SK202022A3 - Method for preparation of 2,2-dimethylolbutanoic acid - Google Patents

Abstract

The invention relates to a method of preparing 2,2-dimethylolbutanoic acid by oxidizing 2,2-dimethylolbutanal with hydrogen peroxide.

Description

The field of technology

The invention relates to a method of preparing 2,2-dimethylolbutanoic acid by oxidizing 2,2-dimethylolbutanal with hydrogen peroxide.

Current state of the art

2,2-dimethylolbutanoic acid (DMBA) is one of the substances used in the so-called green chemistry. It is a field of chemistry that is focused on designing products and processes that minimize the use of environmentally and health hazardous chemicals. It is a raw material for the preparation of polyurethane dispersions for paint materials, for synthetic polyurethane large-area materials (synthetic leather), for water-dilutable products based on alkyd, polyester and epoxy resins (paint materials, adhesives, binders, etc.). These materials have recently been used in the electrical and automotive industries.

According to the patent literature, several procedures are described for the preparation of dimethylolbutanoic acid. These basically differ only in the starting raw materials.

DMBA can be prepared by oxidation of trimethylolpropane. Trimethylolpropane or its derivative can be oxidized directly. If we disregard oxidation by living microorganisms (e.g. US5716815), chromic acid, aluminum alcoholate, nitric acid or an unspecified oxidizing agent using rare metals (Pt, Pd, JP6-192169) are used for direct oxidation. In a newer way - e.g. US7153999, EP1229013, CN1369475 - therefore, cyclic formalin (3) is first prepared from trimethylolpropane (2) by reaction with formaldehyde in an acidic environment. This is oxidized with nitric acid to intermediate product (4), which is decomposed by hydrogenation or heat to DMBA (1) according to the following reaction scheme:

CHjOH CHjOH COOHCOOH

I Acidíc CaUlyst I Ntiràc Acid I Hydroprnaíioo or HeidngI

R—C—CH)OH --------► R—C—CHjO ------” K—C—CH.O ----- . - — , R—C—CH _; OH

I II III

CH,OH CH.O—CH) CHjO—CH)CHjOH (2) (3) W<*>

Although the commercial appeal of this procedure is indisputable (the yield of DMBA in the synthesis up to 60% of theory, the price and availability of trimethylolpropane), its disadvantages are also obvious - working with concentrated nitric acid, resulting in ecological and safety risks, the need for expensive pressure equipment, expensive hydrogenation catalyst and the like.

Another way of preparing DMBA is the oxidation of dimethylolpropyl methyl ketone with sodium hypochlorite. According to GB1177555, the reaction is carried out under alkaline conditions in an ethanol environment according to the following reaction scheme:

ch ₂ oh ch ₂ gh

And Haoc. pH-II I

CH ₅ -CH ₂ - c - COCH _? --------► CH,- CH ₂ - C - COOH

CH ₂ ® ch ₂ oh

From example 1, which is given in the patent, it follows that although the synthesis itself is relatively simple (disregarding temperatures below 10 °C and corrosion), significant complications result from the processing of the reaction mixture (distillations to dryness, extraction of solid distillation residues with ethanol, crystallization for several days ). In addition, the availability of dimethylolpropyl methyl ketone is problematic. There is also a variant of the procedure in which 5-acetyl-5-ethyl-1,3-dioxane is oxidized with sodium hypochlorite to 5-carboxy-5-ethyl-1,3-dioxane, which is finally hydrolyzed to DMBA (GB1167274).

According to CN103304404, DMBA can be prepared from butanoic acid methyl ester in two steps. In the first, DMBA methyl ester is prepared by reacting formaldehyde and butanoic acid methyl ester. This is then hydrolyzed in an acidic environment to DMBA, as shown in the reaction scheme:

SK 20-2022 A3

This is an original procedure that we have not found in any other publication (similar to the oxidation of dimethylolpropyl methyl ketone). However, it raises several questions. Methylolation (or aldolization) of esters under the given conditions is not a "common reaction" used on a technological scale.

