U.S. patent application number 09/850547 was filed with the patent office on 2002-01-31 for synthesis of diacyl peroxide in carbon dioxide.
Invention is credited to Brothers, Paul Douglas, Kipp, Brian Edward, Noelke, Charles Joseph, Uschold, Ronald Earl, Wheland, Robert Clayton.
Application Number | 20020013504 09/850547 |
Document ID | / |
Family ID | 22768819 |
Filed Date | 2002-01-31 |
United States Patent
Application |
20020013504 |
Kind Code |
A1 |
Brothers, Paul Douglas ; et
al. |
January 31, 2002 |
Synthesis of diacyl peroxide in carbon dioxide
Abstract
This invention relates to a process for the synthesis of diacyl
peroxide by contacting acyl halide and peroxide complex in liquid
or supercritical carbon dioxide.
Inventors: |
Brothers, Paul Douglas;
(Chadds Ford, PA) ; Kipp, Brian Edward;
(Wilmington, DE) ; Noelke, Charles Joseph;
(Wilmington, DE) ; Uschold, Ronald Earl; (West
Chester, PA) ; Wheland, Robert Clayton; (Wilmington,
DE) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY
LEGAL DEPARTMENT - PATENTS
1007 MARKET STREET
WILMINGTON
DE
19898
US
|
Family ID: |
22768819 |
Appl. No.: |
09/850547 |
Filed: |
May 7, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60207004 |
May 25, 2000 |
|
|
|
Current U.S.
Class: |
568/558 |
Current CPC
Class: |
Y02P 20/544 20151101;
Y02P 20/54 20151101; C07C 407/00 20130101; C07C 409/34 20130101;
C07C 407/00 20130101; C07C 409/34 20130101 |
Class at
Publication: |
568/558 |
International
Class: |
C07C 409/00 |
Claims
What is claimed is:
1. A process for the synthesis of diacyl peroxide comprising
contacting organic acyl halide with peroxide complex, in liquid or
supercritical carbon dioxide.
2. The process of claim 1 further comprising collecting liquid or
supercritical carbon dioxide containing diacyl peroxide.
3. The process of claim 1 wherein the peroxide complex is selected
from the group consisting of inorganic peroxide complexes and
organic peroxide complexes and mixtures thereof.
4. The process of claim 1 wherein the peroxide complex is
substantially insoluble in liquid or supercritical carbon dioxide
and is present during the reaction as a solid phase.
5. The process of claim 1 wherein the peroxide complex is selected
from the group consisting of sodium percarbonate, sodium perborate,
urea/hydrogen peroxide adduct, and mixtures thereof.
6. The process of claim 1 wherein the mole ratio of hydrogen
peroxide in the peroxide complex to organic acyl halide is at least
about one-to-one.
7. The process of claim 1 wherein the process is carried out at a
reaction temperature between about -40.degree. C. and about
40.degree. C.
8. The process of claim 1 wherein the process is carried out at a
reaction temperature between about -20.degree. C. and about
20.degree. C.
9. The process of claim 1 wherein the process is carried out at a
reaction temperature between about -10.degree. C. and about
10.degree. C.
10. The process of claim 1 wherein the process is carried out at a
reaction temperature selected so that the reaction time is no
greater than one-quarter of the diacyl peroxide half-life at the
reaction temperature.
11. The process of claim 1 wherein the organic acyl halide selected
from the group consisting of fluoroorganic acyl halides.
12. The process of claim 1 wherein the organic acyl halide is
selected from the group consisting of perfluoroorganic acyl
halides.
13. The process of claim 1 wherein the organic acyl halide is
isobutyryl halide.
14. A process for the continuous synthesis of diacyl peroxides
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
comprising diacyl peroxide in liquid or supercritical carbon
dioxide.
15. The process of claim 14 in which the peroxide complex is
selected from the group consisting of perborate, percarbonate,
urea/hydrogen peroxide adduct, and mixtures thereof.
16. The process of claim 14 further comprising collecting said
product stream.
Description
FIELD OF THE INVENTION
[0001] 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
[0002] 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.dbd.O)--O--O--(C.db- d.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.dbd.O)--O--O--(C.dbd.O)--R
.fwdarw.2R--(C.dbd.O)--O.multidot..fwdarw- .2R.multidot.+2CO.sub.2
R.multidot.+CF.sub.2.dbd.CF.sub.2.fwdarw.R--CF.sub-
.2--CF.sub.2.multidot.R--CF.sub.2--CF.sub.2.multidot.+CF.sub.2.dbd.CF.sub.-
2.fwdarw.R--CF.sub.2--CF.sub.2--CF.sub.2--CF.sub.2.multidot.
