JPH0749413B2 - Purification method of unsaturated carboxylic acid isocyanatoalkyl ester - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for purifying an unsaturated carboxylic acid isocyanatoalkyl ester represented by the following general formula [I], which is useful as various synthetic intermediates. .

[In the formula, R is H, a methyl group, a vinyl group, a phenyl group, or
The _{-CH 2 COO-A-NCO,} R ' is H, methyl or, -CH ₂ CO
In O-A-NCO, A represents an alkylene group having 2 to 14 carbon atoms. [Prior Art] Unsaturated Carboxylic Acid Isocyanato Alkyl Ester (eg, Methacrylic Acid-2-Isocyanato Ethyl Ester)
Since it has a vinyl-polymerizable double bond and an isocyanate group in the same molecule, is useful as various synthetic intermediates and polymer intermediates, and its manufacturing method has been studied for a long time. For example, Newman M Boatnick (Newm
an M. Bortnick) in US Pat. No. 2,718,516 show the following two synthetic methods.

One of them is to first react amino alcohol with chlorocarbonic acid ethyl ester to give hydroxycarbamic acid ethyl ester, and then react this with unsaturated carboxylic acid chloride to give uretanoester, and then to the presence of phosphorus pentachloride and the like. The products synthesized in this way by pyrolysis below to give unsaturated carboxylic acid isocyanatoalkyl esters are acidic and also contain large amounts of HCl-adducts as by-products.

Another method is transesterification with unsaturated carboxylic acid methyl ester and chloroalcohol, and the obtained chloroalkyl ester and alkali metal isocyanate,
And an uretanoester of an unsaturated carboxylic acid by a reaction with ethanol and an unsaturated carboxylic acid isocyanatoalkyl ester by the same thermal decomposition as described above, and in this case, the state of the product is the same as that described above. is there.

Also, Hans Holtschmidt
Proposes the following method in US Pat. No. 2,821,544. That is, first, unsaturated carboxylic acid aminoalkyl ester hydrochloride is synthesized by the reaction of unsaturated carboxylic acid chloride and amino alcohol hydrochloride, and phosgene is reacted with this to obtain the target unsaturated carboxylic acid isocyanatoalkyl ester. However, even in this method, the product is acidic and contains a large amount of HCl-adduct as a by-product. In each of the above methods, the amount of by-products produced is very large, and the yield is extremely low. Therefore, it cannot be said that the method is always satisfactory for industrial implementation.

On the other hand, the method disclosed by Dieter Arlt (U.S. Pat. No. 1,252,099) is synthesized by a reaction of 2-alkenyl-2-oxazoline and phosgene, for example, methacrylic acid-2-isocyanato. When synthesizing ethyl ester, 2-isopropenyl-
2-oxazoline is reacted with phosgene in the presence of an aqueous alkaline solution.

This method is excellent in that it is extremely energy-saving and safe, and has been industrially carried out. In addition, several improved methods and a method for producing 2-alkenyl-2-oxazoline which is a precursor have been proposed. ing. (For example,
JP-A-54-5921, JP-B-59-24977, and JP-A-61-152
As described above, the compounds synthesized by these methods have an unsaturated bond and an isocyanate group together in one molecule, and therefore other unsaturated compounds such as methyl methacrylate and bityl acrylate are included. , Copolymerized with styrene, etc. to form a polymer with an isocyanate group for use in paints and adhesives, or with a polymer with an active hydrogen such as a hydroxyl group or an amino group and an isocyanate group. It can be used for various purposes such as reaction to introduce an unsaturated bond into the side chain of the polymer and use it as a material that is cured by ultraviolet rays, electron beams, heat and the like.

In each of the above synthetic methods, the unsaturated carboxylic acid isocyanatoalkyl ester is obtained as a mixture with the reaction solvent. In this mixture, as described above, byproducts and oligomers to which hydrogen chloride is added, Other by-products are also included. Therefore, in order to obtain the desired purity for various uses, it is necessary to remove the solvent by distillation and further separate the various by-products contained therein.

