CHEMICAL NAME = butanoic acid CAS NUMBER = 107–92–6 MOLECULAR FORMULA = C4H8O2 MOLAR MASS = 88.1 g/mol
COMPOSITION = C(54.5%) H(9.2%) O(36.3%) MELTING POINT = −7.9°C
BOILING POINT = 163.5°C DENSITY = 0.96 g/cm3
Butyric acid is a carboxylic acid also classifi ed as a fatty acid. It exists in two isomeric forms as shown previously, but this entry focuses on n-butyric acid or butanoic acid. It is a colorless, viscous, rancid-smelling liquid that is present as esters in animal fats and plant oils. Butyric acid exists as a glyceride in butter, with a concentration of about 4%; dairy and egg products are a primary source of butyric acid. When butter or other food products go rancid, free butyric acid is liberated by hydrolysis, producing the rancid smell. It also occurs in animal fat and plant oils. Butyric acid gets its name from the Latin butyrum, or butter. It was discovered by Adolf Lieben (1836–1914) and Antonio Rossi in 1869.
Butyric acid is one of the simplest fatty acids. Fatty acids, which are the building units of fats and oils, are natural compounds of carbon chains with a carboxyl group (-COOH) at one end. Most natural fatty acids have an unbranched carbon chain and contain an even number of carbon atoms because during biosynthesis they are built in two carbon units from acetyl coenzyme A (CoA). Butyric acid is an unsaturated fatty acid, which means all carbon-carbon bonds are single bonds. Common names for fatty acids stem from their natural sources. In addition to butyric acid, some other common saturated fatty acids include lauric acid, palmitic acid, and stearic acid. Lauric acid was fi rst discovered in Lauraceae (Laurus nobilis) seeds, pal-mitic oil was prepared from palm oil, and stearic acid was discovered in animal fat and gets its name from the Greek word stear for tallow.
Monounsaturated fatty acids have a single carbon-carbon double bond present in the chain, and polyunsaturated fatty acids have more than one carbon-carbon double bond. Oleic
n-butyric acid isobutyric acid
Butyric and Fatty Acids | 53
acid is a monounsaturated fatty acid found in olive oil. In unsaturated fats the arrangement of hydrogen atoms around the double bond can assume a trans or cis confi guration. Trans fatty acids have hydrogen atoms on opposite sides of the double bond as opposed to the cis formation where they are on the same side. Research showing that trans fatty acids increase heart disease has led to food labels reporting the amount of trans fat and a decrease of trans fats in processed foods in recent years. Unsaturated fatty acids can also be characterized by the position of the double bond. One system used in physiology numbers carbon atoms starting from the methyl end of the molecule. Th e methyl carbon is referred to as the omega carbon because omega is the last letter in the Greek alphabet; the fi rst carbon at the carboxyl end of the molecule is the alpha carbon. Th e double bond can then be located based on its displace-ment from the omega carbon. For example, an omega-3 fatty acid has its endmost double bond positioned three carbon atoms away from the omega carbon. Omega fatty acids such as omega-3 are used as dietary supplements for a variety of conditions.
Butyric acid is produced by oxidation of butyraldehyde (CH3(CH2)2CHO) or butanol (C4H9OH). It can also be formed biologically by the oxidation of sugar and starches using bacteria. It is used in plastics as a raw material for the cellulose acetate butyrate (CAB).
CAB is an ester produced by treating fi brous cellulose with butyric acid, butyric anhydride (CH3CH2CH2CO)2O], acetic acid (CH3COOH), and acetic anhydride (CH3CO)2O) in the presence of sulfuric acid. CAB is a tough plastic that resists weathering and is highly transparent.
It is sold in sheets and tubes of various dimensions and is used for signs, goggles, sunglasses, tool handles, pens, and stencils. Reacting butyric acid with alcohols produces esters. For example,
54 | Th e 100 Most Important Chemical Compounds
butyric acid and methanol yield methyl butyrate (C5H10O2). Many butyrate esters have a pleas-ant smell and are therefore used in food fl avorings and perfumes. Other uses of butyric acid are in disinfectants, pharmaceuticals, and feed supplements for plant and animals.
