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Lawesson's reagent



Lawesson's reagent
IUPAC name 2,4-bis(4-methoxyphenyl)-
1,3,2,4-dithiadiphosphetane
2,4-disulfide
Other names Lawesson's reagent, LR
Identifiers
CAS number 19172-47-5
SMILES COC1=CC=C(P2(SP(S2)
(C3=CC=C(OC)C=C3)
=S)=S)C=C1
Properties
Molecular formula C14H14O2P2S4
Molar mass 404.47 g/mol
Appearance Slightly yellow powder
Density , solid
Melting point

228 - 231 °C

Solubility in water Insoluble
Hazards
EU classification Irritant
Harmful (XN)
R-phrases 15/29 20/21/22
S-phrases 22 45 7/8
Related Compounds
Related thiation agents Hydrogen sulfide,
Phosphorus pentasulfide
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)
Infobox disclaimer and references

Lawesson's reagent, or LR, is a chemical compound used in organic synthesis 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.[1]

Contents

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,[2] then 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.[3][4][5][6] 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.[7] Additionally, Lawesson's reagent has been used to thionate enones, esters[8], lactones[9], amides, lactams[10], and quinones.

In one study, reaction of maltol with LR results in a selective oxygen replacement in two positions.[11]

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.

References

  1. ^ Lecher, H. Z.; Greenwood, R. A.; Whitehouse, K. C.; Chao, T. H. (1956). "The Phosphonation of Aromatic Compounds with Phosphorus Pentasulfide". J. Am. Chem. Soc. 78: 5018. doi:10.1021/ja01600a058.
  2. ^ Thomsen, I.; Clausen, K.; Scheibye, S.; Lawesson, S.-O. (1990). "Thiation with 2,4-Bis(4-methoxyphenyl)-1,3,2,4-Dithiadiphosphetane 2,4-disulfide: N-Methylthiopyrrolidone". Org. Synth.; Coll. Vol. 7: 372. 
  3. ^ Cherkasov, R. A.; Kutyrev, G. A.; Pudovik, A. N. Tetrahedron 1985, 41, 2567. (Review)
  4. ^ Foreman, M.S.; Woollins, J.D. (2000). "Organo-P-S and P-Se heterocycles". J. Chem. Soc. Dalton Trans. 2000: 1533-1543.
  5. ^ Martin Jesberger, Thomas P. Davis, Leonie Barner (2003). "Applications of Lawesson’s Reagent in Organic and Organometallic Syntheses". Synthesis 2003: 1929-1958. doi:10.1055/s-2003-41447. (Review)
  6. ^ Cava, M. P.; Levinson, M. I. (1985). "Thionation reactions of Lawesson's reagents". Tetrahedron 41 (22): 5061 - 5087. doi:10.1016/S0040-4020(01)96753-5.
  7. ^ Pedersen, B. S.; Scheibye, S.; Nilsson, N. H.; Lawesson, S.-O. Bull. Soc. Chim. Belg. 1978, 87, 223.
  8. ^ Jones, B. A.; Bradshaw, J. S. Chem. Rev. 1984, 84, 17. (Review)
  9. ^ Scheibye, S.; Kristensen, J.; Lawesson, S.-O. Tetrahedron 1979, 35, 1339.
  10. ^ Shabana, R.; Scheibye, S.; Clausen, K.; Olesen, S. O.; Lawesson, S.-O. Nouv. J. Chim. 1980, 4, 47.
  11. ^ Daniel Brayton, Faith E. Jacobsen, Seth M. Cohen and Patrick J. Farmer (2006). "A novel heterocyclic atom exchange reaction with Lawesson's reagent: a one-pot synthesis of dithiomaltol". Chemical Communications 2006: 206-208. doi:10.1039/b511966a.
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Lawesson's_reagent". A list of authors is available in Wikipedia.
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