Maleic acid and phthalic anhydride w e produced by the vapor-phase catalytic oxidittion of benzene and naphthalene. The cheap production of these compounds and their derivatives has opened diverse .fields of use. The diene synfhesis using maleic anhydride promises important commercial results. .Maleic acid has been proposed us un antioxidant for fats and oils. Succinchlorimide is an eficient water sterilizer. Calcium malate accelerates the aging qf wine by precipitating calcium tartrate. Maleic acid derivatices alone or combined with phthalic anhydride are used for the preparution of synthetic resins of a wide variety of physical properties which adapt them for special purposes. Vnriefies of these resins may be cast or molded, or used for laminating purposes; they are also of increasing importance as enamel and varnish ingredients. Phthalic anhydride is the basis of the zaf dyes and other chemical .syntheses such as the production qf benzoic acid.
Maleic Acid and Phthalic Anhydride C. R. DOWNS Weiss and Downs, Inc., New York, h . Y.
especially maleic anhydride, makes them susceptible to R wide variety of chemical syntheses. Like all new chemical5 with undeveloped applications, their commercial utilization has been delayed.
T
HE cost of producing a chemical product is generally the sum of the raw material costs plus csxpense items and investnient charges. In the synthesis of most organic chemicals several different inorganic chemicals must be used whose quantities and value as compared to the organic raw material are great. Fluctuations in the price of these require continual recalculation of material costs. Catalytic oxidation processes-for example, those now used for the production of maleic acid and phthalic anhydrideare Utopian achievements for the chemical industry since only one raw material must be stocked for use, the other being air which carries no freight charges or other costs except the power t o blow it into the reaction vessel. There are, moreover, no burdensome by-products which must be dumped or for which markets must be found to permit profitable operation. I n addition t o these ideal features, the processes are automatically controlled and continuous. Hence, labor costs are reduced to a minor figure. Both maleic acid and phthalic anhydride, produced by catalytic oxidation in the vapor phase, are distinvtly American accomplihhments. Maleic acid, an unsaturated straight-chain dibasic acid made from benzene, is one example of making available for commercial use a product which prior to the discovery of this synthesis was a chemical curiosity and solely of theoretical interest. It is now also produced in small quantities as a by-product of the catalytic oxidation of naphthalene to phthalic anhydride. I t s growing importance would indicate that this by-product ratio should be increased rather than the reverse by the judicious selection of catalysts. Phthalic anhydride, although a much older product coinmercially, was made by a costly process. The cheap production of these tmo compounds and their deriTqtiveq has opened up diverse fields of use. The direct blood relatives of maleic acid are maleic anhydride, fumaric acid, succinic acid, and malic acid. These are all commercial materials because of the successful synthesis of maleic acid. The three acids are all solid compounds, of varying solubilities and specific physical characteristics, which permits their use per se for many purposes. The unsaturated character of maleic acid, fumaric acid, and
MALEICANHYDRIDE Maleic anhydride is one of the reagents required for ai1 important series of reactions discovered by Diels aiid Alder (3) in which it condenses spontaneously with conj ugatetl diolefins such as butadiene, isoprene, cyclopentadiene, and cyclohexadiene, and with tetrahydrofuran and various UIIsaturated compounds. These reactions are as follows: Butadiene + maleic anhydride + tetrahydrophthalic an hydride HB 0 H?
