PROCESS FOR PREPARING CELLULOSE ESTERS

Abstract: Disclosed is a process for preparing cellulose esters utilizing an acyl anhydride and trifluoroacetic anhydride as an impelling agent. The invention includes formation of a cellulose triester optionally followed by a hydrolysis step. Additionally, a cellulose ester with a degree of substitution of less than substantially 3 can be prepared directly by the additional use of trifluoroacetic acid.

Description: PROCESS FOR PREPARING CELLULOSE ESTERS Field of Invention This invention relates to preparation of cellulose esters by utilization of trifluoroacetic anhydride as an impelling agent in combination with certain acyl anhydrides. Cellulose triesters with a degree of substitution (DS) of about 3 can be prepared as well as cellulose esters with a DS of less than about 3. Background of the Invention Cellulose esters are of great commercial interest. Cellulose acetates, for example, are used in cigarette filters and as photographic film base. Other cellulose esters, e.g., cellulose propionates, cellulose butyrates, cellulose acetate propionates, or cellulose acetate butyrates, have found widespread use in coatings, cosmetics, plastics, and pharmaceuticals. It is clear, therefore, that an improved process for the production of cellulose esters would be of considerable commercial importance. It is well known in the art that cellulose triesters, for example cellulose triacetate (degree of substitution or DS = 3; the degree of substitution is defined as the number of acyl groups per anhydroglucose ring) , can be prepared by treating preactivated cellulose with a mixture of sulfuric acid, acetic acid, and acetic anhydride (H.L.B. Gray and C.J. Staud, U.S. Patent 1,683,347 (1928)). Cellulose triacetate is not suitable for all uses and, consequently, is often hydrolyzed to a cellulose acetate 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 long reaction times and results in a dilute reaction mixture from which the high boiling by-product acetic acid must be recovered. Furthermore, the sulfuric catalyst rapidly degrades the molecular weight of the polymer. An additional drawback of this procedure is that after isolation, the cellulose acetate often contains sulfate esters which diminish the desirable properties of the polymer. 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 acids. In a typical procedure, cellulose was treated with an excess (1.9-9.1 eq per hydro yl) of the impelling reagent, the appropriate fatty acid, and a catalyst. After the required reaction time, the product was isolated by precipitation into a nonsolvent. Such a process typically requires a large excess of the impelling reagent and produces only the cellulose triester. Furthermore, isolation of the high boiling impelling acid from a dilute solution which also contains the esterifying fatty acid is required. Similar work disclosed by H.T. Clarke and C.J. Malm (U.S. Patents 1,690,620 (1928); 1,690,621 (1928); 1,698,048 (1929); 1,698,049 (1929)) as well as by C.J. Malm and G.D. Hiatt (U.S. Patent 2,172,250 (1939)) suffer from the same shortcomings described above. E.J. Bourne, M. Stacey, J.C. Tatlow, and J.M. Tedder (J. Chem. Soc. 1949, 2976-2979) have disclosed 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 eq/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, M. Norimoto, T. Yamada, N. Shiraishi (J. Appl. Polym. 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 3,617,201 (1971), R.J. Beral et al. describe a process in which cellulose fiber is treated with TFAA and a carboxylic acid in an inert solvent (benzene) to produce a cellulose ester with a low degree of substitution (0.1-0.3) suitable for use in cellulose textiles. In this process, the cellulose fibers are not disrupted since the reaction medium remains heterogeneous throughout. U.S. Patent 3,097,051 (R.H. Wade, 1963) and S.U. Patent 1,047,908 (O.S. Bludova, N.I. Klenkova, A.P. Sokorenko, 1983) teach similar processes. There is, therefore, a need for a process for the preparation of cellulose triesters which avoids the inherent problems associated with the use of strong mineral acids, e.g., sulfuric acid, as a catalyst in the esterification of cellulose. The process should be easily amenable to the preparation of cellulose esters with a degree of substitution of less than three (e.g., DS of about 0.6-2.8). The process should not require a large excess of an impelling reagent. The process should allow for easy and economical product isolation and recovery of the impelling reagent. It should require economically short reaction times and practical reaction temperatures . The process should not require prior activation of the cellulose before esterification. The reaction conditions should be such that the molecular weight of the product polymer is not substantially destroyed. The process should also be amenable to the preparation of a wide range of cellulose esters. Summary of the Invention Accordingly, I have discovered a process for the preparation of cellulose triesters and cellulose esters with a DS less than about 3 which meets the needs of the cellulose ester art. More specifically, the present invention is directed to a process for preparing a cellulose ester having a degree of substitution of about 3 comprising: contacting (a) a cellulose polymer having a degree of substitution of less than about 3, (b) trifluoroacetic anhydride, and (c) at least one acyl anhydride of the formula: wherein each of R and R is, independently, H, a straight chain alkyl, a branched alkyl, aryl, or substituted aryl, in the presence of 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"). To prepare cellulose esters with a DS of less than about 3, the cellulose triester formed by the above- described process is subjected to a second step (hereinafter alternatively referred 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 sufficient amount of a reactive hydrolysis solvent under conditions to form the desired cellulose ester which has a DS higher than the cellulose polymer used as a starting material for the triesterification process . Another aspect of