Mechanochemical Phosphorylation of Acetylides Using Condensed Phosphates: A Sustainable Route to Alkynyl Phosphonates

Abstract

In pursuit of a more sustainable route to phosphorus-carbon (P-C) bond-containing chemicals, we herein report that phosphonates can be prepared by mechanochemical phosphorylation of acetylides using polyphosphates in a single step, redox-neutral process, bypassing white phosphorus (P₄) and other high-energy, environmentally hazardous intermediates. Using sodium triphosphate (Na₅P₃O₁₀) and acetylides, alkynyl phosphonates 1 can be isolated in yields of up to 32%, while reaction of sodium pyrophosphate (Na₄P₂O₇) and sodium carbide (Na₂C₂) engendered, in an optimized yield of 63%, ethynyl phosphonate 2, an easily isolable compound that can be readily converted to useful organophosphorus chemicals. Highly condensed phosphates like Graham's salt and bioproduced polyphosphate were also found to be compatible after reducing the chain length by grinding with orthophosphate. These results demonstrate the possibility of accessing organophosphorus chemicals directly from condensed phosphates and may offer an opportunity to move toward a "greener" phosphorus industry.

Figure 1

(A) Overview of key P–C bond formation steps in P-chemical manufacture. (B) The envisioned mechanochemical phosphorylation of carbon nucleophiles. (C) Selected examples of useful phosphonate-based organophosphorus chemicals.

Figure 2

(A) Synthesis of alkynyl phosphonates 1a–j. (B) Synthesis of ethynyl phosphonate 2, yield based on reducible phosphate (1 per Na₄P₂O₇, 2 per Na₅P₃O₁₀). (C) Synthesis of 2a, 2b, and 3 from 2.

Figure 3

Synthesis of triphenylphosphine from 2b (A) and synthesis of 4 from 2′ (B).

Figure 4

Synthesis of ethynyl phosphonate 2 from bio-polyP and Graham’s salt; yield is based on reducible phosphate.