Cleavage reactions proceed via a cyclic intermediate called a periodate ester. The formation of this may be affected by pH and temperature but is most strongly effected by the geometry of the substrate, with "cis"-diols reacting significantly faster than "trans"-diols. The reactions are exothermic and are typically performed at 0 °C. As periodate salts are only readily soluble in water reactions are generally performed in aqueous media. Where solubility is an issue periodic acid may be used, as this is soluble in alcohols; phase transfer catalysts are also effective in biphasic reaction mixtures. In extreme cases the periodate may be exchanged for lead tetraacetate which reacts in a similar manner and is soluble in organic solvents (Criegee oxidation).