2-Mercaptoethanol

Production

2-Mercaptoethanol is manufactured industrially by the reaction of ethylene oxide with hydrogen sulfide. Thiodiglycol and various zeolites catalyze the reaction.

:[[File:Industrial synthesis of mercaptoethanol.svg|400px|upright=2.5|frameless|Reaction of ethylene oxide with hydrogen sulfide to form 2-mercaptoethanol in the presence of thiodiglycol as solvent and catalyst.]]

Reactions

2-Mercaptoethanol cleaves disulfide bonds.

2-Mercaptoethanol reacts with aldehydes and ketones to give the corresponding oxathiolanes. This makes 2-mercaptoethanol useful as a protecting group, giving a derivative whose stability is between that of a dioxolane and a dithiolane.

:[[File:Oxathiolane-formation-with-2-mercaptoethanol-2D-skeletal.svg|400px|Reaction scheme for the formation of oxathiolanes by reaction of 2-mercaptoethanol with aldehydes or ketones.]]

Like most alkylthiols, it adds to Michael acceptors such as acrylonitrile.

Applications

Reducing proteins

Some proteins are denatured by 2-mercaptoethanol. In the case of excess 2-mercaptoethanol, the following equilibrium is shifted to the right: : RS–SR + 2 HOCH2CH2SH 2 RSH + HOCH2CH2S–SCH2CH2OH

:[[File:2-Mercaptoethanol Breaks Disulfide Bonds.png|400px|Reaction scheme for the cleavage of disulfide bonds by 2-mercaptoethanol]]

By breaking the S-S bonds, both the tertiary structure and the quaternary structure of some proteins can be disrupted. Because of its ability to disrupt the structure of proteins, it was used in the analysis of proteins, for instance, to ensure that a protein solution contains monomeric protein molecules, instead of disulfide linked dimers or higher order oligomers. However, since 2-mercaptoethanol forms adducts with free cysteines and is somewhat more toxic, dithiothreitol (DTT) is generally more used especially in SDS-PAGE. DTT is also a more powerful reducing agent with a redox potential (at pH 7) of −0.33 V, compared to −0.26 V for 2-mercaptoethanol.

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

Although 2-mercaptoethanol has a higher volatility than DTT, it is more stable: 2-mercaptoethanol's half-life is more than 100 hours at pH 6.5 and 4 hours at pH 8.5; DTT's half-life is 40 hours at pH 6.5 and 1.5 hours at pH 8.5.

2-Mercaptoethanol and related reducing agents (e.g., DTT) are often included in enzymatic reactions to inhibit the oxidation of free sulfhydryl residues, and hence maintain protein activity. It is often used in enzyme assays as a standard buffer component.{{Cite journal

Denaturing ribonucleases

2-Mercaptoethanol is used in some RNA isolation procedures to eliminate ribonuclease released during cell lysis. Numerous disulfide bonds make ribonucleases very stable enzymes, so 2-mercaptoethanol is used to reduce these disulfide bonds and irreversibly denature the proteins. This prevents them from digesting the RNA during its extraction procedure.

Deprotecting carbamates

Some carbamate protecting groups such as carboxybenzyl (Cbz) or allyloxycarbonyl (alloc) can be deprotected using 2-mercaptoethanol in the presence of potassium phosphate in dimethylacetamide.

Genetic transformation

DNA uptake in Escherichia coli can be facilitated by the addition of 2-mercaptoethanol in genetic transformation.

Safety

2-Mercaptoethanol is moderately toxic and is an irritant to skin and eyes.

References

References

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