Synthesis of carbonated fatty methyl esters using supercritical carbon dioxide

Article abstract of DOI:10.1021/jf0516179

The two-step syntheses of the cyclic carbonates carbonated methyl oleate (CMO) and carbonated methyl linoleate (CML) are reported. First, synthesis of epoxides through well-precedented chemical reactions of unsaturated fatty methyl esters with hydrogen peroxide and formic acid was accomplished. Next, a carbonation reaction with a simple tetrabutylammonium bromide catalyst was performed, allowing the direct incorporation of carbon dioxide into the oleochemical. These syntheses avoid the use of the environmentally unfriendly phosgene. The carbonated products are characterized by IR, ¹H NMR, and ¹³C NMR spectroscopy and studied by thermogravimetric analysis (TGA). Also reported is the synthesis of a similar cyclic carbonate from the commercially available 2-ethylhexyl epoxy soyate. These carbonates show properties that may make them useful as petrochemical replacements or as biobased industrial product precursors.

Full text of DOI:10.1021/jf0516179

9608 J. Agric. Food Chem. 2005, 53, 9608−9614
Synthesis of Carbonated Fatty Methyl Esters Using
Supercritical Carbon Dioxide
KENNETH M. DOLL* AND SEVIM Z. ERHAN
Food and Industrial Oil Research Unit, National Center for Agricultural Utilization Research,
Agricultural Research Service, U.S. Department of Agriculture, 1815 North University Street,
Peoria, Illinois 61604
The two-step syntheses of the cyclic carbonates carbonated methyl oleate (CMO) and carbonated
methyl linoleate (CML) are reported. First, synthesis of epoxides through well-precedented chemical
reactions of unsaturated fatty methyl esters with hydrogen peroxide and formic acid was accomplished.
Next, a carbonation reaction with a simple tetrabutylammonium bromide catalyst was performed,
allowing the direct incorporation of carbon dioxide into the oleochemical. These syntheses avoid the
use of the environmentally unfriendly phosgene. The carbonated products are characterized by IR,
1H NMR, and 13C NMR spectroscopy and studied by thermogravimetric analysis (TGA). Also reported
is the synthesis of a similar cyclic carbonate from the commercially available 2-ethylhexyl epoxy
soyate. These carbonates show properties that may make them useful as petrochemical replacements
or as biobased industrial product precursors.
KEYWORDS: Supercritical carbon dioxide; cyclic carbonate; methyl 8-(2-oxo-5-octyl-1,3-dioxolan-4-yl)-
octanoate; carbonated methyl oleate; carbonated methyl linoleate
INTRODUCTION
Scheme 1. Epoxidation of Methyl Oleate Using Performic Acid
Followed by the Carbonation Using Tetrabutylammonium Bromide
Catalyst
With the price of crude oil near ∼$70/barrel, the need to use
biobased resources is of high priority (1, 2). A recent area of
interest has been in the synthesis of carbonates from agricul-
turally derived oleochemicals (3, 4). These carbonates have been
used as emollients (3), fuel additives (5, 6), polymer precursors
a
(7, 8), lubricants, or chemical solvents (3, 4). One particular
area of interest has been in the synthesis of the cyclic carbonates
of fatty esters, which have shown possible use as plasticizers
(9, 10) or in biomedical applications (11). Both of these older
synthetic methods required the use of phosgene, as well as
organic solvents. Recently, Kenar and Tevis reported a novel
synthesis of the cyclic carbonate methyl 8-(2-oxo-5-octyl-1,3-
dioxolan-4-yl)octanoate (12) (carbonated methyl oleate, CMO)
as well as the 2-ethylhexyl derivative from the corresponding
chlorohydroxy materials. Using these syntheses, they were able
to avoid the use of phosgene and build the cyclic system using
ammonium hydrogen carbonate.
