Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Reexamination Certificate
2000-03-20
2002-09-10
Killos, Paul J. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
C562S887000, C554S151000, C554S161000, C554S229000, C558S056000
Reexamination Certificate
active
06448431
ABSTRACT:
FIELD OF THE INVENTION
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 a carboxylic esterification agent selected from carboxylic acid anhydrides and carboxylic acid halides in the presence of trifluoroacetic acid (TFA).
BACKGROUND OF THE INVENTION
Aryl carboxylate esters such as phenolsulfonate 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 useful as components of liquid crystals and polyarylate liquid crystal polymers. A number of methods for synthesizing aryl carboxylate esters are described in the literature. These known procedures, in general, require relatively harsh conditions and proceed slowly to completion. For example, the reaction of a carboxylic acid with a phenol driven by the removal of water to produce aryl carboxylates via boric acid catalysis is described by William W. Lowrance in
Tetrahedron Letters,
1971, 37, 3453 and in U.S. Pat. No. 3,772,389. A similar boric acid catalyzed phenolsulfonate ester synthesis is described in U.S. Pat. No. 4,478,754 and requires many hours at temperatures greater than 180° C. Related procedures employing the reaction of a carboxylic acid with a aryl ester (transesterification by alcoholysis or acidolysis) have been published. U.S. Pat. Nos. 4,537,724 and 5,534,642 and European Patent Publication 105,672 disclose such processes but these also require harsh conditions, i.e. many hours at temperatures from 160-300° C.
More active carboxylic acid derivatives such as acid chlorides and anhydrides react with an alkali metal salt of phenolsulfonate, e.g., sodium 4-phenolsulfonate (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. The use of carboxylic acid anhydrides as the esterification agent is the preferred route for commercial scale synthesis.
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. 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. 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. 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.
The synthesis of aryl alkanoate esters using an “impeller esterification” technique is known. For example, U.S. Pat. No. 2,082,790 discloses the simultaneous addition of acetic anhydride (Ac
2
O) to a mixture of an alkanoic acid and a phenol to produce the aryl alkanoate ester. The “Ac
2
O impeller” method for the synthesis of phenolsulfonate esters is disclosed in U.S. Pat. Nos. 4,735,740 and 5,650,527, German Patent Publication DE 3,824,901 A1, and European Patent Publication EP 105,672. In each of the processes disclosed in these 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. This method thus also requires prolonged treatment at relatively high temperature to achieve acceptable reaction yields.
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 trifluoroacetic anhydride (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. Bruice at al. disclose treatment of decanoic acid and SPS with TFM at somewhat milder conditions (80° C., 5 hours) than those reported for the Ac
2
O impeller method but do not report reaction yields. TFAA, however, presently is an expensive chemical and economic considerations discourage its use in large-scale synthesis.
The use of carboxylic acid chlorides for the synthesis of aryl carboxylate liquid crystals is disclosed in U.S. Pat. No. 3,923,857 and in the synthesis of polyrarylate polymers in U.S. Pat. No. 5,332,858. These patents disclose the use of very mild conditions (25-80° C.) but require the use of reagents such as pyridine or catalysts such as tin tetrachloride which complicate product purification. U.S. Pat. No. 5,069,828 discloses procedures for the synthesis of phenolsulfonate esters using acid chlorides which require prolonged reaction times at temperatures from 80 to 200° C. Such conditions are known in the art to lead to formation of undesirable color bodies in the product. The use of Schotten-Baumann conditions (pH=9-10, 5-20° C.) to produce phenolsulfonate esters is described in U.S. Pat. No. 5,523,434 but the reaction yields are compromised under these conditions.
A need thus exists for synthetic methods to produce aryl carboxylate esters under mild conditions, i.e. temperatures less than 80° C., which are appropriate for large-scale synthesis. In particular, high-yield methods are needed for the synthesis of phenolsulfonate esters which minimize the production of color bodies and provide for efficient methods of product purification.
BRIEF SUMMARY OF THE INVENTION
I have discovered that the reaction of carboxylic acid anhydrides and carboxylic acid halides with phenols proceeds at improved rates under milder conditions than previously reported when the reaction is carried out in the presence of TFA. The process of the present invention therefore comprises the preparation of an aryl carboxylate ester by reacting a phenol with an esterification agent selected from carboxylic acid anhydrides containing a total of up to about 40 carbon atoms and carboxylic acid halides containing a total of up to about 20 carbon atoms in the presence of TFA, wherein the amount of TFA present initially and during the process gives a TFA:phenol reactant mole ratio of at least about 0.5:1. The process of the present invention utilizes a phenol reactant, an esterification agent and TFA and normally is carried out in the absence of trifluoroacetic anhydride and other perfluorocarboxylic acid anhydrides. The process also is operated under substantially anhydrous conditions to avoid decomposition of the carboxylic anhydride and halide esterification agents.
A second embodiment of the present invention is directed to the use of mixed anhydrides as the esterification agent in the preparation of aryl carboxylate esters by the esterification of a phenol. Such mixed anhydrides are produced by the reaction of TFA with the carboxylic acid anhydrides containing a total of up to about 40 carbon atoms and carboxylic acid halides containing a total of up to about 20 carbon atoms utilized in the embodiment described above. The second embodiment therefore comprises the preparation of an aryl carboxylate ester by reacting a phenol with a mixed anhydride having the formula:
R—C(O)—O—C(O)—CF
3
(I)
in the presence
Blake Michael J.
Eastman Chemical Company
Killos Paul J.
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