JPH0132214B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a process for the production of glycolaldehyde by the reaction of formaldehyde, carbon monoxide and hydrogen in the presence of a rhodium catalyst. Glycolaldehyde is a valuable intermediate in organic synthesis, including the production of serine, and is particularly useful as an intermediate in the production of ethylene glycol by catalytic hydrogenation. Ethylene glycol is a highly valuable industrial chemical with a wide range of uses including use as a coolant, antifreeze, monomer for polyester production, solvent, and intermediate for industrial chemical production. The reaction of formaldehyde with carbon monoxide and hydrogen is a known reaction, especially with ethylene glycol,
Produces methanol and higher polyhydroxy compounds. For example, US Pat. No. 2,451,333 describes the production of a mixture of polyhydroxy compounds including ethylene glycol, glycerol and higher polyols by the reaction of formaldehyde, carbon monoxide and hydrogen over a cobalt catalyst. There are various metal catalysts such as nickel, manganese,
Iron, chromium, copper, platinum, molybdenum, palladium, zinc, cadmium, ruthenium and their compound catalysts have also been published. US Pat. No. 3,920,753 discloses a process for producing glycolaldehyde by reacting formaldehyde with carbon monoxide and hydrogen under controlled reaction conditions in the presence of a cobalt catalyst, but the conversion yield is low. Polyols are also produced by the reaction of carbon monoxide and hydrogen over various metal catalysts. US Patent No.
No. 3,833,634 describes a rhodium-catalyzed reaction that produces ethylene glycol, propylene glycol, glycerol, methanol, ethanol, methyl acetate, etc. Rhodium catalysts are also used in the production of oxygenated derivatives of alkenes, alkadienes and alkenoic acid esters by reaction with carbon monoxide and hydrogen, as described in U.S. Pat. No. 3,081,357.
No. 3527809, No. 3544635, No. 3577219, and
Described in No. 3917661. Traditional ethylene glycol production processes are characterized by a mixture of products, with the main co-products being propylene glycol and glycerin, along with the lower alcohols, methyl and ethyl alcohol. Therefore, when the desired product is ethylene glycol, these processes are hampered by expensive and time-consuming separation procedures. Furthermore, the reaction efficiency with respect to the yield of ethylene glycol is usually not high due to the concomitant formation of considerable amounts of co-products. It has now been discovered that the reaction of formaldehyde, carbon monoxide, and hydrogen over a rhodium catalyst is a two-step reaction that produces glycolaldehyde and methanol in the first step and ethylene glycol in the second step. This reaction is therefore similar to that obtained using cobalt catalysts as disclosed in the above-mentioned US Pat. Shows high selectivity for only ethylene glycol. Furthermore, the yield of glycolaldehyde obtained with the process of the present invention is substantially greater than that obtained with the process described in US Pat. No. 3,920,753. Thus, the present invention produces glycolaldehyde in substantially higher yields than previously obtained from formaldehyde, carbon monoxide, and hydrogen. It produces ethylene glycol as the only detectable polyol product in better yields compared to other methods. Glycolaldehyde is easily separated from the only detectable co-product, methanol, and is produced in high purity. Furthermore, if methanol is not a problem, the reaction product of the present invention can be used as a source of glycolaldehyde in organic synthesis without separation. Since the only aldehyde other than formaldehyde detected in the reaction mixture is glycolaldehyde, the reaction mixture can be used directly to produce ethylene glycol by reduction of glycolaldehyde to produce glycol as the only polyol product. It is, of course, clear that in the conventional process the fact that the reaction product is a mixture of polyols (including ethylene glycol) which is extremely difficult to separate even by multiple fractional distillations is a significant obstacle. The process of the invention is carried out by contacting formaldehyde, carbon monoxide and hydrogen, preferably in a suitable solvent, in the presence of a rhodium-containing catalyst at elevated pressure. The contacting method does not require precision as all of the various methods commonly used for this type of reaction can be used as long as effective gas-liquid