Ester compounds and their use in forming acrylates

Details Ester compounds and their use in forming acrylates Ester compounds and their use in forming acrylates

2000-10-19

2003-04-08

Carr, Deborah D. (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Carboxylic acid esters

C560S185000, C560S211000

Reexamination Certificate

active

06545175

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to certain ester compounds described herein, methods of forming these ester compounds and the use of these compounds in dehydration reactions to form unsaturated compounds.
BACKGROUND OF THE INVENTION
Scientists and Engineers have long sought improvements in reactions in which a or &bgr;-hydroxy esters or carboxylic acids are dehydrated to the corresponding acrylates. In early work, Burns et al. in J. Chem. Soc., p400-406 (1935) reported the reaction of ethyl lactate and methyl hydrogen phthalate with a sulfuric acid catalyst in benzene, with removal of water in an azeotrope with benzene, to yield methyl &agr;-carboxyethyl phthalate. The methyl &agr;-carboxyethyl phthalate was pyrolyzed to phthalic anhydride and a 41% yield of crude ethyl acrylate.
In other work, Völker et al. (in U.S. Pat. No. 3,487,101, issued December 1969) described several reactions in which &agr;-hydroxy isobutyric acid was dehydrated to methacrylic acid. In example 1,&agr;-hydroxy isobutyric acid was added dropwise to a heated mixture containing phthalic anhydride, dimethylphthalate, caustic soda, and pyrocatechol and hydroquinone as inhibitors. 95.6% of the &agr;-hydroxy isobulyric acid was converted to 90% methacrylic acid and 10% methacrylic acid ester. A similar reaction run without the caustic soda, Example 3, produced a yield of 63%. A reaction similar to Example 1, except where all the reactants were added to a single pot (no slow addition) gave a yield of 71%. While it is unknown whether the Völker method can work to dehydrate secondary &agr;-hydroxyls, since it is well-known that secondary hydroxyls are less labile than tertiary hydroxyls, it might be expected that dehydration of the secondary hydroxyl would not proceed, or perhaps proceed only under very harsh reaction conditions that would favor side reactions. See, for example, March, Advanced Organic Chemistry, Third Ed. p522, which states that “because of the electron-releasing inductive effect of alkyl groups, stability and hence rate of formation of the simple alkyl cation follows the sequence 3°>2°>1°, and Burns et al., “just as tertiary carbinols undergo pyrolytic dehydration more readily, in general, than primary and secondary, so it has been found that their acetates undergo pyrolysis at relatively low temperatures.”
Other workers, such as Walkup et al., DeColibus et al., Sawicki, Paprizos et al., and Naito et al. have described methods of dehydrating an alkyl lactate ester or acid to yield the corresponding alkyl acrylate by heating over a catalyst. Walkup et al., in U.S. Pat. No. 5,252,473, described the dehydration of a lactic acid ester to an acrylic acid ester over a catalyst of partially calcined calcium sulfate (see col. 9, line 57 through col. 10, line 56). A long list of other dehydration catalysts that were tested and reported to be inferior is listed by Walkup et al. at col. 11, lines 39-60. DeColibus et al., in U.S. Pat. No. 4,529,816, described a process in which methyl 2-hydroxy-2-methyl propionate is dehydrated in the presence of sulfuric acid to form methyl methacrylate. Sawicki, in U.S. Pat. No. 4,729,978, disclosed a process of selectively converting lactic acid to acrylic acid by dehydrating at about 200 to 400° C. over a phosphate catalyst. Paprizos et al., in U.S. Pat. No. 4,786,756, disclosed a process of converting lactic acid or ammonium lactate to acrylic acid by contacting a mixture of the lactic acid or ammonium lactate and water with aluminum phosphate that has been treated with an inorganic base. Naito et al., in U.S. Pat. No. 5,068,399, described a process in which methyl &agr;-hydroxyisobutyrate in methanol is contacted with a modified molecular sieve aluminosilicate catalyst to yield methyl methacrylate (see Example 1).
Abe et al., in U.S. Pat. No. 5,250,729, described a process similar to Naito et al. except that Abe et al. suggest the substitution of C
