Angewandte
Communications
Chemie
Main-group Chemistry
In memory of Gerd Becker
Abstract: We describe the isolation and spectroscopic charac-
terization of the heavier phosphorus-containing analogue of
isocyanic acid (HPCO), and its isotopologue (DPCO). This
fundamental small molecule, which has been postulated to exist
in interstellar space, has thus far only been observed at low gas
phase concentrations or in inert gas matrices. In this report we
describe its synthesis, spectroscopic properties, and reactivity in
Scheme 1. Known isomers in the HNCO system.
solution.
doubtful because the compound could neither be isolated nor
[
16]
I
n 1830, Wçhler and Liebig investigated cyanic acid (HOCN)
further characterized.
and its reactivity towards ammonia in an effort to synthesize
ammonium cyanate, which was found to afford urea on mild
Numerous theoretical studies have focused on the differ-
ent isomers of the HPCO system, predicting HPCO to be
23 kcalmol more stable than HOCP, with an activation
[1]
À1
heating. Given the technological limitations at the time,
very little was deduced about the constitution of the species
studied. However these discoveries were fundamental in
defining the concept of isomerism, for example, the authors
discovered that the silver salts of cyanate and fulminate have
the same composition. Historic interest in such simple acids
has largely focused on fulminic acid (and salts of its conjugate
À1 [17–22]
barrier for interconversion of 70 kcalmol .
These com-
putational studies have stimulated further research, indicating
that HPCO might be stable in interstellar space. All successful
experimental HPCO studies thus far have tried to mimic
interstellar conditions, such as low gas-phase concentration of
HPCO or the use of noble gas matrices. Thus, there are two
studies of the generation of HPCO by gas discharges of highly
[
2,3]
base) in large part due to its explosive properties.
molecular structures of isocyanic (HNCO) and fulminic acid
HCNO), were not determined until 1950 by Herzberg and
The
dilute PH /CO mixtures (in He or Ar), which allowed the
3
[
23]
[24,25]
(
recording of infrared and microwave spectra of HPCO.
[
4]
[5]
Reid, and 1966 by Beck, respectively. Nowadays, spectro-
scopic evidence for all four isomeric species isocyanic acid,
cyanic acid, fulminic acid, and isofulminic acid is available
These studies have corroborated the presence of HPCO and
not the isomeric HOCP. More recently, HPCO has been
proposed as an intermediate in the formation of phosphine-
carboxamides and phosphinidene-carbene adducts in the
reaction of PCO with ammonium and imidazolium salts,
Without a suitable nucleophile present,
protonation of PCO in solution phase affords an insoluble
yellow precipitate and PH , in agreement with previous
reports by Becker et al.
HPCO has been proposed to exist in interstellar space as
well, but it has not yet been detected there. The only known
phosphorus-containing species in space are HCP,
[6]
[
7]
[5]
[
8]
[9]
[10]
(
Scheme 1). HNCO, HOCN,
and HCNO have even
[11]
À
been detected in interstellar space.
[
26–28]
In contrast, analytical data for the heavier phosphorus-
containing homologues HPCO are scarce. Several reports by
Matveev claim to have synthesized HOCP from phospha-
alkyne precursors,
not be reproducible by the group of Becker and others.
Becker and co-workers suggested the existence of HOCP
after protonation of the 2-phosphaethynolate anion,
PCO ,
respectively.
À
3
[
12,13]
however these studies were found to
[14]
[29]
[30]
PC,
À
[14,15]
[31]
[32]
[33,34]
but clearly emphasized that this hypothesis was
PC2, PO, and PN.
However, it is not necessary to
look for HPCO in space, or mimic interstellar conditions. As
we show in this study, it is possible to generate metastable
solutions of this species with standard Schlenk line tech-
niques.
[
*] Dr. A. Hinz, Prof. J. M. Goicoechea
Department of Chemistry, University of Oxford
Chemistry Research Laboratory
12 Mansfield Road, Oxford, OX1 3TA (UK)
The method employed has been utilized repeatedly in the
E-mail: jose.goicoechea@chem.ox.ac.uk
past to generate HN since Gꢀnther, Meyer, and Mꢀller-
3
M. Sc. R. Labbow, Prof. A. Schulz
Institut fꢀr Chemie, Universitꢁt Rostock
Albert-Einstein-Strasse 3a, 18059 Rostock (Germany)
[35]
Skjøld introduced it in 1935.
More recently, improved
[36]
versions have been used for the generation of HN ,
HNCO, and HNSO.
3
[
6]
[37]
A solid mixture of stearic acid
Dr. C. Rennick
National Physics Laboratory
Hampton Road, Teddington, Middlesex TW11 0LW (UK)
and [Na(dioxane) ]PCO (x = 1) was heated in vacuo
x
[
38]
(Scheme 2), thereby releasing a gas which was condensed
into an NMR tube containing a solvent (toluene, dichloro-
methane or THF) in a bath of liquid nitrogen. The condensate
was yellow and upon warming to À788C dissolved in the
Supporting information and the ORCID identification number(s) for
Angew. Chem. Int. Ed. 2017, 56, 1 – 6
ꢀ 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1
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