Catalytic synthesis of phosphoryl isocyanates

Article abstract of DOI:10.1007/s11172-006-0166-6

A general efficient method for the synthesis of phosphoryl isocyanates was developed. The method involves reactions of phosphoryl chlorides with sodium cyanate in the presence of anhydrous magnesium chloride as a catalyst.

Full text of DOI:10.1007/s11172-006-0166-6

2626
Russian Chemical Bulletin, International Edition, Vol. 54, No. 11, pp. 2626—2628, November, 2005
Catalytic synthesis of phosphoryl isocyanates*,**
E. I. Goryunov,ꢀ G. N. Molchanova, I. B. Goryunova, T. V. Baulina, P. V. Petrovskii,
V. S. Mikhailovskaya, A. G. Buyanovskaya, and E. E. Nifant´ev
A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
28 ul. Vavilova, 119991 Moscow, Russian Federation.
Fax: +7 (495) 135 5085. Eꢀmail: zaq@ineos.ac.ru
A general efficient method for the synthesis of phosphoryl isocyanates was developed. The
method involves reactions of phosphoryl chlorides with sodium cyanate in the presence of
anhydrous magnesium chloride as a catalyst.
Key words: phosphoryl chlorides, sodium cyanate, catalysis, phosphoryl isocyanates, synꢀ
thesis.
Phosphoryl isocyanates XYP(O)NCO are highly reacꢀ
ing the properties of Lewis acids. Most likely, the catalyst
activates a phosphorylating agent by forming a complex
of the metal cation with the O atom of the phosphoryl
group. The formation of this complex increases the posiꢀ
tive charge at the P atom, which promotes the correꢀ
sponding nucleophilic displacement of the chlorine atom.
If such an activation really takes place, these metal
salts should also catalyze other reactions of nucleophilic
replacement of chlorine at the tetrahedral P atom, in
particular, reactions of phosphoryl chlorides 1a—f with
sodium cyanate. Indeed, it turned out that electrophilic
catalysis by metal salts can be successfully employed for
the synthesis of phosphoryl isocyanates 2a—f.
tive and are used as starting reagents for the synthesis of
various types of compounds of potential practical interest:
phosphorylated urethans, ureas, heterocycles, etc. Alꢀ
though such isocyanates have been known since the
midtwentieth century, none of the current methods for
their synthesis combines versatility, efficiency, and use of
accessible and inexpensive starting reagents. Reactions of
phosphoryl chlorides XYP(O)Cl with sodium cyanate***
could serve as such a universal method; however, these
reactions afford only isocyanates of some phosphonic and
phosphinic acids in satisfactory yields, while reactions of
NaOCN with phosphochloridates either give no correꢀ
sponding isocyanates at all or their yields are low.2****
Most likely, such a result can be explained by the lower reꢀ
activities of phosphochloridates compared to phosphonoꢀ
chloridates and phosphinoyl chlorides in SN2(P)ꢀreꢀ
actions.6 This problem could be solved by activation of
the phosphorusꢀcontaining reagent, e.g., in the presence
of an appropriate catalyst.
R = R´ = PhO (a); mꢀMeC6H4O (b); oꢀMeC6H4O (c); CF3CH2O (d);
R = Me, R´ = PhO (e); R = R´ = Ph (f)
Anhydrous acetonitrile was used as a solvent for this
reaction. This polar aprotic solvent possesses a high disꢀ
solving ability and is inert toward the starting phosphoryl
chlorides and the resulting phosphoryl isocyanates 2a—f.
A metal salt combining a high efficiency and solubility
in this reaction medium should be the best catalyst. We
found that for catalytic phosphorylation of polyfluoroꢀ
alkanols with phosphorus acid chlorides, anhydrous chloꢀ
rides of Groups I and II metals (LiCl, CaCl2, and MgCl2)
are the most efficient catalysts.7 These salts were tested
for solubility in acetonitrile—phosphoryl chloride 1 and
MgCl2 proved to be substantially more soluble. For this
reason, this salt was used as a catalyst.
Earlier,7 we found that phosphorylation of weakly nuꢀ
cleophilic polyfluorinated alcohols with phosphoryl chloꢀ
rides XYP(O)Cl is catalyzed by some metal salts exhibitꢀ
* Dedicated to the Corresponding Member of the Russian Acadꢀ
emy of Sciences T. A. Mastryukova.
** For the preliminary report, see Ref. 1.
*** According to data,2 in reactions with phosphorus acid chloꢀ
rides, commercial NaOCN is often even more efficient than
much more expensive silver cyanate conventionally used in such
reactions.
**** It should be noted that dialkoxyphosphoryl isocyanates can
be alternatively obtained by reactions of the corresponding
phosphoramidates with (COCl)2;3 however, this method is unꢀ
suitable for the synthesis of diaryloxyꢀ4 and bis(polyfluoroꢀ
alkoxy)phosphoryl isocyanates5 because of low yields of the tarꢀ
get products.
We studied a reaction of diphenyl phosphochloridate
(1a) with a double excess of NaOCN in boiling acetoniꢀ
trile without a catalyst and in the presence of anhydrous
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2543—2545, November, 2005.
1066ꢀ5285/05/5411ꢀ2626 © 2005 Springer Science+Business Media, Inc.

