A method for producing butanol using two-phase extractive fermentation and recyclable extractant compositions

Provided herein are processes comprising providing a fermentation medium comprising a fermentable carbon source, a recombinant microorganism comprising an engineered butanol biosynthetic pathway, and butanol; contacting said fermentation medium with an extractant composition comprising an effective amount of antioxidant or antioxidant-like compound, whereby at least a portion of the butanol in the fermentation medium partitions into the extractant; recovering at least a portion of the butanol and extractant composition from the fermentation medium; recycling the extractant composition recovered in (c) one or more times in the fermentation medium; optionally adjusting the effective amount of antioxidant or antioxidant-like compound in the extractant composition, whereby the rate of oxidation or effet of oxidized products in the recycled extractant composition is substantially reduced and/or avoided such that the extractant composition may be recycled.