Synthesis of diacyl peroxide in carbon dioxide

Details Synthesis of diacyl peroxide in carbon dioxide Synthesis of diacyl peroxide in carbon dioxide

2001-05-07

2002-05-28

Vollano, Jean F. (Department: 1621)

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

Organic compounds

Oxygen containing

C568S568000, C568S560000

Reexamination Certificate

active

06395937

ABSTRACT:

FIELD OF THE INVENTION
This invention is in the field of the synthesis of diacyl peroxide from acyl halide in liquid or supercritical carbon dioxide.
BACKGROUND OF THE INVENTION
Diacyl peroxides are among the commonly used initiators in the commercial production of polyolefins, particularly fluoroolefins, such as tetrafluoroethylene. They may be represented as R—(C═O)—O—O—(C═O)—R. The peroxide decomposes to give R., known as a free radical, which reacts with olefin monomer to begin the polymerization cycle. Taking tetrafluoroethylene as an example:
R—(C═O)—O—O—(C═O)—R→2R—(C═O)—O.→2R.+2CO
2
R.+CF
2
═CF
2
→R—CF
2
—CF
2
.
R—CF
2
—CF
2
.+CF
2
═CF
2
→R—CF
2
—CF
2
—CF
2
—CF
2
.
The R group arising from the initiator is called an “endgroup” of the polymer.
The classical synthesis of diacyl peroxides is an aqueous synthesis. An alkaline aqueous solution of hydrogen peroxide is contacted with a water-immiscible solution of acid halide. Examples are found in S. R. Sandler and W. Karo, (1974)
Polymer Synthesis
, Vol. 1, Academic Press, Inc., Orlando Florida, p. 451 and U.S. Pat. No. 5,021,516. This is a reaction of two liquid phases, an aqueous phase and a nonaqueous phase. Equation (1) shows the reaction:
2R—(C═O)X+H
2
O
2
+2NaOH→R—(C═O)—O—O—(C═O)—R+2NaX+2H
2
O  (1)
From the stoichiometry of (1) it is clear that one mole of hydrogen peroxide reacts with two moles of acyl halide to yield one mole of diacyl peroxide. The acyl halide is added in a solvent that has low water solubility. The diacyl peroxide as it forms is taken up in the solvent. By this means, exposure of the acyl halide and the diacyl peroxide to the alkaline aqueous phase is minimized, which is desirable because water hydrolyzes both the organic acyl halide starting material and the diacyl peroxide product. Hydrolysis decreases yield and introduces byproducts such as acids and peracids, which are impurities. At the end of the reaction, the nonaqueous solvent with the diacyl peroxide dissolved in it is separated and dried, and purified as necessary.
Carbon dioxide (CO
2
) is among the most economical and environmentally benign nonaqueous solvents for polymerization. Polymerization in CO
2
is simplified if initiator can be supplied in CO
2
. The use of diacyl peroxides in liquid or supercritical carbon dioxide is known (J. T. Kadla, et al.,
Polymer Preparation
, vol. 39, no. 2, pp. 835-836, 1998). However, the peroxides were prepared using the aqueous alkaline peroxide method and were taken up in CF
2
Cl—CFCl
2
(CFC—113). Only then were they added to carbon dioxide.
A direct synthesis of diacyl peroxides in carbon dioxide is needed.
SUMMARY OF THE INVENTION
One form of this invention relates to a process for the synthesis of diacyl peroxide comprising contacting organic acyl halide with peroxide complex, in liquid or supercritical carbon dioxide.
A second form of this invention relates to a process for the continuous synthesis of diacyl peroxide comprised of continuously contacting a feed stream comprised of organic acyl halide in liquid or supercritical carbon dioxide with a bed comprised of peroxide complex, to form a product stream comprised of diacyl peroxide in liquid or supercritical carbon dioxide.