MXPA98004460A - Manufacture of alfa-tocofe - Google Patents

Abstract

A process for the conversion of the non-alpha-tocopherols into alpha-tocopherol by the catalytic permethylation of at least one non-alpha-tocopherol comprising the use of methanol as a methylating agent in the near-critical or super-critical pressure region and temperature, or of a mixture which is equivalent to methanol and which comprises hydrogen and carbon monoxide and / or carbon dioxide, and as a catalyst a mixed oxide catalyst which is produced from hydrotalcites and which contains copper dextrose and magnesium as well as at least one trivalent metal oxide, e.g. aluminum oxide, iron (III) eloxide, vanadium oxide, chromium eloxide and / or rooster eloxide. The non-alpha-tocopherol or the mixture of non-alpha-tocopherols, optionally present in a raw material, which is to be converted to alpha-tocopherol, is preferably dissolved in an inert solvent, eg, a molecular weight alkane medium, a cyclic alkane or an aromatic hydrocarbon. The product of this process has a very high content of alpha-tocopherol, which is the highest value tocopherol from a biological point of view.

Description

DESCRIPTION OF THE INVENTION The present invention relates to a process for the permethylation of so-called "non-to-tocopherols" to α-tocopherol using methanol or an equivalent gas mixture under practically critical or supercritical conditions and using a catalyst special. As it is known, the non-a-tocopherols ß -,? - and d-tocopherol They differ from a-tocopherol, which has the maximum activity of vitamin E and which is the most valuable tocopherol from a biological point of view, due to the absence of one or two methyl groups in position 5 and / or in position 7 of the chroman part of the molecule. Accordingly, there is a need to convert said non-tocopherols into a-tocopherol from a chemical point of view, the main problem being in the effective mono- or, respectively, complete dimethylation of the benzene ring of the substituted chromanyl group. Since the synthetic processes for the manufacture of α-tocopherol of identical nature have proved to be expensive and the natural sources of tocopherols, in particular the plants, generally contain predominantly non-tocopherols in addition to a relatively low content of α-tocopherol. , which is due to the fact that the isolation of a-tocopherol from said natural materials (raw materials) is also expensive, the objective of the present invention is to achieve a process for the conversion of the non-a- REF: 27524 tocopherols, that may be present in the appropriate raw materials or obtained from them, in a-tocopherol, which in many aspects is cheaper than previous processes for this purpose. As far as this object of the invention is concerned, some processes for the conversion of the non-a-tocopherols into α-tocopherol are already known. For example, European Patent Publication (EP) 176 690 (Henkel Corporation) discloses a process for the methylation of non-to-tocopherols "using a methylating agent in the gas / liquid phase and in the presence of a metal oxide catalyst. This is a direct, one-step methylation of the chromic ring, which can be seen as a complete methylation of the tocopherol, ie a permethylation The catalyst used for this purpose has been defined "" functionally "in EP 176 690 in the sense that any catalyst capable of inducing an alkylation reaction can be used, typically, it can be a metal oxide or a mixture of several metal oxides in which the metal atom / s are / are selected / s of groups IIA, IIB, IIIA, IVA, IVB, VB, VIB, VIIB and VIII of the periodic table.The oxides of Be, Mg, Ca, Ti, Zr, V, Mo, Cr, Mn, Tc, Faith, Co, Ni, Zn, Cd, In, Sn, Si, Al, La, Ce, Pr and Nd are considered to be the oxides preferred metallic ones. Said catalysts can be used as such (11 clean) or on an inert carrier material and can be produced in any appropriate way, even in situ. In the case of the in situ production method, for example, a metal salt is introduced into the reactor and then reacted or decomposed to the corresponding metal oxide. Methylation may be effective after the elimination of byproducts and any reactants that have not reacted. According to an example of the "external" production of said catalyst, dry tin hydroxide is added to a solution of ammonium vanadate in aqueous oxalic acid and treated with a solution, also added in activated form, of silicon hydroxide partially polymerized to give a precipitate This is dried, calcined and molded by a press In a later example of EP 176 690, solid titanium dioxide is added to an aqueous mixture of ammonium vanadate and oxalic acid and the new mixture is added. it is heated and dried, then calcined and molded by means of a press, in both cases mixtures of oxides are obtained which, however, can not be crystallographically designed as mixed oxides; rather it is a vanadium oxide on a tin oxide / silicon dioxide or, respectively, a carrier of titanium dioxide. In EP 176 690, there are no data of hydrotalcites or metal hydroxycarbonates similar to hydrotalcite as possible materials containing metals from which metal oxides or mixed oxide catalysts could be manufactured, in addition to catalysts containing copper (copper belongs to group Ib of the periodic table).

