Process for the preparation of tocol acylates and tocopherol acylates

The present invention relates to a process for the preparation of tocol acylates and tocopherol acylates.

The synthesis of (all-rac)-α-tocopherol acetate starting from acetic anhydride and (all-rac)-α-tocopherol, without a catalyst, in an excess of acetic anhydride has been reported by Surmatis et al., U.S. Pat. No. 2,723,278. The mixture was refluxed for three hours to form the product. The yield was not reported. This reaction can also be carried out in the presence of pyridine (as a catalyst) at room temperature to yield, after a reaction time of three days, 96% (all-rac)-α-tocopherol acetate. See Cohen et al., Helv. Chim. Acta 1981, 64, 1158.

The present invention relates to a process for the preparation of tocol and tocopherol acylates, more particularly tocopherol acetates. The main commercial form of vitamin E being (all-rac)-α-tocopherol acetate, the invention, in a preferred embodiment, provides a process for the preparation of (all-rac)-α-tocopherol acetate. However, other tocopherols can be readily acylated by the process of the present invention. Further, by the process of the instant invention, the tocopherols can be acylated in the form of their racemates or individual enantiomers.

One embodiment of the present invention is a process for preparing tocol acylate or tocopherol acylate having the following steps:

a) combining tocol or tocopherol with an acylating agent to form a reaction mixture;

b) irradiating the reaction mixture with microwave energy to form tocol acylate or tocopherol acylate; and

c) isolating the tocol acylate or tocopherol acylate from the reaction mixture.

Another embodiment of the present invention is a process for preparing tocopherol acylate having the following steps:

a) combining tocopherol and an acylating agent to form a reaction mixture;

b) exposing the reaction mixture to microwave energy at about 600 to about 1200 watts; and

c) recovering the tocopherol acylate from the reaction mixture.

A further embodiment of the present invention is a process for preparing tocol acylate or tocopherol acylate having the following steps:

a) providing a reaction mixture consisting essentially of tocol or tocopherol and an acylating agent;

b) irradiating the reaction mixture with microwave energy to form tocol acylate or tocopherol acylate; and

c) isolating the tocol acylate or tocopherol acylate from the reaction mixture.

In accordance with the present invention it has been found that the acylation of tocol and tocopherols can advantageously be effected under irradiation with microwaves. As compared to prior art processes, the process of the present invention requires shorter reaction time, gives better yield, and has a simpler work-up of the reaction mixture. In particular, the process of this invention does not require external heating of the reaction mixture, thus providing uniform reaction conditions throughout the entire reaction mixture.

The present invention is process for preparing tocol acylate or tocopherol acylate having, the following steps:

a) combining tocol or tocopherol with an acylating agent to form a reaction mixture;

b) irradiating the reaction mixture with microwave energy to from tocol acylate or tocopherol acylate; and

d) isolating the tocol acylate or tocopherol acylate from the reaction mixture.

The present invention also provides a process for preparing tocopherol acylate having the following steps:

a) combining tocopherol and an acylating agent to form a reaction mixture;

b) exposing the reaction mixture to microwave energy at about 600 to about 1200 watts; and

c) recovering the tocopherol acylate from the reaction mixture.

Tocol is the compound 2-methyl-2(4,8,12-trimethyl-tridecyl)-chroman-6-ol. The term “tocopherol” as used herein means all the compounds derived from the basic structure of tocol and having vitamin E character, such as, for example, the tocopherols having a saturated (tocol) side chain, such as α-, β-, γ-, δ-, ζ 2 - and η-tocopherol, and the tocotrienols having three double bonds in the side chain such as ε- and ζ 1 -tocopherol. Of the various tocopherols, (all-rac)-α-tocopherol (generally referred to as vitamin E) is preferred.

