Reductive cleavage of the halogen-phosphorus and sulfur-phosphorus bonds with alkali metals

Article abstract of DOI:10.1002/hc.10040

The reduction of thiophosphorus acid chlorides with alkali metals (Na, K) in liq. NH₃/THF solution, potassium anthracenide, and potassium napththalenide was investigated. It was found that these types of phosphorus compounds easily undergo reduction to 〉P-S^- anions. It was also demonstrated that 〉P-O^- and 〉P-S^- anions as well very efficiently undergo sulfurization with elementary sulfur in liquid ammonia to yield 〉P(O)S^- and 〉P(S)S^- anions, respectively.

Full text of DOI:10.1002/hc.10040

Heteroatom Chemistry
Volume 13, Number 4, 2002
Reductive Cleavage of the Halogen–
Phosphorus and Sulfur–Phosphorus Bonds
with Alkali Metals
Marek Stankiewicz, Jacek Nycz, and Janusz Rachon
Department of Organic Chemistry, Chemical Faculty, Technical University of Gdan´sk,
80-952 Gdan´sk, Poland
Received 10 July 2001; revised 16 October 2001
potassium naphthalenide in THF with the cleavage
ABSTRACT: The reduction of thiophosphorus acid
of the P(III) oxygen bond.
chlorides with alkali metals (Na, K) in liq. NH3/THF
The reactions of H¨P(S)Cl compounds (thiophos-
solution, potassium anthracenide, and potassium
phoric acid chlorides, thiophosphonic acid chlori-
naphthalenide was investigated. It was found that
des, thiophosphinic acid chlorides) with alkali met-
these types of phosphorus compounds easily undergo
als are complex, and the data presented in the
reduction to H¨P S anions. It was also demonstrated
literature are often incompatible. For instance,
that H¨P O and H¨P S anions as well very efficiently
Inamoto and co-workers [2] discovered that, in the
undergo sulfurization with elementary sulfur in liquid
attempted preparation of Ph2P S from diphenyl-
ammonia to yield ¨HP(O)S and H¨P(S)S anions, res-
phosphinothioyl chloride and metal (Li or Na),
C
pectively.
2002 Wiley Periodicals, Inc. Heteroatom
desulfurization took place by use of excess amounts
of metal or by heating for a long time. After treatment
of diphenylphosphinothioyl chloride with magne-
sium in THF at 150 C, on the other hand, there
was found in the reaction mixture a small amount
of diphenylphosphinodithioic acid. On the basis of
this observation, Inamoto and co-workers claimed
that, for the desulfurization, a disproportionation
process of Ph2P S is responsible [2]. Moreover,
Inamoto identified in the reaction mixture, after
treatment of diphenylphosphinothioyl chloride with
Li in THF at 150 C, diphenylphosphane oxide,
tetramethylene bis(diphenylphosphinodithioate),
and S,S-tetramethylene diphenylphosphinothioate
diphenylphosphinodithioate [3].
On the other hand, Horner [4] was able to
demonstrate that a phosphane sulfide can be reduced
easily with sodium to the corresponding phosphane.
Also, Issleib [5] reported that treatment of diphos-
phane disulfide with sodium in dioxan furnished the
corresponding diphosphane or sodium phosphinide,
depending on the structures of the starting mate-
rials and the conditions of the reaction. Reductive
Chem 13:330–339, 2002; Published online in Wiley In-
terscience (www.interscience.wiley.com). DOI 10.1002/hc.
10040
INTRODUCTION
The reductive cleavage of the H¨P(Y) Cl [Y: O, S]
bond is an interesting subject from the synthetic
and mechanistic point of view. In our previous pa-
per [1], we reported that phosphorus acid chlo-
rides, as well as hypophosphates and pyrophos-
phates, easily undergo reduction to H¨P O and
H¨P(O) O anions, respectively, with alkali metals in
liq. NH3/THF solution and potassium naphthalenide
in THF. Additionally, we were able to demonstrate
that a mixed P(III) P(V) anhydride is reduced by
Correspondence to: Janusz Rachon; e-mail: rachon@altis.chem.
pg.gda.pl.
Contract grant sponsor: Chemical Faculty Technical University
of Gdan´sk.
c
2002 Wiley Periodicals, Inc.
330

Reductive Cleavage of the Halogen–Phosphorus and Sulfur–Phosphorus Bonds with Alkali Metals 331
desulphurization of organosulfur compounds with
sodium in liquid ammonia has been explored by
Verkade [6]. He observed greater than 95% sulfur
removal when dialkyl mono- or polysulfides were
treated with Na in liquid ammonia. This procedure
is only moderately successful for desulfurizing poly-
cyclic aromatic sulfur compounds, but is quite effi-
cient for dialkyl mono- or polysulfides, dialkyl sul-
fones, and trialkylphosphane sulfides. In contrast,
triphenylphosphane sulphide yields diphenylphos-
phane (99%) in the reaction with sodium in liquid
ammonia. The results of the last experiment strongly
suggest that, in the case of the aromatic phosphane
sulfide, desulphurization as well as the cleavage of
the P C bond occur. It should be mentioned at this
point that liquid ammonia solutions of Li as well as
Na are used for the reductive cleavage of the C P
bond in triphenylphosphanes [7]. On the other hand,
it was reported that, in the reaction of sodium naph-
thalenide with diarylphosphinothioyl chlorides, the
corresponding tetraaryldiphosphane disulfides are
produced [8].
