1-Naphtholphthalein[2]

Updated: 2026-09-27

Overview

1-Naphtholphthalein is an organic compound primarily used as a pH indicator in laboratory settings. It belongs to the phthalein dye family and exhibits a color change from colorless (acidic) to pink or red (basic) within a pH range of 7.3–8.7. Its molecular structure combines naphthol and phthalein components, contributing to its sensitivity in titration experiments. The compound is synthesized through the condensation of 1-naphthol with phthalic anhydride under controlled conditions. Its stability and reversible color transition make it a reliable choice for educational and analytical applications, though it is less common than phenolphthalein due to its narrower pH range.

Physical and Chemical Properties

1-Naphtholphthalein is a fine powder with a pale yellow to light brown appearance. It has a molecular weight of 418.44 g/mol and a melting point around 250–260°C. The compound is soluble in organic solvents like ethanol and acetone but only slightly soluble in water, limiting its use in aqueous solutions without alcohol co-solvents. As a pH indicator, it transitions from colorless to pink/red as the solution turns alkaline. This property is due to structural changes in its conjugated system upon deprotonation. Its stability under standard storage conditions (room temperature, dry environment) ensures a long shelf life when properly sealed.

Main Applications

1-Naphtholphthalein is predominantly used in laboratories as a visual pH indicator for titrations and educational demonstrations. Its narrow transition range (pH 7.3–8.7) makes it suitable for specific applications requiring precise endpoint detection in weakly basic solutions. It is also employed in chemical analysis to monitor reactions sensitive to slight pH changes. Beyond laboratories, the compound finds niche uses in research involving enzyme activity assays or buffer system validation. However, its applications are less widespread compared to universal indicators like phenolphthalein due to its limited pH range and solubility constraints.

Safety and Storage

While 1-Naphtholphthalein is not classified as highly hazardous, standard laboratory safety protocols should be followed. Avoid direct contact with skin, eyes, or inhalation of dust. Use gloves, goggles, and a lab coat when handling. In case of exposure, rinse affected areas with water and seek medical advice if irritation persists. Store the compound in a tightly sealed container in a cool, dry place, protected from light and moisture. Degradation may occur under prolonged exposure to humid conditions or extreme temperatures. Label containers clearly and keep away from incompatible substances like strong oxidizers.

B2B Procurement Guide

For bulk procurement, prioritize suppliers with certifications (e.g., ISO 9001, GMP) to ensure consistent quality. Key specifications to verify include purity (≥95%), batch-to-batch consistency, and packaging (e.g., amber glass bottles for light-sensitive storage). Request safety data sheets (SDS) and certificates of analysis (CoA) for compliance. Pricing varies based on quantity and purity; negotiate discounts for bulk orders (e.g., 1kg+). Logistics should account for proper labeling and non-hazardous transportation. For international shipments, confirm regulatory compliance with local chemical import regulations (e.g., REACH in the EU).