The reactions of dialkyl phosphites and phosphine oxides with iodosylbenzene

Article abstract of DOI:10.1080/10426500210674

The reaction of iodosylbenzene with > P(O)H type of acids (dialkyl phosphites, secondary phosphine oxides) was studied. The acids of >P(O)H type add to iodosylbenzene to yield intermediate 6 which in the aprotic solvents yields oxidation products, it means >P(O)OH acids and/or anhydride of >P(O)OP(O)< type. On the other hand if the reaction is performed in alcohol as a solvent in the presence of sodium alcoholate > P(O)OR ester is the major product.

Full text of DOI:10.1080/10426500210674

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Phosphorus, Sulfur, and Silicon and the Related
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The Reactions of Dialkyl Phosphites and Phosphine
Oxides with Iodosylbenzene
Sławomir Makowiec a & Janusz Rachon a
a Department of Organic Chemistry, Chemical Faculty , Technical University of Gdańsk ,
Gdańsk, Poland
Published online: 27 Oct 2010.
To cite this article: Sławomir Makowiec & Janusz Rachon (2002) The Reactions of Dialkyl Phosphites and Phosphine Oxides
with Iodosylbenzene, Phosphorus, Sulfur, and Silicon and the Related Elements, 177:4, 941-955, DOI: 10.1080/10426500210674
To link to this article: http://dx.doi.org/10.1080/10426500210674
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Phosphorus, Sulfur and Silicon, 2002, Vol. 177:941–955
C
Copyright 2002 Taylor & Francis
1042-6507/02 $12.00 + .00
THE REACTIONS OF DIALKYL PHOSPHITES AND
PHOSPHINE OXIDES WITH IODOSYLBENZENE
Slawomir Makowiec and Janusz Rachon
Department of Organic Chemistry, Chemical Faculty,
Technical University of Gdan´sk, Gdan´sk, Poland
(Received October 15, 2001)
The reaction of iodosylbenzene with >P(O)H type of acids (dialkyl phos-
phites, secondary phosphine oxides) was studied. The acids of >P(O)H
type add to iodosylbenzene to yield intermediate 6 which in the apro-
tic solvents yields oxidation products, it means >P(O)OH acids and/or
anhydride of >P(O)OP(O)< type. On the other hand if the reaction is
performed in alcohol as a solvent in the presence of sodium alcoholate
>P(O)OR ester is the major product.
Keywords: Alkyl phosphinates; dialkyl phosphates; H-phosphonates;
iodosylbenzene; phosphine oxides; tetraalkyl pyrophosphate
INTRODUCTION
Organic compounds of polycoordinated iodine have long been known,
however, it is only recently that iodine compounds in the oxidation state
+3 have gained synthetic and mechanistic significance, as described in
6
several reviews.1
Iodosylbenzene, PhIO, is the most important and best investigated
member of the family of iodosyl compounds. It has found wide synthetic
application as a starting material in the preparation of numerous io-
dine(III) compounds and as an effective oxidant. However, to the best
of our knowledge, iodosylbenzene hasn’t been explored in phosphorus
chemistry.
Financial assistance from the Internal Grants Committee of the Technical University
of Gdan´sk (Poland); Chemical Faculty is gratefully acknowledged.
Presented in part at 13th ICOS, Warsaw 2000, Poland, pp. 169.
Address correspondence to Janusz Rachon, Department of Organic Chemistry, Chem-
ical Faculty, Technical University of Gdan´sk, ul. Narutowicza 11/12; 80-952 Gdan´sk,
Poland. E-mail: RACHON@ALTIS.CHEM.PG.GDA.PL
941

