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3,030,425 United States Patent Office Patenied Apr. 17, 1962 2 upon the total weight of reaction mass. However, only 3,830,425 a small concentration of acetaldehyde with a molecular ALKALINE STABILIZATION OF POLYOXY. weight of 44 can react with a large weight of polyoxyalkyl ALKYLENE GLYCOLS Edward J. Mits, Jr., and William J. Tapp, Charleston, ene glycol whose molecular weight is for example 3000 W. Va., assignors to Union Carbide Corporation, a cor i.e. 44 grams acetaldhyde reacts with 6000 grams of a poration of New York polyoxyalkylene glycol having a molecular weight of No Drawing. Filed May 20, 1958, Ser. No. 736,466 3000. Hydrolysis of such an acetal, as illustrated in step 5 Claims. (C. 260-61.5) 1 which follows, can occur in the presence of small amounts of relative to the weight of polyoxyalkyl This invention relates to polyoxyalkylene compositions 0. ene glycol. To illustrate 18 grams (1 mole of water and to a method for stabilizing polyoxyalkylene com could hydrolyze an acetal formed from 6000 grams of pounds against oxidation. More specifically, the present polyoxyalklene glycol (molecular weight 3000) and 44 invention relates to polyoxyalkylene compounds having grams of acetaldehyde. The reaction mechanism of this incorporated therein a small quantity of an alkaline re degradation is believed to follow the following steps: acting salt of an alkali metal. 5 (1) Polyglycol acetal -- HO (as traces of moisture)--> Polyoxyalkylene compounds, such as polyethylene gly polyglycol -- acetaldehyde cois and polypropylene glycols are commercially produced (2) Acetaldehyde - O (atmospheric)->peracetic acid batchwise by charging a hydroxyl containing compound (3) Peracetic acid -- polyglycol-> acetaldehyde -- acetic such as water, glycol, , dipropyl acid -- formic acid -- glycollic aldehyde -- degraded ene glycol, tripropylene glycol and similar di- and poly 20 polyglycol hydric into a reaction tank. An alkaline cata (4) Aldehydes from step 3 function in steps 2 and 3 lyst is then added to one of the above hydroxyl contain Thus the degradation is autocatalytic and prevention of ing compounds. The concentration of the alkaline cata step 1 can and does produce a stable polyalkylene glycol. lyst usually varies from about 1% to 5% based on the Thus even the presence of a relatively small concentration weight of the hydroxyl containing compound. A few 25 of the polyoxyalkylene glycol acetal in the total reaction such catalysts are: , potassium hydrox mass can effect, ultimately, extensive degradation. ide, cesium hydroxide, rubidium hydroxide or correspond It has now been discovered that the oxidative degrada ing alcoholates and glycolates. It is preferable to purge tion of polyoxyalkylene glycols can be prevented by the the reactors with an inert atmosphere of nitrogen, free of addition of small amounts of certain inorganic alkaline , prior to charging. The contents of the 30 materials. The alkaline materials are added to the gly reactor are then vigorously agitated and heated to ap cols after neutralization and filtration of the reaction proximately 120° C. When the contents of the reactor mass. The concentration of the alkaline material should reach the temperature of about 120° C. , be from about 0.001% to about 0.1% by weight of the propylene oxide or mixtures thereof under pressure (up polyoxyalkaline glycol. Concentrations of the alkaline to about 50-75 p.S.i.g.) is introduced at such a rate that 35 material above about 0.1% to 0.2% which corresponds the exothermic reaction (controlled by external wall cool to a pH, of a 5% solution of the glycol in water, above ing of reactor) is maintained in the range of 120° C. to about 7 is undesirable particularly in topical applications. 150 C. After the oxide has been added the agitation Furthermore concentrations greater than about 0.1% to of the reaction mass is continued until essentially all the 0.2% give glycols an unattractive murky appearance. oxide has reacted. The pH of the reaction mass at this 40 The alkaline stabilizers contemplated by the inventors point is at least about 8.5. The pH is measured using a are alkaline reacting salts of the alkali metals. A few 5 weight percent solution or dispersion of the polyoxyalk Such salts are: disodium hydrogen phosphate, sodium car ylene glycol in water. The catalyst is neutralized by the bonate, dipotassium hydrogen phosphate, trisodium phos addition of an equivalent molar quantity of an acid such phate, tripotassium phosphate, potassium carbonate, lith as HCl, HaSO4, HPO, or an acid form of an ion ex 45 ium acetate, lithium carbonate, trilithium phosphate, di change resin. The neutralized product is then carefully lithium hydrogen phosphate, sodium acetate and potas filtered using a conventional leaf-type filter press and with sium acetate. one of the common filter aids, e.g. diatomaceous earth. The neutralized and filtered product is essentially free of To provide an understanding of the invention, it will be the insoluble neutralization products (ash-forming salts), 50 described by illustrations of the performance of poly particles such as pieces of packing material, rust particles , but it is understood that the method of and any other items of "debris' that might have been the invention is equally applicable to other polyoxyalkyl present in the reactor system. ene compounds. The invention is applicable to either The neutralized and filtered polyoxyalkylene glycols liquid or Solid polyoxyalkylene compounds. show a marked degree of oxidative degradation upon 55 EXAMPLE 1. storage at room temperatures. This degradation is ac One gram of disodium hydrogen phosphate was added companied by the formation of odoriferous formic and to one thousand grams of liquefied polyethylene glycol acetic acids and either glyoxal or glycollic aldehyde. This and thoroughly dispersed therein as the melt solidified. degradation is also accompanied by a continuous decrease Samples of the polyethylene glycol containing the phos in both the melt of the polyoxyalkylene glycol 60 phate Salt and a sample of untreated polyethylene glycol and its pH. The formation of the various organic de Were examined at intervals throughout a five month peri gradation compounds in the polyoxyalkylene glycol and od. Samples 1A and 1B in Table I were taken from the the decrease in viscosity are detrimental to the use of the Same batch of polyethylene glycol. As indicated in glycols for applications such as salves, , cos Table I, the untreated material designated as Sample 1A metics and lubricants. 