CS276463B6 - Process for the preparation of N-butoxymethylmethacrylamide or N-isobutoxymethylmethacrylamide - Google Patents

Abstract

Method for producing N-butoxymethylmethacylamide or N-isobutoxymethylmethacrylamide from a solution of K-methylolmethacrylamide obtained by mutual reaction of paraformaldehyde and methacrylamide in a selected alcohol by etherification with the same alcohol* The molar ratio of alcohol to the starting amide is chosen in the range of 1 to 3 molar parts, with part of the alcohol (0.5 to 1.5 molar parts) being added to the reactor during etherification while simultaneously withdrawing the azeotropic alcohol-water mixture. The rate of withdrawal of the azeotrope and the temperature of the reaction mixture are controlled by gradually reducing the pressure so that the temperature in the reactor does not exceed 105 °C and that of the heating medium does not exceed 110 °C.

Description

supplied to the market.

N-Butoxymethylmethacrylamide and the corresponding N-isoalkoxy derivative are used mainly in the production of thermoreactive self-crosslinking types of acrylate copolymer dispersions intended for applications in the textile industry, as sulfurizing comonomers.

Although the physicochemical characteristics of these monomers, like those of analogous derivatives of N-alkoxymethylacrylamide, are not described in the literature to the extent usual for most other compounds, the industrial production of technical purity products is the subject of a number of patents. As for derivatives of methylmethacrylamide, the frequency of patented processes is not very extensive.

The actual production of all the mentioned N-alkoxy derivatives is a two-step synthesis starting from the respective amide and mostly paraformaldehyde as starting materials. In the case of the production of N-butoxymethylmethacrylamide or N-isobutoxymethylmethacrylamide, methacrylamide is subjected to methylol acid in the first reaction step in an alkaline medium to form N-methylolmethacrylamide (I). This is subsequently etherified in the second reaction step in an acidic medium with a selected alcohol to give the N-alkoxy derivative (II), where R is an n- or isobutyl group, according to the following reaction scheme:

1st stage methylation

CHgsCCONHg ch ₃

(OH")

CH2=CC0NHCH ₂ 0H ch ₃ (I)

2nd stage - etherification

CHgeCCONHCHgOH CH^CCONHCHgOR + HgO ch ₃ ^(b+) ch ₃ (II)

It is clear that during both stages of synthesis a number of competing reactions can occur both in parallel and consecutively. In the case where paraformaldehyde is used as one of the starting materials, the possibility of contamination of the final product is even higher due to the formation of by-products during the depolymerization of the raw material, which is a prerequisite for the further synthesis process.

However, by-products can be formed not only during the depolymerization of paraformaldehyde, but also during the methylolation itself. This mainly concerns the formation of oligomeric products of N-methylolmethacrylamide, which is a necessary intermediate product, and the possibility of the formation of adducts of N-methylolmethacrylamide with the starting materials cannot be completely ruled out. Such substances are, for example, bis/methacrylamidomethyl/ether (III), or N,N-methylenebismethacrylamide (IV):

CH ₂ =CCONHCH ₂ -0-CH ₂ HNOCC=CH ₂ ch ₃ (III)

CH ₀ =CCOBH-CH ₀ -HNOCC=CH, ² 1 ² I '

_CH3CH3 ( _IV )

In addition, the overall synthesis of N-alkoxy derivatives is complicated by the requirement to perform the 1st reaction step in a non-aqueous environment, given that in the subsequent reaction step - etherification - water is one of the products of the reaction itself, so its presence in the reaction environment would slow down the etherification process from the very beginning by shifting the reaction equilibrium in an undesirable direction.

This can be countered by performing depolymerization of paraformaldehyde and subsequent methylation of methacrylamide in the environment of the selected alcohol, but in this case the possibility of undesirable formation of dialkylformal (V), where R is an n- or iso-butyl group, increases, which is of course not possible on an industrial scale.

(V) leads to an undesirable increase in alcohol consumption per unit of production.

