Patented July 11, 1950 2,515,23

UNITED STATES PATENT OFFICE 2,515,123 ACYLATION OF FURAN Howard D. Hartough, Pitman, N. J., assignor to Socony-Vacuum Oil Company, Incorporated, a corporation of New York No Drawing. Application October 3, 1947, Serial No. 777,853 10 Claims. (CI. 260-345) 2 This invention relates to a process for the the acylation of furan. This is probably due to acylation of furan and, more particularly, is di the fact that acyl halides form comparatively rected to a catalytic method for acylating furan stable molecular complexes with aluminum chlo and its derivatives in the presence of a Small ride and the other above mentioned catalysts, amount of boron trifluoride. thereby decreasing their catalytic effect. Acylation reactions are well known in the art While yields as high as 50 per cent of theory and connote the union between acyl radicals have been reported using an aluminum chloride and molecules of organic compounds under COn catalyst, these figures have been the exception ditions of temperature, pressure, and time Ordi rather than the rule. In general, the yields of narily referred to in the art as acylating condi O acyl furans heretofore obtained have averaged tions. The compounds thus produced represent about 35 per cent of theory. These relatively Structurally the Substitution of the original acyl Small yields were believed to be due, at least in radical for a hydrogen atom on the organic corn part, to the relatively large quantities of catalyst pound molecule. being employed, i. e., amounts of the order of As a general rule, the temperature, pressure, 5 molecular quantities with respect to reactants and time of reaction employed in acylation Opera being used. Attempts were accordingly made to tions depend upon whether the acylation is ef overcome the existing difficulties by the use of fected in the absence Or presence of catalysts. traces or catalytic amounts of aluminum chlo The two methods are generally referred to as ride. Minute amounts of this compound, how thermal and catalytic acylation, respectively. The 20 ever, failed to catalytically produce any of the majority of acylation processes fall under the desired furyl ketone. latter category and it is a catalytic acylation It has now been discovered that boron tri process with which the present invention is con fluoride and complexes thereof which release cerned. . boron trifluoride under the acylation conditions Acyl radicals may be furnished in acylation re 25 behave in a distinctive manner as compared actions by various materials commonly referred with the other Friedel-Crafts catalyst hereto to as acylating agents. Thus, the anhydrides of fore used in the acylation of furan. It has been carboxylic acids and acyl halides have served as found that by using a boron trifluoride catalyst, sources of the acyl radical. In particular, acetic the above mentioned difficulties encountered in anhydride and acetyl chloride have found Wide 30 the acylation of furan have largely been over application as acylating agents. come. It would appear that the advantages ob The acylation of furan and furan derivatives tained using a boron trifluoride catalyst can be have previously been carried out employing one attributed to the fact that relatively Small quan of the above mentioned acylating agents in the tities, i.e., less than one mole per mole of acylat presence of various catalysts, including stannic 35 ing agent can be used as effective catalyst in chloride, ferric chloride, aluminum chloride, and the acylation of furan and its derivatives. By titanium tetrachloride. employing a borontrifluoride catalyst in catalytic These catalysts, although applicable. With con amounts, the formation of addition complexes Siderable Success in the acylation of aromatic formerly encountered in the catalytic acyla hydrocarbons, are only moderately successful 40 tion of furan has been substantially eliminated, where furan is involved. It has been postulated the products resulting being almost entirely acyl that this may be accounted for by the fact that furans having one or more side chains corre compounds Such as aluminum chloride form ad Sponding to that of the acylating agent. It has dition complexes with the carbonyl group of the been found, in accordance with this invention, resulting ketone, substantially decreasing the 45 that boron trifluorides employed in quantities yield of desired product and requiring a consider less than one mole per mole of acylating agent able exceSS Of aluminum chloride Over the theo used effect the acylation of furan Smoothly and retical amount required for the acylation reac. specifically in contrast With the more conven tion. Thus, when aluminum chloride is used as tional acylation Friedel-Crafts type catalysts the condensing agent, the ratio of catalyst to 50 heretofore employed. acyl chloride is at least one and in the case of It is accordingly an object of the present in acid anhydrides, at least