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Description  |
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FIELD OF THE INVENTION
This invention relates to safened compositions comprising concentrated
sulfuric acid and a polyamide, preferably a polyamide of alpha-amino acid,
such as gelatin, and to methods of use thereof. The compositions can be
used in place of untreated sulfuric acid, for example, as herbicides and
cleaners.
INTRODUCTION
Sulfuric acid is used for many purposes in industry and agriculture. For
example, it is used as a herbicide, a drain cleaner, a pickling acid, and
a catalyst for many organic reactions. Concentrated sulfuric acid is very
hazardous to workers, producing rapid skin burns. It also chars
hydroxyl-rich compounds such as cellulose and carbohydrates on contact by
abstracting water from the molecules of the compounds.
Adducts of sulfuric acid with urea, biuret, and triuret, and method of
using such adducts, have been disclosed. See U.S. Pat. Nos. 4,722,986,
4,673,522, 4,664,717, 4,402,852, 4,404,116, 4,445,925, 4,447,253, and
4,397,675, the disclosures of which are incorporated by reference herein
in their entirety. Such adducts are much less corrosive and hazardous than
sulfuric acid of equivalent acid concentration, yet they retain
essentially all the acidity of the sulfuric acid. In effect, the activity
of the sulfuric acid is moderated or safened without neutralization of the
acid.
SUMMARY OF THE INVENTION
It has now been found that safened compositions in which the activity of
concentrated solutions of sulfuric acid is moderated can be prepared by
dissolving therein therein a polyamide or mixtures thereof, preferably a
polyamide of an alpha-amino acid or mixtures thereof, most preferably
gelatin.
The compositions are useful as broad spectrum herbicides and as cleaners in
applications where sulfuric acid can be used. They are also capable of
dissolving cellulosic materials without charring, and are thus useful for
treating agricultural products, e.g., for scarifying seeds, delinting
cotton seeds, softening wood pulp, and converting or softening cellulosic
materials to a form suitable for incorporation into animal feeds. The
polyamide itself provides a beneficial source of nitrogen for animal feeds
and for soil treated with herbicides of the invention.
DETAILED DESCRIPTION OF THE INVENTION
Compositions of this invention are made by simply dissolving a polyamide in
sulfuric acid. Usually, and most preferably, standard commercial
concentrated sulfuric acid, i.e., about 98 weight percent, is used.
Throughout the specification and the claims, the term "concentrated
sulfuric acid" shall mean such standard commercial concentrated sulfuric
acid of about 98 weight percent concentration. More concentrated sulfuric
acid, such as anhydrous sulfuric acid, and even oleum, a solution of
sulfur trioxide in sulfuric acid, can be used. Surprisingly, the
polyamide, e.g., gelatin, dissolves in concentrated sulfuric acid
smoothly, without charring, to produce a colored, viscous, but clear
solution.
An polyamide that is soluble in concentrated sulfuric acid, preferably at
ambient temperature, can be used with benefit in the practice of this
invention. The polyamide can be substituted with groups stable in sulfuric
acid, such as alkoxy, hydroxy, and halogen. The nature of any substituents
present is unimportant for the purpose of this invention so long as the
substituents do not react so adversely with sulfuric acid as to render the
composition useless for its intended purpose. For example, some
degradation of the polyamide may be acceptable in a drain cleaner, but
when the compositions are to be used as herbicides, the polyamides
preferably have only substituents which do not react with concentrated
sulfuric acid or, more preferably, are unsubstituted.
Suitable polyamides can be prepared from polyfunctional compounds or
mixtures thereof comprising amino groups and carboxylic acid groups, such
as polyamines, polycarboxylic acids, and amino acids, and by
polymerization of lactams such as caprolactam and 2-pyrrolidone.
Difunctional compounds, e.g., diamines, dicarboxylic acids, and amino
acids having one amino group and one carboxylic acid group per molecule,
are preferred because they form linear polyamides, i.e., polyamides having
little or no crosslinking. Linear polyamides are preferred, since
crosslinking can diminish the solubility of the polyamide. Suitable
polyamides and methods of making suitable polyamides are well known. See,
for example, Kirk-Othmer Encyclopedia of Chemical Technology, 3d Ed. (New
York: John Wiley & Sons), Vol. 18, pp. 328-371, the disclosure of which is
incorporated herein by reference in its entirety. Many suitable polyamides
are commercially available, such as the large family of polyamides known
as nylons, which are reaction products of diamines and dicarboxylic acids.
Aside from solubility in sulfuric acid, the most important property of the
polyamide used in the practice of this invention is the weight percentage
of amido nitrogen in the polyamide. Preferably, the amido nitrogen
constitutes at least about 5 weight percent, more preferably at least
about 10 percent, even more preferably at least about 15 percent, and most
preferably at least about 20 percent of the total weight of polyamide.
