C
Cl
O
H3C
Cl
Cl
CH3
Cl
Cl
CH3
Scheme 2. Synthesis of trimethylvinylammonium (2,4-dichlorophenoxy)acetated
[TMVA][2,4-D], 97% yield.
Fig. 1. Concentration versus time for the decomposition of CCC and [CC][2,4-D] in
water at 30.0 ꢀC (303.2 K).
[CC][2,4-D] and [TMVA][2,4-D] can be made anhydrous by
heating at 70 ꢀC in vacuo and storing over P4O10. The water content
in the prepared salts was determined to be less than 500 ppm by
coulometric Karl Fischer titration. These salts are stable in air and in
contact with water and common organic solvents. They are soluble
in DMSO, alcohols (methanol, ethanol, and propanol), chloroform
and are insoluble in hexane and diethyl ether. The two new salts
were characterized by 1H and 13C NMR spectroscopy and elemental
analysis. Generally, we observed specific signals from the anion and
cation. The 1H NMR spectra of the [CC][2,4-D] and [TMVA][2,4-D]
indicate significantly different chemical shifts for the Nþ(CH3)3
protons (move over 0.20 ppm). Moreover, signals from protons of 2-
chloroethyl groupdNþCH2CH2Cl (3.80 and 4.09 ppm) for [CC][2,4-
D] are absent on the [TMVA][2,4-D] spectra, which possess three
characteristic signals for the vinyl substituent (5.50, 5.80, and
6.77 ppm). The 13C NMR spectra present similar differences in
chemical shifts of the methyl groups in the cationdNþ(CH3)3, in the
range 0.69 ppm. Signals of the carbons from the 2-chloroethyl
group (36.42 and 64.83 ppm) in [CC][2,4-D] spectra are replaced
by two peaks characteristic for the vinyl group (111.24 and
143.20 ppm).
At low temperatures (20e40 ꢀC) there is a considerable impact
on elimination reaction kinetics as is shown in Fig. 1. It is noticeable
that the reaction rate of degradation (k) for CCC is approximately
2.5 times greater than for [CC][2,4-D] at 30.0 ꢀC (303.2 K). At this
temperature [CC][2,4-D] is decomposed much slower than CCC. The
linear relationship in the Arrhenius plots demonstrates the correct
assumption of the kinetic equation and reaction order (Fig. 2). It
means that the reaction with the participation of [CC][2,4-D] is less
dependent on the temperature.
The values of Tonset5% and Tonset, determined using TGA, for [CC]
[2,4-D] were equal to 180 and 255 ꢀC, respectively, and for [TMVA]
[2,4-D]: 170 and 240 ꢀC. Additional physicochemical data were
provided by DSC analysis. For [CC][2,4-D] there was only the glass
transition temperature at 8 ꢀC. For [TMVA][2,4-D] the glass tran-
sition was observed at ꢁ16 ꢀC, the temperature of crystallization at
10 ꢀC and the melting point at 16 ꢀC. At room temperature [CC][2,4-
D] is a solid and melts at 92e94 ꢀC, and [TMVA][2,4-D] is a liquid of
high viscosity. The synthesized [CC][2,4-D] and [TMVA][2,4-D] salts
can be classified as ionic liquids. This is the answer to the first
question posed at the beginning of our work.
Fig. 2. Arrhenius plot of CCC and [CC][2,4-D] E2 elimination reaction in water.
