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Phthalic Acid Formula – Structure, Properties, Uses, Sample Questions

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Phthalic Acid consists of the elements Carbon, Hydrogen, and Oxygen. Carbon is a nonmetallic element present in group-14 of the periodic table. Its atomic number is six and is represented by the symbol C. Hydrogen is the lightest, colorless, odorless, tasteless, and flammable gas. Its atomic number is one and is represented by the symbol H. Oxygen is a highly reactive nonmetal present in the chalcogen group, i.e., group-16. Its atomic number is eight and is represented by the symbol O. 

Phthalic Acid Formula

Phthalic Acid is a colorless, crystalline organic compound invented by French chemist Auguste Laurent through the oxidizing naphthalene tetrachloride. It is an isomer of isophthalic acid and terephthalic acid. The chemical formula of Phthalic Acid is C6H4(COOH)2. It is used as an anhydride to produce chemicals like dyes, perfumes, phthalates, saccharin, and many other useful products. It is also used in the production of anthraquinone, phenolphthalein, and phthalocyanine pigments in smaller amounts. The IUPAC name of Phthalic Acid is 1,2-, benzene dicarboxylic acid. The other names of Phthalic Acid are ortho-Phthalic acid, Benzene-1,2-dioic acid, and 1,2-Benzenedioic acid.

Structure of Phthalic Acid

The structure of Phthalic Acid is very similar to that of aromatic carboxylic acid. Phthalic Acid consists of 2 carboxy groups at ortho positions. It is the conjugate acid of a phthalate(1-) and a phthalate.

Phthalic Acid Structure

Physical Properties of Phthalic Acid

  • Phthalic Acid is colorless.
  • The molecular weight of Phthalic Acid is 166.132 g/mol.
  • It is a dibasic acid.
  • The melting point of Phthalic Acid is 207°C.
  • The density of Phthalic Acid is 1.593 g/cm3.
  • Its solubility of water value is 0.6g/100mL.
  • The nature of Phthalic Acid is an aromatic crystalline organic compound.

Chemical Properties of Phthalic Acid

  • By reducing Phthalic Acid with sodium amalgam in the presence of water, it generates 1,3-cyclohexadiene derivatives.
  • Phthalic acid C6H4(COOH)2 reacts with an alcohol (C2H5OH) to produce Phthalic Acid esters, which are used in diffusion pumps and to replace mercury in manometers.
  • When Phthalic anhydride is treated with alkaline hydrogen peroxide in the cold, it generates acidified monoperoxyPhthalic Acid.

C6H4(CO)2O + H2O2 ⇢ C8H6O5

Uses of Phthalic Acid

  • Anhydrous Phthalic Acid is used mainly in the production of chemicals like dyes, perfumes, phthalates, and saccharin.
  • Phthalic Acid esters (Phthalates) are used in a wide range of consumer goods, construction materials, and commodities.
  • Phthalates are common pollutants in food and the environment. So they present in high concentrations in both the air and dust of homes and workplaces.

Sample Questions

Question 1: Is Phthalic Acid safe?


Any acid is harmful to the human body. Phthalic Acid is very sensitive to extreme heat. If Phthalic Acid is exposed to the body it causes irritations of skin, eyes, respiratory organs. If a high amount of Phthalic acid has been in contact, it can cause narcosis. 

Question 2: Is Phthalic Acid a strong acid?


No Phthalic Acid is not a strong acid. It 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 strong bases.

Question 3: Find the molecular weight of Phthalic Acid.


Phthalic Acid consists of 8 carbons, 6 hydrogens and 4 oxygen atoms.

Atomic weight of each carbon atom = 12.01

Atomic weight of each Hydrogen = 1.00784

Atomic weight of each Oxygen = 15.999

Molecular weight of C6H4(COOH)2 = (8 × 12.01) + (6 × 1.00784) + (4 × 15.999)

= 166.132

Question 4: How to convert Phthalic Acid to Phthalic anhydrate?


By dehydrating the Phthalic Acid we can get Phthalic anhydrate. Phthalic Acid loses water molecules when heated, forming acid anhydrides. This Phthalic anhydrate is a colorless to white lustrous solid that comes in the form of needles.

Question 5: What are the uses of Phthalic anhydrate?


Phthalic anhydride is used in wide variety of applications around the world, from the plastics industry to resin synthesis, agricultural fungicides, and amines. It is also used to catalyze the oxidation of ortho-xylene or naphthalene. Phthalic anhydrate is made by oxidizing o-xylene and naphthalene in the vapor process. It can also be prepared form Phthalic Acid.

Question 6: What happens when Phthalic Acid reacts with ammonia?


Phthalic Acid C6H4(COOH)2 reacts with ammonia (NH3) to give an ammonium salt- Ammonium phthalate. This on further heating gives phthalimide.

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Last Updated : 15 May, 2022
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