GB1565663A

GB1565663A - Production of esters in the presence of amphoteric catalysts and oxalic acid

Info

Publication number: GB1565663A
Application number: GB21616/76A
Authority: GB
Original assignee: BP Chemicals Ltd
Current assignee: BP Chemicals Ltd
Priority date: 1977-05-18
Filing date: 1977-05-18
Publication date: 1980-04-23

Description

(54) PRODUCTION OF ESTERS IN THE PRESENCE OF AMPHOTERIC CATALYSTS AND OXALIC ACID (71) We, BP CHEMICALS LIMITED, of Britannic House, Moor Lane, London, EC2Y 9BU, a British company, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: The present invention relates to a process for the production of esters using amphoteric catalysts, and, in particular, to the use of oxalic acid in such a process for the purpose of inhibiting colour formation in the ester product.

The use of amphoteric catalysts, instead of strong mineral acids such as sulphuric or toluene-para-sulphonic acids, in the production of esters is well-known. Thus British Patent Specification No. 852,110 describes a method for preparing esters using as catalyst a compound having the formula MX4 in which M is titanium or zirconium and X is a hydroxyl group, alkoxy group, aryloxy group, acyloxy group, hydroxyalkoxy group, hydroxpolyalkoxy group, or aminoalkoxy group or a chlorine or bromine atom, at least one X being an organic radical as hereinbefore specified having from 1 to 18 carbon atoms. The use of amphoteric titanium catalysts has also been described in British Patent Specification Nos. 886,750; 1,058,242; 1,061,173;1,070,914 and 1,246,346. Other amphoteric esterification catalysts are disclosed in British Patent Specification Nos. 879,799 (sub203) 733,870 (Al(OH)3/NaOH),747,260 (Ai2(SO4)3/ NaOH); 1,076,702 (ZnO); 1,118,363 (MoS2/ C); 1,372,854 (Zn(R)2) and US Patent No.

3,457,297 (Ph3Bi). Advantages claimed for amphoteric esterification catalysts include an improvement in the colour and a reduction in the acidity of the product ester, in addition to an improvement in the quality of the recovered recycled alcohol reactant. Nevertheless, esters produced in the presence of amphoteric catalysts are often coloured, the colour being to a large degree caused by ingress of air into the reaction vessel during the esterification reaction at high temperatures in the presence of acid, such as the phthalate mono-acid in the case of phthalate ester production.

It is known from British Patent Specification No. 990,297 that certain stannous salts, for example stannous oxalate, catalyse the production of esters having a lower colour intensity than the products obtained by the use of other amphoteric catalysts, such as titanates.

It has now been found that the addition of oxalic acid, over a narrow concentration range, to esterification reactions catalysed by amphoteric compounds surprisingly inhibits colour formation in the product more effectively than does the prior art stannous oxalate catalyst.

This improvement is surprising in view of the known colour-promoting activity of the phthalic carboxylic acid group and of other acids such as toluene-para-sulphonic acid.

Thus according to the present invention there is provided a process for the production of esters which process comprises reacting in the liquid phase a carboxylic acid or an anhydride thereof with an alcohol or phenol or a derivative thereof at elevated temperature in the presence of a catalytically effective amount of an amphoteric esterification catalyst and from 10 to 5,000 ppm, based on the total weight of reactants, of oxalic acid.

The carboxylic acid may be for instance:a monobasic acid containing up to 20 carbon atoms, or an anhydride thereof e.g. alkanoic acids, such as myristic, palmitic and stearic acids, an alkenoic acid such as oleic acid, or deriva tives of such alkanoic and alkenoic acids such as ricino leic acid; an aliphatic dibasic acid containing from 3 to 20, preferably from 3 to 10 carbon atoms such as adipic, azelaic and sebacic acids and anhydrides thereof; tribasic aliphatic acids such as citric acid and anhydrides thereof; monobasic aromatic acids such as those con taining up to 10 carbon atoms e.g. benzoic acid and anhydrides thereof; dibasic aromatic acids and their anhydrides such as phthalic acids or phthalic anhy dride; tribasic aromatic acids and their anhydrides such as hemimellitic, trimellitic and trimesic acids and their anhydrides.

The preferred acids are o-phthalic acid or its anhydride, adipic acid and sebacic acid.