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to the synthesis of diacyl peroxide in liquid or supercritical carbon dioxide by contacting organic acyl halide with peroxide complex in a medium of liquid or supercritical carbon dioxide. As stated above, the usual synthesis of diacyl peroxides is by reaction of aqueous alkaline peroxide with acyl halide. Surprisingly, it has been found that carbon dioxide, a Lewis acid, is an effective solvent for the production of diacyl peroxide by the reaction of acyl halide with peroxide complex. In addition, in a preferred form of the invention, liquid or supercritical carbon dioxide containing the resulting diacyl peroxide is collected as a product of the reaction. This mixture can be directly used in other processes, e.g., initiator supply for polymerization in carbon dioxide. This form of the invention provides a route to the direct synthesis in good yield of diacyl peroxides in carbon dioxide, minimizing the presence of water and eliminating any other organic solvent as would be inevitable in synthetic routes that would prepare the diacyl peroxide first in another solvent, and subsequently replacing that solvent, by whatever means, with carbon dioxide.
Organic acyl halides are compounds of the structure R—(C═O)X. X represents halogen: fluorine, chlorine, bromine, or iodine. The most readily available acyl halides are generally acyl chloride or acyl fluoride. R represents any organic group that is compatible with one or more of the peroxide complexes useful for carrying out this invention under the conditions of the synthesis. A compatible R group is one that does not contain atoms or groups of atoms that are susceptible to oxidation by or otherwise react with the other ingredients in the course of the reaction or in the reaction mixture to give undesirable products. R groups acceptable in the present invention include aliphatic and alicyclic groups, these same groups with ether functionality, aryl groups and substituted aryl groups in which the substituents are compatible with one or more of the peroxide complexes of this invention under the conditions of the synthesis. The R group may be partially or completely halogenated. If perhalogenated, the R group may have only one type of halogen, as with perfluorinated groups, or may have several types, as with, for example, chlorofluorinated groups.
The R group may also contain certain functional groups or atoms such as —COOCH
3
, —SO
2
F, —CN, I, Br, or H. The R group is incorporated in the polymer at the end of the polymer chain, that is, as an endgroup. It is sometimes useful to be able to further react the polymer through the endgroup with other molecules, for example, other monomers or polymer, or to introduce ionic functionality in the endgroup for interaction with polar surfaces such as metals, metal oxides, pigments, or with polar molecules, such as water or alcohols, to promote dispersion. Some of the functional groups above, for example —COOCH
3
and —SO
2
F (the fluorosulfonyl group), are susceptible to hydrolysis, especially base-catalyzed hydrolysis, and reaction with nucleophiles. However, because of the absence of an aqueous phase in a preferred form of this invention and of the specificity of the peroxide complexes useful in carrying out this invention, these functional groups are not affected and the diacyl peroxides corresponding to these acyl halides can be made. For example, from FSO
2
CF
2
(C═O)F, FSO
2
CF
2
(C═O)—O—O—(C═O)CF
2
SO
2
F can be made without hydrolysis of the sulfonyl fluoride functionality to sulfonic acid. It is a further advantage of the process according to this invention that such hydrolysis-sensitive groups can be incorporated in diacyl peroxides and thereby introduced as endgroups in polymers.
In the synthesis of diacyl peroxide in accordance with this invention, no more than one organic acyl halide will normally be used. Although with more than one organic acyl halide the reaction would proceed satisfactorily, more than one diacyl peroxide would be made. For example, if two organic acyl halides are used, A—(C═O)X and B—(C═O)X, three diacyl peroxides would be expected: A—(C═O)—O—O—(C═O)—A, B—(C═O)—O—O—(C═O)—B, and A—(C═O)—O—O—(C═O)—B, a mixed diacyl peroxide. The ratio of the peroxides can be controlled to some extent by the relative concentrations and order of addition of the organic diacyl halides. Such a mixture of peroxides is usually undesirable because the different peroxides will generally have different decomposition rates. However, if a mixed diacyl peroxide is wanted, the process according to this invention may be used, followed if necessary by separation or purification steps to reduce

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