Carboxylic Acids- Structure And Uses

Carboxylic Acids

Carboxylic acids are organic compounds that contain a carboxyl functional group (also known as the carboxylate group). These compounds are widely found in nature and are also synthesized by humans. When a carbonyl carbon (C=O) is also bonded to a hydroxyl group (–OH), we get a carboxylic acid. Here are some key points. The general formula for a carboxylic acid is R-COOH, where, R represents the rest of the molecule to which the carboxyl group is attached. COOH denotes the carboxyl group, which consists of a carbonyl carbon (C=O) and a hydroxyl group (–OH). In this article we will see some important structures and uses of carboxylic acids.

Table of Contents

Important carboxylic acids

Acetic Acid

Structure

Acetic acid (also known as ethanoic acid) has the chemical formula CH₃COOH. It’s a simple organic acid composed of two carbon atoms, four hydrogen atoms, and two oxygen atoms. The central carbon is bonded to a hydroxyl group (OH) and a carbonyl group (C=O). The acetic acid molecule looks like this: CH₃COOH.

Properties

Acetic acid is a colorless liquid with a pungent odor.
It’s miscible with water, meaning it readily dissolves in water.
When undiluted, it’s often referred to as “ice-cold acetic acid” because it forms crystals at temperatures below 16.6°C.

Uses

Food Industry: Acetic acid is a key component in vinegar, which is widely used for culinary purposes, pickling, and food preservation.
Chemical Industry: It serves as a solvent, reagent, and intermediate in various chemical processes. For example, it’s used in the production of synthetic fibers, plastics, and pharmaceuticals.
Laboratories: Acetic acid is commonly used in laboratories for titrations, pH adjustments, and as a solvent.

Lactic Acid

Structure

Lactic acid (C₃H₆O₃) is another organic acid, and it’s a bit more interesting in terms of its structure. It exists in two optical isomers:

L-Lactic Acid: Also known as (+)-lactic acid, it’s the more prevalent form in biological systems.
D-Lactic Acid: Also known as (−)-lactic acid, it’s the mirror image of L-lactic acid.
A mixture of equal amounts of L-lactic and D-lactic acid is called DL-lactic acid or racemic lactic acid.

Properties

Lactic acid is hygroscopic (meaning it absorbs water from the environment).
It’s chiral, which means it has different properties depending on its optical isomer.

Uses

Biological Systems: Lactic acid is a natural byproduct of anaerobic metabolism in our muscles during exercise. It’s responsible for that burning sensation you feel during intense workouts.
Food and Beverage Industry: Lactic acid is used as a food additive (E270) for acidity regulation, flavor enhancement, and preservation. It’s found in yogurt, sauerkraut, and other fermented foods.
Pharmaceuticals: Lactic acid has applications in wound healing, where it promotes tissue regeneration. Additionally, it’s used in some topical creams and lotions.
Chemical Synthesis: Like acetic acid, lactic acid serves as an intermediate in various chemical reactions.

Tartaric Acid

Structure

Tartaric acid has the chemical formula HO₂CCH(OH)CH(OH)CO₂H. It’s a dicarboxylic acid, meaning it contains two carboxyl (COOH) groups. Structurally, it has two chiral centers, which means it exists in four stereoisomeric forms. The most common form is the L-(+)-tartaric acid.

Uses

Food Industry: Tartaric acid is used as an acidulant in food products. It helps control acidity, enhances flavors, and stabilizes certain foods.
Winemaking: In winemaking, tartaric acid plays a crucial role. It helps control the pH of wine, prevents the precipitation of potassium bitartrate crystals (wine diamonds), and contributes to the overall taste profile.
Pharmaceuticals: Tartaric acid and its derivatives find applications in pharmaceutical formulations. For example, it’s used in effervescent salts to improve the taste of oral medications.

Citric Acid

Structure

Citric acid has the chemical formula C₆H₈O₇. It’s a tricarboxylic acid, containing three carboxyl groups. Structurally, it’s a cyclic compound with three carboxyl groups attached to a six-carbon ring.

Uses

Food and Beverages: Citric acid is widely used as an acidulant in food and beverages. It provides a sour taste and enhances flavors. You’ll find it in everything from soft drinks to candies.
Flavoring Agent: It’s a common flavoring agent in various food products.
Household Cleaning Products: Citric acid is also used in household cleaning products due to its ability to remove mineral deposits and stains.
Chelating Agent: It forms complexes with metal ions, making it useful in water softening and as a chelating agent in detergents.

Succinic Acid

Structure

Succinic acid (also known as butanedioic acid) has the chemical formula (CH₂)₂(CO₂H)₂. It’s a dicarboxylic acid. In living organisms, succinic acid exists as an anion called succinate.

Uses

Metabolism and ATP Production: Succinate is a key intermediate in the tricarboxylic acid (TCA) cycle (also known as the citric acid cycle or Krebs cycle). It’s involved in ATP production within mitochondria.
Cellular Signaling: Succinate acts as a signaling molecule, affecting gene expression patterns and cellular function.
Food Additive: Succinic acid is marketed as food additive E363.
Pharmaceuticals: Dysregulation of succinate synthesis can lead to pathological conditions. It’s also used in some pharmaceutical formulations.

Oxalic Acid

Structure

Oxalic acid (also known as ethanedioic acid) has the chemical formula ( H₂C₂O₄ ). It’s a dicarboxylic acid, meaning it contains two carboxyl (COOH) groups. Structurally, it consists of two carboxyl groups attached to a central carbon atom. The molecule looks like this: HOOC-COOH.

Properties

Oxalic acid is a colorless, crystalline solid.
It’s highly soluble in water.
Interestingly, it’s found in some plants (such as spinach and rhubarb) and can form insoluble calcium oxalate crystals in the body, which can lead to kidney stones.