Generally, when a compound having an unsaturated bond is distilled, it is usual to add a polymerization inhibitor such as hydroquinone, p-methoxyphenol, phenothiazine or the like.

Although many have been proposed as polymerization inhibitors that are said to be effective during the distillation of unsaturated carboxylic acids and their esters, for example, phenols and quinones (for example, hydroquinone, p-methoxyphenol, pyrogallol, dimethoxyphenol, Phenyl-p-benzoquinone etc.), amines (eg phenothiazine, p-phenylenediamine, hydrazine etc.), copper compounds (eg
Cupric chloride, cupric acetate, copper dibutyldithiocarbamate, cupric oxide, copper methacrylate, etc.) and others (methylene blue, cuperon, 6,6-substituted fulvene, oxygen, etc.) are known.

Further, it is said that it is effective not only to use these alone but also to use several compounds in combination, such as a combination of phenol and air, hydroquinone and sodium hexametaphosphate, cupric chloride, selenium oxide, phenothiazine. , Dibutyldithiocarbamate, oxygen, nitromethane, etc., p-methoxyphenol and benzoquinone, oxygen, phenothiazine, quinonedioxime, D
Combination with L-alanine, phenothiazine and sulfuric acid-
Combinations with aldehydes, oxygen, etc. have been proposed.

However, the unsaturated carboxylic acid isocyanatoalkyl ester according to the present invention has a very high polymerizability, and only by adding these polymerization inhibitors, so-called popcorn polymerization occurs during distillation, so that it is extremely difficult to purify. Met.

There are many studies on popcorn polymerization. [For example, regarding (meth) acrylic acid esters, Seo et al .: Japan Chemical Journal Vol. 89, No. 12, pages 1230 and 1236 (1968), Industrial Chemistry Vol. 74, No. 12, page 2581 (1971); Tatsumi et al .: Japan The Chemical Society of Japan, pages 1386 (1982), 1200 and 1282 (1983), etc.] According to the research so far, it has been found that a mixture of unsaturated compounds capable of forming a polymer having a network structure is
A polymer such as active oxygen and rusty iron is used as a seed for some reason, and the monomer reaches the radicals embedded inside the mesh structure of this seed polymer,
Polymerization occurs, and the mechanical pressure of the resulting polymer breaks the main chain and crosslinks, and the resulting radicals are said to further accelerate the polymerization. The growth of popcorn polymer is very fast, and it is very dangerous because it may rupture the reaction vessel due to the increase in volume.

To prevent popcorn polymerization, either stop the plant where active seeds are generated and destroy the active seeds with a chemical, or add a seed growth inhibitor continuously. However, it seems that definitive prevention methods and inhibitors have not yet been developed (Polymer Society of Japan: Polymer Dictionary).

Regarding unsaturated carboxylic acid isocyanatoalkyl ester, as a measure to solve this problem, Mark.
Roland Johnson discloses a method of distilling in the presence of gaseous nitrogen oxides (JP 59-7147).
That is, in the distillation of methacrylic acid-2-isocyanatoethyl ester, about 1,000 ppm of phenothiazine was added to the liquid, and, while blowing a gas containing nitric oxide into the liquid,
It was stated that no formation of popcorn polymer was observed after vacuum distillation at 90 to 95 ° C and 9 to 10 mmHg.

However, in this method, there is a problem that a generator for nitrogen oxide is required, the distillate is colored in some cases, and a pollution problem is caused by nitrogen oxides in waste gas. It is hard to say that it is not completely satisfactory in terms of commercialization.

[Problems to be solved by the invention]

In view of the above situation, the present inventors have made various studies on a method for preventing the polymerization of unsaturated carboxylic acid isocyanatoalkyl ester during distillation.