Table 1 summarizes a series of calculated kinetic parameters:
reaction half-life (s1/2), activation energy (Ea), enthalpy of activation
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J. Pernak et al. / Tetrahedron xxx (2013) 1e5
3
Table 1
Summary of calculated kinetic parameters
Substrate
CCC
Temp [K]
k (L molꢁ1 minꢁ1
)
s1/2 (min)
Ea (kJ molꢁ1
)
D
Hs (kJ molꢁ1
)
D
Ss (kJ molꢁ1 Kꢁ1
)
D )
Gs (kJ molꢁ1
293.2
303.2
313.2
323.2
333.2
293.2
303.2
313.2
323.2
333.2
0.011
0.034
0.105
0.261
0.734
0.004
0.014
0.067
0.235
0.691
952.4
295.0
95.5
38.3
13.6
2564.1
694.4
148.4
42.5
85.6
83.2
83.1
83.0
82.9
82.8
104.4
104.3
104.2
104.2
104.1
ꢁ33.0
ꢁ33.1
ꢁ33.1
ꢁ34.2
ꢁ33.8
ꢁ47.0
ꢁ48.0
ꢁ47.7
ꢁ48.2
ꢁ48.2
92.8
93.1
93.4
94.0
94.1
93.1
93.8
94.1
94.6
95.0
[CC][2,4-D]
81.7
14.5
(
(
D
D
H
G
s), entropy of activation (
DS
s), Gibbs free energy of activation
Table 4
s). Bimolecular dehydrochlorination of [CC][2,4-D] requires
The influence of different forms of 2,4-D on weed control, stems length and yield of
spring wheat
less activation energy by about 4 kJ molꢁ1 than CCC. The activation
entropy is strongly negative. This phenomenon could be explained
by the fact that on the route from the initial to the transition state,
vibrational, rotational, and translational motion is extremely
restricted.
Treatmentsa
Chenopodium Centaurea Stems
Yield t haꢁ1
album
Weed control (%)
87 94
cyanus
length (cm)
[CC][2,4-D]
86.2
90.0
101.0
101.5
6.26
5.98
6.15
6.23
CCCþ[DMA] [2,4-D]b 85
93
70
0
Both growth chamber and field experiments were conducted for
[CC][2,4-D] and dimethylammonium (2,4-dichlorophenoxy)acetate
(the active ingredient of the commercial used herbicide)d[DMA]
[2,4-D]. A preliminary study conducted in a growth chamber in-
dicated that the new form of 2,4-D has a better activity compared
with used commercial product. The results of this experiment,
presented in Table 2, show that the fresh weight reduction of white
mustard (Sinapis alba) was higher when [CC][2,4-D] was used. The
activity of this IL increased with increasing the concentration from
0.005 M to 0.01 M.
[DMA][2,4-D]
79
0
Untreated check
a
In all treatments the rate of 2,4-D was 450 g haꢁ1
Tank mixture of commercial products.
.
b
[CC][2,4-D] showed very good herbicidal activity as well as plant
growth inhibition activity. The shorter stems are more resistant to
lodging, which can decrease the yield of cereals. Therefore this
compound can be used not only for effective weed control in ce-
reals, but also for preventing the crop lodging. The combining the
herbicidal activity of this compound with inhibition of cereals stem
elongation is a unique solution for growers.
Table 2
Efficacy of [CC][2,4-D] and [DMA][2,4-D] against white mustard (Sinapis alba) in
growth chamber experiment
[CC][2,4-D] were selective to the cereals and showed a profit-
able influence on the spring wheat yield. On the second question
posed at the beginning of our work, we have received a positive
response. Under the same conditions [TMVA][2,4-D] was tested.
This new IL retained only herbicidal activity. The 2-chloroethyl
group decides that the compound is classified as a plant growth
regulator.
Treatments
Concentration
Dose (g haꢁ1
2,4-D
)
Fresh weight
reduction (%)
CCC
[CC][2,4-D]
[CC][2,4-D]
[DMA][2,4-D]
0.005 M
0.01 M
0.01 M
220
440
158
316
0
50
75
68
600a
a
Dose recommended in spring cereals.
Critical micelle concentration (CMC), surface tension, and
contact angle values of the synthesized ILs are shown in Table 5.
In addition, surface activities for CCC and [DMA][2,4-D] are
given.
[CC][2,4-D] used at rate corresponding to 440 g haꢁ1 of 2,4-D
free acid was more active than [DMA][2,4-D] used at rate of
600 g haꢁ1. The better herbicidal activity of [CC][2,4-D] compared
to [DMA][2,4-D] was also confirmed in field experiments carried
out in spring wheat and spring barley. The results showed in Table 3
indicate that the control of common lambsquarters (Chenopodium
album) by the new form of 2,4-D was more effective compared to
commercial [DMA][2,4-D]. The differences between treatments
were higher in 2011 when there were dramatically low amount of
rainfall in spring. In other experiment carried out in spring wheat
we obtained similar results. The control of both common lambs-
quarters and cornflower (Centaurea cyanus) was better when [CC]
[2,4-D] was used (Table 4).
