PROCESS FOR PURIFICATION OF 2,6-DIISOPROPYL PHENOL BACKGROUND OF THE INVENITON Field of the Invention The present invention relates to a process for the purification of 2,6- diisopropyl phenol and more particularly, to the process for the preparation of 2,6-diisopropyl phenol with extremely high purity expressed by formula (1) by treating with firstly an inorganic acid and secondly a base, extracting with a solvent, and purifying by distillation or crystallization at-20--30 °C.

2,6-Diisopropyl phenol (hereinafter referred to as a DIP) expressed by formula (1) is used in anesthesia. US 5,591,311 discloses a purification method of DIP by dissolving the DIP in hydroxide solution followed by heating, neutralizing with an inorganic acid such as sulfuric acid or phosphoric acid, extracting with an organic solvent, and finally purifying by distillation. US 5,175,376 discloses another purification method of DIP by crystallizing at an appropriate temperature with or without using petroleum ether or hexane. US 5,589,598 discloses another purification method of DIP by transformation of the crude DIP into its ester, crystallization and hydrolysis with potassium hydroxide.

However, the above purification methods necessitate using DIP with a purity of higher than 99.0% as a prerequisite to obtain the desired purity of 99.9%. The major contaminants removed during the purification process are 2- isopropylpheonl expressed by formula (2) and 2,4,6-triisopropyl phenol

expressed by formula (3).

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an industrially advantageous method of DIP purification with extremely high purity of 99.99% by using DIP with 90% purity which is synthesized by the method from the present invention.

Detailed Description of the Invention The present invention is characterized in that the raw DIP with over 90% purity is undergoing a series of sequential treatment first with an inorganic acid and second with a base, extraction with a solvent, and purification by distillation or crystallization at-20°C to-30°C.

The present invention is also characterized in that the raw product with over 99% purity is undergoing a series of sequential treatment first with a base and second with an inorganic acid, extraction with a solvent and purification by distillation or crystallization at-20°C to-30°C.

The detailed description of the present invention is given hereunder.

The method of the present invention provides DIP with over 99% of purity by carrying the raw product containing 2-isopropyl phenol expressed by

formula (2) and 2,4,6-triisopropyl phenol expressed by formula (3). This raw product containing side products, (2) and (3), is prepared by reacting phenol with propylene gas in pH below 1.0 under 250-450 psi at high temperature of 200 ~ 300°C.

1-10 N ouf an inorganic acid selected from the group consisting of hydrochloric acid, sulfuric acid and phosphoric acid was added to the mixture of over 90% purity of DIP containing 2-isopropyl phenol and 2,4,6-triisopropyl phenol. This mixture was stirred for 1-3 hours, extracted with an organic solvent and the water was discarded. The organic layer was occasionally washed with water once or twice. The washed organic layer was basified with 1 of a base selected from the group consisting of sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, magnesium hydroxide and aluminum hydroxide to pH 9-12. The mixture was stirred for 1 hours at room temperature. Organic layer was separated from water layer and water residue was removed by extracting with an organic solvent selected from the group consisting of petroleum ether, n-hexane, carbon tetrachloride, chloroform and methylene chloride. The organic layer was dried over Na2S04 and then carried out by fractional distillation or crystallized at-20°C to-30°C to obtain the desired DIP with a purity of 99.99% or above.

Further, DIP with a purity of 99% or above dissolved in a base selected from the group consisting of potassium hydroxide, lithium hydroxide, calcium hydroxide and magnesium hydroxide was adjusted to pH 2-7 with an inorganic acid selected from the group consisting of hydrochloric acid, sulfuric acid and phosphoric acid. Organic layer was separated from water layer and water residue was removed by extracting with an organic solvent selected from the group consisting of petroleum ether and n-hexane. The organic layer was carried out by fractional distillation or crystallized for further purification.

The following examples are intended to be illustrative for the present

invention and should not be construed as limiting the scope of this invention defined by the appended claims.

Example 1 10 of 2N hydrochloric acid was added to 10 of a reactant containing 91.5% (v/v) of DIP, 2.5% (v/v) of 2-isopropyl phenol, 1% (v/v) of phenol and 5 % (v/v) of 2,4,6-triisopropyl phenol and stirred for 1 hour at room temperature. The organic layer separated from the above mixture was then adjusted to pH 10.0 by adding 1N Sodium hydroxide. The mixture was stirred for 1 hour at room temperature and again the organic layer was separated out.

10 of n-hexane was added to the organic layer to remove water residue. The organic layer was dried over Na2SO4 and distilled to give 8.2 (89. 6%) of DIP with a purity of 99.99% or above.

Example 2 After the organic layer obtained from the procedure of Example 1 was dried over Na2S04, it was crystallized at-25°C for 1 day to give 6.5 C (71 %) of DIP with a purity of 99.99% or above.

Example 3 To a reactant same as in Example 1 was added 10 of 2N hydrochloric acid. The mixture was stirred for 1 hour at room temperature. The separated organic layer was basified with 2N sodium hydroxide to pH 9.5, followed by stirring for additional 1 hour. 10 of petroleum ether was added to the separated organic layer to remove water residue. The organic layer was dried over MgS04 and distilled to give 7.95 (86.9%) of DIP with a purity of 99.99% or above.

Example 4 After drying DIP obtained from the procedure of Example 3, it was crystallized at-25°C for 1 day to give 6.2 (M (67.8%) of DIP with a purity of 99.99% or above.

Example 5 To a reactant same as in Example 1 was added 5 of 5N hydrochloric acid. The mixture was stirred for 1 hour at room temperature. The separated organic layer was basified to pH 10.0 with 2N lithium hydroxide, followed by stirring for additional 1 hour. 10Q of n-hexane was added to the separated organic layer to remove water residue. The organic layer was dried over Na2SO4 and distilled to give 7.65Q (83.5%) of DIP with a purity of 99.99% or above.

Example 6 After drying DIP obtained from the procedure of Example 5, it was crystallized at-25°C for 1 day to give 5.75 (62.8%) of DIP with a purity of 99.99% or above.

Example 7 A reactant was purified by the procedure of Example 1 except using 2N magnesium hydroxide instead of 2N sodium hydroxide to give 7.45 (81.3%) of DIP with a purity of 99.99% or above.

Example 8 A reactant was purified by the procedure of Example 1 except using 2N calcium hydroxide instead of 2N sodium hydroxide to give 5.98 (65.3%) of DIP with a purity of 99.99% or above.

Example 9 10 of 99% (v/v) of DIP was adjusted to pH 11.0 by adding 5% of lithium hydroxide. The mixture was stirred for 1 hour at room temperature.

The separated organic layer was adjusted to pH 5.0 with 2N hydrochloric acid. 10Q Of n-hexane was added to the separated organic layer to remove water residue. The organic layer was dried over Na2SO4 and was crystallized at -25°C for 1 day to give 8.5 (85%) of DIP with a purity of 99.99% or above.

Example 10 A reactant was purified by the procedure of Example 9 except using 2N potassium hydroxide instead of 2N sodium hydroxide to give 8.7 (87%) of DIP with a purity of 99.99% or above.

The present invention makes it possible to provide an economically and industrially advantageous method of purifying DIP with extremely high degree of purity unlike conventional methods.