Butyric acid derivatives play an important role in plant and animal physiology. Gamma-aminobutyric acid (GABA)is the main inhibitory neurotransmitter found in humans and is
present in many other organisms. Indole-3-butyric acid is closely related in structure and function to a natural growth hormone found in plants. Indole-3-butyric acid is used in many nutrient formulations to promote growth and development of roots, fl owers, and fruits, and to increase crop yields.
18. Caffeine
CHEMICAL NAME = 3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione CAS NUMBER = 58–08–2
MOLECULAR FORMULA = C8H10N4O2 MOLAR MASS = 194.2 g/mol
COMPOSITION = C(49.5%) H(5.2%) N(28.9%) O(16.5%) MELTING POINT = 237°C
BOILING POINT = sublimes DENSITY = 1.2 g/cm3
Caff eine is an alkaloid purine belonging to the group of organic compounds called methyl-xanthines. Pure caff eine is a white, crystalline, bitter-tasting compound. Caff eine is found in a number of plants, principally coff ee and tea plants, as well as cola and cacao nuts. In plants, caff eine functions as a natural pesticide to deter insects. Th e consumption of caff eine dates back thousands of years. Tea was consumed in China several thousand years b.c.e. but quite possibly was used in India before that and introduced into China. Coff ee consump-tion is believed to have started in the Kaff a region of Ethiopia around 800 c.e. and over time spread to Arabia, Turkey, and other parts of the Middle East. Th e port city of Mocha on the Red Sea in Yemen became a principal coff ee-growing region and area of export in the Middle East. Rulers in coff ee-growing areas imposed strict laws against the exportation of coff ee plants to exercise their monopolies over the lucrative product. Coff ee plants spread throughout the world from successful smuggling. Tea and coff ee were introduced into Europe in the 17th century, well after its use in other parts of the world. Chocolate drinks from cacao beans (cocoa is often used for the drink or powder product made from the cacao beans) were being concocted by native populations in Central and South America several hundred years b.c.e. Th e Spanish explorer Hernando Cortés (1485–1587) brought cocoa back to Spain around 1528.
Only a small amount of caff eine is found in the cacao plant and chocolate. Th e principal alkaloid in the cacao plant is theobromine, which is almost identical to caff eine, but diff ers by having one less methyl group. Th eobromine does not contain bromine but derives its name
56 | Th e 100 Most Important Chemical Compounds
from the genus Th eobroma of the cacao tree. Th eobroma’s Greek translation is “food of the gods.” Another compound almost identical to caff eine in tea is theophylline. It also contains one fewer methyl group.
Th e discovery of caff eine is attributed to Friedlieb Ferdinand Runge (1795–1867), a German physician and chemist. Runge was working in the laboratory of Johann Wolfgang Döbereiner (1780–1849), when Döbereiner’s friend, Johann Wolfgang von Goethe (1749–1832), paid a visit. Runge performed an experiment for Goethe in which he dilated a cat’s eye with an extract from a nightshade plant. Goethe awarded Runge with a sample of rare coff ee beans and challenged him to determine the compound that gave coff ee its stimulating eff ects. After sev-eral months, Runge isolated caff eine from coff ee in 1819. Caff eine derives its name from the Kaff a region of Ethiopia. Caff eine comes from the German kaff eine, which in turn is derived from the German word for coff ee, kaff ee. In 1827, a compound isolated from tea was named theine, but this was eventually shown to be caff eine.
Caff eine is a stimulant to the central nervous system and cardiac muscle and is a mild diuretic. Caff eine’s physiological eff ects are thought to be the result of caff eine’s interference with adenosine in the brain and body. Adenosine moderates nerve transmissions. As adenosine builds up while a person is awake, it produces a self-regulating mechanism to inhibit nerve trans-mission. As adenosine receptors in the brain acquire more adenosine, the reduction in nerve transmission induces sleep. Caff eine competes with adenosine and interferes with the neural modulation function of adenosine. Th is is why coff ee has a tendency to keep people awake.
