Note: Descriptions are shown in the official language in which they were submitted.
;
PREPARATION OF LOW MOLECULAR WEIGHT CELLU~OSE ESTERS
Field of Invention
This invention relates to the preparation 4~
cellulose esters. In one aspect, it relates to the
preparation of cellulose triesters. In another aspect,
it relates to the preparation of cellulose esters with a
degree of substitution (DS) less than three. In yet
another aspect, it relates to the preparation of low
molecular weight cellulose esters.
Backqround_of the Invention
Cellulose esters are of great commercial
importance. Cellulose acetates, for example, are used
in cigarette filters and as photographic film baseO
Other cellulose esters, e.g., cellulose propionates,
cellulose butyrates, cellulose acetate propionates, or
cellulose acetate butyrates, have found widespread use
in cosmetics, plastics, and pharmaceuticals.
Furthermore, cellulose esters, in particular, cellulose
mixed esters having low molecular weight and high
hydroxyl content, have high commercial utility as
coatings resins (P.M. Cook, U.S. Patent 4,839,230
(1989)). These low molecular weight and high hy~roxyl
25 ~ containing cellulose esters provide for high solids to
liquid ratios in coating formulations, provide reactive
sites ~or crosslinking reactions, and suitable
~unctionality for derivatization of the cellulose
polymer. Therefore, an improved process for the
production of cellulose esters suitable for coating
applica~ions would be of considerable commercial
importance.
,
It is well known in the art that cellulose
~triesters, for example cellulose triacetate (DS = 3; the
dégree oX substitution is de~ined as the number o~ acyl
:~
.
. , . .... .. ~,. . . . . .
. ...... .~ . . . .. . .. . . . . .
, . .,, . , . ~ , . , ,~ , j ,.
- . . . . . . . . .
- . ~ ` ' . ,
,:,
f~ ~
. . -A`
-- 2 --
groups per anhydroglucose ri~g), can he prepared by
treating preactivated cellulose with a mixture of
sulfuric acid, acetic acid, and acetic anhydride (H~LoB~
Gray and C.J. Staud, U.S. Patent 1~683~347 (1928))o
Cellulose triacetate is not suitable for all uses and,
consequently, is often hydrolyzed to a cellulose acet~te
with a degree of substitution of 0.6-2.8 (C.J. Malm;
U.S. Patent 1~984~147 (1934); C.R. Fordyce, U.S. Patent
2~129~052 (1938)~ Such a process requires dilute
reaction mixtures, long reaction times, and requires
isolation o~ the high boiling by-pxoduct acetic acid
from the dilute reaction mixture.
In U.S. Patent 1~880~808 (1932), H.T. Clarke and -~
C.J. Malm disclose the use of chloro, bromo, or alkoxy
containing acetyl anhydrides as an impelling reagent
(i.e., an anhydride which promotes esterification
without contributing any groups to the ester produced~
in the esterification of cellulose with fatty acidsO In
a typical procedure, cellulose was treated with an
~: 20 excess (1.9-9.1 equivalents per hydroxyl) of the
impelling reagent, the appropriate fatty acid, and a -
catalyst. After the required reaction time, the product
was isolated by precipitation into a nonsolven~. Such a
process typically requires a large excess o~ the
25 - -impelling reagent and produces only the cellulose
_ triester. Eurthermore, isolation of the high boiling
impelling acid from a dilute solution which also
contain~ the esterifying fatty acid is required.
Similar work disclosed by H.T. Clarke and C.J. Malm
(U.S. ~atents 1,690,620 (1928); 1,690,621 (1928);
1,698,048 (lg29); 1,~98,049 ~1929)) as well as by C.J.
Malm and G.D. Hiatt (U.S. Patent 2,172,250 ~1939))
su~fer from the same shortcomings described above.
E.J. Bourn~, M. Stacey, J.C. Tatlow, and J.M.
Tedder (J. Chem. Soc. 1949, 2976-2g79) have disclosed
.' ' . ' ~'
' . ' ,, '' ' ' : '. .
'': ' ' : ' ' . '. ' , .' . ' ' :' . "' , '
....
-: -- 3 --
the use of trifluoroacetic anhydride (TFAA) as an
impelling reagent in the acetylation of cellulose and
amylose with acetic acid. By their process, a large
excess of TFAA (8.4 equivalents/hydroxyl) was required
in order to obtain satisfactory yields of the triester.
A process for preparing cellulose acetates with a degree
of substitution of 0.6-2.8 was not described. Work
disclosed by K.S. Barclay, E.J. Bourne, M. Stacey~ and
M. Webb (J. Chem. Soc. 1954, 1501-1505), T. Morooka,
- 10 M. Norimoto, T. Yamadaj N. Shiraishi (J. Appl. PolymO
Sci. 1984, 29, 3981-3990), and T. Yamagishi, T. Fukuda,
T. Miyamoto, J. Watanabe (Polym. Bulletin 1988, 20,
373-377) suffer from the same shortcomings described
above.
