I
^ R IE D E L -C rn fts chemistry was founded in 1877 when Friedel . and Crafts discovered the condensation of aromatic hydrocarbons and alkyl or acyl halides with aluminum chloride. Since then, halides of aluminum, tin, zinc, iron, and other metals, and acids such as sulfuric, phosphoric, and anhydrous hydrofluoric have been found to catalyze a wide variety o f condensation reac
tions. The scope of the condensation reactions has been greatly expanded in the last twenty-five years. The alkylation o f paraf
fins and naphthenes, particularly of isoparaffins, is a recent de
velopment commercialized on a large scale in the production of high-octane hydrocarbons and fuels. These same catalysts have been applied to other types of reactions such as isomerization, transfer of radicals, and cracking.
The application o f silica-alumina and certain homogeneous cat
alysts to reactions of these types presents new fields of scientific endeavor.
S IL IC A -A L U M IN A C A T A L Y S T S
Active heterogeneous catalysts containing silica and alumina are produced either by activation o f some natural clays or by synthesis. Silica gel, notwithstanding its enormous surface, does not catalyze the reactions described in the present paper. A small proportion o f alumina, of the order of 1% by weight o f the silica,
is sufficient to produce an active catalyst. Commercial cracking catalysts contain approximately 10% alumina. Oxides such as thoria or zirconia can be substituted for the alumina. Silica- alumina catalysts were first developed for the catalytic cracking of petroleum oils. Approximately 1,000,000 barrels of oil are now cracked daily over these catalysts.
The alkylation o f aromatic hydrocarbons with olefins, long es
tablished in Friedel-Crafts and strong acid syntheses, was the first application o f silica-alumina to condensations o f the Friedel- Crafts typm Michel (11) described the condensation o f naphtha
lene with propylene under pressure over fuller’s earth to pro
duce tetraisopropylnaphthalene. Schollkopf (19) alkylated naphthalene with ethylene at 230° C. under 20-40 atmospheres pressure over an activated hydrosilicate catalyst. Sachanen and O’K elly (17) described the alkylation o f benzene with propylene, butylenes, and amylenes over silica-alumina at 450° C. and 100 atmospheres. Under these conditions the alkylation proceeded sm oothly but was accompanied by partial cracking of the paraf- finic side chains. As a result, toluene, ethylbcnzene, and xylenes were produced in substantial yields.
Destructive alkylation reactions catalyzed by aluminum chlo
ride, as observed by Ipatieff and co-workers (7), were carried out over silica-alumina catalysts by Sachanen and Davis (15). These investigators reacted benzene with pcntanes over an activated clay for 45 minutes at 480° C. and 1050 pounds per square inch.
Twenty-eight per cent (by weight of benzene charged) of alkyl- benzenes boiling from 105-210° C. was produced. The applica
tion o f silica-alumina to reactions formerly catalyzed by Friedel- Crafts and strong acid catalysts was increased in scope by Hans
ford, Myers, and Sachanen (4) and by Thomas, Hoekstra, and Pinkston (S 3 ). These investigators dealkylated alkylaromatic hydrocarbons in the presence o f silica-alumina at 450-550° C.
An example o f these reactions was the conversion of ethylbcnzene to benzene and ethylene.
44 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y V ol. 38, No. 1
sion of alkylaromatic hydrocarbons by the transfer of alkyl radi
cals from one aromatic nucleus to another or by a dealkylation- alkylation reaction catalyzed by silica-alumina at 450-500° C.
For example, Lacourt (S), and Ipatieff and Pines (S ), who used aluminum chlo
ride as a catalyst.
S Y N T H E S IS O F A N T H R A Q U IN O N E
The analogy between the catalytic effects of silica-alumina and of Friedel-Crafts and strong acid catalysts is further supported by the condensation of benzene with phthalic anhydride over silica-alumina to produce anthraquinone. The materials used in this investigation wore the usual c.p. grade of benzene and phthalic anhydride. Synthetic silica-alumina catalysts were prepared b y coprecipitation o f the hydrous oxides in ratios of 9:1 to 14:1 by weight. The apparatus included an electrically heated salt bath equipped with circulating system, and a reactor of one-inch i.p.s., extra-heavy, iron pipe of about 315-cc. capacity. The re
actor was filled with silica-alumina catalyst. The benzene was pumped by displacement with glycol into the bottom of the re
actor by w ay of a preheater coil immersed in the salt bath. M ol
ten phthalic anhydride was forced by air pressure from a heated, graduated, glass tube into the bottom of the reactor through a second preheater tube immersed in the salt bath. From the re
actor the liquid product passed into a water-cooled condenser of 5-inch inside diameter. The sudden change in rate of linear flow o f the effluent gases into this relatively large cold chamber sub
stantially reduced the phthalic anhydride “ fo g ” that otherwise occurred. The uncondensed benzene and gases formed in the re
action then passed through a filter into another smaller condenser to remove the benzene. The anthraquinone was separated from the unreacted phthalic anhydride by heating the solid product in an excess of distilled water and filtering hot. The quantity of phthalic anhydride recovered per pass was determined by titra
tion of an aliquot o f the resulting solution with standard potas
sium hydroxide solution.
