N-Acetyl Cysteine (NAC)

N-Acetyl Cysteine, or NAC, is N-acetyl-L-cysteine (CAS 616-91-1, C5H9NO3S, MW 163.19) — L-cysteine with an acetyl group on the alpha-amino nitrogen. Blocking the amine changes the practical handling profile considerably: the acetylated molecule is markedly more stable to oxidation than free cysteine, is freely soluble in both water and ethanol, and melts sharply at 109-110 °C. Thovek supplies material to Ph. Eur. monograph 0967 and the USP monograph, with content of 98.0-101.0% (Ph. Eur.) or 98.0-102.0% (USP) on the dried substance, specific optical rotation of +21.0° to +27.0°, loss on drying not more than 1.0% (in vacuo at 70 °C for 3 hours), sulphated ash not more than 0.2%, and heavy metals and zinc each not more than 10 ppm. The zinc limit is specific to the Ph. Eur. monograph and reflects catalyst carry-over from certain manufacturing routes, so buyers formulating to EP should ask for it on the certificate of analysis. Commercially NAC is produced by N-acetylation of L-cysteine or L-cysteine hydrochloride with acetic anhydride under controlled pH and temperature, followed by crystallisation and drying. Because the starting L-cysteine is now widely sourced from microbial fermentation on plant sugars rather than from keratin hydrolysis, non-animal and vegan-declarable NAC is readily available, and Thovek supplies the upstream origin declaration alongside the standard COA, MSDS and BSE/TSE statement. Buyers should note the regulatory position in the United States. FDA takes the view that NAC is excluded from the statutory definition of a dietary supplement, but on 1 August 2022 the agency issued final guidance stating it intends to exercise enforcement discretion for NAC-containing products otherwise lawfully marketed as supplements, pending completion of rulemaking or resolution of the citizen petition. That enforcement discretion remains the operative policy. NAC is also an established pharmaceutical active and a routine component of cell culture media and cosmetic formulations. Export classification is HS 2930 90 99 as an organo-sulphur compound.