In U.S. Patent Application Serial No. 495,186 filed
March 19, 1990, C.M. Buchanan teaches the use of
trifluoroacetic anhydride and acyl anhydride as an
effective means for preparing cellulose triesters as
well as less than ~ully substituted cellulose esters~
By this proeess, smaller amounts of the impelling
reagent are required (typically 0.5-1.0 equivalents~
hydroxyl~ to obtain high molecular weight c~llulose
ester derivati~es with a degree of substitution ranging
~rom 0.5 to 3Ø
25 - -- In U.S. Patent 3,617,201 ~1971), R.J. Beral et alO
describe a process in which cellulose fiber is treated
with TFAA and a carboxylic acid in an inert solvent
(ben~ene) to produce a cellulose ester with a low deqree
of substitution (0.1-0.3) suitable for use in cellulose
textiles. In this process, the cellulose ~ibers are not
disrupted since the reaction medium remains
` heterogeneous throughout. U.S~ Patent 3,097,051 (R~Ho
Wadë! 1963) and S.U. Patent 1,047,908 (O.S. Bludova,
N.I. Klenkova, A.P. Sokorenko, 1983) teach similar
processes.
5~B~TITIJTE ~3HE~
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:` ,,: ` ` ` . : `
, . . . ` `
` - , . . .
.. ,. . . . . ` ,
.- . - .
~ ^
~j f.'^'i;
US-A-1,645,915 describes a process o~ making est~rs
of organic acids such as cellulose acetate by treating
- cellulosic material with an acylating agent, such as
acetic anhydride, the action of which is catalyzed by
means of one or more of the compounds, M(Cl04)~ in which
M, the positive part, or ion, is less positive than
sodium and potassium in the electro-potential scaleO
The valence of M is indicated by ~. M represents not
only any metal, (except the alkali metals) which fo~ms a
perchlorate, but also hydrogen, the ammonium group~ and
many organic bases which form perchlorates.
US-A-2,629,716 describes the use of trifluoroacetic
acid as a catalyst in the preparation of esters ~rom
monomeric or polymeric alcohols and especially of its
catalytic activity in the preparation of cellulose
acetate.
There is, therefore, a need for a process whiGh
provides both cellulose triesters and high hydroxyl
~ cellulose esters having low molecular weight. The
;;; 20 process must provide for fast esterification and
hydrolysis rates. The process should not require an
impelling reagent or excessive amounts of mineral acidsO
It is desirable that degradation of the cellulose
polymer occux in the initial stages of the reaction
25 ~~ thereby permitting concentrated reaction mixtures. The
_ process must allow for practical reaction temperatures
as well as for easy and practical product and carboxylic
acid recovery.
SummarY of the Invention
Accordingly, we have discovered a process for the
preparation of low molecular w~ight cellulose esters
which meets the needs of the cellulose art.
Specifically, cellulose triesters (i.e., cellulose
~ ~ T~ ~F~T
, .. , :., . : -.::.: ',',,: ' ' '~. .' ' :'' , . ' ''
. :' . :. . : : :' ' : : :
,- : . . . . . .
: .: . . : . : : :. : . ..
... .
.. . . . . . .
. ~-?
. -- 5
esters having a DS of about 3) are rapidly prepared by
contacting:
(~) a cellulose pol~mer having a degree of substitu~ion
less than that of the product cellulose ester
(i.e., less than about 3) and also having a
molecular weight greater than that of the product
cellulose ester,
(b) trifluoroacetic acid,
(c) at least one acyl anhydride of the formula
R/ ~o/ ~ 1
wherein each of R and Rl is, independently, H, a
straight chain alkyl, branched chain alkyl, aryl,
or substituted aryl, and
(d) a mineral acid,
in the presence o~ a solubilizing amount of a solvent
and under conditions such that the desired cellulose
ester is formed (such process will alternatively be
referred to herein as the "triesterification process"~
1` To prepare cellulose esters with a DS of less than
about 3, the cellulose triester formed by the above-
described process is suhjected to a second step
" (hereinafter alternatively re~erred to herein as the
"hydrolysis step") in which the cellulose triester
(i.e., cellulose ester with a DS of about 3) is.
contacted with a suf~icient amount of a reactive
- hydrolysis solvent under conditions to form the desired
cellulosa ester with a DS higher than the cellulose
polymer used as a starting material ~or the
triesterification process.
Det~iled Description of the Invention
: In accordance with the present invention, typical
cellulose esters produced by the process of the
. . .
:` , . .
:` ~U STITUT~S~I~T
.` , :
... ,. .. , .. - .. , .. , . ,, . ~ . . ..
: -- 6 --
- invention are Cl to C20 esters of cellulose, have the`................. desired DS, have a lower molecular weight than the
cellulose polymer starting material, and comprise
repeating units of the 6tructure:
:-
~` \ \ CH20R4 RO ~ OR
. _ 3 ~ ~ `
wherein R2, R3, and R~ are selected separately from thegroup consisting of: hydrogen, straight chain alkanoyl,
. branched alkanoyl, aroyl, and heteroaroyl. The
~ alkanoyl, aroyl, and heteroaroyl moieties typically
contain up to 20 carbon atoms, more typically up to 6
carbon atoms. Preferred cellulose esters produced by
the process of the invention include cellulose
triacetate, cellulose tripropionate, cellulose
tributyrate, cellulose acetate, cellulose propionatef
cellulose butyrate, cellulose acetate propionate, and
.: cellulose acetate butyrate.