contact is possible. The process can therefore be carried out by contacting a formaldehyde solution with a mixture of carbon monoxide and hydrogen under constant conditions with a rhodium catalyst. It is also possible to drop the formaldehyde solution onto the catalyst under constant temperature and pressure conditions in a mixture of carbon monoxide and hydrogen. The reaction can be carried out with the subsequent production of ethylene glycol proceeding continuously at suitable temperature and pressure, or alternatively the reaction can be stopped at the end of the first stage when glycolaldehyde is formed and the reaction can be carried out in a continuous manner. The second stage may be carried out under a suitable reduction method to convert the aldehyde groups of glycolaldehyde to monohydric alcohol groups to obtain ethylene glycol. As mentioned above, the main products of the reaction of the present invention are glycolaldehyde and methanol. Glycolaldehyde tends to produce acetals, which is a typical reaction of aldehydes, and since there is a monohydric alcohol group in the molecule, this compound is composed of hemiacetals and acetals, which form linear and cyclic forms as shown in the following formula. Generate acetals: Glycolaldehyde also forms acetals and hemi-acetals with methanol and, if present, ethylene glycol. In particular, acetals resist hydrogenation and require hydrolysis to free aldehydes to enable effective reduction to ethylene glycol. The hydrolysis reaction can be carried out as long as at least equimolar amounts of water are present in the reaction mixture. Therefore, an equimolar amount of water is required for complete hydrolysis; less than an equimolar amount will result in less hydrolysis of the acetal in the mixture and therefore a higher yield of ethylene glycol. It gets lower. It is convenient to hydrolyze the acetal immediately before and/or simultaneously with the reduction step. Often the amount of water necessary for substantial hydrolysis of the acetal is already included in the first stage reaction, and small amounts, such as from about 0.5 to about 10% by volume, are ideal for obtaining best results. If there is insufficient water, the required amount of water can simply be added to the second stage reaction in batches or continuously over the course of the reaction. In this case, experience has shown that the optimum final amount of water is in the range of about 10 to 30% by volume, based on the hydrogenated mixture. The presence of an acid is particularly desirable to effect the hydrolysis. For this purpose, therefore, use is made of hydrohalic acids, strong phosphoric acids such as sulfuric acid and phosphoric acid, or preferably weak organic acids, especially lower alkanoic acids such as acetic acid and propionic acid. If the reaction solvent reacts with strong mineral acids, for example in the case of an amide solvent that is hydrolyzed, strong mineral acids should be avoided. As will be apparent from the following discussion, amide solvents are generally preferred, particularly in the first stage reactions, and when this solvent is used it is preferred to use a weak acid to catalyze the acetal hydrolysis. The amount of acid used is not critical;
As is obvious to those knowledgeable in the field, even trace amounts are effective. It is therefore clear that a separate hydrolysis step is not always necessary since the usual water content of the reactions of the invention will hydrolyze at least a portion of the acetal formed and the hydrolyzed portion will be reduced to ethylene glycol. However, to maximize the ethylene glycol yield, it is necessary to include a hydrolysis step to ensure maximum hydrolysis and thus achieve the maximum yield of ethylene glycol. Therefore, although it is not necessarily important, adding a hydrolysis step is a good method that can be easily carried out with or without acid, since adding water is a simple process. The combined hydrolysis-hydrogenation process is described in US Pat. No. 4,024,197, which is incorporated herein by reference to the combined reaction.
No. 2721223, No. 2888492 and No. 2729650. The catalyst for the reaction of the present invention is rhodium element, or a rhodium compound, composite, or salt, or a mixture thereof, either as such or on a solid support such as molecular sieve zeolite, alumina, silica, anion exchange resin, or polymerizable ligand. Use by depositing or fixing. The active catalyst consists of rhodium in complex bond with carbon monoxide, i.e. rhodium carbonyl with additional ligands.