Hi c/ \
I1
H-C/
+ + maleic
I1
H? Cyclopentadiene
H,
anhydride
+ niethyltetr ahydrophth>tllc
I
17
11
I1
H J
-
0
I
CH3-c\CA/
0
0
+
H
I1
HC\
H
anhydride Hl 0
+ maleic anhydride
I
1 C=Hz
I €1
0
H I
H HCN'
H-A\C/C\c/
H C
+
CHI-C
0 0
0
~
H-c//
H-CiC\C/"\
5 C / H
I1 H2
Hz
'1
0 --
H-C Y C
Isoprene
H
11
Ik
0
IrarLs-erLdo-iuethSlelle-
tetrahvdrophthdic anhvdridr H 0 1 H I H-C '1
H-C\
C=H, /C C H
H
l1 0
I N D U S T R I A L A N D E N G I N E E R I Iv G C H E M I S T R Y
18
Cyclohexadiene
+ maleic anhydride + trans-endo-ethylene
tetrahydrophthalic anhvdride
H
HC
C=Hz
H
NC
!I
0
H
H I
H
Tetrahydrofuran
+
maleic anhydride
0
+ dehydronorcan-
H
H
tharidin O
0
H The similarity of this conlpound to cantharidin is obvious: Cantharidin
It is interesting to note that pyrrole and thiophene, H
H
NH
H Pyrrole
H-CYc\
S
H Thiophene
although considered similar in structure to tetrahydrofuran, either do not react with maleic anhydride in the same way or do not react with it a t all. By this diene reaction new acid anhydrides are formed in quantitative yields by direct addition. These new compounds have been given the name “adducts.” From these anhydrides the acids may be easily produced, and they are susceptible to the various reactions normally associated with anhydrides and acids. They may be transformed by catalytic hydrogenation into fully hydrogenated systems. It seems probable that resins of unusual and useful characteristics will be made commercially from these acids. Further investigation of the diene reaction is certain to be of great coinmercial importance. The use of chloromaleic anhydride naturally enlarges the number of derivatives that can be produced by this reaction. Acetylene dicarboxylic acid, or its esters derived from maleic acid, also reacts with these unsaturated compounds. The more highly cracked gasolines produced by modern processes are unstable, containing unsaturated compounds that absorb oxygen to form gums. These may be removed by severe treatment with sulfuric acid, but this is accompanied by serious losses of valuable antiknock compounds. The conjugated diolefins are largely responsible for this insta-
Vol. 26, No. 1
bility. Diels and Alder have shown that conjugated diolefins react quantitatively with maleic anhydride, and Birch and Scott (1) have isolated several diolefins from cracked gasoline by this method. Martin, Gruse, and L o w (6) have extended our knowledge of the effect of maleic anhydride upon cracked gasolines and have shown that the reaction products are crystalline compounds of definite melting points. These reaction products may be removed from the treated gasoline fractions in which they are insoluble by filtration, and the latter are found to be almost completely stabilized against oxidation with greatly reduced gumforming characteristics. This method provides a new tool for the quantitative examination of highly cracked gasolines. It also gives speculative promise that compounds of value may be produced which may justify commercial treatment of gasoline by this means. It is certain however that the potential sources of diolefins as present in cracked gasolines are ample for any conceivable development. Maleic anhydride has also been suggested as a purifying reagent for the removal of cyclopentadiene from crude benzene. Maleic anhydride reacts with tung oil but not with linseed oil which has no conjugated double bonds. New resins for lacquer and varnish compounding are made from certain turpentine cuts when condensed with maleic anhydride. The terpene-maleic anhydride compounds are tough, hard, and waterproof resins. The original reaction product-Petrex-behaves under certain conditions as a dibasic acid but can be made to react also as a monobasic acid. By variations in its method of production, it may be used in nitrocellulose lacquers and as a varnish resin. When cotton yarn is immersed in a bath of molten maleic anhydride for a short time, and the excess anhydride squeezed out and washed off, it is immunized against direct-dyeing dyestuffs called “substantive” dyes. During this treatment, the fibers are esterified and acquire a strong affinity for basic dyestuffs. This esterification takes place without the necessity for catalysts, and the action is more rapid than with the immunizing agents previously used. The method is stated to be useful with other vegetable fibers (8). The immunized cotton yarn may be woven with untreated cotton or other fibers, and variegated dyeing effects can be obtained. It is hoped that, as the price of maleic anhydride is reduced, i t will become of increasing interest as an esterifying agent for cellulose for the production of various plastic products, The ordinary alcohols easily form esters with maleic anhydride.
