Fatty Acids: Chemistry, Synthesis, and Applications

Fatty Acids: Chemistry, Synthesis and Applications is a comprehensive source of information about a wide range of industrially important fatty acids. This practical resource provides key insights into the chemistry, synthesis, industrial applications, derivatives, and analysis of fatty acids, and the chemical modifications that transform them for use in products from biodiesel fuels to pharmaceuticals.

Written by a team of industry experts, Fatty Acids includes detailed descriptions of fatty acid crystallization, enzymatic synthesis, and microbial production. This book focuses heavily on the chemistry of trans fatty acids, with extensive explanations of their synthesis and measurement. Further, the book addresses advances in the analytical methodology, including mass spectrometry, of fatty acids as well as their derivatives.

This book serves as a reference manual to a new generation of lipid scientists and researchers; a useful resource for oleochemical industries; and a valuable teaching aid for undergraduate and graduate students who are interested in fields related to the chemistry of oils, fats, and food.

• Includes recent developments in the synthesis of fatty acid derivatives, as renewable raw materials for the chemical industry
• Presents efficient synthetic methods for the dietary trans fatty acids in multi-gram scale allowing scientists and researchers to study dietary effects of individual trans fatty acids on human health
• Addresses uses of fats and fatty acids in foods and nutrition
• Identifies the roles of fatty acids and derivatives in cosmetic technology

• Language: English
• Publisher: Elsevier Science
• Release date: Jul 21, 2017
• ISBN: 9780128095447

Book preview

States.

Preface

Moghis U. Ahmad

Fatty Acids, esterified to glycerol, are the main constituents of oils and fats. The oils and fats are the renewable resources for the chemical industry. The industrial exploitation of oils and fats, both for food and oleochemicals, is based on chemical modification of both the carboxyl group and unsaturation present in fatty acids. The oleochemicals could add value to existing crops and provide market for new crops, and research leads to novel fatty acids derivatives. The oleochemical production involves reaction at the carboxyl group, with the chain length, and at unsaturation of the fatty acid chain to give products of the desired structure and properties. Introducing functionality to the alkyl chain through known chemical reactions leads to novel compounds with commercial potential. The carboxyl groups and the unsaturated centers generally react independently, but when they are in proximity, they might react through neighboring group participation. In enzymatic reactions, the reactivity of the carboxyl group can be influenced by the presence of double bond in close proximity.

The coverage in this book is selective, focusing on industrially important fatty acids, their chemistry and synthesis. Historical perspective of important developments in the chemistry of fatty acids in the last 100 years is presented. The main emphasis of this book is on enzymatic and chemical synthesis of fatty acids and derivatives; naturally occurring fatty acids, their purification and preparation for various applications; presence of unusual cyclic fatty acids like epoxy fatty acids and carbocyclic fatty acids in seed oils and their chemical and biological properties; natural and synthetic acetylenic epoxide and their industrial importance; microbial production of fatty acids; biosynthesis of vegetable oils and process improvement, new plant sources to meet future world needs of fatty acids; industrial importance of castor oil and derivatives; crystallization of fatty acids in edible oils and their structure; free fatty acid oils for biodiesel production; advancement in synthesis of sugar fatty acid esters and their applications; fatty acids–based surfactants; fatty acids in Cosmetic Technology; chemistry of long-chain α,β-unsaturated fatty acid and derivatives; synthesis of different types of estolides as next generation of high-performance synthetic lubricant; synthesis of dietary cis- and trans-octadecenoic (18:1) fatty acids present in partially hydrogenated vegetable oils; chromatographic and spectroscopic analyses of dietary fatty acids; mass spectrometry–based methods for the analyses of fatty acids and derivatives.

This book serves as reference manual to new generation of lipid scientists and researchers, useful for oleochemical industries, a valuable teaching resources for undergraduate and graduate students interested in the field of chemistry of oils, fats, and fatty acids, food chemistry, cosmetics and personal care products, and pharmaceuticals. This book also serves as a valuable reference and resource for those interested moving in the field of chemistry and technology of fatty acids. The goal in writing this book is to gather writing from many of the leaders in the field who had published one or several articles in various aspects of fatty acids chemistry. The authors have publications in the field of oils, fats, and fatty acids and are imminently qualified to summarize their own work and related work in their field of expertise. It is hoped that the readers will find it valuable to read and this will help them to understand the field of oils, fats, and fatty acids, and their utilization in oleochemical industries.

I would like to thank all contributors for their magnificent work in the collection of research publications and their devotion to presenting accurate and detailed scientific information. The assistance from Academic Press (Elsevier) and AOCS Press is greatly appreciated with special thanks to Billie Jean Fernandez and Janet Brown.