the present invention provides a process for directly preparing cellulose esters with a DS less than about 3. This process (alternatively referred to herein as the "direct process") can be described as a process for preparing a cellulose ester having a degree of substitution of less than about 3 comprising: contacting (a) a cellulose polymer, (b) trifluoroacetic anhydride, (c) about 0.07 to about 1.0 equivalent per hydroxyl of at least one acyl anhydride of the formula wherein each of R and R is, independently, H, a straight chain alkyl, a branched alkyl, aryl or substituted aryl, and (d) trifluoroacetic acid, in the presence of a solubilizing amount of a solvent and under conditions such that the desired cellulose ester is formed which has a DS higher than the cellulose polymer starting material. Brief Description of the Figures Figure 1 - The 400 MHz proton nuclear magnetic resonance spectrum (NMR) of the methyl acetyl region of the cellulose diacetate obtained by the direct esterification of cellulose in Example 23. Figure 2 - The 400 MHz proton NMR spectrum of the methyl acetyl region of the cellulose diaσetate obtained by a conventional process (prior art process of U.S. Patents 1,984,147 and 2,129,052) as described in Example 23. Figure 3 - The 400 MHz proton NMR spectrum of the methyl acetyl region of the cellulose diacetate obtained after treating the cellulose diacetate as shown in Figure 1 with sulfuric acid and acetic acid as described in Example 23. Detailed Description of the Invention In accordance with the present invention, typical cellulose esters produced by the process of the invention have the desired DS and comprise repeating units of the structure: wherein R , R , and are selected independently from the group consisting of: hydrogen, straight chain alkanoyl, branched alkanoyl, aroyl, heteroaroyl, acyloxy- (straight chain alkanoyl, branched alkanoyl, aroyl, heteroaroyl) alkyl ether, or acyloxy- (straight chain alkanoyl, branched alkanoyl, aroyl, heteroaroyl) aroyl ether. The alkanoyl, aroyl, heteroaroyl, acyloxy alkyl ether, and acyloxy aroyl ether moieties typically contain up to 20 carbon atoms. The cellulose polymer used as a starting material for preparing the cellulose triester can be cellulose, a secondary cellulose ester, a cellulose hydroxy ether, a cellulose hydroxy alkyl ether, or a mixture thereof. Examples of secondary cellulose esters include cellulose acetate, cellulose acetate propionate, and cellulose acetate butyrate, and are described in U.S. Patent 1,984,147. Examples of cellulose hydroxy ethers include hydroxypropyl cellulose, hydroxyethyl cellulose, and hydroxypropylmethyl cellulose, and are described in U.S. Patent 3,278,520. Typical cellulose hydroxy alkyl ethers are also described in U.S. Patent 3,278,520. The cellulose esters useful in the present invention as starting materials, as well as the product cellulose esters produced by the process(es) of the present invention, 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.) of about 0.2 to about 3.0 deciliters/gram as measured at a temperature of 25°C for a 0.25 gram sample in 100 ml of a 60/40 by weight solution of phenol/tetrachloroethane. 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. The acyl anhydride useful in the processes of the present invention is of the formula wherein each of R and R is, independently, hydrogen, a straight chain alkyl, a branched chain alkyl, aryl or substituted aryl. In the acyl anhydride molecule, typical straight chain alkyl groups contain 1 to 20 carbon atoms, typical 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., F, 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 R are the same. Examples of suitable acyl anhydrides useful in the present invention include, but are not limited to, acetic anhydride, propionic anhydride, isobutyric anhydride, butyric anhydride, trimethylacetic anhydride valeric anhydride, hexanoic anhydride, nonanoic anhydride, benzoic anhydride, or a mixture thereof. The more preferred acyl anhydrides are acetic anhydride, propionic anhydride, butyric anhydride, hexanoic anhydride, benzoic anhydride, or a mixture thereof. The trifluoroacetic anhydride (or TFAA) in the processes of the present invention is referred to herein as an "impelling agent" because it is not consumed but still promotes ester formation. In the process for preparing the cellulose triester the amount of component (b) (i.e., the TFAA) is preferably about 0.076 to 2.3 equivalents per hydroxy1, more preferably about 0.5 to about 1 equivalent per hydroxyl; and the amount of component (c) is at least 1 equivalent per hydroxyl. Conditions suitable for the formation of cellulose esters can vary widely. However, for preparing the cellulose triester, temperature typically varies from about 20 to about 60°C, preferably about 50 to about 60°C. Those skilled in the art readily recognize that contact times and cellulose morphology are inter¬ dependent. For example, while the contact time may extend up to 88 hours when acetylating ramie cellulose, the contact time will fall within the range of 1 to 10 hours when acetylating wood pulp. Accordingly, a broad contact time for the triesterification process of the invention is about 1 to about 90 hours, and a preferred contact time is about 1 to about 10 hours . Those skilled in the art will also recognize that contact times and acyl anhydride reactivity are inter¬ dependent. For example, acylation of a dried wood pulp with acetic anhydride may require a contact time of about 6.5 hours. Acylation of the same wood pulp under otherwise similar reaction conditions with hexanoic anhydride can require a contact time of about 65 hours. Those skilled in the art readily recognize that contact time and the quantity of trifluoroacetic anhydride used in the reaction will be interdependent. For example, acetylation of a given wood pulp using 0.76 eq of TFAA per hydroxyl may require about 1 hour to achieve complete esterification whereas, when 0.076 eq of TFAA per hydroxyl is utilized, about 168 hours may be required to achieve complete esterification. Typically, 0.076 to 2.3 