Synthesis of mixed alkylphosphites and alkylphosphates

Article abstract of DOI:10.1080/10426500307865

Some mixed phosphites having two different alkyl chain were obtained as forerunners for mixed phosphates Mixed dialkyl phosphates were obtained in good yields (40-80%) by phase transfer catalysis in liquid-liquid sistem, starting from different dialkyl phosphites and aliphatic alcohols. The reaction conditions were optimized in order to obtain good yields in phosphites and phosphates respectively. Compounds were analyzed by IR, P³¹-NMR.

Full text of DOI:10.1080/10426500307865

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Synthesis of Mixed Alkylphosphites and
Alkylphosphates
Gheorghe Ilia a , Adriana Popa a , Smaranda Iliescu a , Alina Bora a , Gheorghe Dehelean a &
Aurelia Pascariu a
a Institute of Chemistry , Romanian Academy , Timisoara, Romania
Published online: 27 Oct 2010.
To cite this article: Gheorghe Ilia , Adriana Popa , Smaranda Iliescu , Alina Bora , Gheorghe Dehelean & Aurelia Pascariu
(2003) Synthesis of Mixed Alkylphosphites and Alkylphosphates, Phosphorus, Sulfur, and Silicon and the Related Elements,
178:7, 1513-1519, DOI: 10.1080/10426500307865
To link to this article: http://dx.doi.org/10.1080/10426500307865
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Phosphorus, Sulfur, and Silicon, 178:1513–1519, 2003
C
Copyright Taylor & Francis Inc.
ISSN: 1042-6507 print
DOI: 10.1080/10426500390212915
SYNTHESIS OF MIXED ALKYLPHOSPHITES
AND ALKYLPHOSPHATES
Gheorghe Ilia, Adriana Popa, Smaranda Iliescu, Alina Bora,
Gheorghe Dehelean, and Aurelia Pascariu
Romanian Academy, Institute of Chemistry, Timisoara,
Romania
(Received December 17, 2002; accepted January 28, 2003)
Some mixed phosphites having two different alkyl chain were obtained
as forerunners for mixed phosphates Mixed dialkyl phosphates were
obtained in good yields (40–80%) by phase transfer catalysis in liquid-
liquid sistem, starting from different dialkyl phosphites and aliphatic
alcohols. The reaction conditions were optimized in order to obtain good
yields in phosphites and phosphates respectively. Compounds were an-
alyzed by IR, P31-NMR.
Keywords: Mixed phosphates; mixed phosphites; phase transfer
catalysis
The reaction of phosphorus chlorine derivatives with alcohols is
well known and is used for obtaining a wide range of phosphorus
esters,1 but the yields were low. For the synthesis of mixed phos-
phates Steinberg,2 then Kenner and Williams3 proposed the system di-
alkylphosphite/carbontetrachloride/triethylammine and alcohol. This
system has a few major disadvantages: it needs an equivalent mol of
amine; reaction products are impure and contain ammonium chloro-
hydrate; reaction times a very long (more than 12 h); only moderate
yields.
Zwierzak4 showed that alcohols can react with dialkyphosphites
in a biphasic system, carbon trachloride-aqueous sodium hydroxide
(Scheme 1). The studies were limited to a few aliphatic alcohols. We
found that this method can be applied to series of aliphatic alcohols5
and aliphatic phosphite. This article presents the obtained results in
optimal conditions.
Address correspondence to Gheorghe Ilia, Romanian Academy, Institute of Chemistry,
24 M. Viteazu Bvd. 1900 Timisoara, Romania. E-mail: ilia@acad-tim.utt.ro
1513

1514
G. Ilia et al.
SCHEME 1
Also, a new method was found for the synthesis of mixed dialkyl
phosphites6 used in the synthesis of mixed phosphates having three
different alkyl groups (Scheme 2).
SCHEME 2
RESULT AND DISCUSSION
In the phase transfer catalysis reactions are involved a lot of factors
which influence the development of the process as: stirring speed, the
catalyst, reaction time, mass transfer, and the shape of the flask.
Stirring speed was one of the studied factors because it has a ma-
jor influence on the mass transfer processes and reaction speed. As is
known7 phase transfer catalysis reactions took place by putting in con-
tact two immiscible phases when the reagent is transferred from one
phase to another by a catalyst where it reacts with the substrate.
The speed of the reaction increases when the contact between the
two phases is intimate. The studies were performed in a 250 ml flask
and with a teflon stirrer having a semicircle shape and a diameter of
20 mm (Figure 1).
Even when the mixture is not stirred the reaction takes place but the
yields are low. Increasing the speed increases the yield to a maximum
then it decreases again. The best results were obtained at 700–800 rpm.
Furthermore the influence of the reaction time on the yield was studied
(Figure 2).
The yields are optimal when the reagents were kept in contact for
about 3 h, then decrease due to saponification reactions in contact with
aqueous sodium hydroxide; saponification could lead to phosphoric acid.
This process depends on the pH, nature of the radical, temperature,
concentration, and so on.
The influence of phase transfer catalyst was studied (Table I). The
best results were obtained with tetrabutylammonium salts.