The cellulose polymer used as a starting ~aterial
: for preparing the cellulose triester can be cellulose, a
secondary cellulose ester, or a mixture thereof.
Examples of secondary cellulose esters include cellulose
_ acetate, cellulose propionate, and cellulose butyrate,
and are described in U.S. Pat~nt 1,984,147.
The cellulose esters useful in the present
inv2ntion as starting materials have at least 2
anhydroglucose rings and typically have between 2 and
5,000 anhydroglucose rings; also, such polymers
typically have an inherent viscosity (I.V.) o~ about 1.0
to 3.0 deciliters~gram as ~easured at a temperature of
25C for 0.25 gram sample in ~00 ml of a 60~40 by weight
sol~tion of phenol~tetrachloroethane. As these I.V.
values indicake, such polymers have a molecular weight
..
. . .
.... . . .. . .. . . .
. . . . .... . . . . . . . .
. . . . . ~ . . . . . . . .. .. . . .. . .
.. . . . . ... - .. . .
- . .. . . .
-- 7 --
greater than the product cellulose ester; typical number
average molecular weight values range from l.o to
10.0 X 105.
The product cellulose esters produced by the
process of this invention typically have an inh~rent
viscosity (I.V.) of about 0.2 to about 0.6
deciliters/gram as measured at a temperature of 250C
for 0.25 gram sample in 100 ml of a 60~40 by weight
solution of phenol/tetrachloroethane and a number
average molecular weight of less than about 1.0 X 105.
The DS of the cellulose polymer starting material
for the triesterification process is preferably 0 to
about 2.9.
As is known in the art, the theoretical maximum DS .
for a cellulose ester is 3. However, due to normal
error of standard analytical techniques, the maximum DS
will vary experimentally, for example an error of plus
or minus 3 percent is common. When the term "about" is
used herein to describe a given DS, it is contemplated
that this analytical error will be taken into account as
well as minor actual deviations in the DS of the
particular cellulose ester. Therefore, it is
contemplated that the term "about 3" when referring to a
given DS means a measured range of 2.9 to 3.1,
preferably 2.95 to 3.05.
Typical anhydrides suitable for the practice of the
pFesent invention are..:o.f.the structure:
- R/ b ~1 -:
wherein each of R and R~ is, independently, selected
- from the group consisting o~ hydrogen, a straight chain
alkyl, a branched chain alkyl,- aryi or substituted aryl.
In the acyl anhydride molecule, typical straighk chain
alkyl groups contain 1 to 20 carbon atoms, typical
. :
.
.. , . - . .. , . ~ , . .. .. .; . . .. . : . .
. ~ . . ... . . .. ...... .. .. . ..
... . . . . . . . ~ .
- : . i . . . . .
. . . . . .
,: : . , :
~:;
-- 8 --
branched chain alkyl groups have 3 to 20 carbon atoms,
and typical aryl groups have 6 to 12 carbon atoms.
` Substituted aryl groups are typically substituted with
1, 2 or 3 substituents such as lower alkyl (i.e., alkyl
groups having 1 to 3 carbon atoms), halo (i.e., ~, Br,
Cl or I), and lower alkoxy (i.e., alkoxy groups having 1
to 3 carbon atoms). It is preferred that the acyl
anhydride is symmetrical, i.e., that R and R1 are the
same.
Exemplary acyl anhydrides useful in the present
invention are, but are not limited to, acetic anhydride,
propionic anhydride, isobutyric anhydride, butyric
anhydride, trimethylacetic anhydride, ~aleric anhydride,
hexanoic anhydride, nonanoic anhydride, benzoic
anhydride, or a mixture thereof. The most preferred
acyl anhydrides include acetic anhydride, propionic
anhydride, butyric anhydride, or a mixture thereofO
The mineral acid useful as component (d) in the
present invention can be any strong mineral acid which~
when combined with trifluoroacetic acid (TFA), promotes
rapid esterification, hydrolysis, and moleculax weight
loss. Examples of such mineral acids include sulfuric
acid, hydrochloric acid, Mg(Cl04)2 and HCl04. 0~ course,
mixtures of two or more mineral acids are contemplated
for use in the present invention.
_ In the process of preparing the cellulose triester
lQ the amount of component (b) (i . 2., the TFA) is
preferably about 0.25 to 1.0 equivalents per hydroxyl~
more preferably about 1.0 equivalents; the amount of
component (c) is preferably at least 1.0 equiYalent per
hydroxyl, more preferably about }.7 equivalents; and the
amount of component (d) is preferably about 0.0001 to
0.01 equival2nts per hydroxyl; more pxefPrably about
- 0.008 equivalents~
.' .
ST~T~l-E
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- , , .: . , , .. , . , , .:, :
',' . ~ , ', ,:, . ' ' : .
'.' '' !.' i i. ,
!.~, :.