In addition, EP 176 690 mentions a temperature range of approx. 390 to approx. 470 ° C as the temperature range especially favorable and environmental pressure (normal) is mentioned as the most preferred pressure. In addition, the use of an excess of methylating agent or of an inert carrier gas, eg nitrogen, but not of an (additional) solvent, is provided. Surprisingly, it has been discovered that this known process of the Henkel Corporation can be decisively improved by a special choice of catalyst and other reaction conditions. The objective of the present invention is a process of conversion of the non-a-tocopherols into α-tocopherol by the catalyzed permethylation of at least one non-α-ocherol using a methylating agent, whose process comprises the use of methanol as a methylating agent , which is in the range of pressure and temperature almost critical or supercritical or a mixture equivalent to methanol formed by hydrogen and carbon monoxide and / or carbon dioxide and the use as a catalyst of a mixed oxide catalyst, which it is manufactured from hydrotalcites and contains at least copper and magnesium oxide as well as at least one oxide of a trivalent metal. As indicated above, the starting material used in the process according to the invention can in principle be a raw material containing at least one non-a-tocopherol, eg the ß-,? - or d- tocopherol, or a mixture of tocopherols which is produced or otherwise obtained from said raw material, and which also contains at least one non-tocopherol. The tocopherol mixture is produced or obtained in some other way, according to methods that have been known for a long time. As it is known, vegetable oils and fats, such as, for example, soybean oil, rapeseed oil, cottonseed oil, peanut oil, wheat germ oil, corn oil , barley oil, rye oil, oil of thistle and the like, are valuable natural sources of tocopherols (among others, of α-tocopherols and of non-α-tocopherols), said oils or preferably their distillates, concentrates and other products, which have a higher content of tocopherols and contain other less desirable components, eg sterols, free and esterified fatty acids, waxes and glycerides, can be used as the starting material in the process according to the invention. However, the presence of sterols and the other components mentioned does not significantly alter the process according to the invention. Thistle oil and soybean oil in particular have proved to be valuable sources of tocopherols, among others, of a-tocopherol and of non-tocopherols to be converted in accordance with the invention. Of course, it is irrelevant that, among others, a-tocopherol is present or not in the educt, since a-tocopherol does not prevent the conversion of non-to-tocopherols into a-tocopherol and it remains unreacted in the process product. The methanol in the almost critical or supercritical region, which is used in the process according to the invention, is methanol which is heated and which is under pressure, that is to say methanol having a pressure of at least about 50 bar. MPa) and a temperature of at least about 240 ° C. In the case of this minimum temperature, the supercritical margin begins with a pressure of about 77.5 bar (7.75 MPa). Naturally, these physical data also correspond simultaneously to the pressures or temperatures at which the process, according to the invention, is carried out in its entirety ("under almost critical or supercritical conditions"). Up to 20% by volume of water to methanol can increase the selectivity of methylation but reduce its speed As an alternative to methanol in the near critical or supercritical situation, a hydrogen mixture can be used in the process according to the invention and carbon monoxide which is equivalent to methanol or the equivalent mixture of hydrogen and carbon dioxide The first mentioned mixture is comfortably a mixture that is basically suitable for the synthesis of methanol, Accordingly, this mixture contains hydrogen and carbon monoxide in the molar ratio of about 2: 1 or greater; it is used in the same pressure and temperature conditions as methanol. The aforementioned mixture "" the equivalent mixture "is also a mixture basically suitable for the synthesis of methanol, in this case, the molar ratio hydrogen: carbon dioxide is about 