KR810000379B1 - Process for the preparation of an anhydride of a mono carboxylic acid - Google Patents

Abstract

No content.

Description

Process for producing mono carboxylic anhydride

The present invention relates to a process for the preparation of carboxylic acids, more particularly mono carboxylic anhydrides, especially lower anhydrides such as acetic anhydride, by carbonylation.

Acetic anhydride has been known for many years as an industrial chemical and is used in large amounts in the production of cellulose acetate. It is usually prepared on an industrial scale by reacting keron with acetic acid. It is also known that acetic anhydride can also be prepared, for example, by decomposing ethylidene diacetate or by oxidizing acetaldehyde. Since each of these classical methods already has well-known drawbacks and disadvantages, the discovery of an improved method of preparing acetic anhydride has been sought. A method for producing anhydrides by reacting carbon monoxide (carbonylation) with various reactants has been proposed in the United States. However, such methods involving carbonylation must use very high pressures. As a method of preparing acetic anhydride, carbonylation at low pressure has also been proposed. The French patent describes a process for carbonylating a mixture of methanol and methanol to methyl acetate in the presence of iridium, platinum, palladium, osmium and ruthenium compounds and in the presence of bromine or iodine at lower pressures than in the US patent. Similarly, the South African patent describes a process for preparing acetic acid from the same reactant using a rhodium component in combination with bromine or iodine. Recently, a vapor phase process for preparing acetic acid using various catalysts composed of rhodium components dispersed on a carrier has been described in the US patent. However, none of these relatively recent carbonylation methods mention or predict the preparation of acetic anhydride or other carboxylic anhydrides of the present invention.

It is therefore an object of the present invention to provide an improved process for preparing lower alkanoic anhydrides such as carboxylic anhydrides, in particular acetic anhydride.

It is a further object of the present invention to provide a process for producing an improved carboxylic anhydride which does not require high pressure as before.

According to the present invention, an acyl halide such as iodide such as acetyl iodide or bromide such as acetyl iodide, which can be appropriately produced by carbonylating a lower alkyl halide such as hydrocarbyl halide, particularly an iodide such as ethyl iodide or bromide Reaction with hydrocarbyl ether (eg lower alkyl ether) produces carboxylic anhydrides such as lower alkyl acid anhydrides and regenerates halides. Thus, for example, acetic anhydride can be effectively prepared by reacting acetyl iodide. Acetyl iodide can be prepared by reacting methyl iodide with carbon monoxide at moderate carbon monoxide partial pressures, and this carbonylation reaction is carried out in the presence of a Group VIII noble metal catalyst. In the previous reaction, the iodide can be replaced with the corresponding bromide. In this way, other lower alkanoic anhydrides, such as propionic anhydride, butyric anhydride, and lower alkanoic anhydrides such as valeric anhydride, are also acyl halides such as propionyl iodide, propionyl bromide, butyryl iodide, butyryl bromide, etc. It can be prepared by reacting with lower alkyl ether. Similarly, other carboxylic acid anhydrides, such as caprylic anhydride, capric anhydride and lauric anhydride, may be prepared with alkanoic anhydrides having up to 12 carbon atoms, or monocyclic aromatic monocarboxylic acids such as benzoic acid. . As in the case of lower alkanoic anhydrides, these higher anhydrides are captylyl iodide, caprylyl boromide, decanoyl iodide, decanoyl bromide, dodecanoyl iodide, dodecanoyl bromide, benzoyl bromide The corresponding acyl halides, such as benzoyl iodide and the like, are prepared by reacting with a corresponding ether such as heptylethyl, nonylether, phenylether and the like. As described above in lower alkanoic anhydrides, in each case acyl halides can be readily prepared by reacting the corresponding alkyl or aryl halides with carbon monoxide in the presence of a Group VIII noble metal catalyst to effect the carbonylation reaction.

The reactants are preferably chosen such that the resulting anhydride has symmetric anhydrides, ie two identical acyl groups, that is to say that R in formulas (1) and (3) are the same in each case, but the preparation of asymmetric or mixed anhydrides is also It is within the scope of the present invention, which can be readily prepared by incorporating different reactants from one another, for example by using compounds having different R groups in the reaction.

The above reaction can be expressed as follows.

From the stomach

R is a saturated hydrocarbyl group (eg C ₁ -C ₁₁ alkyl), or a monocyclic aryl group (eg phenyl), or an alkali group (eg benzyl), preferably methyl, ethyl, n- C ₁ -C ₄ lower alkyl groups such as propyl, I-propyl, n-butyl, sec-butyl, i-butyl and t-butyl.

X is I or Br.

Hydrocarbyl groups may be substituted with substituents that are inert to the reaction of the present invention.