This is described, for example, in U.S. Pat. No. 3,527,809, and in U.S. Pat. Listed below. Suitable organic ligands, as described in U.S. Pat. No. 3,833,634, have at least one nitrogen atom and/or at least one oxygen atom that has a pair of electrons available for coordination with the rhodium. It is a class of compounds with Examples of organic ligands include various piperazines, dipyridyls,
N-substituted diamines, aminopyridyls, glycols, alkoxy-substituted acetic acids: tetrahydrofuran, dioxane, 1,2-dimethoxybenzene, alkyl ethers of alkylene glycols, alkanolamines, iminodiacetic acid, nitrilo-triacetic acid , ethylenediamine-tetraacetic acid, etc. U.S. Patent No. 3,527,809 includes trialkyl,
Phosphorus-containing ligands such as triaryl and tricycloalkyl phosphites and triarylphosphines and similar antimony and arsenic compounds have been described. The catalyst can be used in dissolved or suspended form in the reaction medium or deposited on a porous support. Catalysts can be manufactured in a variety of ways. For example, the catalyst may be first formed as a complex with carbon monoxide and then mixed into the reaction medium, or the catalyst may be formed in situ by directly reacting rhodium or a rhodium compound with carbon monoxide. produces an organic ligand-carbon monoxide-rhodium complex in the reaction medium in the presence of the selected organic ligand. The products obtained are usually in the form of the acetals mentioned above and can be separated from the co-product methanol and the reaction solvent by fractional distillation if necessary. Gas chromatography and mass spectrometry were used to identify the product as glycolaldehyde. Furthermore, a dimedone derivative (5,5-dimethylcyclohexane-1,3-dione) of pure glycolaldehyde was prepared and compared with the dimedone derivative of the product obtained from a representative reaction according to the method of the present invention, and it was found that the two were identical. . of derivatives
NMR analysis confirmed the product to be glycolaldehyde. Further, the aldehydes detected in the reaction product were only formaldehyde and glycolaldehyde. Glyoxal was not detected by the above analytical method. The production of glycolaldehyde and methanol in the reaction of the present invention is substantially completed in a relatively short time, usually within one hour, and a substantial yield of product is obtained in about 30 minutes or less. Usually only small amounts of ethylene glycol are detected. Naturally, the rhodium catalyst used in the reaction of the invention also serves as a hydrogenation catalyst for the subsequent second stage reaction to produce ethylene glycol. Therefore, if the reaction of the present invention is allowed to continue, the hydrogenation reaction will eventually produce ethylene glycol. Particularly good yields are obtained by adding water as necessary to hydrolyze certain glycolaldehyde acetals from the reaction of the invention, thus resulting in maximum yields of ethylene glycol. Generally, the rhodium catalysts of the present reaction are effective catalysts for the second stage hydrogenation reaction, but do not provide the short reaction times that other hydrogenation catalysts do under common reaction conditions. It is possible to run the reduction step over a metal catalyst such as palladium and nickel to shorten the second stage reaction time, and it is usually preferred to run the second stage reaction in a separate reactor. Therefore, after the reaction of the present invention is carried out in a reactor under the selected temperature and pressure conditions, and after the completion of the production of the present invention, another reaction is carried out under the selected temperature and pressure conditions, whether or not it is separated from the reaction mixture. The mixture is transferred to a reactor and subjected to a hydrogenation reaction under hydrolysis conditions, ie, in the presence of at least a stoichiometric amount of water to hydrolyze the contained glycolaldehyde acetals. Furthermore, the second stage reaction can be carried out in one reactor by adjusting the reaction conditions. A selected hydrogenation catalyst is added to the hydrogenation reaction stage, and if necessary, water for hydrolysis is also added to allow the hydrogenation reaction to proceed. In this latter modification, a hydrogenation catalyst is added to the reaction mixture of the invention with or without the rhodium catalyst of the reaction of the invention. It is generally better to remove the rhodium catalyst, especially if it can be easily removed so that catalyst competition does not interfere with the hydrogenation reaction and, more importantly, allows for more precise control of the reaction. The present invention therefore provides a simple, selective process for the production of glycolaldehyde as the only detectable aldehyde product. The amount of catalyst used during the reaction of this invention does not require precision and can vary considerably. Of course, it is necessary to use at least a catalytically effective amount of catalyst. Generally, an effective amount of catalyst to provide a suitable reaction rate is sufficient. Although as little as 0.001 g atom of rhodium per liter of reaction medium is sufficient, amounts in excess of 0.1 g atom do not appear to significantly affect the reaction rate.
Generally, the effective amount of catalyst is about 0.005 to about 0.025 gram atoms per liter. The reaction conditions do not require great precision as they can be manipulated over a wide range of heating and pressurizing conditions. The practical limits of the manufacturing equipment largely dictate the choice of temperature and pressure at which the reaction is carried out.