.'i`' -- 9 _
.''.' ,
- Conditions suitable for the formation o~ celluloi~e
esters can vary widely. The temperature typically
~ varies from ambient to the temperature at which the
- mixture begins to reflux; typically about 20C to about
150~C. More preferably, the temperature is 700C.
Those skilled in the art readily recognize that
contact time and acyl anhydride reactivity are
interdependent. For example, acylation with a mixture
of propionic anhydride and acetic anhydride requires a
contact time as little as 5 minutes~ When acylating the
same wood pulp with a mixture of butyric acid and acetic
anhydrid~, a contact time of 30 minutes may be requiredO
Those skilled in the art understand that the flat
period (i.e., the period of time after ~ormation of the
cellulose triester and beginning of hydrolysis during
which polymer degradation is occurring) can vary widelyO
Accordingly, a broad flat period for the process of the
~- invention is about 1 minute to about 120 minutes. A
, more preferred ~lat period is about 5 minutes to about
^~ 20 30 minutes.
Thu~, the total reaction period of time (i.e.,
including the period ~or acylation, flat period, and
hydrolysis period) can vary from about 0.5 to about 25
hours. A preferred total reaction period is about 4 to
2~--about 8 hours.
The mixture of the TFA and the mineral acid in the
: ." _ .
triesteri~ication process essentially acts as a
.... . . ......
ca~alyst. In addition, the mineral acid functions to
degrade the ceflulose polymer. By utilizing a mineral
acid in th~ triesterification process, molecular weight
loss occurs during ~ormation of the cellulose triester
which permits more concentrated reaction mixtures and
thereby easier isolation of the product cellulose ester.
For the triesterification process said solvent is
typically a carboxylic acid having 1 to 20 carbon atoms,
,
SUÇ~S~ E S~ ,
.
. .
.: . , , . . :
~: ,
.
. ..
.. ri ~ ` ,
'
, ' ' ;
?, ` ~;
-- 10 --
dimethylformamide, dimethylsulfoxide, or a mixture
thereof; howe~er, excess acyl anhydride can be used as
solvent. The carboxylic acid can optionally be
substituted with halogen atoms such as F, Br, and C1~ an
example of such a substituted carboxylic acid is
trifluoroacetic acid. Preferred is a carboxylic acid,
Pspecially the particular carboxylic acid corresponding
to the acyl anhydride(s) employed, or, in the case of
mixed esters, corresponding to the least reactive acyl
anhydride.
If a carboxylic acid is used as a reaction solvent,
the acid can contribute to the reaction (i.e., act as a
reactant) if the particular carboxylic acid used has a
corresponding anhydride that is more reactive than the
acyl anhydride employed as reactant (c).
The reactive hydrolysis solvent for the hydrolysis
step is typically a polar solvent such as an n-alkanol
having 1 to 4 carbon atoms, water, a branched chain
alkanol having 3 to 4 carbon atoms, an aryl alkanol
having 7 to 12 carbon atoms, and a mixture thereo~O
` Preferred reactive hydrolysis solvents include
methanol, ethanol, n-propanol, n-butanol, isopropyl
alcohol, benzyl alcohol, water, or a mixture thereofO
Most preferred are methanol and water, or a mixture
25 -thereof.
For the hydrolysis step, the preferred amount of
reactive hydrolysis solvent is from about 1 volume % to
that amount which results in the desired product
precipitating from solution. It is more preferred that
the amount of reactive hydrolysis solvent is from about
5 to about 15 volume %.
Preferred reaction conditions for the hydrolysis
: step include a temperature range from ambient to the
temperature at which the mixture begins to reflux
(typically 20C to 150C) and a reaction time of about
~' .
.~ . , .
~ ': ;, ', ~,
- - .. .. ..
. : ,, , . ,, , ~ ~ . ... . .
. . .... ".. .. , , . ,, .: .
., ~
.. , , ': ;
~ ` ~
.~
` !.`~
o.s hours to about 24 hours. Most preferred reaction
conditions are a temperature of 70OC and a reaction time
of about 4 hours to about 7 hours.
The cellulose triester formed by the triesteri,,fi-
cation process can be isolated and~or purified byconventional means known in the art such as by
precipitation into a nonsolvent, distillation, or by
spray drying (and, if desired, subjected to the
hydrolysis step). Alternatively, the cellulose triester
can be hydrolyzed directly in the reaction medium
without the need for any special purification or
isolation steps. After hydrolysis, the desired
cellulose ester can be isolated and purified by
conventional means known in the art such as by a
nonsolvent precipitation, distillation, or by spray
drying. , ,
The preferred cellulose esters produ~ed after khe
hydrolysis step are substantially the same as produced
by the triesterification process except that the DS is
' 20 lower. Thus, preferred products produced by the
hydrolysis step include cellulose acetate, cellulose
propionate, cellulose butyrate, cellulose acetate
propionate, and cellulose acetate butyrate.
Typical desired products produced after the
25 '~hydrolysis step of the invention have a DS o~ about 0O5
" _to about 2.85, more typically about 1.9 to about 2.3
for mixed esters, the 4s refer~ to the combined DS).