[0003] The R group arising from the initiator is called an
"endgroup" of the polymer.
[0004] 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 Fla., 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.dbd.O)X+H.sub.2O.sub.2+2NaOH.fwdarw.R--(C.dbd.O)--O--O--(C.dbd.O)---
R+2NaX+2H.sub.2O (1)
[0005] 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.
[0006] Carbon dioxide (CO.sub.2) is among the most economical and
environmentally benign nonaqueous solvents for polymerization.
Polymerization in CO.sub.2 is simplified if initiator can be
supplied in CO.sub.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.sub.2Cl--CFCl.sub.2 (CFC-113). Only then
were they added to carbon dioxide.
[0007] A direct synthesis of diacyl peroxides in carbon dioxide is
needed.
SUMMARY OF THE INVENTION
[0008] 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.
[0009] 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
[0010] 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.
[0011] Organic acyl halides are compounds of the structure
R--(C.dbd.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.
[0012] The R group may also contain certain functional groups or
atoms such as --COOCH.sub.3, --SO.sub.2F, --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.sub.3 and
--SO.sub.2F (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.sub.2CF.sub.2(C.dbd.O)F,
FSO.sub.2CF.sub.2(C.dbd.O)--O--O--(C.dbd.O)CF.sub.2SO.sub.2F 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.
[0013] 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.dbd.O)X and B--(C.dbd.O)X, three diacyl peroxides would be
expected: A--(C.dbd.O)--O--O--(C.dbd.O)--A,
B--(C.dbd.O)--O--O--(C.dbd.O)--B, and
A--(C.dbd.O)--O--O--(C.dbd.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 or remove the
accompanying unwanted peroxides.
[0014] Diacyl peroxides in which the acyl group is a hydrocarbon
group can be made according to this invention. These hydrocarbon
diacyl peroxides are useful for initiation of olefin
polymerization, including fluoroolefin polymerization when the
presence of a hydrocarbon endgroup is acceptable or desirable.
Isobutyryl peroxide is preferred when a low temperature hydrocarbon
initiator is needed. It can be made from isobutyryl halide,
preferably isobutyryl chloride.
[0015] Synthesis of diacyl peroxides according to this invention is
particularly useful for making initiators for the polymerization of
fluoroolefins such as tetrafluoroethylene, hexafluoroproplyene,
perfluoro(alkyl vinyl ethers), chlorotrifluoroethylene, vinylidene
fluoride, and vinyl fluoride, either as homopolymers, or as
copolymers with each other or with other olefins, such as ethylene
and perfluoroalkylethylenes. Fluoroolefin polymerization is
susceptible to chain transfer if compounds with labile
carbon-hydrogen bonds are present, so it is desirable that
initiators be free of such bonds. Furthermore, because of the high
temperatures at which fluoropolymers are processed and used, the
thermal and hydrolytic stability of the polymer endgroups is
important. The R group of the initiator is one source of such
endgroups. Therefore, except in cases where specific reactivity of
polymer endgroups is wanted, in the interest of minimizing chain
transfer activity of the initiator and of providing endgroups with
thermal and hydrolytic stability comparable to that of the polymer
chain, it is desirable that the R group be free of bonds that are
capable of chain transfer or that are less thermally or
hydrolytically stable than the polymer itself. In polymerizing
fluoromonomers, perhalogenated R groups, and preferably
perfluorinated R groups, meet this requirement. Because ether
functionality in halogenated and fluorinated organic groups has
good thermal and oxidative stability if the oxygen is between
carbon atoms that are perhalogenated or perfluorinated, or between
carbon atoms that are substituted with perhaloalkyl or
perfluoroalkyl groups, such ether functionality is acceptable
also.
[0016] It is a further advantage of diacyl peroxide synthesis in
accordance with this invention that fluoroorganic acyl halides,
that is, acyl halides in which the R group is at least partially
fluorinated, and particularly perfluoroorganic acyl halides, are
readily reacted to form the corresponding diacyl peroxides. An
example of a perfluoroorganic acyl halide useful for this invention
is perfluoro(2-methyl-3-oxa-hexanoyl fluoride), also known as
hexafluoropropylene oxide (HFPO) dimer acid fluoride and as DAF. It
has the formula:
CF.sub.3CF.sub.2CF.sub.2OCF(CF.sub.3)(C.dbd.O)F
[0017] Other suitable perfluoroorganic acyl halides include
CF.sub.3CF.sub.2CF.sub.2(C.dbd.O)Cl (heptafluorobutyryl chloride)
and CF.sub.3CF.sub.2(C.dbd.O)F (pentafluoropropionyl fluoride).