The alcohol or phenol may be for instance:a monohydric alcohol containing up to 20 car bon atoms, preferably an alkanol containing from 4 to 14 carbon atoms e.g. butanol, iso heptanol, iso-octanol, 2-ethylhexanol, no nanol, decanol, tridecanol and mixtures of alcohols, containing for example, 7 to 9 carbon atoms such as are obtained from olefin mixtures by the OXO process; a dihydric alcohol containing up to 20 carbon atoms, e.g. monoethylene glycol, diethylene glycol, triethylene glycol, mono-, di-, and tri propylene glycol, the butylene glycols and 2,2,4-trimethyl pentane diol; a trihydric alcohol such as glycerol, pentaery thritol and dipentaerythritol; an aliphatic cyclic alcohol containing up to 10 carbon atoms such as cyclohexanol; a derivative, preferably an ether derivative of a dihydric or trihydric alcohol, e.g. a lower alkyl ether derivative such as 2-butoxy ethanol; a monohydric phenol containing up to 10 car bon atoms such as phenol itself and; a dihydric phenol such as catechol, resorcinol, hydroquinone and pyrogallol.

Preferably the alcohol is tridecanol or a mixture of Cg to Cl l alcohols, commercially available as "Dobanol" (Registered Trade Mart).

Preferably a stoichiometric excess of the alcohol or phenol is present in the reaction mixture. Up to 50% molar excess, preferably between 10 and 30% molar excess, of the alcohol or phenol over the carboxylic acid or anhydride thereof may be used.

Whilst any amphoteric catalysts may be used, the process of the invention is particularly advantageous when tetra-alkyl titanate cat: alysts, such as tetra-isopropyl or tetra-isobutyl titanate, are employed. Preferably the amphoteric catalyst is present in an amount of from 0.001 to 0.01 moles per kilogramme of reactants.

The amount of oxalic acid present in the esterification mixture is dependent on the structure and purity of the alcohol or phenol or derivative thereof employed. Preferably oxalic acid is present in an amount between 100 and 2,000 ppm based on the total weight of reactants. Amounts of oxalic acid greater than 5,000 ppm are disadvantageous because larger concentrations promote colouration of the ester product.

When the alcohol reactant is too highboiling to produce reflux under the esterification temperature conditions employed, it is preferred to incorporate a relatively low-boiling solvent in the reaction mixture. Preferred solvents are those having a low solubility in water, such as hydrocarbons. Preferably the solvent is ortho-xylene. The amount of solvent incorporated is suitably greater than 5% wlw, preferably from 15 to 30% w/w, based on the weight of the reaction mixture.

The elevated temperature may be any temperature in the range 180 to 275, preferably 200 to 250, even more preferably 200 to 240 C.

The pressure is preferably atmospheric or superatmospheric.

On completion of the reaction it is preferred to neutralise any residual acidity and to deactivate the titanate catalyst. The crude ester product may be neutralised by the addition of a strong inorganic base, such as sodium carbonate or lime, which may be added either in the form of a solid or in aqueous solution. The conditions under which this catalyst deactivation step is accomplished are well known in the art, typically involving elevated temperature.

After neutralisation, or simultaneous with neutralisation, it is preferred to remove excess alcohol from the product, suitably by steam stripping. The recovered alcohol is preferably recycled to a subsequent esterification reaction.

If a solid is employed for deactivating the esterification catalyst, it is necessary to remove the solid, suitably by filtration, from the ester product. This is done preferably by treatment of the essentially anhydrous mixture after the removal of excess alcohol.

The process may be operated batchwise, continuously or semi-continuously.

The invention will now be further described with reference to the following Examples.