To the best of our knowledge, the reductive cleav-
age of the P Cl bond in compounds of the H¨P(S)Cl
type, particularly under homogenous conditions, has
not been the subject of systematic studies. In connec-
tion with our interest in the reactivity of the acids
of trivalent phosphorus, we initiated studies of the
reaction between H¨P(S)Cl type compounds and elec-
tron donors (alkali metals in liquid ammonia, naph-
thalenide radical anion). The results of these studies
are presented herein.
SCHEME 1
Additionally, the action of sodium in liquid am-
monia can results in desulfurization and also a Birch
reduction or cleavage of the P C bond if an aromatic
system is present in the starting material.
First, we carried out reduction experiments with
potassium naphthalenide in THF. In the standard
procedure the H¨P(S)Cl electrophiles are added to
the tetrahydrofuran solution of potassium naph-
thalenide at 78 C. The dark-green color of the
solution disappears in about half an hour after the
addition of the last drop of the phosphorus elec-
trophile. The reaction was quenched by addition of
aqueous KHSO4 solution at 78 C, and, after re-
moval of the solvents, the products were isolated by
radial chromatography. The results of this set of ex-
periments are presented in Scheme 2 and collected
in Table 1 (runs 1–6).
As one can see from the data collected in Table 1,
all of the H¨P(S)Cl electrophiles (1) were reduced with
two equivalents of potassium naphthalenide to the
corresponding H¨P S anion, which, after protona-
tion, yielded a secondary phosphane sulfide or a di-
alkyl thiophosphate (2), respectively. We did not find
in the reaction mixture compounds with a P P bond
(hypothiophosphates or diphosphane disulphide).
RESULTS AND DISCUSSION
As the thiophosphorus electrophilic reagents for
our study, we chose the following compounds:
2-chloro-5,5-dimethyl-[1.3.2]dioxaphosphinane-
2-sulphide, diethyl chlorothiophosphate, methyl
phenylchlorothiophosphonate, diphenylphosphino-
thioyl chloride, and t-butylphenylphosphinothioyl
chloride. These types of thiophosphorus electro-
philes were treated with electron donors, namely,
potassium naphthalenide in THF and sodium in
liquid ammonia/THF mixture.
From the theoretical point of view, the H¨P(S)Cl
electrophile can accept an electron to form a rad-
ical anion, which should collapse to a thiophos-
phonyl radical and chloride anion. According to
the substituents on the phosphorus and the reac-
tion conditions, the thiophosphonyl radical may
(a) dimerize; (b) subsequently accept an electron, be-
ing reduced to H¨P S anion; or (c) undergo further
fragmentation (Scheme 1).
SCHEME 2

332 Stankiewicz, Nycz, and Rachon
TABLE 1 Reduction of the R1R2P(S)Cl Type Electrophiles with Single Electron Donors (ED): Potassium Naphthalenide (NK)
in THF or with Alkali Metals in Liquid Ammonia
Isolated
Yield (%)
Run
R1
R2
ED
ED/ H¨P(S)Cl
1
2
1
2
3
4
5
6
7
8
9
Ph
Ph
Ph
t-Bu
t-Bu
t-Bu
Ph
t-Bu
NK
NK
NK
NK
NK
NK
K
Na
K
K
1
2
2
2
2
2
2
2
2
2
2
53
37
68
71
81
62
82
70
78
80
67
72
EtO
EtO
OCH2C(CH3)2CH2O
OCH2C(CH3)2CH2O
Ph
Ph
t-Bu
EtO
t-Bu
t-Bu
t-Bu
EtO
10
11
OCH2C(CH3)2CH2O
OCH2C(CH3)2CH2O
K
The treatment of t-butylphenylthiophosphinyl chlo-
ride with one equivalent of potassium naphthalenide
produced a low yield of the phosphane sulfide (2)
(Scheme 2; R1 = t-Bu, R2 = Ph). From this reaction
mixture, we isolated t-butylphenylphosphane sulfide
(37%) and starting material (53%). The starting ma-
terial recovered from this reaction mixture strongly
suggests that the thiophosphonyl radical undergoes
a much faster one-electron reduction process to
produce the H¨P S anion than does the H¨P(S)Cl
electrophile.
We also performed reduction experiments with
alkali metal/NH3/THF solution at 78 C. One equiv-
alent of the H¨P(S)Cl type compound was added to the
blue solution of two equivalents of alkali metal (Na,
K) dissolved in the mixture of liquid NH3: THF = 1:1.
The blue color of the solution disappeared in a few
minutes after the addition of the last drop of phos-
phorus electrophile. The reaction was quenched by
solid NH4Cl, and, after removal of the solvents, the
products were isolated by radial chromatography (or
by distillation). The results of this set of experiments
are presented in Table 1 (runs 7–11).
Examination of the data collected in Table 1
(runs 1–6 and runs 7–11) shows that reduction of
the H¨P(S)Cl electrophiles by alkali metal solution in
liquid ammonia is superior to the use of potassium
naphthalenide in THF. Additionally, the high yields
of the t-butylphenylphosphane sulfide (Table 1, runs
7 and 8) show that the reduction of the P Cl bond
is a much faster process than the Birch reduc-
tion or the P C bond cleavage observed under the
same reaction conditions when triphenylphosphane
is subjected to reduction. In the experiments where
t-butylphenylphosphinothioyl chloride was the sub-
ject for the reduction by the action of a solution of
alkali metal (sodium or potassium) in liquid ammo-
nia/THF mixture, we noticed the characteristic odor
of phosphane during the workup of the reaction mix-
ture (Table 1, runs 7 and 8). This observation sug-
gested that, during the reduction process, desulfur-
ization can also take place.
We decided to verify this hypothesis by experi-
ments in which the reduction of the H¨P(S)Cl elec-
trophiles was carried out with four equivalents of a
reducing agent (alkali metals/liquid ammonia, potas-
sium naphthalenide, or potassium anthracenide).