two. Likewise, other vention to provide an efficient process for syn of the above mentioned catalysts of the Frie?el thesizing acylated furans. Another object is to Crafts type must be used in molecular quantities provide a process for catalytically acylating furan with respect to the acyl halide being employed in 55 and its derivatives. A still further object is to 2,515,123 3 4. afford a process for catalytically acylating furan to catalyze the acylation of benzene. Thus, a in a direct manner which can be easily car Small amount of boron trifluoride which is in ried out using a relatively inexpensive catalyst active catalytically in the acylation of benzene in small amounts. A very important object is is, in accordance with the present invention, a to provide a process capable of reacting furan 5 preferred catalyst for the acylation of furan. or its derivatives with an acylating agent in the The acylating agents to be used herein may be presence of an efficient catalyst to give a yield an organic carboxylic acid anhydride or an acyl of acylated furan substantially greater than that halide. Included in the former category are heretofore obtained. compounds Such as the ketenes which, upon ad These and other objectS which Will be recog dition of Water, yield organic carboxylic acids. nized by those skilled in the art are attained in These acylating agentS may be derived by methods accordance with the present invention, wherein well known to the art from mono- or dibasic furan or its derivatives are acylated by reaction organic acids which may be either unSaturated with organic carboxylic acid anhydrides or acyl or Saturated. Thus, representative acylating halides in the presence of a Small amount of boron agentS to be used in this invention include the trifiuoride. anhydrides of Saturated fatty acids, Such as acetic Boron trifluoride conveniently forms complexes anhydride, propionic anhydride, ketene, etc.; the with various organic compounds Such as ethers, acyl halides of Saturated fatty acids, Such as thioethers, alcohols, carboxylic acids, ketones, acetyl chloride, Stearyl chloride, etc.; the acyl amines, carboxylic acid anhydrides, and carboxy 20 haides of dibasic acids, such as phthalyl chlo lic esters. These complexes are easily formed by ride; the anhydrides of Saturated acids, such as saturating the solutions thereof with gaSeous crotonic anhydride; and the acyl halides of un boron trifluoride in a closed preSSure veSSel. For Saturated acids, Such as crotonyl chloride. These example, glacial acetic acid, when Saturated acylating agentS are given merely by Way of ex with boron trifluoride, under preSSure forms the 2 5 amples and are not to be construed as limiting compound CH3COOH-BF3 containing 51.9 per Since other acyl halides or anhydrides of carboxy cent BF3. Similarly, methanol, when Saturated lic acids, Which Will readily Suggest themselves with boron trifluoride, under preSSure forms a to those skilled in the art, may likewise be used. boron trifluoride-methanol complex containing In general, carboxylic acid anhydrides are to be 60 per cent boron trifluoride. Thus, the present 30 preferred as the acylating agentS in the present invention contemplates, in addition to boron tri process, Since greater yields of the desired ketone fluoride itself, the use of boron trifluoride as a were obtained When these Were uSci. catalyst in the form of an organic complex which The acylation of furan may be carried out em allows the gaseous boron trifluoride to be con ploying equimolar quantities of furan and acylat veniently weighed and handled. Representative ing agent. However, the presence of an exceSS of the boron trifluoride complexes contemplated of one of these reactantS has been found to give for use in the present process, are those with an increased yield of the desired product. Thus, ethyl alcohol, methyl alcohol, formaldehyde, ace an exceSS of either acylating agent or furan gave tone, propionic anhydride, and ethyl acetate. an increased amount of ketone aS compared with This group, of course, is not to be considered as those reactions in Which equinolar quantities limiting since other similar organic boron tri were used. fluoride complexes which will yield BF3 under The temperature at which the reaction is the conditions hereinafter set forth may likewise carried out may vary over a wide extent, the be employed as catalysts in promoting the acyla upper limit of temperature being dependent on tion of furan. While the present invention is 45 the boiling point of the reactants at the specific not to be strictly limited to any specific Small preSSure of the reaction. In general, tempera amount of catalyst, it has been found that boron tures varying between about -30° C. and about trifluoride present in amounts less than one mole 150 C. have been found satisfactory for effecting per mole of acylating agent is an effective cata the acylation. However, generally it is preferred lytic agent in promoting the acylation of furan. 