Patented Feb. 24, 1953 r - 2,629,746

UNITED STATES PATENT OFFICE 2,629,746 PROCESS OF PRODUCING PENTAERYTHRTOL Richard F. B. Cox, Wilmington, Del, assignor to Hercules Powder Company, Wilmington, Del, a corporation of Delaware No Drawing. Application June 12, 1948, Serial No. 32,737 i Caim. (C. 260-635) 2 ihis application is a continuation-in-part of The process to which this invention relates my copending application Serial Number 459,709, may broadly be described as involving condensa filed September 25, 1942, and now abandoned. tion of acetaldehyde with formaldehyde in an This invention relates to an improved process aqueous medium in the presence of an alkaline for the preparation of pentaerythritol. More catalyst to form a reaction mixture comprising particularly, it is concerned with an improved pentaerythritol and the formate of the catalyst process for recovering pentaerythritol from a cation, Converting said reaction mixture to an Crude reaction mixture obtained by the alkaline aqueous Solution comprising pentaerythritol and Condensation of acetaldehyde and formaldehyde. free formic acid by addition of a substance yield Pentaerythritol is prepared commercially by O ing hydrogen ions in an amount at least chemi condensation of acetaldehyde with formaldehyde cally equivalent to the formate present, extract in an aqueous medium in the presence of an ing formic acid from Said solution with a formic alkaline catalyst such as Ca (CH)2, NaOH, etc. acid solvent substantially water-immiscible and in the resulting reaction mixture there is pres nonsolvent for the pentaerythritol, applying heat ent in addition to the pentaerythritol a metal 15 to evaporate said extracted solution at least to Salt of formic acid, the particular salt depend a point at which Crystallization takes place, and ing upon the catalyst enployed. Thus, calcium recovering crystalline pentaerythritol. formate is present when Ca(OH)2 is used as The recovery procedure will vary somewhat catalyst. In practice, the reaction mixture is depending upon the composition of the Solution often treated with an acid precipitant to pre 20 Subjected to evaporation. Thus, when an acid cipitate the catalyst cations. This practice yields which is a precipitant for the catalyst cations an aqueous Solution comprising pentaerythritol is employed in accordance with this invention, and free formic acid. Thus, when Ca(OH)2 is for example, oxalic acid in the case of calcium used as catalyst, the calcium ions may be re cations, the Solution subjected to evaporation is moved, for example, by precipitating the same 25 Substantially free of salts. Pentaerythritol can as the Sulfate, oxalate, etc. The resulting solu be recovered from such a solution by evaporation tion is an adueous solution comprising penta to a point at which crystallization of pentaeryth erythritol and free formic acid. In working up ritol takes place, and succeeding crops of the aqueous pentaerythritol-formic acid solution, pentaerythiitol can be obtained by further evapo it has been the practice to concentrate the same rations. If desired, the solution may be evapo to a point at which crystallization of the penta 30 rated to dryness as for example by spray dry erythritol takes place and to recover crystalline ing. However, when a substance which yields pentaerythritol in this manner. The yield of hydrogen ions but which does not precipitate the catalyst cations is employed, then salts will recovered crystalline pentaerythritol, however, is be present in the solution subjected to evapora always Substantially below the theoretical. 35 Now, in accordance With this invention, a tion, and the pentaerythritol can be recovered method has been found for recovering substan by fractional crystallization. If desired, the solu tially higher yields of crystalline pentaerythritol tion may be evaporated to dryness to yield a mix from a crude pentaerythritol reaction rinixture ture of pentaerythritoi and salt which can then be resolved. containing pentaerythritol and free formic acid. 40 The novel step in this new method consists in When free formic acid is permitted to remain extracting formic acid from the formic acid in the pentaerythritol reaction mixture, it ap containing reaction mixture with a formic acid ears to react with pentaerythritol to form a solvent which is substantially Water-immiscible pentaerythritol formate during the concentration and nonsolvent for the pentaerythritol. The 45 Step, i. e., when heat is applied to concentrate formic acid is extracted from the reaction mix the reaction mixture by evaporation. Further ture prior to the application of heat to concen more, it is believed that the formic acid acts as trate the reaction mixture by evaporation. The a catalyst for the condensation of pentaerythritol employment of this technique avoids formation and any unreacted aldehydes which may be of noncrystalline Syrups during the concentration 50 present in the reaction mixture. All of these step. Such noncrystalline syrups seriously inter products which may result due to the presence fere With the crystallization of pentaerythritol. of formic acid consume pentaerythritol and have The overall result of the use of the technique of an adverse affect on the economies of the reac this invention is a substantially increased yield tion. These by-products, moreover, due to their of recovered crystalline pentaerythritol. 55 noncrystalline, Syrupy nature interfere seriously 2,629,746 3. 