P-Chloride-Free Synthesis of Phosphoric Esters: Microwave-Assisted Esterification of Alkyl- and Dialkyl Phosphoric Ester-Acids Obtained from Phosphorus Pentoxide

Abstract

It is a reasonable endeavour to replace P-chloride starting materials (e.g. POCl3) by greener and cheaper reagents. Our purpose was to start from phosphorus pentoxide, i.e. to utilize its reaction with alcohols in the preparation of (HO)2P(O)(OR) and HOP(O)(OR)2, and to convert the mixtures of the corresponding monoester and diester so obtained to the target trialkyl esters. Separate experiments showed that the monobutylphosphate undergo microwave (MW)-assisted esterification with butanol in the presence of [bmim][BF4] catalyst at 200 °C to afford dibutylphosphate in a selective manner (~95%) that, in turn, may be converted to tributylphosphate by alkylation under MW irradiation. In this way, the mixtures of (HO)2P(O)(OR) and HOP(O)(OR)2 obtained by the practical reaction of phosphorus pentoxide and alcohol (ROH) could also be converted in two additional steps to the corresponding trialkyl esters. The three-step synthesis of trialkylphosphates starting from phosphorus pentoxide was also transformed in a one-pot (step 1: preparation of the monoester diester mixture, step 2: diesterification) and telescoping (step 3: triesterification) variation avoiding the isolation and purification of the intermediates, and affording the triesters in 86-93% yields. The three- and two-step P-chloride-free methods developed are “green” and of more general value.

Chemical Recycling of Phosphoric Acid Recovered from Sewage Waste via Direct Esterification with Organosilicate

“…The direct triple esterification of 1, a process previously considered impossible, [21][22][23][24][25][26][27][28] was successfully achieved using tetraalkyl organosilicates. This molecular transformation represents one of notable advancements in the synthesis of phosphorus chemicals, eliminating the need for white phosphorus.…”

“…Azeotropic processes using specific metal-or amine-based catalysts enable the direct esterification of 1 with alcohols. [21][22][23][24] Alternatively, the use of stoichiometric activating reagents 25,26 or microwave reactors 27,28 has also been possible methods. These procedures successfully enable facile production of phosphate monoesters and/or diesters from 1.…”

“…27 Several alternative methods for the preparation of phosphate triesters using copper catalysts, 29,30 iodonium salts 29 and electrophilic https://doi.org/10.26434/chemrxiv-2023-c5m0q-v2 ORCID: https://orcid.org/0000-0002-3041-7638 Content not peer-reviewed by ChemRxiv. License: CC BY-NC-ND 4.0 alkylating reagents 27,28,31 have been developed. However, these reactions require phosphate diesters as the starting materials, as well as toxic or expensive reagents.…”

Chemical upcycling of phosphoric acid recovered from sewage waste

“…Azeotropic processes using specific metal-or amine-based catalysts enable the direct esterification of 1 with alcohols. [15][16][17][18] The use of stoichiometric activating reagents [19,20] or microwave reactors [21,22] has also been reported.…”

“…However, these methods are still limited to the formation of phosphate monoesters and/or diesters. To efficiently form phosphate triesters, which has been estimated to be more energetically difficult, [21] several alternative strategies using copper catalysts, [23,24] iodonium salts [23] and electrophilic alkylating reagents [21,22,25] have been developed, although these methods require phosphate diesters as starting materials.…”