JPS5940384B2 - Method for producing hydroxypropyl methacrylate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing hydroxypropyl methacrylate.

More particularly, the present invention relates to an improved process for producing hydroxypropyl methacrylate by reacting propylene oxide and methacrylic acid with chromium trioxide as a catalyst. U.S. Patent No. 387521
No. 1 discloses a method in which a salt of trivalent chromium is used as a catalyst in the reaction between acrylic acid and alkylene oxide.

US Pat. No. 3,708,524, dated January 2, 1973, suggests the use of chromium compounds in combination with trivalent iron compounds as catalysts in the production of hydroxyacrylates or hydroxymethacrylates.

A similar method is also disclosed in US Pat. No. 3,632,854. However, all of the methods disclosed in these prior art documents produce storage-stable hydroxyalkyl acrylates or hydroxyalkyl methacrylates that do not contain harmful amounts of catalyst (residues) and have sufficient purity, while at the same time removing unreacted alkylenes. Hydroxyalkyl acrylates or hydroxyacryl methacrylates cannot be produced under operating conditions that avoid oxide accumulation. Such highly pure, stable products can be used directly as intermediates in chemical processes, such as polymerization processes to produce industrial resins. Here, the above and related problems are solved by first mixing a solvent capable of dissolving a chromium trioxide catalyst and methacrylic acid with the catalyst, and then continuously adding propylene oxide to the mixture. It has been found that this can be overcome by an improved method of adding

By using a chromium trioxide catalyst rather than prior art chromium compound catalysts such as chromium salts, there is less foreign material (catalyst residue) that reduces the purity of the final product hydroxypropyl methacrylate. According to the invention, in a method for producing hydroxypropyl methacrylate by reaction of methacrylic acid and propylene oxide: methacrylic acid and 0.05 to 5% by weight, based on methacrylic acid.
Based on chromium trioxide and methacrylic acid as a catalyst for 5
~20% by weight of pre-prepared hydroxypropyl methacrylate as catalyst solvent; for a substantially water-free mixture; 0.90-1.5 moles per mole of methacrylic acid in the mixture; Provided is a method for producing hydroxypropyl methacrylate, characterized in that propylene oxide is continuously added in a proportion of .

This reaction can be continued until substantially all of the methacrylic acid is consumed. The starting materials of the invention are methacrylic acid and propylene oxide.

Usually both starting materials are used in approximately equimolar amounts. A preferred ratio for carrying out the present invention is about 0.90 to 1.5 moles of propylene oxide per mole of methacrylic acid, and a more preferred ratio is about 1.0 mole of propylene oxide per mole of methacrylic acid.
0 to 1.2 moles of propylene oxide. Too much excess of propylene oxide tends to increase the formation of undesirable by-products. Preferably, the reaction is carried out at a temperature within the range of about 60-120<0>C, with a more preferred temperature range of about 80-100<0>C.

Lower temperatures tend to reduce the reaction rate, and higher temperatures tend to promote the formation of undesirable polymers. Usually, the reaction is continued until the acid value of the reaction mixture becomes 30 or less. The acid value of the reaction mixture is approximately 5.
˜10 indicates that the reaction is substantially complete. Depending on the reaction temperature and catalyst concentration, the acid number indicating substantial completion of the reaction is:
Obtained in about 20 to 1000 minutes. The lower the reaction temperature and the lower the catalyst concentration, the longer the reaction Ff! A distance between f is required. The catalyst used in the process of the present invention is chromium trioxide ().