The cellulose esters produced by the triesterifica-
tion process ~optionally followed by the hydrolysis
step) have low molecular weight. Typical molecular
weight ranges of cellulose esters produced by the ' ,
process of the present inventio~ have a number average
molecular weight (~) of about 0.01 X 10S to about
l.0 X 105, a weight average molecular weight ~r~) of
abou~ 0.02 X 103,to about 2.0 X 105, and a Z average
`:
.
. . . ... .. .... , ~ . . . ~
,. ~ . -.: . .. , , . : ,. . ~ .
, . ~ .. ` .-, .. . .- .. . . . . .. .
- 12
molecular weight (~) of about 0. 04 X 105 to about
4. 0 X 105. Preferred molecular weight ranges are an
of about 0.2 X 105 to about 0.6 X 105, a MW of about
0.6 X 105 to about 1.0 X 105, and a ~ of about 0.3 X 105
` 5 to about 3.0 X 105. The ratio o~ M~ is preferably
about 1.0 to about 2.0, with about 1.4 to about 1.9
being more preferred.
As is well known in the art, I.V. values are
related to molecular weight. The I.V. of the product
- 10 cellulose ester produced by the triesterification
process toptionally followed by the hydrolysis step) is
typically about 0.2 to about 0.6, preferably about 0O3
to about 0.4 deciliters/gram as measured at a
temperature of 25C for 0.25 gram sample in 100 ml of a
60/40 by weight solution of phenol/tetrachloroethaneO
Some products produced after the hydrolysis step,
especially high hydroxyl (i.e., low DS), mixed esters,
will be soluble in n-propylacetate tn-PrOAc), acetone~
~` CHCl3, ethanol, tetrahydrofuran (THF), and
dimethylsulfoxide (DMS0).
The following examples are to illustrate the
invention but should not be interpreted as a limitation
thereon.
.-.
2~ -- EXAMPLES
In the following examples, water activated
." ._
cellulose was prepared by mechanically blending the
ceIlulose with water. The excess water was removed by
filtration. Résidual water was removed by washing the
damp cellulose with the carboxylic acid which
corr~sponds to an acyl group being attached to the
c~llulose polymer. The activated cellulose was loaded
into a flask equipped ~or mechanical stirring. To the
cellulose was added a mixture o~ acyl anhydride (5) and a
catalyst consisting of TFA and a mineral acid such as
., .
., .
., , . , , , ~ . ~
.,, , . . , ., : ; ~ . . .
. . ,. . . . : ,.
, . . . . . . .
: ' ' ' , ~ . "',, " " ; ~ ' , , ~ ' ' . ' "' ,. . . .
~' ~ ' ~ , ' ' '' ' i , ' , , ,
- - 13 -
"`'
sulfuric acid. The reactor was then heated to 70~Co
The reaction mixture was stirred until a cleax solu.tion
- was obtained which is the indicated contact time ~or
formation of the triester. After formation of the
- 5 triester, the reaction mixture was maintained at 70c
for a period of time to allow degradation of the pol~mer
(i.e., a flat period) before adding a hydrolysis
solution to the reaction mixture. The reaction was
stirred for the indicated time(s) before isolating the
product by addition of a nonsolvent. The TFA, the
carboxylic acid(s), and the unconsumed acyl anhydride(s)
can be recovered from the reaction mixture before the
addition of a nonsolvent. Also, the TFA and carboxylic
acids can be recovered from the ~iltrate ~ollowing
precipitation by distillation techniques familiar to
those skilled in the art. Alternatively, the TFA, the
carboxylic acid(s), and the unconsumed acyl anhydride(s)
can be isolated by spray drying techniques familiar to
those skilled in the art. The results in the examples
indicate yields of isolated, well-characterized
products. The products were typically characterized by
proton NMR spectroscopy, inherent viscosity, gel
permeation chromatography (values are reported in
polystyrene equivalents), and other methods familiar to
2~--those skilled in the art. The abbreviations used herein
have the following meanings: TFA is trifluoroacetic
acid, TFAA is trifluoroacetic anhydride, NMR is nuclear
......
magnetic resonance, Pr DS is propionyl degree of
substitution, ~c DS is acetyl degree of substitution,
TCE is tetrachloroethane, GPC is gel permeation
chromatography, DMF is dimethylformamide, T~F is
tetrahydrofuran, DMSO is dimethylsulfoxide, n-PrOAc is
propy;l acetate, and CAB is ceIlulose acetate butyrate.
. .
5~ E s~E
.. . . . ..
` ` : ` :
. .- . .. .. ... . .... . . . .. . . .... .. . . . ..
~. .. .. . . . .
- .- ~,, . .. . ~ .
- - . .. . I
. . . .. .. : : .. . .
.~ . . . , .~ .. . ., . : .
.