One equivalent of the ¨HP(S)Cl type compound was
added to the solution of four equivalents of a reduc-
ing agent, and, after 30 min, the reaction mixture
was acidified and the products were isolated by ra-
dial chromatography (or by distillation). The results
of this set of experiments are presented in Scheme 3
and collected in Table 2.
From the reaction mixture composed of one
equivalent of phosphinothioyl chloride and four
equivalents of potassium in liquid ammonia (Table 2,
runs 12 and 13), after protonation, we isolated phos-
phane 3, namely, t-butylphenylphosphane (74%) and
diphenylphosphane (62%), respectively. By way of
contrast, the treatment of 2-chloro-5,5-dimethyl-
[1.3.2]dioxaphosphinane-2-sulfide with four equiv-
alents of potassium in liquid ammonia (Table 2,
run 14) resulted in the formation of 5,5-dimethyl-
[1.3.2]dioxaphosphinane-2-sulfide.
On the other hand, from the reaction mixture
composed of one equivalent of t-butylphenylphos-
phinothioyl chloride and four equivalents of potas-
sium naphthalenide or potassium anthracenide
SCHEME 3

Reductive Cleavage of the Halogen–Phosphorus and Sulfur–Phosphorus Bonds with Alkali Metals 333
TABLE 2 Reduction of the R1R2P(S)Cl Type Compounds with Four Equivalents of Potassium/Liquid Ammonia, Potassium
Naphthalenide (NK), or Potassium Anthracenide (AK)
Isolated
Yield (%)
Run
R1
R2
Reducer
2
3
12
13
14
15
16
Ph
Ph
t-Bu
Ph
K/NH3
K/NH3
K/NH3
NK
74
62
OCH2C(CH3)2CH2O
OCH2C(CH3)2CH2O
77
71
72
Ph
Ph
t-Bu
t-Bu
AK
(Table 2, runs 15 and 16) we isolated t-butyl-
phenylphosphane sulfide (2, R1 = Ph, R2 = t-Bu). The
results of this set of experiments show that, for the
desulfurization process, the aromatic system as a
moiety of the electrophile is necessary and this pro-
cess requires a much higher reduction potential than
that of dehalogenation. Also, the results of experi-
ments strongly suggested that, in the first step, the
H¨P(S)Cl electrophile is reduced to the H¨P S anion,
which, if the aromatic system is present in the struc-
ture of the anion, can be further reduced to H¨P and
S2 anions. Probably, the first process of reduction of
the H¨P(S)Cl to the H¨P S anion is faster than that of
desulfurization to the H¨P anion. Furthermore, the
second process, desulfurization, requires the pres-
ence of a group which contains ␲ electrons with near-
est connection to the phosphorus atom. Therefore, a
phosphorus electrophile which contains ␲ electrons
(e.g., a phenyl group) is easily reduced to an H¨P
anion.
experiment, we were able to demonstrate that the
treatment of t-butylphenylthiophosphinide anion 10
(
= 46.92 ppm; generated in the reaction of one
31P
equivalent of t-butylphenylphosphane sulfide 9 in
THF with one equivalent of n-BuLi) with two equiv-
alents of potassium in liquid ammonia produced
only the t-butylphenylphosphinide anion. After pro-
tonation of this reaction mixture we isolated t-
butylphenylphosphane 11 [
212.67 Hz] (Scheme 5) in 65% yield.
=
4.84 ppm, JP
=
31P
H
By way of contrast, after the treatment of
5,5-dimethyl-[1.3.2]dioxaphosphinane-2-sulfide an-
ion 13 (
= 46.92 ppm, generated from n-BuLi
31P
We have proposed a mechanism for the reduc-
tion and desulfurization of the H¨P(S)Cl electrophile
(Scheme 4). In the first step of the reduction pro-
cess of the H¨P(S)Cl electrophile 4, the H¨P S anion
5 is generated (1). Transfer of an electron from a re-
ducing agent (solution of alkali metal in liquid am-
monia) into the LUMO of the acceptor (into the ␲
orbital of the H¨P S anion 5) leads to a radical di-
anion (2). Then the electron is transferred from the
␲* orbital to the ␴* orbital of the P S bond to pro-
duce a frangible species (or transition state) which
collapses with P S bond cleavage to form the phos-
phinyl radical 6 and sulfur anion (pathway “a”) or to
form the H¨P anion 7 and sulfur radical anion (path-
way “b”). Next, the phosphinyl radical is reduced to
the H¨P anion, or the sulfur radical anion is reduced
to the sulfur anion S2 . Therefore, pathway “a” or
“b” provides the same products: the H¨P anion and
sulfur anion S2 .
At this point, it was very important to check
if the H¨P S anion is able to accept electrons and
can be reduced into a H¨P anion. In a separate
SCHEME 4

334 Stankiewicz, Nycz, and Rachon
SCHEME 7
Lawesson reagent. Another method of synthesis of
monothio- and dithiophosphorus acids is based on
the reaction of the H¨P(O)H acids or secondary phos-
phanes with elemental sulfur in the presence of base.
In most cases, this reaction is performed at a temper-
ature between 90 and 110 C [9].
In the course of our study, we developed the
method of generation of H¨P O as well as ¨HP S
anions in liquid ammonia. On the other hand, it is
well known that elemental sulfur is soluble in liq-
uid ammonia. We decided to check if these types of
anions will react with elemental sulfur in liquid am-
monia. In a series of experiments, we treated freshly
generated ammonia solutions of the H¨P O as well
as H¨P S anions (obtained from acid chlorides in the
reduction process using potassium in liquid ammo-
nia) with elemental sulfur (Scheme 7). The results of
this set of experiments are collected in Table 3.
