Influence of the Friedel-Crafts Reaction on the Development of Chemical Industry1 E. C. B R I T T O N , Dow Chemical Co., Midland, Mich.
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BIEDEL and Crafts presented the first summation of their reaction in 1884 (15), and Ashdown (3) has published t h e historical aspect of its original development. Since this publication in 1884 the Friedel-Crafts reaction has found great application in the laboratory in synthetic organic chemistry. However, the progress of chemistry in the world and especially in t h e United States since the World War has forced many of these laboratory reactions to commercial development. I t is the purpose of this paper to discuss the commercial development. N o other inorganic compound has produced such a variety of unusual and useful reactions in the organic field. The diversity of reactions is astounding. Aluminum chloride serves a s a catalyst in reactions between aromatic and aliphatic compounds, aromatic compounds themselves, aliphatic and other aliphatic compounds, inorganic compounds, and organic compounds; in t h e degradation of aromatic and aliphatic compounds, in substitution reactions, and in addition reactions; and in various other reactions as in polymerization. Most of these are classified as Friedel-Crafts reactions and it has become a generally accepted idea that any organic reaction brought about by anhydrous aluminum chloride is a Friedel-Crafts reaction. Many reactions effected by anhydrous aluminum chloride may be brought about b y other reagents such as anhydrous ferric chloride, sulfuric acid, hydrofluoric acid, boron trifluoride, stannic chloride, hydrochloric acid, zinc chloride, etc., and certain workers have regarded these agents as substitutes for aluminum chloride in Friedel-Crafts reactions, regarding the reaction as a modified Friedel-Crafts reaction. Certainly a reaction of such divergence would find a great deal of commercial use, but for one reason or another many of these reactions remained laboratory processes for years, serving only to build u p the catalog of organic compounds which later were t o be referred t o by chemists seeking methods of synthesis for compounds needed i n commerce. Like so many other chemical reactions t h e Friedel-Crafts reaction found little commercial use until a commercial demand arose for products arising from it, and a cheap source of the catalyst, aluminum chloride, was available. Much could be said concerning the situations, such as t h e World War, the oil industry, syn1 Presented at the National Industrial Chemical Conference, National Chemical Exposition, Chicago, III., December 11 to 15, 1940.
thetic dyes industry, automobile industry, and others which arose to create this demand, but the greater emphasis should be placed on the accomplishment of producing cheap aluminum chloride. This was achieved by the Gulf Refining Co. and Sable-Sayre in 1916. T h e D o w Chemical Co. made aluminum chloride during the last World War emergency but did not continue in the manufacture. The first large use of aluminum chloride was in the McAfee process of cracking petroleum hydrocarbons for the production of gasoline (29). This process has now been almost entirely replaced by thermal cracking, as well as catalytic cracking wherein the catalyst is more stable and of longer life. In Europe previous to 1914 the Friedel-Crafts reaction was used to some extent, especially in the preparation of high-priced medicinals and perfume bases, but no really large use for aluminum chloride is t o be found prior to the World War. I n fact, Ullmann's Encyclopedia of Technical Chemistry, of 1914, gives less than a page to aluminum chloride, and lists only acetophenone, methylanthraquinone, and synthetic musk as products prepared by the Friedel-Crafts reaction, and lists the Seholl reaction wherein aromatic nuclei are coupled t o gether.
