diethylphosphite

The compound was probably prepared in the 1850s by combining phosphorus trichloride and ethanol, but intentional preparations came later. It arises as follows:{{cite book|last1=Malowan|first1=J. E.|title=Inorganic Syntheses |chapter=Diethyl Phosphite |journal=Inorg. Synth.|year=1953|volume=4|pages=58–60|doi=10.1002/9780470132357.ch19|isbn=9780470132357 }}

:PCl₃ + 3 C₂H₅OH → (C₂H₅O)₂P(O)H + 2 HCl + C₂H₅Cl

Under similar conditions but in the presence of base, triethyl phosphite results:{{cite journal|first1=A. H.|last1=Ford-Moore|first2=B. J.|last2=Perry |journal=Org. Synth.| title = Triethyl Phosphite | volume=31 | pages = 111| year = 1951 | doi=10.15227/orgsyn.031.0111}}

:PCl₃ + 3 EtOH + 3 R₃N → P(OEt)₃ + 3 R₃NH + 3 Cl⁻

Many analogues of diethyl phosphite can be prepared.{{cite journal|last = Pedrosa|first = Leandro|date = March 20, 2011|accessdate = July 10, 2017|url = http://cssp.chemspider.com/488|title = Esterification of Phosphorus Trichloride with Alcohols; Diisopropyl phosphonate|journal = ChemSpider Synthetic Pages|at = SyntheticPage 488|doi = 10.1039/SP488|publisher = Royal Society of Chemistry|doi-access = free}}{{cite journal|last1=Fakhraian|first1=H.|last2=Mirzaei|first2=A.|title=Reconsideration of the Base-Free Batch-Wise Esterification of Phosphorus Trichloride with Alcohols|journal=Org. Process Res. Dev.|year=2004|volume=8|issue=3|pages=401–404|doi=10.1021/op049958v}} Despite being named as a phosphite the compound exists overwhelmingly in its phosphonate form, {{nowrap|(C₂H₅O)₂P(O)H}}, a property it shares with its parent acid phosphorous acid. Nonetheless many of its reactions appear to proceed via the minor phosphorus(III) tautomer.{{cite journal|last1=Doak|first1=G. O.|last2=Freedman|first2=Leon D.|title=The Structure and Properties of the Dialkyl Phosphonates|journal=Chem. Rev.|year=1961|volume=61|issue=1|pages=31–44|doi=10.1021/cr60209a002}}

:(C₂H₅O)₂P^III(OH) ⇌ (C₂H₅O)₂P^V(O)H, K = 15 x 10⁶ (25°C, aqueous){{cite journal |doi=10.1139/v79-039|title=Tautomerization Equilibria for Phosphorous Acid and its Ethyl Esters, Free Energies of Formation of Phosphorous and Phosphonic Acids and their Ethyl Esters, and p Ka Values for Ionization of the P—H Bond in Phosphonic Acid and Phosphonic Esters |year=1979 |last1=Guthrie |first1=J. Peter |journal=Canadian Journal of Chemistry |volume=57 |issue=2 |pages=236–239 |doi-access=free }}

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

Diethyl phosphite undergoes transesterification upon treating with an alcohol. For alcohols of high boiling points, the conversion can be driven by removal of ethanol:{{cite book|last=Malowan|first=John E.|chapter=Dioctyl Phosphite |title=Inorganic Syntheses |journal=Inorg. Synth.|year=1953|volume=4|pages=61–62|doi= 10.1002/9780470132357.ch20|isbn=9780470132357}}

:(C₂H₅O)₂P(O)H + 2 ROH → (RO)₂P(O)H + 2 C₂H₅OH

Similarly amines can displace ethoxide:{{cite journal|title=Synthesis of Phosphoryl Ynamides by Copper-Catalyzed Alkynylation of Phosphoramidates. Preparation of Diethyl Benzyl(oct-1-yn-1-yl)phosphoramidate|author=John M. Read, Yu-Pu Wang, Rick L. Danheiser|journal=Org. Synth.|year=2015|volume=92|page=156|doi=10.15227/orgsyn.092.0156|doi-access=free}}

:(C₂H₅O)₂P(O)H + RNH₂ → (C₂H₅O)(RN(H)P(O)H + C₂H₅OH

Diethyl phosphite undergoes deprotonation with potassium tert-butoxide. This reactivity allows alkylation at phosphorus (Michaelis–Becker reaction):{{OrgSynth|title = 6-Diethylphosphonomethyl-2,2-dimethyl-1,3-dioxen-4-one (Phosphonic acid, [(2,2-dimethyl-4-oxo-4H-1,3-dioxin-6-yl)methyl]-, diethyl ester)|first1 = Robert K.|last1 = Boeckman|first2 = Robert B.|last2 = Perni|first3 = James E.|last3 = Macdonald|first4 = Anthony J.|last4 = Thomas|year = 1988|volume = 66|page = 194|doi = 10.15227/orgsyn.066.0194|collvol = 8|collvolpages = 192|prep = CV8P0192}}

:(C₂H₅O)₂P(O)H + KO^tBu → (C₂H₅O)₂P(O)K + HO^tBu

:(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 reagents results in initial deprotonation followed by displacement of the ethoxy groups.{{cite journal|last=Hays|first=Hugh R.|title=Reaction of diethyl phosphonate with methyl and ethyl Grignard reagents|journal=J. Org. Chem.|year=1968|volume=33|issue=10|pages=3690–3694|doi=10.1021/jo01274a003}}{{OrgSynth|title = Synthesis of Electron-Deficient Secondary Phosphine Oxides and Secondary Phosphines: Bis[3,5-bis(trifluoromethyl)phenyl]phosphine Oxide and Bis[3,5-bis(trifluoromethyl)phenyl]phosphine|first1 = Carl A.|last1 = Busacca|first2 = Jon C.|last2 = Lorenz|first3 = Paul|last3 = Sabila|first4 = Nizar|last4 = Haddad|first5 = Chris H.|last5 = Senanyake|year = 2007|volume = 84|page = 242|doi = 10.15227/orgsyn.084.0242|prep = v84p0242}} 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)

Diethyl phosphite can add across unsaturated groups via a hydrophosphonylation reaction. For example, it adds to aldehydes 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 the Pudovik reaction and Kabachnik–Fields reaction,{{cite journal |last1=Keglevich |first1=György |last2=Bálint |first2=Erika |title=The Kabachnik–Fields Reaction: Mechanism and Synthetic Use |journal=Molecules |date=1 November 2012 |volume=17 |issue=11 |pages=12821–12835 |doi=10.3390/molecules171112821|pmid=23117425 | pmc=6268146|doi-access=free }}{{open access}} in both cases forming aminophosphonates

• Dimethylphosphite
• Diisopropylphosphite
• Diphenylphosphite

Category:Organophosphites

Category:Ethyl esters