Example 1 A mixture of phthalic anhydride (2.5g mole), "dobanol" (a Cg - C1 l alcohol mixture : 5.6g mole), xylene (1.25g mole), tetraisopropyl titanate (0.0026g mole) and oxalic acid (1.29g = 1,000 ppm based on the weight of reactants) was heated to reflux temperature (2300cm1 bar) under nitrogen atmosphere in a round-bottomed flask (2Q) fitted with a stirrer and a Dean and Stark decanter. The water formed during the esterification reaction was taken overhead into the Dean and Stark decanter. A conversion of 99.8% of the phthalic anhydride to the phthalate ester was obtained Tablet

Esterification conditions Phthalate ester final product Conversion tc Oxalic acid phthalate Example addition ester Scm Acidity (%w/w No. Temp.("C ester (hous) Colour/15cm (tO w/w) (% w/w) cell phthalic acid) 1 0.1 230 3.5 9992 1.3 yellow 0.002 Ored 2 0.06 230 3.0 99.87 1.7 yellow 0.004 0.3 red 3 0.25 230 4 9991 1.8 yellow 0.0008 0.4 red Comparison 0 230 4 99.92 1.8 yellow 0.001 test 1 0.7 red Comparison 097 230 4 99.85 3.5 yellow 0.001 test 2 0.6 red Table 2

Esterification conditions Phthalate ester final product Conversion t Oxalic acid | phthalate Example addition ester No. Temp. ( C Time (hours) Colour/15cm Acidity (tow/w (% w/w) (% w/w) cell phthalic acid) 4 0.025 230 3 9996 0.5 yellow 0.0005 0.1 red 5 0.1 230 3 99.97 0.3 yellow 0.001 0 red Comparison 0 227 3.6 9995 0.7 yellow 0.0005 test 3 0.1 red Table 3

Product colour/15cm Cell Test Additive No. (% w/w) Before After Aeration Aeration YELLOW RED YELLOW RED 1 None 1.6 0.3 3.8 0.2 2 0.4% w/w stannous oxalate 1.6 0.3 2.7 0.3 3 0.2% w/w oxalic acid 1.6 0.3 2.2 0.3 4 03% w/w toluene-para-sulphonic acid 0.8 0.3 24 7.8 after esterification for 3.5 hours.

The crude phthalate ester was then cooled to 1000C and was neutralised with aqueous 50% w/w Na2 C03 solution (()g). The product was vacuum steam stripped for 3 hours at 1500 Cl c'b mbar to remove the xylene and unreacted dobanol as an overhead product. The didobanyl phthalate was filtered subsequently through a 2 cm thick bed of Clarcel (Registered Trade Mark) filter aid. The colour of the product ester* and its acidity were then measured. The results are given in Table 1.

Example 2 Example 1 was repeated except that oxalic acid was present in the reaction mixture at a concentration of 600 ppm. The reaction conditions, colour of the ester product* and its acidity are given in Table 1.

Example 3 Example 1 was repeated except that oxalic acid was present in the reaction mixture at a concentration of 2,500 ppm. The reaction conditions, colour of the ester product* and its acidity are given in Table 1.

Comparison Test 1 (not according to the invention) Example 1 was repeated except that no oxalic acid was present in the reaction mixture. The reaction conditions, colour of the ester product* and its acidity are given in Table 1.

Comparison Test 2 (not according to the invention) Example 1 was repeated except that oxalic acid was present in the reaction mixture at a concentration of 9700 ppm. The reaction conditions, colour of the ester product* and its acidity are given in Table 1.

The results shown in Table 1 demonstrate that a small addition of oxalic acid, viz. 0.1% w/w (= 1,000 ppm), reduces substantially the colour of the phthalate ester final product, while a much larger addition, viz. 0.97% w/w (9700 ppm) increases the colour of the ester product.

Example 4 The procedure described in Example 1 was repeated except that the "dobanol" was replaced by tridecanol (15% molar excess on the phthalic anhydride present) and oxalic acid was present in the reaction mixture at a concentration of 250 ppm. The reaction conditions, colour of the ester product* and its acidity are given in Table 2.

Example 5 Example 4 was repeated except that oxalic acid was present in the reaction mixture at a concentration of 1,000 ppm. The reaction conditions, colour of the ester product* and its acidity are given in Table 2.

Comparison Test 3 (not according to the invention) Example 4 was repeated except that no oxalic acid was included in the reaction mixture. The reaction conditions, colour of the ester product* and its acidity are given in Table 2.

* The colour or the product ester was measured according to a procedure based on ASTM Standard No. D1209.

