Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Reexamination Certificate
2000-03-13
2002-09-10
Killos, Paul J. (Department: 1624)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
C560S130000
Reexamination Certificate
active
06448430
ABSTRACT:
INTRODUCTION
This invention pertains to a process for the preparation of aryl carboxylate esters. More specifically, this invention pertains to a process for preparing aryl carboxylate esters by the reaction of a phenol reactant with an carboxylic acid in the presence of trifluoroacetic acid (TFA) and trifluoroacetic anhydride (TFAA).
BACKGROUND OF THE INVENTION
Aryl carboxylate esters such as phenolsulfonate carboxylate esters are useful bleach activators (Allan H. Gilbert,
Detergent Age
, 1967, June, pages 18-20 and August, pages 30-33). Aryl carboxylate esters also are of commercial interest as components of liquid crystals and polyarylate liquid crystal polymers. A number of methods for synthesizing these aryl carboxylate esters are described in the literature. These known procedures, in general, require relatively harsh conditions and proceed slowly to completion. The synthesis of aryl carboxylate esters by boric acid catalysis is described by William W. Lowrance in
Tetrahedron Letters
, 1971, 37, 3453 and in U.S. Pat. No. 3,772,389. The preparation of carboxylate esters by the reaction of an alkanoic acid with a phenolsulfonate salt, e.g., sodium 4-phenolsulfonate (SPS) in the presence of boric acid as described in U.S. Pat. No. 4,478,754 requires many hours at temperatures greater than 180° C. More active carboxylic acid derivatives such as acid chlorides and anhydrides react with SPS under milder conditions. These reactions are carried out either in a solvent or the carboxylic acid related to the desired ester product at temperatures of 80 to 200° C. Esterification of phenolsulfonate salts using carboxylic acid anhydrides as the esterification agent is the preferred route for commercial scale synthesis although other technologies such as aryl carboxylate ester sulfonation described in the literature: Harold R. W. Ansink and Hans Cerfontain,
Recl. Trav. Chim. Pays
-
Bas
, 1992, 111, 215-21; U.S. Pat. No. 4,695,412.
U.S. Pat. No. 4,587,054 discloses the reaction of a C
6-C
18
carboxylic acid anhydride and substituted phenol at temperatures between 80-120° C. using strong acid catalysis or at temperatures between 180-220° C. using base catalysis. In the examples, the acid-catalyzed process is carried out at 90-100° C. for four hours and the base-catalyzed process is carried out at 200° C. for two hours. Similarly, U.S. Pat. Nos. 4,588,532 and 4,883,612 describe the reaction of a C
7
-C
12
carboxylic acid anhydride in a polar aprotic solvent with SPS in the presence of a catalytic amount of sulfonic acid at temperatures “in excess of about 100° C.” An example illustrates the operation of the process at 115 to 120° C. for a period of six hours. U.S. Pat. Nos. 4,588,532 and 4,883,612 also disclose a base-catalyzed process also using a polar aprotic solvent “in excess of 80° C.” An example describes a base-catalyzed experiment carried out at 90° C. for three hours. U.S. Pat. No. 5,534,642 discloses the reaction of an amido-substituted carboxylic acid anhydride with a phenolsulfonate salt at 180° C. for 3 hours.
A disadvantage of these known processes wherein carboxylic acid anhydrides are reacted with substituted phenols is that one equivalent of by-product carboxylic acid is produced for each equivalent of the desired aryl carboxylate ester. Thus, processes utilizing anhydrides must recycle the by-product carboxylic acid to be economically attractive. Because the carboxylic acids co-produced in commercial processes typically are high boiling, e.g., C
6
-C
18
carboxylic acids, a simple evaporation of the by-product acid, even at reduced pressure, can require elevated temperatures and associated problems such as formation of color bodies. Likewise, a disadvantage of strong acid-catalyzed processes is the coincident catalysis of desulfonation of the phenolsulonate reactant leading to yield losses and darker colored products.
