Lawesson's reagent is a cyclic dithiaphosphine sulfide that converts carbonyls (C=O) into thiocarbonyls (C=S) under mild conditions. It is moisture-sensitive, freely soluble in dichloromethane, chloroform, toluene and hot THF, and rapidly hydrolysed by water. Commercial material is supplied ≥97 % pure and should be stored under inert atmosphere.
Key physicochemical data:
Melting point: 228–230 °C (dec.)
Predicted b.p.: >400 °C (decomp.)
Density: 1.48 g cm⁻³ (20 °C, solid)
31P NMR (CDCl₃): δ ≈ 95 ppm (singlet)
Flash point: >220 °C
Log P (octanol/water): 3.2 (predicted)
Typical uses:
Universal thionating agent for amides, esters, lactones, ketones and aldehydes in pharmaceutical, agro-chemical and material-science syntheses.
Precursor for thio-amides, thio-esters, thio-ureas and thio-ketones under neutral, non-aqueous conditions.
Reagent for trace-water determination and for preparing thio-analogues of natural products and APIs.
Quality specification (commercial grade):
Purity (31P NMR): ≥97 %
Water content (KF): ≤0.3 %
Free P₂S₅: ≤0.5 %
Residue on ignition: ≤0.1 %
Heavy metals: ≤20 ppm
Hazard statement:
Reacts violently with water, liberating toxic H₂S (H260). Causes skin and eye irritation (H315 + H319). Use only with adequate ventilation, gloves and eye protection; store under argon in a desiccator. SDS available on request.