[Means for solving problems]

As a result, it was found that the coexistence of the stannous compound and / or the ferrous compound and the nitrite can effectively prevent the polymerization of the unsaturated carboxylic acid isocyanatoalkyl ester, and the present invention was completed based on this finding. Let

That is, the present invention, when distilling a mixture containing an unsaturated carboxylic acid isocyanatoalkyl ester, in the mixture,
A method for preventing popcorn polymerization of an unsaturated carboxylic acid isocyanatoalkyl ester by adding a stannous compound and / or a ferrous compound and further continuously or intermittently adding a nitrite ester Is.

Hereinafter, the present invention will be described in detail.

The unsaturated carboxylic acid isocyanatoalkyl ester targeted by the present invention is represented by the following general formula [I]. 2-isocyanatoethyl, 2-isocyanatopropyl, 3-isocyanatopropyl, 2-methyl-2-isocyanato, such as acid, methacrylic acid, crotonic acid, maleic acid, sorbic acid, itaconic acid or cinnamic acid Ethyl, 4-isocyanatobutyl, or 2-isocyanatobutyl ester corresponds to this. As these synthetic methods, there are various methods as described above, and the kinds of impurities contained in each method are usually different, but the purification method of the present invention can It also applies to saturated carboxylic acid isocyanatoalkyl esters.

The distillation method to which the present invention can be applied is a method generally performed in the case of purifying volatile organic substances and is not particularly changed, but unsaturated carboxylic acid isocyanatoalkyl ester has a relatively high boiling point. 50 because it is expensive
Vacuum distillation under a pressure of mmHg or less, particularly 15 mmHg or less is preferable.

Further, in the present invention, various aliphatic and aromatic esters can be used as the nitrite ester used for preventing the polymerization of unsaturated carboxylic acid isocyanatoalkyl ester, but they are mixed in the product after distillation. From the viewpoint of preventing the above, it is desirable that the boiling point is higher to some extent than the target unsaturated carboxylic acid isocyanatoalkyl ester. On the other hand, when the boiling point is low, the effect is not fully exerted because it is distilled out immediately even if added, and it is not preferable because it is mixed in the product.

Examples of nitrites suitable for use include nitrites of low vapor pressure glycol monoethers such as diethylene glycol monobutyl ether nitrite, triethylene glycol monomethyl ether nitrite, and triethylene glycol monoethyl ether nitrite, decyl nitrite, Nitrite esters of higher alcohols such as dodecyl nitrite, 2-benzyl-
Examples include nitrite esters of alcohols containing aromatics such as benzyl nitrite. The larger the amount of these nitrites used, the more effective, but it is not economical to use too much. For the mixture containing the target unsaturated carboxylic acid isocyanatonatokyl ester, 1
The weight ratio per hour is 10 to 10,000 ppm, preferably 100 to 5,
A range of 000ppm is appropriate. On the other hand, as the stannous compound or the ferrous iron compound, any compound may be used, but stannous chloride, stannous oxide, stannous sulfate, and pyrophosphate are preferred from the viewpoint of easy availability. Conveniently, stannous, ferrous chloride, ferrous sulfate, ferrous nitrate, etc., and in addition to being soluble in the unsaturated carboxylic acid isocyanatoalkyl ester of interest, stannous chloride is More preferable.

The amount of the stannous compound or the like used is preferably about equimolar to the total amount of the nitrite ester to be added, but a good amount may be sufficient. On the other hand, even if the amount is small, the effect is not insignificant, but as the amount is small, the effect is reduced.

Further, in the method of the present invention, it is desirable to use a polymerization inhibitor commonly used for vinyl compounds in combination. In this case, the polymerization inhibitor may be hydroquinone, p-
Methoxyphenol, BHT, can be used in combination with one or more general ones such as phenothiazine,
A suitable amount thereof is 100 to 10,000 ppm, preferably 100 to 5,000 ppm by weight based on the mixture containing the unsaturated carboxylic acid isocyanatoalkyl ester. This may be newly added, or may be added for storage or in advance during the synthetic reaction.