942
S. Makowiec and J. Rachon
As many iodine(III)-promoted reactions are thought to proceed via
unstable intermediates, often phenyliodonium species, detailed studies
on their mechanisms are scarce. In addition, it is often unclear as to
whether this kind of iodine(III) chemistry proceeds via ionic or radical
pathways. On the other hand it is well documented that, the reactivity
of iodosylbenzene is related to the electrophilic center located on the
iodine(III) atom and nucleophilic one on the oxygen atom. Iodosylben-
zene is an effective oxidizing reagent, however, its insolubility due to
its polymeric structure significantly restricts its practical usefulness.
The overwhelming majority of the known reactions of PhIO require the
presence of a hydroxylic solvent (water or methanol) or a catalyst (Lewis
acid or complexes of transition metals), which actually results in the
generation of activated monomeric species.
As early as in 1977 W. L. Foss at all.7 presented the effectiveness
of iodosylbenzene in the oxidation of the trivalent phosphorus organic
compounds: phosphines and diphosphines which were transformed into
phosphine oxides. For this transformation a phosphorus attack on the
oxygen atom of iodosylbenzene was suggested.
In connection with our interest in the reactivity of phosphorus nucle-
ophiles in the halophilic substitution reactions,8 we took up the studies
of the reaction between >P(O)H acids as well as >P O anions with
iodosylbenzene. Because iodosylbenzene is known as an oxidizing agent
one can expect the formation of dialkyl phosphates and phosphinates
respectively in the reaction under investigation. On the other hand the
effectiveness of such a oxidizing process, influence of solvent (especially
hydroxylic solvents) and substituents on the phosphorus atom as well
as on the course of the reaction were not obvious. Also the question
should be answered: what is the mechanism of this reaction?
In this article we would present the results of our preliminary
experiments.
RESULTS
From the theoretical point of view >P(O)H acids can add to iodosyl-
4
3
benzene to form 4-coordinate (
,
5) and/or 3-coordinate (
,
3) phos-
phorus intermediates (Scheme 1). Looking into the bonds energy the
4-coordinate phosphorus intermediate should be more stable, however
both of them should collapse to iodobenzene and a >P(O)OH type
acid.
In the first set of experiments we treated iodosylbenzene with dialkyl
phosphites as well as secondary phosphine oxides in benzene or THF at
the boiling point of the solvent. The reactions were carried out until the

Reactions of Dialkyl Phosphites
943
SCHEME 1
disappearance of solid iodosylbenzene. It should be pointed out that we
observed much faster rate of the reaction between phosphine oxides and
iodosylbenzene versus dialkyl phosphites; dialkyl phosphites required
much longer reaction time.
The major products we observed in such a reaction mixture were:
phosphoric or phosphinic acids respectively and anhydrides of phos-
phoric and phosphinic acids (Scheme 2). The results of this set of ex-
periments are collected in Table I.
SCHEME 2
As one can see from the data presented in the Table I dialkyl phos-
phites yield in the reaction with iodosylbenzene mainly pyrophos-
phates 4. When diethyl phosphite was treated with iodosylbenzene
in THF, the reaction mixture after 12 h was examined by means of

944
S. Makowiec and J. Rachon
TABLE I The Products Distribution in the Reaction of Iodosylbenzene
with >P(O)H Acids in Aprotic Solvents
Yield %
Run
R0
EtO
iPrO
OCH2C(CH3)2 CH2O
R00
EtO
iPrO
Solvent
Conditions
3
4
1
2
3
4
5
6
7
8
9
PhH
THF
PhH
THF
THF
PhCH3
THF
PhCH3
THF
THF
0.5 h, b.p.
48 h, b.p.
0.5 h, b.p.
48 h, b.p.
12 h, b.p.
0.5 h, b.p.
12 h, b.p.
0.3 h, b.p.
3 h, b.p.
11
90
8
77
5
71
90
77
60
20a
70b
14
40
20
Ph
t-Bu
PhCH2
PhCH2
90
95
10
n-C6H13
n-C6H13
0.3 h, b.p.
aFrom this reaction mixture beside 3 and 4 we isolated 1,4-di-O-t-butylphenyl-
phosphinylbutandiol (40%).
bThe yield was estimated from the NMR spectrum; 70% of 4 and 30% of starting
material.
31P NMR spectroscopy. The 31P NMR spectrum of this reaction mix-
ture displayed one minor signal at P = 4.7 (diethyl phosphite) and two
major signals with identical intensity
= 0.96 (diethyl phosphate)
P
and
=
12.10 (tetraethyl pyrophosphate). Taking into consideration
P
that in the reaction of dialkyl phosphite and iodosylbenzene pyrophos-
phate and water should be produced, somewhat surprisingly for us was
the high yield of tetraisopropyl pyrophosphate observed in this reac-
tion (Table I, runs 3 and 4). In a separate experiment the hydrolytic
stability of tetraisopropyl pyrophosphate was checked under the reac-
tions condition. It was found that compound 4 (R = R0 = iPrO) dis-
solved in THF with one equivalent of water at 56 C was stable within
24 h. The same hydrolytic stability we observed in case of 5,5,50,50-
tetramethyl-2,20-oxy-bis-[1,3,2]dioxaphosphinane 2,20-dioxide 4[R =
R0 = OCH2C(CH3)2CH2O].
On the other hand secondary phosphine oxides in the reaction
with iodosylbenzene produce phosphinic acids 3 as a major product
(Table I, runs 9 and 10). Exemptions is t-butylphenylphosphine ox-
ide, which in the reaction with iodosylbenzene in toluene produces
the anhydride of t-butylphenylphosphinic acid 4 (R0 = tBu; R00 = Ph).
In contrast to that when the reaction of t-butylphenylphosphine ox-
ide with iodosylbenzene was performed in THF we isolated from
the reaction mixture t-butylphenylphosphinic acid (20%) and the
anhydride of t-butylphenylphosphinic acid (20%) beside 1,4-di-O-t-
butylphenylphosphinylbutandiol (40%).