Types of Reactions There are two types of Friedel-Crafts reactions: (1) the catalytic type wherein the aluminum chloride is always available to act as a catalyst, a s in the alkylation of benzene, and can be recovered and reused ; and (2) that type wherein the aluminum chloride reacts with the reaction product and loses its catalytic effect, hence a fresh supply of aluminum chloride must always be available for the reaction, necessitating the use of a t least one molar quantity per mole of product. General considerations concerning the Friedel-Crafts reaction are numerous. The major ones are the conditions of reaction, such as temperature, concentration of organic reactants, a n d molal ratio of aluminum chloride, etc., all of which must be carefully worked out for each preparation owing to the diversity of reactions possible with aluminum chloride. Purity of the reacting chemicals is essential for economy of chemicals and for good yield. This is especially true when using catalytic amounts of aluminum chloride, since an
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impurity, such as thiophene in benzene, will remove aluminum chloride as a double compound, rendering it no longer available as a catalyst. This double compound is often an oily body which even covers the active catalyst to some extent, rendering it less active. Many reactions are especially unfavorably influenced by impurities in the aluminum chloride, such as ferric chloride, titanium tetrachloride, magnesium chloride, excess hydrochloric acid, excess chlorine, etc. The state of aggregation of the aluminum chloride, whether it be lumpy or finely powdered, has considerable influence on the process and should be considered when one establishes conditions of reaction. Owing to absence of moisture most Friedel-Crafts reactions may be run in iron reactors. Certain unstable compounds as iert-hutyl chloride, however, are adversely influenced by metallic iron at the reaction temperature and such reactions are best carried out in enameled vessels. Certain reactants such as phenol are likewise corrosive and offer problems in the selection of proper equipment for a Friedel-Crafts reaction. If the temperature of reaction is excessive, additional problems are encountered which must be solved. Many other anomalies and peculiarities of reactions involving the use of aluminum chloride will be found, especially when one attempts to accommodate the process to plant equipment. Following is a partial list of chemicals that are commercially prepared using aluminum chloride as a catalyst. The Friedel-Crafts process is not necessarily the only method available or in use. Acetophenone p-Amylphenol Anisic aldehyde Benzaldehyde Benzophenone Benzoyibenzoic acid p-£ert-Butylphenol Chloroacetophenone Chlorobenzoylbenzoic acid Diethylbenzene Diphenylmethane
Ethylbenzene Isopropyl benzene M e t h y lacetophenone Phenothiazine Phenothioxine P h e n y l ethyl alcohol Propiophenone Tricresyl phosphate Triphenyl chlorom ethane Triphenyl p h o s p h a t e
Production of A c e t o p h e n o n e Acetophenone is taken as an example of a reaction of the second type. It is prepared by two processes: the reaction of acetyl chloride and benzene, and the reaction of acetic anhydride and benzene. Both reactions are catalyzed by anhydrous aluminum chloride; the first b y equimolar portions based o n acetyl chloride reacting, and the
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252 second by three molar portions of aluminum chloride based on the acetic anhydride reacting. Excess benzene is used in each* case, although the amount of diacetylation is small compared to monoacetylation. Groggins has amply explained (19) the reasons for the amounts of aluminum chloride employed in each reaction. Some factors i o the first process are to be noted. 1. Because of the low-boiling acetyl chloride present, the temperature should be kept around 30° C. 2. In the acetyl chloride reaction one mole of gaseous hydrochloric acid is evolved for each mole of a c e t y l chloride reacting. This hydrochloric acid, as it «volves, continually carries out with it some acetyl chloride (boiling point 53° C.) which is lo*·*. unless the gas is scrubbed with a solvent. The preferred solvent is benzene which is used witii its content of acetyl chloride in the succeeding batch. 3. The scrubbed hydrochloric acid gas is then absorbed in water and the course of the reaction may be followed by titration of the hydrochloric acid produced. In the reaction using acetic anhydride a mole of hydrochloric acid is evolved owing to the fixing of acetic acid by aluminum chloride (19), and thris must be taken care of. The course of "the reaction may be followed by titration of the hydrochloric acid evolved. After the reaction is complete the reaction mixture is run onto cracked ice, with agitation, and some hydrochloric acid is added to dissolve any basic aluminum chloride. The cold batch, is then separated into the oil and water lavyer. The former is washed with alkali a n d is then ready for distillation. The aluminum chloride solution is usually thrown away, recovery of anhydrous aluminum chloride being uneconomical except in very large-scale operation. Production of Ketones Likewise, the use of carboxylic acids to form ketones has been amplified by Groggins and co-worlsers (SI). This reaction is used in t h e preparation of dodecyl benzylsulfonic acid (81) a powerful emulsifying agent wherein undecylic acid is condensed with benzene, the ketone id then reduced to the hydrocarbon which is finally sulfonated. Several commercial products of this type a r e prepared (2). The above description applies to the preparation of propiopbenone from propionyl chloride and benzene, t o benzophenone from, benzoyl chloride and benzene, to stearoyibenzene from stoaryl chloride and benzene, t o chloroacetophenone from chloroacetyl chloride and benzene, to caproylresorcinol from caproyl chloride and benzene, a n d to numerous other ketones, which are used as intermediates in medicinals and perfumes. This description also applies t o the preparation of o-benzoylbenzoic acid from phthalic anhydride and benzene as well as other substituted benzoylbenzoic acids, it being remembered t h a t 2 moles of alu-
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minum chloride must be used per mole of product obtained.
