Lawesson's reagent

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Lawesson's reagent
Lawesson's reagent
3D model of the Lawesson's reagent molecule
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

[edit] 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).

[edit] 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.

[edit] 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.

Thionation of a ketone to give a thioketone using Lawesson's reagent

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

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.

[edit] 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. doi:10.1039/b000620n. 
  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. 

[edit] External links