A reaction temperature of 37 0-3850 C. was found to be most satisfactory in this reactor. Higher temperatures resulted in ex
cessive decomposition of the phthalic anhydride. A t lower tem
peratures the anthraquinone condensed on the catalyst and in the top of the reactor and was recovered only with difficulty. H ow ever, under reduced pressure the premature condensation of the anthraquinone at 320-380° C. might be overcome. This would
permit utilization of the reduced decomposition o f the phthalic anhydride resulting from the use of these lower temperatures.
A sample of crude synthetic anthraquinone, analyzed by the reduction-oxidation technique described by Lewis {10 ), was found to have a purity of about 95% . Table I shows the results o f a series o f five consecutive runs; each was made under similar re
action conditions over the regenerated catalyst from the preced
ing run. The catalyst was regenerated by passing air through the catalyst bed at 500-550 ° C. until the effluent gases were substan
tially free o f carbon dioxide. In this series no material balances were made on coke, gases, and benzene. Since benzene is sub
stantially stable in the presence of silica-alumina catalysts under the conditions employed in these reactions, any benzene losses were considered to be mechanical losses. The phthalic anhydride, however, was recovered with care, and that consumed was con
sidered to have been converted entirely to coke, gas, and anthra
quinone. I t is possible that more could have been recovered by flushing the catalyst with steam after each run and before each regeneration.
The conversion per pass over the fresh catalyst was higher than that o f the next four runs, but the ultimate yield was lower due to excessive cracking of the phthalic anhydride. The regenera
tion of the catalyst lowered its condensing activity somewhat but reduced its cracking activity even more. For this reason the ulti
mate yields were greatly increased after the catalyst had been re
generated at least once.
Although the over-all yield of anthraquinone is higher than that obtained over silica-alumina catalysts, this process consumed 1.5 to 2.0 moles of aluminum chloride per mole of phthalic anhydride charged. The catalyst consumption using silica-alumina, how
ever, is extremely low. The activity o f this catalyst is not per
manently destroyed by one charge of phthalic anhydride and benzone. When the deposit of carbonaceous material on the catalyst has substantially reduced its activity, it is burned off, as in the conventional cracking processes. In this manner the life o f the silica-alumina may be extended to periods ranging from four months to a year.
The conversion per pass over silica-alumina is small. However, the stability of the reactants and product at the tomperature of the reaction and the short catalyst contact time pormit the re
covery of m ost o f the benzene and phthalic anhydrides not con
verted to anthraquinone, for recycling over the catalyst bed.
H O M O G E N E O U S C A T A L Y S T S
Homogeneous catalysts include hydrogen chloride and a wide variety o f inorganic halides, halogenated hydrocarbons, and other organic compounds of low molecular weight which are rela
tively unstable and reactive at elevated temperatures.
The principal applications of these catalysts in the past has been limited to hydrogenation and cracking operations. Their description has been confined m ostly to patent literature. Pier,
January, 1946 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 45
T heoretical ultim ate (based
on b enzoyl chloride) 68 52 76 67 72
Iiroenig, and Donath (13) found that organic chlorinated com
pounds and halides of sulfur are active hydrogenation catalysts.
Pier, Simon, and Eisenhut {14) recommended ammonium chlo
ride as a catalyst for hydrogenation of petroleum resins and as
phalts. Storch and co-workers { S I , 22) investigated the use of halogen-containing compounds as catalysts for hydrogenation of coal tars. Tropsch {24) claimed that the presence of chlorine or chlorinated organic compounds in the cracking of hydrocarbons produced greater yields at lower temperatures than could be ob
tained in the noncatalytic process. According to Hessels, van Krevelen, and Waterman {6 ), cracking of methane is “ induced”
by halogen derivatives or sulfur compounds. The effect, how
ever, seems to be very small.