However, we decided to explore an alternative route (Scheme
) to the synthesis of CMO through a well-precedented epoxide
a
1
If the epoxidation reaction is not monitored directly, a dihydroxy stearate
impurity may be produced. Epoxidized methyl linoleate (EML) and carbonated
methyl linoleate (CML) are also shown.
route. Using this route, we used supercritical carbon dioxide
directly with a catalytic amount of tetrabutylammonium bro-
mide. A similar reaction has been used for the carbonation of
soybean oil under both atmospheric (7, 8) and supercritical
carbon dioxide conditions.
of fatty materials have been preformed in supercritical CO2
including polymerizations (16, 17), hydrogenations (18, 19), and
esterifications (20, 21). In some of these systems, the super-
critical CO2 system has a higher reaction rate. For example, a
transesterification of myristic acid shows 37% conversion in
CO2 versus only 4% in the corresponding acetonitrile system
(21) at similar reaction times. The solubility parameters of fatty
Supercritical CO2 has been used for over 20 years in the
extraction of oils from agricultural products (13-15). Reactions
*
Corresponding author (e-mail dollkm@ncaur.usda.gov).
1
0.1021/jf0516179 This article not subject to U.S. Copyright. Published 2005 by the American Chemical Society
Published on Web 10/29/2005

Synthesis of Carbonated Fatty Methyl Esters
J. Agric. Food Chem., Vol. 53, No. 24, 2005 9609
materials in supercritical CO2 have been well studied (20). Esters
are somewhat soluble in supercritical CO2, with the trend of
increased solubility with increasing fatty chain length (22). The
solubility of hydrocarbons (23-25) and fatty esters (26) has
also been shown to increase at higher reaction temperatures and
pressures.
Our reaction is also environmentally advantageous because
our system uses CO2 directly. The carbonation reaction is
completely atom efficient, following the second principle of
green chemistry (27, 28). Without the use of the supercritical
system, it may not be possible to get a satisfactory reaction rate.
The supercritical CO2 system employed herein is quite simple,
requiring only a high-pressure reactor and a fairly inexpensive
syringe pump.
We used the previously reported synthesis of epoxidized
methyl oleate (EMO) (29) as a starting point to the synthesis
of our desired product, carbonated methyl oleate (CMO).
Additionally, we also report the synthesis of carbonated methyl
linoleate (CML) and the carbonation of a commercially available
epoxidized ester material using similar procedures.
Figure 1. Reaction progress of the epoxidation reaction of methyl oleate
(b) to epoxidized methyl oleate (EMO,
9). At longer reaction times, some
dihydroxy stearate ( ) can be detected.
2
MATERIALS AND METHODS
Materials. Methyl oleate (Sigma-Aldrich, St. Louis, MO), Tech 70%
(Nu Check Prep, Elsyian, MN, >99%), methyl linoleate (Nu Check
Prep, >99%), 2-ethylhexyl epoxy soyate (Arkema, Philadelphia, PA;
VikoFlex 4050, 5.6% oxirane content), hydrogen peroxide (Sigma-
Aldrich, ACS Reagent, 30% solution); formic acid (Sigma-Aldrich,
9
6%, ACS Reagent), hexanes (Sigma-Aldrich,>95%, HPLC grade),
NaCl (Fisher, Fair Lawn, NJ, ACS Reagent), NaHCO (Fisher, ACS
Reagent), NaSO (Sigma-Aldrich 99+%, ACS Reagent), tetrabutylam-
3
4
monium bromide (Sigma-Aldrich 99%), and carbon dioxide (AirGas,
Wilmington, DE; 50 lb siphon type high-pressure cylinder, UN1013)
were used as received.
Figure 2. GC-FID trace of the epoxidation reaction of methyl linoleate at
h. In this trace it is possible to observe starting material ( 10.3 min),
singly epoxidized material ( 14.0 min), and fully epoxidized methyl
linoleate (EML; 16.6 min).
Instrumentation and Equipment. The reactor employed was a Parr
3
∼
(Moline, IL) 4560 mini benchtop unit equipped with a Parr 4843
∼
controller and thermocouple. For the reported experiments, a 300 mL
reactor body equipped with quartz viewing windows was used.
FTIR spectra of the starting material and products were recorded
on a Thermonicolet (Madison, WI) Nexus 470 FTIR with a Smart ARK
accessory containing a 45° ZeSe trough. Data were collected and
processed on a Windows 2000 equipped Dell Optiplex GX260 Pentium
∼
mL round-bottom flask equipped with an overhead stirrer. Next, 102 g
2.2 mol) of formic acid was slowly added, forming a layered mixture.
