Chemists synthesize amino alcohols using light

Amino alcohols are high-quality organic compounds that can be found in many everyday objects. However, their preparation is difficult, and chemists have long tried to develop efficient synthesis methods. In their recent study, published in the journal Nature Catalysis, scientists succeeded. Ordinary light helped.

A group of scientists led by Professor Dr. Frank Glorius from the University of Münster has found a solution for producing a special variant of amino alcohols.

Amino alcohols, especially ethanolamine, are widely used in the manufacture of detergents, emulsifiers, cosmetics, and pharmaceuticals and as absorbers of acid gases (e.g., CO₂). The purpose of using amino alcohols in cosmetics is the replacement of ammonia in ammonia-free formulations, neutralization and buffering of formulations, odor absorption, color stabilization, improved dispersion, and rheology stabilization. The best amino alcohol for this purpose is tromethamine (INCI). Amino alcohols include choline, which plays an important role in metabolism in humans and animals; choline preparations are used to treat the liver. Some alkaloids, such as ephedrine, are amino alcohols, and the important hormone adrenaline also belongs to them.

Vicinal amino alcohols can exist in two different variants – regioisomers, in which the functional groups of the amine and alcohol change positions. Although they are very similar, their biochemical properties differ. Installing both amine and alcohol groups in one step is a major challenge. The discovery of an asymmetric amino hydroxylation reaction, by which one of the regioisomers can be obtained, even led to the Nobel Prize award to chemist Barry Sharpless in 2001. Another regioisomer could not be synthesized by a similar method and remained a long-standing problem. However, with the new chemical method of photoinitiated reaction, the synthesis of another regioisomer has become efficient.

Non-activated alkenes containing a carbon-carbon double bond are frequently used in reaction processes due to their availability. As a rule, the introduction of both amine and alcohol groups in one step through the carbon-carbon double bond of an unactivated alkene is always initiated by the amino group followed by the alcohol group’s addition. As a result, a certain regioisomer of the vicinal amino alcohol is always formed.

Scientists have now identified a special class of amine-like compounds that are reactive yet stable enough to allow an alcohol group to be first attached to a carbon-carbon double bond and then an amino group added.

“Just as plants use chlorophyll to convert light into energy, we use a so-called photocatalyst,” explains Dr. Tuhin Patra, the first author of the study. “These particles can absorb light from blue LEDs and transfer their energy to a molecule directly involved in the reaction. This simultaneously releases amine and alcohol groups. “” This process, in which molecules transfer electrons to each other, is called energy transfer, the scientist explains.

Interestingly, the new method generates the least available regioisomer from vicinal amino alcohols so that both alcohol and amine groups are protected from further reactions.

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