3: 1 or more and the mixture is also used under the same conditions of pressure and temperature as methanol With respect to the synthesis of methanol from said "equivalent mixtures", reference is made for example to the current Catalysis, Vol. ll. No. 2, pages 173-291, especially pages 230-235 (1991). A particularly suitable equivalent mixture is that which contains both carbon monoxide and carbon dioxide and which, accordingly, can be considered as a combination of both aforementioned gas mixtures. The so-called idrotalcites, from which the mixed oxide catalyst used according to the invention is manufactured, are a known class of isomorphic minerals which occur in nature and which in each case are mixed idroxycarbonates of different metals, for example of magnesium and aluminum or magnesium and iron. The "" hydrotalcite "itself has the chemical formula MgßAl2 (OH) 16CO3, H20 and other minerals having a similar structure are present in their natural state or have been synthesized, such as the sjógrenite and pyroaurite. similar to hydrotalcite, within the scope of the present invention, hydrotalcite and compounds similar to hydrotalcite - of the general formula recognized [M (II)? _ XM (III) x (OH) 2] X + (An-x / n) .mH20, where M (II) and M (III) mean divalent and trivalent metal ions, respectively, An_ means an ion interchangeable and x means 0.1-0.33 - all will be included under the abbreviation "" hydrotalcites. "For the relevant bibliography related to hydrotalcites and their production, basically by coprecipitation, and their use as catalysts, partly as such or well after its calcination to mixed metal oxides, see, among others, Catalysis Today, Vol. 11, No. 2, 173-291 (1991) and the references cited therein, Appl. Catalysis A: General 119, 241 -252 (1991) and ibid., 145, 141-153 and 225-230 (1996). The mixed oxide catalyst produced from the hydrotalcites and used according to the invention contains at least copper oxide and magnesium oxide (both copper as magnesium are divalent metals) as well as at least one oxide of a trivalent metal (referred to below) n "" metal oxide (III) "). The respective metal oxides (III) are preferably aluminum and iron (III) oxides. However, oxides of other divalent and / or trivalent metals may also be present. Examples of other divalent (II) and trivalent (III) metals are beryllium (II), calcium (II), vanadium (III), chromium (HI), manganese (II), iron (II), cobalt (II), nickel (II), zinc (II), gallium (III) and cadmium (II). Preferably, the mixed oxide catalyst only contains aluminum oxide and iron (III) oxide in addition to copper oxide and magnesium oxide. In the mixed oxide catalyst which is prepared from the hydrotalcites and which is used according to the invention the atomic ratio of the divalent metals (total) to the trivalent metal or - where several metal oxides are present (III) - compared to the total of trivalent metals is approx. 2: JL versus approx. 10: 1, preferably 3: 1 versus approx. 4: 1 With respect to the atomic ratio between the divalent metals present (among others, essentially copper and magnesium), the atomic ratio of copper to magnesium and other divalent metals present comfortably amounts to approx. 5:95 to approx. 60:40, preferably at approx. 25:75 in front of approx. 50:50. The atomic ratio between the aluminum preferably present and the iron also preferably present or all the other trivalent metals [Al: other metals (III)] is preferably approx. 2: 1 versus approx. 1: 2, in particular at approx. 2: 1 In addition to the copper oxide essentially present, the magnesium oxide and the metal oxide (s) (III) can be present in the mixed oxide catalyst used according to the invention, lithium oxides, sodium and / or potassium, among others, in an amount that can comfortably be of the order of up to 2% of the total weight of the mixed oxide catalyst. These alkali metals are usually present because alkali metal bases are required for the production or processing of the mixed oxide catalyst and are not completely removed. In principle, the process according to the invention is carried out by passing the non-to-tocopherol, the mixture of several non-to-tocopherols or the raw material containing at least one non-to-tocopherol, in each case. optionally dissolved in an inert