Disodium 4-nitrophenylphosphate
[CAS# 4264-83-9]

Identification

• Classification: Organic raw materials >> Organometallic compound >> Organic sodium
• Name: Disodium 4-nitrophenylphosphate
• Synonyms: 4-Nitrophenyl phosphate disodium salt; 4-Nitrophenyl disodium orthophosphate; PNPP
• Molecular Formula: C₆H₄NNa₂O₆P
• Molecular Weight: 263.05
• CAS Registry Number: 4264-83-9
• EC Number: 224-246-5
• SMILES: C1=CC(=CC=C1[N+](=O)[O-])OP(=O)([O-])[O-].[Na+].[Na+]

Properties

• Melting point: 300 °C

Safety Data

• Hazard Symbols: GHS07 Warning
• Risk Statements: H302
• Safety Statements: P264-P270-P301+P317-P330-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Acute toxicity	Acute Tox.	4	H302

Discovery and Applications

Disodium 4-nitrophenylphosphate is an organophosphate compound consisting of a phosphate group esterified to a 4-nitrophenyl moiety and neutralized as a disodium salt. Its molecular formula is C₆H₄NNa₂O₆P, with a molecular weight of approximately 207.04 g/mol. The phosphate group confers water solubility and reactivity toward hydrolysis, while the 4-nitrophenyl group is an electron-withdrawing aromatic substituent that makes the molecule a useful substrate in enzymatic assays. The disodium form increases solubility and provides ionic stabilization in aqueous solutions.

The compound is commonly prepared by phosphorylation of 4-nitrophenol using a suitable phosphate donor, such as phosphorus oxychloride or phosphoric acid derivatives, followed by neutralization with sodium hydroxide to obtain the disodium salt. Reaction conditions are carefully controlled to avoid hydrolysis of the ester bond and to ensure selective formation of the 4-nitrophenyl phosphate. Purification is generally achieved through recrystallization from water or aqueous ethanol to yield the stable disodium salt.

Chemically, disodium 4-nitrophenylphosphate is an ester of phosphoric acid and exhibits reactivity typical of organophosphates. The phosphate group can undergo hydrolysis under acidic, basic, or enzymatic conditions, releasing 4-nitrophenol, which is chromogenic and allows spectrophotometric detection. This property makes the compound highly valuable as a substrate for phosphatases, including alkaline phosphatase and acid phosphatase. The aromatic nitro group stabilizes the leaving phenoxide ion during hydrolysis, enhancing the rate of enzymatic or chemical reactions.

In aqueous solution, disodium 4-nitrophenylphosphate is highly soluble and forms stable solutions suitable for biochemical and analytical applications. The compound is generally stable under neutral to slightly basic conditions but may hydrolyze slowly under strong acidic or strongly basic environments. Its ionic nature facilitates compatibility with buffers commonly used in enzymatic assays, and the chromogenic 4-nitrophenol released upon hydrolysis allows convenient monitoring of reaction kinetics.

In practical applications, disodium 4-nitrophenylphosphate is widely used as a model substrate in biochemical assays to measure phosphatase activity. It is commonly employed in enzyme kinetics studies, high-throughput screening of inhibitors, and educational demonstrations of enzymatic hydrolysis. The combination of a reactive phosphate ester and a chromogenic leaving group enables sensitive and quantitative analysis of enzyme-catalyzed reactions. Beyond enzymology, the compound can serve as a reagent in organic synthesis or as a precursor for preparing other phosphate esters.

Overall, disodium 4-nitrophenylphosphate is a water-soluble organophosphate with a chromogenic aromatic substituent, making it a versatile and widely used intermediate in biochemical and analytical chemistry. Its combination of chemical stability, enzymatic reactivity, and spectrophotometric detectability supports its application in enzyme assays, mechanistic studies, and synthetic transformations.

References

2025. Efficient synthesis of N-(ethylcarbamothioyl)-1-naphthamide: X-ray structure, Hirshfeld surface analysis, DFTs, and molecular modelling investigations as selective inhibitor of alkaline phosphatase. BMC Chemistry, 19.
DOI: 10.1186/s13065-025-01525-y