Note: Descriptions are shown in the official language in which they were submitted.
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Methomvl Solvent Systems
by E. Thomas Marquis and Howard M. Stridde
Cross References to Related Applications
This application claims the benefit of U.S. Provisional Application No.
601073,988 filed February 6, 1998, which is currently still pending.
BackEround Information
1o This invention relates to the preparation and use of solutions containing
dissolved
insecticidal compounds for which the solubility of the insecticide in the
solution is a
limiting factor of the concentration at which stable solutions may be stored.
More
particularly, it relates to the transportation, storage, and use of solutions
containing
methomyl, using an alkylene carbonate in combination with at least one other
oxygen-
15 bearing organic molecule as components of liquid-phase solutions that
contain dissolved
methomyl.
Methomyl is the methyl ester of N-[(methylcarbamoyl)oxy]thioacetimidic acid.
This compound has found widespread use as an insecticide since the early
1970's.
Although being a very effective insecticide of relatively low toxicity, the
tendency of the
2o material to crystallize out of its solutions at low temperatures is widely
known to be a
nuisance to personnel involved in the storage, transportation, and use of its
.solutions.
Since it is convenient to provide agriculturally-active compounds dissolved in
suitable
solvent for later dilution in the field, the tendency of a given material to
crystallize out of
a concentrated solution is a limiting factor of the effective concentration at
which
25 solutions of the material may be prepared for commercial transport and
sale. In the case
of methomyl, inflated amounts of solution relative to other water-emulsifyable
formulations have been found necessary when proceeding according to prior art
methods
for preparing solutions of methomyl. This has meant that proportionately-
inflated'
amounts of solvent or other inert ingredients must be dispersed along with the
active
3o methomyl in a given insecticidal application.
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Owing to increasingly stringent controls on permissible solvent releases to
the
environment by the US EPA and analogous state-level organizations, high levels
of
solvent release simultaneous to insecticide application are becoming less
tolerable. In
addition, an inherent part of the costs associated with methomyl
transportation are
directly attributable to the excess solvent required. There is little doubt
that if a new
solvent system capable of dissolving larger amounts of methomyl and preventing
its low
temperature crystallization were available, widespread acceptance by industry
would be
inevitable. The compositions disclosed herein provide methomyl solutions of
higher
concentrations over prior art, possessive of a decreased tendency for
dissolved methomyl
l0 to crystallize out when the solution is subjected to temperatures near zero
degrees
centigrade for prolonged periods of time.
Summary of the Invention
This invention provides a single-phase, liquid methomyl concentrate
composition
15 comprising methornyl and certain organic solvents that can be diluted with
water for
spray tank use by an end user. A solvent combination according to the
invention useful
for dissolving methomyl and maintaining it at high concentrations in solution
over a wide
temperature range comprises a first component that contains at least one
alkylene
carbonate, and a second component (or co-solvent) that includes least one
organic oxygen
2o compound. The alkylene carbonate component may be selected from propylene
and
butylene carbonate, and the organic oxygen compound may be selected from
classes of
compounds that may include alcohols, glycols, ketones, ethers, lactones and
heterocyclic
compounds in which a member of the ring structure contains a keto function,
such as N-
methyl pyrrolidone.
25 According to the invention, the combination of alkylene carbonate,
methomyl, and
other components) may contain a high concentration of methomyl, preferably 20
% by
weight or more with respect to the total weight of the finished solution, is
not chemically
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reactive under conditions normally encountered in storage of methomyl
solutions, is
easily and quickly dilutable with water to the desired spray concentration,
and the applied
spray does not injure the crops targeted. Additionally, the solution retains a
high degree
of insecticidal qualities, does not have a tendency to separate into separate
liquid layers in
storage, and the ingredients possess low hazard potential during and after
spray
applications as defined by existing local and national environmental
regulations.
Description of the Invention
The present invention is directed at solutions comprising methomyl dissolved
in a
1 o solution combination that comprises a first component containing at least
one alkylene
carbonate and a second component that includes an organic oxygen compound.
According to this invention, a co-solvent (organic oxygen compound) is
combined
with an alkylene carbonate, for example propylene carbonate, to provide a
solvent
combination capable of dissolving high quantities of methomyl, while retarding
the
15 tendency of the methomyl to crystallize out of solution at temperatures as
low as 0
degrees Centigrade when the methomyl concentration is as high as 30 %. The co-
solvent
may be selected from various glycols and ethers thereof; ketones; alcohols;
lactones; and
alkylene carbonates.
To produce a suitable solvent combination according to the invention, one
mixes
20 the components of the solvent combination under ambient or slightly
elevated
temperature, and agitates to produce a homogeneous solution. This typically
requires
between about 5 minutes and '/z hour of agitation, depending upon the type of
vessel in
which the mixing is conducted and the agitation employed. (When using
laboratory-scale
equipment such as a 250 ml beaker and a glass stirring rod, suitable
combination is
25 produced within one minute when vigorous stirring with a glass stirring rod
is employed).
