Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Patent
1991-08-20
1992-10-27
Killos, Paul J.
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
C07C 6952
Patent
active
051591065
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a process for the production of esters of acrylic acid and/or methacrylic acid--hereinafter referred to as (meth)acrylic acid esters--with polyhydric alcohols by reactino of the reactants in the presence of acidic esterification catalysts with addition of polymerization inhibitors to the reaction mixture. The process according to the invention operates in particular with the additional measure of purging the reaction zone with an oxygen-containing gas stream to improve the inhibitor effect and to promote the discharge from the reaction zone of the water accumulating as condensation product from the esterification reaction.
(Meth)acrylic acid esters of polyhydric alcohols, particularly from the group of dihydric to tetrahydric aliphatic saturated alcohols and their alkoxylation products, are being used to an increasing extent as highly reactive constituents in radiation-curing systems. Polyfunctional (meth)acrylic acid esters of the type in question may be used, for example, as paint constituents for hardening by electron beams or as a constituent of UV-hardening printing inks or corresponding paints, surfacing, molding or encapsulating compounds or even in adhesives, particularly anaerobic adhesives. However, their production is not without problems. The end products are required in particular to be colorless with a low acid value, high stability in storage and hardly any odor. (Meth)acrylic acid esters of the type in question generally cannot be purified by distillation on account of their high molecular weight and their high reactivity. Accordingly, the products are intended to accumulate directly as colorless products of the esterification reaction. The esterification reaction requires the presence of highly effective inhibitors which, in turn, should not initiate any unwanted secondary reactions, for example in the form of discoloration. In addition, it may be desirable not only to protect the liquid reaction product against unwanted polymerization reactions during the esterification, but also to ensure adequate inhibition of the entire reaction zone including both the inner gas space and also the wall surfaces in contact with the inner gas space. This counteracts the danger of unwanted polymer formation, for example, on such unprotected wall surfaces, the washing off of such polymers into the reaction product in turn leading to an unwanted increase in viscosity in the end product or to unwanted insoluble particles.
Extensive literature is available on the product of such polyfunctional (meth)acrylic acid esters of polyhydric alcohols, cf. in particular DE-OS 29 13 218 and the relevant literature cited therein. Thus, it is known from DE-AS 12 67 547 and from the Journal "Chem. and Ind." 18 (1970), 597, that polyfunctional (meth)acrylic acid esters can be produced by azeotropic esterification of (meth)acrylic acid with polyhydric alcohols in the presence of acidic catalysts and polymerization inhibitors, such as phenols, phenol derivatives, copper, copper compounds or phenothiazine. Organic or inorganic acids or acidic ion exchangers are used as the acidic catalysts, p-toluene sulfonic acid and sulfuric acid being preferred. The esterification reaction takes place under azeotropic conditions using entraining agents for removal of the water of reaction, for example at temperatures in the range from 40.degree. to 120.degree. C. Suitable entraining agents are, for example, aliphatic or cycloaliphatic or aromatic hydrocarbons or mixtures thereof having boiling ranges within the stated temperature limits.
It is proposed in DE-OS 29 13 218 cited above to carry out the azeotropic esterification in the presence of at least one organic ester of phosphorous acid in addition to a phenol-based inhibitor in order to improve the esterification reaction and to obtain (meth)acrylic acid esters of the type mentioned which are not purified by distillation. This phosphiate-based inhibitor is intended to be added in particularly by means of a carrier gas and is apparently used above all to promote
REFERENCES:
patent: 3896161 (1975-07-01), Borden
patent: 4511732 (1985-04-01), Hicks
patent: 4512910 (1985-04-01), Schmidle
patent: 4859792 (1989-08-01), Powanda et al.
Ritter Wolfgang
Sitz Hans-Dieter
Speitkamp Ludwig
Henkel Kommanditgesellschaft auf Aktien
Jaeschke Wayne C.
Killos Paul J.
Millson Jr. Henry E.
Szoke Ernest G.
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