Patent Application
20080021235
In the inventive process, a C2-C4 carboxylic acid reacts with a dicyclopentadiene. Suitable carboxylic acids are aliphatic carboxylic acids having up to four carbons. Examples include acetic acid, propionic acid, butyric acid, and isobutyric acid. Higher carboxylic acids (C5 and up) are excluded because the esters do not have much of an odor, while formic acid (C1) gives esters with a less-desirable odor. Because it is readily available, acetic acid is most preferred.
While any desired grade of acetic acid can be used to make tricyclodecenyl acetates, I surprisingly found that crude acetic acid (80-95 wt. %, with a balance of organic compounds) can provide a fragrance-quality product. Acetic acid and acetic anhydride are staple reagents for the manufacture of esters used as fragrance components. Often, it is impractical to recover the acetic acid by conventional techniques such as extraction or distillation. Consequently, process streams containing acetic acid, acetic anhydride, and organic contaminants are commonplace in the fragrance industry. One such conveniently available stream contains about 80% acetic acid, 10-15% acetic anhydride, α-pinene, limonene, acetate esters, and other impurities. I found that this material can be used instead of glacial acetic acid (99% pure) in the inventive process to give a commercially acceptable tricyclodecenyl acetate (see Example 3, below).
Suitable dicyclopentadienes have a carbon framework derived from dicyclopentadiene. The framework can be substituted with alkyl, halogen, aryl, or other groups that do not interfere with addition of the carboxylic acid to a carbon-carbon double bond of the dicyclopentadiene during preparation of the tricyclodecenyl ester. Preferred dicyclopentadienes are unsubstituted dicyclopentadiene (DCPD) and alkyl-substituted dicyclopentadienes such as the ones disclosed in U.S. Pat. Nos. 4,453,000 and 4,358,617, the teachings of which are incorporated herein by reference. DCPD is readily available and is most preferred.
The grade of the dicyclopentadiene used is not critical. In fact, this is an advantage of the inventive process because commercial grade DCPD (93-94% pure DCPD) or high-purity DCPD (>98%) is normally needed to achieve desirable fragrance character. Here, however, technical grade DCPD (e.g., >80% pure DCPD such as Lyondell Chemical Company's DCPD-101) can be used as a low-cost alternative with good results. Preferably, the dicyclopentadiene used has a purity within the range of 80 to 90%.
The carboxylic acid and the dicyclopentadiene are combined in roughly equimolar amounts. In particular, up to a thirty mole percent excess of the carboxylic acid can be used, or as little as eighty percent of a molar equivalent. Thus, the molar ratio of carboxylic acid to the dicyclopentadiene is within the range of 0.8 to 1.3. A preferred ratio is from 0.9 to 1.1; more preferred is a ratio within the range of 0.95 to 1.05. The ability to use equimolar amounts of the carboxylic acid and the dicyclopentadiene is another advantage of the invention. Using little or no excess carboxylic acid at the outset can reduce or eliminate the need for subsequent removal of the unreacted portion either by distillation or by neutralization and disposal of the resulting carboxylic acid salt. In contrast, prior-art methods typically require a large excess of the carboxylic acid.
Triflic acid catalyzes the addition reaction between the carboxylic acid and the dicyclopentadiene. The source of the triflic acid is not critical. It can be purchased, for example, from Aldrich Chemical and other suppliers. Only a catalytic amount of triflic acid is needed. Typically, the amount used will be less than 1 wt. % based on the amount of the dicyclopentadiene used. Preferably, less than 0.5 wt. % of triflic acid is used, more preferably less than 0.2 wt. %.
The process is performed under conditions effective to produce tricyclodecenyl esters. By “tricyclodecenyl esters” we mean addition reaction products of one molar equivalent of a C2-C4 carboxylic acid and a dicyclopentadiene. The acid adds across one of the two carbon-carbon double bonds of the dicyclopentadiene. Each of the esters has a tricyclic ten-carbon framework that may have additional alkyl or other substituents that derive from the dicyclopentadiene. The tricyclodecenyl esters are normally generated as a mixture of two or more isomers, with one isomer often predominating. Preferably, the tricyclodecenyl ester derives from dicyclopentadiene. Thus, preferred tricyclodecenyl esters include, for example, tricyclodecenyl acetate (TCDA), tricyclodecenyl propionate, tricyclodecenyl butyrate, and tricyclodecenyl isobutyrate.
Most preferably, the tricyclodecenyl ester is TCDA. Following the reaction of acetic acid and DCPD to produce TCDA, distillation is advantageously used to recover a TCDA-rich product. Commercially acceptable product comprises at least 95 wt. %, more preferably at least 98 wt. %, of TCDA isomers as measured by gas chromatography. The major isomer is preferably at least 90 wt. %, more preferably at least 92 wt. %, of the product. Preferably, the product also has a refractive index (nD20) within the range of 1.49 to 1.50, more preferably from 1.493 to 1.497. Preferred product has a specific gravity (d420) within the range of 1.07 to 1.08, more preferably from 1.071 to 1.076.
To be commercially acceptable, the tricyclodecenyl esters usually must also satisfy well-recognized odor requirements. Relatively minor variations in isomer content may or may not impact commercial suitability. Moreover, a particular ester sample may have an acceptable isomers content but an unacceptable odor.
