Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
1999-07-13
2002-11-12
Shippen, Michael L. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S812000, C568S843000, C568S831000
Reexamination Certificate
active
06479712
ABSTRACT:
BACKGROUND OF THE INVENTION
Perfluorocarbon monomethanols, especially perfluoroalkyl monomethanols represented by the general formula CF
3
(CF
2
)
n
CH
2
OH, are currently used in various applications. The perfluorocarbon methanols are acidic enough to chemically adhere to some surfaces to provide slick (low friction) and chemically inert properties. Polymers of acrylic and methacrylic esters derived from perfluorocarbon methanols are used for protective coatings which exhibit extremely low surface energy.
Among perfluorocarbon dimethanols, perfluoroalkylene dimethanols represented by the general formula HOCH
2
(CF
2
)
n
CH
2
OH, are important intermediates to synthesize various fluoro polymers which are useful as components of protective coatings and paints.
Many commercially available perfluoroalkyl monomethanols and perfluoroalkylene dimethanols possess are of the straight-chain perfluoroalkyl and perfluoroalkylene type. Only a few examples of branched perfluoroalkyl monomethanols and perfluoroalkylene dimethanols have been reported to date. Branched structures generally exhibit lower melting points than straight-chain structures. For example, 1H,1H-perfluoro-3,7-dimethyl-1-octanol (molecular formula: C
9
F
19
CH
2
OH) is a free-flowing liquid at room temperature, while 1H,1H-perfluoro-1-decanol (which has the same molecular formula, but has a straight-chain perfluoroalkyl structure) has a melting point of 82-84° C. Since branched fluoroalkyl groups have multiple perfluoroalkyl groups, they may be able to cover surfaces more effectively than straight-chain perfluoroalkyl groups do. The way branched perfluoroalkylene dimethanols cover surfaces is very similar to that of fluoroalkyl acrylates such as perfluoro-1H,1H-octyl acrylate, CF
3
(CF
2
)
6
CH
2
OCOCH═CH
2
. Fluoropolymers such as poly(perfluoro-1H,1H-octyl acrylate) contain relatively long perfluoroalkyl groups extending out from the polymer backbone, which provides a highly fluorinated surface. These polymers have been reported to give surfaces which have extremely low surface tensions (about 10 dyn/cm
2
, Banks, R. E., “Organofluorine Chemicals and Their Industrial Application,” John Wiley & Sons Inc., p 216, 1979), much lower than that of polytetrafluorethylene (Teflon) (about 18 dyn/cm
2
). It is believed that these surface properties are the result of a tight arrangement of the perfluoroalkyl groups. Though the polymer backbones (i.e., the polyacrylate polymers) do not contain any fluorine atoms, they exhibit excellent resistance against weathering, probably due to the protection provided by the perfluoroalkyl groups. Branched perfluorocarbon dimethanols are, therefore, expected to have many industrial applications.
When a primary perfluorocarboxylic acid ester is reduced, the alkoxy group (e.g., R in Scheme 1), such as a methoxy (CH
3
O—) or ethoxy (CH
3
CH
2
O—) group, can function as a leaving group when the carbonyl group is attacked by hydride ion; this results in formation of a reactive aldehyde group. Then the intermediate aldehyde can be further reduced to give the alcohol as the final reduction product, as shown in Scheme 1, in which R
f
is a perfluorocarbon group.
However, branched perfluoroalkyl groups, such as secondary and tertiary perfluoroalkyl moieties, sometimes act as pseudo halogens and therefore are good leaving groups. Because of this, it is very difficult to synthesize perfluoroalkyl methanols that have branching at the carbon atom next to the CH
2
OH group (this carbon atom can be referred to as the &agr;-carbon atom). For example, it has been observed that, in contrast to primary perfluorocarboxylic acid esters, secondary perfluorocarboxylic acid esters which have branching at the carbon atom next to the carboxyl group (the &agr;-carbon) may not yield the corresponding branched perfluoroalkyl methanols when the esters are chemically reduced under standard conditions for the reduction of esters, such as by treatment of the ester with lithium aluminum hydride (LAH) or sodium borohydride (NaBH
4
). The products of attempted conventional reduction reactions can be quite complicated. It is believed that when there is a branch site at the carbon atom next to the carbonyl group, the secondary perfluoroalkyl group becomes a better leaving group than the alkoxy group because of the two strong electron withdrawing perfluoroalkyl groups. Thus, the secondary perfluoroalkyl group becomes a leaving group upon attack by hydride ion on the carboxylic ester functionality, producing a perfluoroalkyl anion and a formate ester, as shown in Scheme 2, in which R is an alkyl group and R
f
and R′
f
are perfluoroalkyl groups.
