F A T S
Η. J. HARWOOD, Armour & Co., Chicago, III.
The possibilities for exploitation of the fatty chemicals are so numerous it is difficult to predict where continued research and development will lead
Γ ™ , . ™ fats and oils are one of the major classes of chemicals which are produced b y living organisms. Both ani mals a n d plants are important sources of fats; it is not feasible to attempt to dif ferentiate t h e products from t h e two sources in a discussion of their chemistry a n d technology. Characteristics of natural fats are determined b y their source, and t h e fat used as r a w material in a specific process is largely dependent upon t h e end product desired. \Vorld production of fats is enormous; annual consumption is estimated at over 2 5 million tons. T h e 1950 production in t h e United States of vegetable and ani m a l fats (excluding b u t t e r ) is estimated at over 5 million tons divided approxi mately equally between t h e two types. Thus figure represents almost a 1 0 0 % in crease in production over that prior to World War II. Two principal factors in addition t o increased production have encouraged the development of n e w and more profitable outlets for fats. These a r e t h e competition for the soap market of synthetic detergents based on petro leum, and the growing realization that substances with superior properties for many uses may b e obtained by chemical alteration of the fat molecule. Fats are fatty-acid esters of glycerol. T h e acids comprise approximately 9 0 % of the fat. Hence, t h e chemistry of fats is largely the chemistry of fatty acids. These acids are produced from t h e fat b y any one of several simple hydrolytic o r splitting processes. T h e formula shown represents a hypo thetical mixed triglyceride derived from stearic, oleic, a n d palmitic acids. It is e v i d e n t t h a t a fatty acid is nothing more t h a n a carboxyl group with a hydrocarbon
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CH 3 (CH 2 )i e COCH 2 CH 3 (CH 2 ) 1 6 COOH II 1 stearic acid HOCH2 ττ Λ Ο I 3H20 | :K3(CK2)7CK=CH(CH2)7COCH > ΟΗ,(ΟΗο)7ΟΗ=(ΟΗ,)7ΟΟΟΗ + HOCH
Ä I
oleicacid
HOAH,
CH3(CH2)l4C00H2 C H 3 ( C H i ) i 4 C O O H Ο palmitic acid fat Splitting of Fats tail. T h e carboxyl group is chemically reactive and highly polar, with an affinity for water and other polar substances. T h e hydrocarbon tail is relatively inert a n d nonpolar. T h e resulting unbalanced po larity is responsible for most of t h e valu able properties of fatty acids and their derivatives. In t h e course of the follow ing discussion, reference will frequently b e m a d e to surface activity—adsorption at or on surfaces. Surface activity is a prop erty of molecules possessing a polar group linked to a relatively large nonpolar group or combination of groups. Examination of the above formulas re veals the fact that t h e tail, or the h y d r o carbon chain of the fatty acid, is subject to variation both in length a n d in degree of unsaturation. Physical properties, such as melting point, boiling point, and solu bility, of the fatty acids and their deriva tives are largely determined b y the nature of the hydrocarbon chain. Separation of t h e components of naturally occurring fatty-acid mixtures in order to obtain specific acids with specific properties is becoming increasingly important. Two processes are commercially applied to the separation of fatty-acid mixtures—frac tional distillation for separation according to chain length and crystallization w i t h or without solvent for separation according
CHEMICAL
glycerol
to melting point (or degree of unsatura tion). The chemistry of t h e fatty acids largely involves the chemistry of t h e carboxyl group, a n d most known carboxyl reactions have b e e n applied to t h e higher fatty acids. T h e discussion will b e restricted to a n u m b e r of those reactions which h a v e resulted in t h e large-scale production of useful products. Soap M a k i n g Probaljly t h e simplest derivative of a fatty a c i d is produced by o n e of t h e oldest chemical processes, alkaline hydrolysis of fats. Soaps, the metallic salts of fatty acids, a r e well known a n d need little further mention. Common types of soaps and t h e i r principal uses are shown below: RCONa II ο
Types of Soaps RCOK RCONH4 RCONH,R' II II II ο Ο ο Detergents
(RCO) 2 Ca R C O L i
A .. 4
(RCO)*Al
h
(RCO),Zn
h
Grease Cosmetics R u b b e r Although alkali soaps are excellent d e tergents, t h e y suffer from t h e fact that they a r e rendered ineffective b y metallic
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ions found in hard water. One of the first large-scale chemical alterations of the fatty-acid molecule was involved in the production of a type of detergent which is effective in the presence of hard water. Reduction of an ester of a fatty acid results in t h e formation öf the corresponding higher aliphatic alcohol. This reduction may b e accomplished either by metallic sodium or b y catalytic hydrogenation. Esterification of the higher aliphatic alcohol with sulfuric acid yields the alkyl sulfate, which in the form of its sodium salt is widely employed as a household detergent.