eq of TFAA per hydroxyl are contemplated for use in the practice of the present invention. Presently, the preferred range of equivalents of TFAA per hydroxyl is 1.0 to 0.5. For the triesterification process said solvent is typically a carboxylic acid having 1 to 20 carbon atoms, dimethylformamide, dimethylsulfoxide, or a mixture thereof; however, excess acyl anhydride can be used as solvent. The carboxylic acid can optionally be substituted with halogen atoms such as F, Br, and Cl; an example of such a substituted carboxylic acid is trifluoroacetic acid. Preferred is a carboxylic acid, especially 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 aromatic alcohol having 6 to 12 carbon atoms, and a mixture thereof. Preferred reactive hydrolysis solvents include methanol, ethanol, n-propanol, n-butanol, isopropyl alcohol, benzyl alcohol, water, or a mixture thereof,- most preferred are methanol, water, or a mixture thereof. For the hydrolysis step, it is preferred that the 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 of about 20°C to about 70°C and a reaction time of about 0.5 to about 100 hours. More preferred are a temperature of about 50°C to about 60°C and a reaction time of about 0.5 to about 44 hours. The cellulose triester formed by the triesterifi¬ cation process can be isolated and/or purified by conventional means known in the art such as by precipitation into a nonsolvent, distillation, or by spray drying. 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. Typically, trifluoroacetic acid, as well as TFAA, is present in the reaction medium after the desired product is formed. The trifluoroacetic acid can be formed, for example, by reaction of TFAA with residual water present in the cellulose polymer starting material or by means of a transesterification mechanism in the conversion of the cellulose polymer to a cellulose ester. Therefore, it is also preferable to isolate TFAA, trifluoroacetic acid, or a mixture thereof either after the triesterification process or after the hydrolysis step. Such isolation can be accomplished by distillation or by use of a spray drying process. In a similar fashion, the direct process of the present invention can include the additional step of isolating, after reaction, TFAA, trifluoroacetic acid, or a mixture thereof, by distillation or by a spray drying process . Also the direct process of the invention can include the additional step of isolating, after reaction, the desired product by the addition of a precipitating amount of a nonsolvent, by distillation, or by spray drying. Typical nonsolvents for the desired product(s) include water, an n-alkanol having 1 to 4 carbon atoms, a branched alkanol having 3-4 carbon atoms, or a mixture thereof. After performing the direct process, the desired cellulose ester product (which is typically acetone insoluble) can optionally be dissolved in a carboxylic acid corresponding to an acyl group bonded to the cellulose polymer (e.g., acetic acid corresponding to acetyl) wherein the carboxylic acid contains sufficient H 2 S0 4 (e.g., at least about 0.05 weight %, preferably about 0.1 weight %) to promote migration of the bonded acyl group so that a cellulose ester is obtained which is substantially acetone soluble. This acetone soluble product can then be optionally processed by the procedure described hereinabove (e.g., distillation and precipitation) . In the direct process of the invention, it is preferred that the amount of component (b) is about 0.07 to about 2.3 equivalents per hydroxyl; the amount of component (c) is about 0.07 to about 1.0 equivalents per hydroxyl; and the amount of component (d) is about 5 to about 10 parts dry cellulose. It is preferred that the DS of the cellulose polymer starting material for the direct process is less than about 2.85, more preferably less than about 2.5. The most preferred cellulose polymer starting material for the direct process is cellulose. Typical desired products produced by either the hydrolysis step or the direct process have a DS of about 0.5 to about 2.85, more typically about 1.75 to about 2.85. The solvents and other conditions for the direct process are about the same as can be used for the triesterification process . The following examples are to illustrate the invention but should not be interpreted as a limitation thereon. EXAMPLES In the following examples, except where noted, the materials employed were loaded into a flask equipped for mechanical stirring. The reactor was then heated to 50 to 60°C. The reaction mixture was stirred until a clear solution was obtained which is the indicated reaction time for the triesters. Typically, the reaction mixture was filtered before the products were isolated by the addition of a non-solvent. The impelling reagent, the carboxylic acid, and the anhydride can be recovered from the reaction mixture before precipitation or from the filtrate following precipitation by distillation techniques familiar to those skilled in the art. Alternatively, the impelling reagent, the carboxylic acid, the acid anhydride, and the product ester 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 speσtroscopy, intrinsic viscosity, gel permeation chromatography, differential scanning calorimetry, and other methods familiar to those skilled in the art. 