(
The reaction flask is cooled in an ice bath, and 163 g of 30% hydrogen
peroxide (1.44 mol) is added over ∼5 min while the temperature of
the solution is monitored. The peroxide is added slowly enough such
that the temperature of the solution does not exceed 18.4 °C, but rapidly
enough to keep the reaction solution from solidifying. Gas bubbles are
evident as the hydrogen peroxide is added. The reaction is allowed to
proceed at room temperature, and aliquots are taken and analyzed by
GC (Figure 3). The product is purified using a separatory funnel by
dissolving the material in ∼200 mL of hexanes and then discarding
the aqueous/formic acid layer. Then, ∼200 mL of saturated sodium
bicarbonate solution is shaken with the hexane layer and removed. This
is repeated until the pH of the solution is >7 (three times). Next, ∼400
mL of saturated sodium chloride solution is added to the hexane layer,
shaken, and removed with a separatory funnel three times. The hexane
layer is dried over ∼28 g of anhydrous sodium sulfate and filtered
through a fritted funnel, and the hexane is removed with rotary
evaporation (∼60 °C; overnight). The product is a very slightly colored
viscous liquid that slowly became cloudy when cooled below room
temperature. The isolated yield was 221.1 g (97%). The product was
stored over molecular sieves. Product purification has also been
4
, 2.46 GHz computer running Omnic 6.2 software.
Gas chromatography was performed on a Hewlett-Packard (Love-
land, CO) 6890 GC system equipped with a 6890 series injector and
an FID detector. A Supelco SPB 30 (30 m × 320 µm) was used with
-1
a helium flow rate of 1.2 mL min . The temperature ramp used started
-
1
at 180 °C and increased to 250 °C at 5 °C min and then to 290 °C
-
1
at 15 °C min
.
NMR was performed on a Bruker (Boston, MA) Avance 500 NMR
1
13
operating at 500 MHz for H and at 125 MHz for C. Bruker Icon
NMR software was used running on an HP X1100 Pentium 4
workstation. Peaks were referenced to sodium 3-trimethylsilylpropi-
3
onate-2,2,3,3-d
4
(TSP) at 0.0000 ppm. Simulations of 1 C NMR spectra
were performed by ACD/Labs 6.00 ACD/CNMR predictor software,
running on a Gateway Pentium 4 CPU with a 2.53 GHz processor.
Freeze-drying was performed with a Labconco (Kansas City, MO)
Freezone 1. Samples were prefrozen in a dry ice/ethanol bath according
to standard laboratory procedures.
Thermogravimetric analysis (TGA) was performed on a TA (La
Canada, CA) TGA Q500. Data were collected and processed on a
Windows 2000 × 86 Family6 model 8 IBM computer with Advantage
for Q series version 1.5.0.208 Thermal Advantage release 3.2.0
software. Samples were heated under nitrogen using a heating ramp of
performed using Et O instead of hexanes, but solvent removal is more
2
difficult.
The epoxidation of methyl linoleate was performed in an analogous
manner using 200 g of starting material and yielding 221.7 g (95%) of
epoxidized material. The final product is similar in appearance to the
EMO, but tended to become cloudy more rapidly even at room
temperature.
-
1
2
.0 °C min from 25 to 350 °C.
Epoxidations. The reaction was carried out using a slightly modified
synthesis of Bunker and Wool (29). This synthesis was originally used
by Swern (30, 31) and has been refined and studied over the years
EMO: 1H NMR (500 MHz, CDCl
2.85 (t, 2, epoxide ring protons), 2.26 (t, 2, protons on carbon R to
3
) δ 3.61 (s, 3, methoxy protons),
(32-34). First, 200.0 g (0.67 mol) of methyl oleate is placed in a 500

9610 J. Agric. Food Chem., Vol. 53, No. 24, 2005
Doll and Erhan
Figure 3. FT-IR spectra of methyl oleate (bottom), epoxidized methyl oleate (EMO; middle), and carbonated methyl oleate (CMO; top). The appearance
-
1
of the bands at 827 and 840 cm in the EMO spectrum confirm epoxidation. They are not present in the CMO spectrum, but a new carbonyl band at
-
1
1
797 cm is observed.
Figure 4. FT-IR spectra of methyl linoleate (bottom), epoxidized methyl linoleate (EML; middle), and carbonated methyl linoleate (CML; top). The
-
1
-1
appearance of the bands at 823 and 840 cm in the EML spectrum, as well as the loss of the resolvable peak at 3009 cm , confirms epoxidation and
-
1
loss of unsaturated C−H signals. The epoxide peaks are not present in the CML spectrum, but a new carbonyl band at 1793 cm is observed.
