PROCESS FOR SYNTHETIZING POLYOXYALKYLENEGLYCOL-MONO-ETHERS

Abstract: Polyoxyalkylene-glycol-monoethers containing a desired number of oxyalkylene units are prepared by starting from a linear or branched aliphatic alcohol, preferably a primary linear aliphatic alcohol, or from a mono-hydroxy phenol, preferably bearing alkyl-­ substituents on its ring, and mono-halogenated linear oxyalkylene glycols, wherein the halogen is in a terminal position and the hydroxy group is protected by known means, under basic conditions, with polyoxyalkyleneglycol-monoethers being obtained, which contain a protected hydroxy group, from which the protecting group is removed by means of a treatment under acidic conditions, thus the desired product being obtained, which is useful as a non-ionic surfactant, in particular in the cosmetic and/or pharmaceutical field.

Description: The present invention relates to a process for synthetizing polyoxyalkyleneglycol-monoethers and to the products obtained by means of such a process, which find important uses as non-ionic surfactants in the cosmetic and/or pharmaceutical field. The synthesis of polyoxyalkyleneglycol-monoethers containing a predetermined number of oxyalkylene units is a target which the chemistry of surfactants aimed at, in order to obtain non-ionic surfactants endowed with controllable properties. The prior art relating to non-ionic surfactants of ethoxylated type carries out the ethoxylation of the feedstock molecule by means of ethylene oxide, but in this way a random distribution of ethylene oxide units is obtained, and the product only containing the desired number of ethylene oxide cannot be obtained as the only product. In the field of the synthesis of polyoxyalkyleneglycol-monoethers, the present Applicant is aware of the works by Y. Abe and S. Watanabe (Fette, Seifen, Anstrichtmittel, 74 , No. 9, 1972, pages 534-537). According to the procedure followed by Abe and Watanabe, an alcohol or a phenol is reacted with potassium metal with the consequent formation of the corresponding potassium alkoxide or phenate. This latter is then reacted with mono-chloro oxyalkylene-glycol, with the monoether being obtained. The procedure followed is clearly unsuitable for an industrial production, in that metal potassium is not easy to handle from an industrial standpoint. The present Applicant has surprisingly found now, and this is the object of the present invention, that polyoxyalkyleneglycol-monoethers can be prepared in a simple and cheap way, with the drawbacks of the prior art being overcome, by using mono-halo-oxyethylene-glycols with the halogen in a terminal position, and the hydroxy group being protected by known means. A first object of the present invention is a process for the synthesis of polyoxyalkyleneglycol-monoethers which comprises reacting a linear or branched aliphatic alcohol, preferably a primary linear aliphatic alcohol or a ― preferably alkyl-substituted or alkoxy-substituted ― mono-hydroxy-phenol, having the general formula R-OH wherein: R is an alkyl radical containing a number of carbon atoms comprised within the range of from 6 to 20, or a phenyl radical, preferably bearing alkyl-substituents or alkoxy-substituents with a number of carbon atoms comprised within the range of from 1 to 10, or the product of general formula (4), with a linear mono-halo-oxyalkylene glycol having the residual hydroxy group protected by means of a protecting agent, having the general formula Ha-(CH₂) n -(CH₂-O-CH₂) m -(CH₂) n -O-PR wherein: Ha is a halogen selected from Cl, Br, I; PR is a protecting group for the terminal hydroxy; and n and m are integers, either equal to, or different from, each other, having values respectively comprised within the range of from 1 to 2 and of from 1 to 5. The protecting group PR is a hydroxy-protecting group and is selected in particular from ― tetrahydropyranyl, ― 