〔Example〕

Next, the method of the present invention will be described more specifically by showing representative examples, but these are representative examples for the purpose of illustration, and the method of the present invention is not limited to these. Needless to say.

Example 1 300 g (3.45 mol) of 2-oxazolidinone was dissolved in 2 of toluene, 5 g of phenothiazine was added, the mixture was heated to 60 ° C. with stirring, and hydrogen chloride gas was bubbled at a rate of 150 ml / min. 320 g (3.7 mol) of methacrylic acid was injected here over 60 minutes. Further, the reaction was carried out at 60 ° C. for 30 minutes while flowing hydrogen chloride gas. Then, the temperature was raised to 80 ° C., phosgene was bubbled, and the reaction was continued until a homogeneous solution was obtained. After distilling off the toluene,
The reaction mixture contained 282 g of methacrylic acid-2-isocyanatoethyl ester.

Take 230 g of this reaction mixture and add 0.35 g of stannous chloride to it.
Then, 0.07 g of nitrous acid ester of diethylene glycol mono-n-butyl ether was added, and distillation under reduced pressure was performed. During the distillation, 50 g of the reaction mixture plus 0.93 g of the above nitrite was added dropwise at a rate of 10 g per hour.

As a result, 115 g of methacrylic acid-2-isocyanatoethyl ester was obtained as a fraction at 87 to 89 ° C./10 to 12 mmHg.

Comparative Example 1 230 g of the reaction mixture obtained in Example 1 after distilling off toluene
To distill under reduced pressure as it is, it was immersed in an oil bath at 110 to 115 ° C and the pressure was set to about 10 mmHg. During the reflux state before distillate was obtained, the upper part of the distillation apparatus (direct reaction mixture liquid Particles of the polymer were generated in the gas phase part (which is not touched), and when heating was continued as it was, polymer beads were generated in the reaction mixture and grew, resulting in methacrylic acid-2-isocyanato. Only 9 g of ethyl ester was obtained.

Example 2 A stainless steel pipe having an inner diameter of 15 mm and a length of 200 mm was filled with 20 ml of activated alumina of 10 to 20 mesh and kept vertically at 300 ° C.
Heated to. 2-ethyl-2-oxazoline at 59.5 g / hr and formaldehyde gas at 5 g / hr from above.
Delivered over time. The distillate from the bottom was condensed in a cooler. To this, 1,250 ml of methylene chloride was added, the aqueous layer was removed, 3 g of fetothiazine and 3 g of BHT were added to remove the solvent, and the solvent was distilled off to obtain 224 g of 2-isopropenyl-2-oxazoline as a fraction at 70 to 71 ° C / 45 mmHg. It was

To this, 400 ml of water was added to make an aqueous solution, a solution of 300 g of phosgene dissolved in 900 ml of methylene chloride, and 780 ml of a 35 wt% sodium hydroxide aqueous solution were stirred in 225 ml of methylene chloride and the temperature exceeded 15 ° C under cooling. I added them at the same time, taking care not to let them go. After the addition was completed, the mixture was stirred for 10 minutes as it was, then the stirring was stopped, and the mixture was allowed to stand. After the two layers were separated, the aqueous layer was discarded, the organic layer was washed twice with 250 ml of a saturated aqueous solution of sodium hydrogen carbonate, and dried over anhydrous sodium sulfate. After adding 0.3 g of phenothiazine and distilling off methylene chloride, 2.0 g of stannous acetate and 1.0 g of 2-benzylbesidyl nitrite were added and distillation under reduced pressure was performed. On the way, 1.0 g of 2-benzylbenzyl nitrite was added every 30 minutes.

As a result, 288 g of methacrylic acid-2-isocyanatoethyl ester was obtained as a fraction at 85 to 88 ° C./10 mmHg.

Comparative Example 2 The same operation as in Example 2 was carried out except that 2-benzylbenzyl nitrite was not added. Popcorn polymerization occurred during distillation under reduced pressure, and 2-isocyanatoethyl methacrylate was not obtained. The glass distillation unit has become unusable.