Chapter 1

History of Fatty Acids Chemistry*

Gary R. List¹, James A. Kenar² and Bryan R. Moser²,    ¹G.R. List Consulting, Washington, IL, United States,    ²National Center for Agricultural Utilization Research, Peoria, IL, United States

Abstract

Fatty acids are basic renewable chemical building blocks that can be used as intermediates for a multitude of products. Today the global value of fatty acids exceeds 18 billion dollars and is expected to increase to nearly 26 billion over the period from 2014 to 2019. From its auspicious beginnings, the growth of the fats and oils industry has rested upon the shoulders of those that have gone before and worked tirelessly to understand fatty acids and expand their utilization. Because of the important advances made by these and other researchers, renewable oleochemicals are now an important component of the worldwide chemical industry. This chapter provides a brief general historical perspective of some important developments in the chemistry of fatty acids.

Keywords

History; fatty acids; oleochemistry; fats and oils; lipids

Chapter Outline

1.1 Introduction 2

1.2 Early Fatty Acid History 2

1.3 Major Developments in the Oleochemical Industry 9

1.3.1 Fat Splitting 9

1.3.2 Catalytic Hydrogenation 10

1.3.3 Fatty Acid Distillation 11

1.3.4 Fatty Alcohols 11

1.3.5 Estolides 12

1.3.6 Dimer and Trimer Cyclic Fatty Acids 13

1.3.7 Hydroformylation of Fatty Acids 14

1.3.8 Ozonolysis of Fatty Acids and Triglycerides 14

1.4 Contributions of Analytical Chemistry to Fatty Acids 15

1.5 Recent Developments in Fatty Acids 16

1.6 Summary 17

References 18

1.1 Introduction

The history of fatty acids is a complex one with discoveries often coinciding. However, a number of landmark developments that had significant impact are covered here. The historian is often challenged by who discovered what and when. Fortunately, most of the major events and discoveries surrounding the chemistry of fatty acids are well documented in journal literature. The application of these discoveries in industry is often times difficult to discern because they are mainly documented in the patent literature, which can be time consuming to search, difficult to interpret, and most patents contain references to other patents, which in turn must be examined for prior art. A chronological summary of important discoveries in fatty acid, oleochemical, and triacylglycerol chemistry is shown in Table 1.1. This list is compiled from various sources including the open literature, patents, and chronological compilations from Blank (1942) and the Cyberlipid website (Anonymous, 2016).

Table 1.1

Chronological Summary of Important Discoveries in Fatty Acid, Oleochemical, and Triacylglycerol Chemistry

The first comprehensive book written in English that dealt with fats, oils, and waxes appeared in 1895 (Benedikt and Lewkowitsch, 1895). This book was published as an English translation of Benedikt’s German book on the subject and was subsequently revised numerous times up until 1927. The 1895 edition serves as a valuable historical reference for many of the important early discoveries in fatty acid chemistry, although, the original literature references contained therein can be difficult to locate. Eugene Blank (Blank, 1942) reported a chronological list of important dates in the history of fats and waxes through 1915. The chronology stopped at the year 1915 because events beyond this date were considered too new to have assumed an historical perspective at time the list was published. A review of fatty acid history would be incomplete without reference to Klare Markley’s extensive five-volume set on the chemistry of fatty acids appearing in 1964 (Markley, 1964). In 1979 Everett Pryde edited a book that covered the fatty acid literature up to 1979 (Pryde, 1979). A recent review describing the contributions of Wilhelm Heintz (1817–80) is an excellent resource for the early events in fatty acid chemistry (Ramberg, 2013). The aim of this chapter is to provide a brief historical perspective of the events and developments in the field of fats and oils that pertain to fatty acid chemistry and their subsequent application. It is hoped that this chapter serves as a guide for the location of papers that provide further details concerning the history of fatty acids.

1.2 Early Fatty Acid History

Fatty acids have been used by man for thousands of years and specifically in the preparation of soap. The ancient Babylonians were using soap as early as 2500 BC. The Old Testament scriptures mention soap in several passages. An excellent review of the soap industry is found in the book on soaps by Spitz (2004). By AD 800–900, the soap industry was well established in Germany and France and by the 1600s had greatly expanded. The US soap industry is over 200 years old and has undergone much change. As early as 1714 Benjamin Franklin assisted in his father’s soap and candle business and in colonial America, candle production was growing and 500,000 pounds of candles were exported to the West Indies and Great Britain. Over the years, numerous new soap products such as bar, laundry, and deodorant soaps as well as various detergent products have been introduced. More recently, skin care products based on soaps have entered the personal care market. Although many bar soap brands have been introduced, only a few brands such as Cashmere Bouquet (1872), Ivory (1879), Lifebuoy (1887), Camay (1928), Woodbury (1899), and Palmolive (1898) have survived. Despite the long use of fatty acids in soap manufacturing, their structure, composition, and chemistry was not well understood due to the slow development of analytical and purification techniques required for their separation, purification, and identification.