Reactions of Dialkyl Phosphites
945
In the second set of experiments we treated >P(O)H type acids with
iodosylbenzene in alcohol as a solvent in the presence as well as in the
absence of the alcoholate as a base catalyst (Scheme 3). The results of
this set of experiments are presented in the Table II.
SCHEME 3
From the reaction mixture of diethyl phosphite and iodosylbenzene
in ethanol we isolated triethyl phosphate with a quantitative yield
(Table II, run 1). The treatment of diisopropyl phosphite with iodosyl-
benzene in isopropanol produces tetraisopropyl pyrophosphate as a
major product (60%) beside small amounts of diisopropyl phosphate
(7%) and triisopropyl phosphate (24%). In contrast to that the treat-
ment of diisopropyl phosphite with iodosylbenzene in isopropanol in
the presence of sodium isopropanolate (Table II, run 3) produces one
major product, namely triisopropyl phosphate (90%). On the other
hand di-n-hexylphosphine oxide and dibenzylphosphine oxide yield in
TABLE II The Products Distribution in the Reaction of Iodosylbenzene with
>P(O)H Acids in Alcohols as a Solvent
Yield %
Run
R0
EtO
R00
EtO
R
Solvent
Conditions
3
4
5
1
2
3
4
5
6
7
8
9
Et
iPr
EtOH/THF
24 h, b.p.
24 h, b.p.
1 h, b.p.
1 h, b.p.
1 h, b.p.
1 h, b.p.
0.2 h, b.p.
0.25 h, b.p. 94
1 h, b.p.
3 h, b.p.
1 h, b.p.
100
24
iPrO
iPrO
iPrOH/THF
7
60
iPrOH/iPrO Na+
94
iPrO
nC6H13
iPrO
nC6H13
tBu tBuOH/tBuO K+
Et
Me
Me
Et
10
70
62
25
80a
EtOH/THF
MeOH
30
69
MeOH/MeO Na+
EtOH
PhCH2
tBu
PhCH2
Ph
b
EtOH/EtO
MeOH/THF
MeOH/MeO
10
11
Me
4
7
88
90
aMixture of trialkylphosphates.
bComplex mixture of products (probably because of acidic protons in the benzylic posi-
tions).

946
S. Makowiec and J. Rachon
the reaction with iodosylbenzene in alcohol oxidation products namely
di-n-hexylphosphinic acid and dibenzylphosphinic acid, respectively
(Table II, runs 5, 6, and 7). Exemption is t-butylphenylphosphine
oxide, which under the above conditions produces the ester of
t-butylphenylphosphinic acid as a major product (Table II, run 10).
As one can see from the data collected in the Table II the products
distribution in the reaction under investigation strongly depends on
the base catalyst. Trialkyl phosphates as well as alkyl esters of phos-
phinic acids are the major products when >P(O)H acids are treated
with iodosylbenzene in alcohol in the presence of alcoholate anion.
DISCUSSION
The esters of phosphinic acids as well as trialkyl phosphates isolated
from the reaction of >P(O)H acids with iodosobenzene in alcohol as a
solvent strongly suggest the presence of phosphorylating agent in the
reaction mixture. The formation of >P(O)OH acids, >P(O)OR esters,
and pyrophosphates as well as in the reaction of >P(O)H acids with
iodosylbenzene may be explained by the addition of >P(O)H acid to io-
dosylbenzene which will produce intermediate 6 possessing a four coor-
dinate phosphorus atom. The intermediate 6 can collapse to >P(O)OH
acid and iodobenzene. On the other hand the intermediate 6 can be
the target for nucleophilic attack and can phosphorylate nucleophiles
present in the reaction mixture (Scheme 4).
If the reaction is performed in aprotic solvent, in which the concentra-
tion of iodosylbenzene is low, intermediate 6 collapses into iodobenzene
and >P(O)OH acid. In such a situation with the progress of the reaction
the concentration of the >P(O)OH acid is growing in the reaction mix-
ture and it can react with intermediate 6 to yield anhydrides 7, what
we observed in our experiments (see Table I).
We have obtained evidence in other studies that the mixture
of iodosylbenzene and dialkyl phosphite is able to phosphorylate
dialkylphosphates. We treated the mixture composed of 1 equivalent
of diisopropyl phosphite and 1 equivalent of diethylphosphate with
1 equivalent of iodosylbenzene in THF solution, the 31P NMR spectrum
of such a reaction mixture displayed two resonance lines at
=
P
12.50 ppm (d, J = 36 Hz) and 14.20 ppm (d, J = 36 Hz), which were
identified as the resonances of the anhydride 7 (R0 R OEt) (Scheme 5).
In the separate experiment we treated the mixture composed
of 1 equivalent of diisopropyl phosphite and 1 equivalent of
t-butylphenylphosphinic acid with 1 equivalent of iodosylbenzene in
CHCl3 solution. The 31P NMR spectrum of such a reaction mixture

