Carboxylic acids
Carboxylic acids
Carboxylic acids are chemical compounds that contain a carboxyl group, which contains carbon, oxygen, and hydrogen atoms symbolized by the chemical name -COOH. The carboxyl group is attached to another hydrogen (H) atom or to one end of a larger molecule. Examples include formic acid, which is produced by some ants and causes their bites to sting. (In fact, the scientific name for ants, Formica, is what gives formic acid its name.) Another example is acetic acid, which is found in vinegar. Many carboxylic acids dissolve in water. Solutions of many carboxylic acids have a sour taste to them, a characteristic of many acids. Carboxylic acids also react with alkalis, or bases. Generally, however, carboxylic acids are not as chemically active as the non-organic mineral acids such as hydrochloric acid or sulfuric acid. When a carboxyl group is added to a compound, it is called carboxylation, and when a carboxyl group is removed it is called decarboxylation. Carboxylases and decarboxylases are enzymes that catalyze both types of these reactions, respectively.
Biological importance
Carboxylic acids are very important biologically. The drug aspirin is a carboxylic acid, and some people are sensitive to its acidity. The non-aspirin pain reliever ibuprofen is also a carboxylic acid. Carboxylic acids that have very long chains of carbon (C) atoms attached to them are called fatty acids. As their name suggests, they are important in the formation of fat in the body. Many carboxylic acids are present in the foods and drinks that humans ingest, like malic acid (found in apples), tartaric acid (grape juice), oxalic acid (spinach and some parts of the rhubarb plant), and lactic acid (sour milk). Two other simple carboxylic acids are propionic acid and butyric acid. Propionic acid is partly responsible for the flavor and odor of Swiss cheese. Butyric acid is responsible not only for the smell of rancid butter, but also contributes to the odor of sweat. Lactic acid is generated in muscles of the body as the individual cells metabolize sugar and do work. A buildup of lactic acid, caused by over-exertion, is responsible for the fatigue one feels in the muscles by such short-term use. When one rests, the lactic acid is gradually converted to water and carbon dioxide, and the feeling of fatigue passes. A form of vitamin C is called ascorbic acid and is a carboxylic acid.
A special form of carboxylic acids are the amino acids, which are carboxylic acids that also have a nitrogen-containing group called an amine group in the molecule. Aminoacids are very important because combinations of amino acids make up the proteins. Proteins are one of the three major components of the diet, the other two being fats and carbohydrates. Much of the human body, like skin, hair, and muscle, is composed of protein.
Industrial importance
Carboxylic acids are also very important industrially. Perhaps one of the most important industrial applications of compounds with carboxyl groups is the use of fatty acids (which are carboxyl groups attached to long carbon chains) in making soaps,
KEY TERMS
Amino acid— An organic compound whose molecules contain both an amino group (-NH2) and a carboxyl group (-COOH). One of the building blocks of a protein.
Carboxyl group— The -COOH group of atoms, whose presence defines a carboxylic acid.
Ester— A derivative of a carboxylic acid, where an organic group has been substituted for the hydrogen atom in the acid group. Esters contribute to tastes and smells.
Fatty acid— A carboxylic acid that is attached to a chain of at least eight carbon atoms. Fatty acids are important components in fats, and are used to make soaps.
Lactic acid— A carboxylic acid formed during the metabolism of sugar in muscle cells. A buildup of lactic acid leads to a feeling of fatigue.
Mineral acid— An acid that is not organic. Examples include hydrochloric acid and sulfuric acid.
Saponification— A chemical reaction involving the breakdown of triglycerides to component fatty acids, and the conversion of these acids to soap.
detergents, and shampoos. In some such compounds, the hydrogen atom in the carboxyl group is replaced with some metalcation. The modified carboxyl group is soluble in water, while the long chain of carbons remains soluble in fats, oils, and greases. This double solubility allows water to wash out the fat- and oil-based dirt. Many shampoos are based on lauric, palmitic, and stearic acids, which have long chains of 12, 16, and 18 carbon atoms, respectively. To make other cleansing agents, three molecules of fatty acid are combined with one molecule of a compound called glycerin in a reaction called saponification. This reaction also makes a soap molecule that has one end soluble in water and the other soluble in fat or grease or oil. Various fatty acids are used to make soaps and detergents that have different applications in society. Carboxylic acids are also important in the manufacture of greases, crayons, and plastics.
Compounds with carboxyl groups are relatively easily converted to compounds called esters, which have the hydrogen atom of the carboxyl group replaced with a group containing carbon and hydrogen atoms. Such esters are considered derivatives of carboxylic acids. Esters are important because many of them have characteristic tastes and odors. For example, methyl butyrate, a derivative of butyric acid, smells like apples. Benzyl acetate, from acetic acid, has a jasmine odor. Carboxylic acids are thus used commercially as raw materials for the production of synthetic odors and flavors. Other esters, derived from carboxylic acids, have different uses. For example, the ester ethyl acetate is a very good solvent and is a major component in nail polish remover.
See also Acetylsalicylic acid; Acids and bases.
Resources
BOOKS
Carey, Francis A. Organic Chemistry. Dubuque, IA: McGraw-Hill, 2006.
Hoffman, Robert V. Organic Chemistry: An Intermediate Text. Hoboken, NJ: Wiley-Interscience, 2004.
Loudon, G. Mark. Organic Chemistry. Oxford: Oxford University Press, 2002.