Catalytic synthesis of phosphoryl isocyanates
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 11, November, 2005 2627
Table 1. Reactions of phosphoryl chlorides 1a—f with sodium
cyanate
Table 2. Physicochemical constants and elemental analysis data
for RR´P(O)NCO 2a—f
Entry Starting Catalyst Condiꢀ τ/h Content
Yield
Comꢀ
pound (p/Torr)
B.p./°C
Found
Calculated
Molecular
formula
(%)
reagent 1
tions*
of 2 in the of 2
mixture**
(%)
(%)
[M.p./°C]
С
H
—
N
—
P
2a8
2b*
2c*
2d5
2e9
2f10
149
(0.5)
171
(1.0)
177
(1.0)
64—65
(0.5)
115—117
(0.5)
158—160
(0.5)
—
—
—
1
2
3
4
5
6
7
8
9
10
a
—
A
A
A
A
A
A
A
B
A
B
70
4
4
6
3
1
3
3
1
34
70
65
61
50
72
72
93
93
98
25
59
49
46
29
58
52
73
70
78
MgCl2
MgCl2
MgCl2
—
MgCl2
—
MgCl2
—
MgCl2
59.34 4.44 4.58 10.18 C15H14NO4P
59.41 4.65 4.62 10.21
59.41 4.63 4.63 10.09 C15H14NO4P
59.41 4.65 4.62 10.21
—
—
—
b
c
d
—
—
—
—
—
—
—
—
—
—
—
—
e
f
1
* A refers to refluxing and B refers to room temperature.
** According to 31P{1H} NMR spectra.
[53—55]
* Data of this study.
MgCl2 (2.5 mol. %) (Table 1). According to 31P NMR
data, this reaction in the absence of a catalyst (entry 1)
proceeded very slowly and was accompanied by side reacꢀ
tions, the yield of diphenoxyphosphoryl isocyanate (2a)
being only 25%. The use of the catalyst (entry 2) reduced
the reaction time from 70 to 4 h. In addition, the amounts
of byꢀproducts were significantly lowered and, conseꢀ
quently, the yield of phosphoryl isocyanate 2a was apꢀ
proximately doubled.
the isocyanates obtained are given in Table 2. The strucꢀ
tures of phosphoryl isocyanates 2a—f were confirmed
by 1H, 19F, and 31P NMR spectroscopy (Table 3).
Thus, using electrophilic catalysis, we developed a
general and efficient method for the synthesis of the corꢀ
responding isocyanates from phosphorus(V) oxo acid
monochlorides and sodium cyanate.
Introduction of a methyl substituent into the metaꢀpoꢀ
sition of the benzene ring of the starting phosphochloridate
virtually did not change the rate of the catalytic process
(entry 3), while the presence of an orthoꢀmethyl group
substantially reduced the reaction rate (entry 4), probably
because of steric hindrances.
In the case of bis(2,2,2ꢀtrifluoroethyl) phosphochloriꢀ
date (1d), the use of the catalyst (cf. entries 5, 6) also
reduced the reaction time and appreciably increased the
yield of the target isocyanate 2d.
Experimental
1
H and 31P NMR spectra were recorded on a Bruker
AMXꢀ400 instrument (400.13 (1H) and 161.98 MHz (31P)).
19F NMR spectra were recorded on a Bruker WPꢀ200SY instruꢀ
ment (188.31 MHz). Chemical shifts were referenced to signals
for the residual protons of the deuterated solvent as the internal
standard (1H) and CF3COOH (19F) and 85% H3PO4
the external standards; C6D6 was used as a solvent.
(
31P) as
Diphenylphosphinoyl chloride (1f) (Aldrich) was distilled
in vacuo before use. Acetonitrile, benzene, and C6D6 were used
freshly distilled over P2O5. Sodium cyanate (Aldrich) was dried
in vacuo over P2O5 at 120 °C for 4 h. All manipulations were
carried out in an argon atmosphere. Phosphoryl chlorides 1a—e
were prepared according to known procedures.11—14
Catalytic synthesis of phosphoryl isocyanates 2a—f (general
procedure). Compound 1a—f (0.05 mol) was added to a suspenꢀ
sion of finely divided anhydrous MgCl2 (1.25 mmol) in MeCN
(30 mL). The mixture was heated with stirring until the catalyst
was completely dissolved. Then NaOCN (0.1 mol) was added
and the reaction mixture was stirred until the starting comꢀ
pound 1 was completely consumed (31P NMR data). The preꢀ
cipitate of inorganic salts was filtered off (for 2a,d—f) or sepaꢀ
rated by centrifuging (2b,c) and washed with benzene (2×10 mL).
The filtrate was concentrated and the residue was distilled
in vacuo. The synthesis of phosphoryl isocyanates 2a,d—f in the
absence of any catalyst was carried out analogously.
We found that for both phenyl methylphosphonoꢀ
chloridate (1e) and diphenylphosphinoyl chloride (1f),
the use of MgCl2 as a catalyst allows the roomꢀtemperaꢀ
ture synthesis of the corresponding phosphoryl isocyanꢀ
ates 2e,f (cf. entries 7 and 8 and entries 9 and 10, respecꢀ
tively). As with phosphochloridates, the use of this cataꢀ
lyst lowered the content of byꢀproducts in the reaction
mixture and increased the yields of phosphoryl isocyanꢀ
ates. In the reaction of phosphinoyl chloride 1f with
NaOCN in the presence of MgCl2, the content of byꢀ
products was only 2%, which allows isocyanate 2f to be
used subsequently without additional purification.
In all the catalytic reactions studied, the resulting phosꢀ
phoryl isocyanates 2a—f can be sufficiently easily sepaꢀ
rated from organophosphorus byꢀproducts by distillation
in vacuo. The constants and elemental analysis data for