Example 3 Phosgene was blown into a mixture of 300 g of methacrylic acid, 8 g of dimethylformamide and 0.3 g of phenothiazine at 70 ° C. at a rate of about 40 g per hour. After 12 hours, blowing was stopped and the obtained reaction solution was distilled to obtain 222 g of methacrylic acid chloride having a purity of 83.7%.

Meanwhile, 120 g of 2-hydroxypropylamine and toluene
A mixture of 800 ml was heated to 80 ° C., 75 g of hydrogen chloride gas was blown thereinto for 5 hours, and then 200 g of the above-mentioned methacrylic acid chloride was added and reacted for 5 hours.
Then raise the temperature until the liquid refluxes and
After bubbling 0 g for 5 hours, nitrogen gas was blown to remove unreacted phosgene.

7% after cooling the reaction mixture thus obtained to room temperature
It was washed twice with aqueous sodium hydrogen carbonate solution 1 and dried over anhydrous sodium sulfate. 1 g each of phenothiazine and cresol were added thereto, and toluene was distilled off at 10 mmHg. To this, 0.7 g of ferrous chloride / tetrahydrate was added and distilled under reduced pressure at 5 mmHg.

During the distillation, dodecyl nitrite 0.6 g dodecanol 53
What was melt | dissolved in ml was continuously dripped at the rate of 3 ml per hour.

As a result, 89 g of methacrylic acid-2-isocyanatopropyl ester was obtained.

Comparative Example 3 The same operation as in Example 3 was carried out except that ferrous chloride / tetrahydrate was not used, but in the final vacuum distillation process, when 3 hours had elapsed after the start of distillation, the upper part of the distillation pot was used. It was observed that white polymer particles were formed in the gas phase portion of the above, and when 4 hours had passed, distillation was stopped because a white ball-like substance was formed in the solution. The obtained methacrylic acid-2-isocyanatopropyl ester was 21 g.

Example 4 210 g of β-bromopropionitrile was dissolved in xylene 1.5 and heated under reflux in a nitrogen stream. To this, 100 g of monoethanolamine was added dropwise over 1.5 hours. Further, heating and refluxing were continued for 3 hours under the same conditions. After distilling off xylene, distillation is performed under a vacuum of 0.1 mmHg, and a fraction of
28g was obtained.

The above fraction was dissolved in 1.5 methylene chloride and 2 g phenothiazine was added. A solution of 100 g of sodium hydroxide and 4.5 g of trimethylbenzylammonium chloride in 1 of water and a solution of 200 g of phosgene in 1 of methylene chloride at the same time keep the water layer alkaline and the temperature does not exceed 10 ° C. At such a rate for 2 hours. After completion of dropping, stirring was continued for 1 hour as it was, and the mixture was allowed to stand to separate the two layers. The methylene chloride layer was washed with water 3 times and dried over anhydrous sodium sulfate, and then the solvent was distilled off under normal pressure.

10 g of stannous oxide was added to the remaining liquid, and vacuum distillation was performed at 14 mmHg. During the distillation, a solution of 8.8 g of triethylene glycol monoethyl ether nitrite in 10 ml of triethylene glycol monoethyl ether was added every 30 minutes.
Added 2 ml each.

As a result, 140 g of acrylic acid-2-isocyanatoethyl ester was obtained.

Comparative Example 4 When the same operation as in Example 4 was performed except that the tin compound and the nitrite ester solution were not used, the whole was solidified during the final distillation operation.

〔The invention's effect〕

According to the present invention, unsaturated carboxylic acid-2-isocyanatoalkyl ester can be efficiently purified by distillation without causing popcorn polymerization.

Claims (1)

[Claims] 1. Unsaturated carboxylic acid isocyanatoalkyl ester, characterized in that distillation is carried out in the presence of a stannous compound and / or a ferrous compound while continuously or intermittently adding a nitrite ester. Purification method.