Friedel-Crafts Reaction in Dye Industry The benzoylbenzoic acid reaction is of great importance in the dye industry, being an intermediate in the synthesis of anthraquinone. The reaction was discovered by Friedel and Crafts in 1888, but was not used commercially until cheap phthalic anhydride from the catalytic oxidation of naphthalene was available. This preparation has been well described in numerous articles (20, 28) and is well known. However, Ullmann in his encyclopedia (1914) does not list this synthesis of anthraquinone although he does mention the synthesis of chlpro-obenzoylbenzoic acid as an intermediate in the preparation of chloroanthraquinone. The use of the Friedel-Crafts reaction in the dye industry is not limited to the preparation of anthraquinone and substituted anthraquinone but is used extensively in condensation reactions according to the Scholl and Seer reaction whereby aromatic nuclei having activated hydrogens are condensed to large nuclear condensation products which are intermediates in the production of indanthrene, and other vat dyes (16, 41,-45). D u Pont and National Aniline use these reactions in the preparation of some of their dyes.
Production of A l k y l Phenols Para-amylphenol, p-tert-butylphenol, and diamylphenol have been listed as prepared by the Friedel-Crafts reaction. When one sets out to prepare an alkyl phenol, several avenues of approach are available—for example, reaction of an olefin with a phenol; reaction of an alkyl
Vol. 19, No. 5 chloride with a phenol; hydrolysis of a n alkyl chlorobenzene; or conversion of an alkyl aniline to a n alkyl phenol. I n any of these syntheses t h e Friedel-Crafts reaction can play a part. The reaction of an olefin with a phenol is very readily carried out using anhydrous aluminum chloride, but it i s not the only catalyst available—sulfuric acid, boron trifluoride, zinc chloride, ferric chloride, hydrofluoric acid, acid earths, and others having been used. The use of aluminum chloride in this reaction is old and was known in t h e laboratory for years, but t h e Bakélite resin paint industry created a demand for such alkyl phenols and the Friedel-Crafts reaction provided the means of synthesis. I n these reactions only a catalytic amount of anhydrous alum in um chloride is required as is the case with all t h e other catalysts listed, but aluminum chloride, not being capable of causing phenol and propylene or ethylene to react at low temperature, is fairly selective in its activity, whereas butylènes and higher olefins such a s diisobutyiene react readily. This is rather peculiar, inasmuch as aluminum chloride catalyzes the reaction of benzene with ethylene and many higher olefins. This difference of reaction is readily explained by the fact that phenol reacts to some extent with aluminum chloride (as does acetic acid) releasing some hydrochloric acid and forming chloroaluminum phenolate which is by no means s o active as aluminum chloride itself. T o overcome this defect it is recommended t h a t one add anhydrous hydrochloric acid or the corresponding alkyl chloride t o the phenol before reaction (5). In the synthesis using an alkyl chloride and a phenol, the reaction proceeds normally even with methyl chloride, t h e hydrochloric acid liberated being a n activator to some extent. In many of these reactions, as has been noted by several authors, a certain amount of phenyl alkyl ether is formed which may appear in the reaction product if certain temperatures of reaction are not attained. In fact, several authors regard t h e ether as primary reaction product and the alkyl phenol as the rearranged primary product, both reactions being promoted by the catalyst. The reaction of isopropyl chloride with 772-cresol leads t o thymol, the reaction taking place at —10° C , whereas at a higher temperature an isomeric methylisopropylphenol is produced (17). In all these reactions the directing influence of the hydroxyl group causes the alkyl group to enter either the o- or opposition and only in t h e rarest cases is a m-substituted product found. Straightchain alkyl groups tend to enter both p (60 per cent) and o- (40 per cent) if both positions are open, whereas branchedchain groups, especially ten-, enter the imposition almost exclusively, only 1 or 2 per cent of the o-compound being formed. It should be noted that Perkins and Nutting (87) have shown that feri-octylphenol (SB) when heated with phenol and