As one can see from the data collected in Table 3,
the H¨P O as well as H¨P S anions very efficiently
undergo sulfurization with elemental sulfur in liq-
uid ammonia to yield monothio- as well as dithio-
phosphorus anions, respectively. The one-pot proce-
dure is very simple: the addition of elemental sulfur
into the solution of the H¨P O as well as ¨HP S an-
ions in liquid ammonia (freshly obtained from acid
chlorides in the reduction process using potassium
in liquid ammonia) furnished, in 30 min at 33 C,
the desired ammonium salts of the monothio- or
dithiophosphorus acids, respectively. Moreover, we
were also able to demonstrate that ammonium salts
obtained according to this procedure can be used
without further purification in the alkylation pro-
cesses. The acid chlorides were reduced with potas-
sium in liquid ammonia/THF solution, and then the
reaction mixture was treated with elemental sulfur
(sulfur is readily soluble in the solvent system liq.
NH3/THF above 40 C). After evaporation of the
liquid ammonia, the residue was diluted with THF,
methyl iodide was added, and the methyl esters were
isolated. The results of this set of experiments are
presented in Scheme 8 and collected in Table 4. As
one can see from the data collected in Table 4, our
method appears to be a promising one; starting from
the acid chlorides in simple procedures we obtained
methyl esters 15 in very high yields.
SCHEME 5
and 5,5-dimethyl-[1.3.2]dioxaphosphinane-2-sulfide
12) with 2 equivalents of sodium in liquid ammo-
nia, we isolated (after protonation) 5,5-dimethyl-
[1.3.2]dioxaphosphinane-2-sulfide 12 (Scheme 6).
Sulfurization of the H¨P O and ¨HP S Anions
with Sulfur in Liquid Ammonia
Thioacids of various types of phosphorus acids are
extremely important materials of commerce. Thio
derivatives are used as pesticides, flotation agents,
oil and gasoline additives, and rubber vulcanization
accelerators. More recently, they have become im-
portant in studies on the chemical modification of
natural phosphates, especially nucleotides.
Thioacids are formed when the chlorides are re-
acted with H2S or NaSH. The P O group in esters,
as in phosphane oxides, can be replaced with sul-
fur by reaction with phosphorus pentasulfide or the
SCHEME 6

Reductive Cleavage of the Halogen–Phosphorus and Sulfur–Phosphorus Bonds with Alkali Metals 335
in 25 cm3 of THF at 78 C, 10 mmol (run 1)
or 5 mmol (runs 2–6) of each phosphorus ele-
ctrophile (t-butylphenylphosphinothioyl chloride,
diphenylphosphinothioyl chloride, diethyl chloro-
thiophosphate, 2-chloro-5,5-dimethyl-[1.3.2]-dioxa-
phosphinane-2-sulphide) in 5 cm3 of THF was
added. After disappearance of the dark-green color
of the reaction mixture, benzene (200 cm3) and an
aqueous KHSO4 solution (5 cm3) were added. The
aqueous layer was extracted with benzene, and the
combined organic layers were dried over MgSO4.
The solvent was removed in vacuum, and the
products were separated by radial chromatography.
Naphthalene was eluted with hexane, the reduction
products with CHCl3 (Table 1, runs 1–6).
SCHEME 8
EXPERIMENTAL
Tetrahydrofuran, benzene, hexane, and toluene were
dried with sodium–potassium alloy. Melting points
are uncorrected. 31P NMR and 1H NMR spectra were
recorded with a Varian FT NMR spectrometer at
200 or 500 MHz. Potassium naphthalenide (an-
thracenide) was prepared from potassium and naph-
thalene (anthracene) in dry THF under argon and
with protection from oxygen before its use [10].
Some of the compounds which have been
used were produced as follows: t-butylphenylphos-
phinothioyl chloride was obtained according to the
known procedure [11], b.p. 100–104 C/0.04 mm
Run 1: naphthalene 1.314 g (10 mmol, 93%); t-
butylphenylphosphinothioyl chloride (eluted with
chloroform) 1.234 g (5.3 mmol, 53%), 1H NMR
3
(CDCl3) = 1.13 (d, JP = 20 Hz, t-Bu, 9H), 7.03–
H
7.83 (m, aromat, 5H). 31P NMR (CDCl3) = 115.00
ppm; t-butylphenylphosphane sulfide (eluted with
chloroform) 0.734 g (3.7 mmol, 37%), 1H NMR
Hg, m.p. = 71–73 C, 1H NMR (CDCl3)
= 1.15
(d, 3 JP = 19 Hz, t-Bu, 9H), 7.10–7.77 (m, aro-
(CDCl3) = 1.10 (d, 3 JP = 16 Hz, t-Bu, 9H), 6.58
H
H
mat, 5H), 31P NMR (CDCl3) = 115.27 ppm, di-t-
(d, JP = 442 Hz, PH, 1H), 6.80–7.56 (m, aromat,
H
butylphosphinothioyl chloride was obtained accord-
5H), 31P NMR (CDCl3) = 53.9 ppm.
ing to the known procedure [12], eluted with chloro-
Run 2: naphthalene 1.293 g (10 mmol, 92%); t-butyl-
phenylphosphane sulfide 0.671 g (3.4 mmol, 68%).