Reactions of Dialkyl Phosphites
947
SCHEME 4
displayed two resonance lines at
= 49.74 ppm (d, J = 17 Hz) and
P
12.20 Hz ppm (d, J = 17 Hz), which were identified as the resonances
of the anhydride 7 (R0 = tBu, R = Ph) (Scheme 5).
SCHEME 5
The results of this experiments show that diethyl phosphate as
well as t-butylphenylphosphinic acid undergo phosphorylation with a
phosphite/iodosylbenzene mixture (probably by the intermediate 6).

948
S. Makowiec and J. Rachon
We have to add, that the treatment of diethylphosphate and
t-butylphenylphosphinic acid with iodosylbenzene under the same re-
action conditions doesn’t form neither tetraethyl pyrophosphate nor
t-butylphenylphosphinic acid anhydride.
On the other hand if the reaction is performed in alcohol as a sol-
vent, in which concentration of the iodosylbenzene is high, we have two
competition processes: oxidation and nucleophilic attack of the alcohol
on the phosphorus atom of the intermediate 6 to yield >P(O)OR es-
ters. If the alcohol is a week nucleophile the formation of the >P(O)OR
ester will compete with the anhydride formation (Table II, run 2).
Alcoholate anion is a much better nucleophile than alcohol, in other
words if reaction of iodosylbenzene with >P(O)H acid is performed
in alcohol as a solvent in the presence of alcoholate anion, this an-
ion can effectively compete with the >P(O)O anion and will produce
>P(O)OR ester. This situation is nicely demonstrated in the experiment
with diisopropyl phosphite which in the reaction with iodosylbenzene
in iPrOH gives 24% of triisopropyl phosphate versus 94% in the case
of the reaction carried out in the presence of sodium isopropanolate
(Table II, runs 2 and 3). Likewise di-n-hexylphosphine oxide in the re-
action with iodosylbenzene in methanol produces di-n-hexylphosphinic
acid as a major product versus methyl di-n-hexylphosphinate (69%) in
the case when the reaction is carried out in methanol in the presence
of sodium methanolate (Table II, runs 6 and 7).
On the other hand one can also argue that esters 5 may be produced
in the reaction of anhydrides 4 and alcohol; but in such a case esters
5 and acids 3 should be produced with an equal yield. In our experiments
where the reaction was carried out in alcohol or in the mixture of alcohol
and THF as a solvent, in the reaction mixture we observed the esters
5 in much higher concentration than acids 3 (Table II, runs 1, 3, 4,
7, 10, and 11). This observation strongly suggests that the esters 5 are
produced (at least in part) in the direct reaction between intermediate 6
and alcohol. The reaction between >P(O)H acids and iodosylbenzene, as
well as diacetoxyiodobenzene and Coser reagent is under investigation,
and the results will be published subsequently.
EXPERIMENTAL
The Reactions Between Iodosylbenzene and Dialkyl
Phosphites in Aprotic Solvents
General Procedure
To a suspension of PhIO (5 mmol, 1.100 g) in 10 mL of the solvent
(THF, benzene, toluene) a solution of R2P(O)H (5 mmol) in 2 mL of the