While inorganic chemistry had made several key advances during this time, by the early 1800s, the understanding of organic molecules and their chemistry was still in its infancy. Although glycerol was discovered in 1779 by the Swedish chemist Carl Scheele, it would be another 40 years before the nature of fats and oils would be understood. Scheele had reacted fat with lead oxide and isolated a viscous liquid, which became known as Scheele’s sweet principle, but the remaining fatty acid salt byproducts were not characterized.

A pioneer in organic chemistry was Michel Chevreul (1786–1889) (Costa, 1962). Chevreul began his research by examining soap samples around the year 1811 and by 1818 he had discovered a number of fatty acids and had elucidated the chemistry of saponification by showing that fats and oils consisted of three fatty acid molecules esterified to one glycerol molecule. Nearly 50 years later, Chevreul while studying Scheele’s product isolated glycerol in the water phase for which he coined the term glycerin. However, the chemical formula for glycerin was not determined until 1855 by Charles-Adolphe Würtz (Kenar, 2007). Chevreul’s research was published in Annales di Chemie over the period of 1813–18. In 1823 his complete research on fats and oils was published under the title Recherches chimiques sur les gras d orignine animale. This work was republished in 1886 to commemorate his 100th birthday as Chimiques sur les corps gras originine animale. Although republished in 1886, it had never been translated from ancient French to English until Albert Dijkstra translated A chemical study of oils and fats of animal origin in 2009 to mark the 100th anniversary of the American Oil Chemist’s Society (Dijkstra, 2009a). Chevreul was one of the first to use a variety of new techniques such as elemental analysis, melting point determination, fractional solubility, and crystallization as a means of identifying compounds (Dijkstra, 2009a,b). Chevreul identified a fatty acid, named margaric acid (heptadecanoic acid, 17:0), which he thought to be pure substance.

Wilhelm Heintz (1817–80) later showed that Chevreul’s identification of margaric acid was actually a mixture of palmitic (16:0) and stearic acids (18:0) (Ramberg, 2013). The difficulty in separating fatty acids at the time that have similar elemental composition and melting points no doubt accounted for the confusion and illustrates the difficulties organic chemists of this period faced in identifying new compounds using limited tools and crude analytical techniques.

From about 1840–50, a number of fatty acids were discovered, the synthesis of triglycerides was accomplished, and the basic phenomena of polymorphism and interesterification of fats and oils were recognized. Wilhelm Heintz was a major contributor to fatty acid chemistry. Heintz held a position at a small university in Germany (Halle) beginning in 1851 and began to study animal fats, which he called the fat kingdom. He expanded upon Chevreul’s work by developing improved methods to conduct elemental analysis and determine more accurate melting points, both of which were major advances in lipid chemistry (Ramberg, 2013). Heintz was an extremely productive chemist, and authored over 200 publications on physiological chemistry, mineral analysis, and improved methods for elemental analysis and organic chemistry. As mentioned previously, Chevreul introduced some novel approaches to lipid chemistry including elemental analysis and fractional solution/crystallization, and used melting point to identify and judge the purity of fats and fatty acids. At the time, Heintz began his research on fatty acids, others had discovered a number of fats and fatty acids, all of which were defined by their melting point and chemical composition. Heintz was the first to question melting point as a measure of purity for fats and fatty acids and showed that margaric acid, described by Chevreul, was really an impure mixture of palmitic and stearic acids. He then turned his attention to butter where only four fatty acids had been identified. Heintz isolated four additional fatty acids to bring the total to eight. From this, he suggested that as a general rule, the saponification of fats contain only acids whose carbon numbers are divisible by four. His investigations on Spermaceti showed that melting point depression can occur in mixtures of fatty acids. From this discovery, Heintz concluded that the long accepted method for preparing pure compounds by repeated crystallization until the melting point no longer changed was inadequate to identify a fatty acid.

From 1880 to 1900, a number of discoveries were made that had everlasting impact on fatty acid chemistry, including Soxhlet extraction, the saponification index, and iodine value. Unusual fatty acids were discovered, including fatty acids containing the hydroxyl, acetylenic, and cyclopentenyl structures. The structures of unsaturated fatty acids (ricinoleic, oleic, linoleic, linolenic) were also reported in the 1890s.

Although polymorphism was discovered in 1852, the nature of the phenomenon was not fully understood until the late 1920s when Thomas Malkin introduced X-ray methods to explain why trigylcerides may exhibit multiple melting points (Malkin, 1954). Malkin’s work later came under criticism after he reported four polymorphic forms of tristearin. Both Bailey and Lutton maintained that only three polymorphic forms existed for tristearin and Lutton conclusively proved that the fourth form does not exist (Bailey et al., 1945; Lutton, 1945).

