Hydrotropes are used as coupling agents to solubilize the water insoluble and often incompatible functional ingredients of household and institutional cleaning products and personal care products. These hydrotropes are not surfactants but are used to solubilize complex formulations in water. They function to stabilize solutions, modify viscosity and cloud-point, limit low temperature phase separation and reduce foam.
Hydrotropes are amphiphilic substances composed of both a hydrophilic and a hydrophobic functional group. The hydrophobic part of the molecule is a benzene substituted apolar segment. The hydrophilic, polar segment is an anionic sulfonate group accompanied by a counter ion (i.e., ammonium, calcium, potassium or sodium). Hydrotropes are produced by sulfonation of an aromatic hydrocarbon solvent (i.e., toluene, xylene or cumene). The resulting aromatic sulfonic acid is neutralized using an appropriate base (e.g., sodium hydroxide) to produce the sulfonate or hydrotrope.