Reactions of Dialkyl Phosphites
949
same solvent was added. The reaction mixture was stirred for 0.5 to
48 h at the boiling point of the solvent. Then the solvent was removed
in the vacuum and iodobenzene as well as tetraalkyl pyrophosphate
was disstilled off under reduced pressure. The residue from the distil-
lation was dissolved in 50 mL of ether and extracted with 20 mL of
5% NaHCO3 water solution. The water layer was acidified with conc.
HCl and extracted with ether (3 30 mL). The collected ether solutions
were dried over MgSO4, and after removal of the solvent gave dialkyl
phosphate.
The results are collected in Table I.
Run 1. Iodobenzene 0.612 g (60%), b.p. = 30–40 C/0.3 mmHg,
1H NMR (CDCl3) = 6.51–7.02 ppm (m, 3H), 7.22–7.53 ppm (m, 2H);
tetraethyl pyrophosphate 0.558 g (77%), b.p. = 120–125 C/0.3 mmHg,9
31P NMR (CDCl3)
31P NMR (CDCl3)
=
12.20 ppm;10 diethyl phosphate 0.084 g (11%),
1.10 ppm.10
=
Run 2. Iodobenzene 0.714 g (70%), b.p. = 30–40 C/0.3 mmHg,
1H NMR (CDCl3) = 6.51–7.02 ppm (m, 3H), 7.22–7.53 ppm (m, 2H);
tetraethyl pyrophosphate 0.036 g (5%), b.p. = 120–125 C/0.3 mmHg,9
31P NMR (CDCl3)
31P NMR (CDCl3)
=
=
12.20 ppm;10 diethyl phosphate 0.693 g (90%),
1.10 ppm.10
Run 3. Iodobenzene 0.663 g (65%), b.p. = 30–40 C/0.3 mmHg,
1H NMR (CDCl3)
= 6.51–7.02 ppm (m, 3H), 7.22–7.53 ppm
(m, 2H); tetraisopropyl pyrophosphate 0.614 g (71%), b.p. = 150–
160 C/0.4 mmHg,9 31P NMR (CDCl3) 14.20 ppm;11 diisopropyl
phosphate 0.100 g (11%), 31P NMR (CDCl3) 0.90 ppm.12
=
=
Run 4. Iodobenzene 0.683 g (67%), b.p. = 30–40 C/0.3 mmHg,
1H NMR (CDCl3)
= 6.52–7.02 ppm (m, 3H), 7.22–7.53 ppm
(m, 2H); tetraisopropyl pyrophosphate 0.778 g (90%), b.p. = 156–
160 C/0.4 mmHg,9 31P NMR (CDCl3) 14.20 ppm.11
=
The Reactions Between Iodosylbenzene and
5,5-dimethyl-1,3-dioxaphosphorinan-2-oxide in
Aprotic Solvents
To a suspension PhIO (5 mmol, 1.100 g) in 10 mL of the solvent (THF,
toluene) a solution of 5,5-dimethyl-1,3-dioxaphosphorinan (5 mmol,
0.750 g) in 2 mL of the same solvent was added. The reaction mix-
ture was stirred for 0.5 to 12 h at the boiling point of the solvent.
Then the reaction mixture was diluted with 50 mL of ether and ex-
tracted with 20 mL of 5% NaHCO3 water solution. The organic layer
was dried over MgSO4, evaporated to yield 2,20-oxybis[5,5-dimetyl-1,

950
S. Makowiec and J. Rachon
3,2-dioxaphosphorinane]-2,20-dioxide. The water layer was separated,
acidified with conc. HCl and extracted with ether (3 30 mL). The com-
bined ether solutions were dried over MgSO4, filtered, and evaporated
to yield 5,5-dimetyl-2-hydroxy-2-oxo-1,3,2-dioxaphosphorinan. The re-
sults are presented in Table I.
Run 5. Iodobenzene 0.816 g (80%), 1H NMR (CDCl3)
= 6.51–
7.02 ppm (m, 3H), 7.22–7.53 ppm (m, 2H); 2,20-oxybis[5,5-dimetyl-1,3,2-
dioxaphosphorinane]-2,20-dioxide 0.604 g (77%), m.p. = 192–193 C
(AcOEt/Hexane),9 31P NMR (CDCl3)
=
20.07 ppm;10 5,5-dimetyl-2-
hydroxy-2-oxo-1,3,2-dioxaphosphorinan 0.116 g (14%), m.p. = 170–
171 C (AcOEt/Hexane),9 31P NMR (CDCl3) 4.27 ppm.13
=
Run 6. Iodobenzene 0.836 g (82%), 1H NMR (CDCl3)
= 6.51–
7.02 ppm (m, 3H), 7.22–7.53 ppm (m, 2H); 2,20-oxybis[5,5-dimetyl-1,3,2-
dioxaphosphorinane]-2,20-dioxide 0.471 g (60%), m.p. = 192–193 C
(AcOEt/Hexane), 31P NMR (CDCl3)
=
20.07 ppm, 5,5-dimetyl-2-
hydroxy-2-oxo-1,3,2-dioxaphosphorinan 0.332 g (40%), m.p. = 170–
171 C (AcOEt/Hexane), 31P NMR (CDCl3)
=
4.27 ppm.
The Reactions Between Iodosylbenzene and Phosphine
Oxides in Aprotic Solvents
General Procedure
To a suspension of PhIO (5 mmol, 1.100 g) in 10 mL of the solvent
(THF, toluene) a solution of dialkylphosphine oxides (5 mmol) in 2 mL of
the same solvent was added. The reaction mixture was stirred for 0.3 to
12 h at the boiling point of the solvent. Then the reaction mixture was di-
luted with 50 mL of ether and extracted with 25 mL of 5% NaHCO3 wa-
ter solution. The organic layer was dried over MgSO4, evaporated and
separated by radial chromatography. The water layer was acidified with
conc. HCl and extracted with ether (3 30 mL). The combined ether
solutions were dried over MgSO4, filtered and evaporated to yield phos-
phinic acids. The results are presented in Table I.
Run 7. Iodobenzene 0.816 g (80%), 1H NMR (CDCl3)
= 6.51–
7.02 ppm (m, 3H), 7.22–7.53 ppm (m, 2H), t-butylphenylphosphinic acid
0.198 g (20%), m.p. = 150–152 C (AcOEt/Hexane),14 31P NMR (CDCl3)
= 52.44 ppm;15 t-butylphenylphosphinic acid anhydride 0.190 g (20%),
31P NMR (CDCl3) = 50.89; 50.37 ppm (mixture of diasteroisomers);14
1,4-di-O-t-butylphenylphosphinylbutanodiol 0.450 g (40%) (mixture of
diasteroisomers), 31P NMR (CDCl3) = 52.25; 52.29 ppm, H NMR
1
(CDCl3) = 1.12 ppm (d, 9H), 1.23 ppm (d, 9H), 1.71–1.90 ppm (m, 4H),

