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Phthalic Acid – Chemical Formula, Structure, And Properties

Dec 14, 2022

 French scientist Auguste Laurent created phthalic acid by oxidising naphthalene tetrachloride. It is a white crystalline, colourless organic molecule often produced and sold as phthalic anhydride. Phthalic acid has the chemical formula H2C8H4O4. Phthalic anhydride helps produce various chemicals, including colours, fragrances, phthalates, sugar substitutes, and many other valuable items. In lower quantities, it is also used to make the colours anthraquinone, phenolphthalein, and porphyrin. Phthalic acid is known as 1,2-benzene dicarboxylic acid, according to the IUPAC.  

Structure of Phthalic Acid

Because of its structural resemblance to the aromatic carboxylic acid, phthalic acid is considered one of the family’s simpler acids. Since acid phthalic is also referred to as benzene-1,2-dicarboxylic acid, it is obvious from its name that the framework of acid phthalic is made up of a benzene ring with two carboxyl’s covalently bonded at positions 1 and 2, or, to put it another way, a different carboxyl group bonded at the ortho position (1,2).


Phthalic Acid Formula 

Since it has a six-carbon ring containing opposing double bonds, phthalic acid’s chemical equation isH2C8H4O4  or C6H4(CO2H)2. The chemical formula denotes that it contains two carboxyl groups (-COOH), one attached to the aromatic ring’s carbon atom and another in the ortho location. Although this acid is mild in character and is thought to be relatively stable, it interacts strongly with strong bases.

The crystalline, colorless organic molecule known as phthalic acid was created by French chemist Auguste Laurent by oxidizing naphthalene tetrachloride. It is an isomer of both terephthalic acid and isophthalic acid. Phthalic acid’s chemical formula is C6H4(COOH)2. It is utilized as anhydride to create chemicals such as colors, fragrances, phthalates, saccharin, and many other beneficial goods. In smaller quantities, it is also employed in the manufacture of the pigments anthraquinone, phenolphthalein, and phthalocyanine. Phthalic acid is known as 1,2-benzene dicarboxylic acid in IUPAC. Ortho-Phthalic acid, Benzene-1,2-dioic acid, and 1,2-Benzenedioic acid are some of the additional names for phthalic acid


 Production of Phthalic Acid

Naphthalene or ortho-xylene is catalytically converted into phthalic anhydride, which is then hydrolyzed to give phthalic acid. Auguste Laurent, a French scientist, produced acid phthalic for the first time in 1836 by oxidising naphthalene tetrachloride. He called it “naphthalic acid” because he thought the emerging compound was a naphthalene compound. Laurent gave it its current name when Swiss scientist Marignac discovered its accurate formula. In the 1800s, naphthalene tetrachloride was produced by oxidising it with nitric acid. Another method involved oxidising naphthalene tetrachloride with boiling sulfuric acid while employing mercury or mercury(II) sulphate for catalysis.

 Physical Properties of Phthalic Acid

  • Phthalic acid has no colour.
  • It has a molar mass of 166.132 g/mol.
  • It contains two interchangeable hydrogen ions per molecule; in other words, it is a dibasic acid.
  • Phthalic acid has a melting point of 207°C.
  • Its density is around 1.593 g/cm3.
  • It has a water solubility index of 0.6g/100mL.
  • Phthalic acid is a solid, aromatic organic material by nature.

Chemical Properties of Phthalic Acid

  • Under the influence of water, sodium amalgam reduces phthalic acid to produce 1,3-cyclohexadiene compounds.
  • Phthalic acid compounds are employed in vacuum pumps and to substitute mercury in manometers. These compounds are created when phthalic acid H2C8H4O4 interacts with alcohol such as C2H5OH.
  • Phthalic anhydride produces acidified monoperoxyphthalic acid (C8H6O5) when exposed to basic hydrogen peroxide at freezing temperatures.

            C6H4(CO)2O + H2O2 ⇢ C8H6O5


Uses of Phthalic Acid 

In the Food Industry: 

In various consumer goods, phthalic acid esters (also known as phthalates) have been utilized as industrial plasticizers. Phthalates have been utilized in materials that come into touch with food and are typically approved for this usage. Humans may potentially consume phthalates used in the coatings of frequently used medications. Phthalates are primarily utilized in gastrointestinal drug coverings to localize the release of medicines. Phthalates may also be present in the composition of herbal remedies, nutritional supplements, and those used during maternity.

In the Cosmetic Industry

Phthalates are versatile substances in many consumer goods, notably personal care and beauty items. Phthalates are chemical substances created in the last century and are used to increase the durability of plastics. These greasy, colourless solutions are also known as “plasticizers” due to their frequent use. These products comprised lotions (body lotions and body creams), facial cleansers, nail paint, hair care items (shampoos, cremes, and gels), antiperspirants, and infant items. As we can see, many cosmetics and personal care items include phthalates. 


