FR2822823A1 - PROCESS FOR PREPARING AN ESTER USING A CATALYST CONSISTING OF A POLYANILINE SALT - Google Patents

Abstract

The invention relates to a process for preparation of an ester using a polyaniline salt as catalyst.

Description

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 The present invention relates to a process for the preparation of an ester by means of a polyaniline salt catalyst, more particularly to a process for the production of aliphatic esters by direct esterification of aliphatic monocarboxylic acids with aliphatic monofunctional alcohols by means of catalysts consisting of polyaniline salts.

 The esters are useful in many industrial applications, for example for the production of coatings, adhesives, resins, perfumes and plasticizers. Esterification is a limited reaction by a well known equilibrium which involves a mono-, di- or polycarboxylic acid or anhydride and an alcohol or phenol which may be mono-, di- or polyfunctional.

 Although there are several ways to produce esters, most of them do not meet the strict specifications that are applied in the chemical industry. The most acceptable method for producing an ester is to react an acid with an alcohol in the presence of a catalyst.

 Esterification is one of the most fundamental and important reactions in organic synthesis. Conventionally, the processes for producing esters from acids and alcohols can be classified into the following three main categories: (RC Larock, Comprehensive Organic Transformations, VCH, New York, 1989, page 966, and references cited Encyclopedia of Chemical Technology, 9th Edition, Wiley Interscience Publications, page 755, and cited citations, Ullmann's Encyclopedia of Industrial Chemistry, Vol 10, 5th Edition, 1987, page 281, and references cited, Vogel's, Textbook of Practical Organic Chemistry, Longman Group Ltd., England, 5th edition, 1996).

 (a) Liquid phase esterification reactions using a liquid catalyst: this type of process uses as a catalyst a liquid phase acid such as sulfuric acid, phosphoric acid, sulphonic acid or p-toluenesulphonic acid ; (b) liquid phase esterification reactions using a solid catalyst: this type of process typically uses catalysts consisting of inorganic salts, cationic ion exchange resins and solid acids;

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 (c) gas phase esterification reactions: this type of process uses different catalysts such as heteropolyacids, liquid phase acids on solid supports and zeolites in a gas phase reaction.

 One of the problems associated with liquid phase esterification reactions with liquid catalysts is that acidic liquid catalysts such as sulfuric acid or p-toluenesulfonic acid cause corrosion of the reactor. Moreover, these liquid acid catalysts are removed along with the reaction products, which poses serious problems of waste disposal and pollution. The use of a mineral acid as a catalyst has the following disadvantages: (i) the catalyst can not be reused, (ii) the removal of the acid is polluting and expensive, (iii) low selectivity is frequently observed (iv) corrosion of the reactors, (v) manipulation is not easy and (vi) large amounts of catalyst are required.

 Liquid phase esterification reactions using a solid catalyst, in which a cationic ion exchange resin is typically used as the catalyst, alleviate the problems of corrosion and waste disposal that arise with the catalysts. processes in liquid phase with a liquid catalyst, and lead to a simplification of the process of separation of the reaction product and catalysts. However, cationic ion exchange resins typically have poor heat resistance, often lose a significant portion of their activity when subjected to heat and are difficult to regenerate.

 In gas phase esterification reactions, reaction conditions are maintained such that all reagents and products are in the gas phase. Typically, inorganic substances which have excellent heat resistance and which can easily be separated from the reaction products are used as catalysts. However, the gas phase reaction requires a relatively large reactor, which increases costs. Furthermore, if a gas phase esterification reaction is used to produce unsaturated carboxylic esters, the high reaction temperature often results in the production of undesired by-products consisting of

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 polymers or oligomers. In some cases, the high reaction temperature results in dehydration of the alcohol molecules to ethers. These side reactions tend to reduce the activity of the catalysts and lead to difficulties in operation.

 To overcome the above drawbacks, the present invention aims to provide a process for the preparation of esters using catalysts consisting of polyaniline salts, which is non-polluting, which allows a catalyst recycling and which is economical and effective.

 Thus, the present invention relates to a process for the preparation of an ester which comprises the direct esterification of an aliphatic monocarboxylic acid with an aliphatic monoalcohol in the presence of a catalyst consisting of a polyaniline salt at a temperature in the range of 40 to 800C for a time in the range of 8 to 24 hours, and the separation of the ester thus obtained from the reaction mixture.