Reactions of Dialkyl Phosphites
951
3.72–3.91 ppm (m, 2H), 4.00–4.25 ppm (m, 2H), 7.32–7.63 ppm (m, 6H),
7.72–7.91 ppm (m, 4H), FAB MASS M/e = 451 (M + 1) M/e =
253 PhtBuP(O)(CH2)4, M/e = 198 PhtBuP(O)OH.
Run 8. The yield was estimated from the 31P NMR spectrum:
t-butylphenylphosphinic acid anhydride 70%, 31P NMR (CDCl3)
=
50.89; 50.37 ppm (mixture of diasteroisomers), t-butylphenylphosphine
oxide 30% 31P NMR (CDCl3) = 48.71ppm.
Run 9. Iodobenzene 0.714 g (70%), 1H NMR (CDCl3)
= 6.51–
7.04 ppm (m, 3H), 7.22–7.53 ppm (m, 2H). Dibenzylphosphinic acid
1.107 g (90%), m.p. = 190–191 C (AcOEt/Hexane);9 31P NMR (CDCl3)
= 51.70 ppm, H NMR (CDCl3) = 2.95 ppm, (d, 4H, J2PH = 16 Hz),
1
6.63–6.91 ppm (m, 10H).16
Run 10. Iodobenzene 0.765 g (75%), 1H NMR (CDCl3) = 6.54–
7.03 ppm (m, 3H), 7.25–7.52 ppm (m, 2H); di-n-hexylphosphinic acid
1,111 g (95 %), m.p. = 75–76 C (AcOEt/Hexane);9 31P NMR (CDCl3)
= 58.86 ppm.10
The Reaction Between PhIO and > P(O)H Type
Compounds in Alcohols
To a suspension of PhIO (5 mmol, 1.100 g) in 10 mL of the solvent
(alcohol, or a mixture THF: alcohol = 1 : 1) 5 mmol of >P(O)H compound
(diethyl phosphite, diisopropyl phosphite, di-n-hexylphosphine oxide,
dibenzylphosphine oxide, t-butylphenylphosphine oxide) were added.
The reaction mixture was stirred for 0.2 to 24 h at the boiling point of
the solvent. The work up depends on the starting material used in the
experiments.
Runs 1 and 2. The solvent was removed in the vacuum from the
reaction mixture and the residue was separated by distillation under
reduced pressure. The results are collected in Table II.
Run 1. Iodobenzene 0.612 g (60%), b.p. = 30–40 C/0.3 mmHg,
1H NMR (CDCl3) = 6.51–7.02 ppm (m, 3H), 7.22–7.51 ppm (m, 2H);
triethyl phosphate 0.910 g (100%), b.p. = 60–65 C/0.4 mmHg, 31P NMR
(CDCl3);9
=
0.03 ppm.10
Run 2. Iodobenzene 0.663 g (65%), b.p. = 30–40 C/0.3 mmHg,
1H NMR (CDCl3)
= 6.51–7.02 ppm (m, 3H), 7.22–7.51 ppm (m,
2H); tetraisopropyl pyrophosphate 0.519 g (60%), b.p. = 160–170 C/
0.5 mmHg, 31P NMR (CDCl3)
14.01 ppm; diisopropyl phosphate
=