[0018] The peroxide complexes useful for carrying out this
invention include a) complexes of hydrogen peroxide with inorganic
compounds, referred to here as inorganic complexes, and b)
complexes of hydrogen peroxide with organic molecules, referred to
here as organic peroxide complexes. These complexes include those
substances in which hydrogen peroxide is combined with inorganic or
organic compounds by bonds strong enough to permit isolation of the
compounds, though the bonds may be weaker or of a different
character than those between the constituents of hydrogen peroxide
or of the compound with which it is complexed. By this criterion it
can be seen that "sodium percarbonate", which is isolable and has
the composition Na.sub.2CO.sub.3.multidot.11/2H.sub.2O.sub.2, is a
complex of hydrogen peroxide, while an aqueous solution of hydrogen
peroxide, although it may have degrees of hydration that vary with
concentration, is not. Complexes, as the term is used here, also
include compounds such as sodium perborate, in which the elements
of peroxide are reported to be an integral part of the molecule.
The complexes according to this invention do not include
persulfates or monopersulfates, such as potassium monopersulfate
(KHSO.sub.5), which are found to be ineffective. It is believed
that the stability oxygen-sulfur bond in the persulfate is so great
that persulfates cannot provide the elements of hydrogen peroxide
needed for this synthesis. Apart from these stipulations, nothing
is implied as to the structure of the complexes. They may be
combinations of hydrogen peroxide with the inorganic compound or
organic molecule in which the peroxide is associated through weak
or strong bonds. Alternatively, they may be reaction products of
peroxide with the compound or molecule, in which elements of the
peroxide are incorporated in the structure of the compound or
molecule, but are available for reaction with acid halides. For
some complexes, the structures may be unknown. It is preferable
that the complexes be dry. It is more preferable that the complexes
be anhydrous. The term "dry" means essentially free of water,
though water of crystallization may be present. "Anhydrous" means
essentially free of water including water of crystallization. A
number of peroxide complexes and their syntheses are described in
U.S. Pat. No. 5,820,841.
[0019] It is preferred for the peroxide complex to be substantially
insoluble in liquid or supercritical carbon dioxide and to be
present during the reaction as a solid phase. Such peroxide
complexes are easily removed after reaction by filtration or used
in the form of a bed through which the acyl halide in liquid or
supercritical carbon dioxide is passed. Similarly, it is also
preferred that the spent complex after reaction remain insoluble
and in the solid phase.
[0020] Among the convenient inorganic peroxide complexes for the
synthesis of diacyl peroxides according to this invention are
percarbonate and perborate salts. These are most readily available
as the sodium salts, which are used in the detergent industry. The
other alkali metal salts of percarbonate or perborate, as for
example, the potassium salts, may also be used in accordance with
the processes of this invention. Those skilled in the art will
recognize that the alkaline earth percarbonates and perborates, as
for example, the calcium salts, though less desirable because less
readily available, would be expected to be useful according to the
processes of this invention. For the purposes of this invention,
although both the alkali metal and alkaline earth percarbonates and
perborates have utility in the synthesis of diacyl peroxides, the
alkali metal salts are preferable, and the sodium salts are more
preferable. For convenience, the percarbonate salts and perborate
salts will be referred to herein simply as percarbonate and
perborate.
[0021] Sodium percarbonate, Na.sub.2CO.sub.3 11/2H.sub.2O.sub.2, is
hydrolyzed by moisture, and for best results in the synthesis of
diacyl peroxide according to this invention, the percarbonate
should be kept dry. Sodium perborate, though represented as
NaBO.sub.3.multidot.H.sub.2O and sometimes called sodium perborate
monohydrate, is reported to be Na.sub.2(B.sub.2O.sub.8H.sub.4), and
is therefore an anhydrous salt. Analogously, the so-called sodium
perborate tetrahydrate is reported to be the trihydrate:
Na.sub.2(B.sub.2O.sub.8H.sub.4).multidot.3H.sub.2O. The misnamed
sodium perborate monohydrate is the preferred form to be used in
the practice of this invention.