MALEICACID Greenbank ( 5 ) , of the TJnited States Department of Agriculture, has found that maleic acid is a n important antioxidant for preventing the development of rancidity in fats and oils in storage. The addition of only one part of maleic acid in ten thousand parts of the fatty material has been found effective. It is well known that crude vegetable oils keep remarkably well. After refining by the alkali process, the excellent keeping quality is destroyed. The natural antioxidants of these crude oils have never been isolated. It was found that certain water-soluble extracts from cottonseed and soy-bean meal were antioxidants for dairy products. The only property recorded for this fraction was that it was slightly acidic. In a study of the aliphatic acids it was discovered that the structure of maleic acid was similar to hydroquinone. This similarity is discernible only by writing the structure of the two compounds in an unorthodox but structurally sound manner as follows:
I iv 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 i M I S T R 1-
January, 1934
H
H
0
0
Hydroquinone
Maleic acid
The portions to the left of the dotted line are identical. It was found that maleic acid has practically the same antiosygenic value as hydroquinone when used in fats and oils. It is ideal in that it,s solubility in fats and oils is only 0.01 per cent which simplifies its use, since excess acid may be added to the oil and the excess removed by filtration. It adds no taste, odor, or color to the product. It has also been found to inhibit the development of rancidity in milk powder, pastry, and caramels. Although the Bureau of Dairy Industry has riot formally recommended its use, it would seem that the economic importance of this discovery should lead to its wide application. For a purpose of this sort the question of the toxicity of maleic acid is occasionally raised. This is approximately equivalent to oxalic acid, but in the extremely small traces required for this purpose it would appear that it could be used with safety. There are of course large tonnages of fatty oils used which are not converted into edible products. Maleic acid and its derivative acids may be used to replace lactic, formic, and acetic acids in leather tanning. Their advantage resides in the fact that they are solid acids and furthermore that they impart improved qualities to the leather. These acids have not yet become important in this industry largely because of improvements in the processes used in producing lactic, formic, and acetic acids whereby their selling prices have been continually reduced. It iq hoped that maleic acid will be reduced in cost to sell at a price that will justify its use in this field. =Is a matter of scientific interest only, it should be noted that maleic acid a t times crystallizes in the form of prismatic blue crystals. As far as the author knows, this has never heen reported nor its cause determined.
FUMARIC .~CID Fumaric acid has been proposed as a baking powder ingredient. Its low solubility in water varying from less than 1 per cent a t room temperature to less than 10 a t 100” C. indicated that batter made for a considerable period before baking would be stable and not lose its gas. Favorable results were obtained with baking powders containing fumaric acid and magnesium carbonate. Since baking soda is the commonly accepted source of carbon dioxide in baking powders, its use was indicated. However, batters using baking powders of these ingredients liberate very little gas until they reach a certain temperature in the oven, and then the gas is set free much too rapidly, resulting in large holes in the product. Some important work has been done to modify this almost explosive liberation of carbon dioxide, using agents that tend to prevent rapid interaction. It is the objective to attain an effect similar to the automatic regulated action of the bitartrates. They give low gasforming rates a t ordinary temperatures, and those rates gradually increase during the heating period in the oven. The problem of using fumaric acid a t the present time seems to be more economical than technical, owing to the fact that tartaric acid has dropped in price to practically a record low. Dibenzyl fumarate is used as an antispasmodic.
19
~ I A L IACID C Inactive malic acid is made by the direct addition of water to the double-bond linkage of maleic or fumaric acids, and, although levomalic acid is widely distributed in various fruits, its only prior comniercial source was from maple sugar “sand.” Inactive malic acid is a food acidulent with important attributes for use in beverages, jellies, and candies. Its acid taste blends perfectly with the flavors commonly used and is less astringent than tartaric acid. Eoff (4) has recently proposed the use of calcium malate in wine making. All young wines contain cream of tartar and tartaric acid. It usually requires several years of aging for the precipitation of the excess tartar from solution during the process of fermentation and after the conclusion thereof, If the wine is bottled before the precipitation of tartrates is finally completed, the product loses its commerical value