952
S. Makowiec and J. Rachon
0.064 g (7%), 31P NMR (CDCl3)
=
1.57 ppm; triisopropyl phosphate
0.268 g (24%), b.p. = 70–75 C/0.5 mmHg,9 31P NMR
=
2.35 ppm.10
Run 5. The reaction mixture was diluted with 50 mL of ether and
extracted with 20 mL of 5% NaHCO3 water solution. The organic layer
was dried over MgSO4, and evaporated to give iodobenzene 0.765 g
(75%). The water layer was acidified with conc. HCl and extracted
with ether (3
30 mL). The collected ether solutions were dried
over MgSO4, filtered and evaporated to gave di-n-hexylphosphinic acid
0.819 g (70%), m.p. = 75–76 C (AcOEt/Hexane), 31P NMR (CDCl3)
=
58.86 ppm.
Run 6. The reaction mixture was diluted with 70 mL of ether and ex-
tracted with 20 mL of 5% NaHCO3 water solution. The organic layer was
dried over MgSO4, evaporated, and separated by radial chromatogra-
phy (CH2Cl2:MeOH: 20/1) to give methyl di-n-hexylphosphinate 0.390 g
1
(30%), 31P NMR (CDCl3) = 59.83 ppm, H NMR (CDCl3) = 0.82–
2.04 ppm (m, 26H), 3.34 ppm (d, J3PH = 10 Hz, 3H). The water layer
was acidified with conc. HCl and extracted with ether (3 30 mL). The
collected ether solutions were dried over MgSO4, filtered and evapo-
rated to gave di-n-hexylphosphinic acid 0.725 g (62%), m.p. = 75–76 C
(AcOEt/Hexane), 31P NMR (CDCl3) = 58.86 ppm.
Run 8. The reaction mixture was diluted with 70 mL of ether and
extracted with 20 mL of 5% NaHCO3 water solution. The water layer
was acidified with conc. HCl and extracted with ether (3 30 mL). The
collected ether solutions were dried over MgSO4, filtered and evapo-
rated to gave dibenzylphosphinic acid 1.107 g (90%), m.p. = 190–191 C
1
(AcOEt/Hexane), 31P NMR (CDCl3) = 51.70 ppm, H NMR (CDCl3)
= 2.94 ppm, (d, 4H, J2PH = 16 Hz), 6.64–6.91 ppm (m, 10H).
Run 10. The reaction mixture was diluted with 70 mL of ether and
extracted with 20 mL of 5% NaHCO3 water solution. The organic layer
was dried over MgSO4, filtered, evaporated and separated by radial
chromatography (CH2Cl2 : MeOH = 50:1) to give iodobenzene 0.765 g
(75%); t-butylphenylphosphinic acid anhydride 0.069 g (7%), 31P NMR
(CDCl3) = 50.89; 50.37 ppm (mixture of diasteroisomers); methyl
t-butylphenylphosphinate 0.932 g (88%), 31P NMR (CDCl3)
=
1
54.75 ppm, H NMR (CDCl3) = 7.05–7.51 ppm (m, 5H), 3.53 ppm,
(d, J3PH = 10 Hz, 3H), 1.02 ppm (d, JP3H = 16 Hz, 9H).14 The water layer
was acidified with conc. HCl and extracted with ether (3
30 mL).
The collected ether solutions were dried over MgSO4, filtered and evap-
orated to gave t-butyphenylphosphinic acid 0.198 g (4%), m.p. = 150–
152 C (AcOEt/Hexane), 31P NMR (CDCl3) = 52.44 ppm.