solvent, together with the methanol or the equivalent mixture explained in more detail above, under near critical or supercritical conditions (with respect to pressure and temperature), through a reactor charged with the catalyst of mixed oxide, for example, a heated tube loaded with the catalyst. The raw product flowing through the reactor only needs to be separated, eg by distillation, from the gases that give rise to methylation, basically hydrogen and carbon monoxide, as well as excess methanol and some inert solvent residual used. After methylation and gas separation, of the excess methanol, of the solvents etc., the product enriched in a-tocopherol can, if desired, be repeatedly subjected to the process, according to the invention, to obtain a product more enriched in a-tocopherol each time, if the objective of its use considers it necessary, that is, to achieve the degree of conversion required to a-tocopherol. The nature of a catalytic process is such that the desired degree of conversion can also be achieved by lengthening the contact time of the non-to-tocopherol or of the mixture or raw material contained in the catalyst, increasing the amount of catalyst in the catalyst. reactor or decreasing the flow rate of the non-to-tocopherol, the mixture or the raw material used in the reactor. Normally no significant decomposition of the tocopherols occurs during the reaction. When the aforementioned inert solvent is taken into account, it is convenient to use a non-polar organic solvent, preferably an average molecular weight alkane, basically a Cs-io-alkane, eg pentane, hexane or heptane, or mixtures thereof. of them, eg a petroleum ether having a boiling range between 40 ° C and ca. 120 ° C; a cyclic alkane, eg cyclohexane; or an aromatic hydrocarbon, eg toluene. When the no-to-tocopherol, the mixture of several non-tocopherols or the raw material containing at least one non-to-tocopherol to be methylated, is dissolved in an inert solvent - and therefore diluted - the concentration of non-to-tocopherol, of non-to-tocopherols or the content of non-to-tocopherol in the solvent is comfortably from about 10 g / 1 to approx. 500 g / 1, preferably about 100 g / 1 to approx. 500 g / 1. The amount of methanol used as a methylating agent relative to the non-to-tocopherol (s) generally corresponds to at least one equivalent of methylatable (estimated) positions in the non-tocopherol (mixture), appropriately about 10 to 1000 equivalents, preferably about 25 to 250 equivalents. If an equivalent mixture of hydrogen and carbon monoxide and / or carbon dioxide is used as a methylating agent instead of methanol, then the amount of carbon monoxide and / or carbon dioxide will also correspond to a minimum of one equivalent of the positions metilatables (estimated) in the non-a-tocopherol (mixture). Also in this case the amount is comfortably about 10 to 1000 equivalents, preferably about 25 to 250 equivalents.

The rate at which the optionally-diluted non-tocopherol, the no-a-tocopherol mixture or the raw material containing at least one non-tocopherol passes through the mixed oxide catalyst and also the corresponding flow velocity of the methylating agent can be adjusted and correlated with respect to each other, to the amount of catalyst, to the activity of the catalyst, to the reaction temperature and to the reaction pressure, so that the methylation proceeds in the most efficient way possible in terms of the conversion and the duration of the reaction. In this case, the optimum contact times are in the range from 1 to 100 minutes. As mentioned several times, the process according to the invention is carried out in almost critical or supercritical conditions with respect to methanol and the equivalent methylating agent. The critical pressure itself is approx. 77.5 bar (approximately 7.75 MPa) and the critical reaction temperature is approx. 240 ° C. The permethylation is carried out comfortably at pressures between 50 bar and 120 bar (ca. 5 to ca. 12 MPa), preferably at pressures between 70 bar and 90 bar (approx. 7 to approx. 