Everything about Dimethyl Sulfate totally explained
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Dimethyl sulfate is a
chemical compound with
formula (CH
3O)
2SO
2. As the dimethyl
ester of
sulfuric acid, its formula is often written as (
CH3)
2SO4 or even Me
2SO
4, where CH
3 or Me is
methyl. Me
2SO
4 is mainly used as a methylating agent in
organic synthesis.
Under standard conditions, Me
2SO
4 is a colourless oily
liquid with a slight onion-like odour (although smelling it would represent significant exposure). Like all strong
alkylating agents, Me
2SO
4 is highly
toxic. Its use as a laboratory reagent has been superseded to some extent by
methyl triflate, CF
3SO
3CH
3, the methyl ester of
trifluoromethanesulfonic acid.
History
Dimethyl sulfate was first discovered in the early 1800s in an impure form. P. Claesson later extensively studied its preparation.
Production
Dimethyl sulfate can be synthesized in the laboratory by many different syntheses:
» :2 CH
3OH + H
2SO
4 → (CH
3)
2SO
4 + 2 H
2O
Another possible synthesis involves distillation of methyl hydrogen sulfate:
» :(CH
3)
2O + SO
3 → (CH
3)
2SO
4
Uses
Dimethyl sulfate is best known as a reagent for the methylation of
phenols,
amines, and
thiols. Typically, one methyl group is transferred more quickly than the second. Methyl transfer is typically assumed to occur via an S
N2 reaction. Although dimethyl sulfate is highly effective and affordable, its toxicity has encouraged the use of other methylating reagents.
Methyl iodide is a reagent used for O-methylation, like dimethyl sulfate, but is less hazardous and more expensive. In general the toxicity of methylating agents is correlated with their efficiency as methyl transfer reagents.
Methylation at oxygen
Most commonly, Me
2SO
4 is employed to methylate phenols. Some simple
alcohols are also suitably methylated, as illustrated by the conversion of
tert-butyl alcohol to t-butyl methyl ether:
» :2 (CH
3)
3COH + (CH
3O)
2SO
2 → 2 (CH
3)
3COCH
3 + H
2SO
4
Alkoxide salts are rapidly methylated:
» :RO
- Na
+ + (CH
3O)
2SO
2 → ROCH
3 + Na(CH
3)SO
4
The methylation of
sugars is called
Haworth methylation
Methylation at amine nitrogen
Me
2SO
4 is used to prepare both
quaternary ammonium salts or
tertiary amines:
» :C
6H
5CH=NC
4C
9 + (CH
3O)
2SO
2 → C
6H
5CH=N
+(CH
3)C
4C
9 + CH
3OSO
3-
Quaternized fatty ammonium compounds are used as a surfactant or fabric softeners. The methylation of a tertiary amine is illustrated as
» :p-CH
3C
6H
4SO
2Na + (CH
3O)
2SO
2 → p-CH
3C
6H
4SO
2CH
3 + Na(CH
3)SO
4
This method has been used to prepare thioesters:
» :RC(O)SH + (CH
3O)
2SO
2 → RC(O)S(CH
3) + HOSO
3CH
3
Other uses
Dimethyl sulfate can effect the base-specific cleavage of
guanine in DNA by rupturing the
imidazole rings present in guanine. This process can be used to determine base sequencing, cleavage on the DNA chain, and other applications.
Dimethyl sulfate also methylates
adenine in single-stranded portions of DNA (for example, those with
proteins like
RNA polymerase progressively melting and re-annealing the DNA). Upon re-annealing, these methyl groups interfere with adenine-guanine base-pairing.
Nuclease S1 can then be used to cut the DNA in single-stranded regions (anywhere with a methylated adenine). This is an important technique for analyzing protein-DNA interactions.
Safety
Dimethyl sulfate is likely
carcinogenic Symptoms may be delayed 6-24 hours. Concentrated solutions of bases (ammonia, alkalis) can be used to hydrolyze minor spills and residues on contaminated equipment, but the reaction may become violent with larger amounts of dimethyl sulfate (see ICSC). Although the compound hydrolyses in water, plain water can't be assumed to hydrolyze dimethyl sulfate quickly enough for decontamination purposes. The hydrolysis products, monomethyl sulfate and methanol, are environmentally hazardous. In water, the compound is ultimately hydrolyzed to
sulfuric acid and
methanol.
Further Information
Get more info on 'Dimethyl Sulfate'.
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