 Preferably, the aliphatic monocarboxylic acid used is chosen from aliphatic monocarboxylic acids having 2 to 20 carbon atoms, for example caproic acid, caprylic acid, auric acid, myristic acid or stearic acid. .

isopropylique ou l'alcool tertiobutylique. Also preferably, the aliphatic monoalcohol used is chosen from aliphatic monoalcohols having 1 to 20 carbon atoms, such as methanol, ethanol, propanol, butanol, dodecan-1-ol, isopropyl alcohol or tert-butyl alcohol, preferably alcohol

isopropyl or tert-butyl alcohol.

 The polyaniline salt catalyst that is used may be selected from polyaniline sulfate, polyaniline hydrochloride, polyaniline nitrate, polyaniline p-toluenesulfonate and polyaniline phosphate. The reaction temperature may be in a range of 70 to 800C, and the reaction may take place for example for a period of 20 to 24 hours. Preferably, the catalyst is used in an amount of 100 to 400 mg, more preferably in an amount of 150 to 200 mg per gram of carboxylic acid.

 The alcohol may be used in an amount of, for example, 1 to 5, preferably 4 to 5, ml per gram of carboxylic acid.

Finally, the catalyst can be reused six times.

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 The esterification process according to the present invention can be carried out by reacting an aliphatic monocarboxylic acid with an aliphatic monohydric alcohol in the presence of a catalyst and then removing the catalyst by conventional methods. The ester can be isolated by filtration and then column chromatography using an adsorbent such as silica gel and a solvent such as chloroform, ethyl acetate, hexane or a mixture thereof.

 The present invention will be better understood on reading the following nonlimiting examples.

EXAMPLE 1
Three different methods have been used to prepare polyaniline salts using three different oxidizing agents such as benzoyl peroxide, pyridinium chlorochromate and ammonium persulfate.

Process 1: Preparation of polyaniline salts with benzoyl peroxide
In the polymerization process, 25 ml of an aqueous solution containing 1.44 g of sodium laurylsulfate was slowly added with stirring to a solution of 4.85 g of benzoyl peroxide in 150 ml of dioxane. Then, 30 ml of aqueous solution containing 2.4 ml of aniline and 9 ml of concentrated sulfuric acid were added to this mixture with constant stirring. The reaction mixture was stirred for 24 h at 30 ° C.

Then it was filtered, washed with water and with acetone. The product was dried at 100 C to constant weight. By the same process, polyaniline hydrochloride and polyaniline nitrate were prepared using 9 ml of hydrochloric acid and 6 ml of nitric acid, respectively, in place of sulfuric acid.

Process 2: Preparation of polyaniline salts with pyridinium chlorochromate
In the polymerization process, 1.0 ml of aniline and 3.0 ml of concentrated sulfuric acid were dissolved in 70 ml of distilled water.

To this solution was added dropwise (15-20 min) 25 ml of aqueous solution containing 2.0 g of pyridinium chlorochromate. The reaction mixture was stirred for 30 minutes at 30 ° C. and then filtered, washed with water and finally with acetone. The product was dried

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100OC jusqu'à poids constant. Par le même processus, on préparé du chlorhydrate de polyanilin, du nitrate de polyanilin, du phosphate de polyanilin, du p-toluènesulfonate de polyanilin en utilisant 9 ml d'acide chlorhydrique, 6 ml d'acide nitrique, 7 mi d'acide phosphorique, 2 g d'acide p-toluène sulfonique, respectivement, à la place de l'acide sulfurique.

100OC up to constant weight. By the same process, polyaniline hydrochloride, polyaniline nitrate, polyaniline phosphate, polyaniline p-toluenesulfonate were prepared using 9 ml of hydrochloric acid, 6 ml of nitric acid, 7 ml of phosphoric acid. 2 g of p-toluenesulphonic acid, respectively, in place of sulfuric acid.

Process 3: Preparation of polyaniline salts with ammonium persulfate
In the polymerization process, 1.0 ml of aniline and 3.0 ml of concentrated sulfuric acid were dissolved in 70 ml of distilled water.

To this solution was added dropwise (interval 15-20 min) 25 ml of aqueous solution containing 2.3 g of ammonium persulfate. The reaction mixture was stirred for 4 h at 30 ° C then filtered, washed with water and finally with acetone. The product was dried at 100 ° C to constant weight. Using the same process, polyaniline hydrochloride, polyaniline nitrate, polyaniline phosphate and polyaniline p-toluenesulfonate were prepared using 9 ml of hydrochloric acid, 6 ml of nitric acid, 7 ml of phosphoric acid, 2 g of p-toluenesulphonic acid, respectively, in place of sulfuric acid.