The volatile alkyl halides and unreacted acyl halides and ethyl in the final product mixture can be easily removed by distillation and recycled, with the total yield of the product being substantially only the required carboxylic anhydride. In the case of the preferred liquid phase reaction, the organic compound is easily separated from the noble metal catalyst by distillation. The process can be carried out in two reaction steps, namely, the first step of carbonylating the hydrocarbyl halide in the presence of a Group VIII noble metal catalyst and the second step of reacting the carbonylation product (acylhalide) with ether. It has been found that the process can be carried out in a single step by combining the steps in a single reaction zone fed with carbon monoxide, ether, hydrocarbyl halide and noble metal catalysts. In the reaction, water is produced and reactants which are anhydrous or substantially anhydrous are used because it is important to operate under substantially anhydrous conditions.

Therefore, when acyl halide is prepared by carbonylation and the process is carried out in two steps, hydrocarbyl halide (e.g. ethyl iodide) and acyl halide (e.g. acetyl) are reacted in the first reaction zone in the presence of a carbon monoxide noble metal catalyst. Iodide), which is then transferred to a second reaction zone where the acyl halide is reacted with hydrocarbyl ether (e.g. lower alkyl ether) to produce the product carboxylic anhydride and regenerate the hydrocarbyl halide. The hydrocarbyl halide is then separated from the product anhydride by distillation and recycled to the reaction zone of the first stage for carbonylation. Unreacted acyl halides and ethers are also recycled and only carboxylic anhydride is recovered as product.

The temperature at which the reaction between the hydrocarbyl halide and carbon monoxide is carried out is suitably wide, for example 20-500 ° C., preferably 100-350 ° C., more preferably 125-250 ° C. Although a lower temperature than the above may be used, in this case, the reaction rate tends to be slow, and a high temperature may be used, but there is no special advantage in this case.

The reaction time is not a variable of the process, which varies to some extent with the temperature used, but typical residence times are typically 0.1-20 hours. The reaction is, of course, carried out under superatmospheric pressure, but one of the features of the present invention is that it does not require too high a pressure and may be used if desired. In general, the reaction can be effectively carried out by using a carbon monoxide partial pressure of preferably 5-2000p.s.i.g, most preferably 25-1000p.s.i.g (sometimes used 0.1-15000p.s.i.g). In the case of using a liquid phase reaction, the total pressure is required to maintain the required liquid phase. Thus the liquid phase reaction is conveniently carried out in an autoclave or similar device. At the end of the required residence time, the reaction mixture is transferred to the second reaction zone and heated. Preferably, the reaction product is introduced into a distillation zone, which is a distillation column, to separate unreacted hydrocarbyl halides that may be present, and the acyl halides are separated from the catalyst. The catalyst and hydrocarbyl halide may then be recycled to the first reaction zone. Alternatively, this separation may be omitted and the entire reaction mixture may be transferred to the reaction zone of the second stage, or only hydrocarbyl halides or catalysts may be separated there.

In the second reaction zone, the acyl halide reacts with hydrocarbyl ether. This reaction is carried out by heat when the acyl halide is separated from the Group VIII noble metal catalyst, and when this separation is not carried out, the reaction with ether may occur in the presence of a catalyst.

In each case, the temperature used is preferably 0-300 ° C, preferably 20-250 ° C, and most preferably 50-200 ° C. During the reaction, carboxylic anhydrides are formed and hydrocarbyl halides are regenerated. The product mixture includes the product anhydride and the hydrocarbyl halide, and also the unreacted ether and acyl halide and the noble metal catalyst if the catalyst is not separated before the second stage reaction. The organic components are easily separated from each other by conventional fractional distillation. Hydrocarbyl halides are generally the most volatile and the anhydrous rates are generally the least volatile and the anhydrides are easily distilled from the inorganic catalysts present. The recovered hydrocarbyl halide is recycled with the recovered catalyst to the reaction zone of the first stage for carbonylation. Unreacted ether and / or acyl halide can be recycled to the second stage reaction zone and carboxylic anhydride is recovered as product.

In a preferred embodiment of the present invention the two reaction stages described above are combined so that the process is carried out in a single reaction zone, in a two-step embodiment the source of halides supplied to the first reaction zone, for example hydrocarbyl halides and the second reaction. Both hydrocarbyl ethers fed into the zone are fed into a single reaction zone and are preferably reacted together in the presence of carbon monoxide and Group VIII noble metal catalysts in the liquid phase. Hydrocarbyl halides are formed in place and therefore the halides are not only supplied to the system as hydrocarbyl halides, but the halogen moiety is also used as other organic halides or other inorganic halides such as hydrohalides or alkali metals or other metal salts, or as iodine or bromine atoms. Supplied. After the reaction, several components of the reaction mixture are easily separated from each other by fractional distillation.