+
-
carboxy), 0.85 (t, 3, end of fatty chain), urresolvable signals from δ
5.0 mol %, 5.0 wt %) tetrabutylammonium bromide (TBA Br ) was
dissolved into the oil with stirring. The reactor was closed and
1
3
1
.3-1.6; C NMR (125 MHz, CDCl
3
) δ 174 (cafbonyl carbon), 57,
(epoxide carbons), 51 (methoxy carbon signals), 14, (end carbon of
pressurized with CO
°C, causing the pressure to rise. Once the reaction temperature was
reached, the CO pressure was further increased to 1500 psi and
maintained there throughout the reaction with the necessary addition
of CO by the pressure-controlling pump. The reaction was run
overnight (∼15 h). After the reaction was complete, the reactor was
depressurized slowly to allow dissolved CO to leave the carbonated
2
to ∼500 psi. The reactor was then heated to 100
fatty chain), 20-35 (multiple signals). The spectral peaks and assign-
ments are close to computed chemical shift and in order.
2
1
EML: H NMR (500 MHz, CDCl
3
) δ 3.66 (s, 3, methoxy protons),
3
.12, 3.08, 2.98 (m, 4, epoxide ring protons), 2.30 (t, 2, protons on
2
carbon R to carboxy), 0.91 (t, 3, end of fatty chain), unresolvable signals
1
3
from δ 1.3-1.8; C NMR (125 MHz, CDCl
3
) δ 174 (carbonyl carbon)
2
5
4-57, (epoxide carbons), 51 (methoxy carbon signals), 14 (end carbon
product. The carbonated product is light brown and slightly more
viscous than the epoxy material. Isolated yield was 33.03 g (93% yield
of crude product). The product was characterized by H NMR and IR
of fatty chain), 20-35 (multiple signals). The spectral peaks and
assignments are close to computed chemical shift and in order.
Synthesis of Carbonated Fatty Esters. The EMO was heated in a
warm water bath until fluid, and 29.5 g (0.096 mol) was poured into
a 300 mL high-pressure reactor vessel. Next, ∼1.59 g (0.0049 mol,
1
spectroscopy. Carbonated methyl linoleate and carbonated vegetable
oil esters (2-ethylhexyl soyate; VikoFlex 4050) were synthesized in
+
-
an analogous manner always using 5 mol % of the TBA Br catalyst.

Synthesis of Carbonated Fatty Methyl Esters
J. Agric. Food Chem., Vol. 53, No. 24, 2005 9611
Figure 5. 1H NMR spectra of methyl linoleate (bottom), epoxidized methyl linoleate (EML; middle), and carbonated methyl linoleate (CML; top). The
appearance of the peaks 3 3.1 in the EML spectrum confirms epoxidation. The epoxide peaks are not present in the CML spectrum, but new peaks at
.5 4.9 are indicative of the presence of the cyclic carbonate.
−
4
−
Figure 6. FT-IR spectra of carbonated 2-ethylhexyl epoxy soyate. The spectrum is similar to that of other carbonated methyl esters including the large
carbonyl band at 1797 cm-1
.
+
-
The catalyst was removed from the products by a washing and
sonication process. First, 25.79 g of CMO was suspended in 20 mL of
H O and sonicated at 25 °C for 3 h. This was repeated three times.
2
The water and product layers were separated in a separatory funnel,
and the product was dried on a rotary evaporator overnight at 40 °C.
remove TBA Br catalyst by heating the sample to 190 °C and taking
advantage of a Hofmann reaction, which decomposes the catalyst to
volatile product. However, TGA of the carbonated oleates shows some
decomposition or volatilization at ∼190 °C, demonstrating that heat
purification of these carbonates is not feasible.
CMO: H NMR (500 MHz, CDCl
carbonate ring protons), 3.65 (s, 3, methoxy protons), 2.29 (t, 2, protons
+
-
1
The water layer was freeze-dried, yielding 0.351 g of white TBA Br
3
) δ 4.63-4.22 (s, 2, cyclic
1
catalyst, which was confirmed to be intact by H NMR spectroscopy.