About the highest possible percentage of amido nitrogen, 28 percent, would
occur in a polyamide made from diaminomethane and oxalic acid. Approaching
that level is polyglycine, which has a repeating unit of the formula
##STR1##
This unit has a total molecular weight of 57. The amido nitrogen content
is thus (14/57).times.100=24.6 weight percent.
Polyamides of alpha-amino carboxylic acids (sometimes called "amino acids"
herein) and mixtures of such acids are preferred. Alpha-amino acids can be
represented by the formula
##STR2##
wherein R.sub.1, R.sub.2, and R.sub.3 independently represent substituents
which do not react so adversely with concentrated sulfuric acid as to
render the composition unfit for its intended use. Preferably, the
substituents are substantially inert to concentrated sulfuric acid, at
least at ambient temperature, i.e., below about 90.degree. F. (32.degree.
C.). The combined weight of the three substituents is typically no more
than about 226 (amido N content at least about 5%), preferably no more
than about 86 (amido N content at least about 10%), and more preferably no
more than about 16 (amido N content at least about 20%). When polyamides
of mixtures of amino acids are used, the combined weight of the three
substituents refers to the average combined weight thereof in the
polyamide.
R.sub.1, R.sub.2, and R.sub.3 independently are preferably hydrogen or
alkyl groups having up to about 16 carbon atoms, preferably no more than
about 8 carbon atoms, more preferably no more than about 2 carbon atoms.
Even more preferably, one of R.sub.1, R.sub.2, and R.sub.3 is a methyl
group, usually R.sub.2 or R.sub.3, and the other two are hydrogen. Most
preferably, all three are hydrogen.
Proteins constitute a large class of naturally occurring polyamides of
alpha-amino acids, typically comprising mixtures of many different amino
acids. Compositions of the invention which need not be especially pure,
for example a drain cleaner, may be made by dissolving naturally occurring
proteins or protein containing materials, such as soy protein, leather, or
animal by-products, in concentrated sulfuric acid.
Any kind or grade of gelatin can be used in preparing compositions of the
invention. Gelatin is commercially available in various grades prepared
from various starting materials. Properties and preparation of gelatin are
described in the technical literature, for example, Kirk-Othmer
Encyclopedia of Chemical Technology, 3d Ed. (New York: John Wiley & Sons),
Vol. 11, pp. 711-719, the disclosure of which is incorporated herein by
reference in its entirety. Gelatin contains a substantial proportion of
the amino acid glycine, but usually also contains other amino acids as
well, the type and distribution thereof being influenced by the source
materials from which the gelatin is derived. Commercial gelatin typically
contains between about 26.4 and about 30.5 weight percent glycine, between
about 14.8 and about 18 percent proline, and between about 13.3 and about
14.5 percent glutamic acid. In general, any form of gelatin is
satisfactory for preparing compositions to be used as herbicides and heavy
cleaners. More refined grades of gelatin, e.g., food grade gelatin, may be
used where a composition of higher purity is desired. There are two
principal types of gelatin, both of which are suitable for use in the
practice of this invention: Type A, produced by acid hydrolysis of
collagen; and Type B, produced by alkaline hydrolysis of collagen. The
collagen is obtained from a variety of animal by-products, mainly bones
and hides.
Gelatin has the unusual property of undergoing a reversible gel to sol
transition in aqueous solution, making it especially useful for preparing
sulfuric acid compositions of high viscosity that can adhere to substrates
without running or sagging.
Other hydrolysates of collagen include animal glue and liquid protein.
These differ from gelatin in that they have lower average molecular
weights and do not undergo the gel to sol transformation. They are useful
for preparing compositions of the invention which need not have the
highest viscosity or gel-forming properties, but which display the desired
moderated acid activity.
Compositions of the invention can be made simply by dissolving the
polyamide, e.g., gelatin, directly in sulfuric acid. Usually, aqueous
sulfuric acid having an initial concentration of at least about 50 weight
percent is used. Preferably, the sulfuric acid has an initial
concentration of at least about 75 percent, and more preferably at least
about 90 percent. Most preferred is concentrated sulfuric acid, i.e.,
sulfuric acid having an initial concentration of at least about 98 weight
percent, such as ordinary commercial concentrated sulfuric acid. Ambient
temperatures, e.g., between about 10.degree. and 30.degree. C., are
usually satisfactory, although higher temperatures can be used to speed
the process. Moderate agitation such as stirring is useful.
Stable surfactants can be included in the compositions. Suitable
surfactants are described in U.S. Pat. No. 4,722,986, from column 8, line
66 through column 9, line 68. Briefly, classes of stable surfactants
include nonionics such as the alkylphenol polyethylene oxides, anionics
such as the long chain alkyl sulfates, and cationics such as
1-hydroxyethyl-2-heptadecenyl gloxalidin. Of these, the polyethylene oxide
nonionic surfactants are particularly preferred.