[0022] The organic peroxide complexes of this invention include
those that may have some solubility in carbon dioxide, or at least
be volatile enough to make separation from carbon dioxide
difficult. The preferred organic complexes are those that are
insoluble and whose residues are insoluble in carbon dioxide, and
which are present during the synthesis as a solid phase. As such,
they are easily separated from the diacyl peroxide solution. It is
further desirable that the organic complexes be free of labile
atoms or groups, or of bonds that can react with the reactants or
products of the processes according to this invention, especially
if such reactions degrade the organic molecule and such degradation
products get into the reaction mixture.
[0023] Urea/hydrogen peroxide adduct (urea.multidot.H.sub.2O.sub.2)
is a more preferred organic peroxide complex. It is commercially
available (Aldrich Chemical Co. Milwaukee, Wis., USA). It is a
solid and is essentially insoluble in the solvents designated
herein and should small amounts be carried through filters or by
other means into the diacyl peroxides solution, urea, not being
active toward free-radical chain transfer, will have little or no
effect on polymerization.
[0024] A significant advantage of organic peroxide complexes is
that they introduce no metal ions into the reaction mixture and
therefore give diacyl peroxide free of metal ions derived from the
reactants. In polymerization, such diacyl peroxide made from
organic peroxide complexes will introduce no metal ions into the
polymer. Polymers, especially fluoropolymers, of low metal content,
or free of metal ions, are needed for certain applications where
high purity is required, such as the semiconductor industry.
[0025] An important characteristic of percarbonate, perborate, and
urea/hydrogen peroxide adduct of this invention, and of the
carbonate, borate, and urea remaining after the reaction, is their
insolubility in carbon dioxide and because they are in the solid
phase during the synthesis. Because they are solids, they can be
easily separated from reaction mixtures by filtration. For the same
reason, percarbonate, perborate, and urea/hydrogen peroxide adduct
may be used in fixed beds for continuous synthesis of diacyl
peroxides.
[0026] The temperature of the reaction is chosen to balance the
interest in having a fast reaction with the need to prevent
excessive loss of diacyl peroxide through thermal decomposition.
Because diacyl peroxides vary in half-life (the time for one-half
of the diacyl peroxide to be consumed; half-life is a function of
temperature) reaction temperatures will vary, but useful
temperatures are in the range of about -40.degree. C. to about
40.degree. C. For peroxides such as HFPO dimer peroxide,
heptafluorobutyryl peroxide, isobutyryl peroxide, and
bis[perfluoro(fluorosulfonyl)acetyl] peroxide, a temperature range
of about -20.degree. C. to about 20.degree. C. is typical, about
-10.degree. C. to about 10.degree. C. is preferred, and about
-5.degree. C. to about 5.degree. C. is more preferred when sodium
percarbonate or sodium perborate is used. When urea/hydrogen
peroxide adduct is used to make these diacyl peroxides, about
-0.degree. C. to about 10.degree. C. is the more preferred
temperature. Diacyl peroxide loss to thermal decomposition is best
minimized by keeping reaction time a fraction of the diacyl
peroxide's half-life at reaction temperature. A reaction time no
greater than one-quarter of the diacyl peroxide half-life at the
reaction temperature is preferred.
[0027] Because residual acyl halide is an impurity in the product
diacyl peroxide, and is furthermore a source of acid that can cause
corrosion, it is desirable to conduct the synthesis so as to yield
as much of the diacyl peroxide as possible. Yield is preferably at
least about 25%, more preferably at least about 50%, more
preferably still at least about 70%, and most preferably at least
about 90%.
[0028] The carbon dioxide used as solvent according to this
invention will be in the liquid state at the preferred reaction
temperatures for the synthesis of preferred diacyl peroxides.
However, if it is desired to run the reaction at temperatures above
the critical temperature of carbon dioxide, 31.degree. C., that can
be done, in which case carbon dioxide in its supercritical
state.
[0029] When diacyl peroxide is synthesized according to this
invention in a batchwise manner, the reactant organic acyl halide
is mixed with peroxide complex in a vessel containing a medium
comprised of carbon dioxide. Surprisingly, it is found that the
yield of diacyl peroxide increases as the mole ratio of peroxide in
the peroxide complex to acyl chloride increases. It is preferable
that the mole ratio be at least about one to one. It is more
preferable that the mole ratio be at least about two to one. It is
most preferable that the mole ratio be at least about four to one.
Because the peroxide content of the peroxide complex depends upon
the nature of the complex, the weight of complex that contains a
mole of peroxide or its equivalent will depend upon the composition
of the complex under consideration.
