U.S. patent number RE28,809 [Application Number 05/542,929] was granted by the patent office on 1976-05-11 for preparation of starch esters.
This patent grant is currently assigned to National Starch and Chemical Corporation. Invention is credited to Martin M. Tessler.
United States Patent |
RE28,809 |
Tessler |
May 11, 1976 |
Preparation of starch esters
Abstract
Aqueous slurries or dispersions of starch are reacted with
imadazolides of carboxylic or sulfonic acids to yield starch ester
derivatives. These starch products can also be prepared in
non-aqueous solvents or by a dry reaction process.
Inventors: |
Tessler; Martin M. (Edison,
NJ) |
Assignee: |
National Starch and Chemical
Corporation (Bridgewater, NJ)
|
Family
ID: |
26853266 |
Appl.
No.: |
05/542,929 |
Filed: |
January 22, 1975 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
156524 |
Jun 24, 1971 |
03720663 |
Mar 13, 1973 |
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Current U.S.
Class: |
536/110; 428/535;
536/48; 536/103; 536/106; 536/109; 442/108 |
Current CPC
Class: |
C08B
31/02 (20130101); C08B 31/06 (20130101); Y10T
442/2402 (20150401); Y10T 428/31982 (20150401) |
Current International
Class: |
C08B
31/00 (20060101); C08B 31/02 (20060101); C08B
31/06 (20060101); C08B 031/02 () |
Field of
Search: |
;260/233.5,233.3A,233.3R,213,214 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Whistler et al., "Methods in Carbohydrate Chemistry," Vol. IV, pp.
286-288, Academic Press, N.Y., 1964. .
Whistler et al., "Journal of Organic Chemistry," Vol. 26, pp.
4600-4605, Nov. 1961..
|
Primary Examiner: Marquis; Melvyn I.
Claims
I claim:
1. A process for preparing esters of a starch having free reactive
hydroxyl groups comprising the steps of:
a. reacting said starch with an .[.imidazolide-acid reaction
product.]. .Iadd.imidazolide of carboxylic or sulfonic acid
.Iaddend.selected from the .[.group.]. .Iadd.groups
.Iaddend.consisting of ##EQU3## and triimidazolides of
tricarboxylic acids, wherein R.sub.1 is selected from the group
consisting of alkyl, substituted alkyl, unsaturated alkyl,
cycloalkyl, aryl, substituted aryl and arylalkyl, R.sub.2 is
selected from the group consisting of alkylene, substituted
alkylene, bis-alkylene ether, cycloalkylene, arylene and
substituted arylene; and R.sub.1 and R.sub.2 each contain from one
to 20 carbon atoms;
the amount of said imidazolide reagent reacted with said starch
being from 0.05 to 100 percent, based on the weight of the dry
starch; and
b. isolating the resultant starch derivative.
2. A process according to claim 1 wherein said starch is reacted
with said imidazolide in an aqueous medium at a pH of from about
4.0 to about 12.5 and at a temperature of about 35.degree. to
125.degree. F. for a period of from 1 to 24 hours.
3. A process according to claim 1 wherein the reaction is carried
out in a non-aqueous liquid medium at a temperature of about
35.degree. to 125.degree. F. for a period of from 1 to 24
hours.
4. A process according to claim 1 wherein the reaction is carried
out employing a substantially dry reaction medium at a temperature
of about 80.degree. to 160.degree. F. for a period of from 0.5 to 6
hours.
5. A process according to claim 1 wherein said starch is corn
starch.
6. A process according to claim 1 wherein said starch is waxy
maize.
7. A process according to claim 1 wherein the starch is reacted
with 1,1'-carbonyldiimidazole.
8. A process according to claim 1 wherein the starch is reacted
with the diimidazolide of succinic acid.
9. A process according to claim 1 wherein the starch is reacted
with a diimidazolide of adipic acid.
Description
This invention relates to a novel method for the preparation of
starch esters and to the resulting starch ester derivatives and
more particularly to the preparation of such esters by reacting
starch with imidazolides of carboxylic or sulfonic acids.
The modification of starch by chemical derivatization and in
particular the preparation of starch esters is well known in the
art. An excellent review of the preparation of starch esters up to
1968 may be found in J. A. Radley, Starch and Its Derivatives,
Chapman and Hall, Ltd., Chapter 12. However, the prior art does not
teach the preparation of starch derivatives by reaction of starch
with imidazolides of carboxylic or sulfonic acids.