Product losses during the purification process were minimal, at <3%,
giving an overall experimental yield of 90%. The carbonated methyl
linoleate and carbonated VikoFlex 4050 were purified in a similar
manner and in similar yield. We have recently reported a method to
on carbon R to carboxy), 0.87 (t, 3, end of fatty chain), unresolvable
signals from δ 1.2-2.2; 13C NMR (125 MHz, CDCl
) δ 174 (methoxy
3
carbonyl carbon), 154 and 154 (cyclic carbonate carbons), 79-82
(cyclic ring carbons), 51 (methoxy carbon signals), 14 (end carbon of

9612 J. Agric. Food Chem., Vol. 53, No. 24, 2005
Doll and Erhan
Figure 7. TGA of methyl oleate (solid line), epoxidized methyl oleate (EMO, dashed line), and carbonated methyl oleate (CMO, dot
−dash line). The
samples show 50% weight loss at 187, 211, and 260 C, respectively.
°
Figure 8. TGA of methyl linoleate (solid line), epoxidized methyl oleate (EML, dashed line), and carbonated methyl linoleate (CML, dot
samples show 50% weight loss at 189, 231, and 271 C, respectively.
−dash line). The
°
fatty chain), 20-35 (multiple signals). These spectral peaks agree with
the reported NMR for this compound (12), and the peaks and
(cyclic ring carbons), 66 (alkoxy carbon signals), 57 (small residual
epoxide carbons), 14 (end carbon of fatty chain), 11 (end of alkoxy
chain), 20-35 (multiple signals). The spectral peaks and assignments
are close to computed chemical shift and in order.
assignments are close to computed chemical shift and in order.
1
CML: H NMR (500 MHz, CDCl
3
) δ 4.93-4.49 (m, 4, cyclic
carbonate ring protons), 3.67 (s, 3, methoxy protons), 2.32 (t, 2, protons
on carbon R to carboxy), 0.90 (t, 3, end of fatty chain), unresolvable
RESULTS AND DISCUSSION
1
3
signals from δ 1.3-2.2; C NMR (125 MHz, CDCl ) δ 174 (carbonyl
3
carbon), 154 (cyclic carbonate carbonyl carbon), 79-82 (cyclic ring
carbons), 51 (methoxy carbon signals), 14 (end carbon of fatty chain),
The syntheses of EMO and EML were performed using the
well-precedented formic acid and hydrogen peroxide method.
Vigorous stirring with an overhead stirrer was required to keep
the layered system well mixed. The reactions were monitored
by sampling aliquots of the oil layer and analyzing them by
GC-FID. An initial amount of methyl palmitate in the starting
material was used as an internal standard. The reaction was
2
0-35 (multiple signals). The spectral peaks and assignments are close
to computed chemical shift and in order.
1
Carbonated 2-ethylhexyl methyl soyate: H NMR (500 MHz, CDCl
δ 4.95-4.52 (2H-signal, cyclic carbonate ring protons), 3.68 and 3.68
alkoxy protons), 2.91 (small residual epoxide signal <10% compared
to δ 2.32), 2.32 (2-H triplet, protons on carbon R to carboxy), 0.91
6.5-H unresolved multiplit, end of fatty chain and end of alkoxy chain),
3
)
(
>
90% complete in 10 h, when the reaction was stopped (Figure
1). In the GC chromatograms of the final data points, a small
(
1
3
urresolvable signals from δ 1.2-2.2; C NMR (125 MHz, CDCl
1
3
) δ
74 (alkoxy carbonyl carbon), 154 (cyclic carbonate carbon), 75-79
amount of 9,10-dihydroxy methyl stearate could be detected,

Synthesis of Carbonated Fatty Methyl Esters
J. Agric. Food Chem., Vol. 53, No. 24, 2005 9613
Figure 9. TGA of carbonated 2-ethylhexyl soyate. The sample shows 50% weight loss at 301 °C.
demonstrating the importance in following the reaction directly
and stopping it at the appropriate time. A kinetic plot of ln-
that we performed the epoxidation and carbonation reactions
with the highly expensive >99% pure methyl oleate as well as
the inexpensive technical grade methyl oleate of ∼70% purity,
with equal effectiveness.
(
[methyl oleate]initial/[methyl oleate]) versus time gives a pseudo-
-
1
first-order rate constant of 0.005 min , slower than that
observed in a kinetic study of a similar reaction (34) that was
stirred at 1150 rpm. This indicates that the epoxidation reaction
exhibits mass transfer rate limitations under our conditions.
