Dechlorination of diphenyl chlorophosphate with tin and sodium 3,6-di-tert-butyl-ortho-semiquinones

Article abstract of DOI:10.1016/j.ica.2007.02.036

Dechlorination reactions of diphenyl chlorophosphate (PhO)₂P(O)Cl with 3,6-di-tert-butyl-ortho-semiquinone complexes of triphenyl tin, SQSn(Ph)₃ and sodium, SQNa have been investigated by electron spin resonance (ESR) both in solutions at 300 K and in solid phase at 77 K using mechanochemical activation. Paramagnetic 3,6-di-tert-butyl-ortho-semiquinone ligand (SQ) was used as spin probe to monitor changes in the Sn coordination sphere during the dechlorination reaction of (PhO)₂P(O)Cl and consecutive formation of tin chloride derivatives SQSnCl(Ph)₂, SQSnCl₂Ph, and SQSnCl₃. Their structure was revealed based on the analysis of hyperfine interaction constants due to ¹H nuclei in the 4,5-positions of the aromatic ring of the SQ ligand, hyperfine interaction constants due to ³⁵Cl and ³⁷Cl nuclei of chlorine atoms in the Sn coordination sphere, and hyperfine interaction constants due to ¹¹⁷Sn and ¹¹⁹Sn nuclei of the central metal ion. Interaction of SQSnCl₃ with (PhO)₂P(O)Cl leads to the formation of a meta-stable radical-anion complex [SQSnCl₄]^{{radical dot}-} P⁺(O)(OPh)₂, which transforms to SQSnCl₃?P(O)R₃, a stable adduct of SQSnCl₃ with dechlorinated phosphate of a general formula P(O)R₃. Analysis of solution dechlorination reaction products suggests the formation of diphenyl-phosphoryl radical (PhO)₂P^{{radical dot}}(O), which was not observed in solutions. Dechlorination of (PhO)₂P(O)Cl with sodium 3,6-di-tert-butyl-ortho-semiquinone SQNa can proceed in solid phase in liquid nitrogen at 77 K via mechanochemical activation using a ball mill. ESR analysis of the cryo-mechanochemical reaction showed the formation of the adduct of (PhO)₂P^{{radical dot}}(O) radical with 3,6-di-tert-butyl-ortho-quinone.