These catalysts have recently been employed in conventional Friedel-Crafts reactions. Sachancn and D avis {16) alkylated benzene and phenol with olefins in the presence o f small quantities of chloroform and other halogenated organic compounds at tem
peratures of the order of 300 ° C. When phenol was condensed with amylene under these conditions in the presence o f 5 % chloro
form by weight of total charge, the yield of amyl phenols was 9 3% of theoretical. Schmerling and Durinsky {18) alkylated benzene with propylene at 300° C. in the presence of a small amount of hydrogen chloride.
S Y N T H E S IS O F B E N Z O P H E N O N E
Nenitzcscu and co-workers {12) discovered that active aroma
tic hydrocarbons, such as diphenyl and naphthalene, could be alkylated and acylated with alkyl and acyl halides at elevated temperatures without the addition of any extraneous catalyst.
They were unable to react relatively inactive aromatic com
pounds, such as benzene, in this manner.
Under the conditions described in the present paper, benzene can bo alkylated with alkyl halides and acylated with acyl halides in the absence of any separately added catalyst. The acylation of benzene with benzoyl chloride was the principal reaction of this type investigated. It is believed that this type of seemingly noncatalytic condensation reaction is analogous to that catalyzed by chlorinated or halogenated compounds. I f the alkylation of benzene with olefins requires the catalytic action o f a halogen
ated compound, the condensation of the same aromatic with a chlorinated hydrocarbon or benzoyl chloride should be possible without any extraneous catalyst, since the reactant containing chlorine is simultaneously a catalyst in this type of reaction.
The materials used were c.p. benzene and benzoyl chloride.
The apparatus consisted o f an Am inco superpressure unit, com plete with rocker shaker, heating jacket, and stainless steel bom b of 2800-cc. capacity. The benzoyl chloride and benzene in a mole ratio of 1 to 3 were charged to the bom b before sealing it. The bomb was then placed in the heating,jacket, which had been pre
heated to about 150° C. Under application of full.heat, the
uct, removed from the reactor with several benzene washes, was distilled from a side-arm distillation flagk. The cut boiling from 270-325° C. solidified on cooling and was found to be benzophe- none of greater than 9 5 % purity.
From a mixture o f a 10% potassium hydroxide solution and crude benzophenone, about 10 grams o f benzophenone were steam-distilled. Recrystallization of this material from acetone gave colorless rhombic prisms melting at 48.5-49° C. A mixture of these crystals with Eastman c.p. benzophenone gave a melting point o f 48.5-49° C.
Table II shows the general effects o f time and temperature on the condensation o f benzene with benzoyl chloride. Several con
clusions can be drawn from this table. For a batch run, tempera
tures of the order o f 260° C. and a reaction time o f 2 to 3 hours appear to be favorable conditions for the synthesis o f benzophe
none from the standpoint of both conversion per pass and ultimate yield. Low'er temperatures, 210-215° C., give lower conversions per pass without a noticeable increase in ultimate yield. Shorter reaction times also cause a reduced conversion per pass without increasing the yield. A t higher temperatures, 345-350° C., the conversion per pass and ultimate yield o f benzophenone are lower than at 260° C .,as a result of excessive decomposition of benzoyl chloride. However, temperatures of about 345° C. and reaction times of 1 to 5 minutes might be optimum for continuous pres
sure units designed for precise time and temperature control.
A t present, benzophenone is made on a semicommercial scale by the reaction of benzoyl chloride with benzene at moderate temperatures in the presence of anhydrous aluminum chloride.
Although the yield of benzophenone by this process is of the order of 85 % of theoretical based on benzoyl chloride charged, the alumi
num chloride consumption amounts to about one pound per pound of beuzoyl chloride charged. This loss of catalyst is undesirable and is eliminated in the process described here without a prohibi
tive reduction in ultimate yield of benzophenone. (1929); 1,766,344 and 1,767,302 (1930); 1,878,963 (1932).
(12) Nenitzcscu, C. D., Isacescu, D. H., and Ionescu, N. N., Ann.,
(24) Tropsch, H., U. S. Patent 2,063,133 (1936).
A n im proved cation exchange resin o f the p h e n o lfo r m a l- dchyde type con tain in g nuclear su lfon ic acid groups is now available to the in d u stry . T h e exchange capacity o f th is resin is show n to be higher than previously kn ow n cation exchange m aterials in b oth so d iu m and acid cycles. T h e resin is stab le and w ith o u t color throw over a wide range o f pH u p to 100° C . and show s excellent sta b ility to rapid ch anges in salt c o n ce n tration . Field tests on the m a terial have' been ru n in b oth w ater so ften in g and d e
m in eraliza tio n for three years. P h otograph show s the operating floor o f a purification plan t fo r boiler feed w ater.