An even greater possibility of the formation of by-products that contaminate the final product, because their complete removal is practically impossible on an operational scale for economic reasons, is in the 2nd reaction stage.

The range of possible ballasts is increased not only by products resulting from mutual reactions of the residues of the starting raw materials and the intermediate product with the desired product, but also as a result of their reaction with an excess of the alcohol used, especially when sulfuric acid is used as the etherification catalyst, which enormously supports the dehydration reactions of the alcohol itself to form esters and ether-type compounds, of which the main representative is again dialkylformal (V).

N-Butoxymethylmethacrylamide is of course capable of further forming di- to polymeric compounds, adducts and polycondensates, especially if the reaction mixture, containing 30% by weight and more of the main component, is exposed to heat for an excessively long time, as recommended, for example, by the procedure according to US patent No. 3,087,965 of April 30, 1963, when the etherification is carried out for 7 hours.

Representatives of such compounds are, for example, N,N-di(butoxymethyl)-methacrylamide (VI), or an isoalkoxy derivative (VII):

CHgsCCON ^CH 3

CEjO/CH^CHj

CHgsCCON ch ₃

ch ₂ och ₂ ch

_{CH20CH2CH ​}

CH ₃

CH ₃ ch ₃ ch ₃ (VI) (VII)

Another by-product may be compound (VIII), where R is an n- or iso-butyl group:

ch ₂ =cconhch ₂ n

CH ₃ ^000=0¾ ch ₃ (VIII)

In practice, production methods that are a compromise solution between the effort to achieve the highest possible process yield per methacrylamide input and the requirement to produce a product with a minimum content of by-products of competing reactions are therefore preferred.

Thus, the procedure according to DOS 23 10 516 filed on March 3, 1973 practically eliminates the formation of by-products during the depolymerization of paraformaldehyde by replacing it with highly reactive solutions of gaseous formaldehyde in the appropriate alcohol, which are immediately capable of reacting with methacrylamide.

In the Czechoslovak Socialist Republic it is protected by copyright certificate No. 241 674 of 15. 9. 19θ7 Method for preparing N-butoxymethylmethacrylamide or N-isobutoxymethylmethacrylamide, the principle of which consists in gradually reacting a mixture of paraformaldehyde with methacrylamide in an alcoholic environment, thereby preventing the formation of undesirable products in the 1st reaction stage. However, this procedure has proven to be unusable on an industrial scale due to the impossibility of continuous dosing of the prepared mixture of raw materials into the reactor due to the unsatisfactory angle of repose of the mixture, which in addition becomes compact. The expected effect of the proposed solution is also debatable.

Other processes, e.g. according to the already cited US patent no. 3,087,965, focus on suppressing the course of competing reactions in the 2nd reaction stage - etherification, while simultaneously maintaining the yield of the process at an acceptable level.

It is recommended to work with a large molar excess of alcohol (up to ten times the stoichiometric requirement) while simultaneously violating the reaction equilibrium by withdrawing the water formed during etherification in the form of an azeotrope with an auxiliary solvent, which should guarantee the highest possible reduction in the boiling point of the reacting mixture.

The aforementioned patent recommends using benzene for this purpose, which is unsuitable from the point of view of mass production of the subject N-alkoxy derivatives of methyl methacrylamide due to the proven carcinogenicity of benzene.

Furthermore, the excess alcohol used adversely affects the economic aspect of production due to the need for subsequent regeneration and rectification of significant volumes of alcohol, containing mainly dibutyl formal, which must be removed before the recycled alcohol is used in the next operation.

However, even in the case of reducing the molar excess of alcohol to a level that still guarantees operating economy, in these methods, based on violating the etherification reaction equilibrium by withdrawing separated water from the heterogeneous azeotrope, an amount of water is returned to the reactor that corresponds to its solubility in the recycled organic phase under the given conditions. It is not important whether the azeotrope is obtained with or without the use of an auxiliary solvent.