March 10, 1941 aluminum chloride reacts to form tertbutylphenol, the feri-octyl group apparently being split to isobutylene and tertbutylphenol, and thence the former reacts with phenol to form further amounts of teri-butylphenol. This same splitting of the ieri-alkyl long-chain group occurs with triisobutylene and tetraisobutylene which may be reacted with phenol to make tert-b\itylpaenol. Putnam, Britten, and Perkins {39) have shown that the best temperature condition for reacting ierf-butyi cnxonde with phenol is below 50° C. and is fairly critical, higher temperature causing much ài-tertr butylphenol. However, it is further shown by Perkins, Dietzler, and Lundquist {36) that di-teri-butylphenol and o-ieri-butylphenol when reacted with phenol and aluminum chloride produced p-tert-butylphenol; hence, the o- and di-substituted compounds after separation from the p- are returned to the initial condensation whence equilibrium is established. These same phenomena occur with other alkyl phenols as well.
Aromatic Compounds A great deal of laboratory work has been done on the reaction of aliphatic chlorides and olefins with aromatic compounds, but little appears in regard to the commercial application of these reactions. They are used in the commercial preparation of diphenylmethane, benzophenone, triphenylchloromethane, dodecylbenzene, high-polymer products from ethylene halides and benzene, Paraflows from aliphatics and condensed aromatics, ethylbenzene, isopropylbenzene, and polyalkyl halobenzenes. Benzophenone and triphenylchloromethane are prepared by reacting carbon tetrachloride with benzene, using excess carbon tetrachloride in the preparation of benzophenone and excess benzene in the triphenylchloromethane preparation {18). This' shows the possibility of involving two or three aliphatic chlorine atoms in reaction but so far as reported it is not possible, for example, to react ethylene chloride with benzene to make /3-phenylethyl chloride, the reaction not being possible with as much as 100 mole excess of
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ethylene chloride and catalytic amounts of aluminum chloride. The high-polymer products mentioned above are prepared b y General Electric for use in electrical products, especially as addition agents {44, 45)· Similar products are patented by Coleman, Moore, and Stratton {9)t involving the reaction products from ethylene halides and halogenated benzenes. These products are listed as plasticizers for rubber and plastics. The Paraflow compounds are used as addition agents to oils to change their flow characteristics {46) and are condensations of chlorinated paraffins, -vaxes, etc-, with naphthalene, diphenyl, chlorinated diphenyl, and the like. Ethylbenzene is prepared from ethylene and benzene using catalytic amounts of aluminum chloride. The ethylbenzene does not find great use as such but 13 converted by either catalytic or thermal cracking to styrene. The reaction of olefins with benzene and other aromatics as weli as particular features of the use of aluminum chloride in commercial practice is the subject of a series of D o w patents. Dreisbach {11) has shown that a t a temperature of below 50° C. a higher olefin will react preferentially with benzene, even though a large excess of ethylene is present. The benzene may be replaced by halogenated benzenes or alkylated benzenes as well as certain phenol ethers. This difference of reactivity is contrary to that reported by Berry and Reid {6). However, these workers o p erated at normal pressure under highspeed stirring, but at temperatures above 60° C. Dreisbach {12) further elucidates t h e preparation of ethylated diisopropylbenzene and several points of interest are to be noted. H e uses 0.05 to 0.1 mole of anhydrous aluminum chloride and ethylates under a pressure up to 100 pounds per square inch and also finds that the catalyst separates as a sludge which can be re-used in a succeeding reaction. - He can then propylate under usual conditions to make the ethylated diisopropylbenzene. These products have a fair antiknock value and their halogen derivatives are useful as dielectrics. The same author {13) describes the preparation and properties of a considerable number of alkylated halobenzene
253 compounds, conditions for the alkylation of halobenzenes being similar to those for benzene. Coleman and Perkins {10) and Coleman and Dreisbach {8) show the preparation of mono- and poly-alkyl diphenyioxides and halodiphenyloxides. The temperature of reaction (50° to 175° C.) for alkylating the benzene nucleus in diphenyï oxide is generally higher than for benze-n* alone, although the amount of catalyst is oubstantiaily the same. In the&e pater» LS no attempt is made to show the constitution of the products obtained, statements being made that the products are mixtures of isomeric compounds although in certain cases individual compounds m a y be obtained. Dreisbach, Britton, and Perkins {14) describe the production of m-halo-alkyl benzenes by alkylating chlorobenzene with lower olefins or cyclic olefins in t h e presence of aluminum chloride. For e x ample, in ethylating chlorobenzene a t 70° C. and at a pressure of 70 pound·*, per square inch, a monoethyl chlorobenzene