Deuteration

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Deuterated dimethyl sulfoxide (DMSO- d6 )

Deuterium (also known as deuterium labeling ) is a technique of labeling molecules in which some or all of the hydrogen atoms in a molecule are replaced by deuterium atoms, which means that the chemical properties of the molecules are practically unchanged, but the physical ones are. These differences are then used specifically to study molecules. Deuteration is the most common application of isotope labeling .

Techniques of deuteration

Hydrogen-deuterium exchange

The simplest method of exchanging hydrogen atoms for deuterium atoms is to add acidic compounds such as alcohols , amides , carboxylic acids , phenols or amines with a large excess of a simple compound with acidic deuterium atoms such as e.g. B. deuterium oxide (D 2 O) or D4 methanol . According to the law of mass action , the equilibrium is shifted to the side of the desired deuterated compound. As a rule, this technique is only used for the introduction of deuterated heteroatoms in order to determine the number of exchangeable functional groups with the aid of NMR spectroscopy or mass spectrometry; It is also used in the structure elucidation of unknown or synthesized new compounds.

Targeted deprotonation

Another possibility for deuteration is the targeted deprotonation of organic compounds. Since the carbon-hydrogen bond is usually only slightly acidic, strong bases must be used here. Aldehydes , ketones and carboxylic acid esters can be deprotonated in the α position to the enolation . If these are reacted with a deuterium-containing acidic compound such as deuterium oxide or D4- methanol , the corresponding α-deuterated carbonyl compounds are obtained. These are not isotope-stable in protic solvents, since the isotope is exchanged via a tautomerism . However, one can use this type of deuteration to get clues for the direction of attack by an electrophile on the enolation of a prochiral carbonyl compound.

Chemical synthesis

Since a carbon-hydrogen bond is generally not very acidic, a synthetic route often has to be worked out for the targeted production of deuterated compounds.

The interception of organometallic compounds such as Grignard compounds or lithium-organic compounds with deuterium oxide is of particular importance for simple deuteration of molecules . This metalated intermediate product can be easily produced either from the organohalogen compounds by reaction with the metallic alkali or alkaline earth element.

Another way is the catalytic hydrogenation of carbon-carbon multiple bonds with D 2 or the reduction of carbon-heteroatom double bonds with complex deuterated hydrides such as. B. with lithium aluminum deuteride or sodium boron deuteride.

Particularly with per-deuterated compounds such as benzene-d6 , methanol-d4 but also large-scale products such as deuterochloroform , special syntheses are required.

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