IE63824B1 - Process for the preparation of acid anhydrides - Google Patents

Abstract

Process for preparing acid anhydrides by passing a solution of this acid over an acidified clay.

Description

The present invention relates to the preparation of acid anhydrides, and more particularly to the preparation of itaconic anhydride selectively from itaconic acid.

It is kncwn to prepare itaconic anhydride by the convent ional process of trans-anhydride formation by exchange between itaconic acid and acetic anhydride. This process has the disadvantage of using an expensive raw material, namely acetic anhydr ide, and of forming a by-product which has to be removed, namely acetic acid. The reaction is further limited as regards the temperature used, so as to prevent a polymerization reaction from taking place. It is imperative to use a temperature below 75°C. The yields obtained by this process do not exceed 90% of itaconic anhydride. For a long time, industry has therefore been trying to convert itaconic acid to the anhydride direct from the acid without the need to use another anhydride such as acetic anhydride.

It is also known, from the article published in J. Chem. Research (S) 1985, 356-357, to prepare itaconic anhydride by passing itaconic acid over a commercial clay of the TONSIL 13 type from Sud-Chemie (Munich), treated with an aluminium salt. This technique uses clays exchanged with an aluminium salt. On the one hand, this technique has the disadvantage of requiring a fairly - 3 elaborate treatment of the natural clay, which increases the manufacturing cost of the anhydride. On the other hand, the catalyst changes with time into a less active form.

A novel process for the manufacture of acid anhydrides has now been discovered which makes it possible to avoid the disadvantages of the processes of the prior art.

This process consists in bringing the acid into contact with a clay which has undergone one or more acid treatments.

The clays which can be used in the process of the present invention are preferably selected from the natural clays haying a so-called TOT structure, or tetrahedral-octahedral-tetrahedral structure.

These clays are divided into 3 classes: - the smectites, - the vermiculites and - the micas.

The TOT clays are in the form of elementary sheets comprising two layers of tetrahedra of oxygen atoms in which the silicon atoms are included, these layers being separated by a layer of octahedra of oxygen atoms in which the metal W is included, the said octahedra being of the type M04<0H)2z in which R is a divalent or trivalent cation.

IV When all the tetrahedra are occupied by Si elements, the electrical neutrality of the sheet can be provided in two ways according to the charge on the octahedral cation: - if it is divalent (Mg^*, Fe^+, etc.), all the 5 octahedral cavities are occupied, in which case the sheet is said to be trioctahedral; or - if it is trivalent (Al^+, Fe^+, etc.), two out of three octahedral cavities are occupied and the sheet is said to be dioctahedral.

Numerous substitutions are possible, however, both in the tetrahedral layer and in the octahedral layer. These can cause a charge deficit in the sheet and the neutrality of the crystal is then provided by the insertion of compensating cations between the sheets.

Of the ’’TOT clays defined above, it is preferred to use the smectites.

The smectites are classified according to the nature of the metal N (aluminium, magnesium, iron, lithium) and the nature of the compensating cation (sodium, potassium, calcium).

Thus the following may be mentioned from the smectite class: - the montmoriI Ionites of the general formula Si4(Al2-xMgx)0iQ(0H)2.M+x - the beidellites of the formula (Si4-xAIx) A12O1Q( OH>2-M+x the nontronites of the formula - 5 (Si4_xAlx>Fe20lO(OH>2.H+x - the hectorites of the formula Si4xLix)O1o(OH)2-M+x - the stevensites of the formula Si4(Mg3_x)O1o - the saponites of the formula (Si4_xAlx)Hg3Oto2-M+x - the fIuorohectorites of the formula Si4(Al2-xLix)Oio(FzOH)2.M+x - the sauconites of the formula (Si4_xAlx)(Mg3_xZnx)0iQ(0H)2-M+x Among the smectites, the montmoriIlonites are preferably used most particularly within the framework of the present invention. It is also possible to use the commercial clays which are already acid, such as the following clays in particular: . KSF sold by Sud-Chemie (Munich), and . K 10 sold by Sud-Chemie.

The clay KSF has a surface area of 20 to 40 m^/g 20 and a density of 800 to 850 g/l.

The clay K 10 has a surface area of 220 to 270 m^/g and a density of 300 to 370 g/l.

In a first process of the invention, the clays undergo an acid treatment with an aqueous solution of an acid. The concentration of acid in the aqueous solution is variable, but preferably it must not have a pH of less than 2 so as not to destroy the clay, and it must contain a quantity of H+ ion, expressed in mil IiequivaLents, which at least corresponds to the exchange capacity of the clay. The exchange capacity of a clay is defined as the number of cations, expressed in milliequivalents, which can be exchanged on 100 g of sample.