To produce a solution of methomyl in accordance with this invention, one
preferably adds
the desired amount of methomyl to the solvent combination once the solvent
combination
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has been made homogeneous, and agitates the solvent until solution is
effected. This may
be done with or without the assistance of added heat energy, but preferably
the solution is
heated to about 45 degrees Centigrade prior to the methornyl addition, to
facilitate the
rapid dissolution thereof.
Several abbreviations are used throughout this specification to denote various
chemical species. The key to the abbreviations are:
NMP N-methyl pyrrolidone
BLO gamma-butyrolactone
DPNB dipropylene glycol, mono n-butyl
ether
TPM tripropylene glycol, monomethyl
ether
DPM dipropylene glycol, monomethyl
ether
PC Propylene Carbonate
BC Butylene Carbonate
CXN Cyclohexanone
CXL Cyclohexanol
CX Cyclohexane
In Table IV abbreviations S2, S3, etc. are used to indicate the first
component of
the solvent used in making the formulation according to the invention. These
2o designations refer to mixtures containing propylene carbonate ("PC") and
butylene
carbonate ("BC"), the relative percentages of which compositions are set forth
in table I
below. Production of the mixtures set forth in Table I consists in simply
mixing the
materials in a suitable vessel for 10 minutes at ambient temperature. Unless
otherwise
specified, all percentages in this specification are in parts by weight, based
upon the total
weight of the finished solution.
Mixture Designation% PC % BC
S2 90 10
S3 50 50
S4 10 90
.
S5 70 ~:_ 30
S6 30 70
Table I - compositions of mixtures designated S2, S3, S4, S5, and S6
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By our invention, the compositions of several formulations useful for keeping
methomyl in solution at high concentration over a wide range of temperatures
have been
discovered, the formulations of which are set forth in examples l -12 below.
In these
examples, synergistic properties of the solvent combinations are believed
responsible for
their unexpected ability to maintain methomyl in solution in which no
crystallization is
evident even after prolonged storage at 0 degrees C. The unexpectedness of the
success
in examples 1 - 12 is evidenced by the compositions of the samples in tables
III and IV in
which methomyl crystallization was evident after prolonged storage of the
solutions at the
same low temperatures. The mechanism for the synergy is not currently
understood;
1 o however, the solvent combinations provided herein are anticipated as being
useful for
providing stable solutions containing relatively high concentrations of all
normally-solid
insecticides other than methomyl, including but not limited to derivatives and
analogs of
methomyl.
ExamplePC BC TPM DPNB CXN NMP Methomyl
1 64.8 7.2 28.0
2 64.8 7.2 28.0
3 57.6 14.4 28.0
4 57.6 14.4 28.0
5 58.326.48 7.2 28.0
6 32.4 32.4 7.2 28.0
7 32.4 32.4 7.2 28.0
8 19.4445.36 7.2 28.0
9 19.4445.367.2 28.0
6.48 58.2 7.2 28.0
11 56 14.0 30.0
12 18.9 44.1 7.0 30.0
Table II - Successful solution compositions for systems retaining 28.0 and 30
methomyl dissolved at 0 degrees C with no crystallization evident after one
month.
Currently, the most preferred composition is that set forth in example 1. This
is
most preferred because of the low toxicity of the DPNB, its high flash point,
its odorless
character, and its relatively low cost.
Compositions for which methomyl crystallization was evident after 30 days
aging
at 0 degrees C are set forth in tables III and IV below:
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ExamplePC BLO NMP DPM TPM DPNB CXN CXL Methomyl
No.
13 70 30.0
14 63 7.0 30.0
IS 63 7.0 30.0
16 63 7.0 30.0
17 63 7.0 30.0
18 63 7.0 30.0
19 63 7.0 30.0
20 56 14.0 30.0
21 56 14.0 30.0
22 56 14.0 30.0
23 56 14.0 30.0
24 56 14.0 30.0
25 56 14.0 30.0
Table III - Failing solution compositions for which methomyl crystallization
is evident after storage at 0 degrees C for 30 days.
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Examples2 ss ~ SS S6 BLO NMP DPM TPM DPNB C7:L Methomvl
No. S4
26 70 30.0
27 70 30.0
2g 70 30.0
29 70 30.0
30 70 30.0
31 63 7 30.0
32 63 7 30.0
33 63 7 30.0
34 63 7 30.0
35 63 7 30.0
36 63 7 30.0
37 63 7 30.0
38 63 7 30.0
39 63 ? 30.U
40 63 7 30.0
41 63 7 30.0
42 63 7 30.0
43 63 7 30.0
44 63 7 30.0
45 63 7 30.0
46 63 7 30.0
-.