The reactions of imidazolides of carboxylic acids with hydroxy
compounds are known and are described, for example, in H. A. Staab,
Agnew. Chem. Internat. Edit., 1, 351 (1962); H. A. Staab and A.
Mannschreck, Ber., 95, 1284 (1962); and W. Klee and M. Breener,
Helv., Chim. Acta, 44, 2151 (1961). These references, however, all
teach the acylation of alcohols with imidazolides of carboxylic
acids under anhydrous conditions using organic solvents. I have now
discovered that it is unnecessary to use anhydrous conditions and
an organic medium, but that water is actually a very good medium
for reacting starch with imidazolides of carboxylic acids.
It is an object of this invention to provide a novel method for the
preparation of inhibited starch products containing labile ester
linkages so as to permit these linkages to be subsequently
controllably and readily destroyed or eliminated, and whose
presence permits these products to exhibit a combination of
inhibited and normal swelling characteristics.
Another object of this invention is to prepare inhibited starch
products that are free of the undesired effects of non-cross-linked
substitution onto starch, as for example, acetylation.
A further object of this invention is to provide a convenient and
economical new reaction for chemically altering the paste
properties of starch by a reaction which proceeds rapidly with
aqueous slurries or with dispersions of starch in water at room
temperature.
Various other objects and advantages of this invention will be
apparent from the following description.
The objects of this invention are accomplished by reacting starch
with imidazolides of carboxylic or sulfonic acids.
According to this invention starch or a starch derivative is
reacted with an imidazolide of a carboxylic or sulfonic acid in
aqueous or non-aqueous solution or in the dry state to produce a
starch ester derivative. If imidazolides of polyfunctional acids
are used, cross-linked starch esters may be produced. The reaction
may be carried out at temperatures ranging from somewhat below to
somewhat above room temperature. By a suitable choice of starting
materials, reagents, and reaction conditions, very useful modified
starches may be prepared easily and conveniently as will be
explained more fully hereinafter.
The starch base materials which may be used in preparing starch
ester products according to this invention may be derived from any
plant source including corn, potato, sweet potato, wheat, rice,
sago, tapioca, waxy maize, sorghum, high amylose corn, or the like.
Also included are the conversion products derived from any of the
above starch bases including, for example, dextrins prepared by the
hydrolytic action of acid and/or heat; oxidized starches prepared
by treatment with oxidants such as sodium hypochlorite; and
fluidity or thin boiling starches prepared by enzyme conversion or
by mild acid hydrolysis. The term "starch base" is thus seen to
include any amylaceous substances, whether untreated or chemically
modified, which, however, still retain free hydroxyl groups capable
of entering into the acylation reaction. If the desired product is
to be a granular starch obviously the initial starting material
must be in granular form. It is to be noted that the process of
this invention may also be carried out employing gelatinized
starches which will result in the production of non-granular starch
ester products.
For purposes of this invention the term "imidazolides of carboxylic
or sulfonic acids" means compounds corresponding to the general
formulas: ##EQU1## wherein R.sub.1 is selected from the group
consisting of alkyl, substituted alkyl, unsaturated alkyl,
cycloalkyl, aryl, substituted aryl, and arylalkyl, and R.sub.2 is
selected from the group consisting of alkylene, substituted
alkylene, bis-alkylene ether, cycloalkylene, arylene, and
substituted arylene. R.sub.1 and R.sub.2 may each contain between
one and 20 carbon atoms.
It is to be noted that additional compounds analogous to the
compounds of structure III but having more than two carboxyl groups
attached to R.sub.2 may also be used to prepare inhibited starches
according to this invention.
Suitable imidazolides of carboxylic or sulfonic acids corresponding
to structures II - IV may be prepared using acids such, for
example, as acetic acid, propionic acid, stearic acid,
trimethylacetic acid, phenylacetic acid, benzoic acid, cinnamic
acid, trichloroacetic acid, p-bromobenzoic acid, p-methoxybenzoic
acid, p-toluic acid, p-dimethylaminobenzoic acid, succinic acid,
glutaric acid, adipic acid, dimethylmalonic acid, sebacic acid,
1,22-docosanedioic acid, terephthalic acid, diglycolic acid,
3,3'-oxydipropionic acid, benzenesulfonic acid, p-toluenesulfonic
acid, methanesulfonic acid, p-aminobenzenesulfonic acid,
1-naphthoic acid, and cyclohexane-carboxylic acid.