Th e eff ects of coff ee and caff einated drinks vary widely among individuals. Generally, moder-ate consumption leads to restlessness and tends to energize individuals. Caff eine increases blood pressure and has been indirectly associated with heart and pregnancy problems; it increases stomach acid, which can lead to ulcers. Regular users of caff einated drinks can experience with-drawal side eff ects such as anxiety, nervousness, fatigue, and headaches. Th e eff ects of caff eine lasts several hours after consumption. It is carried by the blood to all parts of the body and is eliminated primarily through the urine after a half-life from 4 to 10 hours in most adults.
Health experts advise that moderated amounts of caff eine from 100 to 300 mg per day are acceptable. Adult Americans consume approximately 250 mg of caff eine per day. Th e LD50 (the lethal dose that kills 50% of a test population of individuals subjected to a substance) of caff eine for humans is estimated between 150 and 200 mg per kilogram of body weight. Th e amount of caff eine in some popular food items is given in Table 18.1.
Coff ee beans are the primary source of caff eine. Th ese beans are obtained from a variety of plants but can be broadly grouped into two classes: arabica and robusta. Arabica is obtained from the species Coff ea arabica and robusta from the species Coff ea canephora. Robusta, as the
Caff eine | 57
name implies, is more robust than arabica coff ee but produces an inferior taste. Arabica plants are grown globally, but robusta plants are grown only in the Eastern Hemisphere. Coff ee beans contain 1–2% caff eine, with robusta varieties generally containing twice the content of arabica varieties. Other sources of caff eine contain various caff eine content: kola nut (1–3.5%), tea leaves (1.4–4.5%), and cacao (0.1–0.5%).
Some food processors add caff eine to their products (soft drinks), but others remove caf-feine and advertise the product as decaff einated. Coff ee was fi rst decaff einated in 1906 in Germany through a process founded by the coff ee merchant Ludwig Roselius (1874–1943).
Roselius’s team sought to decaff einate coff ee without destroying the aroma and fl avor. Roselius fortuitously worked on beans that had been soaked with seawater during a storm and found a method to remove 97% of the caff eine in coff ee beans without destroying the fl avor.
Roselius then marketed the product under diff erent names in various European countries. In France, the name of the decaff einated coff ee was Sanka, which is derived from sans caff eine (sans kaff ee). Sanka was introduced in the United States in 1923. Th e traditional method of decaff einating coff ee beans involved steaming the beans and then extracting the caff eine in an organic solvent such as Freon, chloroform, methylene chloride, or ethyl acetate. Because of the environmental problems and costs associated with organic solvents, green decaff eination techniques have been developed in recent years. One popular method is to use supercritical carbon dioxide to extract caff eine (see Carbon Dioxide).
Caff eine has widespread therapeutic use. It is widely used in headache (migraine) rem-edies such as aspirin and other analgesics. Caff eine is a mild vasoconstrictor and its ability to constrict blood vessels serving the brain explains its use to relieve headache. Individuals who consume caff eine regularly through medications and food are susceptible to what is known as a rebound headache or caff eine rebound. Th is occurs when regular caff eine intake is suddenly reduced and the vessels dilate. Caff eine is a common substance in medications to treat apnea in premature infants. Apparently, the area of the brain controlling respiration in premature infants is not fully developed and caff eine helps to stimulate this portion of the
Table 18.1 Approximate Caffeine Content
58 | Th e 100 Most Important Chemical Compounds
brain. Th e combination of caff eine and ephedrine is used in dietary and athletic supplements, and their role as appetite suppressant and energy boosters has been extensively studied. Some individuals claim that a modest dose (200 mg) of caff eine can enhance athletic performance, but its exact eff ect is unclear. Caff eine is used for the treatment of attention defi cit disorder/
attention-defi cit hyperactivity disorder, but health experts do not recommend its use for this condition.