[0030] To prepare diacyl peroxide in a continuous reaction
according to this invention, a feed stream comprised of organic
acyl halide in liquid or supercritical carbon dioxide is
continuously contacted with a bed comprised of peroxide complex to
form a product stream comprising diacyl peroxide in liquid or
supercritical carbon dioxide. The bed may be in the form of a
column filled with peroxide complex and optionally an inert
material. The purpose of the inert material would be to facilitate
flow and temperature control. As stated above, the synthesis should
be run so as to achieve high yield of the diacyl peroxide. The
continuous method is preferred because it allows diacyl peroxide to
be made as needed and consumed promptly. If desired, the diacyl
peroxide in the liquid or supercritical carbon dioxide can be
collected and advantageously used directly in that form. The
continuous process ensures that fresh diacyl peroxide is always
available and eliminates the need for diacyl peroxide storage,
which generally requires low temperatures, and is therefore
vulnerable to power outages and equipment failure. Furthermore, as
with any oxidizing agent, it is sound practice to minimize the
quantities of diacyl peroxide kept on hand. Both batch and
continuous methods are demonstrated in the Examples.
[0031] Diacyl peroxide made according to this invention may be used
in carbon dioxide to initiate polymerization. However, it is one of
the advantages of making the initiator in carbon dioxide that the
initiator may be conveniently transferred to another solvent by
adding the initiator in carbon dioxide to said solvent and letting
the carbon dioxide vaporize away. Any traces of carbon dioxide
remaining can be removed if necessary by sparging, for example with
nitrogen, or under reduced pressure. Using this "solvent transfer
method", diacyl peroxide solutions of any desired concentration can
be safely and easily made, even in solvents that would not be
suitably used in the synthesis of the diacyl peroxide. Thus, the
diacyl peroxide synthesis in carbon dioxide according to this
invention can be the source of initiator solutions in a wide
variety of solvents.
EXAMPLES
Glossary
[0032] HFPO=Hexafluoropropylene oxide
[0033] HFPO Dimer
Peroxide=CF.sub.3CF.sub.2CF.sub.2OCF(CF.sub.3)(C.dbd.O)O-
O(C.dbd.O)(CF.sub.3)CFOCF.sub.2CF.sub.2CF.sub.3 HFPO Dimer Acid
Fluoride=CF.sub.3CF.sub.2CF.sub.2OCF(CF.sub.3)(C.dbd.O)F DAF=HFPO
Dimer Acid Fluoride
[0034] Vertrel.RTM. XF=CF.sub.3CFHCHFCF.sub.2CF.sub.3
(2,3-dihydroperfluoropentane) available from the DuPont Company,
Wilmington, Del., USA
Test Method
[0035] Diacyl peroxides formed by this process are analyzed by
peroxide titration using the following standard procedure. In a
loosely stoppered Erlenmeyer flask, several grams of dry ice are
added to 25 ml of glacial acetic acid. This is done to flush oxygen
from the system. 5.0 ml of a solution of 30 g of potassium iodide
in 70 ml of deoxygenated water is added, and then 5.0 ml of the
peroxide solution to be analyzed is added. The mixture is stirred
for 30 minutes to allow the peroxide to react with the iodide. 100
ml of deoxygenated water is added and the reaction mixture, having
a deep iodine color, is titrated to light yellow with 0.1N sodium
thiosulfate. Then 0.5 g of Thyodene.RTM. (Fisher Scientific Co.)
iodometric indicator is added making the reaction mixture turn
blue. Titration is continued with 0.1N sodium thiosulfate to a
colorless endpoint. The molar peroxide concentration is 0.01 times
the total number of ml of 0.1N sodium thiosulfate solution added to
the reaction.
Example 1
HFPO Dimer Peroxide Synthesis in Liquid Carbon Dioxide
[0036] A 300 ml stainless steel autoclave, equipped with a paddle
stirrer and dip tube, is dried by heating to 100.degree. C. for
several hours under a dry nitrogen purge. Dry sodium percarbonate
(Na.sub.2CO.sub.3.multidot.11/2H.sub.2O.sub.2) (2 g (12.7 mmol)) is
added and the autoclave is sealed, evacuated, and chilled to about
-20.degree. C.
[0037] Separately, a 1-liter stainless steel cylinder is charged
with 5.2 ml (24.7 mmol) of HFPO dimer acid fluoride (DAF). The
cylinder is cooled on dry ice and evacuated, and about 220 g of
carbon dioxide is admitted. The cylinder is then connected to the
autoclave using 1/8 inch (3.2 mm) diameter stainless steel tubing.