The temperature when carrying out the step 1 embodiment of the present invention is suitably a wide range of temperature, for example 20-500 ° C., preferably 100-300 ° C., more preferably 125-250 ° C. Lower temperatures than those described above may be used as in the case of the two-stage embodiment, but this tends to reduce the reaction rate, and higher temperatures may be used but there are no particular advantages. The reaction time is also not a variable of the one-step process and mainly depends on the temperature used, but a typical defrost time is typically 0.1-20 hours. Although the reaction is carried out under superatmospheric pressure, it is a feature of the present invention that, as described above, no high pressure is required for which a special high pressure device is required. In general, the reaction can be effectively used by preferably using a carbon monoxide partial pressure of 5-2000 p.s.i.g, most preferably 25-1000 p.s.i.g, but a carbon monoxide partial pressure of 0.1-15,000 p.s.i.g may also be used. The total pressure is preferably at the level required to maintain the liquid phase, in which case the reaction can advantageously be carried out in an autoclave or similar device. After the required residence time, the reaction mixture is separated into several of its components by distillation. Preferably, the reaction mixture is introduced into a fractionation column or a series of distillation zones separating the hydrocarbylhalite, acyl halide and ether from the resulting anhydride. Since the boiling points of these several compounds are sufficiently different, their separation by conventional distillation does not cause any particular problem. Likewise, anhydrides are easily distilled from noble metal catalysts. Hydrocarbyl halides and precious metal catalysts and acyl halides can then be mixed with fresh ethers and carbon monoxide to react to produce more anhydrides.

The final reaction mixture usually contains an acyl halide with the product anhydride, and after separation from the anhydride, the acyl halide is recycled to the reaction zone and reacted with ether or the second step of the two step embodiments described above (Equations 2 and 3). It is also a feature of the present invention that separate ethers and acyl halides can be reacted to produce additional amounts of anhydrides as in.

The ratio of ether to halides in the reaction system can vary widely. Typically 1-500 equivalents of ether, preferably 1-200 equivalents, are used per equivalent of halide. Thus, in the case of ether, 0.5-250 mol, preferably 0.5-100 mol, per mol of halide is used. By maintaining the partial pressure of carbon monoxide at a special value, a sufficient amount of reactant will always react with the hydrocarbyl halide.

The hydrocarbyl halide carbonylation (formula 1) described above in a second stage embodiment is advantageously carried out in the presence of a solvent or diluent. This solvent or diluent may be an organic solvent which is inert in the environment of the process, which may also be hydrocarbyl ether, so that carboxylic anhydride is produced with the acyl halide, which is the product required in that case. In other words, the halide-forming reaction of the two-step embodiment is based on the features of the one-step embodiment. Similarly, the one-step embodiment is advantageously carried out in the presence of a solvent or diluent, especially when the reactants have a relatively low boiling point as in the case of ethyl ether. The presence of a high boiling solvent or diluent, either the product anhydride itself (eg acetic anhydride in the case of ethyl ether) or the corresponding ester (eg methyl acetate in the case of methyl ether), allows the use of lower total pressures. Alternatively, the solvent or diluent is an organic solvent that is inert in the environment of the process, such as hydrocarbons (eg octane, benzene, toluene) or carboxylic acids (eg acetic acid). This is easily separated since the solvent or diluent is suitably selected to have a boiling point sufficiently different from the components of the reaction mixture.

Group VIII noble metal catalysts, i. For example, the catalyst added may be a fine metal of its own, or the metal carbonate, oxide, hydroxide, bromide, iodide, chloride, low alkoxide (methoxide), phenoxide or carboxylate ion may be C _1. Metal carboxylate derived from an alkali acid of -C ₂₀ . Similarly, for example metal complexes such as iridium carbonyl and rhodium carbonyl, or carbonyl halides (eg iridium tri-carbonyl chloride [Ir (CO) ₃ Cl] ₂ ) or acetylacetonate) such as rhodium acetyl Other complexes such as acetonate Rh (C ₅ H ₇ O ₂ ) ₃ can also be used.

Although carbon monoxide is preferably used in a substantially pure form, inert diluents such as carbon dioxide, nitrogen, methane and cyclone may be present if desired. The presence of an inert diluent does not affect the carbonylation reaction, but if they are present it is necessary to increase the total pressure to maintain the required carbon monoxide partial pressure. However, carbon monoxide must be anhydrous, as in the following reactants: carbon monoxide and other reactants must be free of water. However, the presence of a minimum amount of water, such as that found in commercial forms of reactants, can be tolerated.

