JPS597147A - Distillation of 2-isocyanate alkyl ester of alpha, beta-ethylenic unsaturated carboxylic acid - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the use of 2-
The present invention relates to the use of gaseous nitrogen dioxide or nitric oxide to inhibit vinyl polymerization of incyanato alkyl esters.

Certain common polymerization inhibitors have been used to inhibit the polymerization of 2-incyanatoalkyl esters of alpha, beta-ethylenically unsaturated carboxylic acids during distillation. For example, European Patent Application No. 78100156.5, Publication No. 144, published January 10, 1979, is
Discloses the use of phenothiazines to inhibit polymerization of incyanatoethyl methacrylate.

Although common polymerization inhibitors are generally effective in inhibiting the polymerization of 2-incyanato alkyl esters during storage,
It has not been proven to be effective during the distillation of the incyanato alkyl esters.

In particular, these isocyanatoalkyl esters tend to form hard, brittle, highly cross-linked polymers. Such polymers are referred to in the prior art as bobcone polymers because of their physical appearance. This bobcorn polymer is particularly harmful because once it forms, it initiates further polymerization.

Relatively volatile inhibitors, such as p-methoxyphenol, are used during the distillation of 2-isocyanatoalkyl methacrylate to suppress the formation of poly→- in the gas phase and in the distillate. It's here.

However, it has been observed that these volatile inhibitors are relatively ineffective as polymerization inhibitors in this application.

Nitrogen oxides are known in the art to inhibit the polymerization of certain unsaturated compounds. U.S. Patent 8.964,97
No. 8 discloses the distillation of vinyl aromatic compounds in the presence of nitrogen dioxide to inhibit polymerization. US Patent 8,
No. 964,979 discloses the use of nitrogen oxide to inhibit polymerization of vinyl aromatic compounds during distillation.

British Patent No. 1,265,419 teaches that acrylic acid can be distilled in the presence of nitrogen oxide in the gas phase and phenothiazine in the liquid phase to maximize polymerization.

However, the presence of nitrogen dioxide has been taught to promote the polymerization of acrylic acid and increase the color of the distillate.

Nitric oxide catalyzes the trimerization of certain aliphatic incyanates J, F., Villα and H, B.

Powell Syn, React, Inorg
, Metal-Org.

Chem, + 6.59-68 (1976) K. This disclosure suggests that nitric oxide may not be suitable as a polymerization inhibitor for 2-isocyana i-alkyl esters.

The present invention c) 2- of α, β-ethylenically unsaturated carboxylic acid
an α,β-ethylenically unsaturated carboxylic acid, characterized in that the incyanato alkyl ester is distilled in the presence of an amount of gaseous nitrogen oxides effective to inhibit the total vinyl polymerization of said isocyanato alkyl ester. A method for distilling 2-incyanatoalkylnisder from a liquid mixture,
It is.

An effective amount of nitrogen oxide is an amount that reduces polymerization of the incyanato alkyl ester as compared to polymerization that would occur in the absence of nitrogen oxide under the same conditions.

2-Incyanatoalkyl esters of α,β-ethylenically unsaturated carboxylic acids are represented by the formula 1, where R is independently hydrogen, alkyl, alkenyl, alkoxy, alkaryl, aralkyl, or aryl, and R′ is alkenyl. and n is 2 or 3.

Of course, R can be used for a wide variety of moieties, even ha, methyl,
It can represent ethyl, cyclohexyl, isopropenyl, vinyl, ethoxy, tolyl, phenylethyl or phenyl. Preferably R is hydrogen and .ru is 2.

Preferably R' is vinyl or impropenyl, more preferably impropenyl. Hereinafter, compounds of formula (1) will be referred to as isocyanatoalkyl esters for brevity.

The incyanato alkyl ester can be present in a mixture from which the incyanato alkyl ester can be separated by distillation, so long as the mixture is substantially inert in the subject reaction. In order to preserve added nitrogen oxides, it is advantageous to avoid diluents that react with nitrogen oxides.