Procedures for the synthesis of phenolsulfonate alkanoate esters by transesterification, either by alcoholysis or acidolysis, have been published. For example, U.S. Pat. No. 4,537,724 discloses the alcoholysis of phenyl nonanoate with SPS to obtain sodium 4-(nonanoyloxy)benzenesulfonate in 83% yield after heating for four hours at 290-300° C. Alternatively, European Patent Publication EP 105,672 discloses the acidolysis of C
2
-C
3
alkanoyloxybenzene sulfonates with C
6
-C
18
aliphatic carboxylic (alkanoate) acids, driven by the removal of the lower boiling C
2
-C
3
acids. In an example, nonanoic acid reacts with acetyloxybenzene sulfonate, using sodium acetate as a catalyst, at 166-218° C. over 3.5 hours. Similarly, U.S. Pat. No. 5,534,642 discloses the acidolysis of acetyloxybenzene sulfonate by amido acids, i.e., alkanoylamido-substituted alkanoic acids, at temperatures of about 200° C. for several hours.
The synthesis of aryl alkanoate esters using an “impeller esterification” technique is known. For example, U.S. Pat. No. 2,082,890 discloses the simultaneous addition of acetic anhydride to a mixture of an alkanoic acid and a phenol to produce the aryl alkanoate ester. An improved impeller method for the synthesis of aryl alkanoate was introduced by E. J. Bourne and coworkers in Journal of the Chemical Society 1949, 2976-79. Bourne et al. disclose the use of TFAA in the synthesis of aryl alkanoate esters using milder conditions. The use of the TFAA impeller esterification method for the synthesis of a phenolsulfonate ester was first disclosed by Thomas C. Bruice et al. in the J.Am.Chem.Soc., 1968, 90, 1333-48. However, the Bruice et al. article does not report a reaction yield, uses an excess of both TFAA and carboxylic acid (relative to the SPS) and employs reaction conditions comparable to those reported by others for strong acid-catalyzed phenolsulfonate ester synthesis. Because TFAA is a relatively expensive chemical, economic considerations discourage its use in large-scale synthesis.
European Patent Publication EP 105,672 discloses the use of acetic anhydride (Ac
2
O) as an impeller in the preparation of phenolsulfonate alkanoate esters. According to the disclosure of EP 105,672, a C
2
-C
3
anhydride first is added to a mixture of a phenolsulfonate and C
6
-C
12
carboxylic acid and heated to 140-160° C. and then the temperature is raised so that transesterification (acidolysis) occurs yielding the desired product. Although the reaction conditions are more severe, only one equivalent of nonanoic acid is used, Ac
2
O is inexpensive and the reaction yield is high.
The “Ac
2
O impeller” method for the synthesis of phenolsulfonate esters also is disclosed in U.S. Pat. Nos. 4,735,740 and 5,650,527 and in German Patent Publication DE 3,824,901 A1. In each of the processes disclosed in these three patent documents, Ac
2
O is added to a carboxylic acid of low volatility in the presence of SPS, heated for an extended period of time at relatively high temperatures, e.g., 2-5 hours at temperatures greater than 120° C., and acetic acid is removed at reduced pressure to drive the conversion of SPS to its carboxylic acid ester.
Three disadvantages are inherent to this approach: first, the use of acetic anhydride as an impeller results in a significant amount of acetate ester which must be converted by high temperature transesterification and removal of acetic acid; secondly, not only is transesterification by acidolysis slow, but equilibrium mixtures between acetate esters and other carboxylic esters does not greatly favor the other carboxylic esters and thus the concentration of acetic acid at equilibrium is relatively low; and finally, the low solubility of phenolsulfonate esters in the media employed in these inventions retards reaction progress and is a barrier to clean conversion to the desired products.
BRIEF SUMMARY OF THE INVENTION
I have discovered that when TFA is used as a solvent, or as a major component of the solvent, the reactions of carboxylic acids with phenols impelled by TFAA proceed at unprecedented rates under milder conditions than previously reported. I also have discovered that the use of molar excesses of TFAA is not necessar
Blake Michael J.
Eastman Chemical Company
Graves, Jr. Bernard J.
Killos Paul J.
Tucker Zachary C.
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