Gamma-Butyrolactone (γ-butyrolactone or GBL) is a hygroscopic colorless liquid with a weak characteristic odor which is soluble in water. GBL is a common solvent and reagent in chemistry as well as being used as a flavouring, as a cleaning solvent, as a superglue remover, and as a solvent in some wet aluminium electrolytic capacitors. In humans it acts as a prodrug for GHB, and it is used as a recreational intoxicant with effects similar to alcohol.
GBL has been found in extracts from samples of unadulterated wines. This finding indicates that GBL is a naturally occurring component in some wines and may be present in similar products. The concentration detected was approximately 5 μg/mL and was easily observed using a simple extraction technique followed by GC/MS analysis. GBL can be found in cheese flavourings but typically results in a content of 0.0002% GBL in the final foodstuff.
GBL is a lactone. It is hydrolyzed under basic conditions, for example in a sodium hydroxide solution into sodium gamma-hydroxybutyrate, the sodium salt of gamma-hydroxybutyric acid. Under acidic conditions it forms an equilibrium mixture of both compounds. These compounds then may go on to form a polymer. When treated with a non-nucleophilic base, like lithium diisopropylamide, GBL can become an alpha-carbon nucleophile. The related compound caprolactone can be used to make a polyester in this manner.
GBL is not active in its own right; its mechanism of action stems from its identity as a prodrug of GHB. The hypnotic effect of GHB is enhanced by combination with alcohol. A 2003 rat study showed that GBL in combination with ethanol showed a potentiated hypnotic effect, as the sleep-timing measure was longer than both of the individual components combined