9 MPa), in particular at ca. 80-85 bar (8-8.5 MPa) (at pressures below about 77.5 bar, that is, in the "almost critical" range, a faster reaction occurs, but the dark impurities contained in the raw product are not separated from the reactor and can adversely influence the activity of the catalyst.) Furthermore, an especially high reaction rate is achieved, for example, at about 50 bar (5MPa), all to the detriment of the stability of the catalyst Pressures above 120 bar (12 MPa) reduce the reaction speed and require the use of expensive equipment without providing compensatory advantages.The reaction temperature is conveniently in the range of about 240 ° C to about 350. ° C, preferably in the range of about 280 ° C to 320 ° C. An advantage of the process according to the invention is that there is no recognizable racemization of the optically active centers of the non-to-tocopherols which are going to be permethylates, if a mixture is used of tocopherol from natural sources as educt, the RRR-α-tocopherol having an optical purity of at least 99.5% is typically obtained as a product. During the permethylation, there is no decomposition of the product or the product that is worth highlighting. Another advantage lies in the fact that the catalyst can be used many times, so that, for example, in the case of undesirably low methylation, the product obtained can be reacted again using the catalyst without appreciably reducing the activity of the catalyst. catalyst used repeatedly. In this regard, in general, a large amount of non-to-tocopherols can be methylated with a catalyst without noticeable deactivation of the catalyst. The simplicity of the process and the processing, as well as the high selectivity that can be achieved, make the process according to the invention especially suitable for the large-scale production of α-tocopherol. The present invention is illustrated in the following examples: Example 1 Production of a typical catalyst used according to the invention, and of a typical reactor (laboratory scale) Production: 8 g (20 mmol) of aluminum nitrate, 4 g (10 g) mmol) of iron (III) nitrate, 14 g (60 mmol) of copper (II) nitrate and 15 g (60 mmol) of magnesium nitrate (all as hydrates, ie as the nitrate «9H20, *» 9H2 ?, »3H2? And respectively, * »6H2?) were dissolved in 240 ml of water. The resulting solution was stirred at 90 ° C for 30 minutes in a solution of 30 g (360 mmol) of sodium bicarbonate in 240 ml of water. The mixture was stirred at 90 ° C for another 2 hours. The precipitate was filtered and washed with water until the filtrate gave a neutral reaction. This precipitate in the form of a paste was dried either directly at approx. 120 ° C or was previously molded using a manual syringe resulting in "string-like extrudates" having an I * 5 diameter of about 1.5 mm.The dry catalyst precursor (in the form of fragments or as "extruded ropes-like") was calcined at 250-400 ° C for about 4 hours in the presence of air.The fragments were ground in a mortar, while the "extruded" ones similar to ropes "They broke into pieces of 2-5 mm in length. The catalyst thus produced was introduced into the reactor. Reactor: The reactor consisted of an upright high-pressure tube that was heated by means of a thermostatically controlled oil-heated outer casing. The tube had an inner diameter of 7.8 mm, a heated length of 25 cm and an overall length of about 40 cm. A closed tube on one side and having an external diameter of 3.2 mm occupied the entire length of the reactor and served as a housing for a thermocouple with which the temperature in the longitudinal axis of the entire reactor could be measured. The outlet, which was covered with a filter, was located at the lower end of the reactor. The space between the filter and the start of the heating zone was filled with sea sand. The catalyst was placed on it, giving different bed depths of catalyst according to the amount and density per unit volume. The space on the catalyst bed was empty. The pressure monitor, a fragile disk and the inlet for the educt were located at the upper end of the reactor. Two high-pressure pumps supplied methanol and additional solvent (eg, toluene, hexane, or additional methanol) to the reactor. A liquid stream-usually the upper one-was previously heated. The non-a-tocopherol was mixed as the educt with the unheated stream, so that the adjustment of pure solvent to the solution of the educt could be made. The outlet was connected to a pressure-tight valve with which the pressure in the reactor could be adjusted. From there, the product solution was conducted to a receiver tank. Example 2 A catalyst powder, calcined at 350 ° C and still containing 0.5% sodium, was prepared from a solution of iron (III) nitrates (10 mmol), aluminum (20 mmol), magnesium (60 mmol) and copper (Il) (60 mmol). 