HOME
TheInfoList



Lawesson's reagent, or LR, is a
chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by chemical bonds. A homonuclear molecule, mo ...
used in
organic synthesis Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic chemistry, Organic molecules are often more complex than Inorganic chemistry, inorganic compounds, and the ...
as a thiation agent. Lawesson's reagent was first made popular by Sven-Olov Lawesson, who did not, however, invent it. Lawesson's reagent was first made in 1956 during a systematic study of the reactions of arenes with P4S10.


Preparation

Lawesson's reagent is commercially available. It can also be conveniently prepared in the laboratory by heating a mixture of anisole with phosphorus pentasulfide until the mixture is clear and no more hydrogen sulfide is formed, then recrystallization (chemistry), recrystallized from toluene or xylene. As Lawesson's reagent has a strong and unpleasant smell, it is best to prepare the compound within a fume-hood and to treat all glassware used with a decontamination solution before taking the glassware outside the fume-hood. One common and effective method of destroying the foul smelling residues is to use an excess of sodium hypochlorite (chlorine bleach).


Mechanism of action

Lawesson's reagent has a four membered ring of alternating sulfur and phosphorus atoms. With heating, the central phosphorus/sulfur four-membered ring can open to form two reactive dithiophosphine ylides (R-PS2). Much of the chemistry of Lawessons's reagent is in fact the chemistry of these reactive intermediates. : In general, the more electron rich a carbonyl is, the faster the carbonyl group will be converted into the corresponding thiocarbonyl by Lawesson's reagent.


Applications

The chemistry of Lawesson's reagent and related substances has been reviewed by several groups. The main use of Lawesson's reagent is the thionation of carbonyl compounds. For instance, Lawesson's reagent will convert a carbonyl into a thiocarbonyl. Additionally, Lawesson's reagent has been used to thionate enones, esters, lactones, amides, lactams, and quinones. : In one study, reaction of maltol with LR results in a selective oxygen replacement in two positions. :Image:LR Maltol reaction.png, 300px, Maltol reaction with LR A combination of silver perchlorate and Lawesson's reagent is able to act as an oxophilic Lewis acid with the ability to catalyze the Diels–Alder reaction of dienes with α,β-unsaturated aldehydes. in some cases, alcohols may be converted to thiols by treatment with Lawesson's reagent. Lawesson's reagent reacts with sulfoxides to form thioethers.


See also

* Woollins' reagent


References


External links

* {{cite web , url = https://www.organic-chemistry.org/namedreactions/lawessons-reagent.shtm , title = Lawesson's Reagent , publisher = Organic Chemistry Portal , accessdate = 2007-10-16 Reagents for organic chemistry Sulfur heterocycles Phosphorus heterocycles Four-membered rings Foul-smelling chemicals