In Architecture and Construction

High phthalates are utilized in the construction industry to make a variety of vinyl coverings more resilient and simple to manage. These uses range from flexible bonds and sealants to lasting interior coatings. Vinyl roofing films, durable carpeting, wall panels, acoustic roof coatings, water-resistant membranes, and electrical cable insulation are a few major applications for flexible PVC structures.

Cable and Wire

The electrical wire that links and sustains digital devices has PVC insulation, which contains many phthalates. For instance, the PVC used to cover the electrical cabling in TVs and laptops may contain high phthalates. High phthalate use has various advantages: electrical impedance, adaptability, heat resistance, and low-temperature efficiency.


Outdoor Items

Many outdoor goods, such as outdoor pool lining, garden sprinklers, roof coatings, and water-resistant shoes, such as rain boots, contain high phthalates since they assist flexible PVC to function well in climatic variations – providing flexibility in the freezing environment and resisting deterioration in high temperatures.

In the Textile Industry

High phthalate content in textiles increases the tensile strength and weather resistance of coated fabrics used to produce garments and baggage.


In the Automotive Industry

Because of its sturdiness, Uv protection, and capacity to handle high temperatures, vinyl treated with high phthalates is used in automotive upholstery, seat coverings, and interior decor. Cars’ PVC underbody coverings and other parts prevent weather- and water-induced rust.

 Phthalic Acid Safety Information

On Swallowing

The substance has not been labelled as “harmful by intake.” This is because there isn’t any supporting evidence from either animals or people. After consumption, the substance may still harm the person’s health, mainly if there is already apparent organ damage (such as liver or kidney impairment). Currently, hazardous or toxic compounds are often defined based on dosages that result in mortality (death) as opposed to those that result in morbidity (disease, ill-health). Vomiting and nausea are side effects of digestive tract pain. Unintended ingestion is not a problem in a work environment, though.



 Some people may get eye discomfort and injury from this substance.


This substance may cause skin irritation after coming into touch with this substance. The substance could exacerbate any dermatitis conditions that already exist. Although skin contact causes health problems, it is not believed that the substance may injure the body after entering through cuts, abscesses, or bruises. You shouldn’t introduce this material to skin that is inflamed, abraded, or exposed to the air. Entry into the circulation, such as through wounds, may result in systemic damage with negative consequences. Before using the material, check the skin to ensure that any exterior injury is appropriately protected.


The substance may irritate certain people’s respiratory systems. The body’s reaction to such irritability may result in additional lung damage. If high levels of particulate matter are breathed, those with reduced respiratory function, airway disorders, and illnesses like chronic bronchitis may become even more disabled.


With the equation H2C8H4O4, phthalic acid is a heterocyclic dicarboxylic acid. Even though phthalic acid has little economic impact, its strongly related counterpart, phthalic anhydride, is a widely used compound. Phthalic acid is a white, crystalline organic molecule created by French researcher Auguste Laurent by oxidising naphthalene tetrachloride. Its anhydride derivative is used to make valuable items, including pigments, fragrances, phthalates, and aspartame. In various consumer goods, phthalic acid esters are used as commercial plasticizers. Phthalates have also been utilized in materials that come into touch with food and are typically approved for this usage. Phthalates are also employed in essential goods likely to end up in infants’ mouths, such as baby care products and chewing toys. They blend excellent performance and financial viability to produce vinyl medical items that have enhanced and affordable patient care.

Frequently Asked Questions about Phthalic Acid

Q1. How may Phthalic Acid be changed into Phthalic Anhydride?

A: We can produce phthalic anhydride by dehydrating phthalic acid. When burned, phthalic acid sheds its hydrogen atoms and forms acid anhydrides. This phthalic anhydride is a needle-shaped, colourless to white, glossy solid. Worldwide, phthalic anhydride is utilized in various industries, including resin production, crop insecticides, aldehydes, and plastics. It is currently produced by the vapour method by oxidising naphthalene and o-xylene. Building an alternate production path to the conventional one is highly desirable to lessen the burden on fossil fuel consumption and the effects of oil scarcity challenges.

Q2. Is phthalic acid a powerful acid?

A: Phthalic acid isn’t a powerful acid. It is a mild dibasic acid with pKa values of 2.89 and 5.51; however, when it interacts with strong bases, it interacts quite strongly. The body is adversely affected by all acids. Extreme heat is particularly damaging to phthalic acid—skin, ocular, and respiratory organ damage results from phthalic acid exposure. Narcosis may result from prolonged contact with a high concentration of phthalic acid.

Q3. What are the other names Phthalic Acid is known by?

A: A widely used product is phthalic acid, which is strongly linked to phthalic anhydride. Soil nutrients are the source of phthalic acid. It has the chemical formula H2C8H4O4 .The full name, as given by the IUPAC, is 1,2-benzene dicarboxylic acid. It is also known as o-Phthalic acid, benzene-1,2-dicarboxylic acid, or o-dicarboxybenzene.

phthalic acid


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