The surfactant concentration is preferably sufficient to increase the
ability of the sulfuric acid/polyamide compositions to wet the material to
be treated. Even very minor surfactant concentrations increase the wetting
ability of the compositions to some extent. Surfactant concentration will
usually be at least about 0.05, generally at least about 0.1, and
preferably at least about 0.2 weight percent of the solution as it is
employed in the methods of this invention. Surfactant concentrations of
about 0.2 to about 1 weight percent are adequate in most applications.
The compositions of the invention can be used full strength, or they can be
diluted before use, usually with water. Diluted compositions typically
comprise from about 5 weight percent to about 95 weight percent added
water. The degree of dilution is usually chosen to suit a particular use
of the composition.
When the compositions are used as herbicides, they are applied to plants,
preferably to the foliage thereof, in a sufficient quantity and
concentration to kill the plants, or at least to retard or stop the growth
or reproduction thereof. Herbicidal compositions typically have an
equivalent sulfuric acid concentration of at least about 10 weight
percent, preferably at least about 20 percent, and more preferably at
least about 40 percent; and a polyamide concentration of at least about 2
weight percent, preferably at least about 5 percent, and more preferably
at least about 10 percent. Such compositions are typically applied at the
rate of at least about 5 gallons per acre (47 liters per hectare),
preferably at least about 10 gallons per acre (93 liters per hectare),
more preferably at least about 20 gallons per acre (187 liters per
hectare). Optimum application rates depend upon many factors and must
necessarily be worked out on a case by case basis.
Compositions suitable for heavy cleaning operations, e.g., drain cleaning
and rust removal, usually have equivalent sulfuric acid concentration of
at least about 5 weight percent, preferably at least about 10 percent, and
more preferably at least about 20 percent; a polyamide content of at least
about 1 weight percent, preferably at least about 2 percent, and more
preferably at least about 5 percent; and a water content of at least about
1 weight percent, preferably at least about 10 percent, and more
preferably at least about 20 percent. The water content of these
compositions assists in the cleaning function.
Compositions suitable for treating cellulosic materials, e.g., for
delinting cotton seeds or softening animal fodder, usually have an
equivalent sulfuric acid concentration of at least about 5 weight percent
sulfuric acid, preferably at least about 10 percent, and more preferably
at least about 20 percent; a polyamide content of at least about 1 weight
percent polyamide, preferably at least about 2 percent, and more
preferably at least about 5 percent; and a water content of at least about
1 weight percent, preferably at least about 5 percent, and more preferably
at least about 10 percent.
Surprisingly, as demonstrated in Example 3, compositions of the invention
consisting essentially of concentrated sulfuric acid and a polyamide,
i.e., gelatin, are capable of dissolving cellulose without charring. The
addition of a small proportion of water to the composition further
increases the solubility of cellulose therein. Thus for the dissolution of
cellulosic materials, suitable compositions comprise between about 50 and
78 weight percent H.sub.2 SO.sub.4, preferably between about 55 and 65
percent; between about 5 and about 30 weight percent gelatin, preferably
between about 10 and about 25 percent gelatin; and between about 0.5 and
about 20 weight percent water, preferably between about 5 and about 15
percent water. In these compositions, the solubility of cellulose therein
increases with increasing water content within the preferred proportions.
However, excessive dilution of the compositions would diminish the
solubility of cellulose therein.
The following examples are intended to illustrate particular embodiments of
the invention. The examples are not intended in any way to limit the
invention, the scope of which is defined in the appended claims.
EXAMPLE 1
Sufficient gelatin was dissolved in 98 percent sulfuric acid to produce a
deep red to brown, viscous solution containing 20 weight percent gelatin.
The gelatin dissolved smoothly, without charring.
An 80 weight percent aqueous solution of sulfuric acid causes a burning
sensation almost immediately when spread on the tender skin of the
forearm. However, when the 80:20 sulfuric acid:gelatin solution is applied
to the inner forearm, it produces a burning sensation only after about 1
minute of contact. Thus, the moderated activity and improved safety of the
compositions of this invention is evident.
EXAMPLE 2
A solution of gelatin in sulfuric acid was prepared containing 39 weight
percent sulfuric acid, 36 percent equivalent glycine (the gelatin regarded
as 100% glycine, molecular weight 89), and 25 percent water based on the
final formulation.
EXAMPLE 3
About 3.8 grams of cotton dissolved without charring in about 36 grams of a
20 weight percent solution of gelatin in concentrated (98 weight percent)
sulfuric acid. About 10 grams of water was added to the resulting
solution, enabling an additional 3.4 grams of cotton to be dissolved
therein. This demonstrates the utility of these compositions for the
delinting of cotton seeds.
While particular embodiments of the invention have been described and
illustrated herein, it will be understood that the invention is not
limited thereto, since many obvious modifications can be made. This
invention is intended to include any such modifications as will fall
within the scope and equivalency of the appended claims.
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