mixture was obtained consisting of 20 per cent o-, 80 per cent in-, and practically no p-isomer. The hydrolysis of the alkyl halobenzene produces the desired alkyl phenol. This m-substitution reaction has already been used in the commercial preparation of some of the artificial musks, wherein an alkyl benzene as toluene or xylene is alkylated with tert-butyl chloride and is then nitrated to a synthetic musk perfume. T h e continuous alkylation of benzene is featured by Amos, Dreisbach, and Williams ( i ) . The aluminum chloride which has previously catalyzed the reaction of pure ethylene with pure benzene is used to remove impurities from impure ethylene and benzene, these impurities tending t o poison the catalyst. T h e impurities listed are water, sulfur, polyolefin tars, etc. These features permit economical use of catalyst as well as excellent control of the alkylation proper. A further improvement was made by Robinson {40)— namely, the removal of the dispersed catalyst b y means of a small a m o u n t of water. This perhaps means little in laboratory operation, b u t in plant operation the use of small amounts of water permits the removal of the catalyst as a
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254 flocculent precipitate which contains all the water added. When the alkyl ben zene is then distilled, it is dry and acid cor rosion is reduced to a minimum, permit ting the use of iron apparatus.
Diverse Catalytic Uses There are a few other processes which should be mentioned, illustrating the diversity of aluminum chloride as a catalyst. Ethylene oxide by the use of about 3.5 moles of aluminum chloride will react with benzene to produce /3-phenyl ethyl alcohol (23). Sulfur has been shown to react with aromatic nuclei; the two compounds—phcnothioxine from diphenyl oxide, and phenothiazine from diphenylamine—have recently been commercially synthesized using aluminum chloride as the catalyst. Aluminum chloride is not the only catalyst available for reacting sulfur with aromatic compounds, but it offers some advantages over others proposed. Aluminum chloride has also proved of value in the condensation of phosphorus oxychloride and phenols t o make triaryl phosphates used as plasticizers in cellulose ethers, Koroseal, and other plastics (4). One of the most recent uses of aluminum chloride as a catalyst is in the addition of hydrogen chloride t o olefins. Tulleners, T u y n , and Waterman (47) describe the process using a very low temperature (—70° C ) , stating that the polymerizing action of aluminum chloride on ethylene m a y be avoided by reacting a t such a low temperature. The use of a polychlorinated solvent for the reaction, which per mits operation at ordinary temperatures, is the subject of several D o w patents b y Chamberlain and Williams (7), Pierce (88), and Keyl and Blue (27). Appar ently the aluminum chloride forms a double compound with the polychlorinated solvent which renders it inactive as a polymerization catalyst but not as a cata l y s t for t h e hydrochloric acid addition. T h e use of aluminum chloride for the addi tion of hydrochloric acid to propylene and higher olefins is not at all necessary nor advisable owing t o i t s polymerization ef fect, bismuth trichloride, antimony tri chloride, and other catalysts serving much better in this addition reaction (84)· Aluminum, chloride has likewise been used as a catalyst in the preparation of methylchloroform from vmylidene chloride and hydrochloric acid (22, 88) as well as in the preparation of ethylidene chloride from vinyl chloride and hydrochloric acid in the vapor phase (85). Although for some years little use was made of aluminum chloride in the petro leum industry, there has recently been a decided revival of its use as a catalyst in processes related t o the petroleum indus try. The production of high-octane gaso line has been the goal of m o s t of this work. T h e work of Ipatieff and others (24) of the
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Universal Oil Products Co. has shown t h e alkylation of paraffinic hydrocarbons w i t h olefins to produce these highly desirable branched-chain aliphatic compounds. Ipatieff and co-workers (26) have likewise shown the alkylation of naphthenes with olefins to produce alkylated naph thenes, similarly useful as gasoline, and (25) have shown the destructive dealkylation of gasoline which produces higher oc tane fuels. A further use for aluminum chloride has been found in the isomerization of straight-chain hydrocarbons t o branched-chain as η-butane to isobutane, the reaction being effected at elevated temperatures and pressures, using hydro chloric acid as a n activator (SO). So far as reported these processes have not been developed commercially. However, a widespread use is indicated and no doubt will soon be realized.