According to CN103709025, it is advantageous to prepare DMBA from butyronitrile. The synthesis is carried out in two steps. In the first, dimethoxybutyronitrile is prepared by reacting chloromethyl methyl ether and butyronitrile in the presence of NaOH. This is then hydrolyzed in an acidic environment to DMBA, as shown in the following scheme:

NaOH

H ₃ CCH ₂ CH ₂ -C=N + 2 H ₃ CO—CH ₂ -CI — h ₂ co-ch ₃

H ₃ C-CH ₂ -C--0ΞΝ

H ₃ O ch ₂ -o- ch ₃ h ₂ c-oh

H,C-CHj-C—COOH 3 2 !

ch ₂ oh

Again, this is a procedure that we have not found in any other publication. But it seems that it is more of a preparatory than an industrial procedure. Working with chloromethyl methyl ether - which is a carcinogen and lachrymator - and toxic butyronitrile in a carbonic chloride environment in the presence of powdered NaOH and the amount of waste NaCl and Na ₂ SO ₄ indicate a number of health and environmental problems.

Of all the methods, the most frequent in the patent literature is the preparation of DMBA from butyraldehyde (US3312736, US5994592, US6072082, CN101279912, CN102816058, CN102775296, CN101381299,

JPH11217351 and others). The raw materials are available, the equipment requirements are acceptable. It is a two-step synthesis. First of all, in the first step, dimethylolbutanal is prepared by the reaction of butyraldehyde and formaldehyde in an alkaline environment, which is then oxidized with hydrogen peroxide to DMBA according to the main reaction scheme:

In addition to dimethylolbutanal, during aldolization, a varied mixture of substances is formed - monomethylolbutanal, 2-ethylacrolein, trimethylolpropane, 2-ethylhexa(e)nals and syrup-like substances. It is possible that this is precisely why the patent literature is mainly devoted to the aldolization process.

The production of DMBA from butyraldehyde can be technologically divided into four basic nodes, which are shown in the diagram below:

Aldolization: the range of conditions that are proposed for the aldolization of butyraldehyde with formaldehyde in order to selectively prepare dimethylolbutanal is surprisingly wide. Temperatures range from 0 to 80 °C, reaction times from one to tens of hours (shorter times for higher temperatures). Butyraldehyde is most often dosed into a mixture of formaldehyde and catalyst. The molar ratio of formaldehyde : butyraldehyde is from 1.7 to 10 : 1. The unreacted raw material, butyraldehyde, as well as the by-product, ethylacrolein, can be isolated by distillation and recycled to aldolization. Recommended aldolization catalysts are hydroxides of alkali metals and alkaline earth metals, carbonates or bicarbonates of alkali metals, especially tertiary amines (individually or in combination with anion) and annexes. Among the tertiary amines, it has an exceptional position

SK 20-2022 A3 dimethylaminoneopentanol, dimethylolbutanal yields are the highest. Phase transfer catalysts and surface-active compounds are used to improve the homogeneity of the environment. Dimethylolbutanal yields are between 55 and 90% of theory (higher yields are reported for higher Fd:BA ratios).

Oxidation: the conditions for the oxidation of dimethylolbutanal with hydrogen peroxide, in contrast to its preparation by aldolization, are rarely balanced and are essentially not protected by any of the examined patents. In general, it can be stated that the recommended oxidation temperature is 60 to 95 °C, the peroxide is dosed into a heated aldolized mixture (50 °C), which can be neutralized to a pH of around 7 with formic acid before oxidation. However, the peroxide can also be dosed all at once (even before heating the aldolizate), the temperature is then allowed to rise spontaneously to the reflux temperature. The oxidation time is from two to twelve hours. The recommended ratio of hydrogen peroxide to dimethylolbutanal is 0.5 to 1.2:1 (mol/mol). DMBA yields do not exceed 70% (based on the dimethylolbutanal used).

Isolation of DMBA: water (or catalyst) is removed from the reaction mixture after oxidation, an organic solvent is added, DMBA is allowed to crystallize and is isolated by filtration. Water is removed by distillation under reduced pressure (the lowest mentioned pressure is 0.06 MPa) and a temperature of 60 °C (the lowest mentioned temperature) to a content of up to 1 or 2%. The drainage time is not indicated anywhere. For more thorough dewatering, the mixture can be refluxed at 100 °C after the addition of the solvent. In this context, it should be mentioned that some authors suggest repeatedly adding water to the mixture several times and distilling. The water brings out formic acid, which causes the formation of supersaturated solutions and thus poor or even no crystallization of DMBA. The aldolization catalyst can be removed from the oxidized mixture either before distilling the water using ion exchangers, or by converting it to a salt of a mineral acid (e.g. sulfuric), the resulting salt is removed from the mixture by hot filtration (after evaporation of the water and addition of an organic solvent) or by extraction into a non-polar solvent before oxidation. In order for the DMBA to crystallize, the mixture is cooled to a temperature between 0 and 20°C. Acetic acid esters (ethyl acetate, butyl acetate), ketones (methyl isobutyl ketone, methyl ethyl ketone) and, most recently, dichloroethane are used as solvents.