The preparation of imidazolides of carboxylic and sulfonic acids is
well described in the literature and is ordinarily carried out by
reacting selected sulfonic or carboxylic acids such as those listed
above with 1,1'-carbonyldiimidazole or 1,1'-thionyldiimidazole. An
alternative synthesis reacts the acid chlorides of the carboxylic
or sulfonic acids with imidazole. A discussion of synthetic
procedures and a tabulation of various imidazolides and references
to their preparation may be found in H. A. Staab, Agnew. Chem.
Internat. Edit., 1 351 (1962).
The novel process of this invention comprises reacting a selected
imidazolide of a carboxylic acid, such as described hereinabove,
with a selected starch base which is ordinarily suspended in water.
The reaction of the imidazolides with the suspended starch is
carried out at temperatures ranging from about 35.degree. to
125.degree. F. and preferably at 70.degree. to 100.degree. F. The
pH of the reaction mixture is ordinarily controlled so as to be
above 4.0 and below 11.0 with the preferred range being from about
6.0 to about 10.0. The pH is conveniently controlled by the
periodic addition of a dilute aqueous solution of sodium hydroxide,
but other common bases, such as calcium or potassium hydroxide,
tetramethylammonium hydroxide and sodium carbonate, may also be
used with equal success.
In one variation of the described method, the pH of the reaction
mixture is not controlled. In this variation an excess of base is
added to the system, which results in a pH in the range of
11.0-12.5, with the imidazolide being added and the reaction
mixture neutralized thereafter.
Aqueous suspensions are preferred, but the reaction may be carried
out, if desired, in a non-aqueous system by suspending the starch
base in any common organic solvent as, for example, p-dioxane,
toluene, dichloromethane, and the like, and then adding the
imidazolide.
The amount of imidazolide reagent used to react with the starch
base may vary from about 0.05 to 100 percent, based on the dry
weight of the starch, depending on such factors as the starch base
employed, the degree of stabilization or inhibition which is
desired in the end product, and the particular imidazolide
reagent.
Reaction time will vary from about 1.0 hour to about 24 hours
depending on such factors as the reactivity of the reagent used,
the amount of the reagent used, the temperature employed, etc.
After completion of the reaction, the pH of the reaction mixture is
preferably adjusted to a pH of from about 5.0 to about 7.0 with any
common acid such as hydrochloric acid, sulfuric acid, acetic acid,
or the like, or common base such as 3.0 percent aqueous sodium
hydroxide. The pH of the reaction will determine whether acid or
base is required. The resultant starch product is then recovered by
filtration, washed free of residual salts with water, and dried.
Alternatively the washed product may be drum dried or spray dried,
or gelatinized and isolated by alcohol precipitation.
If desired, the acylated starch products may be also prepared
according to this invention by a dry process. In carrying out a
typical dry procedure, the dry starch is first suspended in water
and the slurry is adjusted to a pH of about 7.0 to about 11.8. The
starch is thereafter dried, using any common means desired by the
practioner. The imidazolide is then blended with the dry starch
base and the resulting mixture thereafter heated (as by placing in
an oven) at temperatures ranging from about 80.degree. to about
160.degree. F. The reaction period (i.e., the heating time) will
vary with such factors as the reactivity of the selected
imidazolide, the selected starch base, etc. Reaction periods
ranging from about 30 minutes to 6 hours have been found sufficient
in most instance, however. At the end of the reaction period, the
treated starch is allowed to cool. If removal of the salts and
organic by-products is desired, the starch is then slurried in
water. The pH of the slurry is adjusted to from 5.0 to 7.0, and the
starch product is recovered from the slurry by filtration, washed
free of residual salts with water, and isolated in a manner such as
described above.
It is to be noted that a large number of variations may be effected
in reacting the starch base with imidazolides in accordance with
either the wet or dry reaction procedure described above without
materially departing from the spirit of the invention. Such
variations will be evident to those skilled in the art.
