PROPOFOL PURIFICATION

Abstract: Propofol is purified by reaction of the raw 2,6-diisopropylphenol with an alkaline agent, by isolation of the alkaline metal salt and by neutralization thereof. There is thus obtained a propofol having a purity of at least 99.90 %.

Description: PROPOFOL PUR I FI CATI ON The present invention concerns a process for the purification of propofol . Propofol , or 2 , 6-diisopropylphenol , having the formula iε a well known compound which iε largely produced for its use as an antioxydant. Processes for its preparation are described, for instance, in US 2,831,898, US 4,103,096, US 4,208,537, US 4,275,248, US 4,447,657, US 4,538,009, US 4,559,465, JP 62-209034 and SU 443,019. Its use as an anaesthetic for parenteral administration iε described in US 4,056,635 and such an use is become common in surgery. Since propofol is administered by parenteral route, its purity degree must be very high and thus involves fractionated distillations which, on one side, need supplemental apparatus and, on the other side, involves a loss of active principle. European patent application No. 551,947 discloses a method for the purification of propofol by fractionated crystallisation at very low temperature which, according to the disclosure of the cited document, allows the obtention of 60 g of propofol with a purity of at least 99.90% starting from 100 g of propofol having a purity degree of 99.7%. It has now been found that a propofol with a pharmaceutical purity for parenteral administration may be obtained by conversion in one of its alkaline metal salt and by neutralization of pure salt thus isolated. Thus, it is an object of the present invention to provide a process for the purification of propofol which comprises treating the raw product with a base of formula (RO) n -R « wherein R is hydrogen or a straight or branched chain alkyl group, preferably a lower alkyl group of from 1 to 4 carbon atoms, R' is an alkaline or an alkaline-earth metal and n is one or two, depending upon the valence of the metal R' , isolating the εalt thus obtained and converting it into pure propofol by neutralization with an organic or inorganic acid, preferably with a mineral acid. According to the process of the present invention, the εalification of the phenolic hydroxy group is carried out by treatment with an alkaline agent such as sodium or potassium (C-- C.)alkanoate, for example sodium or potassium methylate or ethylate, sodium amide or such as sodium or potassium hydroxide. Preferably, sodium methylate is used. The εalt forming reaction is carried out in a polar solvent, preferably in an alcohol expecially when an alkaline metal alcoholate iε used as an alkaline agent; furthermore, in this case, it iε alεo preferable that the alcohol iε the same as the employed alcoholate. The reaction temperature is of 25÷50°C, preferably of 35÷45°C, and the alkaline metal salt thus obtained iε isolated by evaporating the solvent, taking up the residue with an organic solvent wherein the εalt of 2,6-diisopropylphenol (propofol) thus obtained iε insoluble, and thoroughly washing this salt with the same solvent. Thiε solid product (the alkaline or alkaline-earth metal salt of 2,6-diisopropylphenol) thuε obtained in a pure εtate is neutralized with an organic or inorganic acid and propofol iε isolated by extraction, preferably with toluene, evaporation of the solvent and 3 distillation at about 1.7-10 pascal. The neutralization may be made with a mineral acid, such as hydrogen chloride in aqueous εolution, or with an organic acid, such as methanesulfonic, formic or acetic acid. According to a preferred feature, the raw propofol is treated with sodium methylate in methanol at a temperature of 35÷45°C and, after 3 distilling the solvent at about 2.6-10 pascal, the oily residue is taken up with toluene. In thiε solvent, the εodium 2,6-diisopropyl. phenate separates in a solid εtate whilεt all the impuritieε remain dissolved. Thus, by filtration and washing with toluene, the still wet, pure sodium salt iε iεolated and neutralized with an aqueous solution of hydrogen chloride and pure propofol is iεolated by extraction with toluene and distillation at 98÷100°C and 1.7-10 pascal . The chemical method, which takes advantage of the insolubility of the alkaline or alkaline-earth metal εalt of propofol in the solvent which solubilizes the impurities, allows the recovering of the whole propofol which iε present in the raw material and the obtention of a very pure propofol. The following example illustrates the invention without, however, limiting it. EXAMPLE 1 To 2.4 Kg of methanol, previously cooled to 10÷15°C, 380 g of εodium methylate are added, whereby maintaining the temperature constant by an appropriate cooling and by carrying out the addition portionwise. The solution thus obtained is heated to 35÷45°C and 1.19 Kg of raw propofol (purity 97%) are added thereinto. The εuspension thuε obtained is kept under stirring for 30 minutes at 40÷50°C, then it is diεtilled at about 2.6-10 paεcal up to a residue which is taken up with 3 Kg of toluene. There is obtained a suspenεion which iε εtirred for 30 minutes at 5÷10°C. The sodium 2,6- diiεopropylphenate thus obtained is filtered and washed with anhydrous toluene until it becomes colourless. The product, still wet of toluene, iε added to a solution of 1.3 Kg of 37% hydrochloric acid in 4.5 Kg of water and the propofol iε extracted with 2.7 Kg of toluene at 20÷22°C, at a decidedly acid pH. The organic phase is washed with a 10% aqueouε solution of sodium chloride, then it is diεtilled at about 60°C and at about 2.6-10 pascal until an oil is 3 obtained which, in its turn, iε diεtilled under vacuum (about 1.7-10 paεcal) by eliminating the fraction boiling at 60÷98°C and recovering the product at 98÷100°C. Thus, there iε obtained 1 Kg of pure propofol having the following characteriεticε: appearance: colourless or yellowish oil; purity; > 99.90% (determined by HPLC) ; residual solvents: < 0.1% (determined by G C) .

Claims: CLAIMS 1. A process for the purification of 2,6-diisopropylphenol which comprises treating the raw 2,6-diisopropylphenol with a base of formula (RO) n -R' wherein R iε hydrogen or a straight or branched chain alkyl group, R' is an alkaline or an alkaline-earth metal and n is one or two, depending upon the valence of the metal R' , isolating the εalt thus obtained and converting it into pure propofol by neutralization with an organic or inorganic acid. 2. A proceεε according to claim 1 wherein the baεe uεed haε the formula (Rθ) n -R- in which R is sodium or potassium, R' is a lower alkyl group of from 1 to 4 carbon atoms and n is one. 3. A process according to claim 1 wherein sodium methylate is used as a base and the εalification iε carried out in methanol. 4. A proceεs according to claim 1 wherein the neutralization is carried out with a mineral or organic acid. 5. A proceεε according to claim 4 wherein εaid mineral acid iε an aqueous solution of hydrochloric acid. 6. A procesε according to claim 4 wherein εaid organic acid is selected from the group consiεting of methanesulfonic, formic and acetic acid. 7. A procesε according to claim 1, wherein the obtained alkaline or alkaline-earth metal 2,6-diiεopropylphenate is washed with a solvent in which said εalt iε inεoluble. 8. A proceεs according to claim 7 wherein said solvent is toluene. 9. A process according to claim 1 wherein the isolation of the pure 2,6-diiεopropylphenol iε carried out by distillation at 98÷100°C 3 and the presεure of 1.7-10 paεcal.

Inventors: BELLANI PIERO, VELATI MAURIZIO, BELLANI, PIERO, VELATI, MAURIZIO
Applicants: ARCHIMICA SPA, BELLANI PIERO, VELATI MAURIZIO, ARCHIMICA S.P.A., BELLANI, PIERO, VELATI, MAURIZIO
Application year: 1995
Main classification: C07C37
IPC codes: C07C31, C07C37, C07C39