because the bottles will ultimately contain certain of the tartrates in precipitated and visible form. Even in the production of unfermented grape juice, this slow precipitation takes place. This long time of storage greatly increases the cost of production. By the addition of calcium malate in the proper proportions to wine (even when young) and agitation for a short time, any proportion of tartaric acid desired can be removed as insoluble calcium tartrate, leaving the malic acid anion to replace the tartaric anion. The amount required is relatively small. For example, roughly 0.5 per cent of calcium malate is sufficient for unfortified wines and champagnes. Malic acid is a natural constituent of grapes, wines, and musts, and often occurs normally in these products in greater proportion than other acids. It is estimated that there are in excess of one million people in the United States for whom physicians have prescribed a salt-restricted diet. The insipid character of such a diet causes patients to rebel against it, resulting in a loss of appetite or in breaking the diet. Eka Salt has been proposed as a condiment in place of table salt for this purpose, This is essentially 85 per cent disodium malate with about 14 per cent of a mixture of sodium and ammonium citrates and 1 per cent of manganese bromide. It is stated that the ingestion of 4 grams of Eka Salt daily introduces into the system about as much malic acid as one would obtain from two average sized apples, and as much citric acid as from one-tenth of a lemon. Malic acid may be used in place of tartaric and citric acids in the preparation of effervescent salts, but because of trade customs it has not as yet replaced these acids to any extent. The properties of its compounds-for example, magnesium acid malate-are similar to the magnesium citrate. Water solutions of malic acid upon evaporation form thick sirups before crystallization takes place. When a sirup of this type is mixed with a silicic acid hydrogel and the product dried and granulated, the granules may be used in gas mask canisters for the absorption of ammonia vapors. Davidson (9) has proposed the use of malic acid for the production of radio condensers. For this purpose continuous paper or textile strips are run simultaneously with metal foil strips through a concentrated solution which is made up, for example, from sodium borate, sodium carbonate, and malic acid in varying proportions to produce a neutral solution. The strips are coated or saturated during this operation by the constituents of the chemical bath and are wound into a roll of alternate metal and paper strips. At least one of the metal foils must be either aluminum or magnesium. The saturating and coating operation is carried out under the influence of a direct electric current. The films thus formed containing “water of combination” constitute the dielectric
20
INDUSTRIAL AND ENGINEERING
of the condenser. It is essential that the malic acid used for preparing the chemical bath‘be free of metallic salts.
SUCCINIC ACID Succinic acid may be made by the catalytic reduction of maleic or fumaric salts but is now produced commercially by the electrolytic reduction of furmaric acid as proposed by Norris (7). Succinchlorimide developed by Wood (9) is a chlorineliberating solid substance especially useful for the disinfection of drinking water. A tablet weighing 6 mg. is sufficient to disinfect a canteen full of water within a few minutes. A one-ounce (30-cc.) bottle will hold one hundred and fifty tablets which will disinfect enough water per day for a company of men in the field. This would be especially important in war time but is useful a t all times for campers and explorers. The water disinfected in this way possesses no taste other than that of the chlorine. Diethyl succinate is used to a considerable and increasing extent as a solvent for the extraction of flavors from fruits, herbs, and the like. Dibenzyl succinate is used as an antispasmodic. Succinic anhydride and dichlorosuccinic acid are highly reactive compounds of considerable promise. Succinic acid derivatives are used in medicine.
PHTHALIC ANHYDRIDE It is estimated that the productive capacity of equipment for making phthalic anhydride by the vapor-phase catalytic oxidation of naphthalene in the United States is about 10 to 12 million pounds per year. The consumption of phthalic anhydride has increased rapidly owing to the many valuable products which may be synthesized from it. It is used in large volume for the production of synthetic anthraquinone which has displaced that made by the oxidation of anthracene. In this synthesis, phthalic anhydride is condensed with benzene. By substituting monochlorobenzene and toluene for benzene, chloroanthraquinone and methylanthraquinone are made. These compounds as well as phthalimide are essential to our dyestuffs industry. Phenolphthalein, a cathartic drug, is continuing to displace cascara, aloes, and many other cathartics derived from natural products. The dimethyl, diethyl, dibutyl, and diamyl phthalates are extensively employed as plasticizers in lacquers, and diethyl phthalate is useful as a perfume fixative. The continuous increase in output of phthalic anhydride to satisfy its diversified uses has constantly reduced its cost, resulting in a still further broadening of its horizon. For example, large quantities of benzoic acid are now made from phthalic anhydride, thereby releasing large amounts of the valuable solvent, toluene, for other purposes. Despite the fact that these products add up t o a very respectable tonnage, this is undoubtedly small compared to the future requirements of the synthetic resin field. Callahan, twenty years ago, condensed phthalic anhydride and glycerol to