4-methoxy-tetrahydro-pyranyl, ― 4-methoxy-tetrahydro-thio-pyranyl groups, respectively deriving from: ― 3,4-dihydro-2H-pyran, ― 4-methoxy-2,3-dihydro-6H-pyran and ― 4-methoxy-2,3-dihydro-thio-6H-pyran. The reaction is carried out in the liquid phase in the presence of a base preferably selected from NaOH and KOH. The reaction product, having the general formula R-O-(CH₂) n -(CH₂-O-CH₂) m -(CH₂) n -O-PR wherein n and m have the above stated values, is submitted to an alcoholysis at room temperature under acidic conditions, preferably with methanol, and an acidic ion-exchange resin, with said resin preferably, but not limitedly, being a sulphonated styrene-divinylbenzene resin, in particular the commercial resins known on the market under the trade marks Amberlyst 15 by Rohm and Haas and Lewatit P108 by Bayer. The de-protected product according to the present invention, having the general formula R-O-(CH₂) n -(CH₂-O-CH₂) m -(CH₂) n -O H wherein n and m have the above stated values, is filtered off from the resin and can be used as surfactant according to the invention or, if so preferred, can be used as the raw material instead of said compound of formula (1) if the number of oxyalkylene glycol units has to be further increased. The temperature at which the reaction between the compound of general formula (1) and the compound of general formula (2) is carried out is preferably selected within the range of from 80°C to 110°C, and the pressure is preferably the atmospheric pressure. The base is preferably used in an equimolecular amount relatively to the compound of general formula (2). The number of H⁺ milliequivalents of the resin used in the step of removal of the protecting group is equal to that of the compound of formula (3), but a lower number, down to half thereof, can be used as well. In order to obtain the product having the general formula (2), the procedure followed consists in reacting under anhydrous conditions, in the presence of a halogenated solvent, at a temperature comprised within the range of from 10°C to 50°C, and preferably at a temperature comprised within the range of from 20°C to 40°C, a monohalogenated alkoxy-glycol (formula (2) with a terminal ―OH in place of the ―OPR group) with a hydroxy-protecting agent preferably selected from: ― 3,4-dihydro-2H-pyran, ― 4-methoxy-2,3-dihydro-6H-pyran, and ― 4-methoxy-2,3-dihydro-thio-6H-pyran, for a time comprised within the range of from 1 minute to 30 minutes, and in distilling the protected compound (2) of from the halogenated solvent. Some examples are given now in order to better explain the invention, it being understood that the same invention is not to be construed as being limited by them or to them. Example 1 Synthesis of 2-(2-Chloroethoxy)-tetrahydropyranyl-ethanol (Compound of general formula (2)) To a reaction flask containing 15 g (120 mmol) of 2-(2-chloro-ethoxy)-ethanol dissolved in 30 ml of methylene chloride, 12 g (143 mmol) of 3,4-dihydro-2H-pyran dissolved in 25 ml of methylene chloride is added dropwise (addition time = 30 minutes). The reaction is exothermal (initial temperature = 17°C, end temperature = 37°C) and results practically complete after 10 minutes of the end of the addition. The raw reaction product, concentrated under reduced pressure supplies, after distillation, 23 g (yield 92%) of chemically pure 2-(2-chloroethoxy)-tetrahydro-pyranyl-ethanol. Example 2 Synthesis of [2- 2-(2-Chloroethoxy)-ethoxy]-tetrahydropyranyl-ethanol (Compound of general formula (2)) The reaction is carried out at room temperature by a procedure analogous to that as reported for the synthesis of 2-(2-chloroethoxy)-tetrahydro-pyranyl-ethanol, and is complete after 30 minutes of the end of the addition of 3,4-dihydro-2H-pyran. By starting from 105 g (623 mmol) of 2-[2-(2-chloroethoxyl-ethoxy]-ethanol (dissolved in 150 ml of methylene chloride) and from 63 g (750 mmol) of 3,4-dihydro-2H-pyran (dissolved in 100 ml of methylene chloride), after distillation 135 g of chemically pure 2-[2-(2-chloroethoxy)-ethoxy]-tetrahydro-pyranyl-ethanol were obtained (yield 86%). Example 3 Synthesis of dioxyethyleneglycol-monododecylether CH₃-(CH₂)₁₀-CH₂-O-CH₂-CH₂-O-CH₂-CH₂-OH A mixture of 16.80 g (80 mmol) of 2-(2-chloroethoxy)-tetrahydropyranyl-ethanol, 3.22 g (80 mmol) of sodium hydroxide powder and 0.36 cc of water is dipped, while is being mechanically stirred, into an oil bath (pre-heated at 115°C) and to it 5.01 g (27 mmol) of 1-dodecanol is added dropwise (addition time = 10 minutes). Eight hours later, the reaction mixture is cooled to room temperature, to it 20 ml of water and 200 ml of ethyl acetate are added. The organic phase is separated from the aqueous phase and this latter is extracted with a further 100 ml of ethyl acetate. The combined organic extracts are dried over anhydrous sodium sulphate, are concentrated under reduced pressure, are then diluted with methyl alcohol (50 ml) and to them 4 g of Amberlyst 15 resin is added. After a 1-hour stirring at room temperature, the suspension is filtered, concentrated under reduced pressure and is distilled; 3.70 g of product is obtained (yield 50%). Example 4 Synthesis of tetraoxyethyleneglycol-monododecylether CH₃(CH₂)₁₀-CH₂-O-CH₂CH₂-O-CH₂CH₂-O-CH₂CH₂-O-CH₂CH₂-OH The reaction was carried out on 6.85 g (33 mmol) of 2-(2-chloroethoxy)-tetrahydropyranyl-ethanol, 1.31 g (33 mmol) of sodium hydroxide powder, 0.16 ml of water and 3.00 g (11 mmol) of dioxythyleneglycol-monododecylether. After a 4-hour heating at 90°C, the reaction product is hydrolyzed and extracted with ethyl acetate as usual. The organic extracts are combined, dried over anhydrous sodium sulphate, concentrated under reduced pressure and to them 2.34 g of Amberlyst 15 resin is added, after being preliminarily diluted with 50 ml of methyl alcohol. After 2 hours at room temperature, the suspension is filtered, concentrated under reduced pressure and distilled; 2.80 g (yield 70%) of desired product is obtained. In an analogous reaction carried out by starting from a mixture consisting of 10 g (48 mmol) of 2-(2-chloroethoxy)-tetrahydropyranyl-ethanol, 1.92 g (48 mmol) of sodium hydroxide powder, and 4.38 g (16 mmol) of dioxythyleneglycol-monododecylether, 4.34 g of tetraoxyethyleneglycol-monododecylether was obtained (yield 75%). Example 5 Synthesis of hexaoxyethyleneglycol-monododecylether CH₃-(CH₂)₁₀-CH₂-(O-CH₂-CH₂)₆-OH The reaction was carried out on 8.76 g (42 mmol) of 2-(2-chloroethoxy)-tetrahydropyranyl-ethanol, 1.68 g (42 mmol) of sodium hydroxide powder, 0.19 ml of water and 5.00 g (14 mmol) of tetraoxyethyleneglycol-monododecylether. After 5 hours of heating at 110°C, the mixture was hydrolyzed and extracted with ethyl acetate, as usual. The combined organic extracts, after being dried over anhydrous sodium sulphate and concentrated under reduced pressure, were diluted with methyl alcohol (60 ml) and to them 4 g of Amberlyst 15 resin was added. After 2 hours at room temperature, the suspension was filtered, and concentrated under reduced pressure; 47 g of hexaoxyethyleneglycol-monododecylether (yield 75%) was obtained. Example 6 Synthesis of hexaoxyethyleneglycol-monooctylether CH₃-(CH₂)₆-CH₂-(O-CH₂-CH₂)₆-OH The reaction was carried out on 10.22 g (49 mmol) of 2-(2-chloroethoxy)-tetrahydropyranyl-ethanol, 1.96 g (49 mmol) of sodium hydroxide powder, 0.2 ml of water and 5.00 g (16 mmol) of tetraoxyethyleneglycol-monooctylether. After 7 hours of heating, the mixture was treated as hereinabove reported. The combined organic extracts were diluted with methyl alcohol (70 ml), to them 4 g of Amberlyst 15 resin was added, and the whole mixture was kept stirred at room temperature for 2 hours. It was then filtered, concentrated under reduced pressure and distilled. 4.6 g (yield 73%) of the desired product was obtained.