This exchange capacity (or charge per half-mesh) varies between 0.2 and 0.6 for the smectites and between 0.6 and 0.9 for the vermiculites. It is therefore preferable, within the framework of the present invention, to use a solution of acid which contains as many equivalents of H* as there will be cations to be exchanged in the clay, i.e. containing at least 0.2 to 0.6 H* per halfmesh, or at least 50 to 150 milliequivalents of acid per 100 g of clay.

Hydrochloric acid, sulphuric acid, nitric acid, perchloric acid and phosphoric acid may be mentioned in particular among the acids used to acidify the clay. Organic acids, especially trifluoromethanesulphonic acid, could also be used but have no advantage over mineral acids and, in particular, have the disadvantage of being more expensive.

In a second acid treatment process, the clay can be treated with an ammonium salt and then calcined at low temperature so as to remove the ammonia and leave only the proton, H+, behind. The calcination is carried out at a temperature which is less than or equal to 500°C and preferably less than or equal to 400°C. - 7 If desired, after one or other of the acid treatment processes, the clay can be treated with an alcohol such as methanol or isopropanol, or with a ketone such as acetone, and then dried.

The acid which is to be converted to the anhydride is then brought into contact with the pretreated clay in a reactor, in the presence of a solvent selected from optionally halogenated aromatic organic solvents, especially toluene, xylene and chlorobenzene, and chlorinated aliphatic solvents.

In order to carry out the invention more successfully, it is preferred to use an amount by weight of acid which is to be converted to the anhydride, calculated relat ive to the amount of clay, of between 1 and 20. The 15 acid can be introduced continuously or sequentially. If the process is capable of being operated continuously, the amount of acid, calculated relative to the clay, can be considerably greater. An amount by weight of solvent, calculated relative to the acid, of between 20 and 150 is also preferred.

The following may be mentioned among the acids which are to be converted to anhydrides: - aliphatic dicarboxylic acids, - cycloaliphatic dicarboxylic acids and - aromatic polycarboxy I ic acids.

Among the aliphatic dicarboxylic acids, it is possible to use linear or branched, saturated or un- 8 ;saturated acids preferably containing 4 to 8 carbon atoms.

It is preferred to use aliphatic acids whose main chain « 0 is saturated and contains 4 carbon atoms. Succinic acid, itaconic acid, maleic acid and glutaric acid may 5 be mentioned from this class. It is preferred to use itaconic acid.

Among the cycloaliphatic dicarboxylic acids, it is possible to use saturated or partially unsaturated acids. It is nevertheless preferred to use saturated 10 acids. CyclohexenedicarboxyIic acid and cyclohexanedicarboxylic acid may be mentioned from this class.

Among the aromatic polycarboxylic acids, it is preferred to use aromatic dicarboxylic acids. Phthalic ί acid, trimellitic acid, trimesic acid, pyromellitic acid 15 and prehnitic acid may be mentioned from this class.

Acids substituted by various groups which do not influence the cyclization of the molecule can also be used in the invention.

When itaconic acid is used, the anhydride is 20 obtained with a selectivity of more than 90% and citraconic anhydride with a selectivity of less than 5%.

' The reaction between the clay and the acid is carried out at a temperature of between 80 and 200°C and preferably of between 100 and 150°C for dicarboxylic acids.

It is preferably carried out at atmospheric pressure.

The product obtained by the present invention, i.e. the anhydride, is devoid of metal salts, especially aluminium salts, by comparison with the itaconic anhydride obtained by the process described in the article published in J. Chem. Research, where there is a risk of contamination with an aluminium salt. This purity is often essential because these anhydrides are important intermediates for the pharmaceutical and plant health industries (US patent 4 487 777, French patent 2 466 450, French patent 2 480 600). They can also be used in the polymer industry (US patent 4 480 125), where purity -is an essential criterion.

The present invention is illustrated by the following Examples.

The abbreviations used in the Examples have the following meanings: - 0C = degree of conversion = % of itaconic acid converted, and - Y = yield of the anhydride formed, relative to the acid converted.

EXAMPLE 1 (according to the invention): a) Description of the clay The catalyst employed is a clay of the montmorillonite type with acid properties (Ref.: KSF from SudChemie (Munich), FRG). b) Activation treatment of the clay: KSF - HCl - MeOH The following are introduced successively into a -ΙΟΙ litre glass beaker provided with a magnetic stirrer: 800 ml of water, then concentrated hydrochloric acid until a pH of 2.5 is obtained, and then 5 g of KSF clay.