In one preferred embodiment, the isocyanatoalkyl ester to be distilled is a 2-alkenyl-2-oxazoline or a 2-alkenyl-2-oxazine in the presence of phosgene and an aqueous hydrogen chloride acceptor in a water-immiscible solvent;
As described in British Patent No. 1,252.099,
Manufactured by reaction. When the phosgenation reaction is complete, the organic phase containing the 2-incyanatoalkyl ester is preferably separated and optionally dried with customary drying agents, such as CaCl 2 or zeolites. The 2-isocyanatoalkyl ester of the unsaturated acid is then separated by distillation in the presence of the 9 element oxide, as described below.

Nitrogen dioxide and nitrogen oxide, which are used here as the pi-nyl polymerization inhibitor, are both well-known compounds. For If#imk purposes, these two polymerization inhibitors are referred to as nitrogen oxides. Polymerization can be inhibited with either one of these nitrogen oxides, a mixture of such oxides, or a diluent gas containing at least one of these nine oxides. Nitric oxide is preferred as a polymerization inhibitor because it contributes fewer colored impurities to the typically colorless incyanato alkyl ester than other nitrogen oxides. Surprisingly, no incyanaate trimer is observed in the incyanato alkyl ester after treatment with nitric oxide. The gaseous diluent used with the nitrogen oxides should be inert in this reaction. Preferably, the diluent gas is substantially free of oxygen and water at rM, and more preferably the diluent gas present is nitrogen.

Nitrogen oxides, in practice, are introduced in the area immediately above the mass of distilling liquid to suppress polymerization in the gas phase and in the liquid condensing overhead.

However, in this embodiment care must be taken to ensure that the nitrogen oxides penetrate into the space above the medium or into the space where polymerization can occur.

Of course, if nitrogen oxides are not introduced into the liquid medium, a polymerization inhibitor should also be used in the liquid. However, some oxides of nitrogen interact with other polymerization inhibitors to produce colored impurities. If insufficient, p-methoxyphenol reacts with nitrogen oxide to form a yellow impurity that co-distillates with the incyanato alkyl ester.

Less volatile polymerization initiators, such as phenothiazines, may also form colored impurities, but these colored impurities typically do not distill out with the incyanato alkyl ester. Therefore, it is preferred to spark nitrogen oxides through the distillate mixture and to use in the mixture a polymerization inhibiting agent that is significantly less volatile than the incyanato alkyl ester.

When the distillation is carried out continuously, nitrogen oxides can be added to the incoming mixture, preferably containing the incyanato alkyl ester. Gaseous nitrogen oxides are virtually insoluble in the incyanato alkyl esters, and these gases can be easily recovered and recycled. In general, the inhibitor is gradually depleted during the run;
When recycling, only small discontinuous replacements of nitrogen oxides are generally necessary.

The degree of nitrogen oxide required to inhibit polymerization depends on a number of factors, such as the nature of the nitrogen oxide and incyanato alkyl ester, distillation temperature, distillation pressure, residence time and reflux rate. Vary over a wide range.

The purity of the incyanato alkyl ester may even affect the formation of the polymer, as crude starting materials are generally less prone to forming bobcone polymer during distillation than relatively pure isocyanato alkyl esters. Generally at least 0.01, preferably at least 0
．． 0.02% by weight, more preferably at least 0.1% by weight
The concentration of nitrogen oxides in the gas phase immediately above the liquid medium is effective in inhibiting polymerization.

At or near the minimum effective concentration, care must be taken to ensure that the concentration remains uniform over the liquid medium or that polymerization occurs. One convenient method of uniformly distributing the 9-atomic oxide in a large volume is to introduce the nitrogen oxide into the liquid along with a diluent gas. The upper limit for the concentration of nitrogen oxides is determined primarily by economic considerations. the concentration of nitrogen oxides is preferably less than 20% by weight of the gas above the liquid being distilled;
More preferably less than 3%. At concentrations of nine element oxides greater than 2% by weight, the distillate may become visibly colored.

The method of carrying out the distillation is not critical. Distillation should advantageously be carried out at reduced pressure to avoid distillation at temperatures harmful to the incyanato alkyl ester. As with oxides of nitrogen, some of the incyanato alkyl esters are highly toxic and the still should be closed. Impurities having a lower boiling point than the incyanato alkyl ester are preferably distilled before the isocyanato alkyl ester. If desired, azeotropes can be created to completely change the order of distillation.

The temperature of the liquid during distillation is preferably between 65°C and 110°C,
More preferably it is 80°C to 95°C.