Claims: 1. Process for the synthesis of polyoxyalkyleneglycol-monoethers by starting from a linear or branched aliphatic alcohol, preferably a primary linear aliphatic alcohol or a mono-hydroxy-phenol, preferably alkyl-substituted or alkoxy-substituted, having the general formula R-OH wherein: R is an alkyl radical containing a number of carbon atoms comprised within the range of from 6 to 20, or a phenyl radical, preferably bearing alkyl-substituents or alkoxy-substituents with a number of carbon atoms comprised within the range of from 1 to 10, characterized in that the product of formula (1) is reacted with a linear oxyalkylene glycol mono-halogenated in a terminal position, having the residual hydroxy group protected by means of a protecting agent, having the general formula Ha-(CH₂) n -(CH₂-O-CH₂) m -(CH₂) n -O-PR wherein: Ha is a halogen selected from Cl, Br, I; PR is a protecting group; and n and m are integers having values respectively comprised within the range of from 1 to 2 and of from 1 to 5, the reaction being carried out in the liquid phase in the presence of a base, the reaction product, having the general formula R-O-(CH₂) n -(CH₂-O-CH₂) m -(CH₂) n -O-PR wherein n and m have the above stated values, is submitted to an alcoholysis at room temperature under acidic conditions, with methanol, and an acidic ion-exchange resin, and the de-protected product having the general formula R-O-(CH₂) n -(CH₂-O-CH₂) m -(CH₂) n -O H wherein n and m have the above stated values, is filtered off from the resin. 2. Process according to claim 1, characterized in that PR in the above general formula (2) represents a hydroxy-protecting group and is selected in particular from ― tetrahydropyranyl, ― 4-methoxy-tetrahydro-thio-pyranyl groups ― 4-methoxy-tetrahydro-pyranyl. 3. Process according to claim 1, characterized in that the base is in an equimolecular amount relatively to the compound of general formula (2). 4. Process according to claim 1 or 3, characterized in that the base is selected from KOH and NaOH. 5. Process according to claim 1, characterized in that the acidic ion-exchange resin has a number of H⁺ milliequivalents equal to that of the compound of formula (3), or lower than that, down to the half. 6. Process according to claim 1 or 5, characterized in that the acidic ion-exchange resin is a sulphonated styrene-divinyl-benzene resin. 7. Process according to claim 1, characterized in that the reaction of the compound of general formula (1) with the compound of general formula (2) is carried out at a temperature comprised within the range of from 80°C to 110°C, with the pressure preferably being the atmospheric pressure. 8. Process according to claim 1, characterized in that the compound of general formula (4) replaces the compound of general formula (1) in the reaction with the compound of general formula (2). 9. Process according to claim 1, characterized in that the product having the general formula (2) is obtained by reacting under anhydrous conditions, in the presence of a halogenated solvent, at a temperature comprised within the range of from 10°C to 50°C, and preferably at a temperature comprised within the range of from 20°C to 40°C, a halogenated alkoxy-glycol of formula Ha-(CH₂) n -(CH₂-O-CH₂) n -(CH₂) n -OH wherein n and m have the above stated values, with a hydroxy-protecting agent for a time comprised within the range of from 1 minute to 30 minutes, and distilling the compound (2) off from the halogenated solvent. 10. Process according to claim 9, characterized in that the hydroxy-protecting agent is selected from 3,4-dihydro-2H-pyran, 4-methoxy-2,3-dihydro-6H-pyran and 4-methoxy-2,3-dihydro-thio-6H-pyran.

Inventors: TINUCCI, LAURA
Applicants: ENIRICERCHE S.P.A.
Application year: 1988
Main classification: C07C43
IPC codes: C07C43, C07C41