DMBA refining: this part of DMBA production is the least specific. It is written that, after isolation, DMBA is recrystallized from a solvent (methyl isobutyl ketone, butyl acetate, ethanol, water) and washed (e.g. isopropyl ether), or that impurities are removed with methanol, but specific conditions (amounts, temperatures, procedures) are completely missing. The drying temperature ranges from 45 to 80 °C.

We found that DMBA can be advantageously prepared by oxidizing dimethylolbutanal in the presence of oxidizing catalysts from the so-called stable free radicals based on 2,2,6,6-tetramethylpiperidine, e.g. 4-hydroxy2,2,6,6,-tetramethylpiperidine-1-oxyl (HTEMPO), 2,2,6,6,-tetramethylpiperidine-1-oxyl (TEMPO) and others. An aqueous solution of hydrogen peroxide is used as an oxidizing agent. Oxidation can be carried out at a temperature of 30 to 70 °C. Catalyzed oxidation increases the yield of DMBA by up to 10% compared to oxidation without a catalyst.

The essence of the invention

The essence of the invention is a method of preparing 2,2-dimethylolbutanoic acid by catalytic oxidation of dimethylolbutanal with hydrogen peroxide. Stable free radicals are used as catalysts, preferably 4hydroxy-2,2,6,6,-tetramethylpiperidine-1-oxyl. The procedure increases the yield of DMBA by up to 10% compared to oxidation without a catalyst.

Examples of implementation of the invention

Example 1

1 g of HTEMPO was added to 500 g of aldolizate containing 14.0% 2,2-dimethylolbutanal (prepared by the reaction of butyraldehyde and diluted formaldehyde in the presence of a tertiary amine). Then, at a temperature of 55 to 60°C, 90 g of 50% hydrogen peroxide was added over two hours. The mixture was then stirred at 60 °C for another 7 hours and at 70 °C for two hours. An oxidized mixture containing 13.0% DMBA was obtained (isotachophoresis).

Example 2 (comparative)

The procedure according to example 1 was repeated with the difference that HTEMPO was not added. The content of DMBA in the oxidized mixture was 11.8%, which is only 91% of the amount of DMBA that was prepared by oxidation in the presence of a catalyst.

Example 3

1 g of HTEMPO was added to 500 g of aldolizate containing 14% dimethylolbutanal. Then at a temperature of 35 to

SK 20-2022 A3 °C over two hours added 90 g of 50% hydrogen peroxide. The mixture was then stirred at a temperature of up to 40 °C for another 53 hours and another two hours at 70 °C. An oxidized mixture containing 12.3% DMBA was obtained.

Example 4 (comparative)

The procedure according to example 3 was repeated with the difference that HTEMPO was not added. The DMBA content of the oxidized mixture was 11.9%, which is 97% DMBA compared to the catalyzed oxidation.

Industrial applicability

The product is used in the production of polyurethane dispersions for paint materials, for water-dilutable products based on alkyd, polyester and epoxy resins (paint materials, adhesives, binders, etc.). These materials are used in the printing, electrical and automotive industries.

Claims (2)

PATENT CLAIMS 1. A method of preparing 2,2-dimethylolbutanoic acid by oxidizing 2,2-dimethylolbutanal with hydrogen peroxide in an aqueous environment at a temperature of 30 to 70 °C, characterized in that the oxidation is carried out in the presence of stable free radicals based on 2,2,6 of ,6-tetramethylpiperidine, which are added to the reaction in an amount of 0.1 to 3.0 percent by weight, calculated on the amount of 2,2-dimethylolbutanal. 2. Method for preparing 2,2-dimethylolbutanoic acid according to claim 1, characterized in that 4-hydroxy-2,2,6,6,-tetramethylpiperidine-1-oxyl is used as a stable radical.