The term “microwave” as used herein refers to the region of the electromagnetic spectrum having frequencies of 30 GHz to 300 MHz, thus corresponding to wavelengths of 1 cm to 1 m. In order not to interfere with wavelengths for Radar (1 cm-25 cm), household or industrial microwave heaters are required to operate at either 12.2 cm (2.45 GHz) or 33.3 cm (918 MHz). Thus, in a preferred embodiment of the invention, the term microwaves refers particularly to such wavelengths. In the process of this invention, conventional microwave equipment can be used. Microwave equipment suitable in the process of this invention is readily available, e.g., MLS, Leutkirch, Germany (Lavis Multiquant 1000); or MILESTONE Inc., Monroe, Conn. 06468, USA (Ethos reactors). Conveniently, the irradiation in the process of this invention is carried out by applying a power of irradiation of from about 600 to about 1200 W, more preferably from about 800 to about 1000 W.

The acylation can be carried out using any acylating agent conventionally used for the acylation of a phenolic hydroxy group as is present in tocol and tocopherols, e.g., acyl anhydrides or halogenides. The acyl groups in such acylating agent may be derived from aliphatic carboxylic acids, e.g., from alkanoic acids, in particular C1-7 -alkanoic acids such as acetic acid, propionic acid, butyric acid, or pivalic acid, or higher alkanoic acids, such as palmitic acid; or from aromatic carboxylic acids, e.g., benzoic acid; or araliphatic acids, e.g. phenylacetic acid.

The acylation can be carried out in the presence or in the absence of a catalyst such as an organic base, e.g. pyridine or dimethylamino pyridine, or an organic or inorganic acid, e.g., sulfuric acid or p-toluenesulfonic acid. Advantageously, if a catalyst is used, a volatile catalyst is selected. In a preferred embodiment of this invention, the acylation is carried out in the absence of a catalyst. The acylating agent is suitably used in excess, i.e. in an excess of about 100% over the stoichiometrically required amount. Suitably, the reaction is carried out in an inert atmosphere. The desired tocol acylate or tocopherol acylate can be isolated from the reaction product by conventional means, e.g., by heating the reaction mixture under reduced pressure to remove excess acylating agent and catalyst, if any, and other unwanted products. While the process of the present invention is preferably concerned with the acylation of (all-rac)-tocopherols, particularly (all-rac)-α-tocopherol, the process can also be used to acylate optically pure enantiomers, such as (d-)-α-tocopherol.

The following examples are provided to further illustrate the process of the present invention. These examples are illustrative only and are not intended to limit the scope of the invention in any way.

(All-rac)-α-Tocopherol (52.63g, 95% pure, corresponding to 116 mmol) and acetic anhydride (22.69 ml; 242 mmol) were placed in a flask. Pyridine catalyst (0.31ml, 3.9 mmol) was immediately added to the reaction mixture. The reaction mixture was stirred and irradiated with 800 W or 1000 W microwaves using a LAVIS Multiquant reactor under an inert gas atmosphere (Argon). The reaction product obtained was purified by heating to 70° C. under 25 mbar. The residue was analyzed by gas chromatography (GC) (XTI-5, 30m×0.32 mm, Film 0.25 mm, fused silica; 150° C. (0 min) 5° C./min 335° C. (8 min), He 2.0 ml/min) against an internal standard (1.0 g octacosan in 100 ml n-heptane). The conversion of the tocopherol to its acetate after 5, 10, 20 and 30 minutes is shown in Tables 1 and 2 below. (Deviations in the sum of the percentages from 100 are due to analytical errors.)

When carrying out the above reaction under conventional conditions (no irradiation, heating to 100° C.) 91% of tocopherol acetate and 0% of tocopherol were found in the reaction product after 30 minutes of reaction time.

The acetylation of tocopherol was carried out using the procedure in Example 1, but in the absence of the catalyst (pyridine). The conversion of tocopherol to its acetate after 5, 10, 20 and 30 minutes is shown in Tables 3 and 4 below. (Deviations in the sum of the percentages from 100 are due to analytical errors.)

When carrying out the above reaction under conventional conditions (no irradiation, no catalyst, reflux temperature, reaction time 3.5 hours) the conversion of tocopherol to its acetate proceeded as shown in Table 5 below (Deviations in the sum of the percentages from 100 are due to analytical errors.)

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention and all such modifications are intended to be included within the scope of the following claims.