Run 3: naphthalene 1.311 g (10.2 mmol, 93%);
diphenylphosphane sulfide 0.769 g (3.1 mmol, 71%),
1H NMR (CDCl3) = 7.48–7.82 (m, aromat, 10 H),
1
form, H NMR (CDCl3) = 1.47 (d, 3 JP = 18 Hz,
H
2 t-Bu, 18H), 31P NMR (CDCl3) = 146.16 ppm,
diphenylphosphinothioyl chloride was obtained ac-
cording to the known procedure [13], b.p. 156 C/0.01
mm Hg, 31P NMR (CDCl3) = 81.4 ppm, 2-chloro-
2-thiono-5,5-dimethyl-[1.3.2]-dioksafosfinan was
8.05 (d, JP = 467 Hz, PH, 1H), 31P NMR (CDCl3)
H
= 23.4 ppm.
obtained according to the known procedure [14], 31
P
Run 4: naphthalene 1.308 g (10.2 mmol, 93%); di-
NMR (CDCl3) = 59.42 ppm.
t-butylphosphane sulfide 0.722 g (4.0 mmol, 81%),
3
1H NMR (CDCl3) = 1.26 (d, JP = 16 Hz, 2 t-Bu,
H
18H), 6.58 (d, JP = 418 Hz, PH, 1H), 31P NMR
H
Reduction of the R1 R2 P(S)Cl Type
Phosphorus Compounds
Reduction of the R1 R2 P(S)Cl Type Phospho-
rus Compounds with Potassium Naphthalenide in
THF. General procedure for runs 1–6: Into the
freshly prepared potassium naphthalenide (from
1.410 g of naphthalene and 0.390 g of potassium)
(CDCl3) = 76.3 ppm.
Run 5: naphthalene 1.176 g (9.2 mmol, 84%); O,O0-
1
diethyl thiophosphate 0.479 g (3.1 mmol, 62%), H
NMR (CDCl3) = 1.18 (t, 3 JH = 6 Hz, CH3, 6H),
3.87 (dq, 3 JH = 10 Hz, 3 JP =H3 Hz, CH2, 4H), 7.57
H
H
(d, JP = 648 Hz, PH, 1H), 31P NMR (CDCl3)
=
H
70.1 ppm.
TABLE 3 Synthesis of Monothio- and Dithiophosphorus Acids
Run
R1
R2
Y
Yield of 14 (%)
17
18
19
20
21
22
23
EtO
i -PrO
OCH2C(CH3)2CH2O
EtO
i -PrO
OCH2C(CH3)2CH2O
O
O
O
O
S
S
S
62
82
78
95
66
81
85
Ph
t-Bu
EtO
OCH2C(CH3)2CH2O
Ph
EtO
OCH2C(CH3)2CH2O
t-Bu

336 Stankiewicz, Nycz, and Rachon
TABLE 4 Synthesis of Monothio- and Dithiophosphorus Acid Methyl Esters
Run
R1
R2
Y
Yield of 15 (%)
24
25
26
27
Ph
Ph
EtO
t-Bu
t-Bu
EtO
O
O
S
S
82
85
85
94
OCH2C(CH3)2CH2O
OCH2C(CH3)2CH2O
Run 6: naphthalene 1.176 g (9.2 mmol, 84%); 5,5-
12–14: Alkali metal (20 mmol) was added to the
mixture composed of liquid ammonia (25 cm3)
and THF (25 cm3). The reaction mixture was
stirred up to the point of complete dissolution
of the alkali metal, then cooled to 78 C, and
5 mmol of each chlorothiophosphorus compound
(t-butylphenylphosphinothioyl chloride, diphenyl-
phosphinothioyl chloride, 2-chloro-5,5-dimethyl-
[1.3.2]dioxaphosphinane-2-sulphide) in 5 cm3 of
THF was added. The reaction mixture was stirred
at 78 C for 30 min. Then, 0.45 g (8.4 mmol) of
NH4Cl was added and the ammonia was evaporated
at 10 mm Hg. The products were distilled (Table 2;
runs 12 and 13) or poured into the mixture of
toluene and aqueous KHSO4 solution. The water
layer was extracted with toluene and the combined
organic phase was dried over MgSO4. The solvent
was removed in vacuum, and the products were
separated by radial chromatography (Table 2; run
14)
dimethyl-[1.3.2]dioxaphosphinane-2-sulfide 0.681 g
1
(1 mmol, 82%), H NMR (CDCl3) = 0.77 (s, CH3,
3H), 1.17 (s, CH3, 3H), 3.50–10 (m, CH2, 4H), 7.58
(d, JP = 601 Hz, PH, 1H), 31P NMR (CDCl3)
=
H
67.2 ppm.
Reduction of the R1 R2 P(S)Cl Type Phosphorus
Compounds with Alkali Metals in Liquid Ammonia
in the Molar Ratio 1:2. General procedure for runs
7–10: Alkali metal (10 mmol) was added to the
mixture composed of liquid ammonia (25 cm3)
and THF (25 cm3). The reaction mixture was
stirred until complete dissolution of the alkali metal
was realized; it was then cooled to 78 C, and
5 mmol of each chlorothiophosphorus compound
(t-butylphenylphosphinothioyl chloride, diethyl
chlorothiophosphate, 2-chloro-5,5-dimethyl-[1.3.2]-
dioxaphosphinane-2-sulphide) in 5 cm3 of THF was
added. The reaction mixture was stirred at 78 C.
The blue color of the solution disappeared in a few
minutes after the addition of the last drop of phos-
phorus electrophile. Then 1.5 g of NH4Cl was added
and the ammonia was evaporated at 10 mm Hg.
The residue was poured into a mixture of toluene
and aqueous KHSO4 solution. The water layer was
extracted with toluene and the combined organic
phase was dried over MgSO4. The solvent was re-
moved in vacuum and the products were separated
by radial chromatography. The reduction prod-
ucts were eluted with CHCl3 (Table 1, runs 7–11).
