(S)-(+)-γ-Butyrolactone-γ-carboxylic acid (CAS NO.: ), which is also known as 2-carboxylic acid, tetrahydro-5-oxo-, (S)-, could be produced through the following synthesis route.

A 6-L Erlenmeyer flask which contains a large magnetic stirring bar is charged with 294 g (2 mol) of L-glutamic acid and 2 L of distilled water. The suspension is stirred vigorously while solutions of 168 g (2.4 mol) of sodium nitrite in 1.2 L of water and 1.2 L of aqueous 2 N sulfuric acid are added simultaneously from separatory funnels. After the addition is complete, the solution is stirred at room temperature for an additional 15 hr. The water is then removed by heating below 50°C under reduced pressure with a rotary evaporator. The resulting pasty solid is triturated with 500 mL of boiling acetone and the hot solution is filtered and set aside to cool. This operation is repeated four times. Removal of solvent with a rotary evaporator affords 312 g of crude (+)-γ-butyrolactone-γ-carboxylic acid as a slightly yellow oil.

A 250-mL, round-bottomed flask is equipped with a magnetic stirring bar and charged with 100 g of the foregoing crude lactone acid. The flask is fitted with a Claisen distillation apparatus and connected to a vacuum pump. The flask is gradually heated with an oil bath (160°C) until gas evolution ceases. At this point the oil bath is removed and the black, viscous oil is distilled with the use of a flame. The product, 58 g (70%), is collected as a colorless oil at 146–154°C (0.03 mm). The distillate crystallizes in the receiver, mp 66–68°C.

Notice: This procedure should be conducted in a well-ventilated hood to avoid inhalation of poisonous NO₂ vapors. To protect the operator the distillation must be carried out with the usual precautions associated with vacuum distillation.