Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Reexamination Certificate
2000-06-13
2002-10-01
Geist, Gary (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
C560S205000
Reexamination Certificate
active
06458991
ABSTRACT:
The present invention relates to an improved process for the preparation of light esters of acrylic acid and/or methacrylic acid from alcohols which may be alkoxylated, in the presence of an acidic esterification catalyst and of a copper compound as polymerization inhibitor.
Radiation-curable binders based on monomeric and oligomeric acrylates of alcohols have become increasingly interesting commercially as coating resins and other coating materials, owing to their solvent-free and easy processability. There is therefore a continuing need for improved preparations of the (meth)acrylates of in particular polyhydric alcohols, their alkoxylated derivatives, polyether polyols or polyester polyols, as shown by the numerous patent applications in this area. Thus, reference may be made to the German Patent Applications DE-A 3316593, DE-A 3704098, DE-A 3843854, DE-A 3843930, DE-A 3843938, DE-A 4019788 and DE-A 4430086 as prior art.
The esterification of alcohols and in particular polyols with methacrylic acid and preferably acrylic acid have been described in many publications. Apart from a preparation by transesterification, the preferred method of preparing (meth)acrylates is the direct esterification of alcohols or polyols with acrylic acid or methacrylic acid in the presence of an esterification catalyst and of a solvent which forms an azeotropic mixture with water and serves as a water-entraining agent. To accelerate the esterification reaction, it is desirable to choose reaction temperatures of more than 90° C. and in particular more than 100° C., also for the subsequent rapid distillative removal of the acrylic acid and/or methacrylic acid generally used in excess. High reaction temperatures require the use of larger amounts of polymerization inhibitors in order to achieve good yields of the esterification products and for effectively suppressing the polymerization of (meth)acrylic acid and esters thereof. Since said polymerization inhibitors remain in the reaction product even after the excess (meth)acrylic acid has been distilled off, the concomitant use of polymerization inhibitors imparting a strong color, such as copper salts, phenothiazine, hydroquinone and derivatives thereof, is not expedient for the preparation of light esterification products. They generally lead to dark end products. Although the use, known per se, of a copper salt as a polymerization inhibitor in the preparation of (meth)acrylates permits high esterification temperatures, it was then necessary, for the preparation of light products, to wash out the copper salt in a wash step, which is time-consuming, reduces the ester yield, increases the requirement of solvents as a water-entraining agent, which have to be distilled off again, and furthermore leads to a high level of pollution of waste water.
It is an object of the present invention to provide a simple process for the preparation of (meth)acrylates which gives light esterification products in good yield.
We have found that this object is achieved by a process for the preparation of (meth)acrylates by esterification of acrylic acid/and or methacrylic acid with at least one compound having one or more alcoholic hydroxyl groups at an esterification temperature of from 90 to 150° C. in the presence of an acidic esterification catalyst and of a polymerization inhibitor with the addition of a hydrocarbon having a boiling point of from 40 to 120° C. as a water-entraining agent, the water-entraining agent and excess (meth)acrylic acid being distilled off at from 90 to 150° C. at atmospheric pressure or reduced pressure after the esterification and, if required, the acidic product obtained after the distillation being neutralized with at least one basic inorganic compound, wherein the polymerization inhibitor used is a copper(II) salt, a copper(I) salt or a mixture thereof, the copper being precipitated as copper sulfide after the esterification and being separated off.
The novel process thus combines the advantages of using a high temperature for a more rapid esterification and rapid distillative removal of the excess of (meth)acrylic acid with the advantage of a low requirement of solvent as water-entraining agent, with the advantage of effective removal of the copper salt as polymerized inhibitor without the use of a wash step and with the advantage of the preparation of light end products (iodine number≦5, preferably≦3, in particular≦2) in good yield.
Acids used for the esterification reaction are methacrylic acid, acrylic acid or mixtures thereof, the preferred acid being acrylic acid.
Suitable compounds having one or more alcoholic hydroxyl groups, in addition to alcohols, such as lauryl alcohol or 2-ethylhexyl alcohol, are in particular polyols having 2 to 6 alcoholic hydroxyl groups. Examples of compounds having alcoholic hydroxyl groups are alcohols having 2 to 20, preferably 2 to 10, carbon atoms, such as ethylene glycol, propylene glycol, 1,2-, 1,3- and 1,4-butanediol, neopentylglycoi, di- and triethylene glycol, di- and tripropylene glycol, 1,5-pentanediol, 1,6-hexanediol, glycerol, trimethylolethane, trimethylolpropane, ditrimethyloipropane, sorbitol, pentaerythritol or dipentaerythritol. Very suitable components having alcoholic hydroxyl groups are also alkoxylation products such as alcohols and in particular ethoxylated and/or propoxylated polyhydric alcohols such as oxyethylated trimethylolpropane, ethoxylated and/or propoxylated pentaerythritol. In general, such alkoxylated alcohols contain 1 to 20 and preferably 1 to 10 alkoxy groups in the polyol molecule. In addition to polyether polyols, other polyols used may be polyester polyols, ether-modified polyesterpblyols, polyepoxy resins having a plurality of aliphatic hydroxyl groups or corresponding polyurethanes. Liquid to viscous low molecular weight and oligomeric compounds having alcoholic hydroxyl groups are particularly suitable for the esterification reaction.
For the esterification reaction, the components containing acid and hydroxyl groups are used in particular in amounts of from 1 to 1.5 mol of acid per hydroxyl group of the mono- or polyol component. However, the amount of acid can also be correspondingly reduced if only some of the hydroxyl groups of polyols are to be converted into acrylates and/or methacrylates.
Suitable acidic esterification catalysts are strong organic or inorganic acids, which are generally used in amounts from 0.1 to 5% by weight, based on the sum of the amounts of alcohol and of (meth)acrylic acid component. Preferred acidic esterification catalysts are sulfuric acid, p-toluenesulfonic acid, methanesulfonic acid and strongly acidic ion exchangers.
The esterification can be carried out at atmospheric, subatmospheric or reduced pressure.
Polymerization inhibitors used in the novel process for the esterification reaction and for distilling off the excess (meth)acrylic acid are copper(II) salts, in particular copper(II)chloride, copper(II)nitrate or copper(II) sulfate, or a mixture of a copper(II) salt and a copper(I) salt. The amount of inhibitor should be sufficient for effective inhibition of the polymerization of the (meth)acrylic acid and esters thereof during the esterification reaction and the subsequent distilling off of the excess (meth)acrylic acid. It is preferable to use the copper salts in an amount of at least 0.02 and in particular from 0.2 to 0.6% by weight, based on the resulting amount of (meth)acrylate.
It has proven advantageous also to add to the esterification mixture, before the esterification reaction, hypophosphorous acid (H
3
PO
2
), triphenyl phosphite or an organophosphonic acid, such as 1-hydroxyethane-1,1-diphosphonic acid, as a color stabilizer in an amount of 0.01 to 3% by weight, based on the resulting amount of ester. Further conventional polymerization inhibitors, color stabilizers, etc., such as hydroquinone compounds, e.g. hydroquinones monomethyl ether, can be added to the batch in conventional amounts in the novel process after the excess (meth)acrylic acid has been distilled off, without substantially impairi
Beck Erich
Jaworek Thomas
Königer Rainer
Paulus Wolfgang
Reich Wolfgang
BASF - Aktiengesellschaft
Forohar Farhad
Geist Gary
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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