Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Reexamination Certificate
2001-03-20
2002-05-21
Siegel, Alan (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
C564S306000, C564S308000, C570S124000, C570S127000, C570S129000, C570S143000, C570S144000
Reexamination Certificate
active
06392097
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to processes for the preparation of parylene dimers, and more particularly to processes for the preparation of derivatives of octafluoro-[2,2]paracylophane, otherwise known as AF4.
BACKGROUND AND SUMMARY OF THE INVENTION
Parylene is a generic term used to describe a class of poly-p-xylylenes which are derived from a dimer having the structure:
wherein X is typically a hydrogen, or a halogen. The most commonly used forms of parylene dimers include the following:
Parylene coatings are obtained from parylene dimers by means of a well-known vapor deposition process in which the dimer is vaporized, pyrolized, i.e. cleaved into a monomer vapor for, and fed to a vacuum chamber wherein the monomer molecules polymerize, and deposit onto a substrate disposed within the vacuum chamber.
Due to their ability to provide thin films and conform to substrates of varied geometric shapes, parylene materials are ideally suited for use as a conformal coating in a wide variety of fields, such as for example, in the electronics, automotive, and medical industries.
Parylene polymers are usually formed by chemical vapor deposition (CVD) processes. One such process is the Gorham process in which a parylene dimer having the molecular structure:
is vaporized and the dimer bonds are then cleaved to yield parylene monomers. The parylene monomers are deposited onto a surface and subsequently polymerized. Because the dielectric constant and melting temperature of parylene polymers usually increases as the number of fluorine atoms within the polymer increases, it is desirable to use octafluoro-[2,2]paracylcophane (AF4).
Octafluoro-[2,2]paracyclophane, more precisely 1,1,2,2,9,9,10,10-Octafluoro-[2,2]paracyclophane, and more commonly referred to in the industry as AF4, is a fluorine substituted version of the above-noted dimers and has the structure:
It is known that parylene coatings (Parylene AF
4
) which are derived from the AF
4
dimer by the vapor deposition process have a very high melting temperature (about 540° C.), and a low dielectric constant (about 2.3). These characteristics make Parylene AF
4
ideally suited for many high temperature applications, including electronic applications, and potentially as an inter-layer dielectric material for the production of semiconductor chips. However, up to the present time, AF4, which is used as the dimer starting material for depositing Parylene F coatings, has been commercially unavailable due to high costs of production. Both OFP and AF4 are used interchangeably herein and are intended to refer to the same compound.
One known method of producing AF4 is described in U.S. Pat. No. 5,210,341 wherein the process of preparing AF4 utilizes a low temperature in conjunction with a reduced form of titanium in order to produce dimerization of dihalide monomers. One aspect of the '341 patent provides a process for preparing octafluoro-[2,2]paracyclophane, which comprises contacting a dihalo-tetrafluoro-p-xylylene with an effective amount of a reducing agent comprising a reduced form of titanium and an organic solvent at conditions effective to promote the formation of a reaction product comprising octafluoro-[2,2]paracyclophane.
While the process described in the '341 patent is effective for its intended purpose, it has been found that the process is still too expensive for commercial realization due to low yields, that there are some impurities in the AF4 dimer, and furthermore that it would be difficult to adapt to a large scale commercial production.
TFPX-dichloride having the following structure:
is another preferred starting material for the preparation of AF4. Heretofore, the only useful preparation of TFPX-dichloride has been via a high yield, photo-induced chlorination of &agr;,&agr;,&agr;′,&agr;′-tetrafluoro-p-xylene (hereinafter “TFPX”) having the molecular structure:
The conventional procedure for synthesizing TFPX involves the fluorination of terephthaldehyde, which has the molecular structure:
SF
4
and MoF
6
are the most commonly used reagents for terephFthaldehyde fluorination. However, SF
4
and MoF
6
are expensive, reducing the industrial utility of this synthetic scheme. In addition, SF
4
and MoF
6
are toxic materials, so a large amount of hazardous waste is produced using these reagents.
Russian patent 2,032,654 discloses an alternative method of synthesizing TFPX in which &agr;,&agr;,&agr;′,&agr;′-tetrabromo-p-xylene (hereinafter “TBPX”) having the molecular structure:
is reacted with SbF
3
to produce TFPX. This method employs the well established electrophilic catalyzed S
N
1 reaction mechanism for replacement of benzylic halogen atoms of the TFPX with fluorine atoms. According to this method, the anitmony in SbF
3
acts as an elctrophile which removes bromine from TBPX to form a carbocation. The carbocation subsequently reacts with fluorine to form TFPX. While this reaction is reported to provide good yield when carried out under comparatively mild reaction conditions, antimony containing compounds are highly toxic and explosive. Furthermore, the SbF
3
is used in a stoichiometric amount rather than a catalytic amount, resulting in large quantities of hazardous waste materials. This method of synthesizing TFPX thus has limited use for industrial applications.
AF4 is a member of the class of paracyclopenones. Paracyclophenone (PCP) chemistry has grown considerably since the isolation of the parent compound in 1949. Braun et al., NATURE (1949) 164, 915. Besides finding commercial application as monomers for the parylene type polymers, these molecules have spawned an unusual and unique chemistry. The close proximity of the face-to-face aromatic rings, coupled with the rigid skeleton and high strain energy translates into such effects as trans-annular interactions, thermal racemization and isomerism, surprising directing effects in multiple electrophilic substitution and unusual spectroscopic phenomena. The use of ring-substituted [2,2] PCP skeletons as chiral backbones is of considerable current interest. Highly fluorinated cyclophanes on the other hand, have received much less attention, even though these compounds have desirable industrial properties and should at least display as equally rich a chemistry as their hydrocarbon counterparts. This imbalance is being redressed following the syntheses of the bridge fluorinated cyle 1,1,2,2,9,9,10,10 octafluoro[2,2]paracyclophane (abbreviated as OFP, and more commonly referred to in the industry as AF4) that have been reported previously.
Two complementary synthetic methods for the introduction of two substituents into the rings of octaflouroparayclophane have thus been developed. Nitration gives three isomers with the nitro functionalities in different rings, oriented pseudo meta, pseudo para and pseudo ortho. Bromination on the other hand gives a dibromide where both halogens are in the same ring, para to each other. All such products serve as versatile starting materials for the preparation of a variety of novel homo- and hetero-annular disubstitututed OFP derivatives. The compounds synthesized have also been found to be precursors of a variety of other disubstituted OFP derivatives. The synthesis, characterization and thermal isomerization of a variety of both homo- and hetero-annularly disubstituted OFP derivatives has also been developed and described.
The instant invention provides improved processes for the preparation of octafluoro-[2,2]paracyclophane which involve contacting a OFP with dry nitrogen, nitronium tetrafluoroborate dissolved in sulphophane to provide pseudo meta-, pseudo para-, and pseudo ortho-dinitro-1,1,2,2,9,9,10,10-octafluoroparacyclophanes. Reduction of these three products using iron powder/concentrated hydrochloric acid provided the corresponding diamino products in good isolated yields. The three diamino products proved to be versatile starting materials for further transforma
Dolbier, Jr. William R.
Duan Jian-Xin
Roche Alex J.
Marenberg, Esq. Barry J.
Mintz Levin Cohn Ferris Glovsky and Popeo
Siegel Alan
Specialty Coating Systems Inc.
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