If the pH changes after the clay has been added, it is readjusted to 2.5.

The suspension is stirred at 25°C for 1 hour. The clay is recovered by filtration on a glass frit, washed with Permutit-softened water and resuspended in 400 ml of MeOH. After stirring at 25°C for 1 h 30 min, the clay is isolated by filtration on a glass frit, washed with methanol and dried for 16 hours at 40°C under 100 mm Hg. c) Use of the KSF - HCl - MeOH catalyst in the anhydride formation reaction g of itaconic acid, 0.5 g of the catalyst 15 prepared according to 1b) and 50 to 55 ml of toluene are introduced, under argon, into a 100 ml three-necked glass reactor provided with a central stirrer, a Vigreux column (equipped with a head analyser with passage of the toluene-water azeotrope over a column of 3 A molecular sieve and recycling of the toluene through a siphon), a 20 ml dropping funnel, a gas inlet and a heating system.

The mixture is refluxed for 3 hours.

After the reaction, the mixture is left to cool to room temperature. The catalyst is recovered by fil— tration on a glass frit and washed with 4 x 30 ml of acetone (recovery of the adsorbed itaconic acid, if appropriate). The filtrates are combined and the solvents are evaporated off under reduced pressure (rotary evaporator equipped with an oil pump) at 40°C.

The itaconic acid and the itaconic and citraconic anhydrides are determined by H NMR (360 MHz). A par5 ticular integration technique makes it possible to obtain the different titres to within plus or minus 0.25%. The degree of conversion of the itaconic acid is 93% and the itaconic and citraconic anhydrides are obtained with selectivities of 94% and 5% respectively.

EXAMPLE 2 (comparative): - Preparation of an Al^+-exchanged clay 5 g of TONSIL 13 (alkaline montmoriI Ionite (Ca^+, Na*) marketed by Su’d-Chemie) are introduced gradually into a 0.24 M aqueous solution of AICI3 at 25°C, with thorough stirring. These conditions are maintained for minutes. After centrifugation (5200 rpm for 8 minutes), the solid is washed twice with 80 ml of Permutit-softened water, each wash being followed by a centrifugation. The TONSIL 13-Al^* obtained is dried at 80°C for 17 hours.

- Use of TONSIL 13-Al^* in the anhydride formation reaction The procedure is the same as in Example 1 except that the Al^*-exchanged clay is employed as the catalyst. The degree of conversion of the itaconic acid is 62% and the itaconic and citraconic anhydrides are obtained with selectivities of 91% and 7% respectively.

EXAMPLE 3: The procedure is the sane as in Example 1, the clay employed being the same clay which has been treated only with aqueous HCl (pH = 2.5): KSF - HCl. The degree of conversion of the itaconic acid is 76% and the itaconic and citraconic anhydrides are obtained with selectivities of 92% and 3% respectively.

EXAMPLE 4 (comparative): The procedure is the same as in Example 1, the clay employed being the same clay (KSF) which has not been treated. The degree of conversion of the itaconic acid is 9% and the itaconic and citraconic anhydrides are obtained with selectivities of 67% and 43% respectively.

EXAMPLES 5 to 8: These Examples describe the use of various acids for acidifying the clay and various organic solvents for dispersing the clay after acidification.

They are carried out under the conditions of Example 1 except that, in step c), 1 g of catalyst is introduced instead of the 0.5 g introduced in Example 1.

Ex. No. CLAY OF MONT- MORILLONITE TYPE (REF. OF ORIGIN) ACID SOLVENT 5 KSF HCl CH3OH 6 KSF F3CSO3H CH3OH 7 K10 HNO3 (CH3>2C=0 8 K10 H2SO4 (CH3)2C=0 Ex. DC (X) Y (X) Y (X) No . ITACONIC ITACONIC CITRACONIC ACID ANHYDRIDE ANHYDRIDE 5 96 95 2 6 96 90 2 7 94 90 3 8 95 90 4 EXAMPLES 9 to 11; These Examples describe the use of different 5 organic solvents which enable the itaconic acid to be brought into contact with the clay KSF - HCl - methanol prepared according to Example 1.

Ex . No. T °C t h SOLVENT DC ITACONIC ACID X Y ITACONIC ANHYDRIDE CITRACONIC ANHYDRIDE 9 10 11 111 138 138 3 1.5 0.7 toluene xylenes It 98 97 96 96 92 97 1 2 1 EXAMPLES 12 to U: These Examples make it possible to describe the 5 use of clays which differ from the KSF or K10 used in the previous Examples, but have been treated once or several times with different acids and different alcohols or ketones (see Table below).