The tricyclodecenyl esters are easy to prepare. The dicyclopentadiene, triflic acid, and acetic acid are combined in any desired order. In one aspect, the dicyclopentadiene is added gradually to a well-agitated mixture of the acetic acid and triflic acid. See Examples 1 and 4.
While the reaction temperature is not critical, it is preferred to perform the reaction at a temperature within the range of 60° C. to 150° C., more preferably from 110° C. to 140° C. The reaction is normally complete within 1 to 10 hours, depending upon the conditions selected.
The tricyclodecenyl ester is isolated from the reaction mixture by any convenient means. Distillation is particularly preferred. Commercially acceptable esters are normally obtained by distilling the mixture at reduced pressure, preferably <10 torr, more preferably <2 torr, and collecting a center cut containing material having an acceptable boiling range.
The process of the invention can be practiced in any desired mode. Thus, a batch, semi-continuous, or continuous process can be employed.
The following examples merely illustrate the invention. Those skilled in the art will recognize many variations that are within the spirit of the invention and scope of the claims.
Dicyclopentadiene (DCPD, 1048 g, purity 86%) is added dropwise at 90-110° C. to a stirred mixture of glacial acetic acid (420 g) and triflic acid (1.18 g) over 5.7 h. The reaction mixture is then stirred for 2.5 h at 120° C. Brine (98 g, d420 1.202), water (49 g), and 50% aq. NaOH solution (61 g) are added at 50° C., and the mixture stirs for 0.5 h. After the layers settle, the organic phase is isolated and washed with brine (2×125 g). Distillation of crude material (1409 g) at 1 torr provides commercial grade TCDA (888 g, 67% based on DCPD). Major isomer by gas chromatography (GC): 92.4%; Isomer A: 1.6%; Isomer B: 4.3%; Isomer C: 0.5%.
Targeted ranges: Major isomer: >90%; Isomer A: <2%; Isomer B: 1-6%; Isomer C: <3%.
Dicyclopentadiene (DCPD, 1048 g, purity: 86%) is added dropwise at 90-140° C. to a stirred mixture of glacial acetic acid (420 g) and boron trifluoride:acetic acid, 1:2 adduct (15.9 g) over 3.25 h. The reaction mixture is then stirred for 0.75 h at 140° C. Brine (100 g), water (50 g), and 50% aq. NaOH solution (68 g) are added at 50° C., and the mixture stirs for 0.5 h. After the layers settle, the organic phase is isolated and washed with brine (2×125 g). Distillation of crude material (1415 g) at 1 torr provides TCDA (786 g, 60% based on DCPD) that is dissimilar to commercial TCDA in terms of isomer content. Major isomer: 90.5%; Isomer A: 4.1%; Isomer B: 3.7%; Isomer C: 1.4%.
Example 1 shows that the inventive process provides a TCDA product that falls within the targeted isomer requirements. When the procedure is modified (Comparative Example 2), too little of the major isomer is made, and too much of Isomer A is produced. An additional comparative experiment demonstrated that commercially acceptable TCDA can be made with the BF3 catalyst by using a large excess of acetic acid and DCPD having a purity of 93%.
Step A. Hydrolysis of acetic anhydride. A by-product stream containing about 80 wt. % of acetic acid, acetic anhydride (about 13 wt. %), α-pinene, limonene, acetate esters, and other impurities, is combined with enough water (12.3 mL) to hydrolyze the acetic anhydride. Triflic acid (1.36 g) is added, and the mixture is heated with stirring to 110° C. and kept at this temperature for 30 min. GC of the resulting dark brown mixture indicates the absence of acetic anhydride, about 90 wt. % of acetic acid, and the balance of a complex mixture of organic compounds.
Step B. Synthesis of TCDA. DCPD (1048 g, 86% pure) is added dropwise at 110-120° C. to the mixture obtained in Step A over 5.7 hrs. The reaction mixture is stirred for an additional 2.5 h at 120° C. and is then cooled to 40° C. Brine (98 g, d420 1.20), water (49 g), and 50% aqueous NaOH (61 g) are added at 50° C. and the mixture stirs for 30 min. The layers are separated and the organic phase is washed with brine (2×125 g). Crude material (1423 g) is distilled at 1 torr to provide commercial grade TCDA (925 g, 69% based on DCPD).
Example 3 demonstrates that fragrance-quality TCDA can be made from crude, recycled acetic acid and technical grade DCPD.
A mixture of DCPD (1048 g, 87-88%), triflic acid (1.19 g), and glacial acetic acid (420 g) is heated with stirring to 130° C. over 55 min. The mixture is kept at 130-135° C. for an additional 2.4 h, then cooled to 40° C. Brine (104 g, d420 1.20), water (52 g), and 50% aqueous NaOH (66 g) are added at 50° C., and the mixture stirs for 30 min. The phases are separated, and the organic layer is washed with brine (2×125 g). Crude material (1284 g) is distilled at 1 torr to provide commercial grade TCDA (690 g, 51% based on DCPD).
Examples 1 and 4 show that the yield of commercially acceptable TCDA is enhanced by gradual addition of DCPD to a mixture of acetic acid and triflic acid.
The examples are meant only as illustrations. The following claims define the invention.