The starch products resulting from the practice of this invention
are starch esters with the general reactions employing imidazolides
I, II, III and IV being represented as follows: ##EQU2## wherein
StOH represents the starch molecule and R.sub.1 and R.sub.2 are as
defined hereinabove. These are schematic equations which describe
the chemical changes occurring during the reaction. The
practitioner will recognize that the starch molecule is a polymer
of glucose and contains three free hydroxyl groups per
anhydroglucose unit in the polymer. (The non-reducing end glucose
units contain four free hydroxyl groups.) Each of these hydroxyl
groups can react as described in these equations. It is also known
that the relative reactivity of each of the hydroxyl groups is not
equivalent, some being more reactive than others, and that many
hydroxyl groups from the same starch molecule will react to give
the products of this invention.
The inhibited, granular products formed in equations (I) and (III)
may show varying degrees of inhibition depending on the extent of
the reaction and the consequent number of resulting crosslinkages.
The amount of granule inhibition may be determined by performing a
sediment volume test. In this procedure, an aqueous suspension of
the inhibited product having a concentration of 1 percent solids,
by weight, is cooked on a boiling water bath for about 30 minutes.
The resulting dispersion is then allowed to stand in a graduated
vessel, such as a 100 ml graduated cylinder, at room temperature
for a period of about 16 hours. The cooked product will separate
into layers on the basis of relative inhibition. In extreme cases
it will completely settle out with the sediment so formed occupying
different volumes depending on the degree of inhibition of the
reaction product. These sediments are composed of insoluble
granules of the starch derivative whose swollen volumes are
relative to the degree of inhibition of the derivatives. Thus,
because of their lower swelling and hydration capacity, the more
inhibited, i.e., the more crosslinked products will yield smaller
sediment volumes than correspondingly less inhibited products.
Where, however, the original starch base exhibits no sediment
formation because of the completely swollen, highly hydrated and/or
disrupted nature of its granules, e.g., in the case of waxy maize
starch, inhibition in the product will be evidenced by the
subsequent formation of sediment. The result is directly
attributable to the toughened state of the cross-linked
granules.
The cross-linked products of this invention, because of their
unique combination of properties, can be utilized in many
applications. Thus, in the food industry, they can be used as
thickening agents for pies, sauces, soups, etc. They are
particularly of interest in the canning industry as a result of
their unique behavior during retorting of the canned food products.
In the retorting process the crosslinkages of the inhibited starch
products of this invention are initially intact and the starch
dispersion is in a thin state, thereby enabling the heat utilized
for sterilizing the food product to penetrate the can and its
contents rapidly. As the heating is continued, however, the
crosslinkages of the inhibited starch thickeners are destroyed
thereby activating their delayed thickening properties to produce
desirable high viscosity dispersions. The cross-linked products of
this invention may also be used in various sizing, coating, and
adhesive applications. In addition, these novel starch products may
be used as dusting powders for surgical and cosmetic purposes,
etc.
The stabilized cereal starch ester products of the invention formed
in equations (II) and (IV) are characterized by the stability of
their dispersions. Thus the cooked pastes derived from the water
dispersible form of these esters display improved clarity and
resistance to gelling on cooling. This highly desired property
permits these derivatives of this invention to be widely utilized
as, for example, in the sizing of paper and textiles, and in foods.
Another characteristic of the starch products of this invention is
lowered gelatinization temperature as compared to untreated starch.
This is of importance in many industrial processes (particularly in
food manufacture), since it permits operation at lower
temperatures.
The following examples will illustrate the practice of this
invention but are not intended to limit its scope. In these
examples, all parts given are by weight unless otherwise noted.
EXAMPLE I
This example illustrates the use of various imidazolides of
carboxylic and sulfonic acids in preparing starch esters according
to the process of this invention by means of milk reactions wherein
the resulting products are not inhibited and display an intact
granule structure.
In preparing the starch derivatives, listed in Table I, 1.00 parts
of corn starch were suspended in 1.25 parts of water, whereupon the
indicated amounts of the selected imidazolide of a carboxylic or
sulfonic acid were added to the dispersion. The pH was controlled
at the indicated value by periodic addition of 3.0 percent aqueous
sodium hydroxide solution during the course of the reaction. The
reaction was allowed to proceed at room temperature (RT) until
there was no further change in pH. The resulting starch ester
derivatives were then acidified with dilute sulfuric acid,
recovered by filtration, and subsequently washed with water to
remove residual salts. The acyl content of each of the reacted
starches calculated from the saponification number, was determined
and is listed in Table I.