The cylinder is inverted to transfer the entire contents of the
cylinder to the autoclave. Prior vacuum of the autoclave and prior
chilling of the autoclave promotes good transfer. About 199 g of
the HFPO dimer acid fluoride/liquid carbon dioxide mix is
transferred from the stainless steel cylinder into the
autoclave.
[0038] The contents of the autoclave are stirred at about 5000 rpm
for four hours at 0.degree. C. Temperature fluctuates mildly during
this time from -2.degree. C. to 0.5.degree. C. The internal
pressure in the autoclave varies from 477 psi (3.29 MPa) at
-2.degree. C. to 520 psi (3.59 MPa) at 0.5.degree. C. After about
four hours, the autoclave is chilled to -27.degree. C. with the
contents still stirring. Chilling to -27.degree. C. reduces the
internal pressure of the autoclave to 184 psi (1.27 MPa). A 1-liter
pressure-resistant cylinder is evacuated and cooled in a liquid
nitrogen bath. The cylinder is then connected to the dip tube
outlet on the autoclave using an 18 inch (45 cm) length of 1/8 inch
(3.2 mm) diameter stainless steel tubing. The contents of the
autoclave are then vented into the stainless steel cylinder through
the dip tube. At the end of the transfer, the pressure in the
cylinder is 0.2 atm (20 kPa). A valve on the top of the cylinder is
removed and 100 ml of Vertrel.RTM. XF is added so that the diacyl
peroxide in the carbon dioxide can be transferred into the
Vertrel.RTM. XF to facilitate measurement of reaction yield. The
valve is replaced on the cylinder. The cylinder is removed from the
liquid nitrogen bath. Contents of the cylinder are allowed to warm
until rapid carbon dioxide evolution ceases. Evolution of carbon
dioxide is judged by periodically opening and closing the cylinder
valve and noting pressure changes.
[0039] Once carbon dioxide is no longer being rapidly evolved and
frost on the sides of the cylinder shows the first signs of thawing
(about 30-45 minutes), the valve is removed from the top of the
cylinder. Contents of the cylinder, a hazy gray/blue fluid, are
poured into a polyethylene bottle chilled on dry ice.
[0040] Opening the 300 ml autoclave at this point reveals residual
white solid on the bottom and traces of white film on the walls of
the autoclave. On visual inspection, the amount of solids left in
the autoclave is observed to be approximately the same volume as
the amount of sodium percarbonate added at the start.
[0041] The gray/blue fluid recovered from the reactor measures 85
ml in volume. Peroxide titration of 5.0 ml takes 5.95 ml of 0.1 N
thiosulfate. This titration corresponds to a 41% yield of HFPO
dimer peroxide.
[0042] The remaining gray/blue fluid, measuring 80 ml, is warmed
from -78.degree. C. to room temperature and washed three times in a
separatory funnel with water. This water wash removes any unreacted
sodium percarbonate and hydrogen peroxide that would titrate the
same as the HFPO dimer peroxide. A 5 ml aliquot of the solution now
takes 6.40 ml of 0.1 N thiosulfate in peroxide titration (the
increase in peroxide concentration may reflect some evaporation of
the Vertrel.RTM. XF solvent during the water wash).
Example 2
Continuous Synthesis of HFPO Dimer Peroxide in Liquid Carbon
Dioxide
[0043] A 150 ml stainless steel cylinder is evacuated and charged
with 7.90 g of perfluoro(2-methyl-3-oxa-hexanoyl) fluoride
(CF.sub.3CF.sub.2CF.sub.2OCF(CF.sub.3)COF) ("DAF") and 50 g carbon
dioxide. The cylinder, equipped with a pressure gauge is inverted
and placed in a stand fixed to a balance. {fraction (1/16)} inch
(1.6 mm) diameter stainless steel tubing is connected from the
cylinder to the top of a stainless steel column about 0.56 cm in
diameter and 10 cm in length. The column is packed with 10.0 g of
sodium percarbonate. A plug of glass wool at the bottom of the
column keeps the sodium percarbonate in the column. The column is
immersed in a constant temperature bath at 0.degree. C. A short
length of {fraction (1/16)} inch (1.6 mm) stainless steel tubing
runs from a valve at bottom of the column, through a rubber septum,
and into a cold trap that is immersed in a dry-ice/acetone slurry
and vented to the atmosphere. The trap contains about 50 g
Vertrel.RTM. XF.