Full text of DOI:10.1016/j.ica.2007.02.036

Inorganica Chimica Acta 360 (2007) 3033–3039
www.elsevier.com/locate/ica
Dechlorination of diphenyl chlorophosphate with tin and sodium
3,6-di-tert-butyl-ortho-semiquinones
a,
b
a
a
Rakhim R. Rakhimov *, Alexander I. Prokof’ev , Ramatoulie Bah , Shannel A. Pegram ,
c
b
d
d
Jimmy S. Hwang , Alexander A. Khodak , Ivan A. Alexandrov , Aleksey I. Aleksandrov
a
Center for Materials Research and Department of Chemistry, Norfolk State University, Unit 3125, 700 Park Avenue, Norfolk, VA 23504-8060,
United States
b
Institute of Organoelement Compounds, Russian Academy of Sciences, Moscow 117813, Russia
c
Texas A&M University at Qatar, Education City, P.O. Box 23874, Doha, Qatar
Institute of Synthetic Polymer Materials, Russian Academy of Sciences, Moscow 117393, Russia
d
Received 20 September 2006; received in revised form 20 February 2007; accepted 24 February 2007
Available online 12 March 2007
Abstract
Dechlorination reactions of diphenyl chlorophosphate (PhO)2P(O)Cl with 3,6-di-tert-butyl-ortho-semiquinone complexes of triphe-
nyl tin, SQSn(Ph)3 and sodium, SQNa have been investigated by electron spin resonance (ESR) both in solutions at 300 K and in
solid phase at 77 K using mechanochemical activation. Paramagnetic 3,6-di-tert-butyl-ortho-semiquinone ligand (SQ) was used as
spin probe to monitor changes in the Sn coordination sphere during the dechlorination reaction of (PhO)2P(O)Cl and consecutive
formation of tin chloride derivatives SQSnCl(Ph)2, SQSnCl2Ph, and SQSnCl3. Their structure was revealed based on the analysis
1
of hyperfine interaction constants due to H nuclei in the 4,5-positions of the aromatic ring of the SQ ligand, hyperfine interaction
constants due to 35Cl and 37Cl nuclei of chlorine atoms in the Sn coordination sphere, and hyperfine interaction constants due to
117Sn and 119Sn nuclei of the central metal ion. Interaction of SQSnCl3 with (PhO)2P(O)Cl leads to the formation of a meta-stable
radical–anion complex [SQSnCl4]ꢀꢀ P+(O)(OPh)2, which transforms to SQSnCl3ꢁ ꢁ ꢁP(O)R3, a stable adduct of SQSnCl3 with dechlo-
rinated phosphate of a general formula P(O)R3. Analysis of solution dechlorination reaction products suggests the formation of
diphenyl-phosphoryl radical (PhO)2Pꢀ(O), which was not observed in solutions. Dechlorination of (PhO)2P(O)Cl with sodium 3,6-
di-tert-butyl-ortho-semiquinone SQNa can proceed in solid phase in liquid nitrogen at 77 K via mechanochemical activation using
a ball mill. ESR analysis of the cryo-mechanochemical reaction showed the formation of the adduct of (PhO)2Pꢀ(O) radical with
3,6-di-tert-butyl-ortho-quinone.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Phosphorus(V) compounds; Tin(IV) complexes; ortho-Quinone ligands; Semiquinone radicals; ESR spectroscopy
1. Introduction
compound in studies of the reactivity of organophosphorus
P(V) compounds and developing of methods for their
decomposition. One of the ways to decompose chemical
warfare agents like sarin and soman is their dehalogen-
ation. The existing methods for decomposition of chemical
warfare agents are based on the traditional solution chem-
istry [1,2], or heterogeneous reactions of liquid agents with
nanosize magnesium or calcium oxides [3,4], hydrolysis via
low-temperature microemulsions [5], and decomposition of
chemical warfare simulants by micellar iodoso- and
Diphenyl chlorophosphate (PhO)2P(O)Cl is a structural
analog of fluorophosphates (RO)(CH3)P(O)F, chemical
warfare agents known as sarin (R = CH(CH3)2) and soman
(R = CH(CH3)[C(CH3)3]). As a chemical warfare agent
simulant, diphenyl chlorophosphate can be used as a model
*
Corresponding author. Tel.: +1 757 8232297; fax: +1 757 8239054.
E-mail address: rrakhim@nsu.edu (R.R. Rakhimov).
0020-1693/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2007.02.036