Snyder, Carl H. The Extraordinary Chemistry of Ordinary Things. Hoboken, NJ: John Wiley & Sons, 2003.
Stwertka, Albert. A Guide to the Elements. New York: Oxford University Press, 2002.
David W. Ball
Carboxylic Acids
Carboxylic acids
Carboxylic acids are chemical compounds that contain a carboxyl group , which is -COOH. The carboxyl group is attached to another hydrogen atom or to one end of a larger molecule . Examples include formic acid, which is produced by some ants and causes their bites to sting. (In fact, the scientific name for ants, Formica, is what gives formic acid its name.) Another example is acetic acid , which is found in vinegar. Many carboxylic acids dissolve in water . Solutions of many carboxylic acids have a sour taste to them, a characteristic of many acids. Carboxylic acids also react with alkalis, or bases. Generally, however, carboxylic acids are not as chemically active as the non-organic mineral acids such as hydrochloric acid or sulfuric acid .
Biological importance
Carboxylic acids are very important biologically. The drug aspirin is a carboxylic acid, and some people are sensitive to its acidity. The non-aspirin pain reliever ibuprofen is also a carboxylic acid. Carboxylic acids that have very long chains of carbon atoms attached to them are called fatty acids . As their name suggests, they are important in the formation of fat in the body. Many carboxylic acids are present in the foods and drinks we ingest, like malic acid (found in apples), tartaric acid (grape juice), oxalic acid (spinach and some parts of the rhubarb plant ), and lactic acid (sour milk). Two other simple carboxylic acids are propionic acid and butyric acid. Propionic acid is partly responsible for the flavor and odor of Swiss cheese. Butyric acid is responsible not only for the smell of rancid butter, but also contributes to the odor of sweat. Lactic acid is generated in muscles of the body as the individual cells metabolize sugar and do work . A buildup of lactic acid, caused by overexertion, is responsible for the fatigue one feels in the muscles by such short-term use. When one rests, the lactic acid is gradually converted to water and carbon dioxide , and the feeling of fatigue passes. A form of vitamin C is called ascorbic acid and is a carboxylic acid.
A special form of carboxylic acids are the amino acids, which are carboxylic acids that also have a nitrogen-containing group called an amine group in the molecule. Aminoacids are very important because combinations of amino acids make up the proteins . Proteins are one of the three major components of the diet, the other two being fats and carbohydrates. Much of the human body, like skin, hair, and muscle, is composed of protein.
Industrial importance
Carboxylic acids are also very important industrially. Perhaps one of the most important industrial applications of compounds with carboxyl groups is the use of fatty acids (which are carboxyl groups attached to long carbon chains) in making soaps, detergents, and shampoos. In some such compounds, the hydrogen atom in the carboxyl group is replaced with some metal cation . The modified carboxyl group is soluble in water, while the long chain of carbons remains soluble in fats, oils, and greases. This double solubility allows water to wash out the fat- and oil-based dirt. Many shampoos are based on lauric, palmitic, and stearic acids, which have long chains of 12, 16, and 18 carbon atoms, respectively. To make other cleansing agents, three molecules of fatty acid are combined with one molecule of a compound called glycerin in a reaction called saponification. This reaction also makes a soap molecule which has one end soluble in water and the other soluble in fat or grease or oil. Various fatty acids are used to make soaps and detergents that have different applications in society. Carboxylic acids are also important in the manufacture of greases, crayons, and plastics .
Compounds with carboxyl groups are relatively easily converted to compounds called esters, which have the hydrogen atom of the carboxyl group replaced with a group containing carbon and hydrogen atoms . Such esters are considered derivatives of carboxylic acids. Esters are important because many of them have characteristic tastes and odors. For example, methyl butyrate, a derivative of butyric acid, smells like apples. Benzyl acetate, from acetic acid, has a jasmine odor. Carboxylic acids are thus used commercially as raw materials for the production of synthetic odors and flavors. Other esters, derived from carboxylic acids, have different uses. For example, the ester ethyl acetate is a very good solvent and is a major component in nail polish remover.
See also Acetylsalicylic acid; Acids and bases.
Resources
books
Loudon, G. Mark. Organic Chemistry. Oxford: Oxford University Press, 2002.
Snyder, Carl H. The Extraordinary Chemistry of Ordinary Things. New York: John Wiley & Sons, 1992.
Periodicals
Murray, Frank. "Hydroxycitric Acid." Better Nutrition for Better Living 56 (1994): 34–39.
David W. Ball
KEY TERMS
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .- Amino acid
—An organic compound whose molecules contain both an amino group (-NH2) and a carboxyl group (-COOH). One of the building blocks of a protein.
- Carboxyl group
—The —COOH group of atoms, whose presence defines a carboxylic acid.
- Ester
—A derivative of a carboxylic acid, where an organic group has been substituted for the hydrogen atom in the acid group. Esters contribute to tastes and smells.
- Fatty acid
—A carboxylic acid which is attached to a chain of at least 8 carbon atoms. Fatty acids are important components in fats, and are used to make soaps.
- Lactic acid
—A carboxylic acid formed during the metabolism of sugar in muscle cells. A buildup of lactic acid leads to a feeling of fatigue.
- Mineral acid
—An acid that is not organic. Examples include hydrochloric acid and sulfuric acid.
- Saponification
—A chemical reaction involving the breakdown of triglycerides to component fatty acids, and the conversion of these acids to soap.