Run 12: t-butylphenylphosphane (Kugelrohr, 60–
61 C/0.9 mm Hg) 0.615 g (3.7 mmol, 74%), 1H NMR
3
(CDCl3) = 1.00 ( d, JP = 12 Hz, t-Bu, 9H), 5.60
H
(d, JP = 209 Hz, PH, 1H), 6.60–7.43 (m, aromat,
H
5H), 31P NMR (CDCl3)
=
4.84 ppm.
Run 13: diphenylphosphane (Kugelrohr, 60–61 C/0.9
mm Hg) 0.577 g (3.10 mmol, 62%), 1H NMR (CDCl3)
= 4.93 (d, JP = 208 Hz, PH, 1H), 6.57–7.33 (m,
H
aromat, 10H), 31P NMR (CDCl3)
=
39.9 ppm.
Run 14: 5,5-dimethyl-[1.3.2]dioxaphosphinane-2-
sulfide (eluted with chloroform) 0.640 g (3.85 mmol,
77%), 1H NMR (CDCl3) = 0.77 (s, CH3, 3H), 1.17 (s,
Run 7: t-butylphenylphosphane sulfide 0.694 g (3.5
mmol, 70%).
Run 8: t-butylphenylphosphane sulfide 0.773 g (3.9
mmol, 78%).
CH3, 3H), 3.50–4.10 (m, CH2, 4H), 7.58 (d, JP = 601
H
Hz, PH, 1H), 31P NMR (CDCl3) = 67.2 ppm.
Run 9: di-t-butylphosphane sulfide 0.714 g (4.0
mmol, 80%).
Reduction of the R1 R2 P(S)Cl Type Phospho-
rus Compounds with Potassium Naphthalenide or
Potassium Anthracenide in the Molar Ratio 1:4.
General procedure for runs 15 and 16: Into the
freshly prepared potassium naphthalenide (from
1.410 g of naphthalene and 0.390 g of potassium)
or anthracenide (from 1.960 g of anthracene and
0.390 g of potassium) in 50 cm3 of THF at 78 C,
2.5 mmol of the t-butylphenylphosphinothioyl
Run 10: O,O0-diethyl thiophosphate 0.515 g (3.3
mmol, 67%).
Run 11: 5,5-dimethyl-[1.3.2]dioxaphosphinane-2-
sulfide 0.598 g (3.6 mmol, 72%).
Reduction of the R1 R2 P(S)Cl Type Phosphorus
Compounds with Alkali Metals in Liquid Ammonia
in the Molar Ratio 1:4. General procedure for runs

Reductive Cleavage of the Halogen–Phosphorus and Sulfur–Phosphorus Bonds with Alkali Metals 337
chloride in 5 cm3 of THF was added. The reaction
mixture was stirred at 78 C for an hour, and then a
mixture composed of 200 cm3 of benzene and 10 cm3
aqueous KHSO4 solution was added. The aqueous
layer was extracted with benzene and the combined
organic layers were dried over MgSO4. The solvent
was removed in vacuum and the products were
separated by radial chromatography (Table 2, runs
15 and 16).
NH4Cl was added. Ammonia was removed in vac-
uum and a sample of the reaction mixture was
taken off, and after addition of aqueous KHSO4
solution and C6D6, the 31P NMR spectrum was
recorded. The 31P NMR spectrum of the crude
reaction mixture showed one resonance line at-
tributable to 5,5-dimethyl-[1.3.2]dioxaphosphinane-
2-sulfide ( = 66.64 ppm, JP = 601.2 Hz). The
31
H
product was isolated by radial chromatography; 5,5-
dimethyl-[1.3.2]dioxaphosphinane-2-sulfide (eluted
with chloroform), 0.614 g (3.70 mmol, 74%).
Run 15: t-butylphenylphosphane sulfide (eluted with
chloroform) 0.352 g (1.8 mmol, 71%), 1H NMR
(CDCl3) = 1.10 (d, 3 JP = 16 Hz, t-Bu, 9H), 6.58
H
Sulfurization of the H¨P O and ¨HP S Anions
with Sulfur in Liquid Ammonia
(d, JP = 442 Hz, PH, 1H), 6.80–7.56 (m, aromat,
H
5H), 31P NMR (CDCl3) = 53.9 ppm.
The Synthesis of Mono- and Dithiophosphorus
Acids. General procedure for runs 17–23: Potas-
sium (0.39 g, 10 mmol) was added to the mixture
composed of liquid ammonia (25 cm3) and THF
(25 cm3). The reaction mixture was stirred up
to the complete dissolution of alkali metal, then
cooled to 78 C, and 5 mmol of each chlorophos-
phorus compound (diethyl chlorophosphate, di-
isopropyl chlorophosphate, 2-chloro-5,5-dimethyl-
[1.3.2]dioxaphosphinane, t-butylphenylphosphinoyl
chloride, O,O0-diethyl chlorothiophosphate, 2-
chloro-5,5-dimethyl-[1.3.2]-dioxaphosphinane-2-
sulphide, t-butylphenylphosphinothioyl chloride)
in 5 cm3 of THF was added. The reaction mixture
was stirred at 78 C. The blue color of the solution
disappeared in a few minutes after the addition of
the last drop of the phosphorus electrophile. Then,
0.192 g of sulfur was added, the cooling bath was
removed, and the reaction mixture was stirred at
33 C for 30 min. The ammonia was evaporated at
10 mm Hg. The residue was poured into a mixture
of toluene and aqueous K2CO3 solution. The water
layer was acidified with hydrochloric acid. Then,
water was evaporated at 10 mm Hg, and the residue
was extracted with 200 cm3 of CH2Cl2. The organic
phase was dried over MgSO4. The solvent was
removed under a vacuum and the products were
separated (Table 3, runs 17–23).