Introduction of nitrogen into the fattyacid molecule has resulted in the devel opment of an extremely versatile class of products. One method for introducing nitrogen involves treatment of an organic acid with ammonia. Elimination of one molecule of water leads to the formation of amide. Amides RCOH 4- N H , >* R C N H , + H a O
>- RCH 2 OH -
ROH
A RCH 2 OHJ-f H 2 S O < - ^ RCH 2 OS0 2 OH(Na) + H 2 0 Alky] Sulfate The higher aliphatic alcohols are also employed as chemical intermediates, principally in the production of the alkyl halides, which i n turn are used in the production of other chemicals such as the mereaptans, used in the processing of rubber, and the amines, which will b e discussed in greater detail later. •
Substituted Amides RCOH + R ' N H 2 > R C N H R ' -+- H 2 0
A
17 -
A
VO
A. Nitriles of the higher fatty acids are liquids or low-melting solids which have found usefulness as plasticizers. The pres ent value of these chemicals, however, lies largely in their use as intermediates in the preparation of higher aliphatic amines by catalytic hydrogenation. Either primary or secondary amines are pro duced depending upon the conditions employed. Primary Amines R C = N + 2H 2 > RCH,NH, Secondary Amines RCH 2 Ν Η -f N H ,
2 R C = N -f 4112
R C s N + 2H*0
Alkyl Halides RCH 2 OH -f- H X > R C K S X -f- H 2 0 the corresponding acid chlorides by means of chlorinating agents such as phosphorus trichloride. The acid chloride is an ex tremely reactive compound and is useful i n the introduction of the fatty-acid radi cal into other molecules. One such reac tion is commercially used in the produc tion of another type of synthetic detergent —again one w h i c h is effective in the pres ence of hard water.
CH, Detergent
RCH 2 A third higher aliphatic amine which has assumed a position of considerable im portance is the tertiary derivative con-
J. HAHWOOD, assistant director of research at Armour & Co. since 1948, is interested in guanidine derivatives, polypeptide synthesis, isoquinoline derivatives, pyrimidines, proteins and amino acids, fatty acids and their derivatives, and chemical, physical, and biological properties of each. He has published 30 technical articles and is the owner of 16 patents. With degrees from the University of Utah and Iowa State College, the year 1931 saw him as a postdoctoral research fellow at Yale, and in 1933 he began his tenure at Armour as a research chemist. He belongs to the ACS, the American Oil Chemists Society, and Sigma Xi.
H•
V O L U M E
3 0,
NO.
13
»
»
Tertiary
Amines
CH, / RCHaX + H N
NaOH >CH,
Amides of the fatty acids are relatively inert chemicals and are used today in the production of water-repellent coatings for fabrics, as foam stabilizers, and in the production of surface-active agents. Sub stitution of an amine for ammonia in the reaction shown above will lead to the formation of a nitrogen-substituted amide.
Fatty Alcohols RCOR'
taining one long chain and two lower aliphatic groups, usually methyl or ethyl groups. Tertiary amines of this type m a y b e prepared by the reaction of the alkyl halide with a lower aliphatic secondary amine.