Comparison Test 4 (not according to the invention) 200g of a test mixture comprising about 90% w/w of ditridecyl phthalate, approximately 10% w/w of tridecylhydrogen phthalate and containing no additional additive in the first test and in subsequent tests (2) 0.4% w/w stannous oxalate, (3) 0.2% w/w oxalic acid and (4) 0.3% w/w toluene-para-sulphonic acid respectively, were aerated (with 100 cm3 of air) at 2000C over one hour.

The colour intensity of the test mixture as measured before and after aeration is given in the following Table 3.

The above results show that oxalic acid is a more effective colour formation inhibitor than stannous oxalate. This observation is surprising in view of the colour production resulting from the addition of a strong acid such as toluenepara-sulphonic acid, as shown by Test No. 4.

WHAT WE CLAIM IS: 1. A process for the production of esters which process comprises reacting in the liquid phase a carboxylic acid or an anhydride thereof with an alcohol or phenol or a derivative thereof at elevated temperature in the present of a catalytically effective amount of an amphoteric esterification catalyst and from 10 to 5,000 ppm, based on the total weight of reactants, of oxalic acid.

2. A process according to claim 1 wherein the carboxylic acid is a monobasic acid containing up to 20 carbon atoms.

3. A process according to claim 2 wherein the monobasic acid is an alkanoic or an alkenoic acid or a derivative thereof.

4. A process according to claim 3 wherein the monobasic acid is myristic, palmitic, stearic, oleic or ricinoleic acid.

5. A process according to claim 1 wherein the carboxylic acid is an aliphatic dibasic acid containing from 3 to 20 carbon atoms.

6. A process according to claim 5 wherein the aliphatic dibasic acid is adipic, azelaic or sebacic acid.

7. A process according to claim 1 wherein the carboxylic acid is a tribasic aliphatic acid.

8. A process according to claim 7 wherein the tribasic aliphatic acid is citric acid.

9. A process according to claim 1 wherein the carboxylic acid is a monobasic, dibasic or tribasic aromatic acid.

10. A process according to claim 9 wherein the aromatic acid is benzoic acid, phthalic acid, hemimellitic, trimellitic or trimesic acid.

11. A process according to claim 1 wherein the carboxylic acid is o-phthalic acid, adipic acid or sebacic acid.

12. A process according to any one of the preceding claims wherein the alcohol is a monohydric or dihydric alcohol containing up to 20 carbon atoms or a trihydric alcohol.

13. A process according to claim 12 wherein the monohydric alcohol is an alkanol containing from 4 to 14 carbon atoms.

14. A process according to claim 13 wherein the alkanol is butanol, isoheptanol, iso-octanol, 2-ethylhexanol, nonanol, decanol, tridecanol, or a mixture of alcohols containing 7 to 9 carbon atoms such as are obtained from olefin mixtures by the OXO process.

15. A process according to claim 12 wherein the dihydric alcohol is monoethylene glycol, diethylene glycol, triethylene glycol, mono-, di- or tri-propylene glycol, a butylene glycol or 2,2,4-trimethyl pentane diol.

16. A process according to claim 12 wherein the trihydric alcohol is glycerol, pentaerythritol or dipentaerythritol.

17. A process according to any one of claims 1 to 11 wherein the alcohol is an aliphatic cyclic alcohol containing up to 10 car