65 exhibited a marked indication of degradation as indicated During the formation of the polyoxyalkylene glycols it by a decrease in its melt viscosity during storage at am is believed that some of the oxide (e.g. ethylene oxide) bient temperatures in closed containers containing air. isomerizes to acetaldehyde which in turn reacts with the On the other hand the polyethylene glycol sample con polyalkylene glycols to form polyalkylene glycol acetals. taining a phosphate additive (Sample 1B) showed a The extent of such acetal formation occurs only to a 70 marked stability as indicated by a relatively small de very slight extent in terms of percent acetaldehyde based crease in its viscosity over the same period of storage. 3,030,425 3. 4. This application is a continuation-in-part of applicants' EXAMPLE 2 copending application Serial No. 538,260, filed on Octo Samples of two polyethylene glycols were manufac ber 3, 1955, and now abandoned. tured by conventional methods and divided into two por What is claimed is: tions. Samples 2A and 2B were both prepared from the 5 1. In a process for the production of polyethylene gly same batch of polyethylene glycol. Samples 3A and 3B col having a melting point of at least about 37° C. where were prepared from a different batch of polyethylene gly in an alkaline catalyst is employed and wherein upon the col. Samples 2A and 3A are unstabilized polyglycol formation of said polyethylene glycol said alkaline cata samples, while samples 2B and 3B are stabilized in ac lyst is neutralized and the crude reaction product thereby cordance with the method of the invention. As shown 10 formed is subsequently filtered, the improvement of add in Table I, a comparison is made between sampies 2A ing to and dispersing in the filtered polyethylene glycol and 2B, and 3A and 3B. One of each (Samples 2A and product, at a temperature above the melting point of said 3A) was filtered to remove all contained salts. The re polyethylene glycol, from about 0.001 percent to about maining portions of each of these two production runs 0.2 percent by weight based upon said polyethylene glycol were filtered through filter presses which had been pre 5 of a stabilizer selected from the group consisting of diso coated with . Some sodium carbonate dium hydrogen phosphate, dilithium hydrogen phosphate, about 0.1% was allowed to pass through with the molten dipotassium hydrogen phosphate, , filter products. Samples 2B and 3B represent material trilithium phosphate, tripotassium phosphate, sodium car so produced. The four samples were finished in the form bonate, lithium carbonate, potassium carbonate, sodium of flaked products and stored at ambient temperatures in 20 acetate, lithium acetate and potassium acetate, the amount closed containers containing air. As indicated in Table of said stabilizer being commensurate with a pH of up I, the uninhibited samples showed marked deterioration. to about 7 in the resulting product, thereby stabilizing The samples containing sodium carbonate (Samples 2B said polyethylene glycol to oxidative degradation. and 3B) were stable. 2. The improvement according to claim 1 wherein The methods used to introduce the basic inhibitors as said stabilizer is sodium carbonate. described above are not limiting. It is necessary only to 3. The improvement according to claim 1 wherein said get uniform distribution of the alkaline inhibitor through stabilizer is potassium carbonate. out the polyethylene glycols and any method which will 4. The improvement according to claim 1 wherein said accomplish this is suitable. Addition of the basic com stabilizer is disodium hydrogen phosphate. pound can be made at any temperature above the melting 30 5. The improvement according to claim 1 wherein said point of the polyoxyalkylene glycol. This temperature stabilizer is dipotassium hydrogen phosphate. varies generally from about 37° C. to about 63 °C. References (Cited in the file of this patent The method of the invention requires no special equip ment. It is convenient to use for the mixing process, an UNITED STATES PATENTS apparatus equipped with a device adequate for stirring 35 2,450,079 Brown ------Sept. 28, 1948 the fluid mixture. Where solid salt inhibitors are em 2,711,401 Lally ------June 21, 1955 ployed, the mixer should be capable of stirring the poly 2,721, 183 White et al. ------Oct. 18, 1955 glycol. 2,733,272 Horsley et al. ------Jan. 31, 1956 Table I STABILITY OF FLAKED SOLID POLYETHYLENE GLYCOLSDURING STORAGE IN CLOSED CONTAINERS AT AMBEN TEMPERATURES

Sample No-...- 1A B 2A Additive------None Disodium Hydrogen None Phosphate pH of a 5% pH of a 5% pH of a 5% Storage Viscosity, Solution of Viscosity, Solution of Viscosity, Solution of Time, Centistokes Poly- Centistokes Poly- Centistokes Poly Months at 210° F. Glycolethylene in at 210° F. Glycolethylene in at 210°F. Glycolethylene in Water Water Water

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Sample No.---- 2B 3A 3B Additive.------Sodium Carbonate None Sodium Carbonate pH of a 5% pH of a 5% pH of a 5% Storage Time, Viscosity, Solution of Viscosity, Solution of Viscosity, Solution of Months Centistoices Polyethyl- Centistokes Polyethyl-Centistokes Polyethyl at 210° F. ene Glycol at 210° F. ene Glycol at 210 F. ene Glycol in Water in Water in Water

847 5.2 5.2 863 4.7 4, 9 792 4.0 5. 38 3.7 4.8 660 3.5 5.0 558 3.4 5.0

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