5-CHLOROTHIOPHENE-2-CARBOXYLIC ACID

China [CN]

Physical and Chemical Properties

1. Physical Properties

Appearance and State: White to off-white crystalline powder at room temperature and pressure (the higher the purity, the lighter the color; low-purity products may have a slightly yellowish tint. No noticeable odor).

Melting Point: Consistent with literature and industrial data, the melting point range is 158-162°C (stable when heated, gradually melts above the melting point. Further heating may cause decarboxylation, so the heating temperature must be controlled).

Boiling Point: No clear boiling point at room pressure (carboxyl groups are susceptible to decarboxylation at high temperatures, so decarboxylation is usually achieved through vacuum distillation of derivatives such as esters, rather than direct distillation of the carboxylic acid). Solubility: It exhibits typical carboxylic acid solubility characteristics—slightly soluble in cold water (approximately 0.5-1 g/L at 25°C) and soluble in hot water. It is readily soluble in polar organic solvents such as methanol, ethanol, acetone, and ethyl acetate, with excellent solubility in DMF (N,N-dimethylformamide) and DMSO (dimethyl sulfoxide). It is insoluble in non-polar solvents such as petroleum ether and n-hexane. (This solubility is useful for recrystallization purification, typically using an ethanol-water mixture.)

Acidity: The dissociation constant (pKa) of the carboxyl group (-COOH) is approximately 3.5-4.0 (stronger than acetic acid, due to the electron-withdrawing effect between the thiophene ring and the chlorine atom, which enhances the acidity of the carboxyl group). It reacts with bases to form stable carboxylates (e.g., sodium and potassium salts).