Temperatures higher than those in the preferred range can be employed, but will reduce separation and may cause substantially all of the incyanato alkyl ester to decompose or polymerize at long residence times. Lower temperatures generally cannot be used when distilling incyanato alkyl esters, even when distillation is attempted under vacuum. Preferably the pressure above the liquid to be distilled is between 5 and 15 rta during the distillation.
nl-1fI (0.6-2.Okpa).

The following examples further illustrate the method of the invention. All parts and percentages are by electric mode unless otherwise specified.

EXAMPLE 82.2% by weight of 2-in cyanatoethyl methacrylate (IBM) was added to a round bottom flask equipped with a 6 inch (15.2 m) straight tubular distillation column with a distillation head on top, stirring means and temperature measuring means. , 0.6% methylene chloride, 11080 pp of phenothiazine, less than 1% epoxy resin and the remainder relatively non-volatile impurities. The epoxy resin reacts with the hydrolyzable chloride present during distillation and eliminates this impurity from the distillate.

Flask ff: 10mwHg (1,8kpa) at 95°C
) during which the liquid is oxidized to 0.8%. The oxidation in the gas phase was sparged with nitrogen gas containing nitrogen for 1 min. IE, 'Vf was refluxed for 1.25 h and then distilled for 2 h. The nitrogen concentration was 876 ppm.

The recovered distillate was analyzed by conventional gas-liquid chromatographic techniques and was found to be essentially pure monomeric IEM. The recovered distillate of 851 is 70%
The total yield is shown. The tar that was not distilled was a clear fluid. No bobcone polymer was observed.

In the method described in Comparative Experiment Example 1°, the coarse IE of 507
M was refluxed at 95° C. under a pressure of 10 im#r (L8 kpa) without introducing nitrogen oxide. 15
After heating for minutes, bob cone polymer was observed inside the column and flask. After one additional hour, the entire contents of the flask were polymerized.

Example 2 Same procedure as Example 1 except that pure heptad oxide was sparged through crude IBM while IEMf was first refluxed at 95° C. for 1 hour and then distilled over 2 hours. Bobcorn polymer was not observed in either the distillate or non-distilled material.

Example & Method similar to Example 2, but with 86.6%
of IEM and crude containing 700 ppm of phenothiazine! l! 8! IBM's 204.4 f was refluxed at 90° C. for 1 hour and then distilled. During reflux distillation, 0.8
% of nitrogen oxide was introduced immediately above the liquid medium into the test. At 2.5 hours after the start of reflux, all of the material remaining in the flask was bob cone polymer. Distillate is 112.5 ii'
essentially pure IEM, representing a yield of 55%.

Real cloth E-siri 4゜ In the same manner as in Example 1, 81% of IEM was obtained.

Crude 91EM of 1512 containing 1000 ppm phenothiazine and small amounts of methylene chloride and epoxy resin
was refluxed at 92° C. under a pressure of 9 tantlif while 0.16% nitrogen dioxide was sparged through the entire liquid through a gas mixture containing nitrogen gas. This gas mixture was passed through the liquid at a rate of 168.8 g/min. After 2 hours, distillation of the sparged liquid with the gas mixture was started. Over 3 hours, 85.69 essentially pure IBM was recovered in the distillate, representing a 70% yield. The undistilled residue remained fluid and no bob corn polymer was formed in this system.

Claims (1)

[Scope of Claims] 1. Perforation of poisonous gases: oxides which are effective for controlling the vinyl polymerization of 2-incyanatoalkyl esters of α,β-ethylenically unsaturated carboxylic acids. A process for distilling 2-in cyanatoalkyl esters of α,β-ethylenically unsaturated carboxylic acids from a liquid mixture, characterized in that the 2-incyanatoalkyl esters of α,β-ethylenically unsaturated carboxylic acids are distilled in the presence of . 2.9 The method according to claim 1, wherein the elementary oxide is nitrogen oxide. The method according to claim 2, wherein the distillation is carried out in an oxygen-free atmosphere. 4. Nitric oxide sparks through the liquid mixture th
i+ The method according to claim 2. 5. The method according to claim 4, wherein the concentration of nitrogen oxide in the gas phase immediately after the liquid mixture is 0.01 to 3% by weight.