Lawesson's reagent

Chembox new
Name = Lawesson's reagent
ImageFile = Lawesson's_Reagent_Structure.png ImageName = Lawesson's reagent
ImageFile1 = Lawesson's-reagent-3D-ball.png ImageName1 = 3D model of the Lawesson's reagent molecule
IUPACName = 2,4-bis(4-methoxyphenyl)-
1,3,2,4-dithiadiphosphetane
2,4-disulfide
OtherNames = Lawesson's reagent, LR
Section1 = Chembox Identifiers
SMILES = COC1=CC=C(P2(SP(S2)
(C3=CC=C(OC)C=C3)
=S)=S)C=C1
CASNo = 19172-47-5
RTECS =
Section2 = Chembox Properties
Formula = C₁₄H₁₄O₂P₂S₄
MolarMass = 404.47 g/mol
Appearance = Slightly yellow powder
Density = , solid
Solubility = Insoluble
MeltingPt = 228 - 231 °C
Section7 = Chembox Hazards
ExternalMSDS =
EUClass = Irritant
Harmful (XN)
FlashPt =
RPhrases = 15/29 20/21/22
SPhrases = 22 45 7/8
Section8 = Chembox Related
Function = thiation agents
OtherFunctn = Hydrogen sulfide,
Phosphorus pentasulfide

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. [cite journal | author = Lecher, H. Z.; Greenwood, R. A.; Whitehouse, K. C.; Chao, T. H. | journal = J. Am. Chem. Soc. | year = 1956 | volume = 78 | pages = 5018 | title = The Phosphonation of Aromatic Compounds with Phosphorus Pentasulfide | doi = 10.1021/ja01600a058]

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, [OrgSynth | author = Thomsen, I.; Clausen, K.; Scheibye, S.; Lawesson, S.-O. | collvol = 7 | collvolpages = 372 | year = 1990 | prep = cv7p0372 | title = Thiation with 2,4-Bis(4-methoxyphenyl)-1,3,2,4-Dithiadiphosphetane 2,4-disulfide: N-Methylthiopyrrolidone] 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.

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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. [cite journal | author = Cherkasov, R. A.; Kutyrev, G. A.; Pudovik, A. N. | journal = Tetrahedron | year = 1985 | issue = 41 | pages = 2567 | format = Review | doi = 10.1016/S0040-4020(01)96363-X | title = Tetrahedron report number 186 Organothiophosphorus reagents in organic synthesis | volume = 41] [cite journal | author = Foreman, M.S.; Woollins, J.D. | title = Organo-P-S and P-Se heterocycles | journal = J. Chem. Soc., Dalton Trans. | year = 2000 | pages = 1533–1543 | doi = 10.1039/b000620n] [cite journal | journal = Synthesis | year = 2003 | volume = 2003 | pages = 1929–1958 | doi = 10.1055/s-2003-41447 | title = Applications of Lawesson’s Reagent in Organic and Organometallic Syntheses | author = Martin Jesberger, Thomas P. Davis, Leonie Barner | format = Review] [cite journal | title = Thionation reactions of Lawesson's reagents | author = Cava, M. P.; Levinson, M. I. | journal = Tetrahedron | year = 1985 | volume = 41 | issue = 22 | pages = 5061–5087 | doi = 10.1016/S0040-4020(01)96753-5 ] 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. [cite journal | author = Pedersen, B. S.; Scheibye, S.; Nilsson, N. H.; Lawesson, S.-O. | journal = Bull. Soc. Chim. Belg. | year = 1978 | issue = 87 | pages = 223] Additionally, Lawesson's reagent has been used to thionate enones, esters [cite journal | author = Jones, B. A.; Bradshaw, J. S. | journal = Chem. Rev. | year = 1984 | issue = 84 | pages = 17 | format = Review | doi = 10.1021/cr00059a002 | title = Synthesis and reduction of thiocarboxylic O-esters | volume = 84] , lactones [cite journal | author = Scheibye, S.; Kristensen, J.; Lawesson, S.-O. | journal = Tetrahedron | year = 1979 | issue = 35 | pages = 1339 | doi = 10.1016/0040-4020(79)85027-9 | title = Studies on organophosphorus compounds—XXVII Synthesis of thiono-, thiolo- and dithiolactones | volume = 35] , amides, lactams [cite journal | author = Shabana, R.; Scheibye, S.; Clausen, K.; Olesen, S. O.; Lawesson, S.-O. | journal = Nouv. J. Chim. | year = 1980 | issue = 4 | pages = 47] , and quinones.

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In one study, reaction of maltol with LR results in a selective oxygen replacement in two positions. [cite journal | title = A novel heterocyclic atom exchange reaction with Lawesson's reagent: a one-pot synthesis of dithiomaltol | author = Daniel Brayton, Faith E. Jacobsen, Seth M. Cohen and Patrick J. Farmer | journal = Chemical Communications | year = 2006 | volume = 2006 | pages = 206–208 | doi = 10.1039/b511966a]

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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

External links

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