M A R C H
3 1,
1952
CH, RCHtN
X
N a X -f- Η,Ο CH,
Processes based on t h e primary amine as the starting material are also available. A variety of secondary and tertiary amines is of course possible. Those discussed are in commercial production at the present time. A fourth type of compound w h i c h is closely related to t h e amines has four organic radicals attached t o the nitrogen atom and is designated as a quaternary ammonium salt. . T w o processes are a p plied on a commercial scale to the pro duction of these compounds. O n e is based on the reaction of a primary amine with methyl chloride, and the other on the reaction of a tertiary amine with an alkyl halide. Quaternary Ammonium Salts R C H 2 N H 2 + 3CH3C1 + 2 N a O H >CH 3 RCH2—N—CH3
CH,
CI + 2NaCl + 2 H 2 0
J
CH 3 RCH2N
+ C ft H 6 CH,Ci
>-
\ CH, CH, RCHa—N—CH 2 CeH B
CI
CH 3 Choice of process is determined b y the end product desired. The first process is more economical but is disadvantageous in that sodium chloride is produced as a by-product. T h e second process is usually employed where the introduction of a group differing from those present in the tertiary amine is desired or where a saltfree product is required. T h i s process is used in the production of quaternary am monium salts such as the benzyl type com monly used in antiseptic preparations. Amines including the higher aliphatic derivatives are basic in their reactions and form ammonium salts with most acids. In most uses salts of the higher aliphatic amines are required. A brief discussion of the properties of the higher aliphatic ammonium salts as contrasted with the properties of soaps follows. Soaps, the salts of the fatty acids, like other salts, ionize in solution to produce the positive sodium ion and the negative 1283
surfaces and imparting antistatic prop- aliphatic groups or one aliphatic and one aromatic group. erties. The quaternary ammonium salts are extremely active antiseptics, killing Ketones microorganisms in dilutions of 1 t o 50,000 or higher. Adsorption of these comRx 2RCOH pounds on metal surfaces results in the ^ > C = 0 -f C0 2 -l· H 2 0 II inhibition of corrosion. An interesting ο use of quaternary ammonium salts is as combined bactericides and corRCC1 -f- H < f ~ ~ ^ > A1C13 RC+ HC rosion inhibitors in the secondary oil-recovery industry. The quaterΟ nary arnmonium salts are substantive The first reaction above is a high-tempera to many fabrics^ a n d are employed as ture catalytic reaction. The second is softeners. usually brought about by Friedel-CraftsThe quaternary ammonium salts contype catalysts. In general, the ketones taining two higher aliphatic chains are derived from saturated fatty acids are soluble in oil. As a result of this propwaxy solids and are employed as plastierty these compounds are excellent emulcizers, as antiblocking agents for plastics, sifying agents. An interesting application as flatting agents for paints, and as wax of these compounds is in their reaction additives. with bentonite. A quaternary ammoniumReactions of the fatty acids discussed betonite complex is formed which is emthus far have all involved the carboxyl ployed in lubricating grease and in printgroup. A number of reactions of the ing ink. A recent development in the use hydrocarbon chain are applied on a com of quaternary ammonium salts involves mercial scale. Oxidation of oleic acid their application as a coating for phlebotresults in the formation of a nine-carbon omy needles. The adsorbed film markedly dibasic acid and a nine-carbon monobasic inhibits the coagulation of blood in the acid. bore of the needle. A third class of surface-active agents Oxidation of Oleic Acid consists of those which are nonionic in character. Three important types of these (O) CH 3 (CH 2 ) 7 CH=CH(CH 2 ) 7 CO0H > substances are produced by the reaction of ethylene oxide with fatty acids, fattyCH 3 (CH 2 ) 7 COOH -f- HOOC(CH2)7COOH acid amides, or fatty amines. Dibasic acids are in great demand in Nonionic Surface-Active Agents the field of polymers and nylon-type plastics. The medium long chain fatty RCOH -h xCH 2 CH 2 >acids such as pelargonic produced by the II \ / above