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 forth below. Starting Cellulosic Cellulose (Placetate, Lot A) Weight (g) 5 Equivalents of 0.76 TFAA/hydroxyl Acyl Anhydride Acetic Anhydride Equivalents/hydroxyl 2.1 Carboxylic Acid Acetic Acid Weight (g) 30 Contact Time (h) Product, Yield Cellulose Triacetate, 96% Degree of Substitution 3.03 (From 1 H NMR) Intrinsic Viscosity 1.65 (Phenol/TCE) DSC (°C) T„ = 309; T„, = 201; T„ = 160 GPC (DMF, Polystyrene M n = 25.0 X IO 4 ; M^ = 6.2 X IO 5 equivalents) M z = 14.0 X IO 5 ; 1-^ M jj = 2.48 This example demonstrates that less than one equivalent of TFAA rapidly promotes the esterification of cellulose with acetic anhydride. It also demonstrates that TFAA can be used to produce high molecular weight cellulose triacetate in high yield. In Examples 2-5, the reagents set forth below were subjected to the standard procedure described above under the indicated reaction conditions. The results, in terms of identity and yield of the desired cellulose ester, and key analyses of the product, are also set forth below. These examples show the relationship between rate of reaction and the number of equivalents of TFAA/hydroxyl. These examples also demonstrate that as little as 0.076 eq of TFAA can be used to prepare high molecular weight cellulose triacetate in high yield. EXAMPLE 2 Starting Cellulosic Cellulose (Placetate, Lot A) Weight (g) 5 Equivalents of 0.60 TFAA/hydroxyl Acyl Anhydride Acetic Anhydride Equivalents/hydroxyl 2.1 Carboxylic Acid Acetic Acid Weight (g) 30 Contact Time (h) Product, Yield Cellulose Triacetate, 78' Degree of Substitution 2.99 (From 1 H NMR) Intrinsic Viscosity 2.12 (Phenol/TCE) DSC (°C) 'm = 306; • c,h = 200; = 167 GPC (DMF, Polystyrene M n = 28.9 X 10 M w = 4.7 X 10- equivalents) M z = 7.5 X 105 J ; M w /M n = 1.63 EXAMPLE 3 Starting Cellulosic Cellulose (Placetate, Lot A) Weight (g) 5 Equivalents of 0.50 TFAA/hydroxyl Acyl Anhydride Acetic Anhydride Equivalents/hydroxyl 2.1 Carboxylic Acid Acetic Acid Weight (g) 30 Contact Time (h) 8.5 Product, Yield Cellulose Triacetate, 68% Degree of Substitution 2.98 (From 1 H NMR) Intrinsic Viscosity 2.07 (Phenol/TCE) DSC (°C) T m = 300; Tch " 209 ' T g - 165< - T cc = 225 GPC (DMF, Polystyrene M n equivalents) M z EXAMPLE 4 Starting Cellulosic Cellulose (Placetate, Lot A) Weight (g) 5 Equivalents of 0.30 TFAA/hydroxyl Acyl Anhydride Acetic Anhydride Equivalents/hydroxyl 2.1 Carboxylic Acid Acetic Acid Weight (g) 30 Contact Time (h) 50 Product, Yield Cellulose Triacetate, 77% Degree of Substitution 3.03 (From 1 H NMR) Intrinsic Viscosity 2.12 (Phenol/TCE) DSC (°C) Tch - 198 ' ' T g - 168 '- GPC (DMF, Polystyrene M n = 25.2 X 10*; w = 4.8 X 10" equivalents) M z = 8.6 X IO 5 ; M w /M n = 1.90 EXAMPLE 5 Starting Cellulosic Cellulose (Placetate, Lot A) Weight (g) 5 Equivalents of 0.076 TFAA/hydroxyl Acyl Anhydride Acetic Anhydride Equivalents/hydroxyl 2.1 Carboxylic Acid Acetic Acid Weight (g) 30 Contact Time (h) 168 Product, Yield Cellulose Triacetate, 67% Degree of Substitution 3.03 (From NMR) Intrinsic Viscosity 1.76 (Phenol/TCE) DSC (°C) T m = 307 '- T ch - 197 '- T g " 166 '- T cc = 249 GPC (DMF, Polystyrene M n = 15.1 X IO 4 ; M w = 3.4 X IO 5 equivalents) M z = 5.7 X IO 5 ; /M n = 2.24 EXAMPLE 6 (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 analyses of the product, are also set forth below. Starting Cellulosic Cellulose (Placetate, Lot A) Weight (g) 5 Equivalents of 0.76 TFAA/hydroxyl Carboxylic Acid Acetic Acid Weight (g) 50 Contact Time (h) 240 Product, Yield No reaction This example differs from the standard procedure in the following way: Acetic anhydride was omitted and enough acetic acid was employed so that the total solid/liquid ratio remained the same relative to Example 1. This example demonstrates that acetic anhydride is essential to the practice of this invention. It also illustrates one aspect of how this process differs from that taught by E.J. Bourne, M. Stacey, J.C. Tatlow, and J.M. Tedder (J. Chem. Soc. 1949, 2976-2979) . EXAMPLE 7 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 below. Starting Cellulosic Cellulose (Placetate, Lot A) Weight (g) 5 Equivalents of 0.50 TFAA/hydroxy1 Acyl Anhydride Acetic Anhydride Equivalents/hydroxyl 5.4 Contact Time (h) 8.5 Product, Yield Cellulose Triacetate, 42% Degree of Substitution 3.03 (From λ E NMR) Intrinsic Viscosity 2.24 (Phenol/TCE) DSC (°C) k m = 303; • ch = 201; T, 163; cc = 231 GPC (DMF, Polystyrene M n . = 20.8 X IO 4 ; 5 equivalents) M z = 11.6 X IO 5 ; This example differs from the standard procedure in the following way: Acetic acid was omitted and enough acetic anhydride was employed so that the total solid/liquid ratio remained the same as previous examples . With reference to Example 3, this example demonstrates that acetic acid does not play an essential role in controlling reaction rates. It also illustrates another aspect of how this process differs from that taught by E.J. Bourne, M. Stacey, J.C. Tatlow, and J.M. Tedder (J. Chem. Soc. 1949, 2976-2979). EXAMPLE 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 analyses of the product, are also set forth below. Starting Cellulosic Cellulose (Placetate, Lot A) Weight (g) 5 Equivalents of 0.76 TFA/hydroxyl Acyl Anhydride Acetic Anhydride Equivalents/hydroxyl 2.1 Carboxylic Acid Acetic Acid Weight (g) 30 Contact Time (h) 172 Product, Yield Cellulose Triacetate, 58% Degree of Substitution 3.02 (From 1 H NMR) Intrinsic Viscosity 1.74 (Phenol/TCE) DSC (°C) T m = 302; T ch = 194; 157; T cc = 237 GPC (DMF, Polystyrene M n = 25.7 X IO 4 ; M w = 4.4 X IO 5 equivalents) M z = 7.6 X IO 5 ; M-^/^ = 1.70 This example differs from the standard procedure in the following way: Trifluoroacetic acid was substituted for trifluoroacetic anhydride. This example demonstrates the importance of TFAA in that, relative to Example 1, substitution of TFA for TFAA results in a significant drop in reaction rate. EXAMPLE 9 (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 analyses of the product, are also set forth below. Starting Cellulosic Cellulose (Placetate, Lot A) Weight (g) 5 Equivalents of 0.76 TCAA/hydroxyl Acyl Anhydride Acetic Anhydride Equivalents/hydroxyl 2.1 Carboxylic Acid Acetic Acid Weight (g) 30 Contact Time (h) 25 Product, Yield Cellulose Triacetate, 72% Degree of Substitution 3.05 (From 1 H NMR) Intrinsic Viscosity 1.70 (Phenol/TCE) DSC (°C) T_m = 304;' T Ch " 197 ' " T q = 163 ' T cc = 229 GPC (DMF, Polystyrene M n = 22.0 X 10 4 ; M w = 4.3 X 10" equivalents) M z = 8.1 X IO 5 ; 1-^ M JJ = 1.95 This example differs from the standard procedure in the following way: Trichloroacetic anhydride (TCAA) was substituted for trifluoroacetic anhydride. This example demonstrates that the use of TFAA as an impelling reagent results in a 25-fold increase in reaction rate relative to when TCAA is used (H.T. Clarke and C.J. Malm, U.S. Patent 1,880,808 (1932)). In Examples 10-14, the reagents set forth below