All of the above disadvantages can be eliminated in the case of the production of N-butoxymethylmethacrylamide or N-isobutoxyderivative by the method according to the invention. Its essence lies in the fact that the necessary molar excess of alcohol is not introduced into the reaction all at once, but is added to the crude N-methylolmethacrylamide gradually at a rate that approximately corresponds to the rate of formation of the alcohol-water azeotrope. However, the latter is withdrawn from the reactor without the possibly separated organic phase being returned.

The composition of the crude etherified product obtained by the process according to the invention and the etherified product obtained according to copyright certificate No. 241,674 can be compared in the following table:

Table

N-Butoxymethylmethacrylamidecrude etherified quality

PROCEDURE ...... Found (% wt.) Main ingredient n-butanol Water N-methylol methacrylamide Methacrylamide DibUtylformal Free formalin Polymers According to the invention 67.70 26.10 0.90 1.80 2.80 0.08 1.00 - According to AO No. 241 674 31.99 54.34 5.50 1.80 3.50 0.78 2.04 +

The technical effect of the process according to the invention is evident at first glance from the table. The concentration of the main component in the etherified product is more than double at a comparable level of molar ratios of the starting materials, which brings an economic effect especially in other production nodes, which are extraction, which can be carried out e.g. according to

AO 217 342 issued on 1.8.1985 for a method of washing a butanol solution of N-butoxymethylmethacrylamide and subsequent vacuum distillation of the organic phase thus obtained. The volumes of streams containing alcohol which need to be regenerated are also minimized in the method of operation according to the invention.

The final products contain L=»95% by weight of N-alkoxymethyl derivatives and their quality is fully comparable to products supplied to the market by foreign companies.

The total yield of the process, when converted to 100% product, is 84 to 90% of theory for methacrylamide and 79 to 82% of theory for paraformaldehyde used in methylation.

Example

We introduce 1,500 kg of crude alkaline solution of N-methylolmethacrylamide obtained by the reaction of paraformaldehyde and methacrylamide in n-butanol into the reactor and dilute it with another 1,000 kg of alcohol. We adjust the acidity of the batch by adding 85% phosphoric acid to pH = 4 and after adding 0.7 kg of phenothiazine as a polymerization inhibitor, we heat the reactor contents to 90 °C,

After 30 minutes of holding at the specified temperature, we reduce the pressure in the reactor to the value

CS 276463 Β6 corresponding to the boiling point of the n-butanol-water azeotrope under given conditions, which is discharged outside the reactor after condensation in the cooler.

After another 30 minutes from the start of the azeotrope withdrawal, we start dosing another 450 kg of n-butanol into the reactor at a rate of 100 kg/h and continue the azeotrope withdrawal. The rate of its withdrawal is regulated by gradually reducing the pressure in the reactor so that the temperature of the reaction mixture does not exceed 105 °C and the temperature of the reactor heating circuit does not exceed 110 °C.

After all the n-butanol has been dispensed, we stop heating and, by reducing the pressure in the reactor to the maximum achievable, we distill off further portions of alcohol while simultaneously cooling the crude etherified product.

Yield: 2,600 kg of etherified product containing 63 to 68 wt. % N-butoxymethylmethacrylamide, 25 to 30 wt. % n-butanol, 1 to 2 wt. % N-methylolmethacrylamide, 2 to 3 wt. % methacrylamide, 1 to 1.5 wt. % formaldehyde, 0.5 to 1.5 wt. % water ' and -==1 1 wt. % dibutylformal.

Claims (1)

Process for the preparation of N-butymethylmethacrylamide or N-isobutoxymethylmethacrylamide based on paraformaldehyde and methacrylamide, characterized in that the alkaline solution of N-methylolmethacrylamide obtained in them in n-butanol or isobutanol is etherified in an acidic medium with the appropriate excess alcohol. to 2 molar parts per methacrylamide used, by introducing 0.5 to 1.5 molar parts into the reactor and reacting the molar excess of alcohol during the reaction, while collecting a condensing alcohol-water azeotrope and a pressure guaranteeing that: the temperature in the reactor does not rise to 105 ° C during the etherification.