New Approach to the Synthesis of Phosphorodichloridites, Phosphorochloridites, and Trialkyl Phosphites

Abstract

Different trivalent organophosphorus esters such as phosphorodichloridites, phosphorochloridites, and mixed trialkyl phosphites have been easily synthesized in good yields using a HCl-catalyzed reaction of the corresponding chlorophosphine and alkoxytrimethylsilane by mutual exchange of the alkoxy and chlorine ligand (P ^III Cl/ROSiR′ ₃ ; exchange reaction). Chemoselectivity of the exchange reaction with primary and secondary alkoxytrimethylsilanes, as well as with alkoxytrimethylsilanes and thioalkoxytrimethylsilanes, respectively, has also been examined. It has been also found that the substitution reaction of chlorophosphines with secondary amine occurs more rapidly than the exchange reaction with ROSiR′ ₃ .

Keywords:

• Mixed trialkyl phosphites
• phosphorochloridites
• phosphorodichloridites

Dedicated to Professor Marian Mikołajczyk from the CBMiM PAN in Łódź, Poland, on the occasion of his 70th birthday.

Notes

^a Yield of distilled products.

^b Reaction time: a– d 24 h, e– i 1 week, f– h, j two weeks, k 1 h; the reaction is carried out in the presence of stoichiometric amount of pyridine.

^c Crude oil contains 96–98 mol % of product.

^d Reaction mixture was filtered, then evaporated and kept 15 min under vacuum (40 °C / 2 Torr).

^e Two rotamers.

^f Product is unstable at room temperature forming during one week cyclic chlorophosphoroamidite, (3l), (³¹P NMR, δ = 153.9 ppm, ref. [10]).

^g Satisfactory microanalyses obtained: C ± 0.35, H ± 0.25, P ± 0.30. All new compounds shown IR (film) absorption bands characteristic for a POC moiety: broad bands between 1170–1105 cm^{− 1}, ref. [28].

^a Reaction time: 4a, b, 5a 14 days; 5b 24 h, 6a, b 3 d; in case of 5a two equivalents of silylated alcohol were used.

^b Crude oil contains 95 mol % of product and 5 mol % of CH₃(CH₂)₈CH₂OP(OCH₂C₆H₅)₂.

^c Crude oil contains 97–98 mol % of product and (C₆H₅-CH₂O)₂PCl.

^d Unstable at elevated temperature.

^e Crude oil contains 95–97 mol % of product.

^f Satisfactory microanalyses obtained: C ± 0.35, H ± 0.25, P ± 0.30. All compounds show IR (film) absorption bands characteristic for the POC moiety: broad bands between 1170–1105 cm^{− 1}. ²⁸

^a Crude oil contains 96–98 mol % of product; the isomer mixture has not been subjected to elemental microanalysis; reaction time in each case 24 h at –65°C and then 4 h at 20°C.

^b The ratio of the isomers has been confirmed chemically. The exchange products were hydrolyzed to HOCH₂CH(OH)CH₂OP(O)H(OH) (9c) and (HOCH₂)₂CHOP(O)H(OH) (9d), as well as HSCH₂CH(OH)CH₂OP(O)H(OH) (9e) and HSCH₂CH[OP(O)H(OH)]CH₂OH (9f), respectively, and their molar ratio has been determined by ¹H and ³¹P NMR spectroscopy. The ratio was 5:1 in each case (see the Experimental section). There is no evidence for the formation of thiophosphitylated esters.