were subjected to the standard procedure described above under the indicated reaction conditions. The results, in terms of identity and yield of the desired cellulose ester, and key analyses of the product, are also set forth below. These examples show the relationship between rate of reaction, cellulose morphology, and the content of water absorbed in the cellulose fibers . EXAMPLE 10 Starting Cellulosic Cellulose (Placetate, Lot B) Weight (g) 5 Equivalents of 0.76 TFAA/hydroxyl Acyl Anhydride Acetic Anhydride Equivalents/hydroxyl 2.1 Carboxylic Acid Acetic Acid Weight (g) 30 Contact Time (h) 8 Product, Yield Cellulose Triacetate, 56% Degree of Substitution 3.03 (From -""H NMR) Intrinsic Viscosity 1.95 (Phenol/TCE) DSC (°C) T m = 310 '- T ch - 20 ° ; T g " 171 ' " T cc - 243 GPC (DMF, Polystyrene M n = 20.4 X IO 4 ; M w = 3.0 X IO 5 equivalents) M z = 4.2 X IO 5 ; l^/U n = 1.46 EXAMPLE 11 Starting Cellulosic Cellulose (Placetate, Lot B) Dried for 4 days at 0.1 torr Weight (g) 5 Equivalents of 0.76 TFAA/hydroxyl Acyl Anhydride Acetic Anhydride Equivalents/hydroxyl 2.1 Carboxylic Acid Acetic Acid Weight (g) 30 Contact Time (h) 7.5 Product, Yield Cellulose Triacetate, 60% Degree of Substitution 3.01 (From NMR) Intrinsic Viscosity 1.93 (Phenol/TCE) DSC (°C) T m - 306; T ch - 1 - 95 ' T g = 165 '- T cc = 243 GPC (DMF, Polystyrene M n = 19.6 X IO 4 ; M w = 4.4 X IO 5 equivalents) M z = 9.0 X IO 5 ; M w /M n = 2.25 EXAMPLE 12 Starting Cellulosic Cellulose (Placetate, Lot C) Dried for 4 days at 0.1 torr Weight (g) 5 Equivalents of 0.76 TFAA/hydroxyl Acyl Anhydride Acetic Anhydride Equivalents/hydroxyl 2.1 Carboxylic Acid Acetic Acid Weight (g) 30 Contact Time (h) 6.5 Product, Yield Cellulose Triacetate, 67% Degree of Substitution 3 . 02 (From 1 H NMR) Intrinsic Viscosity 2 . 04 (Phenoi/TCE) DSC (°C) T m m = 300 ; T -c ,h = 207 ; = 168 GPC (DMF, Polystyrene 10 - equivalents) EXAMPLE 13 Starting Cellulosic Cellulose (Cotton Linters) Dried for 4 days at 0.1 torr Weight (g) 5 Equivalents of 0.76 TFAA/hydroxyl Acyl Anhydride Acetic Anhydride Equivalents/hydroxyl 2.1 Carboxylic Acid Acetic Acid Weight (g) 30 Contact Time (h) 23 Product, Yield Cellulose Triacetate, 88% Degree of Substitution 3.02 (From 1 H NMR) Intrinsic Viscosity 1.69 (Phenol/TCE) DSC (°C) T m " 309< - T ch - 192 GPC (DMF, Polystyrene n = 21.4 X 10 * M w = 3.4 X 10- equivalents) M z = 5.0 X IO 5 ; M w /M n = 1.58 EXAMPLE 14 Starting Cellulosic Cellulose (Ramie Cellulose) Weight (g) 5 Equivalents of 0.76 TFAA/hydroxyl Acyl Anhydride Acetic Anhydride Equivalents/hydroxyl 2.1 Carboxylic Acid Acetic Acid Weight (g) 30 Contact Time (h) 88 Product, Yield Cellulose Triacetate, 78% Degree of Substitution 2.97 (From -Η. NMR) Intrinsic Viscosity 0.72 (Phenol/TCE) DSC (°C) T m = 300; Tch " 195 ' T g = 162 ' T cc = 236 GPC (DMF, Polystyrene M n = 8.7 X 10 4 ; M„ = 1.7 X IO 5 equivalents) M z = 2.4 X IO 5 ; M^/^ = 1.91 EXAMPLE 15 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 below. Starting Cellulosic Cellulose (Placetate, Lot A) Weight (g) 5 Equivalents of 0.76 TFAA/hydroxyl Acyl Anhydride Propionic Anhydride Equivalents/hydroxyl 2.1 Carboxylic Acid Propionic Acid Weight (g) 37 Contact Time (h) 6.5 Product, Yield Cellulose Tripropionate, 80% Degree of Substitution 2.95 (From 1 H NMR) Intrinsic Viscosity 1.16 (Phenol/TCE) DSC (°C) k m = 233; Tch 168; T_ = 116 GPC (DMF, Polystyrene M n = 6.5 X 10 4 ; w = 2.3 X 10" equivalents) M z = 8.9 X IO 5 ; H^/IΛ^ = 3.56 This example demonstrates that less than one equivalent of TFAA promotes the esterification of cellulose with propionic anhydride. EXAMPLE 16 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 below. Starting Cellulosic Cellulose (Placetate, Lot A) Weight (g) 5 Equivalents of 0.76 TFAA/hydroxyl Acyl Anhydride Butyric Anhydride Equivalents/hydroxyl 2.1 Carboxylic Acid Butyric Acid Weight (g) 44 Contact Time (h) 8 Product Yield Cellulose Tributyrate, 38% Degree of Substitution 3.02 (From NMR) Intrinsic Viscosity 0.98 (Phenol/TCE) DSC (°C) l m 183; m-- — 86 GPC (DMF, Polystyrene M„n = 8.5 X 10 M w = 2.1 X 10- equivalents) M„ = 4.4 X 10" M w /M n = 3.56 This example demonstrates that less than one equivalent of TFAA promotes the esterification of cellulose with butyric anhydride. EXAMPLE 17 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 below. Starting Cellulosic Cellulose (Placetate, Lot C) Weight (g) 2.5 Equivalents of 2.0 TFAA/hydroxyl Acyl Anhydride Hexanoic Anhydride Equivalents/hydroxyl 2.0 Carboxylic Acid Hexanoic Acid Weight (g) 58 Contact Time (h) 65 Product, Yield Cellulose Trihexanoate, 64% Degree of Substitution 3.06 (From 1 H NMR) Intrinsic Viscosity 1.10 (Phenol/TCE) DSC (°C) Tm = 9 y 9 y ' • Tg = 55 GPC (DMF, Polystyrene M 22.0 X 10»4. n = M^^ = 4.5 X 10" equivalents) „ = 8.2 X IO 5 ; M w /M n = 2.10 This example demonstrates that TFAA promotes the esterification of cellulose with the anhydrides of long- chain fatty acids. EXAMPLE 18 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 below. Starting Cellulosic Cellulose (Placetate, Lot C) Dried for 4 days at 0.1 torr Weight (g) 5 Equivalents of 0.76 TFAA/hydroxyl Acyl Anhydride Benzoic Anhydride Equivalents/hydroxyl 2.1 Carboxylic Acid Trifluoroacetic Acid Weight (g) 10 Contact Time (h) 14 Product, Yield Cellulose Tribenzoate, 93% Degree of Substitution 2.89 (From λ E NMR) Intrinsic Viscosity 0.28 (Phenol/TCE) GPC (DMF, Polystyrene Mn = 5.5 X 10 M w = 1.2 X 10- equivalents) M„ = 1.9 X 10- M w /M n = 2.10 This example demonstrates that TFAA promotes the esterification of cellulose with aromatic anhydrides and that trifluoroacetic acid can be used as a solvent in the esterification of cellulose. EXAMPLE 19 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 below. Starting Cellulosic Cellulose (Placetate, Lot A) Weight (g) Equivalents of 0.76 TFAA/hydroxyl Acyl Anhydride Propionic Anhydride Equivalents/hydroxyl 2.1 Carboxylic Acid Acetic Acid Weight (g) 30 Contact Time (h) 96 Product Cellulose Acetate Propionate Degree of Substitution Ac = 1.96, Pr = 0.97 (From 1 H NMR) Intrinsic Viscosity 1.14 (Phenol/TCE) DSC (°C) τ m - 261 ' Tg = 153 GPC (DMF, Polystyrene