Therefore, using commercially available manufacturing equipment, the selected temperature should be at least 75°C to about 250°C or even slightly higher. Generally preferred operating temperatures are about 100 to about 175°C. Pressures should be at least about 10 atmospheres to as far as the manufacturing equipment allows. Since extremely high pressure equipment is very expensive, pressures up to about 700 atmospheres are suggested. Suitably, the pressure is from about 250 to about 400 atmospheres, especially using the preferred temperature ranges noted above. The reaction is preferably carried out in a suitable solvent to dissolve polar substances and maximize selectivity. There are many types of suitable solvents, but examples include N-substituted amides in which each hydrogen of the amide nitrogen is replaced with a hydrocarbon group, such as 1-methylpyrrolidin-2-one, N,N-dimethyl-acetamide, N,N-diethylacetamide, N-methylpiperidone, 1,2-dimethylpyrrolidine-2-
on, 1-benzylpyrrolidin-2-one, N,
N-dimethylpropionamide, hexamethyl-
phosphoric triamides and similar liquid amides; nitriles such as acetonitrile, benzonitrile, propionitrile etc.; cyclic ethers such as tetrahydrofuran, dioxane and tetrahydropyran; diethyl ether, alkylene glycols and polyalkylenes. Ethers such as 1,2-dimethoxy-benzene alkyl ethers of glycols, such as ethylene glycol, propylene glycol and methyl ethers of di-, tri- and tetraethylene glycols; such as acetone, methyl isobutyl ketone and cyclohexanone esters such as ethyl acetate, ethyl propionate and methyl laurate; organic acids such as acetic acid, propionic acid and caprylic acid; and methanol,
Alkanols such as ethanol, propanol, 2-ethylhexanol, etc.; and mixtures thereof. Many of the solvents are inert in the medium, while others can be functionalized as ligands. It is necessary that the chosen solvent be liquid under the reaction conditions. The nature of the solvent used will affect the product yield and selectivity to ethylene glycol. For example, when lower alkanoic acids, such as acetic acid, are present in the reaction of the invention, eg as a co-solvent, the reaction appears to proceed more rapidly, but the glycol yield is somewhat reduced while the methanol yield is increased. When acetic acid was used at about 10% to about 20% by volume of the reaction mixture, the reaction proceeded in about half the time required with the same solvent without acetic acid, but methanol production increased (55% vs. 40%). Glycol production was reduced (30% vs. 48%). Furthermore, basic amines such as pyridine, triethylamine, and amines with comparable basicity appear to have a negative effect on the resulting glycolaldehyde yield, and this effect decreases as the amine to rhodium molar ratio increases. Become bigger. Therefore, even when amines are included as co-solvents, the yield of glycolaldehyde tends to decrease when compared to solvent systems without amines. Large amounts of protective solvents such as water, phenols, and carboxylic acids, such as acetic acid, such as greater than about 30-40% by volume, have a similar negative effect on glycolaldehyde yield. In most cases, a decrease in glycolaldehyde yield results in an increase in methanol yield; in some cases, formaldehyde conversion decreases, reducing both yields. Therefore, basic amines or large amounts of protective solvents should generally be avoided, especially in the reactions of this invention if optimum yields of glycolaldehyde and ethylene glycol and minimal yields of methanol are desired. Conversely, some solvent systems exhibit high selectivity for glycolaldehyde and ethylene glycol production. Also, substantially low yields of methanol are often obtained. In particular, solvents such as organic amides are preferred because they exhibit high selectivity for glycolaldehyde and ethylene glycol formation, often resulting in substantially lower yields of methanol. Hydrocarbon solvents can also be used but result in lower yields of glycolaldehyde and ethylene glycol than better solvents. Preferred solvents are aprotic organic amides. Possible amides include cyclic amides in which the amide group is part of the ring structure, such as in pyrrolidines and piperidones; N-acylpiperidines, pyrroles, pyrrolidines, piperazines, morpholins, etc. acylated cyclic amines, or those whose acyl group is derived from a lower alkanoic acid, such as acetic acid; and amide groups such as in acetamides, formamides, propionamides, caproamides, There are acyclic amides that are not part of the structure. The most preferred amides are those in which the amide hydrogen atoms are fully substituted with hydrocarbon groups having up to 8 carbon atoms. Hydrocarbon groups include alkyl, lower alkyl such as methyl, ethyl, and butyl;
aralkyls such as benzyl and phenethyl; cycloalkyls such as cyclopentyl and cyclohexyl; and alkenyls such as allyl and pentenyl. Preferred amide nitrogen substituents are lower alkyl, especially methyl, ethyl and propyl groups and aralkyl, especially benzyl. The most preferred amide solvent is 1-methylpyrrolidine-2-