1.8 g (3.5 ml) of this catalyst were introduced into the reactor. At 320 ° C, 1.25 ml / min of preheated hexane was pumped into the reactor with the first pump and 0.625 ml / min of methanol with the second. The pressure was adjusted to 100 bar (10 MPa). Then, with the second pump, 3 ml of a methanolic solution containing 1 g of RRR-α-toco-ferol was pumped instead of methanol. Next, more methanol was pumped for 40 minutes to flow the reactor product. The total solution of the product was collected in the receiver tank, evaporated and analyzed by gas chromatography (GC). The evaporation residue contained 86.0% by CG area of α-tocopherol and 3.9% by CG area of β-tocopherol. Further investigations indicated that the optical activity of the educt had been maintained and that at most 1% by weight of the 2S-isomers had been obtained. In another experiment with the same catalyst and under the same conditions (temperature, pressure and flow rates) as the previous one, 3 ml of a methanolic solution containing 1 g of RRR-d-tocopherol was pumped. The solution of the evaporated product contained 53.85% by GC area of α-tocopherol and 21.94% by CG area of β / β-tocopherol. Example 3"" Strip-like exudates ", calcined at 350 ° C, were produced as a catalyst for a solution of nitrates of iron (III) (10 mmol), aluminum (20 mmol), magnesium (60 mmol) and copper (II) (60 mmol) 3.0 g (6 ml) of this catalyst were introduced into the reactor At 300 ° C, 2.25 ml / min of hexane were pumped into the reactor with the first pump and 0.75 ml / min. of methanol / water preheated (9/1 v / v) with the second, the pressure was adjusted to 90 bar (9 MPa), then 9 ml of a solution containing 1 g of RRR-d-tocopherol in hexane were pumped Instead of hexane with the first pump, hexane was then pumped again for about 60 minutes to make the reactor product flow in. All the product solution was collected in the receiver tank, evaporated and analyzed by GC. of evaporation hexane was added to 9 ml and as before it was pumped through the reactor and analyzed.

In this way, the tocopherol was pumped through the reactor a total of eleven times. The analytical results of each of the methylation stages are shown in table i below. Table 1 *: never more detectable. Using 4"" Strip-like exudates ", calcined at 350 ° C, was produced as the catalyst for a solution of nitrates of iron (III) (10 mmol), aluminum (20 mmol), magnesium ( 90 mmol) and copper (II) (30 mmol), 3.0 g (7 ml) of this catalyst were introduced into the reactor at 300 ° C, 3 ml / min of hexane were pumped into the reactor with the first pump and 0.75 ml / min of methanol / water preheated (8/2 v / v) with the second, the pressure was adjusted to 90 bar (9 MPa), then 9 ml of a solution containing 1 g of RRR-d - Tocopherol in hexane was pumped in place of hexane with the first pump, then hexane was pumped again for about 60 minutes to flow the reactor product in. All the product solution was collected in the receiver tank, evaporated and analyzed by GC, the evaporation residue was brought up to 9 ml with hexane and, as before, it was pumped through the reactor and analyzed. Octooferol was pumped through the reactor a total of six times. The analytical results of each of the methylation steps are shown in Table 2 below. Table 2 *: never more detectable Example 5 A catalyst powder, calcined at 400 ° C, was produced from a solution of iron (III) nitrates (10 mmol), aluminum (20 mmol), magnesium (60 mmol) and copper (II) (60 mmol). 