4. with the recovery of the desired product, penta ritol and calcium formate. This procedure was erythritol. repeated until 5 crops of crystals had been ob Now, having indicated in a general Way the tained. Ethyl alcohol was added to the final fil nature and purpose of the invention, the follow trate to separate an additional crop of penta ing examples are illustrative of the invention. 5 erythritol and calcium formate from the alcohol but are not to be construed as limiting the Sane. Soluble noncrystalline syrups. The total of crys In the examples, the parts and percentages are talline pentaerythritol and calcium formate sepa by weight unless otherwise indicated. rated in accordance with the above procedure Eacample 1 amounted to 46 parts. 10 The pentaerythritol-calcium formate crystal 22 parts of acetaldehyde and 20 parts of cal line mixture was dissolved in 100 parts of water cium hydroxide were added simultaneously With and acidified with 25 parts of aqueous 50% sul agitation to 175 parts of Formalin (35% form furic acid. The precipitated calcium sulfate was aldehyde) and 370 parts of water. After 6 hours removed by filtration, and the precipitate washed had elapsed, the reaction was considered to be 5 With Water. The combined filtrate and wash complete. During this period, the temperature Water Were then extracted with 6 portions of of the reaction mixture varied from 18 C. to ethyl ether equal in volume to the aqueous Solu 41° C. At the end of the reaction period, the tion to remove formic acid. The aqueous solution reaction mixture was acidified with 47 parts of thus freed of formic acid was concentrated in aqueous 50% sulfuric acid. Precipitated calcium 20 Vacuo (pot temperature 50° C.) to a point at sulfate was removed by filtration, and the pre which pentaerythritol crystals formed upon cool cipitate was given a displacement wash with hot ing of the concentrate to room temperature. Ad water. The combined filtrate and wash water ditional cirops of crystals were obtained by fur was then treated with a Small amount of Oxalic ther concentration and crystallization. The last acid to remove additional calcium not precipi of the pentaerythritol was removed from the tated by the sulfuric acid, and the precipitated In other liquor by the addition of ethyl alcohol. calcium oxalate Was fittered from the Solution. The total yield of pentaerythritol obtained was The clear, colorless solution of pentaerythritol 23 parts. This announted to an 80% yield based and formic acid was then extracted With ethyl On the acetaldehyde. acetate to substantially completely remove the The conditions employed in effecting the con free formic acid. The resulting solution of penta densation of formaldehyde and acetaldehyde to erythritol was then concentrated in vacuo (50° yield pentael'ythritol may be varied widely in ac C. pot temperatule) to a point at which penta Cordance with the knowledge of the art. Thus, erythlitol crystallized out upon cooling to room although calcium hydroxide has been used in the temperature. After removal of the first crop of i5 exailples, alkaline catalysts such as sodium hy pentaerythritol, the solution was again concern droxide, potassium hydroxide, barium hydroxide, trated in vacuo to get further crops of penta magnesium hydroxide, strontium hydroxide, etc. erythritol crystals. The last crop of pentaerythri may be employed. The formaldehyde-acetalde tol was obtained by adding ethyl alcohol to the hyde molar ratio used may be varied in accord concentrate. Pentaerythritol can be separated ance with the teachings of the art. These factors from the noncrystalline Syrups in this nanner and Iiumerous others relate specifically to the due to the fact that it is relatively in Soluble in Condensation Step of the overall process. The ethyl alcohol. Whereas the noncrystalline Syrups Subject invention, however, is not limited to any are soluble. The total yield of pentaerythritol particular procedure or procedures for effecting thus obtained amounted to 54 parts by weight. condensation, and accordingly any crude reaction This amounted to a yield of 80% by weight based mixture resulting from any prior art process may On the acetaldehyde. be employed in carrying out this invention. The Eacample 2 Crude reaction mixture will in an any event COml This example represents a modification of the prise pentaerythritol and the metal formate cor process of Example 1 wherein the crude penta responding to the catalyst employed in the con densation. - - - - erythritol reaction mixture is subjected to a pre It is essential in accordance with this inven liminary processing to separate pentaerythritol tion that the crude reaction mixture be converted and calcium formate from the noncrystalline to an aqueous solution comprising pentaerythritol Syrup S Which are formed during the initial con 5 5 densation step. Once the mixture of pentaeryth andyielding free hydrogenformic acid ions by inaddition an amount of a substance at least ritol and calcium formate crystals has been Sepa chemically equivalent to the metal formate preS rated from the crude reaction mixture, this mix ent. Any acid which precipitates the catalyst ture is dissolved in Water to provide an aqueous cations may be used. For example, assume a re Solution comprising pentaerythritol and calcium 60 action mixture comprising pentaerythritol and formate which can be subjected to the process calcium formate. If sulfuric acid is added in an With which this invention is concerned. The ex mount slightly in excess of the amount which ample Was carried out as follows: scheinically equivalent to the formate, calcium 11 parts of acetaldehyde and 9.5 parts of cal Sulfate. Will precipitate out. The resulting solu cium hydroxide Were added simultaneously with tion will be one containing pentaerythritol and agitation to 90 parts of Formalin (35% form free formic acid. Similarly, oxalic acid may be aldehyde) and 200 parts of water. The reaction employed in place of sulfuric acid. was carried out under Substantially the same con It is not necessary to employ an acid substance ditions as those given in Example 1. At the end Which precipitates the metalion present. Thus, of the 6 hour reaction period, the reaction mix 70 hydrochloric acid may be added in an amount ture was filtered to remove line and other in slightly in excess of the amount which is chem. Soluble material. The filtrate was then concen ically equivalent to the formate present. In this trated in vacuo (50° C. pot temperature) to a case, the resulting solution will contain free point at which the concentrate upon cooling to formic acid which can be extracted with a selec room temperature yielded crystals of pentaeryth 75 tive solvent for formic acid. other acids

2,629,746 5 employed in place of hydrochloric acid, for ex characteristics. Whether or not any particular ample, mineral acids such as hydrobromic acid, substance possesses these characteristics can be phosphoric acid, sulfuric acid, etc. Similarly, easily ascertained by one skilled in this art by Various cation exchange agents may be employed resort to simple testing. The extraction process to convert the crude reaction mixture compris may be of the Continuous or batch type. ing pentaerythritol and the metal formate to an The improved process for manufacturing aqueous solution comprising pentaerythritol and pentaerythritol described herein is advantageous free formic acid. For example, sulfonated poly in that it provides a substantial increase in yield hydroxybenzene - formaldehyde resin may be of product. This process also avoids formation employed as a cation exchange agent to remove O of noncrystalline Syrups during the concentra the calcium ion from a crude pentaerythritol tion step. These syrups seriously interfere with reaction mixture and to provide an aqueous Solu and prolong the recovery of crystalline penta tion comprising pentaerythritol and free forming erythritol. acid. In those cases wherein an acid Substance What I claim and desire to protect by Letters which does not precipitate the catalyst cations 5 Patent is: is employed, it is desirable that the acid substance The process for producing pentaerythritol be comparatively less soluble in the solvent em Which comprises condensing acetaldehyde with ployed to extract formic acid than in the aqueous formaldehyde in an aqueous medium in the reaction mixture. presence of calcium hydroxide as catalyst to It is generally desirable, although not abso 20 form a reaction mixture comprising pentaeryth lutely necessary, to remove the catalyst cations ritol and calcium formate, converting said re at some time prior to the concentration step. action mixture to an aqueous solution compris If the catalyst cations are not removed prior to ing pentaerythritol and formic acid by addition this step, the Solution subjected to evaporation of an acid which precipitates the calcium cations Will contain a Salt of the Catalyst cation and 2 5 in an amount sufficient to substantially com pentaerythritol, and the recovery of pentaeryth pletely precipitate Said calcium cations, the re ritol will be complicated due to the presence of Sulting precipitate being separated from said the salt. The most satisfactory procedure from Solution at Some time prior to the ensuing evapo the standpoint of efficiency is to effect the con ration step, extracting formic acid from said Version of the reaction mixture to an aqueous 3) Solution with ethyl ether, applying heat to solution comprising pentaerythritol and free evaporate Said extracted solution at least to a formic acid by addition of an acid which pre point at which crystallization of pentaerythritol cipitates the catalyst cations. takes place, and recovering crystalline penta One having converted the crude pentaeryth erythritol. ritol reaction mixture to an aqueous solution RICHARD F. B. COX, comprising pentaerythritol and free formic acid, the latter is extracted with a substance which is REFERENCES C TED a liquid at the extraction temperature. This The following references are of record in the liquid must be a solvent for formic acid, and it file of this patent: must be substantially Water-immiscible and non 40 solvent for the pentaerythritol. The Substance UNITED STATES PATENTS employed must be unreactive with pentaeryth Number Name Date ritol and unreactive with formic acid under 1,716,110 Burke ------June 4, 1929 extraction conditions. Thus, aliphatic ketones 1930,146 Othmer ------Oct. 10, 1933 such as ethyl butyl ketone, ethyl propyl ketone, 2,107,527 Evans et al. ------Feb. 8, 1938 methyl propyl ketone, diethyl ketone, etc.; ali phatic acetates such as ethyl, propyl, butyl, amyl, FOREIGN PATENTS hexyl, etc. acetates; and aliphatic ethers such as Number Country Date diethyl ether, diisopropyl ether, etc. are particul 736,379 France ------Nov. 23, 1932 larly satisfactory. Numerous Substances other OTHER REFERENCES than those specifically mentioned can be em ployed as extractants in accordance with this Chimie et Industrie (Des vergnes), vol. 29, invention if they possess the aforementioned pp. 1263-67 (1933).