The epoxidation of the linoleic acid also went as expected
and was slightly faster in the oleate case, as was observed by
Wool et al. (34). At 3 h of reaction time, it is possible to detect
the intermediate product with one epoxy group (Figure 2) as
well as the final product; however, it was not isolated.
A study of the thermal stability of the carbonates was also
warranted, especially for potential application as fuel or lubricant
additives. We performed a TGA, under nitrogen, on a sample
of each of the carbonates, and a comparative experiment was
performed for each epoxide. The TGA (Figures, 8, and 9) of
the samples shows that CMO and CML show 50% weight loss
at 251 and 271 °C, respectively. This is an improvement in high-
temperature stability compared to ordinary methyl oleate and
methyl linoleate, which show 50% weight loss at 187 and 189
The carbonation reaction (Scheme 1) proceeded as expected.
This reaction was considerably faster than the corresponding
reaction observed for epoxidized soybean oil. Overnight reac-
°
C under identical conditions. The epoxides show behavior
1
13
intermediate between the carbonate and the olefinic material.
This improved stability may allow the carbonates, and possibly
the epoxides, to be used as lubricant additives (36). All of the
carbonates are light brown materials and do not show the large
increase in viscosity that has been observed in the carbonation
of soybean oil.
tions showed complete reaction by IR, H NMR, and C NMR
spectroscopic methods. The IR spectra of the products (Figures
3
and 4) were very similar to that of carbonated soybean oil.
As the methyl oleate (Figure 3) is changed from the unsaturated
ester to the epoxide to the carbonate, corresponding spectral
-
1
changes can be observed. Bands at ∼823 and 847 cm appear
in the epoxide product and then disappear as the material forms
the carbonate. More obvious is the appearance of the second
We have performed the synthesis and characterization of
cyclic carbonates from commercially readily available ole-
ochemical products using a simple two-step reaction. Our
synthesis uses environmentally friendly supercritical CO2 as a
reactant and avoids the use of phosgene. Continuous flow of
this type of reaction has been shown to be feasible (37) and
may be necessary for commercialization. The synthesized
carbonates show higher temperature stability compared to the
corresponding methyl esters or epoxidized methyl esters. They
have potential uses as industrial lubricants or fuel additives, and
they may prove to be effective starting materials in the
development of non-isocyanate polyurethanes, polyesters, or
polycarbonate materials, derived from natural sources. Other
possibilities include use in the surfactant, personal care, and
biomedical industries.
-
1
carbonyl band (CdO stretch) at ∼1790 cm . Similar changes
in the spectra of the linoleate system (Figure 4) were observable
as well as the disappearance of a more noticeable band at 3009
-
1
cm , corresponding to the higher quantity of unsaturated cis-
configured double bonds in the methyl linoleate starting material
1
(
35). The H NMR spectra (Figure 5) of the products show
reaction progress. Peaks corresponding to the protons on the
epoxy carbons of EML can be seen at δ 2.98, 3.12, and 3.08.
They disappear upon carbonation and are replaced by new
1
3
signals at δ 4.49-4.93. A similar occurrence in the C NMR
spectra shows the change of the epoxy carbons as δ 54-57
being replaced by the cyclic carbonate ring carbons at δ 79-
8
2. The new cyclic carbonyl carbon at δ 154 is also easily
observed. The NMR spectra in the oleate system show similar
results. Our reaction methodology also works on the com-
mercially available 2-ethylhexyl epoxy soyate (VikoFlex 4050;
Arkema), which has >5.2% oxirane content. This epoxide was
carbonated in the same manner as EMO and EML and also
gave a characteristic IR spectrum (Figure 6). It is also of note
ACKNOWLEDGMENT
We acknowledge D. Knetzer for synthesis of the epoxy products
and TGA and IR characterization of the final products.

9614 J. Agric. Food Chem., Vol. 53, No. 24, 2005
Doll and Erhan
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Received for review July 6, 2005. Revised manuscript received
September 29, 2005. Accepted September 30, 2005. The use of trade,
firm, or corporation names in this publication is for the information
and convenience of the reader. Such use does not constitute an official
endorsement or approval by the U.S. Department of Agriculture or
the Agricultural Research Service of any product or service to the
exclusion of others that may be suitable.
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