PROCESS FOR THE PREPARATION OF CARBOXYLIC ACIDS AND ESTERS THEREOF BY OXIDATIVE CLEAVAGE OF UNSATURATED FATTY ACIDS AND ESTERS THEREOF

Abstract: A process for the preparation of carboxylic acids and esters thereof, comprises the operation of mixing an unsaturated fatty acid or corresponding ester with an oxidative substance, in the presence of a catalyst belonging to the group consisting of oxides of tungsten and molybdenum and their acids and alkaline salts, obtaining an intermediate reaction product, and directly reacting said intermediate product without subjecting it to purification techniques, with oxygen or an oxygen containing gas in the presence of a cobalt containing compound which acts as catalyst.

Description: "Process for the preparation of carboxylic acids and esters thereof by oxidative cleavage of unsaturated fatty acids and esters thereof" The present invention relates to a process for the produc¬ tion of carboxylic acids and esters thereof comprising the oper¬ ation of: Reacting an unsaturated fatty acid or corresponding ester with an oxidising compound, in the presence of a catalyst bel- onging to the group consisting oxides of molybdenum and tungsten and their corresponding acids and alkaline salts, obtaining an intermediate reaction product and reacting said intermediate product with oxygen or an oxygen containing gas in the presence of a cobalt compound which acts as a catalyst. A process of the above mentioned type, that is defined on the whole as an oxidative cleavage, is described in the follow¬ ing consecutive reaction I and II, where the intermediate prod¬ uct is a vicinal diol in which the hydroxy groups are attached to the carbon atoms that in the starting compound were connected with a olefinic double bond: (I) oxidising agent {R,-CH=CH- [(CH 2 ) p -CH=CH] m - (CH 2 ) t -COθ} z -A > catalyst {R CH(OH) -CH(OH) - [ (CH 2 ) p -CH(OH) -CH(OH)] m - (CH 2 ) t -COθ} z -A (ID {R,-CH(OH) -CH(OH) - [ (CH 2 ) p -CH(OH) -CH(OH) ] m - (CH 2 ) t -C00} z -A 0 2 > zR, - COOH + mzHOOC - ( CH ) r - C00H catalyst + {HOOC- (CH 2 ) t -COθ} z -A where p=0-l, m=0-2, t=0-ll, z=l-3; R,= H, C C g alkyl or a CH 3 - (CH 2 ) 3 -CH(OH) -CH 2 radical and in which if z=l, A is H or C^Cs,- if z=2-3, A is the residue of a bivalent or trivalent alcohol. The US patent 4,606,863 describes a process of the above indicated type in which in certain embodiments the starting fatty acid/ester is oxidised with hydrogen in the presence of a catalyst based on tungsten or molybdenum and a solvent such as acetic acid. The intermediate reaction product so obtained, which may contain vicinal diols or epoxy groups, ethers or esters, are purified from the solvent and water formed in the course of the reaction. They are then subjected to further oxidation with oxy¬ gen or an oxygen containing gas in the presence of a heavy metal compound, for example cobalt, and a bromine or chlorine compound. In addition, if the intermediate product has a high melting point or if it is necessary to get rid of a notable heat of reaction, a polar organic solvent, such as C 2 -C 10 saturated carbo¬ xylic acid, is used as the reaction solvent . The process described by US patent 4,696,863 has the incon- venience of requiring a purification treatment of the interme¬ diate reaction products and the additional presence of a bromine or chlorine compound, in order to activate the heavy metal act¬ ing as a catalyst, and optionally an organic solvent. The pro¬ cess as a whole moreover lacks selectivity with respect to the formation of specific compounds. US patent 3,711,523, US patent 3,816,525 and British Patent 1,405,578 describe oxidation processes of vicinal diols or epoxides in order to obtain carboxylic acids with an oxidising system consisting of peroxides such as peracetic acid, and oxy- gen or an oxygen containing gas in the presence of a cobalt based catalyst. Such processes are not adapt for industrial scale produc¬ tion as they use dangerous and costly reagents such as peracetic acid. Moreover, they are preferably carried out in organic sol- vents with the additional complication arising from the separ¬ ation of the reaction products there from, which in itself cre¬ ates an additional cost. British Patent 1,330,205 describes a process for the pro¬ duction of carboxylic acids through oxidation of vicinal diols using a catalyst system comprising a cobalt salt such as acetate in the presence of a pertungsten or permolybdenum acid or simi¬ lar compounds in a bipolar aprotic solvent. Such a process has the disadvantage of requiring the use of costly and difficultly recyclable solvents and requires that the diols to be oxidised are anhydrous. It is in fact known that water has an adverse effect on the bipolar aprotic solvents in that it eliminates a positive effect that said solvents have in the oxidative cleavage reaction (see Tetrahedron Letters 54, pag. 5689, 1968, Pergamon Press). The reason for such an effect is probably due to the fact that the catalytic action of the cobalt salt