EXAMPLE 2
In a typical experiment, 1.0 g of auric acid was charged to a 10 ml round bottom flask and 5.0 ml of methanol and 200 mg of catalyst powder (1-polyaniline sulfate) were added. . The reaction mixture was refluxed at 70 ° C for different times. Then, the reaction mixture was filtered and the mixture was washed with chloroform to recover the catalyst. Chloroform and unreacted methanol were evaporated. The compound was introduced into a silica gel column of fineness greater than 75 μm (200 mesh). The product was eluted with 400 ml of a mixture of chloroform and hexane 20:80. The solvent mixture was recovered to obtain the pure ester.

 The yields of ester prepared during different reaction times are reproduced in Table 1 below.

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TABLE 1

<Tb>
<tb> Time <SEP> of <SEP><SEP> reaction <SEP> (h) <SEP> Yield <SEP> (%)
<tb> 4 <SEP> 1
<tb> 8 <SEP> 63
<tb> 12 <SEP> 80
<tb> 16 <SEP> 88
<tb> 20 <SEP> 99
<tb> 24 <SEP> 99
<Tb>

EXAMPLE 3
In one experiment, 1.0 g of auric acid was charged to a 10 ml round-bottomed flask and 5.0 ml of methanol and various amounts of catalyst powder (1-polyaniline sulfate) were added. The reaction mixture was refluxed at 70 ° C for 24 h and then filtered and the mixture was washed with chloroform to recover the catalyst. Chloroform and unreacted methanol were evaporated. The compound was introduced into a column containing silica gel fineness greater than 75 μm (200 mesh). The product was eluted with 400 ml of a mixture of chloroform and hexane 20:80.

The solvent mixture was recovered to obtain the pure ester.

 The ester yields obtained with different amounts of catalyst are reproduced in Table 2 below.

TABLE 2

<Tb>
<tb> Quantity <SEP> of <SEP> Catalyst <SEP> (mg) <SEP> Yield <SEP> (%)
<tb> 100 <SEP> 90
<tb> 200 <SEP> 99
<tb> 30099
<tb> 400 <SEP> 83
<Tb>

EXAMPLE 4
In a typical experiment, 1.0 g of lauric acid was placed in a 10 ml round bottom flask and various amounts were added.

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de méthanol et 200 mg de poudre de catalyseur (procédé 1-sulfate de polyanilin). On a chauffé le mélange réactionnel à reflux à 70 C pendant 24 h puis on l'a filtré et on a lavé le mélange avec du chloroforme pour récupérer le catalyseur. On a évaporé le chloroforme et le méthanol qui n'avait pas réagi. On a introduit le composé dans une colonne de gel de silice de finesse supérieure à 75 um (200 mesh). On a élué le produit avec 400 ml d'un mélange de chloroforme et d'hexane 20 : 80. On a récupéré le mélange de solvants pour obtenir l'ester pur.

of methanol and 200 mg of catalyst powder (1-polyaniline sulfate method). The reaction mixture was refluxed at 70 ° C for 24 h and then filtered and the mixture was washed with chloroform to recover the catalyst. Chloroform and unreacted methanol were evaporated. The compound was introduced into a silica gel column of fineness greater than 75 μm (200 mesh). The product was eluted with 400 ml of a mixture of chloroform and hexane 20:80. The solvent mixture was recovered to obtain the pure ester.

 The ester yields obtained with different amounts of methanol are reproduced in Table 3 below.

TABLE 3

<Tb>
<tb> Quantity <SEP> of <SEP> methanol <SEP> (mil) <SEP> Yield <SEP> (%)
<tb> 1 <SEP> 55
<tb> 2 <SEP> 90
<tb> 3 <SEP> 92
<tb> 4 <SEP> 99
<tb> 5 <SEP> 99
<Tb>

EXAMPLE 5
In a typical experiment, 1.0 g of auric acid was charged to a 10 ml round bottom flask and 5.0 ml of methanol and 200 mg of catalyst powder (1-polyaniline sulfate) were added. . The reaction mixture was refluxed at various temperatures for 24 h and then filtered and washed with chloroform to recover the catalyst. Chloroform and unreacted methanol were evaporated. The compound was introduced into a silica gel column of fineness greater than 75 μm (200 mesh).

The product is eluted with 400 ml of chloroform / hexane 20:80. The solvent mixture is recovered to obtain the pure ester.

 The ester yields obtained at different temperatures are reproduced in Table 4 below.

