Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Reexamination Certificate
2000-05-03
2001-12-11
Geist, Gary (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
C560S217000, C560S231000
Reexamination Certificate
active
06329543
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to processes for synthesis of isobornyl (meth)acrylate by reacting camphene with (meth)acrylic acid in the presence of sulfuric acid and at least one compound having an inhibiting action.
2. Discussion of the Background
Monomeric isobornyl (meth)acrylate is widely used in the manufacture of varnish binding agents. An example of how this compound is synthesized is the reaction of camphene with (meth)acrylic acid in the presence of an acidic cation-exchange resin. This type of synthesis is described, for example, in European Patent Application EP A 0718271 (Atochem) and in German Unexamined Application DE-OS 4419686 (Hoechst AG); both incorporated herein by reference. Although ion-exchange catalysis appears elegant at first sight, it has the disadvantage in industrial practice that the catalyst loses activity after repeated use. One possible explanation of this loss is that a polymer film is formed on the resin despite good process control. Even regenerative cleaning and activation, for example by washing with acid followed by drying with a suitable solvent such as acetone, does not restore the original activity level, and so the catalyst must be replaced after a few cycles of use.
It is also known that camphene can be reacted with (meth)acrylic acid in the presence of concentrated sulfuric acid to obtain isobornyl (meth)acrylate. The use of concentrated sulfuric acid as catalyst is described in, for example, Japanese Unexamined Application JP-OS-54/126293; incorporated herein by reference. It should be noted immediately, however, that the yield of about 80% described in the Japanese document was unattainable by far (see Comparison Example 2).
Moreover, a very large quantity of N,N′-diphenyl-p-phenylenediamine (about 8% relative to the acrylic acid) must be used in order to prevent undesired polymerization of the (meth)acrylate. The great majority of this inhibitor must be removed from the mixture, however, because the inhibitor prevents the desired polymerization of isobornyl (meth)acrylate.
Furthermore, the proposed inhibitor has a yellow color, and so for this reason already it must be separated as completely as possible. The required cleaning steps, such as multiple distillation, lower the yield to very small quantities of pure product. Attempts can be made to replace this inhibitor by other inhibitors or mixtures of compounds having inhibiting action, but a conversion of only about 10% is obtained.
OBJECTS OF THE INVENTION
In view of the prior art cited and discussed herein, one object of the present invention is to provide a process for synthesis of isobornyl (meth)acrylate by reacting camphene with (meth)acrylic acid in the presence of sulfuric acid, in which process high conversions are achieved without the need to use large quantities of N,N′-diphenyl-p-phenylenediamine, which is difficult to separate.
Another object of the invention is to provide an inhibitor combination that is effective in particularly small quantities.
Yet another object of the invention is to provide a process for distillation of isobornyl (meth)acrylate from a mixture containing sulfuric acid without causing polymerization of the isobornyl (meth)acrylate.
DESCRIPTION OF THE INVENTION
These objects are achieved by the herein described processes for synthesis of isobornyl (meth)acrylate.
In a first aspect of the present invention there is provided, by the fact that aqueous sulfuric acid with an acid concentration preferably in the range of 65 to 85 wt % is used, including all values and sub-ranges therebetween, a process for synthesis of isobornyl (meth)acrylate by reacting camphene with (meth)acrylic acid in the presence of sulfuric acid and at least one compound having inhibiting action, by means of which process the desired isobornyl (meth)acrylate is obtained particularly inexpensively in high yield and in pure form.
In a second aspect of the present invention there is provided, by the fact that distillation is performed in the presence of 2,6-di-tert-butyl-&agr;-(dialkylamino)-p-cresol, a process for distillation of isobornyl (meth)acrylate from a mixture containing sulfuric acid, without causing polymerization of a large proportion of the isobornyl (meth)acrylate in the distillation flask.
The objects of the invention are achieved in excellent manner by each individual one of these two aspects.
In particular, the following advantages among others are achieved by the features according to the invention:
Processes according to the invention lead to very high conversions and high purity of the products.
Commercially available inhibitors can be used in the process according to the invention.
The process can be performed inexpensively, since high-priced ion-exchange resins do not have to be used.
Furthermore, in particularly preferred embodiments, such small quantities of compounds having inhibiting action are needed that they can be removed completely without relatively large yield losses.
As used herein the notation “(meth)acrylic acid” includes methacrylic acid, acrylic acid and mixtures of the two acids.
Isobornyl (meth)acrylate can be represented in general by formula (I)
in which the group R denotes hydrogen or a methyl group.
Also covered by formula (I) are, in particular, isomeric forms of isobornyl (meth)acrylate that correspond, for example, to different positions of the acid group on the isobornyl ring.
The compounds camphene (2,2-dimethyl-3-methylenebicyclo[2.2.1]heptane), methacrylic acid and acrylic acid are widely known to those skilled in the art. These compounds can be obtained commercially from a large number of suppliers.
The same is true for aqueous sulfuric acid, which in the process according to the invention is used in an acid concentration in the range of 65 to 85 wt %, including 66, 67, 68, 69, 70, 72, 74, 75, 77, 79, 80, 81, 82, 83, and 84%, preferably 70 to 80 wt %, inclusive of all specific values between 70 and 80.
To prevent polymerization of the isobornyl (meth)acrylate or of the (meth)acrylic acid, it is preferred in the process according to the invention to use at least one compound having polymerization inhibiting action. Such compounds are widely known to those skilled in the art. Examples include hydroquinone alkyl ethers, sterically hindered phenols and/or sterically hindered piperidine N-oxyl derivatives.
Hydroquinone alkyl ethers can be represented by general formula (II)
in which
R
1
denotes hydrogen, a straight-chain or branched alkyl group with one to eight carbon atoms, halogen or aryl, preferably an alkyl group with one to four carbon atoms, especially preferably methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl;
n is an integer in the range of zero to four, preferably zero, one or two; and
R
2
denotes hydrogen, a straight-chain or branched alkyl group with one to eight carbon atoms or aryl, preferably an alkyl group with one to four carbon atoms, especially preferably methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl or tert-butyl.
Preferred sterically hindered phenols can be represented in general by the general structure (III)
in which
R
1
denotes a straight-chain or branched alkyl group with 1 to 8 carbon atoms, aryl or aralkyl, propionic acid esters with monohydric to tetrahydric alcohols, which can also contain hetero atoms such as S, O and N, preferably a propionic acid ester with an octadecyl group.
A further advantageous substance class is represented by hindered phenols on the basis of triazine derivatives of formula (IV)
with R=a compound of formula (V)
in which
R
1
=C
n
H
2n+1
with n=1 or 2.
Sterically hindered piperidine N-oxyl derivatives can be represented by, for example, formula (VI)
in which R
1
denotes hydroxyl, an ether or an ester group, wherein the latter groups can have up to 20 carbon atoms. A plurality of sterically hindered piperidine N-oxyl groups can also be bonded via the group R
1
.
Furthermore, compounds with 1,4-benzoquinone as the parent co
Knebel Joachim
Saal Doris
Geist Gary
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Reyes Hector M.
Roehm GmbH & Co KG
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