Run 16: t-butylphenylphosphane sulfide (eluted with
chloroform) 0.357 g (1.8 mmol, 72%).
Reduction of the Lithium t-Butylphenylthio-
phosphane Sulphide with Potassium in Liquid
Ammonia in the Molar Ratio 1:2
Into the solution of 5 mmol of t-butylphenylphos-
phane sulphide in 5 cm3 of THF at 78 C, 2.5 cm3 of
a 2 M solution of BuLi in cyclohexane (5 mmol) was
added. After 30 min, a sample of the reaction mix-
ture was removed, C6D6 was added, and the 31P NMR
spectrum was recorded. The 31P NMR spectrum of
the reaction mixture showed one resonance line
attributable to lithium t-butylphenylthiophosphane
(
= 46.92 ppm). Next, the solution of the lithium
31P
t-butylphenylthiophosphane sulphide in THF was
dropped into a solution of the potassium in liq-
uid ammonia (0.390 g of potassium in 50 cm3 of
ammonia–THF mixture) at 78 C. The reaction mix-
ture was stirred for 30 min, and then 0.45 g of NH4Cl
was added. Ammonia was removed in vacuum and
the residue was distilled; t-butylphenylphosphane
(Kugelrohr, 60–61 C/0.9 mm Hg) 0.515 g (3.1 mmol,
62%).
Attempted Reduction of the Lithium 5,5-
Dimethyl-[1.3.2]dioxaphosphinane-2-sulfide
with Potassium in Liquid Ammonia in the
Molar Ratio 1:2
Run 17: thiophosphoric acid O,O0-diethyl ester
1
0.527 g (3.1 mmol, 62%), H NMR (CDCl3) = 1.23
3
Into the solution of 5 mmol of 5,5-dimethyl-
[1.3.2]dioxaphosphinane-2-sulfide in 5 cm3 of THF
at 78 C, 2.5 cm3 of a 2 M solution of BuLi in cy-
clohexane (5 mmol) was added. Next, the solution
of lithium 5,5-dimethyl-[1.3.2]dioxaphosphinane-2-
thiolate in THF was dropped into the solution
of potassium in liquid ammonia (0.390 g of
potassium in 50 cm3 of ammonia–THF mixture)
at 78 C. After 30 min, 0.45 g (8.4 mmol) of
(t, JH = 7 Hz, CH3, 6H), 3.45–4.28 (m, CH2, 4H),
H
8.70 (s, OH, 1H), 31P NMR (CDCl3) = 64.21 ppm.
Run 18: thiophosphoric acid O,O0-diisopropyl ester
1
0.812 g (4.1 mmol, 82%), H NMR (CDCl3) = 1.27
(d, 3 JH = 10 Hz, CH3, 12H), 4.20–4.87 (m, CH, 2H),
H
8.70 (s, OH, 1H), 31P NMR (CDCl3) = 58.50 ppm.
Run 19: 2-hydroxy-5,5-dimethyl-2-thio-[1.3.2]-di-
1
oxaphosphinane 0.710 g (3.9 mmol, 78%), H NMR
(CDCl3) = 1.00 (s, CH3, 3H), 1.12 (s, CH3, 3H),

338 Stankiewicz, Nycz, and Rachon
3
3.95 (s, CH2, 4H), 4.60 (s, SH, 1H), 31P NMR (CDCl3)
= 57.93 ppm.
NMR = 1.10 (d, JP = 17 Hz, CH3, 9H), 2.03 (d,
H
3 JP = 12 Hz, CH3, 3H), 6.80–7.80 (m, aromat, 5H),
H
Run 20: t-butylphenylphosphinothioic acid 1.017 g
(4.8 mmol, 71%), m.p. = 124–126 C, 1H NMR
31P NMR (CDCl3) = 94.83 ppm.
Run 26: S-methyl-O, O0 -diethyldithiophosphate
(CDCl3) = 1.13 (d, 3 JP = 17 Hz, CH3, 9H), 3.50
(eluted with CHCl3) 0.807 g (4.2 mmol, 85%), H
1
H
(s, SH, 1H), 6.60–7.51 (m, aromat, 5H), 31P NMR
NMR = 1.31 (t, 3 JH = 7 Hz, CH3, 6H), 2.25 (d,
H
(CDCl3) = 94.85 ppm.
3 JP = 16 Hz, CH3, 3H), 4.23 (dq, 3 JH = 7 Hz,
H
H
Run 21: dithiophosphoric acid O,O0-diethyl ester
3 JP = 11 Hz, CH2, 4H), 6.83–7.93 (m, aromat, 5H),
H
1
0.615 g (3.3 mmol, 66%), H NMR (CDCl3) = 1.24
31P NMR (CDCl3) = 93.25 ppm.
3
(t, JH = 7 Hz, CH3, 6H), 3.53–4.18 (m, CH2, 4H),
Run 27: 5,5-dimethyl-2-(methylthio)-[1.3.2]-dioxa-
phosphorinane-2-sulfide (eluted with CHCl3) 0.996 g
H
3.28 (s, SH, 1H), 31P NMR (CDCl3) = 83.91 ppm.
