Diethylphosphite is the

organophosphorus compound Organophosphorus compounds are organic compounds containing phosphorus. They are used primarily in pest control as an alternative to chlorinated hydrocarbons that persist in the environment. Some organophosphorus compounds are highly effective in ...

with the formula (C₂H₅O)₂P(O)H. It is a popular reagent for generating other organophosphorus compounds, exploiting the high reactivity of the P-H bond. Diethylphosphite is a colorless liquid. The molecule is

tetrahedral In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular faces, six straight edges, and four vertex corners. The tetrahedron is the simplest of all the o ...

Synthesis and properties

The compound was probably prepared in the 1850s by combining

phosphorus trichloride Phosphorus trichloride is an inorganic compound with the chemical formula PCl3. A colorless liquid when pure, it is an important industrial chemical, being used for the manufacture of phosphites and other organophosphorus compounds. It is toxic a ...

and ethanol, but intentional preparations came later. It arises as follows: :PCl₃ + 3 C₂H₅OH → (C₂H₅O)₂P(O)H + 2 HCl + C₂H₅Cl Many derivatives can be prepared similarly. Despite being named as a phosphite it exists overwhelmingly in its phosphonate form, , a property it shares with its parent acid

phosphorous acid Phosphorous acid (or phosphonic acid (singular)) is the compound described by the formula H3PO3. This acid is diprotic (readily ionizes two protons), not triprotic as might be suggested by this formula. Phosphorous acid is an intermediate in th ...

; despite this many of its reactions are difficult to rationalise without assuming the existence of the following

tautomerism Tautomers () are structural isomers (constitutional isomers) of chemical compounds that readily interconvert. The chemical reaction interconverting the two is called tautomerization. This conversion commonly results from the relocation of a hyd ...

equilibrium between phosphorus(V) and phosphorus(III) forms: :(C₂H₅O)₂P^V(O)H ⇌ (C₂H₅O)₂P^III(OH)

Reactions

Alkoxide exchange

Diethylphosphite undergoes

transesterification In organic chemistry, transesterification is the process of exchanging the organic group R″ of an ester with the organic group R' of an alcohol. These reactions are often catalyzed by the addition of an acid or base catalyst. The reaction can ...

upon treating with an alcohol. For alcohols of high boiling points, the conversion can be driven by removal of ethanol: :(C₂H₅O)₂P(O)H + 2 ROH → (RO)₂P(O)H + 2 C₂H₅OH Similarly amines can displace ethoxide: :(C₂H₅O)₂P(O)H + RNH₂ → (C₂H₅O)(RN(H)P(O)H + C₂H₅OH

P-alkylation

Diethylphosphite undergoes deprotonation with potassium ''tert''-butoxide. This reactivity allows alkylation at phosphorus: :(C₂H₅O)₂P(O)H + KO^''t''Bu → (C₂H₅O)₂P(O)K + HO^''t''Bu :(C₂H₅O)₂P(O)K + RBr → (C₂H₅O)₂P(O)R + KBr For converting aryl halides, palladium-catalysis can be employed. The C-P coupling process is reminiscent of the Buchwald-Hartwig amination. Reaction of diethylphosphite with

Grignard reagent A Grignard reagent or Grignard compound is a chemical compound with the general formula , where X is a halogen and R is an organic group, normally an alkyl or aryl. Two typical examples are methylmagnesium chloride and phenylmagnesium bromide ...

s results in initial deprotonation followed by displacement of the ethoxy groups. This reactivity provides a route to secondary phosphine oxides, such as dimethylphosphine oxide as shown in the following pair of idealized equations: :(C₂H₅O)₂P(O)H + CH₃MgBr → (C₂H₅O)₂P(O)MgBr + CH₄ :(C₂H₅O)₂P(O)MgBr + 2 CH₃MgBr → (CH₃)₂P(O)MgBr + 2 MgBr(OC₂H₅) :(CH₃)₂P(O)MgBr + H₂O → (CH₃)₂P(O)H + MgBr(OH)

Hydrophosphonylation

Diethylphosphite can add across unsaturated groups via a hydrophosphonylation reaction. For example, it adds to

aldehyde In organic chemistry, an aldehyde () is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl grou ...

s in a manner similar to the Abramov reaction: :(C₂H₅O)₂P(O)H + RCHO → (C₂H₅O)₂P(O)CH(OH)R It can also add to

imines In organic chemistry, an imine ( or ) is a functional group or organic compound containing a carbon–nitrogen double bond (). The nitrogen atom can be attached to a hydrogen or an organic group (R). The carbon atom has two additional single bo ...

in the Pudovik reaction and Kabachnik–Fields reaction,{{open access in both cases forming aminophosphonates

References