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TABLE 4

<Tb>
<tb> Temperature <SEP> (OC) <SEP> Yield <SEP> (%)
<tb> 30 <SEP> 2
<tb> 50 <SEP> 47
<tb> 70 <SEP> 99
<Tb>

EXAMPLE 6
In a typical experiment, 1.0 g of auric acid was placed in a 10 ml round bottom flask and 5.0 ml of an alcohol among different alcohols and 200 mg of catalyst powder (Method 1 polyaniline sulphate). The reaction mixture was refluxed at 70 ° C for 24 h and then filtered and washed with chloroform to recover the catalyst. Chloroform and unreacted alcohol were evaporated. The compound was introduced into a silica gel column of fineness greater than 75 μm (200 mesh). The product was eluted with 400 ml of a 1: 99 mixture of ethyl acetate and hexane. The solvent mixture was recovered to obtain the pure ester.

 The ester yields obtained with different alcohols are reproduced in Table 5 below.

TABLE 5

<Tb>
<tb> Alcohol <SEP> Yield <SEP> (%)
<tb> Methanol <SEP> 99
<tb> Ethanol <SEP> 95
<tb> Propanol <SEP> 99
<tb> Butanol <SEP> 99
<tb> Dodecan-1-ol <SEP> 99
<tb> Isopropyl alcohol <SEP><SEP> 26
<tb> Terbutyl alcohol <SEP><SEP> 71
<Tb>

EXAMPLE 7
In a typical experiment, 1.0 g of one of several acids was placed in a 10 ml round-bottomed flask and added

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 5.0 ml of methanol and 200 mg of catalyst powder (1-polyaniline sulfate method). The reaction mixture was refluxed at 70 ° C for 24 h and then filtered and washed with chloroform to recover the catalyst. Chloroform and unreacted methanol were evaporated. The compound was introduced into a silica gel column of fineness greater than 75 μm (200 mesh). The product was eluted with 400 ml of a mixture of chloroform and hexane 20:80. The solvent mixture was recovered to obtain the pure ester.

 The ester yields obtained with different acids are reproduced in Table 6 below.

TABLE 6

<Tb>
<tb> Acid <SEP> Yield <SEP> (%)
<tb><SEP> caproic acid <SEP> 90
<tb><SEP> caprylic acid <SEP> 99
<tb> Acid <SEP> auric <SEP> 99
<tb> Acid <SEP> myristic <SEP> 98
<tb> Stearic acid <SEP><SEP> 99
<Tb>

EXAMPLE 8
In a typical experiment, 1.0 g of auric acid was placed in a 10 ml round bottom flask and 5.0 ml of methanol and 200 mg of catalyst powder (1-polyaniline sulfate) were added. .

The reaction mixture was refluxed at 70 ° C for 24 h and then filtered and washed with chloroform to recover the catalyst.

Chloroform and unreacted methanol were evaporated.

The compound was introduced into a silica gel column of fineness greater than 75 μm (200 mesh). The product was eluted with 400 ml of a mixture of chloroform and hexane 20:80. The solvent mixture was recovered to obtain the pure ester. The experiment was repeated six times using the recovered catalyst.

 The ester yields obtained with the recovered catalyst are reproduced in Table 7 below.

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TABLEAU 7

TABLE 7

<Tb>
<tb> RepeatabilityPerformance <SEP> (%)
<tb> 1st <SEP> times <SEP> 99
<tb> 2nd <SEP> times <SEP> 99
<tb> 3rd <SEP> times <SEP> 99
<tb> 4th <SEP> times <SEP> 99
<tb> Seventh <SEP> times <SEP> 99
<tb> 6th <SEP> times <SEP> 99
<tb> 7th <SEP> times <SEP> 99
<Tb>

EXAMPLE 9
In a typical experiment, 1.0 g of auric acid was placed in a 10 ml round bottom flask and 5.0 ml of methanol and 200 mg of catalyst powder (prepared by three different processes) were added. The reaction mixture was refluxed at 70 ° C for 24 h and then filtered and washed with chloroform to recover the catalyst. Chloroform and unreacted methanol were evaporated. The compound was introduced into a silica gel column of fineness greater than 75 μm (200 mesh). The product was eluted with 400 ml of a mixture of chloroform and hexane 20:80. The solvent mixture was recovered to obtain the pure ester.

 The ester yields obtained with different catalysts are reproduced in Table 8 below.

