Organic compounds -- part of the class 532-570 series – Organic compounds – Nitriles
Reexamination Certificate
1999-11-19
2001-06-12
Ambrose, Michael G. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Nitriles
C558S375000, C558S443000
Reexamination Certificate
active
06245933
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The invention relates to a method for making cyanoacrylates.
2. Description of Related Art
Monomer and polymer adhesives are both used in industrial (including household) and medical applications. Included among these adhesives are 1,1-disubstituted ethylene monomers and polymers, such as &agr;-cyanoacrylates. Since the discovery of the adhesive properties of such monomers and polymers, they have found wide use due to the speed with which they cure, the strength of the resulting bond formed, and their relative ease of use. These characteristics have made &agr;-cyanoacrylate adhesives the primary choice for numerous applications such as bonding plastics, rubbers, glass, metals, wood, and, more recently, biological tissues.
Medical applications of 1,1-disubstituted ethylene adhesive compositions, such as &agr;-cyanoacrylate compositions, include use as an alternate and an adjunct to surgical sutures and staples in wound closure as well as for covering and protecting surface wounds such as lacerations, abrasions, burns, stomatitis, sores, and other surface wounds. When an adhesive is applied, it is usually applied in its monomeric form, and the resultant polymerization gives rise to the desired adhesive bond.
U.S. Pat. No. 5,624,669 to Leung et al. describes a process for making cyanoacrylates. In the method, &agr;-cyanoacrylates are prepared by condensing a cyanoacetate and either formaldehyde or paraformaldehyde in the presence of a catalyst at a molar ratio of 0.5-1.5:1 to obtain a condensate; depolymerizing the condensation reaction mixture either directly or after removal of the condensation catalyst to yield crude cyanoacrylate; and distilling the crude cyanoacrylate to form a high purity cyanoacrylate. In order to prepare a particular &agr;-cyanoacrylate, the '669 patent discloses making a corresponding cyanoacetate by esterifying cyanoacetic acid with the corresponding alcohol or by transesterifying an alkyl cyanoacetate with the corresponding alcohol before the cyanoacetate undergoes the condensation reaction with the formaldehyde or paraformaldehyde.
U.S. Pat. No. 4,364,876 to Kimura et al. describes reaction conditions for forming &agr;-cyanoacrylates by the method described in the '669 patent.
U.S. Pat. No. 2,721,858 to Joyner et al. and U.S. Pat. No. 2,763,677 to Jeremias et al. also describe reaction conditions for forming &agr;-cyanoacrylates from the corresponding cyanoacetate.
As used herein the terms “corresponding” or “corresponds” with reference to a cyanoacetate and an &agr;-cyanoacrylate means that the same R group is attached to oxygen of the carboxyl group in the two compounds. Thus, methylcyanoacetate corresponds to methyl &agr;-cyanoacrylate. The term “corresponding alcohol,” as used herein, refers to an alcohol having the same R group attached to the hydroxyl group as the corresponding cyanoacetate or &agr;-cyanoacrylate has attached to the oxygen of the carboxy group. Thus, methyl alcohol corresponds to methylcyanoacetate and to methyl &agr;-cyanoacrylate.
In all of the above mentioned references, the cyanoacetate that undergoes the condensation reaction corresponds to the &agr;-cyanoacrylate that is obtained.
U.S. Pat. No. 5,637,752 to Nakamura et al. describes reaction conditions for the transesterification of a lower alkyl cyanoacetate with an alcohol to form a higher alkyl cyanoacetate.
SU 726,086 describes a process for producing &agr;-cyanoacrylates by reacting ethyl &agr;-cyanoacrylate monomer with excess alcohol in the presence of an acid or metal chloride catalyst. The process is simplified and polymerization of the final product is prevented by conducting the transesterification reaction at 100-140° C. in the presence of sulfuric or para-toluene sulfonic acid or zinc chloride catalyst.
U.S. Pat. No. 2,756,251 to Joyner et al. describes a method for depolymerizing polymeric &agr;-cyanoacrylates.