50 to employ temperatures in the range of from In general, it has been preferable to use an about 0° C. to about 50 C. Pressures between amount of boron trifluoride between about 0.001 about one and about 10 atmospheres have been and about 0.1 mole per mole of acylating agent. found Satisfactory in the acylation process. The While, in some respectS, the chemical behavior effect of increased pressure, theoretically, is to of furan is similar to that of benzene, there are 55 Ward increased reaction but from a practical some very striking differences. This is illustrated Standpoint, this is not a very great effect with by the fact that the acylating catalysts ordinarily reactions. Such as those involved herein, which used for the acylation of benzene are not Suit go readily at normal pressures. The reaction able for the acylation of furan. Moreover, cata period necessary will be dependent largely upon lysts which readily effect the acylation of furan 60 the temperature employed, in general being less Will not always effect the acylation of benzene. at the higher temperature. Under the condi This is particularly true in the present invention. tions Set forth above, however, the reaction time The Small quantities of boron trifluoride which will generally vary from about . 1 to about 10 permit the acylation of furan to proceed Smoothly hourS. . and efficiently are inactive in the acylation of 65 The following detailed examples are for the benzene. As those in the art know, boron tri purpose of illustrating modes of effecting the fluoride has previously been employed as a cata acylation of furan in accordance with the proc lyst in the acylation of benzene. In all of these ess of this invention. It is to be clearly under reactions heretofore carried out, however, it has stood that the invention is not to be construed been necessary to use relatively large quantities as limited to the specific acylating agents used of catalyst to effect condensation, i.e., amounts or to the specific conditions set forth in the equal to or greater than One mole of catalyst per examples. mole of acylating agent used. The Small quan Eacample I tities of boron trifluoride, under the conditions herein employed in the acylation of furan, fail 5 To a mixture of 204 grams (3 moles) of furan 2,515,128 S 6 and 107 grams (1 mole) of 95 per cent acetic an acting the same with an acylating agent selected hydride, cooled to 10° C. by means of an ice from the group consisting of acyl halides and bath, were added 4 grams of boron trifluoride anhydrides of carboxylic acids in the presence of methanol complex containing 60 per cent boron an amount of a boron trifluoride-organic com trifluoride, equivalent to 0.03 mole of boron tri plex equivalent to less than one mole of boron fluoride. The temperature rose to about 13° C. trifluoride per mole of acylating agent. and when it finally subsided to 5° C., the ice 2. A process for acylating furan, comprising re bath. Was removed and the reaction mixture acting the same with an acylating agent selected Warmed to 25° C. for a period of 2 hours. Two from the group consisting of acyl halides and an hundred milliliters of water were then added. - 0 hydrides of carboxylic acids in the presence of The mixture was agitated for 15 minutes and the an amount of boron trifluoride-etherate complex lower organic layer drawn off and washed with equivalent to less than one mole of boron tri 10 per cent sodium carbonate solution until neu fluoride per mole of acylating agent. tral and distilled. Fifty-three grams of 2-ace 3. A process for acylating furan, comprising re tylfuran, representing a yield of 48 per cent of 15 acting the same with an acylating agent selected theory, were obtained. from the group consisting of acyl halides and anhydrides of carboxylic acids in the presence Eacample II of an amount of borontrifluoride-fatty acid COm plex equivalent to less than one mole of boron To two hundred four grams (3 moles) of furan 20 trifiuoride per mole of acylating agent. were added 71 grams (0.5 mole) of benzoyl 4. A process for acylating furan, comprising re chloride and 4 grams of boron trifluoride-ethyl acting the same with an acylating agent selected etherate containing 51 per cent boron trifluo from the group consisting of acyl halides and ride. The mixture turned dark but no evolution anhydrides of carboxylic acids in the presence of hydrogen chloride could be detected at am 25 of an amount of boron trifluoride-aliphatic al bient temperatures. The mixture was then re cohol complex equivalent to less than one mole fluxed at 38° C. for 2 hours, during which time of boron trifluoride per mole of acylating agent. evolution of hydrogen chloride could be de 5. A process for acylating furan, comprising re tected. Considerable amounts of insoluble ma acting the same with an acylating agent selected terial formed during this period. The organic 30 from the group consisting