EXAMPLES 12 to 14 Ex . Type of clay T radename Acid Alcohol or ketone 12 montmor iIloni te VOLCLAY H3PO4 i. C3H7OH 13 montmor i11 on i te TONSIL OPTIMUM FF HCl CH3OH 14 montmor iI Ion i te COPISIL 04 HCl CH3OH Ex. DC itaconic acid Y itaconic anhydr i de c itraconic anhydr ide 12 33 68 14 13 97 93 2 14 14 46 18 EXAMPLES 15 to 23; These Examples make it possible to illustrate the conversion to anhydrides of acids which differ from i taconic ac id.

The following are used in each Example: - 16.7 mmol of substrate, - 60 ml of solvent, the nature of which is indicated in each Table, and - 0.5 g to 2 g of catalyst.

The catalyst is prepared according to Example 1 (a to c).

The temperatures and reaction times are indicated in the following Tables: Table 1 Results of anhydride formation in toluene temperature: 110°C reaction time: 3 hours weight of catalyst: 0.5 g Ex . Catalyst Substrate DC (%) Product obtained Y (%) 15 KSF - HCl - MeOH 0 OH V 96 0 0 95 16 KSF - HCl - MeOH 0 OH CC* 66 Gj. _ 99 Table 2 Results of anhydride formation in xylene temperature: 140°C reaction time: 0.8 to 1 hour weight of catalyst: 0.5 g Ex . Catalyst Substrate DC (X) Produc t obtained Y (X) 17 KSF - HCl - MeOH X X o o p 96 0 97 ΐ 0 0 18 TONSIL 0 95 0 92 OPTIMUM FF r^OH A V0H 0 8 0 Y 19 KSF - HCl - MeOH r" -CQgH \—C02H 28 o o 86 1 20 KSF - HCl - MeOH \x^SC02H 73 0 100 CIS 0 21 KSF - HCl - MeOHIX^yC02H \Aco2h 100 Y 100 0 - 18 Table 3 Results of anhydride formation in mesitylene (1,3,5-trimethylbenzene) temperature: 165°C Ex. Catalyst Weight of catalyst (g) Substrate DC (%) 22 KSF - HCl - MeOH 1 zii^s^CO-H CT COgH CO H 2 87 I ί ! 23 I I i KSF - HCl - MeOH 2 HO C CO_H ΓΤ ho2c A^Aco2h 36 Ex . T ine (h) Product Y (X) 22 1 97 23 6 0 0 •w . 64

Claims (13)

C LA I MS

1. λ process for the preparation of an acid anhydride from the corresponding acid, which comprises contacting the said acid to be converted into an anhydride with a clay which has undergone one or more treatments with one or more acids.

2. Process according to claim 1, in which the said acid to he converted into an anhydride is an aliphatic, cycloaliphatic or aromatic polycarbozylic acid.

3. Process according to claim 2, in which the said acid is an aliphatic dicarboxylic acid saturated in the main chain.

4. Process according to claim 3, in which the said acid is itaconic acid or succinic acid.

5. Process according to claim 2, in which the said acid is a saturated cycloaliphatic dicarboxylic acid.

6. Process according to claim 2, in which the said acid is an aromatic dicarboxylic acid.

7. Process according to any one of claims 1 to 6, in which the clay has been treated with one or more of hydrochloric acid, sulphuric acid, nitric acid, perchloric acid, phosphoric acid and trifluoromethanesulphonic acid. -218. Process according to any one of claims 1 to 7, in which the acid treatment of the clay is carried out with an amount of acid, expressed in milliequivalents, which at least corresponds to the exchange capacity of the clay. 5 9. Process according to any one of claims 1 to 8, in which, after the acid treatment, the clay is treated with an alcohol or a ketone.

8. 10. Process according to claim 9, in which the clay is treated with methanol, isopropanol or acetone. 10

9. 11. Process according to any one of claims 1 to 10, in which the acid to be converted into an anhydride is brought into contact with the clay in the presence of a solvent which is an optionally halogenated aromatic organic solvent or a chlorinated aliphatic solvent. 15

10. 12. Process according to claim 11, in which the amount of solvent used is such that the weight ratio of the solvent to the acid to be converted to the anhydride is between 20 and 150.

11. 13. Process according to any one of claims 1 to 12, 20 in which the reaction temperature is between 80 and 200°C.

12. 14. Process according to claim 1 substantially as described in any one of Examples 1,3 and 5 to 23.

13. 15. An acid anhydride when produced by the process of any one of claims 1 to 14.