Reactions of Dialkyl Phosphites
953
The Reaction Between PhIO and > P(O)H Type
Compounds in Alcohols in the Presence of Alkoholates
To the mixture composed of 10 mL of a solvent (alcohol, or a mixture
THF : alcohol = 1 : 1), sodium alcoholate (5 mmol) and PhIO (5 mmol,
1.100 g), 5 mmol of >P(O)H type compounds (diisopropyl phosphite,
di-n-hexylphosphine oxide, t-butylphenylphosphine oxide) were added.
The reaction mixture was stirred for 0.2 to 1 h at the boiling point of
the solvent. The work up depends on the starting material used in the
experiments. The results are collected in Table II.
Run 3. From the reaction mixture the solvent was removed in the
vacuum and the residue was separated by distillation under reduced
pressure to give: iodobenzene 0.765 g (75%), b.p. = 30–40 C/0.3 mmHg),
1H NMR (CDCl3) = 6.51–7.03 ppm (m, 3H), 7.22–7.51 ppm (m, 2H);
triisopropyl phosphate 1.052 g (94%), b.p. = 70–75 C/0.5 mmHg), 31P
NMR (CDCl3)
=
2.35 ppm.
Run 4. The yield was estimated by 31P NMR (CDCl3)
[(iPrO)3PO, 31%]; 5.58 ppm [(iPrO)2 t-BuOPO, 38%]; 9.14 ppm
[(t-BuO)2 iPrOPO, 15%]; 12.50 ppm [(t-BuO)3PO, 1%]; 1.70 ppm
[(iPrO)2P(O)OH, 13%].
=
2.29 ppm
Run 7. The reaction was diluted with 50 mL of ether and washed
with 10 mL of water. The ether layer was dried over MgSO4, the solvent
was removed in the vacuum and the residue was separated by radial
chromatography (CH2Cl2 : MeOH : 20/1) to give: iodobenzene 0.785 g
(77%), 1H NMR (CDCl3) = 6.54–7.02 ppm (m, 3H), 7.22–7.51 ppm (m,
2H); methyl di-n-hexylphosphinate 0.855 g (69%), 31P NMR (CDCl3)
= 59.83 ppm, 1H NMR (CDCl3) = 0.82–2.01 ppm (m, 26H), 3.32 ppm
(d, 3H, J3PH = 10 Hz). The water layer was acidified with conc. HCl and
extracted with ether (3
30 mL). The collected ether solutions were
dried over MgSO4, filtered, and evaporated to give di-n-hexylphosphinic
acid 0.292 g (25%), m.p. = 75–76 C (AcOEt/Hexane), 31P NMR (CDCl3)
= 58.86 ppm.
Run 11. The reaction mixture was diluted with 50 mL of ether and
washed with 10 mL of water. The ether layer was dried over MgSO4,
removed in the vacuum and the residue was separated by radial chro-
matography (CH2Cl2 : MeOH : 50/1) to give: iodobenzene 0.765 g (72%),
1H NMR (CDCl3) = 6.51–7.02 ppm (m, 3H), 7.22–7.51 ppm (m, 2H);
methyl t-butylphenylphosphinate 0.954 g (90%), 31P NMR (CDCl3)
=
1
54.75 ppm, H NMR (CDCl3) = 7.01–7.53 ppm, (m, 5H), 3.51 ppm,
(d, 3H, J3PH = 10 Hz), 1.01 ppm (d, 9H, JP3H = 16 Hz).

954
S. Makowiec and J. Rachon
The Reaction Between Iodosylbenzene and Diisopropyl
Phosphite in the Presence of Diethyl Phosphate
To a suspension of PhIO (5 mmol, 1.100 g) in 10 mL of THF and
diisopropyl phosphite (5 mmol; 0.830 g) diethyl phosphate (5 mmol,
0.770 g) was added. The reaction mixture was stirred for 24 h at the
boiling point of the solvent. Then the solvent was removed in the
vacuum and 31P NMR (CDCl3) was measured. The 31P NMR spec-
trum exhibited five resonance lines:
= 0.137 ppm (intensity 40)
diisopropyl phosphate; 0.45 ppm (intensity 50) diethylphosphate,
=
= 5.30 ppm (intensity 5) diisopropyl phosphite, = 12.58 ppm (inten-
sity 20), and 14.28 ppm (intensity 20) O,O-diethyl-O’,O’-diisopropyl
pyrophosphate.
The Reaction Between Iodosylbenzene and Diisopropyl
Phosphite in the Presence of t-butylphenylphosphinic
Acid
To a suspension of PhIO (5 mmol, 1.100 g) in 10 mL of CHCl3 and
diisopropyl phosphite (5 mmol, 0.830 g) phenyl t-butylphosphinate
(5 mmol, 0.990 g) was added. The reaction mixture was stirred for 24 h
at the boiling point of the solvent. Then the solvent was removed in the
vacuum and 31P NMR (CDCl3) was measured. The 31P NMR spectrum
exhibited six resonance lines: = 0.16 ppm (intensity 2) diisopropyl
phosphate; = 52.90 ppm (intensity 4) phenyl t-butylphosphinic acid;
= 5.59 ppm (intensity 10) diisopropyl phosphite,
=
12.30 ppm, d,
J3PP = 39 Hz, (intensity 4) and 49.74 ppm, d, JP3P = 39 Hz (intensity 5)
O’,O’-diisopropylphenyl t-butylphosphate;
tertraisopropylpyrophosphate.
=
13.95 ppm (intensity 5)
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Reactions of Dialkyl Phosphites
955
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