appears to be connected to the formation of a super red Co(III) complex (see R.A. Sheldon, and J. . Kochi in "Metal-Catalysed Oxidations of Organic Compounds", 1981, Academic Press, Pages 75 and 144) and the for- mation of Co(III) compound is highly disactivated by the pres- ence of water (see F.A. Cotton and G. Wilkinson in "Advanced Inorganic Chemistry", Editor John Wiley & Sons, page 768). US Patent 3,865,856 describes a process for the production of carboxylic acids by oxidation of vicinal diols with oxygen or an oxygen containing gas in the presence of a transition metal, which acts as a catalyst, and a solvent such as a hydrocarbon or saturated carboxylic acid containing at least 5 carbon atoms. According to US patent 3,865,856, such solvents are necessary in order to retain aldehydes which constitute intermediate reaction products. The oxidative gas flow is moreover used to continu¬ ously eliminate water formed during the reaction. Also said process has the inconvenience of requiring the presence of an organic solvent. With the aim of overcoming these inconveniences, the subject of the present invention consists of a process of the above mentioned type, characterised by the fact that water, the cobalt containing compound and the oxygen or oxygen containing gas is directly added to the said intermediate reaction product, without previously having undergone any purification treatments. The process according to the present invention has the ad¬ vantage of not requiring any purification of the intermediate reaction product, essentially consisting of vicinal diols, nor does it require the presence of organic solvents in order to carry out further oxidation of the vicinal diols, which is carried out with a more than sufficient yield in the presence of water. Such a result is completely unpredictable and surprising considering the numerous prior art documents mentioned above relating the opposite effect, which would be the effect of water on the catalytic properties of cobalt, and also the scarce solu- bility of oxygen in water with respect to other organic solvents (see the table reported on page 320 of "Chemistry and Industry" no. 22, 1985) . On the whole, the oxidative cleavage process according to the present invention uses a cobalt based catalyst, easily found in the market, a gaseous oxidant such as pure oxygen or air and water, resulting in an economical, non polluting and simple to carry out process, whilst at the same time allowing high yields and selectivity to be obtained. The cobalt compounds which are particularly adapt as cat¬ alysts for the oxidation reaction (II) of the diols are cobalt acetate, cobalt chloride and cobalt sulphate, used in quantities between 0.1 and 3% by mole with respect to the diol. Water is preferably added to the diols obtained by reaction (I) in order to have a weight ratio of water/diol between 1:1 and 5:1. The oxidising substance used in carrying out reaction (I) is preferably an aqueous solution of hydrogen peroxide in con¬ centrations comprised between 50 and 70% and used in a quantity comprised between 100 and 140% of the stoichiometric quantity with reference to the starting materials, which corresponds to one mole of oxidising substance to one mole of double bonds to be oxidised. The catalyst in reaction (I) is preferably present in a quantities comprised between 0.1 and 1.1% by weight with respect to the unsaturated fatty acid or ester starting materials. The preferred reaction temperature is comprised between 50 and 90°C. Preferably the time necessary in order to carry out the reaction (I) is comprised between 2 and 8 hours, while the time necessary to carry out reaction (II) is comprised between 5 and 12 hours. Examples of compounds to undergo the process of oxidative cleavage are the most common fatty acids such as oleic acid, erucic acid, palmitoleic acid, myristoleic acid, 9-decalenic acid, 9-dodecalenic acid, ricinoleic acid, linoleic acid, linolenic acid, or corresponding esters with mono and polyvalent alcohols and mixtures thereof. The process according to the present invention can be con- ducted by firstly carrying out reaction (I) , and then charging the reactor with the diol or mixtures of diol products from reaction (I) , water and the cobalt based catalyst all at once in the desired proportions. The mixture is then heated to a fixed temperature and stirred in a flow of oxygen or in the presence of air. The reaction process is determined by controlling, from time to time, the composition of the reaction mixture by the appropriate analytical methods such as for example gas phase chromatography. At the end of the reaction, stirring is stopped and the organic phase is separated from the aqueous phase which contains the cobalt based catalyst that can be recycled. The reaction products can be separated using conventional techniques. The saturated mono or dicarboxylic acid esters can be, in particular, separated by fractional distillation under vacuum, while the saturated carboxylic acids can be