Compositions – Chemically interactive reactants
Reexamination Certificate
2000-08-24
2004-03-16
Toomer, Cephia D. (Department: 1714)
Compositions
Chemically interactive reactants
C252S183120, C252S403000, C252S404000
Reexamination Certificate
active
06706209
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a stabilized monomer composition that includes N,N-diethylhydroxylamine and N-nitroso-N-phenylhydroxyl amine or its salt and to processes for synthesis and purification of a stabilized monomer composition.
2. Discussion of the Background
Stabilization of monomer compositions is a widely recognized problem. For example, methacrylic acid derivatives exhibit undesired premature polymerization. The polymerization rate increases strongly, especially at elevated temperatures. However, many processes for synthesis of acrylic monomers typically include process steps such as distillation, in which the temperature is elevated. To ensure that these purification processes can nevertheless be achieved, the monomers to be purified must be stabilized. In addition, prolonged storage leads to polymerization of the monomers. Such aging phenomena occur especially under exposure to light.
It is indeed possible to reduce such polymerization by addition of high concentrations of known inhibitors. However, the consequence is that the desired polymerization can then only be achieved by addition of correspondingly high concentrations of initiators. If the inhibitor is added in an extremely high concentration, it must be separated prior to polymerization. Otherwise it is impossible to achieve high molecular weights. For this reason, the lowest possible inhibitor concentrations should be used.
Known polymerization inhibitors for acrylates include, for example, phenothiazine, hydroquinone, especially hydroquinone monomethyl ether and benzoquinone. The use of N,N-diethylhydroxylamine is also known. European Patent Application EP A 0266906 discloses the synergistic activity of hydroxylamines in combination with phenylenediamines. It has been found, however, that this combination alone is inadequate in processes for synthesis of hydroxyalkyl (meth)acrylates. Thus yield losses are suffered in particular during purification by distillation.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide a stabilized monomer composition which remains stable during prolonged storage. It is also an object to achieve high degrees of polymerization without separation of the inhibitor by, for example, addition of initiators.
A further object of the invention is to find a stabilized monomer composition which is suitable in particular for distillation.
Yet another object of the invention is to find compositions which permit a high product yield during the synthesis of hydroxyalkyl (meth)acrylates.
These and other objects of the invention have been satisfied by the discovery of a stabilized monomer composition, comprising:
at least one ethylenically unsaturated monomer;
N,N-diethylhydroxylamine; and
N-nitroso-N-phenylhydroxylamine or its salt;
wherein a weight ratio of N,N-diethylhydroxylamine to N-nitroso-N-phenylhydroxylamine or its salt is from 1:1 to 10:1, and by the discovery of methods for its preparation and its use in purifying 2-hydroxyalkyl (meth)acrylates.
DETAILED DESCRIPTION OF THE INVENTION
The first embodiment of the present invention includes a stabilized monomer composition, comprising:
at least one ethylenically unsaturated monomer;
N,N-diethylhydroxylamine; and
N-nitroso-N-phenylhydroxylamine or its salt;
wherein a weight ratio of N,N-diethylhydroxylamine to N-nitroso-N-phenylhydroxylamine or its salt is from 1:1 to 10:1.
Another embodiment of the invention includes a process for synthesis of a stabilized monomer composition, comprising:
mixing at least one ethylenically unsaturated monomer, N,N-diethylhydroxylamine and N-nitroso-N-phenylhydroxylamine or its salt;
wherein a weight ratio of N,N-diethylhydroxylamine to N-nitroso-N-phenylhydroxylamine or its salt is from 1:1 to 10:1.
A third embodiment of the invention includes a process for synthesis of a 2-hydroxyalkyl (meth)acrylate, comprising:
reacting an oxirane compound with (meth)acrylic acid in the presence of a catalyst;
adding at least one inhibitor;
adding an aqueous solution of N,N-diethylhydroxylamine and N-nitroso-N-phenylhydroxylamine or its salt, thereby providing a mixture; and
distilling said mixture.