~;
- 14
EXAMPLE 1
.~ Reagents set forth below were subjected to the
~` standard procedure described above under the indicated
reaction conditions. The result, in terms of identity
and yield of the desired cellulose ester, and key
analyses of the product, are also set f orth below~
Starting Cellulosic Cellulose
Weight (g) 50
Equivalents of 1.0
TFA/hydroxyl
Equivalents of 0.008
H2SO4/hydroxyl
: Acyl Anhydride Acetic Anhydride
Equivalents/hydroxyl 0.03
20 Acyl Anhydride Propionic Anhydride
Equivalents/hydroxyl 1.7
Carboxylic Acid Propionic Acid
Weight (g) 107
: 25
. Hydrolysis Mixture 76.5 g water
Contact ~ime (min) 10
30 Flat Period (min) 30
HydrolysisPr DS Ac DS I.V.
~ Time (h~ (IH NMR) !IH NMR~ .(Phenol~TCE)
; 0 3.00 0.05 0.35
2.0 2.59 0.03 0.37
--.. ... .. .
4.0 2.24 0.02 0.39
.
5.0 2.06 0.01 0.41
~.0 1.93 0.01 0.42
: 7.0 1.84 0.01 0.42
7.8 1.70 0.01 . 0.44
. - - .
This exa~ple demonstrates that a catalyst system
consisting o~ TFA~H2SO4 rapidly promotes the
.
~3~Bs r~ E S~
: ~ . - , . .' , ' ' ' ': . . ' , , :
' . . . , '.
-
: .
, . "', ' ~ ', ,, ' . ' ': ' . .
.
3 .~
~ . ' .
:,~',. .' . /; :'.
: . I f~,,
:.
- 15 -
. .
esterification of cellulose with propionic anhydride and
acetic anhydride to provide a triester, provldes ~or
rapid degradation of the cellulose polymer, and gives
: excellent rates of hydrolysis.
: . 5
EXAMPLE 2
Reagents set forth below were subjected to ~he
standard procedure described above under the indicated
reaction conditions. The result, in terms of identity
lo and yield of the desired cellulose ester, and key
analyses of the product, are also set forth below.
Starting Cellulosic Cellulose
Weight (g) 50
15 Equivalents of 1.0
TFA/hydroxyl
Equivalents of 0.008
; Mg(Cl04)~hydroxyl
Acyl Anhydride Acetic Anhydride
Equivalents/hydroxyl 0.03
.~ Acyl Anhydride Propionic Anhydride
: 25 Equivalents/hydroxyl 1.7
: Carboxylic Acid Propionic Acid
Weight (g) 86
30 Hydrolysis ~ixture 76.5 g water
Contact Time (min) 7
- Flat Period (min) g
39.-. . . . .. ..
Hyd~olysis Pr DS Ac DS I.V.
Time th) (IH NMR) ~lH NMR~ Lphenol~TcE)
0 3.05 0.04 0.54
1.0 2.77 0.04 0.3~
1.8 2.51 0002 . 0.34.
3.3 2.16 0.00 0.36
5.3 1.79 0.01 0.38
6.3 1.59 0.00 0.39
~;lJB~
. .. , ....... . . . , . . . ~ . .. . . . .
., ,, . ,. , ` .. .. . . .. . . ..
.. .... ... ~ .. . . .. . . . .... ... . . . . .
, : . . . . . .. . . .
- . ~ ` ~ . ` .: . . .
.. ~ , ` -. ~ . . .
. , .. , . . . ~ ." . , ` . .
,. . . . . . . . ` ..
... .
- 16 -
This example demonstrakes that a catalyst system
consisting of TFA~Mg(Cl04)2 rapidly promotes the
esterification of cellulose with propionic anhydride and
acetic anhydride to provide a triester, proYides ~or
rapid degradation of the cellulose polymer, and gives
excellent rates of hydrolysis.
EXAMPLE 3
Reagents set forth below were subjected to the
standard procedure described above under the indicated
reaction conditions. The result, in terms of identity
and yield of the desired cellulose ester, and key
analyses of the product, are also set forth belowO
.
~,
.
' -.. ' , ,
5~ -3~
... . . . . . . .
.. .. ..
' " " ',,. ,' .: . . :'
.. . .
.:- . - . .. . . .
' ': . ' ','' , , ~ ' . ': . .
.
-. . .. . ;: : - . : .
... . . . . .
-, .. .
: . , :
17 -
Starting Cellulosic Cellulose
Weight (g) 50
-~ Equivalents of 1.0
TFA~hydroxyl
E~uivalents of 0.008
H2SO4/hydroxyl
10 Acyl Anhydride Acetic Anhydride
Equivalents/hydroxyl 0.03
Acyl Anhydride Propionic Anhydride
Equivalents/hydroxyl 1.7
Carboxylic Acid Propionic Acid
Weight (g) 75
Hydrolysis Mixture 76.5 g water
Contact Time (min) 5
Flat Period (min) 30
25 Hydrolysis Time (h) 4.5
DS Pr(lH NMR) 2.08
. DS Ac(lH NMR) O.02
GPC M~ = O.4 X 105; M~ = 0~7 X
105;
(DMF~LiBr, ~ = 0.4 X 105; ~ = 1092
Polystyrene
equivalents)
IV (Phenol~TCE) 0.33
'~ , Solubility Data Soluble in organic solvents
4~ . . ... such as n-PrOAc, acetone~
CHCl3, THF, alcohol, and DMSO
~. '
.
~
.. . . . . . . .
... . . . . . . .