SUMMARY OF THE INVENTION
The parameters for conducting a condensation reaction of methyl or ethyl cyanoacetate with formaldehyde or paraformaldehyde to form methyl or ethyl &agr;-cyanoacrylate, respectively, with maximum yield are well established. However, the parameters for the condensation of other cyanoacetates to form other &agr;-cyanoacrylates are not as well established. In addition, due to steric considerations, it is difficult to polymerize higher alkyl cyanoacetates and the reaction generally results in smaller oligomers. When cracking an oligomer, the last two monomers, which are joined as cyanoglutarate, are generally difficult to crack. Thus, if a greater number of smaller oligomers are formed, then more of the starting material monomers may be lost. As a result, the final yield of monomers from the overall process may not be as ideal as with methyl or ethyl cyanoacetates. Therefore, it is advantageous to form &agr;-cyanoacrylates other than methyl and ethyl &agr;-cyanoacrylates using processes that do not require the condensation of cyanoacetates other than methyl and ethyl cyanoacetates.
The present invention provides a process for forming &agr;-cyanoacrylates, particularly &agr;-cyanoacrylates of formula (I) where R
1
is a carbon containing organic group other than a methyl or ethyl group:
The process comprises reacting a particular cyanoacetate, particularly methyl or ethyl cyanoacetate, with paraformaldehyde or any other convenient form of formaldehyde to prepare an &agr;-cyanoacrylate oligomer or polymer. The cyanoacrylate oligomer or polymer condensation product is then transesterified with an alcohol to form a different cyanoacrylate oligomer or polymer before undergoing a depolymerization to form the target &agr;-cyanoacrylate. The process may be demonstrated in the following reaction scheme:
In this reaction scheme, R
1
and R
2
both represent any carbon containing organic group as long as they are different from one another. Preferably, n is from 2 to 100.
Although an embodiment of the invention is directed to a process in which R
2
is a methyl or ethyl group and R
1
is a group other than a methyl or ethyl group, the present invention is not limited to such an embodiment. Thus, R
2
may be a group other than a methyl or ethyl group and/or R
1
may be a methyl or ethyl group.
By conducting the transesterification reaction after the condensation reaction, better yield can be obtained. In particular, by using lower alkyl cyanoacetates, longer oligomers or polymers may be obtained, which results in higher yield during the cracking reaction. In addition, because it is not necessary to use the corresponding cyanoacetate to form particular &agr;-cyanoacrylate monomers, a different cyanoacetate for which optimal condensation conditions are more well established and/or more readily available may be effectively used to produce the particular &agr;-cyanoacrylate monomers at relatively high yield.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The process of the present invention comprises reacting a particular cyanoacetate, particularly methyl or ethyl cyanoacetate, with paraformaldehyde or any other convenient form of formaldehyde to prepare an &agr;-cyanoacrylate oligomer or polymer. Conditions for achieving this condensation reaction are known in the art. In particular, U.S. Pat. No. 5,624,669 to Leung et al., U.S. Pat. No. 4,364,876 to Kimura et al., U.S. Pat. No. 2,721,858 to Joyner et al. and/or U.S. Pat. No. 2,763,677 to Jeremias et al., each of which is hereby incorporated herein by reference, describe conditions for the condensation reaction.
As used herein the term “formaldehyde” is intended to include any source of formaldehyde that may be used to achieve the condensation reaction of the present invention including formaldehyde itself, as well as polymers thereof, such as paraformaldehyde or the like, and aqueous solutions of formaldehyde, such as formalin.
The cyanoacrylate oligomer or polymer formed generally contains from about 2 to 100 cyanoacrylate monomer units. However polymers having a larger number of cyanoacrylate monomers may also be formed. Preferably,
Badejo Ibraheem T.
Malofsky Bernard
Ambrose Michael G.
Closure Medical Corporation
Oliff & Berridg,e PLC
Sacket Ebenezer
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