GB2119373A - Production of ethylene glycol monoaryl ethers - Google Patents

Abstract

Ethylene glycol monoaryl ethers useful as fragrance chemicals are obtained by the process of this invention whereby a phenol containing an alkali metal borohydride and alkali metal hydroxide is monoethoxylated. Ethylene glycol monophenyl ether having a consistent mild rose odor profile and free of undesirable metallic notes is obtained by the present process.

Description

SPECIFICATION Production of ethylene glycol monoaryl ethers The present invention relates to an improved processforthe monoethoxylation of phenols wherebyfragrancequalityethyleneglycol monoaryl ethers, such as ethylene glycol monophenyl ether, are produced.

Ethylene glycol monoaryl ethers are known. These compounds are usually obtained by reacting phenol with ethylene oxide in the presence of an alkaline catalyst. Processes utilizing a variety of basic catalysts such as ammonia, urea, amides, hydroxides and phenates of sodium and lithium, potassium hydroxide and the like are described in U.S. Patent Nos. 2,852,566,3,354,227, 3,364,267,3,525,773, 3,642,911 and 3,644,534.

Whereas products obtained by such processes are suitable for most commercial applications they are notcompletely acceptablefor use in cosmetic preparations and fragrances due to the presence of an objectionable pungent "metallic" odor. ethylene glycol monophenyl ether obtained by such processes, for example, cannot be utilized in cosmetic preparations or as a solvent and fixative for perfumes withoutfurther purification since the undesirable metallic note masks the pleasant odor of the ethylene glycol monophenyl ether and anyotherfragrance chemicals employed therewith.Even when the ethylene glycol monophenyl ether is carefully distilled afterethoxylationto obtain high puritywater- white product essentially free of catalyst residue, unreacted phenol and higher ethylene oxide adducts, the undesirable metallic note is still not completely removed.

In West German Offenlegungschrift 3221170 a post-treatment procedure whereby ethylene glycol monophenyl ether is contacted with sodium borohydride to eliminate the undesirable metallic note and thus obtain a highly useful fragrance grade ethylene glycol monophenyl ether is disclosed. Treating with sodium borohydride also generally obviates the need for distilling the product.

The post-treatment of polyethoxylated products (having 3to 80 moles ethylene oxide condensed therewith) with sodium borohydride to improve color is reported in the technical literature of Ventron Corporation Chemicals Division in a brochure entitled "Hydride Chemicals for Process Stream Purification." It is also suggested that another method oftreatment ofthepolyethoxylateswould betoaddthesodium borohydridewith the caustic used as a catalystforthe condensation to prevent the darkening that normally occurs during reaction. Asimilarprocedure is sug gested for the production of ethoxylated fatty alcohol surfactants in PROCESS STREAM PURIFICATION NEWSLETTER, December1979, Issue No.3, pub lished byThiokolNentron Division. All of the above procedures deal with the treatment or manufacture of polyethoxylates and there is no indication that fragrance quality ethylene glycol monoaryl ethers be obtained by similar methods.

We have now unexpectedly discovered thatfragrance grade ethylene glycol monoaryl ethers can be obtained bya process in which a phenoliccompound is monoethoxylated in the presence of alkali metal hydroxide and alkali metal borohydride. Quite surprisingly, in addition to obtaining product suitable for fragrance applications and wherein most or all of the undesirable metallic note typically associated with such products is eliminated it has further been observed that the rate of reaction may be enhanced and, in some instances, the yield of monoethoxylate increased.

The process preferably involves reacting essentially one molar equivalent ethylene oxide with a phenol maintained art a temperature above its melting point to which has been added from 0.01 to 1 weight percent alkali metal hydroxide and 0.01 to 1 weight percent alkale metal borohydride. The phenols may be of to the formula

where R' and R" are independently H or alkyl, alkenyl or alkoxy group having from 1 to 8 carbon atoms. The process is particularly adaptable for use with phenol and monosubstituted phenols wherein the substituent has from 1 to 4 carbon atoms. Suitably, 0.05 to 0.5 weight percent lithium hydroxide, sodium hydroxide or potassium hydroxide is employed with 0.05 to 0.5 weight percent sodium borohydride.Preferably the monoethoxylation is carried out at a temperature from 11 00C. to 130"C. and pressure from about 1 psi to 50 psi. The process is particularly adaptable for the preparation of ethylene g lycol monophenyl ether useful in cosmetic and fragrance applications.