Synthesis of Mixed Alkylphosphites and Alkylphosphates
1515
FIGURE 1 The influence of stirring speed on the yield of phosphates.
Preliminary studies alowed a few observations: a) In order to obtain
good yields it needs 50% aqueous sodium hydroxide; b) it needs an
excess of dialkylphosphite due to saponification reactions; c) the order
of reagent addition is important; and d) the solvent is important.
Based on these observation it can be concluded that, in the phospho-
rylation reaction of alcohols by the phase transfer catalysis method, the
phosphite is oxidized to dialkylchlorophosphate which reacts with alco-
hols by nucleophilic substitution, and mixed phosphates are obtained
(Scheme 3).
SCHEME 3
FIGURE 2 The influence of the reaction time on the yields of phosphates.

1516
G. Ilia et al.
TABLE I The Influence of the Catalyst on the Yield
Synthesis
Catalyst
Yields (%)
0
1
2
TEP
TEAC
TEAC
TEAC
TEAC
TEAB
TEAB
TEAB
TEAB
TBAC
TBAC
TBAC
TBAC
TBAB
TBAB
TBAB
TBAB
50,1
58,2
54,1
56
DEBP
DBEP
TBP
TEP
55,2
63,3
59,8
60,2
63,3
71,4
68,7
69,8
68,9
75
DEBP
DBEP
TBP
TEP
DEBP
DBEP
TBP
TEP
DEBP
DBEP
TBP
72,3
71
TEAC(B) = tetraetylammonium chloride (bromide).
TBAC(B) = tetrabutylammonium chloride (bromide).
Side reactions, with formation of dihalocarbene, apear when 50%
aqueous sodium hydroxide is used (Scheme 4). Dihalocarbene can reacts
also with alkohols.
SCHEME 4
In accordance with the general procedure, the reactions were per-
formed with different alcohols and diethylphosphite, dipropylphosphite
and dibutylphosphite by the phase transfer catalysis method in liquid-
liquid system (Table II, Table III, and Table IV).
In all syntheses, the reaction temperature was kept at 15 C and
the reaction time was 3 h. Decreasing the reaction temperature below
15 C did increase the reaction time and side reactions and the yields
did decrease. Mixed phosphates obtained from C1–C4 were chromato-
graphically pure. The obtained products were analyzed also by IR. In
the IR spectra, the disappearance of the band at 2430–2440 cm 1(P H)
was used for the reaction control.
Also mixed phosphites were obtained, by direct hydrolysis of dialkyl
phosphites with 20% aqueous tetraethylammonium hydroxide followed

Synthesis of Mixed Alkylphosphites and Alkylphosphates
1517
TABLE II Experimental Results in the Synthesis of Some Phosphates
Starting from Diethylphosphite (Catalyst-Tetrabutylammonium Bromide
0.5 mmol %)
Yield
(%)
Yield from
lit (%)
b.p. Lit.,
C/mm Hg
b.p.
C/mm Hg
31P NMR
(ppm)
Synthesis
R2OH
0
1
5
72
68.9
70.5
75
69
41
47
45
6
—
—
67
71
—
—
—
—
7
100.2/20
116/30
50/0.2
123/15
—
8
9
DEMF
TEP
Methanol
Ethanol
109/30
123/40
116/35
138/25
150/25
162/25
173/26
!79/25
1.04
1.00
0.97
1.10
1.25
1.03
1.20
1.13
DEPP
DEBP
DEPnP
DEHP
DEHPP
DEOP
n-Propanol
n-Butanol
n-Pentanol
n-Hexanol
n-Heptanol
n-Octanol
—
—
—
= [4]; = [8].
TABLE III Experimental Results in the Synthesis of Some Phosphates
Starting from Dipropylphosphite (Catalyst-Tetrabutylammonium Bromide
0.5 mmol %)
Yield
(%)
b.p.
C/mm Hg
31P NMR
(ppm)
Synthesis
R2OH
DPMP
DPEP
TPP
DPBP
DPPnP
DPHP
DPHpP
DPOP
Methanol
Ethanol
63
71
70
73.5
73
54.5
55
52
113/15
126/14
130/15
138/14
147/12
153/12
169/11
179/10
0.72
1.07
0.76
1.00
0.97
0.98
1.02
1.09
n-Propanol
n-Butanol
n-Pentanol
n-Hexanol
n-Heptanol
n-Octanol
TABLE IV Experimental Results in the Synthesis of Some Phosphates
Starting from Dibutylphosphite (Catalyst-Tetrabutylammonium Bromide
0.5 mmol %)
Yield
(%)
Yield
lit (%)
b.p. Literat.
C/mm Hg
b.p.
C/mm Hg
31P NMR
(ppm)
Synthesis
R2OH
DBMP
DBEP
DBPP
TBP
DBPnP
DBHP
DBHpP
DBOP
Methanol
Ethanol
65
72
68
71.6
78
69
62
60
—
71
—
—
—
—
—
—
—
60–1/0,1
—
180-3/25
95/10
103/15
121/20
190/30
186/15
175/10
182/10
198/10
0.65
1.00
1.09
0.97
1.03
1.10
1.09
1.12
n-Propanol
n-Butanol
n-Pentanol
n-Hexanol
n-Heptanol
n-Octanol
—
—
—
—
= [4]; = [8].