of acyl halides and layer was decanted from the sludge into cracked anhydrides of carboxylic acids in the presence ice. One mole of sodium hydroxide as a 10 per of an amount of boron trifluoride-ethyl etherate cent solution was added and the mixture al complex equivalent to less than one mole of lowed to stand until all odor of benzoyl chloride boron trifluoride per mole of acylating agent. had disappeared and the furan evaporated off. 6. A process for acylating furan, comprising re The semicrystalline mass was filtered off and di. acting the same with an acylating agent selected gested with alcohol. Evaporation of the alco from the group consisting of acyl halides and hol gave 8.5 grams of crude crystalline 2-ben anhydrides of carboxylic acids in the presence ZOylfuran. of an amount of boron trifluoride-acetic acid Eacample III 40 complex eduivalent to less than one mole of To tWO hundred four grams (3 moles) of furan boron trifluoride per mole of acylating agent. were added 100 grams (0.44 mole) of benzoic 7. A process for acylating furan, comprising re anhydride. The mixture was cooled to 7° C. and acting the same with an acylating agent selected 3 grams of boron trifluoride-acetic acid complex, from the group consisting of acyl halides and an equivalent to approximately 0.025 mole of boron hydrides of carboxylic acids in the presence of trifluoride, were added. The mixture was al an amount of boron trifluoride-methanol con lowed to warm to 32° C. (room temperature) and nlex edivalet to less than one mole of boron Was stirred at this temperature for two hours. trifluoride per mole of acvlating agent. It was then cooled to 8 C., 400 grams of 10 per 8. A process for acylating furan, comprising cent Sodium hydroxide Solution were added, and reacting the same with an acylating agent the mixture was stirred for 30 minutes longer. selected from the group consisting of acyl halides The organic layer was separated off and washed and anhydrides of carboxylic acids in the pres Once with water, and the excess furan recovered ence of an amount of a boron trifluoride-organic by distilation. Sixty-six grams of Semi-solid complex equivalent to between about 0.001 and residue were distilled to produce pure 2-benzoyl 5 about 0.1 mole of boron trifluoride per mole of furan, having a boiling point of 126° C. at 0.5 acylating agent. millimeters of mercury and a melting point of 9. A process for acylating furan with an acylat 43.5-44 C. after recrystallization from alcohol. ing agent selected from the group consisting of From the above examples, it will be seen that acyl halides and anhydrides of carboxylic acids Small amounts of boron trifluoride are effective 60 in the presence of an amount of a boron tri catalysts for the acylation of furan. Likewise, fluoride-organic complex equivalent to between furan derivatives having one or more substitu. about 0.001 and 0.1 mole of boron trifluoride per ent groups attached to the furan ring may be mole of acylating agent, comprising the steps of acylated in accordance with this invention. The mixing furan, acylating agent, and boron tri acylated furans as produced in accordance With fluoride-organic complex, reacting the mixture at the process described herein have found a va a temperature of between about -30° C. and riety of uses and may be employed as solvents, about 150° C. until the reaction is substantially addition agents for petroleum fractions, plasti complete, and thereafter removing acylated cizers, resin intermediates and intermediates for furan from the reaction product mixture. chemical synthesis. Long chain alkyl furyl ke 10. A process for acylating furan with an acyl tones may be utilized as synthetic lubricants, di ating agent selected from the group consisting electrics, waxes, and extreme pressure additives of acyl halides and anhydrides of carboxylic for mineral oils. acids in the presence of an amount of a boron I claim: trifluoride-organic complex equivalent to between 1. A process for acylating furan, comprising re about 0.001 and about 0.1 mole of boron trifluor 2,515,123 -7 8 ide per mole of acylating agent, comprising the UNIFEE STATES PATENTES steps of mixing furan, acylating agent, and boron trifluoride-organic complex, reacting the "Number Name Oate mixture at a temperature of between about 0° C. 2004,069 Bruson -...------June 4, 1935 and about 50° C. until the reaction is substantially 5 2,158,031 Loder ------May 9, 1939 complete, and thereafter removing acylated OTHER REFERENCES furan from the reaction-product mixture. Groggins, Unit Processes in Organic Synthesis, HOWARD ID. HAROUGH. 2nd edition (1938), McGraw-Hill Book Co., New York, pp. 657-658. - s REFERENCES, CEO Groggins, Unit Processin Organic Chemistry, The following references are of record in the pages 634 to 637, 2nd ed., (1938), McGraw-Hill "file of this patent: Book Co., Inc., N.Y. Calloway, "Chemical Reviews,' vol. 17, pages 330, 360-362,374-377, 371 (Aug.-Dec. 1935).