ITALIANCENTRAL SULFURSALES BUREAU FORMED. FOllOWing the dissolution of the Sicilian Sulphur Consortium in July, 1932, an unsuccessful attempt was made to form a national sulfur consortium which would control the output on the mainland, as well as Sicilian production. I t is alleged that producers, released from quota restrictions and faced with the necessity of reducing their production costs, actually mined more sulfur during 1932-33 than has been mined in Sicily in years. The output has been estimated as high as 280,000 to 290,000 tons. With the aid of the fund put at the disposal of the consortium by the government, the stocks of the old consortium were moved out rapidly and probably do not now exceed 50,000 tons. However, stocks of private producers have accumulated and are said to be
CHEMISTRY
Vol. 26, Xo. 1
form resins which were called “Glyptals.” Other polybasic acids, such as succinic, maleic, and the like, also form resins, and glycol may be substituted for glycerol. As phthalic anhydride became progressively cheaper, these resins began to play a more important role, and numerous investigators were attracted to this fertile field. Variations in the proportions of the constituents and methods of treatment have produced an almost bewildering variety of products. These alkyd resins may be cast or molded into shapes or used as bonding agents for various organic and inorganic materials. They may be converted into the so-called rosin-modified foriris for varnish gum substitutes. Again, by the replacement of a part of the dibasic acids by monobasic acids, other varnish and lacquer resins are produced which possess a surprising resistance to weathering. They give tough, elastic films that are practically immune to vibration or shock. They are used extensively as paint and enamel vehicles in marine work; for steel freight and passenger railroad cars; for truck, trolley car, and bus bodies; for automobile wire wheels; for steel bridges; for mechanical refrigerators in place of porcelain; for house shutters and blinds; for interior architectural paints and decorative outdoor metal signs. It is hoped that their superior immunity to weathering will ultimately permit their universal use as exterior house paints. The alkyd resins and their related products are sold on the market under trade names such as Resyls, Teglacs, Clyptals, Dulux, Beckasol, and Paranol. The commercial expansion of these various resin compounds is already being felt by the older orthodox drying oils and varnish gums, but each will find its place where its inherent characteristics best fit it for use. The same observation holds true for the nitrocellulose lacquers which in the last decade have enjoyed such wide success. From this we again realize that the chemist is continually upsetting long-established and even more recent commercial practices, but he a t the same time creates new industries whose products possess properties not hitherto obtainable from natural sources. In this way the gaps between the branches of progress are filled in as the branches themselves grow, preserving a symmetrical but creating a more complicated system.
LITERATURE CITED (1) Birch and Scott, IND. ESG. CHEM.,24, 49 (1932). (2) Davidson, U. S. Patent 1,891,345 (Dee. 20, 1932). (3) Diels, 2. angew. Chem., 42, 911 (1929); Diels and Alder, British Patent 300,130 (1930). (4) Eoff, U. S. Patent 1,915,273 (June 27, 1933). (5) Greenbank, Ibid., 1,898,363 (Feb., 1933). (6) Martin, Gruse, and Lowy, IND. EKG.CHEW,25, 381 (1933). (7) Sorris, U. S. Patent 1,457,791 (June 5, 1923). (8) SOC. Anon. pour 1’Ind. Chim. a Rile, British Patent 316,434 (1929). (9) Wood, C . B., U. S. Patent 1,891,462 (Dee. 20, 1932).
RECEIVED October 5, 1933. Presented before the General Meeting at the 86th Meeting of the American Chemical Society, Chicago, Ill., September 10 to
15,1933.
comparatively heavy-from 100,000 to 200,000 tons. Furthermore, during the past year the Montecatini production brought the mainland production t o over 100,000 tons. Until last spring, Sicilian producers were able to meet world market prices. With the fall of the dollar the situation rapidly became critical, and Sicilian producers can no longer operate except at a considerable loss. The government has therefore intervened and has announced that a Central Sulphur Sales Bureau would be formed t o market all Italian sulfur, both Sicilian and mainland, on the domestic market and for export. Furthermore, the government will subsidize the industry to the extent necessary to bridge the gap between Italian production costs and world market prices.