Uses

Cleaning and Rust Removal: Oxalic acid is used as a cleaning agent for rust and mineral deposits. It’s effective in removing rust stains from fabrics and metal surfaces.
Bleaching Agent: It’s used in bleaching wood and removing ink stains.
Analytical Chemistry: Oxalic acid is used in complexometric titrations to determine the concentration of metal ions.
Photography: It’s used in developing photographic films.
Textile Industry: Oxalic acid is used in dyeing and printing textiles.

Salicylic Acid

Structure

Salicylic acid has the chemical formula (C7H6O3). It’s a beta hydroxy acid (BHA) and phenolic acid. Structurally, it contains a benzene ring with a hydroxyl group (-OH) attached to it. The molecule looks like this: HO-C6H4COOH.

Properties

Salicylic acid is a white, crystalline powder.
It’s slightly soluble in water but more soluble in organic solvents.
It’s commonly used in skincare products due to its exfoliating properties.

Uses

Skincare: Salicylic acid is widely used in acne treatments, as it helps unclog pores and exfoliate dead skin cells.
Wart Removal: It’s used in over-the-counter wart removers.
Anti-Inflammatory: Salicylic acid has anti-inflammatory properties and is sometimes used for conditions like psoriasis.
Aspirin Synthesis: Salicylic acid is a precursor for aspirin (acetylsalicylic acid).

Benzoic Acid

Structure

Benzoic acid has the chemical formula C6H5COOH. It’s a simple aromatic carboxylic acid. Structurally, it consists of a benzene ring with a carboxyl group (-COOH) attached. The molecule looks like this: C6H5COOH.

Properties

Benzoic acid is a white, crystalline solid.
It’s moderately soluble in water.
It has a characteristic aromatic odor.

Uses

Food Preservative: Benzoic acid and its salts (such as sodium benzoate) are commonly used as preservatives in food and beverages.
Pharmaceuticals: It’s used in some topical medications.
Chemical Intermediates: Benzoic acid is an intermediate in the synthesis of various chemicals.
Resin Production: It’s used in the production of certain resins and plastics.

Benzyl Benzoate

Structure

Benzyl benzoate has the chemical formula C₆H₅COOC₆H₅. It’s an ester formed by the condensation of benzoic acid and benzyl alcohol. Structurally, it consists of a benzene ring (benzyl group) attached to a carboxylate group (benzoate).

Uses

Medical

Benzyl benzoate is an inexpensive topical treatment for human scabies. It effectively treats this parasitic skin infestation.
Asthma and Whooping Cough Medicines: It’s also used in some asthma and whooping cough medications.
Testosterone Replacement Medicines: Benzyl benzoate is present in testosterone replacement therapies for hypogonadism.
Veterinary Hospitals: Veterinarians use it to treat acaricidal, scabicide, and pediculicide conditions in animals.

Non-Medical

As a mosquito, tick, and chigger repellent.
In the perfume industry as a dye carrier, plasticizer, cellulose derivative solvent, and fixative1.

Dimethyl Phthalate

Dimethyl phthalate has the molecular formula C₆H₄(COOCH₃)₂. It’s a colorless liquid and a methyl ester of phthalic acid. The molecule consists of two methyl groups (CH₃) attached to the phthalate group.

Uses

Plastics and Safety Glass: Dimethyl phthalate is used in the production of plastics and safety glass.
Insect Repellents: It’s an ingredient in some insect repellents.
Lacquer Coatings: Used in lacquer coatings for various applications1.

Methyl Salicylate

Methyl salicylate, also known as wintergreen oil, has the chemical formula C₇H₆O₃. Structurally, it’s closely related to salicylic acid.

Uses

Flavoring Agent: Methyl salicylate appears in low concentrations in candy, chewing gum, cough drops, and toothpaste.
Aromatherapy: Wintergreen oil is commonly used in aromatherapy.
Cosmetics and Sports Massage Products: It acts as a rubefacient (causing redness and warmth when applied to the skin).
Anti-Inflammatory Properties: Ointments and liniments containing methyl salicylate can help with joint and muscle pain due to its anti-inflammatory effects1.

Acetyl Salicylic Acid (Aspirin)

Structure

Acetyl salicylic acid, commonly known as aspirin, has the chemical formula C₉H₈O₄. It’s an acetylated derivative of salicylic acid.

Uses

Pain Relief and Anti-Inflammatory: Aspirin is widely used for pain relief, reducing fever, and its anti-inflammatory properties.
Cardiovascular Health: It’s also used for its blood-thinning effects to prevent heart attacks and strokes.
Fever Reduction: Aspirin helps reduce fever.
Preventive Measures: Some people take low-dose aspirin as a preventive measure against heart disease.
Other Applications: Aspirin has applications in various fields, including research and cosmetics.

Summary

Acetic acid (CH₃COOH) is found in vinegar and has applications in food preservation, textiles, and even cancer treatment. Lactic acid (C₃H₆O₃) is abundant in dairy products and plays a role in wound healing and anaerobic metabolism during exercise. Tartaric acid, present in citrus fruits, is crucial in winemaking and food flavor enhancement. Citric acid (C₆H₈O₇) serves as an acidulant in food and beverages, while succinic acid is used in polymers and pharmaceuticals. Oxalic acid (HOOCCOOH) finds use in cleaning and rust removal. Salicylic acid is essential in skincare and as a precursor for aspirin. Lastly, benzoic acid (C₆H₅COOH) acts as a food preservative. Additionally, compounds like benzyl benzoate, dimethyl phthalate, methyl salicylate, and acetyl salicylic acid (aspirin) have diverse applications, from insect repellents to pain relief.

Carboxylic Acids- Structure and Uses