Table 5
The CMC, surface tension (gCMC), and contact angle CA (paraffin) of aqueous solution
of salts, at 25 ꢀC
Salt
CMC (mol Lꢁ1
)
gCMC (mN mꢁ1
)
CA (ꢀ)
[CC][2,4-D]
[TMVA][2,4-D]
CCC
0.158
0.079
0.201
0.086
41.5
36.7
47.1
52.5
71.7
63.4
84.7
89.1
[DMA][2,4-D]
Table 3
The control of common lambsquarters by different forms of 2,4-D applied in spring
barley
In comparison with the standard herbicide ([DMA][2,4-D]) and
plant growth regulator (CCC) the designed values of surface tension
and contact angles for the synthesized ILs were significantly lower.
In accordance with our expectations, the results of surface tension
measurements were consistent with biological data of [CC][2,4-D]
and [TMVA][2,4-D]. The low value of contact angle and surface
tension should result in good wetting of plants, enhancing
spray retention, absorption, cuticle penetration, and translocation
of active ingredient.
Treatmentsa
2011
2012
% of fresh weight reduction
[CC][2,4-D]
95
d
47
72
61
54
CCCþ[DMA][2,4-D]b
[DMA][2,4-D]
a
In all treatments the rate of 2,4-D was 450 g haꢁ1
Tank mixture of commercial products.
.
b
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4
J. Pernak et al. / Tetrahedron xxx (2013) 1e5
3. Conclusion
7.47 (d, J¼2.6 Hz, 1H, ClCCH]CCl); 13C NMR (DMSO-d6, 298 K,
100 MHz)
d
ppm¼53.28, 68.67, 111.24, 114.97, 121.56, 122.88, 127.50,
New ionic liquids: 2-chloroethyltrimethylammonium and
trimethylvinylammonium (2,4-dichlorophenoxy)acetates were
synthesized in high yields. The obtained salts exhibited higher
surface activity than the currently used herbicide (2,4-D salt)
and plant growth regulator (CCC). The biological activities of the 2-
chloroethyltrimethylammonium cation and (2,4-dichlorophenoxy)
acetate anion were maintained in the new IL. In conclusion, [TMVA]
[2,4-D] and [CC][2,4-D] showed very good herbicidal activity, and
[CC][2,4-D] could also be used as a plant growth regulator.
128.68, 143.20, 153.76, 168.67. Elemental analysis calcd (%) for
C
13H17Cl2NO3 (M¼306.18) C 51.00, H 5.60, N 4.57; found: C 50.79, H
5.41, N 4.41; IR (KBr) nmax: 3306, 3087 (eCH]CH2, CeHst, m), 3018,
2970, 2926, 1657 (eCH]CH2, C]Cst, m), 1644, 1609, 1483, 1430,
1424, 1390, 1347, 1282, 1266, 1244, 1231, 1159, 1107, 1064, 1044, 950
(eCH]CH2, CeHd, m), 895, 868, 836, 801, 764, 722, 715, 697, 685,
647, 556 cmꢁ1
.
4.3. Thermal analysis
4. Experimental section
4.1. General
Thermal transitions of the prepared salts were determined by
DSC, with a Mettler Toledo Stare TGA/DSC1 (Leicester, UK) unit,
under nitrogen. Samples between 5 and 15 mg were placed in
aluminumꢁp1ans and heated from 25 to 120 ꢀC at a heating rate of
10 ꢀC min ꢁ1 and cooled with an intracooler at a cooling rate of
1H NMR spectra were recorded on a Mercury Gemini 400
spectrometer operating at 400 MHz with tetramethylsilane as the
internal standard. 13C NMR spectra were obtained with the same
instrument at 100 MHz. CHN elemental analyses were performed at
Adam Mickiewicz University, Poznan (Poland).
10 ꢀC min
to ꢁ100 ꢀC. Thermogravimetric analysis was per-
formed using a Mettler Toledo Stare TGA/DSC1 unit (Leicester, UK)
under nitrogen. Samples between 2 and 10 mg were placed in
aluminum pans and heated from 30 to 450 ꢀC at a heating rate of
10 ꢀC minꢁ1
.