M n 3.2 X IO 5 equivalents) M z = 1.67 This example demonstrates that TFAA promotes the synthesis of mixed esters from cellulose. EXAMPLE 20 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 below. Starting Cellulosic Cellulose Diacetate (DS = 1.75) Weight (g) 5 Equivalents of 2.7 TFAA/hydroxyl Acyl Anhydride Propionic Anhydride Equivalents/hydroxyl 2.1 Carboxylic Acid Propionic Acid Weight (g) 37 Contact Time (h) 16 Product Cellulose Acetate Propionate Degree of Substitution Ac = 1.75, Pr = 1.27 (From 1 H NMR) Intrinsic Viscosity 0.73 (Phenol/TCE) DSC (°C) T m - 264 ' T ch = 200; = 135 τ cc = 224 GPC (DMF, Polystyrene M n = 11.7 X 10 M w = 1.8 X 10" equivalents) M ^ = 2.5 X IO 5 , M w /M n = 1.57 This example demonstrates that TFAA promotes the esterification of secondary cellulose esters without removing or scrambling the first acyl group. EXAMPLE 21 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 below. Starting Cellulosic Hydroxypropyl Cellulose Weight (g) 5 Equivalents of 0.76 TFAA/hydroxyl Acyl Anhydride Acetic Anhydride Equivalents/hydroxyl 2 Carboxylic Acid Acetic Acid Weight (g) 40 Contact Time (h) 15.5 Product (Acetoxypropyl) Cellulose GPC (DMF, Polystyrene M n = 10 X IO 4 ; M w = 1.6 X IO 5 equivalents) M z = 2.3 X IO 5 ; M w /M n = 1.59 This example demonstrates that TFAA promotes the esterification of cellulose ethers. EXAMPLE 22 The following example demonstrates the preparation of cellulose esters with a degree of substitution less than three. The example differs from the standard procedure in the following indicated ways : The materials employed (60 g of cellulose, 0.76 eq of TFAA, 2.1 eq of AC2O, and 360 g of AcOH) were loaded into a flask equipped for mechanical stirring. The reactor was then heated to 55°C and the reaction mixture was stirred until a clear solution was obtained (2.5 h) . An aliquot was removed before adding 700 g of AcOH and 208.5 g of water to the homogeneous solution. The reaction was stirred at 50°C with aliquots being removed at the following indicated times . All aliquots were processed by the standard procedure and analyzed by the standard methods. in p-) r~ o vø cθ " >< σ. ι -s* -~- H o ^ -n vø vø !ø !ø ιø ,n -n ιn c. rπ CN CN CN fN CN CN CN O- CN CN ιn oo « vø cN }< m N r~ CO (n oo oo r~- vø ιχ> ro r H co vø Q CN CN C CN CN CN CN CN CN r-l rH EXAMPLE 23 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 below. Starting Cellulosic Cellulose (Placetate, Lot B) Weight (g) 5 Equivalents of 0.76 TFAA/hydroxyl Acyl Anhydride Acetic Anhydride Equivalents/hydroxyl 0.8 Carboxylic Acid Trifluoroacetic Acid Weight (g) 44 Contact Time (h) 1.5 Product, Yield Cellulose Diacetate, 81% Degree of Substitution 2.56 (From 1 H NMR) Intrinsic Viscosity 1.81 (Phenol/TCE) GPC (DMF, Polystyrene M n = 24.3 X 10 M w = 5.3 X 10" equivalents) M z = 10.4 X 10 J ; M w /M n = 2.17 This example demonstrates that cellulose acetate can be prepared directly from cellulose using trifluoroacetic acid as the carboxylic acid solvent. In this example, the reaction was processed by the standard procedure immediately after obtaining a clear solution. This cellulose diacetate (CDA) (see Figure 1) is different from CDA prepared by conventional methods (see Figure 2) (C.J. Malm, U.S. Patent 1,984,147 (1934); C.R. Fordyce, U.S. Patent 2,129,052 (1938)) in that it has a different acetyl distribution and it is insoluble in acetone. This acetone insoluble CDA can be converted to acetone soluble CDA simply by dissolving the acetone insoluble CDA in acetic acid containing 0.1% H 2 S0 4 . After processing by the standard procedure, the cellulose acetate is acetone soluble and has the same acetyl distribution as conventional acetone soluble CDA (see Figures 2 and 3). EXAMPLE 24 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 below. Starting Cellulosic Cellulose (Placetate, Lot B) Weight (g) Equivalents of 0.76 TFAA/hydroxyl Acyl Anhydride Acetic Anhydride Equivalents/hydroxyl 0.4 Carboxylic Acid Trifluoroacetic Acid Weight (g) 44 Contact Time (h) 23.3 Product Cellulose Diacetate Degree of Substitution 2.40 (From E NMR) Intrinsic Viscosity 0.47 (Phenol/TCE) This example demonstrates that when extended reaction times are employed and trifluoroacetic acid is the carboxylic acid solvent, both acetyls of the acetic anhydride are incorporated into the cellulose ester. EXAMPLE 25 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 below. Starting Cellulosic Cellulose (Placetate, Lot D) Weight (g) 250 Equivalents of 1.37 TFAA/hydroxyl Acyl Anhydride Propionic Anhydride Equivalents/hydroxyl 1.7 Acyl Anhydride Acetic Anhydride Equivalents/hydroxyl 0.05 Carboxylic Acid Propionic Acid Weight (g) 1490 Reactive Hydrolysis Water Solvent Weight (g) 420 Contact Time (h) 23 (Esterification = 8 h; Hydrolysis = 15 h) Product Cellulose Acetate Propionate, 6-4 '■ Degree of Substitution Ac = 0.03, Pr = 2.33 (From 1 H NMR) Intrinsic Viscosity 1.88 (Phenol/TCE) DSC (°C) T m = 182; T g = 135 GPC (DMF, Polystyrene M n . 23.6 X 10 4 ; M w = 4.8 X IO 5 equivalents) Mr = 10.5 X IO 5 ; M^ JJ = 2.05 This example differs from the standard procedure in that a reactive solvent was added to the homogeneous reaction mixture at the triester stage (DS. = 0.06; DSp = 3.0) to promote hydrolysis of the triester to a mixed ester with a degree of substitution of less than three. This example demonstrates that TFAA promotes the synthesis of cellulose acetate propionates with a degree of substitution of less than three from cellulose. Furthermore, this example also demonstrates that high molecular weight, high hydroxyl mixed cellulose esters can be obtained. EXAMPLE 26 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 below. Starting Cellulosic Cellulose (Placetate, Lot D) Weight (g) 50 Equivalents of 1.5 TFAA/hydroxyl Acyl Anhydride Butyric Anhydride Equivalents/hydroxyl 1.73 Acyl Anhydride Acetic Anhydride Equivalents/hydroxyl 0.08 Carboxylic Acid Butyric Acid Weight (g) 289 Reactive Hydrolysis Water Solvent Weight (g) 91 Contact Time (h) 49.3 (Esterification = 20.3 h; Hydrolysis = 29 h) Product Cellulose Acetate Butyrate, 73' Degree of Substitution Ac = 