Conclusion From the foregoing summary of the in dustrial application of aluminum chloride as well as the large use indicated by re search it can be seen that t h e influence of the Friedel-Crafts reaction on chemical industries is very great. T h e production of cheap aluminum chloride should again be emphasized a s the key t o the commer cial development of the Friedel-Crafts reaction. The first knowledge of the re actions in which aluminum, chloride finds commercial application was gathered for the most part in t h e laboratory m a n y years ago. Fundamental research will continually add t o t h e knowledge already gained, and more and more commercial applications of the Friedel-Crafts reaction will be found.
Literature Cited (1) Amos, Dreisbach, and Williams, U. S. Patent 2,198,595 (1940). (2) Armour and Co., Ibid. 2,033,540 and 2,033,542 (1936); 2,075,765 (1937). (3) Ashdown, Α. Α., Ind. Eng. Chem., 19, 1063 (1927).
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(4) Bass, U . S. Patent 2,033,916 (1936). (5) Beck and Koller, Ibid. 1,892,990 (1933). (6) Berry and Reid, J. Am. Cfiem. Soc, 49, 3144 (1927). (7) Chamberlain and Williams, U. S. Patents 2,140,507, 2,140,508, and 2,125,284 (1938). (8) Coleman and Dreisbach, Ibid. 2,170,989 (1939). (9) Coleman, Moore, and Stratton, Ibid. 2,186,366 (1940). (10) Coleman and Perkins, Ibid. 2,170,809 (1939). (11) Dreisbach, Ibid. 2,078,238 (1937). (12) Ibid., 2,149,762 (1939). (13) Ibid., 2,183,552 (1939) and 2,186,960 (1940). (14) Dreisbach, Britton, and Perkins, Ibid. 2,193,760 (1940). (15) Friedel and Crafts, Ann. chim. phys., [6] 1, 449 (1884). (16) Friedel and Crafts, Bull, soc. chim., [2] 39, 195 (1883). (17) Givaudan-Delawanna, U. S. Patent 2,064,885 (1936). (18) Gomberg, Ber., 33, 3144 (1900). (19) Groggins, Ind. Eng. Chem., 26, 1313 (1934). (20) Heller, Z. angew. Chem., 19, 699 (1906). (21) I . G. Farbenindustrie, French Patent 801,499 (1936). (22) I . G. Farbenindustrie, German Patent 523,436 (1931). (23) Ibid., 594,968 (1934). (24) Ipatieff et al., J. Am. Chem. Soe.t 57, 1616 (1935); 58, 913-15 (1936); U. S. Patents 2,112,846, 2,112,847 (1938); J. Org. Chem.t 3, 448 (1938). (25) Ipatieff et al., J. Am. Chem. Soc, 58, 918-19 (1936) ; J. Org. Chem., 3, 13745 (1938). (26) Ipatieff et al., Zhur. Obshcheï Khim. (U. S. S. R.), 6, (68) 423-38 (1936). (27) Keyl and Blue, U. S. Patent 2,209,981 (1940). (28) Klipstein, Ind. Eng. Chem., 18, 1327 (1926). (29) McAfee, U. S. Patent 1,478,444 (1913) ; Chem. & Met. Eng., 36, 422 (1929). (30) Montgomery, McAte