It has been surprisingly found that the activity of Group VIII noble metal catalysts can be greatly improved, especially with regard to reaction rates and product concentrations, by the use of accelerators in parallel. Effective promoters include elements having an atomic weight of 5 or more of groups IA, IIA, IIIA, IVB, and VIB, non-noble metals of Group VIII, and metals of lactanites and actanides of the periodic table. Particularly preferred are these crowded low molecular weight metals, for example metals having a molecular weight of 100 or less, and particularly preferred are Groups IA, IIA and IIIA metals. In general, the most suitable elements are lithium, magnesium, potassium, titanium, chromium, iron, nickel and aluminum. Most preferred are lithium, aluminum and potassium, especially lithium. Accelerators are used in their elemental form, for example in finely pulverized or powdered metals, or they are used as compounds of various forms of organic and inorganic which are effective for introducing the element into the reaction system. Thus, typical compounds of the promoter element include oxides, hydroxide halides (eg bromide and iodide), oxyhalides, hydrides, alkoxides and the like. Particularly preferred organic compounds are, for example, salts of organic mono-carboxylic acids such as alkanoates and benzoates such as acetates, butyrates, decanoates and laurates and the like. Other compounds include metalalkyl carbonyl compounds and chelates, compounds and enol salts. Especially preferred are compounds such as elemental form, bromide or iodide and organic salts (eg salts of mono-carboxylic acids corresponding to the resulting anhydrides). If desired, compounds of promoters, in particular mixtures of elements from different groups of the periodic table, can be used. The exact reaction mechanism of the promoter, or the exact form in which the promoter reacts, is not known, but some induction period was observed when the promoter was added in elemental form, for example, a fine metal.

The amount of promoter may vary widely but is preferably used in an amount of 0.001-10 moles per mole of Group VIII noble metal catalyst.

When treating the reaction mixture by distillation or the like as described above, the promoter generally remains as one of the least volatile components with the Group VIII noble metal catalyst and is continually circulated as appropriate or treated with the catalyst.

It was found that reaction (3) proceeded in two steps as follows.

The reaction between the acyl halide and the hydrocarbyl ether can thus be used to prepare the corresponding ester, which can be removed from the system as a recoverable intermediate if desired. Since accelerators tend to help the formation of anhydrides, that is to say increase the rate of the second reaction of equation (4), accelerators should not be used when recovering intermediate esters.

The reaction is carried out in one step or in two steps or the above reaction is easily carried out in a continuous process so that the reactants and the catalyst are continuously supplied to a suitable reaction zone, preferably with an accelerator, and the reaction mixture is continuously distilled to obtain volatile organic components. The whole product, which is separated and composed of other organic constituents, which are recycled with carboxylic anhydride, is provided, and in the case of a liquid phase reaction, the part containing the Group VIII noble metal (and promoter) is also recycled. In the case of such a continuous process, it is clear that the halogen moiety always remains in the system. Sometimes the small amount of halogen forming moiety required is preferably carried out by feeding halogen in the form of a hydrocarbyl halide, but as described above the halogen moiety can also be used to It may be supplied as an inorganic halide or an iodine atom or a bromine element.

As described above, the carbonylation reaction in the process of the present invention can be carried out in the gas phase by appropriately adjusting the total pressure with respect to temperature so that the reactant is in gaseous form when it comes in contact with the catalyst, if desired.

In the case of gas phase reactions and liquid phase reactions, catalysts and accelerators, i.e. catalyst components, are sometimes supported, that is, they are conventional carriers such as alumina, silica, silicon carbide, zirconia, carbon, bauxite, attafulgas clay, etc. It may also be dispersed in the phase. The catalyst component can be applied to the carrier by conventional methods, for example by immersing the carrier in a catalyst or a solution of the catalyst and promoter and then drying. The concentration of the catalyst component on the carrier varies widely, for example from 0.01-10% by weight or more.

The following examples are intended to illustrate the invention in more detail, and do not limit the invention. All parts and percentages in the examples are by weight unless otherwise indicated.

EXAMPLE

Dimethylethyl (375 parts), methyl iodide (75 parts) and rhodium trichloride hydrate (3 parts) were added to the mixture under a carbon monoxide (total pressure 800p.sig, co partial pressure 190p.sig) atmosphere in a stirred stainless steel autoclave. Heated at ° C. CG analysis of the reaction mixture after 2 hours of reaction time included 16.3% (80 parts) of methyl acetate and 2.4% (12 parts) of acetic anhydride.

Claims (1)

A process for preparing anhydrides of monocarboxylic acids by reacting alkyl ethers, carbon monoxide and alkyl iodides or bromides in the presence of Group VIII noble metal catalysts under substantially anhydrous conditions.