γ-Butyrolactone (GBL) is a hygroscopic colorless, water-miscible liquid with a weak characteristic odor. It is the simplest 4-carbon lactone. It is mainly used as an intermediate in the production of other chemicals, e.g. methyl-2-pyrrolidone. In humans GBL acts as a prodrug for γ-hydroxybutyric acid (GHB), and it is used as a recreational CNS depressant with effects similar to barbiturates.

Occurrence

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.

Production and synthesis

γ-Butyrolactone is produced industrially by dehydrogenation of 1,4-butanediol at a temperature of 180–300 °C and atmospheric pressure in the presence of a copper catalyst.

The yield of this process is approximately 95%. The purification takes place with a liquid-gas-phase extraction.

In the laboratory, it may also be obtained via the oxidation of tetrahydrofuran (THF), for example with aqueous sodium bromate. An alternative route proceeds from GABA using the Sandmeyer reaction.

Reactions

As a lactone, GBL is hydrolyzed under basic conditions, for example in a sodium hydroxide solution into sodium gamma-hydroxybutyrate, the sodium salt of gamma-hydroxybutyric acid. In acidic water, a mixture of the lactone and acid forms coexist in an equilibrium. These compounds then may go on to form the polymer poly(4-hydroxybutyrate) as well as the dimer 1,6-Dioxecane-2,7-dione. When treated with a non-nucleophilic base, such as lithium diisopropylamide, GBL undergoes deprotonation alpha to the carbonyl. The related compound caprolactone can be used to make a polyester in this manner.

Polymerization

The ring-opening polymerization of butyrolactone gives polybutyrolactone. The resulting reverts to the monomer by thermal cracking.It is claimed that poly(GBL) is competitive with commercial biomaterial poly(4-hydroxybutyrate), or P4HB. It is further claimed that poly(GBL) is cheaper to make than P4HB, although both are bio-derived.

Uses

Butyrolactone is principally a precursor to other chemicals. Reaction with methylamine gives NMP. Ammonia gives pyrrolidone. It is also used as a solvent in lotions and some polymers.2-Methyl-4-chlorophenoxybutyric acid is an herbicide produced from butyrolactone.

Butyrolactone, with its wide liquid range, chemical stability and high dielectric constant, is used in some batteries but primarily is found in electrolytic capacitors as the organic solvent. In this capacity, it is frequently mixed with a small ratio of ethylene glycol, “9:1” being common, to vary internal resistivity.

Recently GBL has become an important solvent for the development of organic perovskites (such as Methylammonium lead halide), novel solar cell materials that can be processed from solution. GBL is a good solvent for the precursor salts such as lead halides and methylammonium iodide or formamidinium iodide. Often mixtures of GBL and DMSO yield best results. GBL is an alternative to the more toxic solvent dimethylformamide that was used in the earlier stages of the development of the perovskite solar