2-Mercaptoethanol (also known as beta-mercaptoethanol, BME, 2BME, 2-ME, or β-met) is a compound with the formula HOCH2CH2SH. ME or βME, as it is often abbreviated, is used to reduce disulfide bonds and can act as a biological antioxidant by scavenging hydroxyl radicals (among others). It is widely used because the hydroxyl group imparts water solubility and reduces volatility. Its odor, while unpleasant, is less objectionable than related mercaptans due to its reduced vapor pressure.
2-Mercaptoethanol is produced industrially by the reaction of ethylene oxide with hydrogen sulfide. Thiodiglycol catalyzes the reaction with various zeolites. [3]

In the presence of thiodiglycol as solvent and catalyst, ethylene oxide reacts with hydrogen sulfide to form 2-mercaptoethanol.
reaction[edit]
beta mercaptoethanol reacts with aldehydes and ketones to give the corresponding oxathiolanes. [4] This allows 2-mercaptoethanol to be used as a protecting group, resulting in derivatives with stability between those of dioxolane and dithiolane. [5]

Reaction scheme for the formation of oxathiolanes via the reaction of 2-mercaptoethanol with aldehydes or ketones.
application[edit]
Reduced protein[edit]
Some proteins can be denatured by 2-mercaptoethanol, which cleaves disulfide bonds that may form between the thiol groups of cysteine residues. In the presence of excess 2-mercaptoethanol, the following equilibrium shifts to the right:

RS–SR + 2 HOCH2CH2SH ⇌ 2 RSH + HOCH2CH2S–SCH2CH2OH
Reaction Scheme for Cleavage of Disulfide Bonds by 2-Mercaptoethanol
By breaking S-S bonds, both the tertiary and quaternary structures of some proteins can be disrupted. [6] Because of its ability to disrupt the structure of proteins, it is used in protein analysis, for example, to ensure that protein solutions contain monomeric protein molecules rather than disulfide-linked dimers or higher oligomers. However, since 2-mercaptoethanol forms adducts with free cysteine and is somewhat more toxic, dithiothreitol (DTT) is generally more commonly used, especially in SDS-PAGE. DTT is also a more powerful reducing agent, with an redox potential (at pH 7) of −0.33 V compared to −0.26 V for 2-mercaptoethanol. [7]

2-Mercaptoethanol is often used interchangeably with dithiothreitol (DTT) or the odorless tris(2-carboxyethyl)phosphine (TCEP) in biological applications.

Although 2-mercaptoethanol is more volatile than DTT, it is more stable: the half-life of 2-mercaptoethanol exceeds 100 hours at pH 6.5, and 4 hours at pH 8.5; the half-life of DTT is 40 hours at pH 6.5, and 4 hours at pH 8.5. 8.5 hours is 1.5 hours