Although terephthalaldehyde (CAS 623-27-8) and terephthalic acid (CAS 100-21-0) have similar molecular structures (both contain a benzene ring and two oxygen-containing functional groups), their different functional groups lead to vastly different applications: the former is a fine chemical intermediate, while the latter is a bulk basic chemical raw material.
I. Core Differences:
1. Functional Groups: Terephthalaldehyde has two aldehyde groups (-CHO), while terephthalic acid has two carboxyl groups (-COOH).
2. Molecular Formula: The molecular formula of terephthalaldehyde is C₈H₆O₂, and the molecular formula of terephthalic acid is C₈H₆O₄.
3. Molecular Weight: The molecular weight of terephthalaldehyde is 134.13, and the molecular weight of terephthalic acid is 166.13.
4. Product Positioning: Terephthalaldehyde is a fine chemical intermediate, while terephthalic acid is a chemical intermediate. Terephthalic acid is a major basic chemical raw material.
5. Annual production scale: Terephthalaldehyde's annual production scale is small-batch, while terephthalic acid's annual production scale is in the tens of millions of tons.
6. Main uses: Terephthalaldehyde is mainly used in the production of fluorescent whitening agents, pharmaceuticals, and dyes, while terephthalic acid is mainly used in the production of polyester fibers, PET bottles, and films.
7. Price level: Terephthalaldehyde is more expensive (fine chemical), while terephthalic acid is less expensive (commodity).
II. Differences in chemical properties:
1. Oxidizing property: Terephthalaldehyde (aldehyde group) is easily oxidized to terephthalic acid, while terephthalic acid (carboxyl group) is already in an oxidized state and is stable.
2. Reducing property: Terephthalaldehyde (aldehyde group) can be reduced to terephthalic acid, while terephthalic acid (carboxyl group) is not easily reduced.
3. Condensation reaction: Terephthalaldehyde (aldehyde group) reacts with amines to form Schiff bases, while terephthalic acid (carboxyl group) reacts with alcohols to form esters.
4. Polymerization method: Terephthalaldehyde (aldehyde group) can self-polymerize or copolymerize with other monomers, while terephthalic acid (carboxyl group) condenses with glycols to form polyesters.
5. Acidity and alkalinity: Terephthalaldehyde (aldehyde group) is neutral, while terephthalic acid (carboxyl group) is a dibasic weak acid.