1-ethylpyrrolidin-2-one, 1-benzylpyrrolidin-2-one, N,N-diethylacetamide, and N,N-diethylpropionamide. Nitrile solvents include all organic nitriles containing up to about 8 carbon atoms, such as acetonitrile, benzonitrile, phenylacetonitrile, capronitrile, and the like. Solvent mixtures can also be used. When solvents containing basic nitrogen are used, the use of rhodium carbonyl complexes with ligands containing basic nitrogen is generally associated with lower selectivity for ethylene glycol production and usually increased methanol production. Catalysts containing coordinations with basic nitrogens are generally avoided as this reduces the desired ethylene glycol production. Ligands with oxygen appear to give better results in terms of ethylene glycol yield and are therefore preferred over the aforementioned ligands with basic nitrogen. Rhodium complex salt formed with acetylacetonate anion, Rh
(CO ₂ )(C ₅ H ₇ O ₂ ) and hexalodium hexadicarbonyl, Rh ₆ (CO) ₁₆ give the best results and are most preferred as they are easily available or manufactured. Reaction pressure refers to the pressure of all the gases contained within the reactor, ie, carbon monoxide and hydrogen, and any inert diluent gases such as nitrogen. In gas systems, the total pressure is the sum of the partial pressures of the component gases. In this reaction, the molar ratio of hydrogen to carbon monoxide is in the range of about 1/10 to about 10/1, preferably about 1/5 to about 5/1, and the reaction pressure is the pressure of these gases in the reactor. Adjust it to make it suitable. For best results, the molar ratio of carbon monoxide to hydrogen is kept high in the reaction of the present invention, where a high partial pressure of carbon monoxide favors the formation of glycolaldehyde. In the second stage reaction for producing ethylene glycol, a high partial pressure of hydrogen is desirable for the reduction reaction. Therefore, in the reaction of the present invention to produce glycolaldehyde, the partial pressure of carbon monoxide is usually adjusted to about 3 to about 10 times that of hydrogen. In the second stage hydrogenation reaction, the partial pressure of hydrogen is adjusted to a high value that promotes the reaction. This adjustment of the feed gas is easily carried out, for example by lowering the pressure in the reactor after the completion of the reaction according to the invention and then increasing the hydrogen gas pressure to obtain a high partial pressure of hydrogen. The carbon monoxide in the gas system of the reaction of the present invention does not need to be completely evacuated from the reactor before raising the hydrogen gas pressure. Of course, carbon monoxide is known to possibly poison some catalyst systems, reducing their effectiveness, so it is better to vent the carbon monoxide when using such catalyst systems. If the second phase reaction is carried out in a separate reactor, whether over the initial rhodium catalyst or over other metal hydrogenation catalysts, the reaction is carried out under hydrogen gas without diluent gas as in ordinary catalytic hydrogenation reactions. This is usually done. The formaldehyde source of the present invention can be any commonly used in this process, including paraformaldehyde, methylal, formalin solution, and polyoxymethylenes. Of these, paraformaldehyde is preferred because it provides the best results. A solution of formaldehyde in a solvent (conveniently the solvent is the reaction solvent), for example a solution of formaldehyde in an aqueous reaction solvent such as N-methyl-pyrrolidin-2-one, can be used. Use of methylal reduces ethylene glycol yield. If trioxane is used because of its good stability, it is necessary to use a hydrolyzing agent due to the release of formaldehyde. As with all processes of this type, the process of the invention can be operated in batch, quasi-continuous and continuous processes. The reactor must be constructed of materials that can withstand the temperatures and pressures used and the interior surfaces of the reactor must be substantially inert. Attach a normal regulating device such as a heat exchanger to regulate the reaction. The reactor is subject to vibration, agitation, stirring,
It is necessary to provide a mixing device for the reaction mixture using vibration or the like. The first or second stage reactor can be accessed at any time during operation to replenish catalyst and reactants. The recovered catalyst, solvent and unreacted raw materials can be recycled. The relative yields of ethylene glycol and methanol do not require much precision since the product mixture can be easily separated into its components by known methods, especially fractional distillation, regardless of their proportions in the mixture. Therefore, even if ethylene glycol is 10-20% of the reaction mixture, it can be easily separated from the mixture, especially in continuous ethylene glycol production processes, and the methanol can be recycled as formaldehyde. The reaction time is at least about 100 to obtain a suitable reaction rate.