The amount of catalyst used is at least 0.0 of methacrylic acid.
It should be 5% by weight. For economic reasons, of course, no more catalyst than necessary should be used in the practice of this invention. Although higher amounts of catalyst, such as 5% by weight of methacrylic acid, can be used, it must be recognized that as the amount of catalyst used increases, the purity of the resulting hydroxypropyl methacrylate decreases. If the purity of the product obtained is not a concern, the use of higher amounts of catalyst, up to 5% by weight, may be desirable to reduce the reaction time. Hydroxypropyl methacrylate of sufficient purity to be used without further purification for applications such as the production of unsaturated thermosets can be obtained at catalyst concentrations of about 0.2% by weight of the raw methacrylic acid or less. It will be done. Before adding propylene oxide,
methacrylic acid and a catalyst, 5 to 20% of the methacrylic acid
By premixing in a solvent (preformed hydroxypropyl methacrylate) in an amount of can be caused.

When the starting amount of solvent is about 15% by weight of the methacrylic acid, the amount of propylene oxide present during the reaction is such that the rate of addition of propylene oxide per minute is about 0.5% by weight of the total amount of propylene oxide used. It has been found that, if present, a safe level of about 7-10% by weight of the total weight of the reaction mixture is not exceeded. The initial solvent concentration is 5 of methacrylic acid.
Below % by weight, the reaction proceeds undesirably slowly, and initial solvent concentrations higher than 20% by weight of methacrylic acid do not provide any particular benefit, reducing the economic advantages of the process. Therefore 5-20% by weight of methacrylic acid
With a solvent concentration of , the accumulation of unreacted propylene oxide is avoided and the risk of exothermic overheating and explosion is thus greatly reduced. Also, unexpectedly,
It has also been found that similar or higher reaction rates can be achieved with much smaller amounts of catalyst than those used in traditional alkylene oxide and acrylic (or methacrylic) acid reactions.

Since the process of the invention can be carried out at such low catalyst concentrations, surprisingly high purity of hydroxypropyl methacrylate can be obtained. It is desirable to include a small amount of a polymerization inhibitor in the reaction mixture to prevent the polymerization reaction between methacrylic acid and hydroxypropyl methacrylate from occurring during the reaction between propylene oxide and methacrylic acid. Such measures are particularly desirable when the reaction is carried out at somewhat high temperatures, such as above 130° C., since without such measures the reaction product hydroxypropyl methacrylate may be contaminated with methacrylate polymer. . Examples of suitable polymerization inhibitors include hydroquinone, hydroquinone monomethyl ether, parabenzoquinone, t-
Butylcatechol, etc. Two examples of particularly desirable polymerization inhibitor systems are the combination of t-butylcatechol and hydroquinone monomethyl ether, and the combination of hydroquinone or parabenzoquinone with hydroquinone monomethyl ether. The use of oxygen mixtures during the reaction provides an improvement in maintaining the efficacy of the polymerization inhibitor over long reaction cycles. The solvent for the chromium trioxide catalyst in the process of the invention is hydroxypropyl methacrylate, which is miscible with propylene oxide and methacrylic acid.

Therefore, since the product and the solvent are the same, their separation can be omitted. When the product hydroxypropyl methacrylate is used in a solvent polymerization reaction, it is economically advantageous to use an additional solvent such as styrene. The product hydroxypropyl methacrylate of the invention dissolved in styrene is suitable for the production of unsaturated thermosetting urethane resins as described in US Pat. No. 3,876,726 and US Pat. No. 4,218,537. Although the process of the present invention provides hydroxypropyl methacrylate of sufficient purity for immediate use in subsequent polymerization reactions, even higher purity products can be obtained by removing the chromium trioxide by washing with citric acid, distillation, or other well-known purification methods. is obtained.

Since the presence of water in the hydroxypropyl methacrylate product will adversely affect the usefulness of the hydroxypropyl methacrylate in subsequent polymerization reactions, care is taken to remove substantially all water from the starting material, e.g. by vacuum stripping. Should. It has been found that the product of the process of the invention has a reduced storage stability as defined by the length of time until gelation occurs when it is stored at 55°C.

The invention is further illustrated in the following examples.