In an especially useful embodiment of this inven tiontheethyleneglycol monoaryl ether obtained by the above process is steam sparged by the introduction of (e.g. up to about 1 0wt. percent) water. The water is introduced subsurfacely and dispersed into the ethylene glycol monoaryl ether which is maintained at an elevated temperature and reduced pressure. Suitably 0.5 to 5 wt. percent water is employed for the sparging while maintaining the ethyleneglycol monoaryl etheratatemperature of 75" C. to 1200 C. and pressure less than 100 mm Hg.

Instead or additionally, the pH ofthe ethylene glycol monoaryl ether may be lowered, e.g. to about pH 6.5-7.5, by the addition of a suitable inorganic or organic acid thereto. Di- and higherpolycarboxylic acids and hydroxy acids, particularly citric acid, whose salts are insoluble in the ethylene glycol monoaryl ether product and which therefore may be readily removed by filtration are especially useful for this purpose. Neutralized ethylene glycol monoaryl ethers may also be stam sparged with a view to obtaining fragrance grade products having consistent odor profiles and which are free of any metallic odor.

The improved process of this invention forthe preparation ofethylene glycol monoaryl ethers may comprise combining an alkali metal hydroxide and alkali metal borohydride with a phenol maintained at a temperature above its melting point and then reacting with essentially one molar equivalent ethylene oxide at a temperature from about 1000 C. to 150 and pressure from atmospheric up to 1000 psi. In some embodiments ofthe invention the resulting ethylene glycol monoaryl ether is then neutralized and, depending in the acid employed forthe neutralization, may be filtered to remove insoluble acid salts which are formed; additionally or instead the process may involvethe step of sparging the ethylene glycol monoaryl etherwith steam.

Is should be noted that phenols having substituents in the ortho ring position will react more slowlythan other substituted phenols. Illustrative phenols which can be monoethoxylated in accordance with this invention are phenol, cresol, ethyl phenol, methoxy phenol, t-butyl phenol, di-methyl phenol, chavicol and the like.

For the process, 0.01 weight percent upto 1 weight percent, based on phenol, alkali metal hydroxide and 0.01 to 1 weight percent, based on phenol, alkali metal borohydride may be combined with the phenol priorto introducing the ethylene oxide. The alkali metal borohydride preferably employed is sodium borohydride, but other alkali metal borohydrides such as lithium borohydride and potassium borohydride can be utilized in the process. Most preferably, 0.05to 0.5 weight percent each of alkali metal hydroxide and alkali metal (e.g. sodium) borohydride are utilized. Suitable alkali metal hydroxides include lithium hydroxide, sodium hydroxide and potassium hydroxide.

To facilitate addition of the alkali metal hydroxide and alkali metal borohydride,the phenol may be in a molten state, e.g. atanytemperatureabove its melting point up to the temperature at which the ethoxylation reaction isto be carried out. In the usual practice the alkali metal hydroxide and sodium borohydrideare charged to the reactor containing the phenol while it is being raised to the reaction temperature.

The alkali metal hydroxide and borohydride may be added in anyorderorthey may be added simultaneously. The exact nature of the resulting specie is not known, but it is believed to be a mixture of alkali metal and boron phenolateswhich results from the reactionlinteraction of the alkali metal hydroxide and alkali metal borohydride with phenol.

The ethoxylation reaction is typically carried out at a temperature from about 100' C. to 1500 C. and, more usually, from 110t C. to 130 C. Whereas the reaction can be carried out at atmospheric pressure or at superatmospheric pressures up to 1000 psi or higher, most generally the pressure is between about 1 psi and about 50 psi.