0.03, Bu = 2.14 (From 1 H NMR) Intrinsic Viscosity 1.49 (Phenol/TCE) DSC (°C) T m = 173 GPC (DMF, Polystyrene M n = 24.0 X IO 4 ; M^ = .2 X 10 5 equivalents) M z = 6.5 X 10 5 ; M w /M n = 1.74 This example differs from the standard procedure in that a reactive solvent was added to the homogeneous reaction mixture at the triester stage (DS, = 0.09; DS βu = 3.0) to promote hydrolysis of the triester to a mixed ester with a degree of substitution of less than three. This example demonstrates that TFAA promotes the synthesis of cellulose acetate butyrates with a degree of substitution of less than three from cellulose. Furthermore, this example also demonstrates that high molecular weight, high hydroxyl mixed cellulose esters can be obtained. EXAMPLE 27 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 below. Starting Cellulosic Cellulose (Placetate, Lot C) Weight (g) 200 Equivalents of 1.0 TFAA/hydroxyl Acyl Anhydride Equivalents/hydroxyl Carboxylic Acid Weight (g) Reactive Hydrolysis Solvent Weight (g) Contact Time (h) 19 (Esterification = 8 h; Hydrolysis = 11 h) Product Cellulose Acetate, 59% Degree of Substitution 2.39 (From 1 H NMR) Intrinsic Viscosity 2.00 (Phenol/TCE) DSC (°C) T m m = 223; T g = 171 GPC (DMF, Polystyrene M :. n n = 2θ.o x ioc *; M w = 4.1 X 10- equivalents) = 7.1 X 10 D ; M w /M n = 1.99 This example differs from the standard procedure in that a reactive solvent was added to the homogeneous reaction mixture at the triester stage to promote hydrolysis of the triester to a cellulose acetate with a degree of substitution of less than three. The product of this example was isolated by spray drying (inlet temperature = 180°C; outlet temperature = 30°C; flow rate = 58 g/min) . This example demonstrates that TFAA promotes the synthesis of cellulose acetates with a degree of substitution less than three from cellulose. Further¬ more, this example also demonstrates that high molecular weight, high hydroxyl cellulose acetates can be obtained. The invention has been described in detail with particular reference to preferred 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 are incorporated herein by reference in their entirety.

Claims: Claims I Claim: 1. A process for preparing a cellulose ester having a degree of substitution of 3 comprising: contacting (a) a cellulose polymer having a degree of substitution of less than 3, (b) trifluoroacetic anhydride, and (c) at least one acyl anhydride of the formula: wherein each of R and R is, independently, H, a straight chain alkyl, a branched alkyl, aryl, or substituted aryl, in the presence of a solubilizing amount of a solvent and under conditions such that the desired cellulose ester is formed. 2. The process of Claim 1 wherein component (a) is a cellulose polymer having a degree of substitution of 0 to 2.9 and is selected from the group consisting of cellulose, a secondary cellulose ester, a cellulose hydroxy ether, a cellulose hydroxy alkyl ether, and a mixture thereof. 3. The process of Claim 1 wherein component (c) is selected from the group consisting of acetic anhydride, propionic anhydride, isobutyric anhydride, butyric anhydride, trimethylacetic anhydride, valeric anhydride, hexanoic anhydride, nonanoic anhydride, benzoic anhydride, and a mixture thereof. 4. The process of Claim 1 wherein the amount of component (b) is 0.07 to 2.3 equivalents per hydroxyl and the amount of component (c) is at least 1 equivalent per hydroxyl. 5. The process of Claim 1 wherein component (c) is selected from the group consisting of acetic anhydride, propionic anhydride, butyric anhydride, hexanoic anhydride, benzoic anhydride, and a mixture thereof; and the amount of component (b) is 0.5 to 1 equivalent per hydroxyl. 6. The process of Claim 1 carried out at 20°C to 60°C for 1 to 90 hours. 7. The process of Claim 1 carried out at 50°C to 60°C for 1 to 10 hours. 8. The process of Claim 1 wherein said solvent is selected from the group consisting of a carboxylic acid having 1 to 20 carbon atoms, dimethyl— formamide, dimethylsulfoxide, and a mixture thereof. 9. The process of Claim 1 wherein said solvent is acetic acid. 10. The process of Claim 1 wherein R and R are the same. 11. The process of Claim 1 including the additional step of isolating, after reaction, trifluoroacetic anhydride, trifluoroacetic acid, or a mixture thereof by distillation or by spray drying. 12. The process of Claim 1 including the additional step of isolating, after reaction, the desired product by the addition of a precipitating amount of a nonsolvent. 13. The process of Claim 1 including the additional step of isolating, after reaction, the desired product by distillation or by spray drying. 14. A process for preparing a cellulose ester having a degree of substitution of less than 3 comprising: (A) contacting (a) a cellulose polymer having a degree of substitution of less than 3, (b) trifluoroacetic anhydride, and (c) at least one acyl anhydride of the formula: wherein each of R and R is, independently, H, a straight chain alkyl, a branched alkyl, aryl, or substituted aryl, in the presence of a solubilizing amount of a solvent and under conditions such that a cellulose ester having a degree of substitution of 3 is formed, and (B) contacting the cellulose ester formed by step (A) with a sufficient amount of a reactive hydrolysis solvent under conditions to form the desired cellulose ester which has a degree of substitution higher than the original cellulose polymer of step (A) (a) . 15. The process of Claim 14 wherein for step (A), component (a) is a cellulose polymer having a degree of substitution of 0 to 2.9 and is selected from the group consisting of cellulose, a secondary cellulose ester, a cellulose hydroxy ether, a cellulose hydroxy alkyl ether, and a mixture thereof. 16. The process of Claim 14 wherein for step (A), component (c) is selected from the group consisting of acetic anhydride, propionic anhydride, isobutyric anhydride, butyric anhydride, trimethylacetic anhydride, valeric anhydride, hexanoic anhydride, nonanoic anhydride, benzoic anhydride, and a mixture thereof. 