1.3 Major Developments in the Oleochemical Industry

The modern oleochemical manufacturing industry was extensively reviewed in a book by Gunstone and Hamilton (2001). Included are chapters on basic oleochemicals, amine- and anionic-based surfactants, lubricants and hydraulic fluids, biofuels, coatings and inks, analysis, new chemistry, and the environment. Applications are well covered and referenced. Normann Sonntag authored a number of review articles appearing in the Journal of the American Oil Chemists’ Society, including fat splitting, new applications for fatty acids and derivatives, and short-chain fatty acids from alcohols, olefins, and Zeigler intermediates (Sonntag, 1968). Kadesch reviewed the chemistry of fat-derived dibasic acids (Kadesch, 1954, 1979). Hastert reviewed the hydrogenation of fatty acids (Hastert, 1979). E.C. Leonard published an excellent review of polymerization and dimer acids (Leonard, 1979). Nitrogen derivatives of fatty acids were reviewed by Reck and manufacture of amides, diamides, nitriles, primary amines, and oxides as well as applications are discussed in detail (Reck, 1985). The aforementioned A.J. Stirton was a pioneer in soaps and detergents made from fats and fatty acids. He also authored five chapters for the 3rd edition of Bailey’s Industrial Oil & Fat Products (Stirton, 1964). The following sections outline some of the more important developments in various aspects of the oleochemical industry.

1.3.1 Fat Splitting

Perhaps the most important discovery of the 19th century was the introduction of an industrially relevant method to split fats and oils into fatty acids and glycerin. Up until this time, fats and oils were saponified in open kettles using alkali. However, Ernst Twitchell patented a catalytic method in 1898, that became known as the Twitchell process (Twitchell, 1898). The acid catalyst was prepared by the reaction of oleic acid with sulfuric acid and naphthalene. In 1900 he reported that treatment of oleic acid and benzene with concentrated sulfuric acid yields benzene stearosulphonic acid useful as a fat-splitting reagent (Twitchell, 1900) along with additional papers on the synthesis of sulfonic acid containing stearic acid (Twitchell, 1906, 1907). In this process, melted fats with 25%–50% by weight of water were mixed and then agitated while sparging with steam in an open tank for 16–28 hours in the presence of the catalyst. After allowing the reaction mixture to settle, the water and glycerin phase was removed and the fatty acids were recovered. Catalysts for the reaction were added at levels between 0.5% and 1.5%. Later, A.J. Stirton and colleagues showed that catalysts based on alkyl aryl sulfonates were more effective than Twitchell’s catalyst. Despite long reaction times operated in batch mode and the need for specially prepared catalysts, the Twitchell process was extensively used in the United States and England while a modified process using the improved alkylbenzene-based catalysts (Stirton et al., 1944) came to be used elsewhere in Europe. Twitchell was awarded the Perkin Medal in 1917 by the Society of Chemical Industry in recognition of his landmark achievement as well as an honorary doctorate.

1.3.1.1 Continuous Fat Splitting

Although the Twitchell process represented a significant improvement over previous methods, the conditions were highly corrosive and energy intensive, and the batch method gave poor quality fatty acids having dark colors. Over time, more efficient and continuous splitting processes were developed. Several major advances in continuous fat splitting were introduced in the late 1930s. Ittner patented a countercurrent contact process with water and oil at temperatures of 200°C under pressure to yield soaps and glycerin (Ittner, 1933). Victor Mills described a continuous rapid fat-splitting method claimed to give higher yields of split fat and glycerin and a superior grade of fatty acids (Mills, 1939a,b). At various points, Procter & Gamble, Colgate, and Emery held patents similar to those of the original Mills and Ittner patents on continuous fat splitting (Ittner, 1938, 1948, 1949). Today many modern fat-splitting plants use the Colgate-Emory method, which is a continuous fat-splitting process employing a countercurrent hydrolysis reaction using steam in a pressure tower with internal heat exchange. The Colgate-Emory process does not require catalysts, can be completed in 2–3 hours with splitting efficiencies of approximately 98%, and gives high-quality light-colored fatty acids that can subsequently be purified or separated by molecular distillation and fractionation (Barnebey and Brown, 1948).