Run 22: 2-thiolo-2-thiono-5,5-dimethyl-[1.2.3]-di-
(4.7 mmol, 94%), 1H NMR (CDCl3) = 0.93 (s,
1
3
oxaphosphinane 0.802 g (4.0 mmol, 81%), H NMR
CH3, 3H), 1.12 (s, CH3, 3H), 2.34 (d, JP = 17 Hz,
H
(CDCl3) = 1.03 (s, CH3, 6H), 3.82 (d, 2 JH = 14
CH3, 3H) 3.94 (m, CH2, 4H), 31P NMR (CDCl3)
=
H
Hz, CH2, 4H), 3.58 (s, SH, 1H), 31P NMR (CDCl3)
86.42 ppm.
= 69.04 ppm.
Run 23: t-butylphenylphosphinodithioic acid 0.978 g
1
(4.2 mmol, 85%), m.p. = 71–72 C, H NMR (CDCl3)
CONCLUSION
= 1.13 (d, 3 JP = 18 Hz, CH3, 9H), 2.93 (s, SH,
H
1H), 6.80–7.80 (m, aromat, 5H), 31P NMR (CDCl3)
It was found that the acid chlorides of the type
H¨P(S)Cl undergo reduction with sodium and potas-
sium in liquid ammonia to provide the correspond-
ing H¨P S anions. Moreover, the reduction process is
much faster than ammonolysis. If, in the acid chlo-
ride, an aromatic moiety is connected to the phos-
phorus atom, reduction and desulfurization pro-
cesses occur under the action of potassium in liquid
ammonia. Radical anions of aromatic hydrocarbons
can also reduce H¨P(S)Cl chlorides to H¨P S anions,
but, in contrast to potassium in liquid ammonia,
desulfurization does not occur, and this was rational-
ized on the basis of redox potentials. We were able
to demonstrate that H¨P O as well as ¨HP S anions
obtained in such a procedure can undergo sulfur-
ization with elemental sulfur in liquid ammonia to
provide H¨P(O)S and H¨P(S)S anions, respectively,
which can be used for further syntheses without
purification.
= 85.82 ppm.
Synthesis of Monothio- and Dithiophosphorus
Acids Methyl Esters. General procedure for runs
24–27: Potassium (0.390 g, 10 mmol) was added to
the mixture composed of liquid ammonia (25 cm3)
and THF (25 cm3). The reaction mixture was
stirred up to the complete dissolution of the al-
kali metal, then cooled to 78 C, and 5 mmol of
each chlorophosphorus compound (t-butylphenyl-
phosphinoyl chloride, t-butylphenylphosphinothioyl
chloride, diethyl chlorothiophosphate, 2-chloro-5,5-
dimethyl-[1.3.2]-dioxaphosphinane-2-sulphide) in
5 cm3 of THF was added. The reaction mixture
was stirred at 78 C. The blue color of the solution
disappeared in a few minutes after the addition
of the last drop of phosphorus electrophile. Then,
0.192 g of sulfur was added and the cooling bath
was removed, the reaction mixture being stirred
at 33 C for 30 min. Next, the ammonia was
evaporated at 10 mm Hg. The residue was diluted
with 25 cm3 of THF. Then, 5 cm3 of methyl iodide
was added and the reaction mixture was stirred at
room temperature for 3 h. The methyl esters were
separated by radial chromatography (Table 4, runs
24–27).
REFERENCES
[1] Nycz, J.; Rachon, J. Phosphorus Sulfur Silicon, Relat
Elem 2000, 161, 39–59.
[2] Emoto, T.; Gomi, H.; Yoshifuji, M.; Okazaki, R.;
Inamoto, N. Bull Chem Soc Jpn 1974, 47, 2449–2452.
[3] Goda, K.; Yoshifuji, M.; Okazaki, R.; Inamoto, N. Bull
Chem Soc Jpn 1975, 48, 2484–2486.
[4] Horner, L.; Beck, P.; Hoffmann, H. Chem Ber 1959,
92, 2088–2094.
[5] Issleib, K.; Tzschach, A. Chem Ber 1960, 93, 1852–
1856.
[6] Yu, Z.; Verkade, J. G. Phosphorus Sulfur Silicon, Relat
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[7] Budzelaar, P. H. M.; van Doorn, J. A.; Meijboom, N.
Recl Trav Chim Pays-Bas 1991, 110, 420–432.
[8] Meinhardt, N. A. US Patent 3065273, 1962/1961,
Lubrizol Corp.; Chem Abstr 1963, 58, 9139a.
Run 24: S-methyl-t-butylphenylphosphinothioate
(eluted with CHCl3) 0.936 g (4.1 mmol, 82%), H
1
3
NMR (CDCl3) = 1.16 (d, JP = 17 Hz, CH3, 9H),
H
2.15 (d, 3 JP = 12 Hz, CH3, 3H), 6.83–7.93 (m,
H
aromat, 5H), 31P NMR (CDCl3) = 69.40 ppm.
Run 25: S-methyl-t-butylphenylphosphinodithioate
1
(eluted with CHCl3) 1.038 g (4.2 mmol, 85%), H

Reductive Cleavage of the Halogen–Phosphorus and Sulfur–Phosphorus Bonds with Alkali Metals 339
[9] Kabachnik, M. I.; Golubiewa, E. I. Dokl Acad Nauk
[12] Kuchen, W.; Haegele, G. Chem Ber 1970, 103, 2114–
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[10] Freeman, P. K.; Hutchinson, L. L. J Org Chem 1980,
45, 1924–1930.
[11] Maier, L.; Diel, P. J. Phosphorus Sulfur Silicon, Relat
Elem 1996, 115, 273–300.
[13] Harger, M. J. P. J Chem Soc, Perkin Trans 1 1997,
3205–3209.
[14] Zwierzak, A.; Stec, W. Can J Chem 1967, 45, 2513–
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