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. conditions, colour of the ester product* and its acidity are given in Table 1. Comparison Test 1 (not according to the invention) Example 1 was repeated except that no oxalic acid was present in the reaction mixture. The reaction conditions, colour of the ester product* and its acidity are given in Table 1. Comparison Test 2 (not according to the invention) Example 1 was repeated except that oxalic acid was present in the reaction mixture at a concentration of 9700 ppm. The reaction conditions, colour of the ester product* and its acidity are given in Table 1. The results shown in Table 1 demonstrate that a small addition of oxalic acid, viz. 0.1% w/w (= 1,000 ppm), reduces substantially the colour of the phthalate ester final product, while a much larger addition, viz. 0.97% w/w (9700 ppm) increases the colour of the ester product. Example 4 The procedure described in Example 1 was repeated except that the "dobanol" was replaced by tridecanol (15% molar excess on the phthalic anhydride present) and oxalic acid was present in the reaction mixture at a concentration of 250 ppm. The reaction conditions, colour of the ester product* and its acidity are given in Table 2. Example 5 Example 4 was repeated except that oxalic acid was present in the reaction mixture at a concentration of 1,000 ppm. The reaction conditions, colour of the ester product* and its acidity are given in Table 2. Comparison Test 3 (not according to the invention) Example 4 was repeated except that no oxalic acid was included in the reaction mixture. The reaction conditions, colour of the ester product* and its acidity are given in Table 2. * The colour or the product ester was measured according to a procedure based on ASTM Standard No. D1209. Comparison Test 4 (not according to the invention) 200g of a test mixture comprising about 90% w/w of ditridecyl phthalate, approximately 10% w/w of tridecylhydrogen phthalate and containing no additional additive in the first test and in subsequent tests (2) 0.4% w/w stannous oxalate, (3) 0.2% w/w oxalic acid and (4) 0.3% w/w toluene-para-sulphonic acid respectively, were aerated (with 100 cm3 of air) at 2000C over one hour. The colour intensity of the test mixture as measured before and after aeration is given in the following Table 3. The above results show that oxalic acid is a more effective colour formation inhibitor than stannous oxalate. This observation is surprising in view of the colour production resulting from the addition of a strong acid such as toluenepara-sulphonic acid, as shown by Test No. 4. WHAT WE CLAIM IS:

1. A process for the production of esters which process comprises reacting in the liquid phase a carboxylic acid or an anhydride thereof with an alcohol or phenol or a derivative thereof at elevated temperature in the present of a catalytically effective amount of an amphoteric esterification catalyst and from 10 to 5,000 ppm, based on the total weight of reactants, of oxalic acid.

bon atoms.

18. A process according to any one of claims 1 to 11 wherein the alcohol is an ether derivative of a dihydric or trihydric alcohol.

19. A process according to claim 18 wherein the derivative is 2-butoxy ethanol.

20. A process according to any one of claims 1 to 11 wherein the phenol is a monohydric phenol containing up to 10 carbon atoms or a dihydric phenol.

21. A process according to claim 20 wherein the phenol is phenol, catechol, resorcinol, hydroquinone or pyrogallol.

22. A process according to any one of claims 1 to 11 wherein the alcohol is tridecanol or a mixture of Cg to Cl 1 alcohols.

23. A process according to any one of the previous claims wherein the elevated temperature is in the range 180 to 2750C.

24. A process according to claim 23 wherein the temperature is in the range 200 to 2400 C.

25. A process according to any one of the previous claims wherein the amphoteric catalyst is a tetraalkyl titanate.

26. A process according to claim 25 wherein the tetraalkyl titanate catalyst is tetraisopropyl or tetraisobutyl titanate.

27. A process according to any one of the previous claims wherein the amphoteric catalyst is present in an amount of from 0.001 to 0.01 moles per kilogramme of reactants.

28. A process according to any one of the previous claims wherein up to 50who molar excess of the alcohol or phenol over the carboxylic acid or anhydride thereof is used.

29. A process according to claim 28 wherein the molar excess is in the range 10 to 30So.

30. A process according to any one of the preceding claims wherein oxalic acid is present in an amount between 100 and 2,000 ppm based on the total weight of reactants.

31. A process according to any one of the preceding claims wherein there is incorporated in the reaction mixture a relatively low-boiling solvent when the alcohol reactant is too highboiling to produce reflux under the esterification reaction conditions.

32. A process according to claim 31 wherein the solvent is ortho-xylene.

33. A process according to either one of claims 31 or 32 wherein the amount of lowboiling solvent incorporated is greater than 5% wlw.

34. A process according to claim 33 wherein the amount of low-boiling solvent incorporated is in the range 15 to 30% w/w.

35. A process according to any one of the preceding claims wherein any residual acidity is neutralised by the addition of a strong inorganic base.

36. A process according to claim 35 wherein the strong inorganic base is sodium carbonate or lime, either in the form of a solid or as an aqueous solution.

37. A process according to either one of claims 35 or 36 wherein after, or simultaneous with, neutralisation excess alcohol is removed from the product.

38. A process according to any one of claims 35 to 37 wherein, following neutralisation, the ester product is filtered.

39. A process for the production of esters substantially as hereinbefore described with reference to Examples 1 to 5.

40. Esters whenever produced by a process as claimed in any one of the preceding claims.