2628
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 11, November, 2005
Goryunov et al.
Table 3. NMR spectra of phosphoryl isocyanates RR´P(O)NCO 2a—f
Comꢀ
pound
R
R´
1H, δ (J/Hz)
19F{1H}
31P{1H}
R
R´
δ (s)
2a
2b
2c
2d
PhO
PhO
6.90—7.24 (m)
—
—
—
2.03a
–22.34
–22.54
–22.13
–12.24b
mꢀMeC6H4O
oꢀMeC6H4O
CF3CHAHBO
mꢀMeC6H4O
oꢀMeC6H4O
CF3CHAHBO
2.02 (s, 6 H, Me), 6.78—7.15 (m, 8 H, C6H4)
2.18 (s, 6 H, Me), 6.88—7.45 (m, 8 H, C6H4)
3.90 (m, НA), 3.92 (m, НB)
(2JH,H = 12.4, 3JH,F = 8.0, 3JH,P = 9.8)
2e
2f
Me
Ph
PhO
Ph
1.39 (d, 3 H,
6.94—7.30
(m, 5 H)
—
—
15.31
17.60
2JH,P = 18.0 )
7.02—7.15 (m, 6 H, mꢀ, pꢀPh);
7.72—7.80 (m, 4 H, oꢀPh)
a 19F NMR, δ: 2.03 (t, 3JH,F = 8.0 Hz).
3
b 31P NMR, δ: –12.24 (quint, JH,P = 9.5 Hz).
7. M. I. Kabachnik, L. S. Zakharov, E. I. Goryunov, I. Yu.
Kudryavtsev, G. N. Molchanova, M. A. Kurykin, P. V.
Petrovskii, T. M. Shcherbina, and A. P. Laretina, Zh. Obshch.
Khim., 1994, 64, 902 [J. Gen. Chem. USSR, 1994, 64 (Engl.
Transl.)].
8. M. V. Kolotilo, A. G. Matyusha, and G. I. Derkach,
Zh. Obshch. Khim., 1970, 40, 758 [J. Gen. Chem. USSR,
1970, 40 (Engl. Transl.)].
This work was financially supported by the Council on
Grants of the President of the Russian Federation (Proꢀ
gram for State Support of Leading Scientific Schools in
Russia, Grant NShꢀ1100ꢀ2003ꢀ3), the Russian Founꢀ
dation for Basic Research (Project No. 05ꢀ03ꢀ08017),
and the Russian Academy of Sciences (State Contract
No. 10002ꢀ251/Pꢀ09/118ꢀ125/100603ꢀ589).
9. G. I. Derkach and E. I. Slyusarenko, Zh. Obshch. Khim.,
1967, 37, 2069 [J. Gen. Chem. USSR, 1967, 37 (Engl.
Transl.)].
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Received June 24, 2005;
in revised form September 15, 2005