3.95 g (9 ml) of this catalyst were introduced into the reactor. At 320 ° C, 9 ml / min "of preheated hexane was pumped into the reactor with the first pump and 2.8 ml / min of methanol with the second, the pressure was adjusted to 90 bar (9 MPa), then 10 ml of a methanolic solution that contained 2.5 g of a non-to-tocopherol concentrate (educt), of which only about half was made up of tocopherols, was pumped instead of methanol with the second pump. Next, more methanol was pumped for about 60 minutes with the second pump to flow the product through the reactor. The collected product solution was evaporated and analyzed by GC (product 1). In a second experiment (as above), 10 ml of a methanolic solution containing 1 g of the no-a-tocopherol concentrate (educt) described above, was pumped instead of methanol with the second pump. Then more methanol was pumped for about 60 minutes with the second pump to make the reactor product flow. The collected product solution was evaporated and analyzed by GC (product 2). The results are summarized in table 3 below: Table 3 *: not detectable **: not measured In another experiment with this catalyst, 5 ml / min of hexane preheated to 320 ° C were pumped into the reactor with the first pump and 2 ml / min of methanol with the second. The pressure was adjusted to 90 bar (9 MPa). Then, with the second pump 100 ml of a methanolic solution containing 1 g of d-tocopherol, instead of methanol, was pumped. The product solution was collected separately every 6.5 minutes (corresponding to 12.5 ml of educt solution), evaporated and analyzed by GC. The results are summarized in table 4 below: Table 4 Eiempl? 6 Extruded "rope-like extrudates" were manufactured, calcined at 350 ° C, as the catalyst for a solution of iron (III) nitrates (10 mmol), aluminum (20 mmol), magnesium (60 mmol) and copper (II). ) (60 mmol) 3.0 g (7 ral) of this catalyst were introduced into the reactor At 300 ° C, 1 ml / min of hexane was pumped into the reactor with the first pump and 3 ml / min of methanol / water preheated (9/1 v / v) with the second, the pressure was adjusted to 85 bar (8.5 MPa), then 3 ml of a solution containing 0.5 g of RRR-d-tocopherol (educt) in hexane instead of hexane with the first pump. Next, more hexane was pumped for about 60 minutes to flow the reactor product. All the product solution was collected in the receiver tank, evaporated and analyzed by GC (% area method). The evaporation residue was again brought up to 3 ml with hexane and, as before, was pumped through the reactor and analyzed. In this way, the tocopherol was pumped through the reactor a total of eleven times. After the last "pass" there were still 0.4 g of product, since eleven analytical samples, each of 5-10 mg, had to be removed from the reaction mixture. The analytical results of the individual methylation steps are collected. in the following table 5: Table 5 *: never more detectable In another experiment with this catalyst, 2.5 ml / min of methanol / toluene mixture (4/1 v / v) preheated to 320 ° C was pumped into the reactor with the first pump and 0, 5 ml / min of toluene with the second. The pressure was adjusted to 85 bar (8.5 MPa). Then, 210 ml of a solution containing 7.089 g of non-a-tocopherol was pumped in place of toluene with the second pump. After this product solution had been pumped it was replaced again by toluene for 1 hour to make the product flow in its entirety from the reactor. The collected product solution evaporated. The product and the product were weighed and analyzed accurately. The following summary (table 6) confirms that practically all tocopherol had been converted to RRR-a-tocopherol without any significant decomposition.

Table 6 Another container of the previous 3 g catalyst (6 ml) was introduced into the reactor. At 270 ° C, 1 ml / min was pumped into the reactor with the first pump and 2 ml / min of preheated methanol with the second. The pressure was adjusted to 85 bar (8.5MPa). Then 5 solutions were pumped in succession, each of which had 30 ml and contained 0.5 to 8 g (see table) of non-tocopherol concentrate, instead of toluene, with the first pump. More toluene was pumped between the tocopherol solutions for about 30 minutes to make the reactor product flow. Once the individual solutions of tocopherol had been pumped, a product sample was extracted and analyzed by GC (area percentage method). The results mentioned in table 7 below show a clear conversion to α-tocopherol, which depends on the reactor load and consequently the time of presence or passage through it.

In another series of experiments, 1 ml / min of toluene was pumped into the reactor at 300 ° C with the first pump and 2 ml / min of preheated methanol with the second. The pressure was adjusted again to 85 bar (8.5 MPa).