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R.R. Rakhimov et al. / Inorganica Chimica Acta 360 (2007) 3033–3039
iodoxybenzoate [6]. Nucleophilic or free radical attacks on
the P-atom are desirable for deeper decomposition of orga-
nophosphorus P(V) compounds [1,7–9]. Mechanochemical
decomposition of toxic organic compounds is considered as
an emerging technology in the field of waste disposal.
Mechanochemical dehalogination of chlorinated organic
pollutants has been reported in several studies [10–15],
and the results show great potentials for environmentally
safer deposition of pollutants.
ortho-Quinones are very attractive molecules for
organic, element-organic, and coordination chemistry due
to their ability to form chelate complexes and exist in dif-
ferent oxidation forms including ortho-semiquinone radical
anions. Reactions of ortho-quinones with P(V) organic
compounds have been reviewed in Ref. [16], showing broad
variety of reaction pathways along with different transfor-
mations in phosphorus coordination. Organophosphorus
radicals, such as phosphoryl radicals, react with ortho-qui-
nones by possible addition to any position in the aromatic
system or to the oxygen atoms of ortho-quinones leading to
the formation of P-containing phenoxide or semiquinone
radicals [17]. One may expect that similar radical products
could be obtained by the reaction of semiquinone radicals
with initial P(V) organic compounds. It is of interest to
consider the reactivity of quinones with organophosphorus
P(V) compounds in terms of the ability of quinones to
decompose or transform toxic P(V) compounds to less
harmful chemicals.
(I). Diphenyl chlorophosphate was purchased from Sig-
ma–Aldrich with 99% purity mark. Deachlorination
reaction of (PhO)2P(O)Cl by SQSnPh3 radical (I) was
studied via consecutive changes in the electron spin reso-
nance (ESR) spectra of samples along with the formation
of 3,6-di-tert-butyl-2-diphenylchlorostannyl-oxyphenox-
ide, SQSnCl(Ph)2, radical (II), 3,6-di-tert-butyl-2-phen-
yldichlorostannyl-oxyphenoxide,
SQSnCl2Ph,
radical
(III), and 3,6-di-tert-butyl-2-trichlorostannyl-oxyphenox-
ide, SQSnCl3, radical (IV). As it is discussed below, rad-
ical (IV) forms an intermediate complex with the
(PhO)2P(O)Cl molecule. To study this complex formation
process, the radical (IV) was directly synthesized by the
exchange reaction of sodium 3,6-di-tert-butyl-ortho-semi-
quinone SQNa with tin tetrachloride SnCl4. Tin tetra-
chloride was purchased from Sigma–Aldrich with 99%
purity mark. Equimolar amounts of Q and SnCl4 were
dissolved in 0.1 M solution of NaOH in methanol, so
that SQNa was formed and reacted with SnCl4. Then
the radical (IV) was extracted to toluene for further
ESR investigation and study of its interaction with
(PhO)2P(O)Cl.
Concentrations of the radicals in solutions never
exceeded 10ꢀ4 M, to exclude concentration effects on line
broadening. Solutions of the radicals were placed in
quartz ESR tubes and deoxygenated at 10ꢀ2 atm. ESR
spectra were recorded with a Bruker EMX spectrometer
operating at 9.6–9.8 GHz of microwave frequency,
modulation frequency 100 kHz, microwave power
2 mW. For EPR spectra in liquid solutions we used
0.05 G modulation amplitude, which is far below the
lowest linewidth of 0.2 G observed for individual line
components. Hyperfine interaction constants and the line
widths were determined using WIN-EPR software from
Bruker.
In this paper we report on thermal dechlorination of
(PhO)2P(O)Cl by tin(IV) 3,6-di-tert-butyl-ortho-semiqui-
nones in solutions, and on cryo-mechanochemical dechlori-
nation of (PhO)2P(O)Cl by sodium 3,6-di-tert-butyl-ortho-
semiquinone.
2. Experimental
Cryo-mechanochemical activation of the reaction
between SQNa and (PhO)2P(O)Cl in liquid nitrogen at
77 K were performed using a Fritsch Vibratory Micro Mill
Pulverisette 0 with cryogenic camera. SQNa was first
obtained by 10 min mechanochemical treatment of solid
state mixture of 150 mg of NaOH and 2 mL of frozen
0.1 M solution of Q in toluene. Then 2 mL of frozen
0.1 M solution of (PhO)2P(O)Cl in toluene was added to
solid state reaction mixture at 77 K and exposed to addi-
tional 10 min mechanochemical treatment. The mechano-
chemical reaction products were placed in a quartz dewar
for ESR analysis.
To obtain tin and sodium 3,6-di-tert-butyl-ortho-semiq-
uinones, we used 3,6-di-tert-butyl-ortho-quinone (Q) and
3,6-di-tert-butyl-pyrocatechol (QH2) as initial reagents. Q
and QH2 were synthesized as described in Ref. [18]. Triphe-
nyl-tin 3,6-di-tert-butyl-ortho-semiquinone (SQSnPh3), i.e.
3,6-di-tert-butyl-2-triphenylstannyl-oxyphenoxide radical
(I), was obtained by the reaction of QH2 with triphenyl-
tin hydroxide in toluene according to the method by Steg-
mann et al. [19]
3. Results and discussion
ð1Þ
3,6-Di-tert-butyl-ortho-semiquinone (SQ) ligand is a
convenient spin probe to study coordination chemistry of
elements. In Fig. 1a, we present electron spin resonance
(ESR) spectrum of radical (I) in toluene at 300 K. This rad-
ical exhibits intramolecular transition of Sn(Ph)3 group
between two oxygen atoms,
Reaction of radical (I) with diphenyl chlorophosphate
(PhO)2P(O)Cl was investigated by adding different
amounts of (PhO)2P(O)Cl in toluene solution of radical

