Lawesson's reagent

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Lawesson's reagent
Lawesson's reagent
3D model of the Lawesson's reagent molecule
Identifiers
CAS number 19172-47-5
PubChem 87949
ChemSpider 79346 YesY
Jmol-3D images Image 1
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 (77 °F), 100 kPa)
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Infobox 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]

Preparation[edit]

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[edit]

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.

Dithia.png

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[edit]

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.

Alcohols may be converted to thiols by treatment with Lawesson's reagent.[12]

See also[edit]

References[edit]

  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 (19): 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. (1985). "Tetrahedron report number 186 Organothiophosphorus reagents in organic synthesis". Tetrahedron (Review) 41 (41): 2567. doi:10.1016/S0040-4020(01)96363-X. 
  4. ^ Foreman, M.S.; Woollins, J.D. (2000). "Organo-P-S and P-Se heterocycles". J. Chem. Soc., Dalton Trans. (10): 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 (Review) 2003 (13): 1929–1958. doi:10.1055/s-2003-41447. 
  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. (1978). Bull. Soc. Chim. Belg. (87): 223. 
  8. ^ Jones, B. A.; Bradshaw, J. S. (1984). "Synthesis and reduction of thiocarboxylic O-esters". Chem. Rev. (Review) 84 (84): 17. doi:10.1021/cr00059a002. 
  9. ^ Scheibye, S.; Kristensen, J.; Lawesson, S.-O. (1979). "Studies on organophosphorus compounds—XXVII Synthesis of thiono-, thiolo- and dithiolactones". Tetrahedron 35 (35): 1339. doi:10.1016/0040-4020(79)85027-9. 
  10. ^ Shabana, R.; Scheibye, S.; Clausen, K.; Olesen, S. O.; Lawesson, S.-O. (1980). Nouveau Journal de Chimie 1980 (4): 47. 
  11. ^ Brayton, D.; Jacobsen, F. E.; Cohen, S. M.; Farmer, P. J. (2006). "A novel heterocyclic atom exchange reaction with Lawesson's reagent: a one-pot synthesis of dithiomaltol". Chemical Communications 2006 (2): 206–208. doi:10.1039/b511966a. PMID 16372107. 
  12. ^ Nishio, Takehiko (1989). "A novel transformation of alcohols to thiols". Journal of the Chemical Society, Chemical Communications 1989 (4): 205–206. doi:10.1039/C39890000205. 

External links[edit]