[59547-92-1] · C6H15I2O3P · Triethoxydiiodophosphorane · (MW 419.98)
(Arbuzov-type intermediate; can be used as a dehydrating or condensing agent1)
Physical Data: not isolated; prepared in situ.
Solubility: prepared and used in ether, dichloromethane, or acetonitrile.
Preparative Methods: was first prepared1 as an unstable intermediate during the reaction between Phosphorus(III) Iodide and Triethyl Phosphite. It was reported as being unstable at room temperature, decomposing to give ethyl iodide and diethyl phosphoriodate.1 This same report also indicated that the reaction between triethyl phosphite and iodine at -5 °C gave the same two products. A subsequent report2 described similar reactions with similar results. In 1979, it was reported3 that the reaction between methyl phosphite and iodine at 0 °C in ether, dichloromethane, or acetonitrile gave a 1:1 adduct with a single 31P NMR absorption which was assigned the triethoxydiiodophosphorane structure. This solution was stable over several days at room temperature.
Handling, Storage, and Precautions: in solution the phosphorane has a half-life of several days.
Phosphoranes such as (2) are considered to be intermediates in the Arbuzov reaction (eq 1).
Only in exceptional cases can they be isolated, but they can be observed by 31P NMR.4 The relative stability of triethoxydiiodophosphorane allows it to be used as a dehydrating or condensing agent.3
Benzamide and benzaldoxime have been dehydrated to benzonitrile (eqs 2 and 3) by addition of the amide or oxime to an iodine solution in dichloromethane or acetonitrile at 0 °C followed by 1 equiv of Triethyl Phosphite and 2 equiv of Triethylamine.3 Stirring for 2 hours at room temperature leads to dehydration. Ease of workup is aided by the water soluble nature of the byproducts.
A solution of triethoxydiiodophosphorane allows the preparation of amides from amines and acids (eq 4).3
In the absence of the amine, a slower Arbuzov reaction takes place to give a mixed anhydride via the phosphonium salt (eq 5).3
This reagent has also been used as a condensing agent in the synthesis of a dipeptide from N-benzoyl-L-leucine and ethyl glycinate in high yield. The dipeptide obtained was entirely racemic. Addition of 1-Hydroxybenzotriazole to the reaction gave the dipeptide in 83% yield and 39% ee.
King's College London, UK