Carboxylic acids are a large group of chemical compounds that all have a certain structure in common, composed of the three most important elements on earth — carbon, oxygen and hydrogen. These various compounds make up the most abundant, naturally occurring organic acids. The slightly stinging sourness of citrus fruits, such as lemons, comes from one example called citric acid. Most of the compounds are relatively simple chemically, and as an acid, quite weak. Carboxylic acids by themselves have vital uses, but more importantly, they are fairly easy to break apart and recombine with other chemical compounds to create more complex substances.
The acids always have a chemical sub-structure consisting of a carbon atom, and a hydrogen atom, and two oxygen atoms called a carboxyl group. Also attached to the carbon atom is a wide variety of organic molecules, some quite complex. There can also be more than one carboxyl group. Dicarboxylic acids have two while a tricarboxylic acid has three, and some acids may have as many as 20 carboxyl groups.
One of the characteristics of carboxylic acids making them so useful to organic life is that they readily dissolve into individual molecules in solvents, including water. Even the most complex and stubborn of them are usually soluble in an alcohol solution. The tricarboxylic citric acid is a common ingredient in soda pop beverages and in other processed food.
Another common food additive is the acetic acid in vinegar. It is also used commercially to halt chemical reactions during photographic film processing. Nearly half of the world’s supply of acetic acid, however, is chemically converted into vinyl acetate, one of the essential ingredients in glues and paints. Similarly to other compounds such as acrylic acid, vinyl acetate can be further chemically processed into plastics.
This versatility of carboxylic acids comes from the ease of breaking their chemical bonds. One demonstration of this is a child’s volcano model containing a bottle of vinegar. When a teaspoon of baking soda, or sodium bicarbonate, is added, the bottle violently bubbles over in a froth of water, carbon dioxide and sodium acetate. Humans and most other animals derive the majority of their energy from digested food through a series of chemical reactions called the “citric acid cycle.”
Amino acids are also among nature’s most important carboxylic acids. They are nicknamed “the building blocks of proteins.” Proteins, in turn, create the nearly infinite diversity of organic tissues, from hair, skin, heart to tree bark. Scientists have taken this cue, to utilize the acids in, or chemically covert them into, a vast variety of applications. Perfumes, industrial bleaches, food preservatives and pharmaceutical drugs are just a few more examples.