1518
G. Ilia et al.
TABLE V Preparation of Tetraethylammonium Hydrogenphosphites (2),
Mixed Phosphites (3), and Phosphates
Product
R
R1
R2
31P NMR (ppm)
Yield (%)
2a
2b
3a
3b
C2H5
n-C4H9
C2H5
C2H5
n-C4H9
C2H5
—
—
CH3
n-C4H9
C2H5
CH3
n-C4H9
C2H5
—
—
—
—
—
n-C3H7
n-C3H7
n-C3H7
—
—
75
80
61
73
72
67
76
75
4.3
6.6
6.6
0.89
1.0
1.0
3b
EMPP
BEMP
BEMP
C2H5
n-C4H9
by reaction with alkyl iodides in acetonitrile. They are the forerunners
for mixed phosphates having three different alkyl chains (Table V).
The yields were good in all syntheses. Mixed phosphites were used
for obtaining phosphates with three different alkyl radicals.
EXPERIMENTAL
General Procedure for the Synthesis
of Mixed Phosphates
To a stirred solution of 50% aqueous sodium hydroxide (60 ml), alkyl
alcohol (0.2 mmol), carbon tetrachloride (50 ml), methylene chloride
(50 ml) and a phase transfer catalyst, was added dropwise a solu-
tion of a phosphite (0.25 moles) in carbon tetrachloride (60 ml). The
temperature was kept at 15 C. Then the mixture was kept under
stirring 3 h at 15 C. The mixture is diluted with methylene chloride
(50 ml), filtered, separated, and the organic layer washed with 2%
aqueous hydrogen chloride (25 ml), and water (2 25 ml), and dried
with anhydrous sodium sulfate and the solvents distilled under reduced
pressure.
General Procedure for the Synthesis of Mixed Phosphites
A 20% aqueous solution of tetrabutylammonium hydroxide (0.2 mmol)
is added to stirred phosphite (0.2 mmol) at 5–10 C and the mixture is
kept at this temperature for 2 h. The salt is extracted with methylene
chloride, the solvent is distilled and the crude intermediate mixed with
50 ml acetonitrile and the appropriate alkyl iodide and heated for 6 h at
60 C. The solvent is distilled and the product is purified by distillation
under reduced pressure.

Synthesis of Mixed Alkylphosphites and Alkylphosphates
1519
CONCLUSIONS
Mixed phosphites were obtained with good yields. Mixed phosphates
starting from diethyl-, dipropyl-, dibutyl phosphite and mixed phos-
phites, respectively, were synthesized using a liquid-liquid system. The
best results were obtained when 50% NaOHaq was used, the reaction
temperature was 15 C, and the reaction time 3 h and the molar ra-
tio phosphite : alcohol = 1.25:1. P31-NMR spectra, performed with a
Bruker Avance DRX 400 spectrometer, showed chemical shift values
of = 0.6–1.25 ppm (ref. H3PO485%). Mixed phosphates obtained from
C1 C4 were chromatographically pure.
REFERENCES
[1] W. E. Keller, Phase Transfer Reactions (Georg Thieme Verlag, Sttutgard, 1990), Fluka
Compendium, vol. 3.
[2] G. M. Steinberg, J. Org. Chem., 15, 637 (1950).
[3] G. W. Kenner and N. R. Williams, J. Chem. Soc., 522 (1955).
[4] A. Zwierzak, Synthesis, 305 (1976).
[5] G. Ilia, S. Iliescu, G. Dehelean, A. Popa, L. Pacureanu, L. Macarie, and A. Pascariu,
Phosphorus, Sulfur, and Silicon, 177, 2049 (2002).
[6] G. Ilia, L. Kurunczi, G. Dehelean, S. Iliescu, and L. Macarie, Phosphorus, Sulfur, and
Silicon, 147, 191 (1999).
[7] C. M. Starks and C. Liotta, Phase Transfer Catalysis (Academic Press, New York,
1978).
[8] G. M. Kosolapoff and L. Maier, eds., Organic Phosphorus Compounds (Willey,
New York, 1973), vol 6, pp. 409.