[0044] The cylinder valve is opened allowing the liquid
DAF/CO.sub.2 mixture to fill the column. The valve between the
bottom of the column and the cold trap is then opened slightly to
permit a controlled flow of material through the column at a rate
of 0.154 g/min. The void volume in the column is 6.0 ml. The void
volume divided by the flow rate of material through the column is
taken as the contact time. The contact time is 39 minutes. The
non-volatile effluent from the column is taken up in the cold trap
to form a solution in Vertrel.RTM. XF. The low temperature of the
trap preserves the diacyl peroxide formed, and the solvent provides
a convenient medium for subsequent product analysis. Most of the
CO.sub.2 is vented spontaneously to the atmosphere from the trap.
At the conclusion of the experiment, the cold trap is warmed to
0.degree. C. in ice water and vigorously agitated until the weight
of the trap remains constant to remove any remaining CO.sub.2.
Peroxide titration of aliquots of solution from the cold trap shows
that 4.81 g of peroxide is formed. Its identity is confirmed from
absorption at 1858 cm.sup.-1 and 1829 cm.sup.-1 in its infrared
spectrum arising from carbonyl groups in the diacyl peroxide. The
amount of DAF remaining in the collected product is 2.19 g as
determined from the intensity of the infrared absorption at 1881
cm.sup.-1 arising from the acid fluoride carbonyl group. From these
data a yield of peroxide is calculated to be 68.7%.
Example 3
Continuous Synthesis of HFPO Dimer Peroxide in Liquid Carbon
Dioxide
[0045] The procedure and equipment are as described in Example 2
except the 4.74 g DAF is charged in the cylinder, the feed rate is
0.129 g/min, and the contact time is 46 minutes. Product collected
is 4.02 g, and 0.67 g remains on the column. The product consists
of 2.94 g peroxide and 1.41 g of recovered DAF. Yield is 67.6%.
Example 4
Continuous Synthesis of HFPO Dimer Peroxide in Liquid Carbon
Dioxide
[0046] The procedure and equipment are as described in Example 2.
The feed rate is 0.0697 g/min, and the contact time is 86 minutes.
Product collected is 7.01 g and 1.53 g remain on the column. The
product consists of 6.23 g peroxide and 0.43 g of recovered DAF.
Yield is 93.56%.
Example 5
Continuous Synthesis of HFPO Dimer Peroxide in Liquid Carbon
Dioxide
[0047] The procedure and equipment are as described in Example 2
except the temperature of the bath around the column is maintained
at 10.degree. C., the feed rate is 0.165 g/min, and the contact
time is 32 minutes. Product collected is 5.87 g, and 1.89 g remains
on the column. The product consists of 5.36 g peroxide and 0.43 g
of recovered DAF. Yield is 91.3%.
Example 6
Continuous Synthesis of HFPO Dimer Peroxide in Liquid Carbon
Dioxide
[0048] The procedure and equipment are as described in Example 2
except the temperature of the bath around the column is maintained
at 15.degree. C., the feed rate is 0.242 g/min, and the contact
time is 20 minutes. Product collected is 5.92 g, and 1.69 g remains
on the column. The product consists of 5.13 g peroxide and 1.02 g
of recovered DAF. Yield is 83.4%.
Summary of Examples 2 to 6
[0049] Table 1 summarizes the results of the examples of the
continuous synthesis of diacyl peroxide. Yields are increased with
longer contact time or with higher reaction temperature.
1 TABLE 1 Contact Time Temperature Example (min) (.degree. C.)
Yield (%) 2 39 0 68.7 3 46 0 67.6 4 86 0 93.6 5 32 10 91.3 6 20 15
83.4
Example 7
HFPO Dimer Peroxide Synthesis in Carbon Dioxide using Urea Hydrogen
Peroxide Adduct
[0050] A jacketed autoclave of 125 ml volume is heated to
60.degree. C. and purged with nitrogen for several hours. The
autoclave is then cooled to room temperature and 3.0 g (30.9 mmoles
H.sub.2O.sub.2 equivalent) urea/hydrogen peroxide adduct (Aldrich
Chemical Co.), containing 35.0% H.sub.2O.sub.2 by peroxide
titration, is added under a stream of nitrogen. The autoclave is
closed, evacuated, and cooled to -20.degree. C. A cylinder, into
which 16.0 g of HFPO dimer acid fluoride (48.2 mmoles) and 60 g of
carbon dioxide had been charged, is connected to the autoclave and
the contents of the cylinder are transferred into the autoclave.