TABLE I ______________________________________ Deriv-
Esterification Reaction conditions ative Reagent % controlled on
Time % Number Name Starch pH Hours Acyl
______________________________________ 1 N-acetylimi- 6.0 8.0 2.0
1.57 dazole 2 N-benzoylimi- 7.0 8.0 2.0 3.29 dazole 3 N-benzoylimi-
7.0 9.0 2.0 3.08 dazole 4 N-acryloylimi- 7.0 8.0 1.75 0.48 dazole 5
N-methanesul- 10.0 8.0 16.0 0.53 fonylimidazole 6 N-(p-toluene- 7.0
sulfonyl) imi- dazole 10.0 8.0 2.18 7 N-stearylimi- 20.0 9.0 18.0
4.43 dazole ______________________________________
EXAMPLE II
This example illustrates the use of 1,1'-carbonyldiimidazole in
preparing inhibited starch esters by the milk reactions of this
invention.
In preparing these derivatives, listed in Table II, 1.00 part of
the respective starch bases was suspended in 1.25 to 1.50 parts of
water whereupon the indicated amounts of 1,1'-carbonyldiimidazole
were added to suspension. The pH was controlled at the indicated
value by periodic addition of 3.0 percent aqueous sodium hydroxide
solution during the course of the reaction. The reaction was
allowed to proceed, with agitation, at the desired temperature
until there was no further change in pH. Most of the reactions were
completed in about 1 hour. The resulting starch ester derivatives
were then acidified with dilute sulfuric acid, recovered by
filtration, and washed with water to remove residual salts.
The degree of inhibition was determined by cooking an aqueous
suspension of the resulting starch product having a concentration
of 1 percent, by weight, solids in a boiling water bath for a
period of 30 minutes.
TABLE II
__________________________________________________________________________
Parts by Reaction Sediment wt. 1,1'- conditions volume (ml.)
carbonyl- Deriv- diimid- Reac- Reac- ative azole per Con- tion tion
Num- 100 parts trolled temp. prod- ber Starch base starch pH (C.)
uct Base
__________________________________________________________________________
10 Corn starch 1.5 8.0 RT 13.0 62.0. 11 Waxy maize 1.5 8.0 RT 29.0
None. (acid con- verted to a degree known in the trade, as 85
fluidity). 12 Oxidized corn 1.5 8.0 RT 16.0 Do. starch (con- verted
by re- action with NaOCl to a degree known, in the trade, as 75
fluidity). 13 Corn starch 1.5 8.0 RT 23.0 91.0. which was
previously hydroxypro- pylated with 5% propylene oxide. -14 Potato
starch 1.5 8.0 RT 21.0 75.0. 15 Waxy maize 1.5 4.0 RT 56.0 None. 16
do. 1.5 5.0 RT 33.0 Do. 17 do. 1.5 6.0 RT 18.5 Do. 18 do. 1.5 7.0
RT 19.2 Do. 19 do. 1.5 8.0 RT 24.5 Do. 20 do. 1.5 9.0 RT 23.5 Do.
21 do. 1.5 10.0 RT 45.0 Do. 22 do. 1.5 8.0 2-3 15.5 Do. 23 do. 1.5
7.5 48 63.0 Do. 24 do. 75.0 8.0 RT 8.0 Do. 25 do. 0.1 8.0 RT 40.5
Do. 26 do. 0.2 8.0 RT 35.0 Do.
__________________________________________________________________________
The cooked dispersion was then allowed to stand at room temperature
in a 100 ml graduated cylinder for a period of approximately 16
hours. In order to show comparative values, the sediment volume of
the base starch was also determined by this method.
TABLE III
__________________________________________________________________________
Esterification reagent Reaction conditions Sediment volume (ml.)
Deriva- Percent Con- tive on trolled Time, Temp., Reaction Number
Imidazolide of starch pH hours .degree.C. product Base
__________________________________________________________________________
30 Succinic acid 2.0 8.0 1.0 RT 12.0 None. 31 1,22-docosanedioic
acid 2.0 8.0 2.0 RT 49.0 Do. 32 Adipic acid 10.0 8.0 18.0 RT 5.0
Do. 33 1,3,5-pentanetricarboxylic acid 10.0 8.0 17.0 RT 5.0 Do. 34
1,3,5-benzenetricarboxylic acid 10.0 8.0 16.0 RT 6.0 Do.