A fourth embodiment of the invention includes a method of purifying a 2-hydroxyalkyl (meth)acrylate, comprising:
adding at least one inhibitor to said 2-hydroxyalkyl (meth)acrylate:
adding an aqueous solution of N,N-diethylhydroxylamine and N-nitroso-N-phenylhydroxylamine or its salt, thereby providing a mixture; and
distilling said mixture.
In particular the following advantages are achieved by the inventive steps:
Monomer compositions stabilized according to the invention remain stable during prolonged storage even if exposed to light.
Monomers stabilized according to the present invention can be purified particularly easily by distillation.
Stabilized monomer compositions can also be transformed by known reactions, in which the monomer is modified while preserving the ethylenically unsaturated double bond and ensuring that this transformation does not lead to particularly high losses of yield.
It is very surprising that even monomers existing in the gas phase can be stabilized by the inventive combination.
Ethylenically unsaturated monomers are compounds which contain at least one, double bond that can undergo radical polymerization. These ethylenically unsaturated monomers include among others vinyl esters; (meth)acrylic acid; (meth)acrylic acid esters such as methyl and ethyl (meth)acrylate; vinyl chloride; vinylidene chloride; vinyl acetate; styrene; substituted styrenes with an alkyl substituent in the side chain, such as &agr;-methylstyrene and &agr;-ethylstyrene; substituted styrenes with an alkyl substituent on the ring, such as vinyltoluene and p-methylstyrene; halogenated styrenes, such as monochlorostyrenes, dichlorostyrenes, tribromostyrenes and tetrabromostyrenes; vinyl and isopropenyl ethers; maleic acid derivatives, such as maleic anhydride, methylmaleic anhydride, maleimide, methylmaleimide; and dienes, such as divinylbenzene.
The notation (meth)acrylic derivatives includes methacrylic derivatives, acrylic derivatives and mixtures of the two.
Preferred ethylenically unsaturated monomers are (meth)acrylic acid as well as derivatives of (meth)acrylic acid. These compounds can be represented by, for example, Formula I
where R
1
denotes hydrogen or a methyl group, R
2
denotes hydrogen, an aryl group, which can also contain hetero atoms, such as phenyl and imidazole, or a straight-chain, branched or cyclic alkyl group with up to 30 carbon atoms, which may or may not be saturated, and which can also contain hetero atoms such as nitrogen and/or oxygen, examples being methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclopentyl, cyclohexyl, isobornyl, vinyl, propenyl, butynyl, 2-(N,N-dimethylamino)ethyl, 2-(N,N-dimethylamino)propyl, 2-hydroxypropyl and 2-hydroxyethyl.
Preferably, the ethylenically unsaturated monomers include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobornyl (meth)acrylate, hydroxyalkyl (meth)acrylates, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate and 3,4-dihydroxybutyl (meth)acrylate, as well as aminoalkyl (meth)acrylates, such as dimethylaminoethyl methacrylate (DMAEMA).
The (meth)acrylic acid amides corresponding to the (meth)acrylic acid esters also comprise a preferred group of ethylenically unsaturated monomers. An example of this group is N-dimethylaminopropyl methacrylamide (DMAPMA).
The ethylenically unsaturated monomers can be present individually or as mixtures in the inventive composition.
The compounds N,N-diethylhydroxylamine and N-nitroso-N-phenylhydroxylamine (“cupferron”) are widely known among those skilled in the art and are commercially available from numerous suppliers. N-nitroso-N-phenylhydroxylamine is an acid compound whose salts, such as the ammonium, aluminum, copper, lithium, sodium, potassium and rubidium salts, are also intended to be inclu
Goetzen Friedrich
Rau Hartmut
Scharf Jakob
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Roehm GmbH & Co. KG
Toomer Cephia D.
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