4.2. Preparation
4.2.1. 2-Chloroethyltrimethylammonium (2,4-dichlorophenoxy)-acet
ated[CC][2,4-D]. In a round-bottom flask, equipped with reflux
condenser and dropping funnel, the sodium salt of (2,4-
dichlorophenoxy)acetic acid (0.03 mol), dissolved in distilled wa-
ter (30 mL) was added. Then a stoichiometric amount of 2-
chloroethyltrimethylammonioum chloride was added and the
mixture was stirred for 3 h at room temperature. The water was
evaporated using a rotary evaporator and the residue was dissolved
in methanol. The product, deposited in the methanol phase, was
separated from the insoluble inorganic saltdsodium chloride. After
removal of methanol the product was dried under reduced pressure
at 70 ꢀC for 24 h. The obtained compound was solid at room tem-
perature and the reaction yield was 95%. 1H NMR (DMSO-d6, 298 K,
4.4. Kinetics analysis
During the kinetics measurements, constant temperature was
maintained with an accuracy of 0.1 ꢀC. Concentration of reactants in
water was determined using a new generation of semi-automated
reactor system for the laboratory synthesisdEasyMaxÔ from
Mettler Toledo. The temperature of the reactor contents was con-
trolled with an accuracy of 0.01 ꢀC using a Pt100 sensor. Connecting
SevenMulti Mettler Toledo instrument, equipped with a suitable
electrode allowed for precise measurement of decrease in pH of the
mixture as a result of proceeding reaction.
The reactions order (n) was calculated by the OstwaldeZawicki
method, using the equation:
400 MHz)
d
ppm¼3.18 (s, 9H, (CH3)3Nþ), 3.80 (t, J¼7.0 Hz, 2H,
ꢀ
Cm0;
Cm0;
ꢁ
NþCH2CH2Cl), 4.09 (t, J¼7.0 Hz, 2H, NþCH2CH2Cl), 4.28 (s, 2H,
OCH2COOꢁ), 6.84 (d, J¼8.9 Hz, 1H, ClCCH]CHC), 7.26 (dd,
J1,2¼8.8 Hz, J1,3¼2.6 Hz, 1H, ClCCH]CHC), 7.47 (d, J¼2.6 Hz, 1H,
s1=2;
s1=2;
I
log
II
ꢀ
ꢁ
n ¼ 1 þ
I
ClCCH]CCl); 13C NMR (DMSO-d6, 298 K, 100 MHz)
52.59, 64.83, 68.35, 114.95, 121.63, 123.05, 127.51, 128.75, 153.66,
d
ppm¼36.42,
log
II
168.79. Elemental analysis calcd (%) for C13H18Cl3NO3 (M¼342.65) C
where: s1/2 is the reaction half-life, and Cm0 is the initial concen-
tration of reactants. Measurements of 1/2 were performed both in
water at initial concentrations of both reactants equal to 0.100 and
0.050 mol Lꢁ1
45.57, H 5.29, N 4.09; found: C 45.83, H 5.22, N 4.15; IR (KBr) nmax
:
s
3364, 3076, 3023, 2968 (eCH2eCH2Cl, CeHst, m), 1645, 1606, 1484,
1476, 1464 (eCH2eCH2Cl, CeHd, m), 1430, 1424, 1389, 1347, 1331,
1283, 1264, 1252, 1231, 1154, 1104, 1066, 1037, 975, 951, 919, 896,
869, 838, 802, 775, 734 (eCH2eCH2Cl, CeClst, m), 722, 699, 648,
.
Activation energy (Ea) and entropy (DS
s) were calculated from
the equation of Arrhenius and Eyring.
556 cmꢁ1
.