obtained by hydrolysis of the corresponding esters or directly from the reaction mixture, exploiting the different water solubilities and boiling points. Other advantages and characteristics of the process acco¬ rding to the present invention will be exemplified in the fol¬ lowing examples, which in themselves are not intended to limit the scope of the present invention. Example 1 Into a round bottomed flask equipped with a mechanical stirrer, thermometer, dropping funnel and a condenser, 80 g of crude oleic acid (80% purity) containing 9% linoleic acid and 0.56 g of H 2 W0 4 are added. The stirred mixture is brought to 60 - 65°C and 24 g of 60% w/w H 2 0 2 is added. The addition of H 2 0 2 is gradual over about 30 mins in order to maintain the temperature between 65 - 75°C. Once the addition of H 2 0 2 is completed the mixture is left for 1.5 hours at said temperature. The crude reaction product so obtained is charged into a stirred 1000 ml autoclave containing 300 ml of water and 1.2 g of hydrous cobalt acetate. The autoclave is then pressurised with 70 atm of air and the temperature is raised to 66°C. The reaction mixture is stirred at said temperature for 4.5 hours, then cooled to 50°C and the aqueous layer is separated form the organic layer. The aqueous phase that contains the cobalt salt can be reused for the successive tests. The organic phase is extracted another time with water at 90°C in order to separate azelaic acid. Once cooled 30.5 g of azelaic acid is obtained. The organic phase is then fractionally distilled under vacuum (10 mm Hg) giving 25 g of pelargonic acid. The distillation residue is then saponified with aqueous NaOH at 90°C for 1 hour. After acidification 5.5 g of azelaic acid and 2 g of pelargonic acid are separated in the above described way. The total yield is 75% of azelaic acid and 75.4% for pelargonic acid, which is reduced to about 15% carrying out a test under analogous conditions to example 1 without the pres¬ ence of cobalt acetate as catalyst. Example 2 The same conditions as used for example 1 are used with the exception that 0.5 g of cobalt acetate is used instead of 1.2 g in the oxidation phase of the diol mixture. Proceeding as described in example 1 a yield of 70.2% of azelaic acid and 71% of pelargonic acid is obtained. Example 3 Into a 500 ml round bottomed flask equipped with a mechan¬ ical stirrer, thermometer, dropping funnel, gas influx tube and a condenser, 100 g of crude oleic acid (80% purity) containing 9% linoleic acid and 0.75 g of H 2 W0 4 is added. The stirred mix- ture is brought to 60 - 65°C and 28 g of 60% w/w H 2 0 2 is added. The H 2 0 2 is gradually added over about 30 mins in order to main¬ tain the temperature between 65 - 75°C. Once the addition of H 2 0 2 is completed the mixture is left at that temperature for 1.5 hours. Then, 200 ml of water and 1 g of hydrous cobalt acetate is added to the mixture. The temperature is raised to 70°C by passing an oxygen stream through the reactor bottom for 4 hours. At the end of the reaction, the reaction products are recovered by the process as described in example 1, obtaining 42.5 g of azelaic acid (yield = 70.9%) and 31.3 g of pelargonic acid (yield =70%) . Example 4 Using the same apparatus as in Example 1, 100 g of crude oleic acid (80% purity) containing 9% linoleic acid and 0.75 g of H 2 W0 4 is added. The stirred mixture is brought to 60 - 65°C and 28 g of 60% w/w H 2 0 2 is added. The H 2 0 2 is gradually added over about 30 mins in order to maintain the temperature between 65 - 75°C. Once the addition of H 2 0 2 is completed the mixture is left at that temperature for 1.5 hours. The crude reaction prod¬ uct so obtained is charged into an stirred 500 ml autoclave con- taining 150 ml of water and 1.0 g of hydrous cobalt chloride. The autoclave is then pressurised with 65 atm of air and the temperature is raised to 70°C. The reaction mixture is treated according to the way described in example 1 obtaining 42 g of azelaic acid (yield = 70%) and 30.9 g of pelargonic acid (yield = 69%) . Example 5 Into the same apparatus of example l, 100 g of erucic acid (95% purity) and 0.75 g of H 2 W0 4 is added. The stirred mixture is brought to 60 - 65°C and 23.3 g of 60% w/w H 2 0 2 is added. The H 2 0 2 is gradually added over about 45 mins. The temperature is raised to 85°C in order to keep the reaction mixture fluid. Once the addition of H 2 0 2 is completed the mixture is left at that tem¬ perature for 3 hours. The crude reaction product so obtained is charged into an stirred 500 ml autoclave containing 200 ml of water and 1.0 g of hydrous cobalt acetate. The autoclave is then pressurised to 75 atm. of air and the temperature is raised to 85-90°C. The reaction mixture is stirred at this temperature for 7 hours. At the end the reaction mixture is then cooled and extracted with ethyl ether. The ether is evaporate and the resi- due extracted at ambient temperature with heptane in order to separate brassilic acid from pelargonic acid. In fact a phase