To obtain the ethylene glycol monoaryl ethers ethylene oxide is then reacted with the phenol. The ethylene oxide can be added to the phenol as a liquid or as agas, butto maximize the yield of monoethoxylate and minimize the formation of higher ethoxylation products no more than 10 percent molar excess should be charged if a closed systemisemployed. Preferably, less than 5 percent molar excess ethylene oxide will be present. While some water can be present in the reaction mixture it is preferred that the amount of water be kept as low as possible. Ethylene oxide addition is maintained at a rate such thatthe reaction exotherm can be controlled and so that a large excess of ethylene oxide is not present in the reactor at any time during the couFse of the reaction.

An external cooling source will typically be required to maintain the reaction temperature within acceptable limits. The reaction time is primarily dependent on thetemperature of the reaction and the particular phenol being used. The reaction is terminated when essentially one molar equivalent ethylene oxidehas been reacted or all the phenol has been ethoxylated.

This is accomplished by simply cooling the reaction mixture and venting any excess ethylene oxide from the reactor.

A preferred procedure for conducting the reaction consists of charging the phenol to a reactorwith agitation. For ease of handling the phenol is usually charged in a molten state, however, this is not necessary. Heating isthen begun and the alkali metal hydroxide and sodium borohydride charged. The mixture is usually agitated and sparged with nitrogen while pulling a vacuum to facilitate removal of gases being evolved. When gas evolution is essentially complete, the mixture is broughttothe reaction temperature and ethylene oxide charged. The reaction is maintained at the desired temperature until one molar equivalent of the ethylene oxide has reacted with the phenol.Whereas the process is typically carried out in the above manner as a batch reaction, with suitableequipmentand modification it can also be performed on a semi-continuous or continuous basis.

The ethylene glycol monoaryl ether as obtained by the above procedure may be used as such and is suitable for some general applications without further purification. For example, this product is suitable for use in some preservative and textile applications and is acceptableforfurther reaction with various carboxylic acidsforthe preparation of esters.

Ethylene glycol monophenyl ether obtained bythe above process has markedly improved odorcharacteristics as compared to product prepared under similar conditions but without the addition of sodium borohydrideto the reaction. This is quite surprising in view ofthefactthatthe color of both products can be essentially the same.

In spite of the much improved odor of products obtained bythe presentprocess, where the product is to be used for cosmetic and fragrance applications, it is advantageous to further treatthe product. In this manner it is possible to obtain ethylene glycol monoaryl ethers, and particularly ethyleneglycol monophenyl ether, having consistent odor profiles with no trace of undesirable metallic odor. To achieve this result, in an especially useful embodiment of this invention,the product is spargedwith steam at the completion oftheethoxylation reaction. This may be accomplished bysubsurfacely introducing and dispersing up to 10 wt. percent water into the product which is maintained at a temperature from 75" C.to 120' C. and at a pressure lessthan 100 mm Hg. The water is introduced into the product th rough a sparge ring orothersuitable apparatus.Preferably from 0.5 to 5 weight percent water is employed and the sparging operation is carried out at a temperature from 90 C.to 110 C.and pressure lessthan 50 mm Hg. Afterthe desired amount of water has been introduced, the product can be dried to the desired moisture level -- usually less than 1 percent and, more preferably, less than 0.5 percent. This is typically accomplished by maintaining the vacuum and heating after the addition of water has been discontinued. A dry inert gas, such as nitrogen, may be passed through the product to facilitate removal of thewaterduring the drying operation.

It may also be desirableto lowerthe pH of the ethylene glycol monoaryl etherwhich, as obtained from the process, typicalFy has a pH of 9 or above. For many applications, primarily those involving cosmetic, preservative and fragranceformulations,the ethyleneglycol monoaryl ether should be essentially neutral (pH 6.5-7.5) and in these instances the product is neutralized by the addition ofan inorganic or organic acid. Inorganic acids, such as sulfuric acid and phosphoric acid, can be used.Useful organic acids include monocarboxylic acids. polycarboxylic acids and hydroxy carboxylic acids such as formic acid, acetic acid, propionic acid, octanoic acid, pelargonic acid, lauric acid, stearic acid, isostearic acid, phenylstearic acid, benzoic acid, toluic acid, oxalic acid, malonic acid, adipic acid, azelaic acid, dodecanedioic acid, phthalic acid, citric acid, tartaric acid, glycolic acid, lactic acid and the like.