1.3.2 Catalytic Hydrogenation

Catalytic hydrogenation was a major advance in fatty acid chemistry. In 1897 Sabatier described the hydrogenation of organic compounds in the presence of finely disintegrated metals for which he was awarded the Nobel Prize in chemistry. In 1903 Normann received a patent on the hydrogenation of fatty acids and their glycerides (Normann, 1903). Normann subsequently licensed the hydrogenation technology to Joseph Crossfield, a businessman in Great Britain manufacturing soaps. Within a few years, Crossfield was convinced that hydrogenation offered the soap industry a new technology. Completely hydrogenated fats and oils would serve as a feedstock for fat splitting and a source of fatty acids for soap and candle manufacturers. Crossfield brought the hydrogenation patents to the United States and sold them to Procter & Gamble around 1907. Procter & Gamble subsequently discovered that hydrogenated fats had applications in the edible oil arena and by 1911 Procter & Gamble marketed the first all vegetable oil solid shortening made by blending partially hydrogenated and liquid cottonseed oil. In 1920 the US Supreme Court ruled that the Procter & Gamble patents were void, thereby opening up hydrogenation as a fat processing technology (List and Jackson, 2007, 2009).

1.3.3 Fatty Acid Distillation

The modern US oleochemical industry developed largely on the efforts of Ralph Potts (1900–81), a member of American Oil Chemists’ Society (AOCS) who is often referred to as the father of the oleochemical industry (List, 2004b). Potts worked for the American meatpacking company, Armour and Company, and his research began with the belief that fatty acids could be distilled. With a crude-fractionating column, his belief was confirmed and by 1933 Armour built a distillation plant based on Potts’ distillation process. Armour sold fatty acids at a profit but supplies of tallow and grease exceeded the demand for fatty acids. Potts and Victor Conquest developed a plan to find new uses for fatty acids and by 1938 they had discovered a process to make fatty amines. The amine business was profitable but keeping up with the growing demand was difficult, so a new plant was built and operational by 1951. Potts designed similar plants in England, Canada, Japan, Belgium, and Brazil. Potts held numerous patents on the distillation of fatty and tall oil acids as well as patents on production of fatty acid nitriles and amines (Pool and Potts, 1944; Potts, 1948a,b, 1950, 1951, 1954, 1964, 1967; Potts and Christensen, 1943; Potts and McKee, 1936; Potts and Olson, 1953; Potts and Smith, 1957; Potts and Stalioraitis, 1971). Potts, authored numerous publications, was the second recipient of the Alton E. Bailey Award recognizing outstanding research and exceptional service in the field of lipids and associated products. Ralph Potts’ contributions to the modern oleochemical industry cannot be overemphasized, as the purification of fatty acids by distillation is a well-established industrial practice and still the most common and efficient means of producing high-purity fatty acids (Reck and Sonntag, 1984).

1.3.4 Fatty Alcohols

Fats and oils are major sources of raw materials for soaps and detergents, with about 30% used as fatty acids and about 55% as fatty alcohols (Egan, 1968; Egan et al., 1984). Fatty alcohols can be derived from two main groups of natural raw materials, namely, fats and oils of plants and animals and wax esters from sources such as sperm (whale) oil or jojoba oil. Prior to 1973, fatty alcohols were produced by hydrolysis of the wax esters from sperm oil followed by fractionation of the fatty alcohols and fatty acids. However, the worldwide ban on whaling (1973) prompted the use of fats and oils for oleyl and other fatty alcohol production. The fats and oils are transesterified with methanol to give fatty acid methyl esters, which are then converted into the corresponding fatty alcohols through reduction chemistry. The fatty acid esters are reduced by either reaction with sodium and alcohol or hydrogenation in the presence of a suitable catalyst (Kastens and Peddicord, 1949). Typically, the hydrogenation reaction is carried out in the presence of hydrogen at 3500–4200 psi and temperatures of 300–350°C using mixed catalysts that may contain chromium, zinc, copper cadmium, and aluminum. Obviously, the hydrogenation process is not suitable for preparing unsaturated fatty alcohols. For example, oleyl alcohol can be produced by sodium reduction of using tallow, olive oil, and canola oil as raw materials, which contain approximately 43%–45%, 61%–63%, and 60% oleic acid, respectively.

1.3.4.1 Guerbet Alcohols

In 1907 Guerbet reported that linear alcohols can be converted to branched chain isomers by catalytic reactions at high temperatures (Guerbet, 1907). The product from the reaction is an alcohol with twice the molecular weight of the reactant minus one mole of water. Until recently, Guerbet alcohols have received little attention in oleochemical applications despite having many advantages over linear ones. These include good oxidative stability and low-temperature operability as well as light colors. Guerbet alcohols can be further modified to yield Guerbet acids. For example, the Guerbet alcohol, 2-octyl dodecanol, when treated with sodium hydroxide, yields the corresponding fatty acid in high yield. A recent publication reported the synthesis of a number of Guerbet alcohols and their lubrication properties (Waykole and Bhowmick, 2014). Excellent reviews of the chemistry and properties of Guerbet alcohols are given by O’Lenick (O’Lenick, 2001, 2016).