C., although somewhat lower reaction temperatures may be used to obtain lower reaction rates. Approximately 1
For reaction times of hours or less, the temperature is approximately 100
The temperature should be from about 175°C to about 175°C, preferably from about 120 to about 140°C. It is better for the partial pressure of carbon monoxide to be higher than the partial pressure of hydrogen, and the ratio is about 2:1 to about 10:
1 is preferable, and about 3:1 to about 8:1 is more preferable. The total pressure of the gas used is generally about 1000 to about
Maintained at 9000 psi, preferably from about 3000 to about 7000 psi. Of course, higher temperatures and pressures can be used, but are usually avoided as they do not offer any corresponding benefits and require special high pressure equipment. Example 1 A stainless steel reaction vessel with a glass liner of 71 ml capacity was charged with the following reaction mixture: Rh(CO) ₂ (C ₇ H ₅ O ₂ ) 2.5 mmol 95% paraformaldehyde 237 mmol H ₂ O 5 ml N-Methylpyrrolidinone 114 ml Container pressure 2500 psi (P _CO = 2000 psi and P _H2 =
500 psi) and then heated and stirred at 130°C and 1750 rpm. Samples were taken every 15 minutes and analyzed, and the results are as follows. (concentration = mmol)

[Table] The aldehydes in the final reaction solution were identified as formaldehyde and glycolaldehyde, and no other aldehydes or carboxyl compounds were detected. The glycolaldehyde can be separated from the reaction mixture, for example by distillation, or the reaction mixture can be used in the second stage reaction as in Example 2. If this method is repeated at 160°C, the first 30
The glycolaldehyde yield decreases substantially after 50 minutes. This method can be used at low total pressure (P _CO = 2000psi
and P _H2 =500 psi), the yield loss of glycolaldehyde is slight. Example 2 The method of Example 1 was repeated, except that the first stage reaction was completed after 1 hour, and after the gas was evacuated from the vessel and the pressure was lowered, hydrogen was added so that the hydrogen amounted to 80 mol% of the total gas.
I set it to 5000psi. Then proceed with the second stage reaction 15
Samples were taken and analyzed every minute, and the results are as follows. (concentration is mmol)

[Table] In Experiment 2, 10 ml of glacial acetic acid was added to the reaction mixture before starting hydrogenation. In Test 3, 20 ml of water was added at the start of hydrogenation. Example 3 A pressure vessel was charged with the following mixture: N-methylpyrrolidinone 4 ml 95% paraformaldehyde 7.58 mmol Rh(CO) ₂ (C ₇ H ₅ O ₂ ) 0.7 mmol The vessel was filled with CO (80 mol%) and H ₂ (20 mol%)
It was heated at 4000 psi and 130°C for 90 minutes. Product analysis was as follows: MeOH 1.2 mmol H ₂ CO 0.5 mmol Glycolaldehyde 4.7 mmol The reaction mixture was then pressurized with hydrogen to 75 mol% H ₂ and 25 mol% CO and heated at 150° C. for 5 hours. The following composition was obtained: MeOH 2.2 mmol Ethylene glycol 3.6 mmol The reduction step was repeated using 0.5 g nickel on diatomaceous earth and adding 0.5 ml each of water and acetic acid to the reaction mixture. The composition of the product obtained was as follows: Ethylene glycol 1.4 mmol MeOH 1.0 mmol High-boiling residue This process was carried out using Pd/C (5
The composition of the replicated product was as follows: Ethylene glycol 1.8 mmol MeOH 1.7 mmol High-boiling residue Pd/C using pure glycolaldehyde and hydrogen pressure using N-methylpyrrolidinone as solvent.
An almost quantitative yield of ethylene glycol was obtained when the reduction reaction was repeated at 3000 psi and 150° C. for 5 hours. When nickel on diatomaceous earth was used instead of Pd/C, the yield of ethylene glycol decreased.

Claims (1)

[Claims] 1. A method for producing glycolaldehyde, which comprises reacting formaldehyde, carbon monoxide and hydrogen under heat and pressure in the presence of a rhodium catalyst. 2. The method according to claim 1, wherein the temperature is 100 to 175°C and the pressure is 250 to 400 atmospheres. 3. Process according to claim 1 or 2, in which the rhodium catalyst comprises rhodium in complex combination with carbon monoxide. 4 Claims 1 to 4 in which the rhodium catalyst comprises rhodium dicarbonylacetylacetonate
The method described in any one of Section 3. 5. The method according to any one of claims 1 to 4, wherein the reaction is carried out in a reaction solvent comprising an aprotic organic amide. 6 Amide is N-lower alkylpyrrolidine-2-
6. The method of claim 5, comprising: on. 7. The method of claim 6, wherein the amide comprises N-methylpyrrolidin-2-one. 8. The method according to claim 5, wherein the amide comprises N,N-di-lower alkyl acetamide. 9. The method of claim 8, wherein the amide comprises N,N-diethylacetamide.