If the product is to be neutralized, it is especially advantageous to utilize an organic acid which forms salts which are insoluble inthe ethylene glycol monoaryl ether and which therefore can be readily removed byfiltration. Useful organic acids forthis purpose include hydroxyacidsand di-and higher polycarbocylic acids. The organic acids usually containfrom about2to 16 and, more preferably4to 72, carbon atoms and aliphatic organic acids are especially useful.Especially useful aliphatic dicarboxylic acids include adipic acid, azelaic acid, sebacic acid and dodecanedioic acid Especially useful hydroxy aliphatic acids include g lycolic acid, lactic acid, tartaricacid and citric.acidrwiththelatterbeing particularly useful forthese neutralizations. To facili- tate addition of the acid tote ethylene glycol monoaryl ether, acid may be added as an aqueous solution. Ethylene glycol monoaryl ethers which have been neutralized may also be steam sparged in accordance with the previously described procedure to further enhancethe odor qualities of the neutralized product.

The invention is more fully illustrated by the following examples: EXAMPLE I Phenol was heated to 60 C. under nitrogen and charged to a standard ethoxylation kettle. After sparging the phenol with nitrogen, 0.1 weight percent potassium hydroxide and 0.1 weight percent sodium borohydride were added to the phenol. Avacuum was app5ied tothe reactor and whena vacuum of 30 mm Hg could be maintained the reactorwas sealed, heated to 11 0o C. and ethylene oxide added. The rate of addition of ethylene oxide was controlled to achieve a maximum pressure of 25 psig while maintaining the temperature at 120 C. to 130 C. with full cooling.The reaction mixture was continuously sampled and when the phenol content reached 500 ppm, ethylene oxide addition was terminated, the reactor cooled to under 100" C. and vented. The resulting product which contained 94% monoethoxylate (ethylene glycol monophenyl ether) had a color of 98/100 (percent transmittance measured at 440 and 550 mu). The product had a pleasant mild rose odor and there was no detectable metallic odor associated with the product.

EXAMPLE II Forthe purpose of comparison and to demonstrate the superior quality of the product obtained bythe improved process of this invention, the above processwas repeated omitting the sodium borohydride.

Potassium hydroxide was added to the phenol art a 0.2 weight percent level. The ethoxylation was accom polished without difficulty but at a somewhat slower rate. The final product had a color of 76/94 (percent transmittance measured at 440 and 550 mu) and contained 90% monoethoxylate (ethylene glycol monophenyl ether).Thernwas, however, a harsh pungent metallic odor associated with the product which essentially masked the subtle rose notes ofthe ethylene glycol monophenyl ether.

EXAMPLE 111 To demonstratethe abilityto further enhance the desirable fragrance characteristics of products obtained by the process ofthis invention, ethylene glycol monophenyl ether product obtained bythe process of Example I was neutralized to a pH of 7 by the addition of 50% aqueous citric acid solution and then steam sparged. Steam spargingwasaccom- plished by heating to 115" C. while adding 1.5 weight percentwaterthrough a sparge ring in the bottom of the reactor. The rate of addition was controlled so that avacuum of 60 mm Hg. was maintained. When water addition was complete, the heating was continued undervacuum until the water content was less than 0.2 weight percent. The product was cooled and filtered to remove insoluble salts formed as a result of the neutralization. The ethylene glycol monophenyl ether (boiling point 245 C.) contained 94% monoethoxylate and had no measurable phenol content. The resulting product had a pleasant mild rose odorwith subtle fresh green nuances and is a highly useful and desirable extenderforthe rose note of phenethyl alcohol in various fragrance formulations. For example, formulating 5 parts phenethyl alcohol, 2 parts d-citronellol, 2 parts 1-citronellol, 5 parts geraniol and 1.5 parts of the ethylene glycol monophenyl ether yields a fragrance having excel lent rose notes.