47 63 7 30.0
48 63 7 30.0
49 63 7 30.0
50 63 7 30.0
51 63 7 30.0
52 63 7 - 30.0
53 63 7 30.0
54 63 7 30.0
55 63 7 30.0
56 63 7 30.0
57 63 7 30.0
58 63 7 30.0
59 63 7 30.0
60 63 7 30.0
Table IV - More examples of systems that displayed methomyl
crystallizing out when stored at 0 degrees C for 30 days.
The solutions described by the formulae set forth in examples 1 through 12
above
are suitable compositions of matter for admixture with water either alone or
in
combination with various emulsifying agents known to those skilled in the art
as being
useful for producing final emulsions which may be applied to various crops
using spray
'~85i1't~'!~'f E~~'~
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or other well-known techniques. These solutions are suitable for use (after
appropriate
dilution) in the control of pestiferous insects belonging to such orders as
Lepidoptera,
Homoptera, Hemiptera, Diptera, and Coleoptera, including but not limited to
cotton
bollworm, tobacco budworm, southern armyworm, soybean looper, beet armyworm,
cotton aphid, tarnished plant bug, and white flies. The insects are controlled
by applying
the solutions to the area to be protected, or to the pests themselves. In the
case of
agricultural applications, a dispersion or emulsion of the solvents are
applied to the
foliage to be protected. Effective amounts depend upon the species to be
controlled, its
life stage, its size and location, the amount of rainfall, time of year,
moisture, temperature.
type of application and other variables, all of which are known or readily
determinable by
those of ordinary skill in the art. Generally, dosage levels of between about
0.0625 to 4
kilograms per hectare of methomyl are required, with levels between about
0.125 to 2.0
kilograms per hectare being sufficient in most instances.
The solutions of this invention may be combined with surfactants, wetting
agents,
dispersing agents, antifoam agents and the like, as such admixtures are
typical in the
agricultural field and are well-known to methomyl users having ordinary skill.
Additionally, the formulations herein set forth may be mixed with fungicides,
bacteriocides, acaricides, nematicides, or other biologically active
compounds. Suitable
surfactants are known to those skilled in the art, and include without
limitation sodium
lauryl sulfate and its functional anionic, non-ionic and cationic equivalents,
as such are
well-known to artisans of ordinary skill.
As used in this specification and the appended claims, the term "concentration
of
methomyl" relates to the amount of methomyl that is dissloved in either a neat
or a mixed
liquid solvent combination. Methomyl is known to be soluble in various organic
solvents
to varying degrees; however, most solvents in which it has appreciable
solubility are not
approved for spray use on crops or foliage. Of those solvents that are
acceptable for
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s
spray use, the solubility of methomyl therein is not as high as is desired,
and is typically
on the order of only about 20 % by weight. As used in this specification and
the
appended claims, the term "high concentrations of methomyl" means a
concentration of
methomyl in solution of at least 20 % by weight based upon the total weight of
the
solution. According to this invention, stable solutions having methomyl
concentrations as
high as 30 % may be prepared, which pen~nits one-and-a-half times as much
active
chemical to be transported per given volume over prior art solutions
containing only 20%
methomyl.
As used throughout this specification and the appended claims, the term
"organic
i o oxygen compound" means a chemical compound whose molecular structure
includes
carbon atoms and oxygen atoms, including compounds belonging to the classes:
alcohols,
ethers, glycols, polyalkylene glycols, ethers of glycols, ethers of
polyalkylene glycols,
ketones, pyrrolidones, and lactones, including substituted analogs or
derivatives of
compounds within these classes, whether the substituents are straight chain,
branched,
aromatic, or aliphatic. Although specific members of these classes of
compounds are
illustrated herein as being employable for achievement of the results desired
with respect
to the spirit of this invention, other members of each class of these
compounds are useful
as functional equivalents in such regard, when employed at effective amounts
readily
determinable by an artisan of ordinary skill without undue experimentation, in
accordance
with the teachings herein.
A typical means by which the instant invention may be employed in the
destruction of unwanted pests is by diluting a composition of any one of
examples 1
through 12 with a desired amount of water, either alone or with additional
diluents, which
may include but are not limited to dyes, oils, fungicides, bacteriocides,
acaricides,.
nematicides, or fungicides, to produce an emulsion of desired methomyl
concentration.
The emulsion is sprayed through a conventional atomizer, including as an
example
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illustrative and not delimitive hereof, a DeVilbiss No. 152 atomizing nozzle
available
from the DeVilbiss Company, Somerset, Pennsylvania 15501 using atomizing air
at 12
p.s.i. onto a cotton, corn, tomato, or other food-bearing plant. Non-food-
bearing plants,
such as tobacco, may also be the target.
5 Although this invention has been shown and described with respect to certain
preferred embodiments, it is obvious that equivalent alterations and
modifications will
occur to others skilled in the art upon reading and understanding of this
specification and
the appended claims. The present invention includes all such modifications and
alterations, and is limited only by the scope of the claims which follow.
io
