4-Aminophthalic acid
[CAS# 5434-21-9]

Identification

• Classification: Biochemical >> Amino acids and their derivatives >> Other amino acid derivatives
• Name: 4-Aminophthalic acid
• Molecular Formula: C₈H₇NO₄
• Molecular Weight: 181.14
• CAS Registry Number: 5434-21-9
• EC Number: 226-596-4
• SMILES: C1=CC(=C(C=C1N)C(=O)O)C(=O)O

Properties

• Density: 1.6±0.1 g/cm³ Calc.^*
• Melting point: 344 °C (Decomposes) (Expl.)
• Boiling point: 465.1±40.0 °C 760 mmHg (Calc.)^*
• Flash point: 235.1±27.3 °C (Calc.)^*
• Index of refraction: 1.684 (Calc.)^*

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Safety Data

• Hazard Symbols: GHS07 Warning
• Risk Statements: H315-H319-H335
• Safety Statements: P261-P264-P264+P265-P271-P280-P302+P352-P304+P340-P305+P351+P338-P319-P321-P332+P317-P337+P317-P362+P364-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Eye irritation	Eye Irrit.	2	H319
Skin irritation	Skin Irrit.	2	H315
Specific target organ toxicity - single exposure	STOT SE	3	H335

Discovery and Applications

4-Aminophthalic acid is an aromatic dicarboxylic acid derivative characterized by an amino group substituted at the 4-position of the phthalic acid core. The phthalic acid moiety consists of a benzene ring bearing two adjacent carboxyl groups (ortho-dicarboxylic acid), while the amino substituent is positioned para to one carboxyl group, modifying the compound’s chemical behavior and physical properties.

The synthesis of 4-aminophthalic acid can be achieved by selective nitration of phthalic acid or its derivatives, followed by catalytic reduction of the nitro group to an amino group. Alternative synthetic routes involve functional group transformations on substituted phthalic acid precursors. Control over reaction conditions is essential to obtain regioselective substitution and to prevent overreaction or side product formation.

Chemically, 4-aminophthalic acid exhibits properties typical of both amino-substituted aromatics and dicarboxylic acids. The amino group can act as a nucleophile and base, while the carboxyl groups provide acidic functionalities capable of forming salts, esters, and amides. The proximity of these groups allows for intramolecular hydrogen bonding and facilitates chelation of metal ions. This interplay influences solubility, reactivity, and molecular conformation.

Applications of 4-aminophthalic acid include its use as an intermediate in the synthesis of dyes, pharmaceuticals, agrochemicals, and polymers. Its dual functional groups enable its incorporation into various chemical frameworks through condensation, amidation, and esterification reactions. The compound can serve as a building block for fluorescent probes, corrosion inhibitors, and coordination complexes.

Analytical characterization typically involves nuclear magnetic resonance (¹H and ¹³C NMR) spectroscopy to confirm the substitution pattern and chemical environment of protons and carbons. Infrared (IR) spectroscopy identifies characteristic absorption bands for amino groups (around 3300–3500 cm^–1) and carboxyl groups (broad O–H stretch near 2500–3300 cm^–1 and C=O stretch near 1700 cm^–1). Mass spectrometry provides molecular weight confirmation and fragmentation patterns consistent with the amino dicarboxylic acid structure.

Physically, 4-aminophthalic acid is typically a crystalline solid with moderate solubility in polar solvents such as water and alcohols. Its melting point depends on purity and crystalline form. The compound is stable under normal storage conditions but can undergo degradation upon prolonged exposure to strong acids or bases.

In summary, 4-aminophthalic acid is a multifunctional aromatic compound combining amino and dicarboxylic acid groups, making it a versatile intermediate in chemical synthesis and industrial applications. Its distinct structural features contribute to its reactivity and utility in various fields including materials science and medicinal chemistry.

References

2021. Composites based on graphite oxide and zirconium phthalocyanines with aromatic amino acids as photoactive materials. Chemical Papers, 75(11).
DOI: 10.1007/s11696-021-01731-7

2017. Development of an immunochromatographic assay as a screen for detection of total phthalate acid esters in cooking oil. Journal of Toxicology and Environmental Health, Part A, 80(23-24).
DOI: 10.1080/15287394.2017.1414023

1987. Agylation of aromatic aminodicarboxylic acids. Bulletin of the Academy of Sciences of the USSR, Division of chemical science, 36(8).
DOI: 10.1007/bf00960132