Abstract
Abstract The optimized HCl-catalyzed hydrolysis of alkyl diphenylphosphinates is described. The reaction times and pseudo-first-order rate constants suggested the iPr > Me > Et ∼ Pr ∼ Bu order of reactivity in respect of the alkyl group of the phosphinates. The MW-assisted p-toluenesulfonic acid (PTSA)-catalyzed variation means a better alternative possibility due to the shorter reaction times, and the alkaline hydrolysis is another option. The transesterification of alkyl diphenylphosphinates took place only in the presence of suitable ionic liquids, such as butyl-methylimidazolium hexafluorophosphorate ([bmim][PF6]) and butyl-methylimidazolium tetrafluoroborate ([bmim][BF4]). The application of ethyl-methylimidazolium hydrosulfate ([emim][HSO4]) and butyl-methylimidazolium chloride ([bmim][Cl]) was not too efficient, as the formation of the ester was accompanied by the fission of the O–C bond resulting in the formation of Ph2P(O)OH. This surprising transformation may be utilized in the phosphinate → phosphinic acid conversion.
Highlights
2 Materials and methodsThe esters of phosphinic acids prepared in most cases by the reaction of the corresponding phosphinic chloride with alcohol [1,2], or recently, by the microwave-assisted direct esterification of the phosphinic acids in the presence of an IL additive [2,3,4,5] areThe 31P, 13C, 1H NMR spectra were taken on a Bruker DRX500 spectrometer operating at 202.4, 125.7, and 500 MHz, respectively
We have recently investigated the acidic hydrolysis of a series of cyclic alkyl phosphinates in detail [18]
LC-MS measurements were performed with an Agilent 1,200 liquid chromatography system coupled with a 6,130 quadrupole mass spectrometer equipped with an ESI ion source (Agilent Technologies, Palo Alto, CA, USA)
Summary
The esters of phosphinic acids (alkyl phosphinates) prepared in most cases by the reaction of the corresponding phosphinic chloride with alcohol [1,2], or recently, by the microwave-assisted direct esterification of the phosphinic acids in the presence of an IL additive [2,3,4,5] are
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