UNITED STATES PATENT OFFICE 2,515,123 ACYLATION of FURAN Howard D

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.

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