Organic acid

Lore & Background

Organic acids include carboxylic acids, sulfonic acids, and compounds with thiol, enol, or phenol groups. Their acidity depends on the stability of their conjugate base. Lower molecular mass organic acids like formic and lactic acids are miscible in water, while higher molecular mass ones like benzoic acid are insoluble in neutral form. Most are very soluble in organic solvents. p-Toluenesulfonic acid is a comparatively strong acid used in organic chemistry because it dissolves in organic reaction solvents.

Reader's Guide

Organic acids are significant for their role in food preservation, where undissociated acids penetrate bacterial cell walls and disrupt physiology, particularly in pH-sensitive bacteria such as Escherichia coli and Salmonella species. They are used in oil and gas well stimulation as less reactive alternatives to mineral acids, and in rust removal via dissolution of iron oxides and chelation of metal ions. In animal feeds, organic acids improve performance and reduce intestinal pathogens without the public health concerns of antibiotic growth promoters. Research has tested acetic, formic, and propionic acids for wood preservation, but leaching and chemical degradation limited effectiveness. Their conjugate bases, like citrate and lactate, are used in biologically compatible buffer solutions.

Did You Know?

• Organic acids are generally weak acids and do not dissociate completely in water, unlike strong mineral acids.
• Lower molecular mass organic acids such as formic and lactic acids are miscible in water, while higher molecular mass ones like benzoic acid are insoluble in neutral form.
• Organic acids are used in food preservation because undissociated acids can penetrate bacterial cell walls and disrupt normal physiology of pH-sensitive bacteria.
• Citric and oxalic acids are used for rust removal because they dissolve iron oxides without damaging the base metal as stronger mineral acids do.