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TABLEAU 8

TABLE 8

<Tb>
<tb> Process <SEP> Salt <SEP> of <SEP> polyaniline <SEP> Yield <SEP> (%)
<tb> 1 <SEP> Hydrochloride <SEP> of <SEP> polyaniline <SEP> 99
<tb> Sulfate <SEP> of <SEP> polyaniline <SEP> 99
<tb> Nitrate <SEP> of <SEP> polyaniline <SEP> 99
<tb> II <SEP> Hydrochloride <SEP> of <SEP> polyaniline <SEP> 99
<tb> Sulfate <SEP> of <SEP> polyaniline <SEP> 99
<tb> Nitrate <SEP> of <SEP> polyaniline <SEP> 99
<tb> p-toluenesulfonate <SEP> of <SEP> polyaniline <SEP> 99
<tb> Phosphate <SEP> of <SEP> polyaniline <SEP> 65
<tb> III <SEP> Hydrochloride <SEP> of <SEP> polyaniline <SEP> 99
<tb> Sulfate <SEP> of <SEP> Polyaniline <SEP> 99
<tb> Nitrate <SEP> of <SEP> polyaniline <SEP> 99
<tb> p-toluenesulfonate <SEP> of <SEP> polyanillin <SEP> 99
<tb> Phosphate <SEP> of <SEP> polyaniline <SEP> 75
<Tb>

Le procédé selon la présente invention permet d'utiliser des catalyseurs constitués par des sels de polyanilin dans l'estérification en phase liquide d'acides monocarboxyliques aliphatiques et de monoalcools aliphatiques. L'utilisation de sels de polyanilin comme catalyseurs présente les avantages suivant par rapport à l'utilisation d'autres catalyseurs : on observe une haute activité catalytique, le catalyseur ne corrode pas les réacteurs, une utilisation répétée du catalyseur est possible, un recyclage du catalyseur est possible, la séparation du catalyseur d'avec le mélange réactionnel est aisée et l'élimination du catalyseur usé ne pose pas de problème car il n'est pas polluant, tandis que l'élimination non polluante d'un catalyseur constitué par un acide minéral est très coûteuse.

The process according to the present invention makes it possible to use catalysts consisting of polyaniline salts in the liquid phase esterification of aliphatic monocarboxylic acids and aliphatic monoalcohols. The use of polyaniline salts as catalysts has the following advantages over the use of other catalysts: a high catalytic activity is observed, the catalyst does not corrode the reactors, repeated use of the catalyst is possible, recycling of the catalyst is possible. catalyst is possible, the separation of the catalyst from the reaction mixture is easy and the removal of the spent catalyst does not pose a problem because it is not polluting, while the non-polluting removal of a catalyst consisting of a mineral acid is very expensive.

Claims (11)

 1. A process for preparing an ester by means of a catalyst consisting of a polyaniline salt, characterized in that it comprises the direct esterification of an aliphatic monocarboxylic acid with an aliphatic monoalcohol in the presence of a catalyst. consisting of a polyaniline salt at a temperature in a range of 40 to 800C for a time in a range of 8 to 24 hours and the separation of the ester thus obtained from the reaction mixture.  2. Process according to claim 1, characterized in that the aliphatic monocarboxylic acid used is chosen from aliphatic monocarboxylic acids having 2 to 20 carbon atoms.  3. Method according to claim 2, characterized in that the aliphatic monocarboxylic acid used is selected from caproic acid, caprylic acid, lauric acid, myristic acid and stearic acid.  4. Process according to any one of the preceding claims, characterized in that the aliphatic monoalcohol used is chosen from monoalcohols having 1 to 20 carbon atoms.  5. Method according to claim 4, characterized in that the aliphatic monoalcohol used is selected from methanol, ethanol, propanol, butanol, dodecan-1-ol, isopropyl alcohol and tertiary butyl alcohol.  6. Process according to any one of the preceding claims, characterized in that the catalyst consisting of a polyaniline salt used is chosen from polyaniline sulphate, polyaniline hydrochloride, polyaniline nitrate, polyaniline p-toluenesulphonate and polyaniline phosphate.  7. Method according to any one of the preceding claims, characterized in that the reaction is conducted at a temperature of 70 to 80Oc.  8. Process according to any one of the preceding claims, characterized in that the reaction is carried out for a period of 20 to 24 hours. <Desc / Clms Page number 13>  9. Process according to any one of the preceding claims, characterized in that the amount of catalyst used is 150 to 200 mg per gram of said aliphatic monocarboxylic acid.  10. Process according to any one of the preceding claims, characterized in that the amount of alcohol used is 4 to 5 ml per gram of said aliphatic monocarboxylic acid.  11. Method according to any one of the preceding claims, characterized in that the catalyst is reused six times.