EXAMPLE IV To demonstrate the versatility of the present process and the ability to obtain monoethoxylated productsderived from substituted phenolsthe fol lowing reaction was conducted. A reactor was charged with 300 gms p-(t-butyl)phenol,0.56 gm potassium hydroxide and 0.59 gm sodium morohydride. The reaction mixture was heated to 125 C. and sparged with nitrogen. When there was no further evidence of gas evolution, the reactor was sealed and 98 gms ethylene oxide added at a rate such that the temperature and pressure were maintained at 130 140 C. and 30-40 psig, respectively. The reaction was continued for an additional 30 minutes. There was no trace of any unåesirable metallic odor in the resulting ethylene glycol mono-p-(t-butyl)phenyl ether product.

EXAMPLE V Ethylene glycol monophenyl ether containing 96% monoethoxylate and 0.05% phenol was prepared in a mannersimilartothatdescribed in Example I. After ethoxylation,the product had a pH of 1.8. Samples of the product were neutralized with a variety of organic and inorganic acids to lowerthe pH as follows: Acid Final pH Phosphoric acid 6.76 Hydrochlic acid 6.83 Formic acid 6.68 Acetic acid 7.10 Propionic acid 6.97 Octanoicacid 7.16 Pelargonic acid 6.46 Lauric acid 7.02 Stearic acid 6.00 Benzoic acid 7.05 EXAMPLE VI of the ethylene glycol monophenyl ether were neutralized with various organic dicarboxylic acids In a manner similar to that of Example V, samples and organic hydroxy acids as follows:: Acid- Final pH Malonic acid 6.68 Adipic acid 7.17 Azelaic acid 7.06 Dodecanedioic acid 6.84 Hexadecanedioicacid7.07 Glycolic acid 7.05 Citric acid 6.41 Insoluble salts were formed during the neutralization with all ofthe above acids. The neutralized products were then steam sparged with about 1.Sweight percent water in accordance with the usual proce dure.Afterdryingtoa moisture content of less than 0.2%, the products were filtered to remove the insoluble precipitates and the ethylene glycol monophenyl ether recovered. In all instances the odor of the ethylene glycol monophenyl ether products thus obtained was significantly improved overthat ofthe starting material.

EXAMPLE VII The following comparative experiments demonstratethe ability to obtain improved rates of reaction by the process of this invention. For this example two experiments were carried out reacting 300 gms phenol with 157 gms ethylene oxide at 125-135" C.

and 30-40 psig. Forthefirst reaction (identified as Run A) 0.9 gm potassium hydroxide and 0.9 gm sodium borohydride were added to the phenol in accordance with the process of this invention prior to carrying out the ethoxylation and in the second reaction (identified as Run B) only potassium hydroxide (1.82 gms) was added to the phenol. For Run A, reaction with ethylene oxide was complete in 45 minutes and the resulting product was devoid of any metallic odor.

Sixty minutes were required to complete the ethoxylation for Run B and the resulting product had a severe metallic odor. The marked superiority of the odor qualities of the ethylene glycol monophenyl ether obtained from Run Awas quite surprising in view ofthefactthat both products had essentially the same color.

EXAMPLE Vlil In accordance with the previously described procedures 300 gms p-methoxyphenol, 0.67 gm potassium hydroxide and 0.70 gm sodium borohydridewere charged to an autoclave. ethylene oxide was then added over a 2-1/2 hour period while maintaining the temperature at 130-140 C. and pressure in the range 30-40 psig. When the ethylene oxide addition was complete heating was continued at 135 C. for 30 minutes. there was no trace of undesirable metallic odor in the resulting product which was confirmed by chromatographic analysis to contain 95.2% monoethoxylated product.

Claims (29)

1. A process forthe production of ethylene glycol monoaryl ether which comprises monoethoxylation of phenolic compound in the presence alkali metal hydroxide and borohydride.

2. A process according to claim 1 which employs phenoliccompound selectedfrom those of the formula

where Rand R"areselected independentlyfrom hydrogen and alkyl, alkenyl and alkoxy groups having from 1 to 8 carbon atoms.

