This study investigates the synthesis of herbicides based on p-chlorophenol (Cl-C₆H₄OH) and focuses on the polythermal solubility behavior of the NaOH – Cl-C₆H₄OH – H2O system. Understanding the solubility and phase transitions within this system is essential for optimizing the synthesis of herbicides. Solubility measurements were performed over a temperature range of -54.3°C to 59.0°C. A polythermal solubility diagram was constructed, identifying crystallization fields of ice, NaOH, NaOH•3.5H₂O, NaOH•5H₂O, NaOH•7H₂O, Cl-C₆H₄OH, and Cl-C₆H₄ONa. The compound Cl-C6H4ONa was isolated from its predicted crystallization region and identified using chemical and physico-chemical analysis, including infrared (IR) spectroscopy and scanning electron microscopy (SEM). The solubility diagram revealed distinct crystallization fields for various hydrates of NaOH and p-chlorophenol derivatives. Despite the high solubility of the initial components, the system exhibited a slight salting-out effect on the Cl-C6H4OH compound. The structure of the isolated Cl-C₆H₄ONa was further characterized using IR and SEM analyses, confirming its composition and morphology. The study provides valuable insights into the polythermal solubility of the NaOH – Cl-C₆H₄OH – H₂O system and the conditions necessary for the efficient synthesis of herbicides. The identification of specific crystallization fields and the detailed analysis of the isolated compound enhance the understanding of the phase behavior, contributing to more effective herbicide production processes.