... . , , ,.. ., .... . . . . ~
. . . . . . .. . . . . ..
.. . ... . . .
.~ . . .
- . . . . . .
: . . ,, . - , . . .
.. . . . . . . .
- . . . . .. . . ..
~ - 18 -
. . ,
This example demonstrates that a catalyst system
:- consisting of TFA~H2SO4 can be used to obtain a CAP mixed
.,"! ester with high hydroxyl content and low molecular
weight. This mixed ester gives high solids to liquid
ratios in organic solvents such as n-propyl acetate
,: t25~
EXAMPLE 4
Reagents set ~orth below were subjected to the
standard procedure described above under the indicated
reaction conditions. The result, in terms of identity
and yield of the desired cellulose ester, and key
analyses of the product, are also set forth below.
15 Starting Cellulosic Cellulose
Weight tg~ 50
Equivalents of 1.0
TFA~hydroxyl
.. 20
Equivalents of 0.008
,. H2SO4~hydroxyl
Y Acyl Anhydride Acetic Anhydride
25 Equivalents~hydroxyl 0.03
. Acyl Anhydride Butyric Anhydride
Equivalents~hydroxyl 1.7
3~ --Carboxylic Acid Butyric Acid
Weight (g) 75
.,, _
. Hydrolysis Mixture 76.5 g water
.. -- . . . ..... .
; 35 Contact Time (min) 15
. Flat Period (min) 30
:
~ .
.
:
.- :
.~`. .
. , .
.
~ ;q ;~ ~ ~
: .
:,~ , , . . . . :
:: . . . , . .. : -
-: ~ :. : .: .
.- . , - - .-' . : :: : - : , ' : '
.: ~ :- : . - . . . .
'~3~ . .
-- 19 --
HydrolysisBu DS Ac DS I.V.
Time (h)~IH NMR) (IH NMR) (Phenol/TCE)
0 3.02 0.07 0.40
2.0 2.74 0.06 0.37
4.0 2.43 0.0~ 0.36
5.0 2.36 0.03 0.37
6.0 2.28 0.03 0.35
7.0 2.12 0.02 0.40
This example demonstrates that a catalyst system
consisting of TFA~H2SO4 rapidly promotes the
esterification of cellulose with butyric anhydride and
acetic anhydride to provide a triester, provides for
rapid degradation of the cellulose polymer, and gives
excellent rates of hydrolysis.
. :
EXAMPLE 5
Reagents set forth below were subjected to the
standard procedure described above under t~e indicated
reaction conditions. The result, in terms of identity
and yield of the desired cellulose ester, and key
analyses of the product, are also set forth below.
.
'.,,,' '-- -. ~'
:
.
.
. - ; .
.. . . .
: : , : , ., ;. . .
. . - ~
.
- 20 -
Starting Cellulosic Cellulose
Weight (g) 50
Equivalents of 1.0
TFA/hydroxyl
Equivalents of 0.008
H2SO4/hydroxyl
10 Acyl Anhydride Acetic Anhydride
Equivalents/hydroxyl 0.07
Acyl Anhydride Butyric Anhydride
Equivalents/hydroxyl 1.7
Carboxylic Acid Butyric Acid
Weight (g) 75 ~:
Hydrolysis Mixture 76.5 g water
; 20
Contact Time (min) 25
Flat Period (min) 30
25 Hydrolysis Time (h) 7
DS Bu(lH NMR) 2.18
. DS Ac(~H NMR) 0.06
GPC ~ = 0.5 X 105; MW = loO X
105;
(DMF/LiBr, ~ = 1.5 X 105; M~ = 1.45
Polystyrene
eguivalents)
IV (Phenol~TCE) 0.39
Solubility Data Solubl~ in organic solvents
40 - - such as n-PrOAc, acetone,
CHCl3, THF, alcohol, and DMSO
, , ;
, .
EE~
~ : .
~ . , .
. .
............
. . .
:' r~
'~'.i
.-,, 1,,~
- 21
This example demonstrateS that a catalyst syste~
consisting of TFA~H2SO4 can be used to obtain a CAB m.i~ed
ester with high hydroxyl content and low molecular
weight. This mixed ester gives high solids to liquid
ratios in organic solvents such as n-propyl acetate
(25%).
. .
EXAMPLE 6 ~ :
Reagents set forth below were sub~ected to the
standard procedure described above under the indicated
reaction conditions. The result, in terms of identity
and yield of the desired cellulose ester, and key
analyses of the product, are also set forth belowO
~,
,
.
.~ ." _ ' .
..
. .
T~TF~
: , . ~ .. , ` , . . . . . . .
... . , . : `
.. ... : ` ., ; . .. , . : , .- . . . . ` . . . .
.. . . , ~ . . . .
. : ` ~. `: ` ` ` ,:
- .. ` ' . : ` . ` . `, .. .. .
. , . . . . . . . , . ~ ,
.
.; .
"~
,:'.: (.:,~.'.;;
- 22 -
starting Cellulosic Cellulose
weight (g) 50
Equivalents of 1.5
TFAA~hydroxyl
.