1.3.5 Estolides

Estolides are a unique class of compounds derived from fatty acids and may occur naturally as polyacylglycerides in vegetable oils or can be synthesized from unsaturated fatty acids or triglycerides (Isbell, 2011). Fatty acids with hydroxyl or epoxy groups are particularly attractive as estolide precursors. Castor and lesquerella oils are converted to estolides via successive esterifications of mid-chain hydroxyl moieties at a temperature of 250°C. The patent literature reports the synthesis of triglyceride estolides from the reaction of castor and lesquerella oils with various fatty acids using a p-toluenesulfonic acid catalyst at 150°C (Lawate, 1995). This allows the removal of water formed during the reaction as an azeotrope. Estolides generally have excellent cold flow properties and viscosity indices, thereby rendering them suitable as low-temperature lubricants. Estolides prepared from meadowfoam seed oil have poor low-temperature properties but provide good moisturizing properties for use in shampoo and conditioners (Isbell et al., 2000). Cermak and colleagues reported the synthesis of estolides from oleic and saturated fatty acids as well as their applications in lubricant formulations (Cermak et al., 2013; Cermak and Isbell, 2001). Isbell recently authored a comprehensive review of estolide studies carried out at the National Center for Agricultural Utilization Research (NCAUR) in Peoria, Illinois (Isbell, 2011).

1.3.6 Dimer and Trimer Cyclic Fatty Acids

Cyclic acids were discovered in 1876 and, historically, interest in dimer acids was an outgrowth of work surrounding the thermal polymerization of vegetable oils known as heat bodying (Kappelmeier, 1933; Scheiber, 1929). When vegetable oils are heat bodied, complex oligomeric structures are formed through cyclization reactions at unsaturated sites of fatty acids. Although cyclization of unsaturated fatty acids was known and dimer acids were discovered in 1920, neither received much attention until the 1940s because the understanding of polymers and polymer chemistry was in its infancy. However, the pioneering work of Wallace Carothers, Carl Marvel, and Roger Adams at the University of Illinois gave better understanding of polymers and chemists new tools to modify fats and fatty acids. An early pioneer in the field was John Cowan, who received his PhD under Marvel at the University of Illinois. His early research at the newly opened Northern Regional Research Laboratory (now NCAUR) focused on the polymerization of fatty acids, resulting in rubber substitutes and plastics (Cowan, 1961).

Fatty acids containing the trienoic structure such as linolenic acid found in linseed oil (50%–55% linolenic acid), when treated with alkali at high temperatures, form a ring structure which after hydrogenation yields a saturated cyclic acid that can be esterified with alcohols (Friedrich, 1967, 1968; Friedrich et al., 1965). Friedrich synthesized a number of cyclic diesters and evaluated them for possible use as lubricants in the aviation and aerospace industries (Friedrich et al., 1965). Tetramethyl cyclobutanediol diesters from vicinally substituted cyclic acid mixtures were patented and met military specifications for aviation lubricants (Friedrich, 1968).

Dimer and trimer acids are di- and polycarboxylic acids and are commercially produced by reacting unsaturated fatty acids found in vegetable oils such as tall oil, canola oil, or oleic acid in the presence of a clay catalyst. By using C18 unsaturated fatty acids, a wide variety of complicated isomeric oligomeric cyclic structures containing 36 and 54 carbon dimer and trimer acids, respectively, can be obtained. These liquid oligomerized materials are unique since they never crystallize, have a molecular weight of around 560, distill with difficulty, are soluble in hydrocarbons, and are unsaturated but not conjugated. Dimer acids are reactive toward oxygen and sulfur but these reactions are easily controlled. Dimer acids are an important part of the oleochemical economy and have been commercialized and find uses in a number of applications in lubricant, pigment, cosmetic, personal care, and surfactant formulations.

1.3.7 Hydroformylation of Fatty Acids

Carbon monoxide can react with unsaturated olefins (focus on unsaturated fatty acids) in a variety of ways. In the first method known as the oxo process, an unsaturated fatty acid is reacted with carbon monoxide in the presence of hydrogen and metal catalysts under high pressure to give hydroformylated products and dates back to the late 1930s (Pryde et al., 1972). The catalyst is a cobalt hydrocarbonyl complex formed in situ from a variety of cobalt compounds. Typically, extensive double bond isomerization occurs before hydroformylation thereby resulting in a mixture of isomers. Frankel reported that the use of a rhodium triphenylphosphine catalyst prevented isomerization and oleic acid gave exclusively methyl 9(10)-formylstearate (Frankel and Pryde, 1977).