reaction are useful as flotation RCO(CH 2 CH 2 0) x H agents and as chemical intermediates. ο ο Ο Sebacic acid, the 10-carbon dibastic acid, is produced from ricinoleic acid ( obtained RCNH 2 + (x y)CH 2 CH 2 • from castor oil) by fusion with alkali. Pyrolysis of ricinoleic acid leads to the Ο formation of an 11-carbon unsaturated /(CH2CH20)xH acid, 10-undecenoic acid, and heptanal. RCN< || XCH 2 CH 2 0) y H Pyrolysis of Ricinoleic Acid Ο CH 3 (CH 2 ) 5 CHOHCH 2 CH = CH (CH2)7COOH *RCH 2 NH 2 + (x + y)CH 2 CH 2 > CH2=CH(CH 2 ) 8 COOH + CH3(CH2)5CHO Ο (CH 2 CH 2 0) x H A polymerization reaction is applied to RCH 2 N· fatty chemicals containing two double (CH 2 CH 2 0) y H bonds (linoleic acid or derivatives there of). The "dimer" acid thus produced is These products a r e excellent detergents a high-molecular-weight dibasic acid and emulsifying agents. Properties of which may be used in the production of the compounds can be varied not only polyamide-type plastic coatings. Deriva by the nature of the aliphatic chain of the tives of the dimer acid, such as the difatty chemical but also by the length of nitrile or the diamine, are also of interest. the polyoxyethylene chain introduced. The variety of processes and products Accordingly it is possible to prepare prod mentioned serves to illustrate t h e potenti ucts to fit specific needs. In the case of alities of the fatty acids as chemical raw the polyoxyethylene derivatives of the materials. Those familiar with this field higher aliphatic amines, the basicity of are convinced that only a good start has the nitrogen atom is reduced to such an been made in the exploitation of the fatty extent that these compounds can be re chemicals. The possibilities are so num garded as being essentially nonionic. erous that it is difficult to predict where Ketones derived from the higher fatty continued research and development will acids, although in only limited com lead. mercial production at the present time, PRESENTED at a Symposium on Chemistry of have properties which suggest a promising Meat and Other Products of the Meat-Packing Industry, Division of Agricultural and Food future. Compounds of this type may b e Chemistry, ACS Diamond Jubilee Meeting, Newprepared containing either two higher York, September 1 9 5 1 .
A
Fatty acid stills and nitrile conversion unit at McCook plant of Armour & Co. alkylcarboxylate ion. It is the latter which is responsible for the surface-active prop erties of soaps. Higher aliphatic ammo nium salts have an analogous structure in which, however, the surface-active ion is positive. For this reason this type of compound is sometimes referred to as an "invert soap." Soaps are designated as anionic surface-active agents and higher aliphatic ammonium salts as cationic sur face-active agents. Ionic Surface Active Agents Anionic Cationic RCONa
II ο
RCH 2 OS0 2 Ö Na
RCH 2 NH 8 CI RCH 2 N(CH 3 )tci (RCH 2 ) 2 N(CH 3 ) 2 CI
Almost all uses of the cationic compounds are related to their tendency to adsorb on surfaces. Most surfaces carry a negative electrical charge. Consequently there is a tendency for the nitrogen-containing polar group of the cationic surfaceactive salt to b e adsorbed upon the surface. The resulting orientation of the hydrocarbon chains away from the surface is reflected in a marked alteration of the properties of the surface. The three types of cationic surface-active chemicals shown above are finding commercial application at the present time. Amine salts, usually the acetates, are employed in flotation separation of phosphate rock from silica. These materials are also effective in the separation of potassium chloride or sylvite from sodium chloride or halite. Amine salts are effective antistripping or bonding agents used in the preparation of asphalt road mixes. The surface-active chemical not only results in a more stable bond between the asphalt and the gravel but also permits the use of wet aggregate in the preparation of the mix. Amine or quaternary ammonium salts are adsorbed on plastic or fiber surfaces, thereby reducing the electrical resistance of the 1284
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