The temperature of the autoclave is then raised to 0.degree. C.
while its contents are agitated for 6 hrs. The bottom port of the
autoclave is fitted with a sintered metal filter containing 15
micrometer pores to retain urea and unused urea/hydrogen peroxide
adduct. The contents of the autoclave are vented into an accurately
weighed nitrogen flushed cold trap immersed in a dry ice/acetone
bath. The trap contained about 50 g of Vertrel.RTM. XF. The solvent
is used to absorb the reaction mixture as most of the carbon
dioxide is vented to the atmosphere. This also provided a
convenient medium for infrared analysis of the reaction mixture at
room temperature and atmospheric pressure.
[0051] The cold trap and its contents are warmed to 0.degree. C. in
an ice bath with shaking to expel remaining carbon dioxide from the
Vertrel.RTM. XF solution. The trap is dried and weighed and used to
determine the weight of the product solution obtained. A portion of
the solution is then placed in a liquid infrared cell and its
spectrum measured. A reference spectrum of Vertrel.RTM. XF
previously obtained in the same liquid cell is subtracted from that
of the product mixture and intensities of bands occurring at 1858
cm.sup.-1 and 1829 cm.sup.-1 for the HFPO dimer peroxide, 1880
cm.sup.-1 for the HFPO dimer acid fluoride and 1774 cm.sup.-1 for
the HFPO dimer acid are determined. Calibration curves determined
from solutions of known concentration are used to calculate the
amounts of each compound from the intensity of the appropriate
infrared band in the spectrum of the product mixture. We found
60.6% HFPO dimer peroxide, 36.5% HFPO dimer acid fluoride and 3.0%
HFPO dimer acid in the product mixture weighing 13.35 g.
Example 8
HFPO Dimer Peroxide Synthesis in Carbon Dioxide using Urea Hydrogen
Peroxide Adduct
[0052] The procedure given in Example 7 is used except the
temperature of the autoclave is raised to 5.degree. C. We found
83.0% HFPO dimer peroxide, 12.5% HFPO dimer acid fluoride and 4.5%
HFPO dimer acid in the product mixture weighing 15.32 g.
Example 9
HFPO Dimer Peroxide Synthesis in Carbon Dioxide using Urea Hydrogen
Peroxide Adduct
[0053] The procedure given in Example 7 is used except the
temperature of the autoclave is raised to 10.degree. C. and
agitation is continued for 3 hrs. We found 76.1% HFPO dimer
peroxide, 15.5% HFPO dimer acid fluoride and 8.4% HFPO dimer acid
in the product mixture weighing 12.36 g.
Example 10
HFPO Dimer Peroxide Synthesis in Carbon Dioxide using Urea Hydrogen
Peroxide Adduct
[0054] The procedure given in Example 7 is used except 2.9 g of
urea is added to the autoclave along with urea/hydrogen peroxide
adduct to serve as a mild base to absorb HF generated during the
reaction. The temperature of the autoclave is also raised to
5.degree. C. We found 81.4% HFPO dimer peroxide, 15.4% HFPO dimer
acid fluoride and 3.2% HFPO dimer acid in the product mixture
weighing 7.11 g.
Example 11
HFPO Dimer Peroxide Synthesis in Carbon Dioxide using Urea Hydrogen
Peroxide Adduct
[0055] The procedure given in Example 7 is used except the amount
of urea/hydrogen peroxide adduct charged to the autoclave is 5.0 g
(51.5 mmoles H.sub.2O.sub.2 equivalent) and the temperature of the
autoclave is raised to 5.degree. C. We found 87.8% HFPO dimer
peroxide, 6.4% HFPO dimer acid fluoride and 5.8% HFPO dimer acid in
the product mixture weighing 16.39 g.
Summary of Examples 7 to 11
[0056] Table 2 summarizes the results of the examples of the
synthesis of diacyl peroxide using urea/hydrogen peroxide adduct.
Yields are increased with longer contact time or with higher
reaction temperature. Increasing the ratio of urea/hydrogen
peroxide adduct to acyl fluoride (DAF) increases yield. Added urea
has little or no effect.
2TABLE 2 Contact Time Temperature DAF:H.sub.2O.sub.2 Example (hour)
(.degree. C.) (mmoles) Yield (%) 7 6 0 48.2:30.9 47.2 8 6 5
48.2:30.9 83.0 9 3 10 48.2:30.9 76.1 10* 6 5 48.2:30.9 81.4 11 6 5
48.2:51.5 87.8 *Urea added as mild base.
* * * * *