In the second method known as the Koch process, unsaturated fatty acids are reacted with carbon monoxide at the double bond position in the presence of sulfuric acid and water or alcohol to give a carboxylic acid or ester, respectively. The Koch process was reported in 1955 and was the first to demonstrate a feasible route to dicarboxylic acids. However, oleic acid was not reported. Subsequently, Roe and Swern reported the preparation of the corresponding diacid from oleic acid in good yields (Roe and Swern, 1960). Oleic acid was dissolved in 97% sulfuric acid and five moles of water was reacted with carbon monoxide at atmospheric pressure to give the diacid. Oleyl alcohol may also serve as the starting material. Other routes to diacids from oleic acid were reported by Reppe and Kroeper in the early 1950s (Reppe and Kroeper, 1952).

1.3.8 Ozonolysis of Fatty Acids and Triglycerides

From 1960 to 1980, a considerable amount of research was reported describing the ozonolysis of fatty acids, esters, and trigylcerides (Pryde and Cowan, 1962). Ozone reacts with double bonds to form an ozonide intermediate that can be catalytically reduced to aldehydes or oxidized to shorter chain fatty acids (Kadesch, 1963). For example, oleic acid yields azelaic (9-carbon diacid) and pelargonic (nonanoic acid) acids upon oxidative ozonolysis and was commercialized in the late 1950s. Aliphatic alcohols were prepared in good yield by reductive ozonolysis of methyl oleate, followed by hydrogenation with a nickel catalyst in aprotic solvents (Pryde et al., 1968).

1.4 Contributions of Analytical Chemistry to Fatty Acids

A major contributor to the chemistry and composition of fatty acids was George Jamieson, who directed the Bureau of Chemistry and Soils at the US Department of Agriculture in Washington, DC (Jamieson, 1943; List, 2004a). Over the period of 1918–47, Jamieson and colleagues characterized the fatty acid compositions of numerous now commonplace oils including cottonseed, peanut, olive, safflower, corn, and soybean, all of which developed into important commodity oils. Jamieson also investigated a number of lesser known sources of fatty acids, some of which are of current interest as healthy oils. They include walnut, grapefruit seed, apricot, cherry seed, pecan, and avocado oils. Jamieson reviewed the literature up till 1943 (Jamieson, 1943). By the 1950s, a third revision was required and was authored by E.W. Eckey (Eckey, 1954). Some 70 years later, it remains a valuable resource for fatty acid data on plant oils from numerous species.

Another pioneer in this area was Thomas Percy Hilditch (1886–1965). Hilditch devised or improved many procedures related to fats and oils including: ester fractionation, the use of thiocyanogen values, oxidative cleavage as a means to determine unsaturation, low-temperature crystallization, and alkali-isomerization to measure linoleic and linolenic acids (Gunstone, 2003). These contributions in analysis of fats and oils along with others relating to hydrogenation, autoxidation, and cis/trans isomerism have led many to refer to him as the father of fats and oils chemistry (Lie Ken Jie, 2015). His book, The Chemical Composition of Natural Oils, first published in 1940 and updated three times, is a seminal and influential contribution to chemical analysis of oils (Hilditch, 1940).

By the early 1960s, gas chromatography (GC) offered fatty acid chemists, a new tool for the analysis of plant oils and fatty acids. Prior to the widespread use of GC, determination of fatty acid composition was a laborious and time-consuming endeavor, involving fractional crystallization, distillation, and subsequent chemical derivatization to determine chain length, functional group presence, and location (Lie Ken Jie, 2015). GC, along with spectroscopic methods such nuclear magnetic resonance (NMR), mass spectroscopy (MS), and Fourier transform infrared spectroscopy (FT-IR), greatly accelerated the determination of fatty acid composition from weeks to hours. Frank Gunstone, a former graduate student of Hilditch, was a prolific pioneer in the application of these methodologies to lipid chemistry (Gunstone et al., 1967; Lie Ken Jie, 2015).

Chemists at NCAUR began screening germplasm for unique fatty acid compositions with potential industrial uses in the 1950s (e.g., Earle et al., 1959). A number of unusual fatty acids were found in addition to the more common ones encountered in plant oils. Among them are epoxy acids, hydroxy acids, and short-chain as well as very long-chain (>C18) acids. Notable examples include meadowfoam and crambe oils (Miller et al., 1964; Miwa and Wolff, 1962). The ban on commercial whaling in 1973 brought jojoba oil (a long-chain wax ester) to commercialization as a result of research done at NCAUR (Miwa, 1984). Oil from cuphea is an excellent source of short-chain saturated fatty acids (70% caprylic acid) having a composition similar to coconut oil (Miller et al., 1964). Since the supply of coconut oil is limited, cuphea shows promise as a source of short-chain fatty acids for the oleochemical industry. Efforts are underway to bring cuphea oil to commercialization. Similarly, meadowfoam oil is a rich source of unusual very long-chain fatty acids that can be converted into estolides and other products. As mentioned previously, estolides prepared from a variety of fatty acids show great promise as lubricant additives (Isbell, 2011; Lawate, 1995). Crambe oil is a rich source of erucic acid (Miwa and Wolff, 1963). Research conducted at NCAUR showed that ozonolysis provides a route to erucamide, a monomer for nylon 13,13 production (Nieschlag and Wolff, 1971).

