Mendeleev Commun., 2019, 29, 328–330
of bromide 1a (78–92%) were disclosed.† The essential change
of KOH/PhMe/BnEt3NCl) has been developed. The reaction easily
proceeds at 60–62°C when the equivalent ratioAlkBr:P:KOH =
= 1:3.33:(10–14) is applied.
in the equivalent ratio 1a : P : KOH (from 1:1.25:5 up to
1:3.33:8–9) and conducting the process in toluene instead of
THF was the crucial prerequisite, the optimal reaction tempe-
rature having been 60–62°C. Acid 2a was isolated from the
reaction mixture by extraction of the aqueous layer after its
acidification. The residue after concentrating the toluene organic
layer contained trihexyl- and dihexylphosphine oxides 3a, 4a in
the ratio of ~1:2 and in the total yield of ~36% (the 31P NMR
data). Note that for driving the reaction towards acid 2a it was
necessary to slowly add (dropwise) a toluene solution of n-hexyl
bromide 1a to the P/KOH/H2O/PhMe/BnEt3NCl system.†
Diverse alkyl bromides 1b–f were then examined in the
reaction with elemental phosphorus (see Table 1). n-Alkyl-
H-phosphinic acids 2c,e,f were obtained in moderate or good
yields. The exceptions were acids 2b and 2d obtained in 7 and 11%
yields, respectively (entries 7 and 10), which can be explained by
side hydrolysis and/or dehydrobromination of the starting isoalkyl
bromides 1b,d under the action of potassium hydroxide.
The hydrophosphorylation of alkyl bromides herein studied
proceeds likely via the initial formation of polyphosphide A
and polyphosphinite B anions resulted from the disassembling
of Pn or P4 lattice under the action of hydroxide anion.16 The
nucleophilic reaction of polyphosphinite anions B with alkyl
bromide and the consecutive cleavage of the remaining P–P bonds
in the intermediates C and D by hydroxide anions lead finally to
phosphinic acids 2 (Scheme 2).
This work was supported by the Russian Science Foundation
(grant no. 18-73-10080). The main results were obtained using
the equipment of Baikal Analytical Center of Collective Using,
Siberian Branch of the Rusiian Academy of Sciences.
Online Supplementary Materials
Supplementary data associated with this article can be found
in the online version at doi: 10.1016/j.mencom.2019.05.030.
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Scheme 2
Chloroform extract A and toluene layer were combined, the volatiles
were removed in vacuo, the residue (data are given for reaction with
hexyl bromide 1a, 0.4 g was returned) contained 1.15 g of a mixture
of n-Hex2P(O)H (dP 32 ppm) and n-Hex3P=O (dP 45 ppm) in the ratio
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2H, CH2P), 7.00 (d, 1 H, PH, 1JHP 545 Hz), 11.7 (s, 1H, OH). 31P NMR
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Found (%): C, 48.29; H, 9.8; P, 20.82. Calc. for C6H15O2P (%): C, 47.99;
H, 10.07; P, 20.63.
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