Diethyl phosphite is the

organophosphorus compound Organophosphorus chemistry is the scientific study of the synthesis and properties of organophosphorus compounds, which are organic compounds containing phosphorus. They are used primarily in pest control as an alternative to chlorinated hydrocarbo ...

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. Diethyl phosphite is a colorless liquid. The molecule is

tetrahedral In geometry, a tetrahedron (: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular Face (geometry), faces, six straight Edge (geometry), edges, and four vertex (geometry), vertices. The tet ...

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 ...

and ethanol, but intentional preparations came later. It arises as follows: :PCl₃ + 3 C₂H₅OH → (C₂H₅O)₂P(O)H + 2 HCl + C₂H₅Cl Under similar conditions but in the presence of base, triethyl phosphite results: :PCl₃ + 3 EtOH + 3 R₃N → P(OEt)₃ + 3 R₃NH + 3 Cl⁻ Many analogues of diethyl phosphite can be prepared. Despite being named as a phosphite the compound exists overwhelmingly in its phosphonate form, , a property it shares with its parent acid

phosphorous acid Phosphorous acid (or phosphonic acid) is the Compound (chemistry), compound described by the chemical formula, formula . It is diprotic (readily ionizes two protons), not triprotic as might be suggested by its formula. Phosphorous acid is an in ...

. Nonetheless many of its reactions appear to proceed via the minor phosphorus(III)

tautomer In chemistry, 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 reloca ...

. :(C₂H₅O)₂P^III(OH) ⇌ (C₂H₅O)₂P^V(O)H, K = 15 x 10⁶ (25°C, aqueous)

Reactions

Hydrolysis and alcoholysis

Diethyl phosphite hydrolyzes to give phosphorous acid. Hydrogen chloride accelerates this conversion.: Diethyl phosphite undergoes

transesterification Transesterification is the process of exchanging the organic functional 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. Strong acids catalyze the r ...

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

Diethyl phosphite undergoes deprotonation with potassium ''tert''-butoxide. This reactivity allows alkylation at phosphorus ( Michaelis–Becker reaction): :(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 diethyl phosphite with

Grignard reagent Grignard reagents or Grignard compounds are chemical compounds 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 bromi ...

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

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

aldehyde In organic chemistry, an aldehyde () (lat. ''al''cohol ''dehyd''rogenatum, dehydrogenated alcohol) is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred ...

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