1.5 Recent Developments in Fatty Acids

A number of other important developments in the fatty acid field have occurred within the past 30 years or so. Biotechnology and the use of enzymes to modify fats, oils, and fatty acids have and are revolutionizing the entire fats and oils industry. Once thought impossible, the use of enzymes in edible oil processing has become a reality. Enzymatic degumming of crude oils and the interesterification of fat blends for trans free edible products have been commercialized in the United States and Europe (Orthoefer and List, 2015). Biotechnology led to the discovery that single cell oils offer potential for production of numerous fatty acids needed for human nutrition. These include EPA and DHA found in fish oils. Algal oils show promise as high oil yield sources for biofuel production (Chisti, 2007).

The use of renewable resources represents a significant development in fatty acid chemistry and offers much potential for using green chemistry to protect the environment. Olefins can undergo a reaction known as metathesis, which has been exploited in the petroleum industry for decades. The foundations for metathesis were laid in the 1950s with the pioneering work of Anderson and Merckling (1955), who reported the first carbon–carbon double bond rearrangement reaction in the titanium-catalyzed polymerization of norbenene. Banks and Bailey (1964) later discovered that olefins undergo disproportionation in the presence of catalytic tungsten and molybdenum hexachloride and tetramethyltin. In essence, olefins are cleaved and reformed to give new smaller and larger olefins. For example, propylene yields mostly ethylene and butenes, with lesser amounts of pentenes and hexenes also formed. The first successful application of metathesis chemistry to lipids was accomplished by van Dam and coworkers (van Dam et al., 1972, 1974), who reported that tungsten hexachloride/tetramethyl tin catalysts were effective at metathesis of fatty esters to alkenes and dicarboxylic acid dimethyl esters. Verkuijlen and coworkers (Verkuijlen et al., 1977) subsequently demonstrated that metathesis of fatty acid esters can be achieved with a heterogeneous catalyst based on rhenium oxide supported on alumina promoted by a small amount of tetramethyl tin.

Grubbs and Schrock are pioneers in development of well-defined metathesis catalysts with broad functional group tolerance and high activity (Grubbs, 2004; Vougioukalakis and Grubbs, 2010). The original metathesis catalysts were ill defined, subject to poisoning and had poor functional group tolerance. In 2005 Grubbs, Schrock, and Chauvin were awarded the Nobel Prize in Chemistry for their pioneering work in metathesis catalyst development (Grubbs and Schrock) and elucidation of the reaction mechanism (Chauvin). Applications of metathesis to fatty esters were limited until the work of Grubbs and Schrock led to stable metal alkylidine complexes based on ruthenium, molybdenum, and tungsten. Several research groups in Europe and the United States have since made substantial progress in fatty ester metathesis chemistry using these new catalysts (Biermann et al., 2000, 2011; Fürstner, 2000; Meier et al., 2007; Montero de Espinosa and Meier, 2012; Ngo et al., 2006; Rybak et al., 2008).

Advances in plant biochemistry and traditional plant breeding have led to the development of a number of oils with modified fatty acid compositions. To date, trait-modified canola, soybean, and sunflower oils have been developed and commercialized through plant breeding and are non-genetically modified organism (GMO). Several new soybean oil varieties are nearing commercialization, including a low saturate high oleic variety and an omega-3 enriched oil. Both have been developed through a combination of plant breeding and gene insertion (Wilkes, 2008; Wilkes and Bringe, 2015).

1.6 Summary

In summary, fatty acids have long been important to man. Historically, from soap to candles to detergents and surfactants to biodiesel, a steady stream of new products based on fatty acids has appeared. Developments in chemistry and analytical techniques have played a major role in this progression, with fat-splitting hydrogenation, distillation, structure determination, and gas chromatographic analysis of fats and oils representing some of the most significant early developments in the chemistry and composition of fats and oils. Pioneers in these areas include Bailey, Chevreul, Heintz, Hilditch, Ittner, Jamieson, Potts, Sabatier, Twitchell, and Wurtz. Because of the important advances made by these and other researchers, renewable oleochemicals are now an important component of the worldwide chemical industry.

Recent advances, including application of biotechnology and metathesis to fats and oils, demonstrate that the chemistry of fats, oils, and fatty acids is diverse and not yet fully realized, even after over 200 years of collective effort. Research efforts currently underway and those surely to be conducted in the future represent the next generation of important discoveries in fatty acid chemistry.

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