3. A process according to claim 1 or 2 which employs from 0.01 to 1 % alkali metal hydroxide and from 0.01 to 1% alkali metal borohydride, both based on the weight of phenolic compound.

4. A process according to any preceding claim wherein a combination isfirstformed of thealkali metal hydroxide and borohydride with said phenolic compound above the melting point thereof.

5. A process according to any preceding claim wherein the monoethoxylation is con ducted at a temperature offrom 100 to 1 500C.

6. A process according to claim wherein the monoethoxylation is carried out at a temperatureoffrom 110to 1300C.

7. A process according to any preceding claim wherein the monoethoxylation is carried outata pressureoffrom atmospheric up to 1,000 psi.

8. A process according to claim 7 wherein the said pressure is from about 1 psi to about 50 psi.

9. Aprocessforthe preparation of ethylene glycol monoaryl ether which comprises combining 0.01 to 1.0 wt.% (based on phenoliccompound) alkali metal hydroxide and 0.01 to 1 wt.% (based on phenolic compound) alkali metal borohydridewith phenolic compound selected from those of the formula

wherein R' and R" are selected independently from hydrogen and alkyl, alkenyl and alkoxyl groups of 1 to 8 carbons, said phenolic compound being maintained atatemperature above its melting point, and reacting with essentially one molar equivalent ethylene oxide at a temperature from 1 OO"C. to 150"C.

and pressure from atmospheric up to 1,000 psi.

10. A process according to any preceding claim wherein the alkali metal borohydride is sodium borohydride.

11. A process according to any preceding claim which employsfrom 0.05to 0.5 % alkali metal hydroxide and from 0.05 to 0.5 % alkali metal borohydride, each based on the weight of phenolic compound.

12. A process according to any preceding claim wherein the phenolic compound is selected from phenol and mono-substituted phenols in which the substituent contains from 1 to4carbon atoms.

13 A process according fo any preceding claim including the step of reducing the pH of the ethylene glycol monoaryl ether by adding acid thereto.

14. Aprocess according to claim 13 wherein the ethylene glycol monoaryl ether is neutralisedto pH 6.5 to 7.5.

15. Aprocessaccordingtoclaim 13or14 wherein organic acid selected from those of 2 to 16 carbon atoms is employed for the pH reduction.

16. A process according to any of claims 13 to 15 wherein organic acid selected from aliphatic di- and polycarboxylic acids and hydroxy acids is employed forthe pH reduction.

17. A process according to claim 13 or 14 wherein the acid used comprises citric acid.

18. A process according to any preceding claim including steam sparging the ethylene glycol monoaryl ether.

19. Aprocessaccordingtoclaim 18 wherein the sparging involves subsurfacely introducing and dispersing water into the ethylene glycol monoaryl etherwhilstthe latter is maintained at an elevated temperatureand reduced pressure.

20. A process according to claim 19 wherein up to 10 wt.% water is employed with the ether at a temperature of 75 to 1 200and a pressure less than 100 mm Hg.

21. A process according to claim 20 wherein the sparging is conducted at a temperature of 90 to 11 00C. and a pressure lessthan 50 mm Hg using from 0.5to 5wt.% water.

22. A process according to anyofclaims 18 to 21 wherein the steam sparging is followed by drying.

23. A process according to claim 22 wherein the sparged product is dried to a moisture content below 1%.

24. A process according to any preceding claim including filtering the ethylene glycol monoaryl etherto remove any insoluble salts presenttherein.

25. A process according to any preceding claim forthe production of ethylene glycol monophenyl ether.

26. A process according to any preceding claim wherein the alkali metal hydroxide comprises potassium hydroxide.

27. Aprocessforthe preparation of ethylene glycol monoaryl ether, the process being substantially as hereinbefore described in any one of Examples 1,3to 6,7 (Run A) and 8.

28. Ethylene glycol monoaryl ether prepared by a process according to any preceding claim.

29. Afragrantformulation including an ether according to claim 28.