Phthalic Acid Meaning

Phthalic acid IUPAC name is 1, 2-,benzenedicarboxylic acid. It is a colourless, crystalline organic compound that is usually manufactured and marketed as anhydride. In the late twentieth century, annual phthalic anhydride production surpassed 1,000,000 metric tonnes; the majority of it was used as a component of polyesters, such as alkyd resins. 

In the production of anthraquinone (a dye intermediate), phenolphthalein (a laxative and acid-base indicator), and phthalocyanine pigments, smaller amounts were used. Phthalic Acid is the main chemical compound that is applied as an anhydride to create chemicals like dyes, phthalates, saccharin, perfumes, and many other useful products. The phthalic acid boiling point is 289 °C (1013 hPa) (decomposition).


Phthalic Acid Structure

The phthalic acid structure is very similar to that of the aromatic carboxylic acid and thus is known as one of the simplest acids of this family. As phthalic acid is chemically known as benzene-1,2-dicarboxylic acid, thus it is clear from its naming that phthalic acid structure consists of a benzene ring that is attached with two carboxyl groups at 1 and 2 positions or in other words an additional carboxyl group attached to the benzoic acid at the ortho position. Thus the chemical formula of phthalic acid or phthalic acid formula is  C6H4(CO2H)2 which means there is a six carbon ring with alternating double bond that makes it aromatic in nature with a carboxyl group ( -COOH) to one of the carbon atom of the aromatic benzene ring and the other carboxyl group ( -COOH) at the ortho position. This acid is very stable in nature and is considered as weak acid but it reacts vigorously with the strong bases. Thus, phthalic acid structure is illustrated below.


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Production of Phthalic Acid

Phthalic acid is generated by the catalytic oxidation of naphthalene or ortho-xylene straight to phthalic anhydride and following hydrolysis of the anhydride.

Auguste Laurent, a French chemist, developed phthalic acid in 1836 by oxidizing naphthalene tetrachloride. 

He called the resulting product "naphthalic acid" because he thought it was a naphthalene derivative. 

Laurent gave it its current name after Swiss chemist Jean Charles Galissard de Marignac determined its right formula. The oxidation of naphthalene tetrachloride with nitric acid, or, better still, the oxidation of the hydrocarbon with fuming sulfuric acid, using mercury or mercury(II) sulfate as a catalyst, was a popular manufacturing process in the nineteenth century.


Reactions of Phthalic Acid 

With pKas of 2.89 and 5.51, it is a dibasic acid. In analytical chemistry, potassium hydrogen phthalate, a monopotassium salt, is a regular acid. Typically, phthalate esters are made from phthalic anhydride, which is readily available. The 1,3-cyclohexadiene derivative is generated by reducing phthalic acid with sodium amalgam in the presence of water.


Phthalic Acid Properties 


Phthalic Acid Formula

C8H6O4 or C6H4(COOH)2 or H2C8H4O4

Molecular Weight

166.132 g/mol

Density

1.593 g/cm3

Chemical Names

ortho-Phthalic acid, 1,2-Benzenedioic acid,

Benzene-1,2-dioic acid

Solubility in Water

0.6 g / 100 mL

Melting Point

207 °C


Phthalic Acid Formula

Phthalic acid is a dicarboxylic acid of benzene that has two carboxy groups in ortho places. It acts as a xenobiotic metabolite in humans. It's the phthalate(1-) and phthalate conjugate acid. The phthalic acid structure is depicted in the diagram below.

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Phthalic Acid Uses 

There are various phthalic acid uses :

  • Phthalic acid is used mainly in the form of anhydride to produce other chemicals such as dyes, perfumes, saccharin, phthalates, and many other useful products.

  • Plasticizers such as phthalic acid esters (phthalates) are used in a wide range of consumer goods, commodities, and construction materials. 

  • As a result, phthalates can be present in high concentrations in both the air and dust of human homes and workplaces. 

  • Phthalates are also common pollutants in food and the environment.

Can Phthalic Acid be Dangerous?

Irritation of the skin, eyes, mucous membranes, and respiratory passages may occur after exposure to this compound. It can cause narcosis at high concentrations. 

Phthalic acid is a carboxylic acid. Extreme heat has a negative impact on this chemical.


Anhydride Phthalic: Meaning, Uses, and Formula

The organic compound is phthalic anhydride, formula - C8H4O3. It is phthalic acid's anhydride. 

The most common commercial form of phthalic acid is phthalic anhydride. It was the first commercially available dicarboxylic acid anhydride.

Phthalic anhydride is a colourless to white lustrous solid that comes in the form of needles and has a slight odour. Skin irritant and moderately harmful by inhalation or ingestion.

The oxidation of naphthalene in concentrated sulphuric acid in the presence of mercury sulfate was the first step in the production of phthalic anhydride. The effluent gases are cooled before passing into switch condensers, where the phthalic anhydride solidifies on the walls and is retrieved by sublimation.

Anhydride phthalic is used in a wide variety of applications around the world, from the plastics industry to resin synthesis, agricultural fungicides, and amines. It is currently made by oxidizing o-xylene and naphthalene in the vapour process. This is phthalic anhydride structure :

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Reactions of Phthalic Anhydride

The reaction of phthalic anhydride or the acid with alcohol produces phthalic acid esters, which are used in diffusion pumps and to replace mercury in manometers. 

Diethyl and dihexyl esters are commonly used in this application. Insect repellents such as dimethyl phthalate are effective. In the production of so-called alkyd resins, phthalic anhydride is widely used. Polyesters of acids with two carboxyl groups and polyhydric alcohols make up these resins.

The acidic imino hydrogen atom between the two carbonyl groups causes phthalimide to form metallic salts. The potassium salt of phthalimide is used in Gabriel's synthesis of amines and amino acids, as you might remember. As previously mentioned, the Hofmann degradation of phthalimide provides a convenient method of obtaining anthranilic acid. When phthalic anhydride is treated in the cold with alkaline hydrogen peroxide, acidified monoperphthalic acid is created.

FAQs (Frequently Asked Questions)

1. How Do You Make Phthalic Anhydride?

Ans. Phthalic anhydride is used to catalyze the oxidation of ortho-xylene or naphthalene. To keep phthalic anhydride separate from by-products like o – xylene in water or maleic anhydride, a collection of "switch condensers" is required. Phthalic anhydride can also be made with phthalic acid. Phthalic anhydride is being used in a wide variety of applications around the world, from the plastics industry to resin synthesis, agricultural fungicides, and amines. It is currently made by oxidizing o-xylene and naphthalene in the vapour process. To reduce the strain on fossil usage and the consequences of oil depletion issues, the construction of an alternative production route to the petrochemical one is highly desirable. 

2. How to Convert Phthalic Anhydride to Phthalic Acid?

Ans. We can transform phthalic acid into phthalic anhydride by dehydrating it. Since phthalic acid is a dicarboxylic acid with two or three carboxylic groups divided by two or three carbon atoms, it loses water molecules when heated, forming acid anhydrides. That’s how the conversion goes on. Phthalic anhydride is a colourless to white lustrous solid that comes in the form of needles and has a slight odour. Skin irritant and moderately harmful by inhalation or ingestion. The melting point is 64°F, and the flashpoint is 305°F. When combined with water, it produces a corrosive solution. 

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3. Is Phthalic Acid Strong?

Ans. Phthalic acid is a weak dibasic acid that has a  pKa values 2.89 and 5.51 but it reacts very vigorously when it comes in contact with any strong bases.