17. The process of Claim 14 wherein for step (A) , the amount of component (b) is 0.07 to 2.3 equivalents per hydroxyl and the amount of component (c) is at least 1 equivalent per hydroxyl. 18. The process of Claim 14 wherein for step (A) , component (c) is selected from the group consisting of acetic anhydride, propionic anhydride, butyric anhydride, hexanoic anhydride, benzoic anhydride, and a mixture thereof; and the amount of component (b) is 0.5 to 1 equivalent per hydroxyl. 19. The process of Claim 14 wherein step (A) is carried out at 20°C to 60°C for 1 to 90 hours. 20. The process of Claim 14 wherein step (A) is carried out at 50°C to 60°C for 3 to 10 hours. 21. The process of Claim 14 wherein said reactive hydrolysis solvent is selected from the group consisting of an n—alkanol having 1 to 4 carbon atoms, water, a branched chain alkanol having 3 to 4 carbon atoms, an aromatic alcohol having 6 to 12 carbon atoms, and a mixture thereof. 22. The process of Claim 14 wherein said reactive hydrolysis solvent is selected from the group consisting of methanol, ethanol, n—propanol, n-butanol, isopropyl alcohol, benzyl alcohol, and water. 23. The process of Claim 14 wherein said reactive hydrolysis solvent is selected from the group consisting of methanol, water, and a mixture thereof. 24. The process of Claim 14 wherein the amount of reactive hydrolysis solvent is from 1 volume % to that amount which results in the desired product precipitating from solution. 25. The process of Claim 14 wherein the amount of reactive hydrolysis solvent is from 5 to 15 volume %. 26. The process of Claim 14 wherein step (B) is carried out at a temperature from 25°C to 70°C for 0.5 to 100 hours. 27. The process of Claim 14 wherein the cellulose ester formed by step (B) has a degree of substitution of from 0.5 to 2.85. 28. The process of Claim 14 wherein the solvent for step (A) is selected from the group consisting of a carboxylic acid having 1 to 20 carbon atoms, dimethylformamide, dimethylsulfoxide, and a mixture thereof. 29. The process of Claim 14 wherein the solvent for step (A) is acetic acid. 30. The process of Claim 14 wherein R and R are the same. 31. The process of Claim 14 including the additional step of isolating, after reaction, trifluoroacetic anhydride, trifluoroacetic acid, or a mixture thereof by distillation. 32. The process of Claim 14 including the additional step of isolating, after reaction, the desired product by the addition of a precipitating amount of a nonsolvent. 33. The process of Claim 14 including the additional step of isolating, after reaction, the desired product by spray drying. 34. A process for preparing a cellulose ester having a degree of substitution of less than 3 comprising: contacting (a) a cellulose polymer, (b) trifluoroacetic anhydride, (c) 0.07 to 1.0 equivalents per hydroxyl of at least one acyl anhydride of the formula K I v 1 v wherein each of R and R is, independently, H, a straight chain alkyl, a branched alkyl, aryl or substituted aryl, and (d) trifluoroacetic acid, in the presence of a solubilizing amount of a solvent and under conditions such that the desired cellulose ester is formed which has a degree of substitution higher than the cellulose polymer starting material. 35. The process of Claim 34 including the additional step of isolating, after reaction, trifluoroacetic anhydride, trifluoroacetic acid, or a mixture thereof by distillation or by spray drying. 36. The process of Claim 34 including the additional step of isolating, after reaction, the desired product by the addition of a precipitating amount of a nonsolvent. 37. The process of Claim 34 including the additional step of isolating, after reaction, the desired product by spray drying. 38. The process of Claim 34 wherein the amount of component (b) is 0.07 to 2.3 equivalents per hydroxyl; the amount of component (c) is 0.07 to 1.0 equivalents per hydroxyl; and the amount of component (d) is 5 to 10 parts dry cellulose. 39. The process of Claim 34 wherein component (a) is a cellulose polymer having a degree of substitution of 0 to 2.9 and is selected from the group consisting of cellulose, a secondary cellulose ester, a cellulose hydroxy ether, a cellulose hydroxy alkyl ether, and a mixture thereof. 40. The process of Claim 34 wherein component (c) is selected from the group consisting of acetic anhydride, propionic anhydride, isobutyric anhydride, butyric anhydride, trimethylacetic anhydride, valeric anhydride, hexanoic anhydride, nonanoic anhydride, benzoic anhydride, and a mixture thereof. 41. The process of Claim 34 wherein the amount of component (b) is 0.07 to 2.3 equivalents per hydroxyl and the amount of component (c) is at least 1 equivalent per hydroxyl. 42. The process of Claim 34 wherein component (c) is selected from the group consisting of acetic anhydride, propionic anhydride, butyric anhydride, hexanoic anhydride, benzoic anhydride, and a mixture thereof; and the amount of component (b) is 0.5 to 1 equivalent per hydroxyl. 43. The process of Claim 34 carried out at 20°C to 60°C for 1 to 90 hours. 44. The process of Claim 34 carried out at 50°C to 60°C for 1 to 10 hours. 45. The process of Claim 34 wherein said solvent is selected from the group consisting of a carboxylic acid having 1 to 20 carbon atoms, dimethyl— formamide, dimethylsulfoxide, and a mixture thereof. 46. The process of Claim 34 wherein said solvent is acetic acid. 47. The process of Claim 34 wherein R and R are the same. 48. The process of Claim 34 wherein the product from said process is substantially acetone insoluble and is dissolved in a carboxylic acid corresponding to an acyl group bonded to the cellulose ester product wherein the carboxylic acid contains a sufficient amount of sulfuric acid to result in the cellulose ester product being substantially acetone soluble. 49. The process of Claim 48 wherein the cellulose ester is cellulose acetate and the carboxylic acid is acetic acid.

Inventors: BUCHANAN CHARLES MICHAEL, BUCHANAN, CHARLES, MICHAEL
Applicants: EASTMAN KODAK CO, EASTMAN KODAK COMPANY
Application year: 1991
Main classification: C08B3
IPC codes: C08B3, C08B11, C08B13