4.2.2. Trimethylvinylammonium
(2,4-dichlorophenoxy)acetated
4.5. Growth chamber experiment
[TMVA][2,4-D]. In a round-bottom flask 2-chloroethyltrimethylam-
monioum (2,4-dichlorophenoxy)acetate (0.02 mol) was dissolved
in distilled water (15 mL). Then, a stoichiometric amount of KOH,
dissolved in distilled water, was added and the mixture was stirred
for 24 h at 50 ꢀC. Then, water was evaporated using a rotary
evaporator and the residue was dissolved in acetonitrile. The in-
organic by-product (potassium chloride) precipitated as a white
solid and was separated carefully from the solution. After removal
of acetonitrile the product was dried under reduced pressure at
70 ꢀC for 24 h. The reaction yield was 97%. 1H NMR (DMSO-d6,
The seeds of white mustard (Sinapis alba) were sown into soil-
filled plastic pots to the depth of 1 cm. After emergence the
plants were thinned to 5 plants in each pot. The treatments were
applied at fourth leaf stage using a spray chamber with Tee Jet 1102
flat-fan nozzles delivering 200 L of spray solution per 1 ha at
0.2 MPa pressure. The sprayer was moving above the plants at
a constant speed of 3.1 m sꢁ1. The distance from nozzles to the tips
of the plant was 40 cm. The plants were treated once with a water
solution of tested herbicides and they were placed in a growth
chamber at a temperature of 20 ꢀC, humidity of 60% and photo-
period (day/night hours)d16/8. The standard herbicide was the
commercial product containing [DMA][2,4-D] (Aminopielik Stan-
dard 600 SLd600 g 2,4-D per 1 L).
298 K, 400 MHz)
d
ppm¼3.38 (s, 9H, (CH3)3Nþ), 4.23 (s, 2H,
OCH2COOꢁ), 5.50 (m, 1H, NþCH]CHH), 5.80 (d, J¼15.3 Hz, 1H,
NþCH]CHH), 6.77 (m, 1H, NþCH]CH2), 6.84 (d, J¼9.0 Hz, 1H,
ClCCH]CHC), 7.29 (dd, J1,2¼9.0 Hz, J1,3¼2.7 Hz, 1H, ClCCH]CHC),
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J. Pernak et al. / Tetrahedron xxx (2013) 1e5
5
The study was carried out in 4 replications in a completely
randomized setup. After 2 weeks, the plants were cut to soil level
and weighed (0.1 g accuracy). The reduction of plant fresh weight as
compared to control (no sprayed plants) was measured.
controlled using a Fisherbrand FBH604 thermostatic bath (Fisher,
Germany, accuracy þ0.1 ꢀC). The values of the critical micelle
concentration (CMC) and the surface tension at the CMC (gCMC
)
were determined from the intersection of the two straight lines
drawn in low and high concentration regions in surface tension
4.6. Field experiments
curves (g vs log C curves) using a linear regression analysis method.
The field trials were carried out in spring wheat (2009) and
spring barley (2011 and 2012) at the Experimental Station in Winna
Gora, western Poland (E: 17ꢀ260, N: 52ꢀ120). Cereals were cultivated
according to the local agricultural practice. Plot size was 16.5 m2.
The experimental design was a randomized block with four repli-
cations. The water solutions of the tested herbicides were applied
at the end of tillering (BBCH 30) using a small plot spraying
equipment with XR 11003 flat-fan nozzles with a water volume of
200 L haꢁ1 and an operating pressure of 0.3 MPa. The standard
products were the herbicide containing [DMA][2,4-D] (Aminopielik
Standard 600 SLd600 g 2,4-D per 1 L) and plant growth regulator
containing chlormequat chloridedCCC (Antywylegacz Plynny 725
SLd725 g CCC per 1 L). The doses used in the experiments were
showed in the Tables with results.
Weed control was evaluated visually 4 weeks after herbicide
application using a scale of 0 (no control) to 100% (complete weed
destruction). In spring barley the reduction of weed species fresh
weight as compared to control (no sprayed plants) was measured.
In this case 4 weeks after treatments the plants were cut right to
the soil level and weighed (0.1 g accuracy). The stem lengths of 25
randomly chosen plants on each plot were measured from soil level
to the tip of ears at growth stage when grains reached final size
(scale BBCH 77).
Acknowledgements
This work was supported by grant No. N N310 784040 and No. N
N209 754840.
References and notes
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4.7. Surface activity
Surface tension measurements were carried out by the use of
a DSA 100 analyzer (Kruss, Germany, accuracyþ0.01 mN mꢁ1), at
€
25 ꢀC. The surface tension was determined using the shape drop
method. Basically, the principle of this method is to form an axi-
symmetric drop at the tip of a needle of a syringe. The image of the
drop (3 mL) is taken from a CCD camera and digitized. The surface
tension (g in mN mꢁ1) is calculated by analyzing the profile of the
drop according to the Laplace equation. Temperature was
Please cite this article in press as: Pernak, J.; et al., Tetrahedron (2013), http://dx.doi.org/10.1016/j.tet.2013.03.097