The formate ester may then be further reduced. The perfluoroalkyl anion can rapidly decompose into an olefin (Scheme 3), which can react further with the reducing reagent or with solvent to give a complicated product mixture.
Possibly for the above-described reasons, there are few reports of syntheses of perfluorocyclohexylmethanol compounds by reduction of the corresponding esters. In one of the few successful preparations, (perfluorocyclohexyl)methanol was successfully prepared by the reduction of perfluorocyclohexanecarboxylic acid fluoride with sodium borohydride (Scheme 4; the “F” in the cycloalkyl ring in Scheme 4 indicates that the cyclohexyl ring is perfluorinated) (Gambaretto, Giampaolo, et al.
Att. Ist. Veneto Sci., Lett. Arti. Cl. Sci. Mat. Nat
. 1973, 132, 289-93; C. A. 83, 163685e). However, this procedure may require the synthesis of the corresponding carboxylic acid, followed by conversion to the acid halide (e.g., acid fluoride. Such a two-step procedure can be cumbersome and inefficient.
Similarly, perfluoropolyether alkyl methanols were synthesized as shown in Scheme 5 (Vilenchik, Ya. M.; Lekentseva, G. I. 'neifel'd, P. G. and Pospelova, N. B., Zh. Vses. Khim. O-va. 1981, 26(2), 212-3.; C. A. 95, 96946y).
Certain perfluoropolyethers (e.g., as shown in Scheme 5) have perfluoroalkoxy groups directly attached to the carbon atom next to the carbonyl group (the &agr;-carbon). Perfluoroalkoxy groups generally do not have as strong an electron withdrawing effect as perfluoroalkyl groups, possibly because of the electron rich oxygen atom, and may therefore make a perfluoroalkylene group which is substituted with the perfluoroalkoxy moiety a poorer leaving group than a corresponding perfluoroalkyl group. Thus, while poor results are often obtained upon reductive treatment of branched (perfluoralkyl) carboxylic methyl esters (e.g., Scheme 2, in which R is a methyl group, see supra), perfluoropolyether methanols can be prepared by the reduction of alkyl esters (e.g., methyl esters, as shown in Scheme 6) (Tamaru, Sinji, European Patent Application No. EP 79,590).
SUMMARY OF THE INVENTION
The present invention relates to methods for producing perfluorocarbon-substituted methanols, including straight- and branched-chain perfluoralkylmethanols, straight- and branched-chain perfluoroalkylene dimethanols, and perfluorocycloalkyl methanols. The method also provides novel perfluorocarbon-substituted methanols, including straight- and branched-chain perfluoralkylmethanols, straight- and branched-chain perfluoroalkylene dimethanols, and perfluorocycloalkyl methanools. The invention further provides perfluorocarbon-substituted methanols prepared according to the methods of the invention.
In one embodiment, the invention provides a method for preparing a perfluorocarbon methanol. The method includes reacting a perfluorocarbon ester of a perfluorocarbon carboxylic acid with a reducing reagent under reducing conditions, such that a perfluorocarbon methanol is prepared. The perfluorocarbon ester of a perfluorocarbon carboxylic acid can be represented by the formula R
f
—C(O)OR″
f
, in which R
f
and R″
f
are each independently a substituted or unsubstituted perfluoroalkyl group. In certain embodiments, R″
f
can be —CF
2
R′″
f
, in which R′″
f
is a perfluoroalkyl group. In some embodiments, the perfluorocarbon methanol can be
DeConti, Jr. Giulio A.
Exfluor Research Corporation
Lahive & Cockfield LLP
Shippen Michael L.
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