1
-C
5
alkoxy groups on the position &agr; or &bgr; the ester group having the same alkoxy moiety. These reactions are shown below:
where R
1
and R
2
represent H or a C
1
-C
3
alkyl and R
3
represents a C
1
-C5 alkyl. In Example 3, Abe et al. disclose a process in which methyl &agr;-methoxyisobutyrate in methanol is contacted with a molecular sieve aluminosilicate catalyst to yield methyl methacrylate.
Stephens in U.S. Pat. No. 5,679,832 disclose a process of making an &agr;,&bgr;-unsaturated-&bgr;-trifluoromethyl carboxylate from the &bgr;-hydroxy alkyl ester. This process is illustrated below:
A distillate was collected at 145-160° C. that was found to be 93 wt % ethyl (E)-4,4,4-trifluorobut-2-enoate (87% yield) and 7 wt % butyric acid (see Example 3). In Example 1, ethyl 3-acetyloxy-4,4,4-trifluorobutanoate was heated in the presence of K
2
CO
3
and a distillate was collected at a bath temperature of 140-180° C. Stephen reported the distillate as a 60:40 molar mixture of ethyl (E)-4,4,4-trifluorobut-2-enoate (87% yield) and acetic acid.
Kiely et al. in U.S. Pat. No. 4,617,405 disclosed a process of (a) reacting an acid anhydride and the beta-hydroxy carbonyl compound in the presence of an acid catalyst to form an ester; (b) reacting the ester in the presence of a base catalyst to form an &agr;,&bgr;-unsaturated carbonyl compound and a carboxylic acid, and (c) separating the &agr;,&bgr;-unsaturated carbonyl compound and the carboxylic acid.
Despite these and many other efforts, there remains a need for improved methods for producing acrylates from &agr;-hydroxy esters or &agr;-hydroxy carboxylic acids. There is a particular need for new methods for dehydrating &agr;-hydroxy esters or &agr;-hydroxy carboxylic acids, where the hydroxy moiety is a secondary hydroxy.
SUMMARY OF THE INVENTION
The present invention provides compositions comprising a compound having the formula (III):
wherein: n is 0 or 1; R
4
through R
12
are independently selected from hydrogen, C
1
to C
10
alkyl, C
6
to C
10
aryl, C
1
to C
10
alkoxy, C
1
to C
10
aryloxy, C
1
to C
10
aralkyl; and R
1
through R
3
are hydrogen, C
1
to C
10
alkyl, C
6
to C
10
aryl, or C
1
to C
10
aralkyl. In preferred embodiments, when R
1
is hydrogen, R
2
is hydrogen. In some preferred embodiments, where R
1
is not hydrogen, R
1
is the same as R
3
and the concentration of the compound of formula III is more than twice the concentration of analogous compounds where R
1
is not the same as R
3
; by “analogous compounds” it is meant compounds that have the same structure as the compound of formula III except that R
1
and R
3
are not equal (R
1
≠R
3
), and R
1
is not H, and R
3
is not H. In some other preferred embodiments, the compound of formula III is present in a concentration greater than the concentration of anhydride and greater than the concentration of the compounds of formula I.
The invention also provides methods of making compounds having the structure of formula III. Preferably, this method comprises reacting a compound having formula I:
with a compound having formula II:
wherein the R groups are defined as above.
The invention also includes compositions made by the reaction of I and II.
The invention also provides a method of making acrylates (and methods of using compounds of formula III) wherein a compound of formula III is heated to yield an acrylate and an anhydride. Preferably, the method of making an acrylate is a two step process in which a compound of formula I is reacted with a compound of formula II under a first set of conditions, then the compound of formula III is thermolyzed at a higher temperature to form the acrylate. In preferred embodiments of this two step method, the compound of formula III is isolated from the compounds of formulas I and II before it is decomposed to produce the acrylate.
In the present invention, the term “acrylate” refers to a compound having the C═C—C(O)OR moiety.
Various embodiments of the invention can provide numerous advantages including: few side reactions, high yield, volatile starting materials and products that can be conveniently distilled an

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