__________________________________________________________________________
EXAMPLE III
This example illustrates the use of imidazolides of polycarboxylic
acids in preparing inhibited starches by means of milk reaction
according to this invention.
The procedure of Example II was used to prepare the starch
derivatives listed in Table III, using in each case the listed
reagent in place of the 1,1'-carbonyldiimidazolide of that example.
The starch base in each case was waxy maize.
TABLE III
__________________________________________________________________________
Esterification reagent Reaction conditions Sediment volume (ml.)
Deriva- Percent Con- tive on trolled Time, Temp., Reaction Number
Imidazolide of starch pH hours .degree.C. product Base
__________________________________________________________________________
30 Succinic acid 2.0 8.0 1.0 RT 12.0 None. 31 1,22-docosanedioic
acid 2.0 8.0 2.0 RT 49.0 Do. 32 Adipic acid 10.0 8.0 18.0 RT 5.0
Do. 33 1,3,5-pentanetricarboxylic acid 10.0 8.0 17.0 RT 5.0 Do. 34
1,3,5-benzenetricarboxylic acid 10.0 8.0 16.0 RT 6.0 Do.
__________________________________________________________________________
EXAMPLE IV
This example illustrates the preparation of inhibited starch
products according to this invention utilizing a non-aqueous
solvent system.
A total of 20 parts of waxy maize was suspended in 60 parts of
dichloromethane. The starch suspension was stirred at room
temperature while 1.0 part of 1,1'-carbonyldiimidazole was added
slowly over a 10 minute period. After the addition was complete,
the starch suspension was stirred for 1 hour and recovered by
filtration. The product was then washed with water and dried. The
starch carbonate ester product had a sediment volume of 31.0 ml
while the base starch had no sediment. This indicates that
inhibition had occurred.
EXAMPLE V
This example illustrates the preparation of a non-granular,
cross-linked starch product prepared by using a previously
gelatinized starch base in the process of this invention.
A total of 20 parts of an acid hydrolyzed waxy maize (85 fluidity)
was suspended in 80 parts of water. The suspension was heated on a
boiling water bath for 20 minutes and then cooled to about room
temperature, and the pH of the thus-gelatinized starch was adjusted
to 8.0 with dilute sodium hydroxide. Thereafter, the cooled starch
dispersion was stirred and 1.0 parts of 1,1'-carbonyldiimidazole
was added over a period of 10 minutes. A pH of 8.0 was maintained
during the entire reaction. The reaction mixture exhibited a
significant increase in viscosity and formed a gel after 45
minutes. This indicated that cross-linking had occurred.
EXAMPLE VI
This example illustrates the preparation of starch ester products
according to this invention in the presence of excess alkali.
A total of 40 parts of corn starch was added to a solution of 1.2
parts sodium hydroxide and 12.0 parts of sodium sulfate in 50 parts
of water. The starch suspension was stirred at room temperature
while 3.0 parts of N-(p-toluenesulfonyl) imidazole was rapidly
added. After stirring for an additional 3 hours, the pH was lowered
from 12.1 to 5.0 with 6 N sulfuric acid and the starch was isolated
by filtration. The starch product was washed three times with water
and air dried. The starch product was found to contain 3.72 percent
p-toluenesulfonyl groups.
EXAMPLE VII
This example illustrates the preparation of a starch ester product
according to this invention by means of a dry reaction.
A total of 30 parts of corn starch was penetrated by suspending the
starch in 37.5 parts of water, adjusting the pH to 8.0 with 3.0
percent sodium hydroxide, and stirring at room temperature for 15
minutes. The suspension was thereafter filtered and the recovered
starch was air dried to a moisture content of 17.4 percent. To 15
parts of the pretreated starch were added 1.5 parts of
N-acetylimidazole and the mixture was then placed in an oven at a
temperature of 50.degree. C. for a period of 3 hours. The starch
was then cooled and poured into 20 parts of water. The pH of this
suspension was adjusted to 5.0 with dilute sulfuric acid, and the
starch was recovered by filtration, washed three times with water,
and air dried. The starch ester product contained 2.06 percent
acetyl groups.
In summary, this invention provides a novel and improved process
for making starch esters and novel starch ester derivatives
obtained thereby.
Variations may be made in materials, proportions, and procedures
without departing from the scope of this invention.
* * * * *