Acyl Anhydride Acetic Anhydride
Equivalents/hydroxyl 0.15
10 Acyl Anhydride Propionic Anhydride
Equivalents/hydroxyl 1.7
Carboxylic Acid Propionic Acid
Weight (g) 152
Hydrolysis Mixture 76.5 g water, 152 g Propionlc
Acid
Contact Time (min) 1080
. 20 :.
Reaction Temperature 55C :
,
..
" . . . . ... . ..
.
.
.-. ;
sU~3 ~
... ... . . .
.~ . ~ , . .
. ,, ~ , .
' ' . .:
' ' ' . ', :
r; .
~' '.
- 23 -
~ydrolysis Pr DS Ac DS I~Vo
Time (h) (IH NMR) (IH NMR) (Phenol~TCE~
0 3.04 0.09 1.44
2.2 2.90 0.08 1.37
- 54.7 2.63 0.10 1.37
7.2 2.46 0.08 1.38
This example differs from the standard procedure in that
the sulfuric acid was omitted, T~AA was substituted for
TFA, and the reaction was at 55~C. The result is a
- longer contact time, slower hydrolysis rate, and higher
molecular weights as illustrated by I.V.
With reference to Example 1, this example :.
demonstrates the critical role of sulfuric acid and
~ 15 illustrates how the process of this invention differs
; fro~ a process devoid of sulfuric acid and ~FA.
EXAMPLE 7 (Comparative)
` Reagents set forth below were subjected to the
0 standard procedure described above under the indicat@d
réaction conditions. The result, in terms of idsntity
and yield of the desired cellulose ester, and key
analyses of the product, are also set forth below.
.
" _
..... . . . ... . . .
. ' ' .. .
~' .
- - -,
': '
; . . , . . , : ~ , . .. :- , . . . . .
: . . : .. . ~ . , ., :,. , . : . . . -: . , , , :
.. . - !
` '`.: `-.
. - 24 -
`
Starting Cellulosic Cellulose
Weight (g) 5
. Equivalents of . 0.8
TFA/hydroxyl
Acyl Anhydride Acetic Anhydride
Equivalents/hydroxyl 2.1
10 Carboxylic Acid Acetic Acid
Weight (g) 30
Contact Time (m.in) 10320
15 Reaction Temperature 55C
Product Cellulose Triacetate
Degree of Substitution 3.02
(From IH NMR)
Intrinsic Viscosity 1.74
(Phenol~TCE)
GPC (DMF, Polystyrene ~ = 25.7 X 104; Mw = 4O4 X
105
equivalents) ~ = 7.6 X 105; M~ = 170
... . .
: This example differs from the standard procedure in that
the sulfuric acid was omitted and the reaction was at
55 C.
With reference to Examples 1 and 6, this example
demonstxates the critical role of sulfuric acid and
. ..illustrates how the process o~ this invention dif~ers
from a process using TFA but devoid o~ sulfuric acid.
.
......
E~AMPLE 8 (Comparative)
Reagents set forth below were subjected to the
standard procedure described above under the indicated
reaction conditions. The result, in terms of identity
and yield of the desired cellulose ester, and key
- ana~yses o~ the product, are also set forth below.
.. .. : : . ~ . . . .
. - ,, : .- . , . . ~ :
, .. ~: . .. . . .
,. . .- ., .,, . ~,.. . .
.. - . . . . .. . ..
- 25 -
Starting CellulosiC Cellulose
Weight (g) 50
Equivalents of 1.0
TFA/hydroxyl
Equivalents of H2S04/ 0.008
hydroxyl
10 Carboxylic Acid Acetic Acid
Weight (g) 1.9
Carboxylic Acid Propionic Acid
Weight tg) 230
contact Time (min) 1510
DS (From IH NMR) No Reaction
; This example differs from the standard procedure in that
the appropriate molar amount of carboxylic acid was
substituted for the acyl ~nhydrides.
With reference to Example l, this example
demonstrates the critical role of acyl anhydrides and
illustrates an aspect of how this process differs from
i~i; that taught by H.T. Clar~e and C.J. Malm (U.SO Pat2nt
1,880,80~ (1932)).
The invention has been described in detail with
particular reference to pxe~erred embodiments thereof,
but it will be understood that variations and
modifications can be effected within the spirit and
., - scope of the invention. All of the U.S. patents cited
--in the specification a~ incorporated herein by
35 reference in their entirety. -
,
-
.
'~" '''''" ' '' ,'.' '':", '',', ',";''" ~',,,',.' ., " '''', ' " ''"' " ' '' ''' ,
' .,: , ., , ' ' , ' ' . ' , ' ' ' . , ' , ' , ' ' ' , . , ,' . ,
' " ' ;'', ' ' , ' "' '," ,' ,,' . :' '' , ' .' ,.. . ', " '~'' ' ' '
~ ' . ' ' ' , " ' , . ' .' . . '' ' ' ' , - , ' '
:: ~ , : .' . ' . . ' ' ' ' ' .' . . .
' : - :~ ~ ' - . , . ' . ' '
~', ' . ' . . , ' ' ' ,. ' ' ".' ' ' ' . , , . : ' . . .
