Using Acetic Acid and Sodium Chloride to convert methylene blue to leucomethylene blue

Methylene blue is a redox-active thiazine dye that turns colorless when reduced to leucomethylene blue. Stronger acids, such as hydrochloric acid is commonly used to speed up these reactions, but its corrosive nature may make the environment hazardous and has safety risks when in smaller lab settings. This study tested whether acetic acid could support the reduction of methylene blue when paired with reducing agent, vitamin C, and sodium chloride. To determine whether acetic acid could replace hydrochloric acid, 4 different factors were tested; vitamin C (5 mg/mL, 7.5 mg/mL, 10 mg/mL, and 12.5 mg/mL), sodium chloride (100, 150, 200, and 250 equivalents relative to methylene blue), acetic acid concentrations (2.0 mL, 5.0 mL, and 7.5 mL), and temperature (35°C, 45°C, 55°C, and 65°C). Each trial changed one variable; the total volume and the methylene blue concentrations were kept constant. The fastest decolorization occurred at 65°C, 0.005 mg/mL methylene blue, 10mg/mL vitamin C, 50% vinegar, and 250 equivalents of sodium chloride. Under these conditions, complete decolorization took approximately 17 minutes. These results suggest that acetic acid can effectively reduce methylene blue under optimized conditions, offering a safer and more accessible alternative to strong acids for smaller scale redox chemistry experiments.