Then another 5 solutions, each of 30 ml and containing 0.5 to 8 g (see table) of non-tocopherol concentrate in toluene, were pumped instead of toluene with the first pump. More toluene was pumped between the tocopherol solutions for about 30 minutes to make the reactor product flow. After each of the tocopherol solutions had been pumped, a sample of the product was extracted and analyzed by GC (% per area method). The results mentioned in table 8 below show again a clear conversion to α-tocopherol, which depends on the reactor load and the residence time in it. That is to say, this series demonstrates, in comparison with previous series, that at a higher temperature a greater conversion occurs in similar conditions. Table 8 It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, property is claimed as contained in the following:

Claims (7)

1. CLAIMS 1. A process for the conversion of non-to-tocopherols into α-tocopherol by catalytic permethylation of at least a non-tocopherol with a methylating agent, the process is characterized because it consists of the use of roethanol as a methylating agent in the almost-critical or super-critical region of pressure and temperature, or of a mixture that is equivalent to methanol and which "comprises hydrogen and carbon monoxide and / or carbon dioxide, and as a catalyst a mixed oxide catalyst produced from hydrotalcites and containing at least copper and magnesium oxide as well as less an oxide of a trivalent metal 2. A process according to claim 1, characterized in that the aluminum oxide, the iron oxide (III), the vanadium oxide, the chromium oxide and / or the oxide of gallium, preferably the aluminum oxide and / or the iron oxide (IIU) are used as the oxide (s) of a trivalent metal 3. A process according to the reification io with claim 2, characterized because in the oxide catalyst mixed the atomic proportion of the divalent metals (total) versus the total amounts of trivalent metals is approx. 2: 1 to 10: 1, preferably of approx. 3: 1 to 4: 1, and the atomic ratio of copper to magnesium and other divalent metals present is approx. 5: 95 to 60: 40, preferably from 25: 75 to 50: 50. Four . A process according to any of claims 1 to 3, characterized in that the alumino oxide, the Merro oxide and optionally the oxides of other trivalent metals are present in the mixed oxide catalyst and the atomic ratio between the aluminum and the iron or between the aluminum and all the other trivalent metals is approx. 2: 1 to 1: 2, especially 2: 1. 5. th proae ** »of acuescb with aJ ßatde the reivipdicaaaes 1 to 4, Gara ± erizai) because the non-to-tocopherols that have to be converted into α-tocopherol, optionally present in a raw material, are dissolved in an inert solvent, said inert solvent being an average molecular weight alkane, preferably a C5-IO -alkan, eg, pentane, hexane or heptane , a mixture of C5 -.10-alkanes, eg petroleum ether having a boiling range between 40 ° C and 120 ° C; a cyclic alkane, eg the exano cycle; or an aromatic hydrocarbon, eg toluene. 6. A process according to any of claims 1 to 5, characterized in that the amount of methanol or the amount of carbon monoxide and / or carbon dioxide in a mixture, equivalent to methanol, used as a methylating agent with respect to the non-tocopherols. corresponds to approx. 10 a 1000 equivalents, preferably about 25 to 250 equivalents, of the methylatable positions in the non-α-tocopherol (mixture). 7. A process according to any of claims 1 to 6, characterized in that the permethylation is carried out at a pressure comprised between 50 bar and 120 bar (approx. 5 to 12 MPa), preferably between 70 bar and 90 bar (approx. 7 to 9 MPa), in particular at about 80-85 bar (about 8-8.5 MPa) and at a reaction temperature in the range of about 240 ° C to 350 ° C, preferably in the range of 280 ° C. C at 320 ° C. SUMMARY OF THE INVENTION A process for the conversion of non-to-tocopherols to α-tocopherol by the catalytic permethylation of at least one non-to-tocopherol comprising the use of methanol as a methylating agent in the quasi-critical or super-atomic region. -pressure and temperature criticism, or of a mixture that is equivalent to methanol and that comprises hydrogen and carbon monoxide and / or carbon dioxide, and as a catalyst a mixed oxide catalyst that is produced from the hydrotalcites and which contains at least copper and magnesium oxide and at least one oxide of a trivalent metal, for example aluminum oxide, iron (III) oxide, vanadium oxide, chromium oxide and / or the gallium oxide. The no-a-tocopherol or the non-tocopherol mixture, optionally present in a raw material, which is to be converted to α-tocopherol, is preferably dissolved in an inert solvent, eg a medium molecular weight alkane, a cyclic alkane or an aromatic hydrocarbon. The product of this process has a very high content of a-tocopherol, which is the highest value tocopherol from a biological point of view.