insoluble in heptane is obtained which is filtered and washed in heptane. The 51 g of solid phase obtained contained 43 g of brassilic acid and 4 g of pelargonic acid. From this phase prac- tically pure brassilic acid can be obtained by crystallisation with ethanol and water. The heptane extracts are reunited and evaporated. The resi¬ due is distilled under vacuum recovering 22.7 g of pelargonic acid. The distillation residue is treated as indicated in example 1 obtaining 2.3 g of pelargonic acid and 3.6 g of brassilic acid. The total yield of pelargonic acid is 64.9% and that of brassilic acid 68%. Example 6 Into the same apparatus as in Example 1, 100 g of crude methyl oleate (82% purity) containing 9.9% methyl linoleate, 0.75 g of H 2 W0 4 and 1.25 g of dihydroxystearic acid is added. The stirred mixture is brought to 60 - 65°C and 28.6 g of 60% w/w H 2 0 2 is added. The H 2 0 2 is gradually added over about 30 mins in order to maintain the temperature between 60 - 70°C. Once the addition of H 2 0 2 is completed the mixture is left at that tem¬ perature for another 4 hours. The crude reaction product so obtained is charged into a stirred 500 ml autoclave containing 150 ml of water and 1.0 g of hydrous cobalt chloride. The autoclave is then pressurised with 75 atm of air and the tem¬ perature is raised to 65°C. The reaction mixture is stirred at this temperature for 7 hours. At the end, NaOH is added to the reaction mixture until an alkaline pH is reached and saponified for 2 hours at 95°C. After acidification with sulphuric acid, the crude reaction products are treated in the same way as described in example 1. 40.8 g of azelaic acid (yield = 70%) and 33.5 g of pelargonic acid (yield = 68.8%) are obtained.

Claims: CLAIMS 1. Process for the preparation of carboxylic acids or esters thereof comprising the operations of: reacting an unsaturated fatty acid or corresponding ester with an oxidising substance, in the presence of a catalyst belonging to the group consisting oxides of molybdenum and tungsten and corresponding acids and alkaline salts, obtaining an intermediate reaction product and - reacting said intermediate product with oxygen or an oxygen containing gas in the presence of a cobalt com¬ pound which acts as a catalyst. Said process being characterised by the fact that to the said intermediate reaction product, without having undergone any purification treatments, water, the cobalt containing compound and the oxygen containing gas are directly added. 2. Process according to claim 1 characterised by the fact that the cobalt containing compound is selected from the group consisting of cobalt acetate, cobalt chloride and cobalt sulphate. 3. Process according to any of the preceding claims, characterised by the fact that the cobalt containing com¬ pound is used in quantities comprised between 0.1 and 3% by mole with respect to the said intermediate product. 4. Process according to any of the previous claims, characterised by the fact that the water is added to the intermediate product in quantities such that the ratio by weight of water/intermediate product is comprised between 1:1 and 5:1. 5. Process according to any of the previous claims, characterised by the fact that the oxidising substance is an aqueous solution of hydrogen peroxide in concentrations comprised between 50 and 70% and in quantities of between 100 and 140% of the stoichiometric quantities with respect to the unsaturated fatty acid or ester of the starting materials. 6. Process according to any of the preceding claims, characterised by the fact that the catalyst, belonging to the group consisting of tungsten or molybdenum oxides and their acids and alkaline salts, is present in a quantity comprised between 0.1 and 1.1% by weight with respect to the unsaturated fatty acid or ester of the starting materials. 7. Process according to any of the previous claims, characterised by the fact that it is conducted at a tem¬ perature comprised between 50 and 90°C 8. Process according to any of the previous claims characterised by the fact that the reaction time necessary for the formation of the intermediate product is comprised between 2 and 8 hours while the time necessary for ulterior oxidation of the intermediate product is comprised between 5 and 12 hours. 9. Process according to any of the previous claims, characterised by the fact the starting compound to be oxidised is selected form the group consisting oleic acid, erucic acid, palmitoleic acid, myristoleic acid, 9- decalenic acid, 9-dodecalenic acid, ricinoleic acid, linoleic acid, linolenic acid, or corresponding esters with mono and polyvalent alcohols and mixtures thereof.

Inventors: FOA MARCO, GARDANO ANDREA, SABARINO GIAMPIERO, FOA', MARCO, GARDANO, ANDREA, SABARINO, GIAMPIERO
Applicants: FOA MARCO, GARDANO ANDREA, NOVAMONT SPA, SABARINO GIAMPIERO, FOA', MARCO, GARDANO, ANDREA, NOVAMONT S.P.A., SABARINO, GIAMPIERO
Application year: 1993
Main classification: C07C51
IPC codes: B01J23, C07B61, C07C51, C07C53, C07C55, C07C67