Example 1 2.04 kg of hydroxypropyl methacrylate (molecular weight 144.17) as catalyst solvent; 13.61 kg (158.1 gram molecules) of methacrylic acid (molecular weight 86.09); pure T as polymerization inhibitor - 9.37 ppm each of butylcatechol and hydroquinone monomethyl ether (i.e. 683 ppm each based on the above methacrylic acid); and 1 chromium trioxide catalyst.
7.77 (i.e. 13 based on the above methacrylic acid)
00 ppm); charged into the reactor.

The mixture was heated to 90° C. in a pressure reactor, purged with nitrogen, and then vacuum applied. Release this reduced pressure, 5%
A nitrogen atmosphere containing oxygen was provided to maintain the effectiveness of the polymerization inhibitor. The contents are heated to a temperature of 90°C and a pressure of 2
．． Maintained 81k9/Cd for a total of 9.62
K9 propylene oxide was added over 200 minutes. The per minute feeding rate of propylene oxide at that time is
It was 0.5% by weight of the total amount charged. The reaction was continued until the acid number was approximately 15, after which the reaction mixture was heated to 40°C.
It was cooled to Although a pressurized reactor was selected and used above for safety reasons, this reaction can also be carried out at atmospheric pressure.
Excess propylene oxide can be easily removed by treatment such as aspirator vacuum, but the small amount of residual propylene oxide contained in the product hydroxypropyl methacrylate is advantageous for the stability of the saturated thermosetting resin made from hydroxypropyl methacrylate. It turned out to be.

The hydroxypropyl methacrylate obtained above showed a conversion yield of 98% based on permethacrylic acid, and had a purity of approximately 96%, and could be used without further purification.

Example 2 5607 methacrylic acid with addition of 0.56f7 hydroquinone monomethyl ether polymerization inhibitor; 0.737 chromium trioxide (0.0675% by weight as Cr expressed based on the above methacrylic acid, 0.5% as CrO3) 1
(3% by weight); and 847 hydroxypropyl methacrylate as a solvent were charged into the autoclave.

The autoclave was purged with a gas mixture of 95% nitrogen and 5% oxygen, then heated to and maintained at 80°C.

4167 propylene oxide (10% excess over the above methacrylic acid) was slowly pumped into the autoclave over a period of 75 minutes.

The acid number was measured from time to time until it dropped to a value below 15, indicating completion of the reaction. Comparative Example This comparative example was carried out in comparison with Example 2.

*
560y of methacrylic acid with the addition of a hydroquinone monomethyl ether polymerization inhibitor of 0.567%; 1.967% of chromium acrylate (expressed on the basis of the above methacrylic acid, 0.0675% by weight as Cr, 0 as chromium acrylate) .35% by weight); was charged into an autoclave.

The autoclave was purged with a gas mixture of 95% nitrogen and 5% oxygen, then heated to and maintained at 80°C.

4167 propylene oxide (10% excess over the above methacrylic acid) was slowly pumped into the autoclave over a period of 75 minutes.

And the acid value of the reaction mixture was measured from time to time. At the end of the work on the day this experiment was conducted, the reaction was not yet complete. The results of the above Example 2 and Comparative Example are shown in the following table.

Claims (1)

[Claims] 1. In a method for producing hydroxypropyl methacrylate by reaction of methacrylic acid and propylene oxide: methacrylic acid,
For a substantially water-free mixture of 5% by weight of chromium trioxide as catalyst and 5-20% by weight of pre-prepared hydroxypropyl methacrylate as catalyst solvent based on methacrylic acid; A method for producing hydroxypropyl methacrylate, characterized in that propylene oxide is continuously added at a ratio of 0.90 to 1.5 moles per mole of methacrylic acid in the mixture. 2 The amount of chromium trioxide catalyst is 0.0 based on methacrylic acid.
5-2% by weight. 3. A process according to claim 1 or 2, wherein the reaction is carried out at a temperature of about 60-120°C. 4 Claim 1, which is carried out in the presence of a polymerization inhibitor,
The method according to item 2 or 3.