R.R. Rakhimov et al. / Inorganica Chimica Acta 360 (2007) 3033–3039
3035
phenoxide, SQSnCl(Ph)2, radical (II) that, in contrast to
radical (I), exhibits significantly lower rate of intramolecu-
lar transition of SnCl(Ph)2 group between two oxygen
atoms [20]. These leads to the coordination of Sn atom
only by one oxygen atom,
ð2Þ
ð3Þ
ð4Þ
At 300 K the transition is fast in an ESR time scale, i.e.
Sn(Ph)3 group is symmetrically located between oxygen
atoms, as shown in scheme (3), and the two protons at 4,5-
positions of the aromatic ring of the 3,6-di-tert-
butyl-ortho-semiquinone
ligand
are
equivalent
(aH,4 = aH,5 = 3.9 G). Satellite lines in the ESR spectra are
due to hyperfine interaction of the unpaired electron with
117Sn and 119Sn nuclear isotopes (both isotopes have I = 1/
2 nuclear spin with slightly different magnetic momentum).
In the case of radical (I) the corresponding hyperfine interac-
tion constants are aSn-117 = 12.0 G and aSn-119 = 12.75 G.
We chose radical (I) as a reagent towards (PhO)2P(O)Cl
and to see the changes in the ESR spectrum during the
reaction. The ESR spectrum in Fig. 1a, was obtained for
radical (I) in toluene. In Fig. 1b, we present the ESR spec-
trum observed after adding ꢂ0.1 M of (PhO)2P(O)Cl to the
original toluene solution of radical (I). This ESR spectrum
belongs to 3,6-di-tert-butyl-2-diphenylchlorostannyl-oxy-
and the two protons at 4- and 5-positions of the aromatic
ring of the 3,6-di-tert-butyl-ortho-semiquinone ligand are
non-equivalent (aH,4 = 4.9 G, aH,5 = 2.9 G). Hyperfine
interaction constants due to central metal ion are
aSn-117 = 15.9 G and aSn-119 = 16.7 G. The formation of
radical (II) is a result of dechlorination of (PhO)2P(O)Cl
by radical (I) according to scheme (4). The Sn–Cl chemical
bond in radical (II) lies in the p-plane of the 3,6-di-tert-bu-
tyl-ortho-semiquinone ligand, so that no hyperfine interac-
tion constant is observed due to chlorine [20].
In Fig. 1c, we present the ESR spectrum observed after
further increase of the concentration of (PhO)2P(O)Cl in
toluene to ꢂ0.5 M. This ESR spectrum shows the forma-
tion of 3,6-di-tert-butyl-2-phenyldichlorostannyl-oxyphen-
oxide, SQSnCl2Ph, radical (III), for which hyperfine
interaction due to one of the two chlorine atoms is seen
aCl = 0.7 G (nuclear spin I = 3/2 for both 35Cl and 37Cl):
a
b
c
d
ð5Þ
3425
3430
3435
3440
3445
3450
3455
Magnetic Field, G
Fig. 1. ESR spectra of 3,6-di-tert-butyl-ortho-semiquinone complexes of
tin recorded at 300 K during the reaction of SQSn(Ph)3 with (PhO)2-
P(O)Cl: (a) ESR spectrum of the initial SQSn(Ph)3 radical (I) in toluene;
(b) ESR spectrum of the SQSnCl(Ph)2 radical (II), a product of the
dechlorination reaction (4); (c) ESR spectrum of the SQSnCl2Ph radical
(III), a product of the dechlorination reaction (5); (d) ESR spectrum of the
SQSnCl3 radical (IV), a product of the dechlorination reaction (6) when
excess amount of (PhO)2P(O)Cl was used.
The Cl atom that contributes to the quartet hyperfine
structure in the ESR spectrum of radical (III) is located
off the p-plane of the 3,6-di-tert-butyl-ortho-semiquinone
ligand. This is in accordance with the hyper-conjugation

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R.R. Rakhimov et al. / Inorganica Chimica Acta 360 (2007) 3033–3039
mechanism of hyperfine interaction in organic p-radicals
[21]. Compared to radical (II), the Sn atom in radi-
cal (III) experiences more symmetrical oxygen coordina-
tion, since hyperfine interaction constants due to two
protons in the aromatic ring of the ligand are close to
each other (aH,4 = 3.95, aH,5 = 3.75 G). However, the
structure of the radical (III) is still asymmetric, and smaller
difference in proton hyperfine interaction constants
Da = aH,4 ꢀ aH,5 = 0.2 G is typical for ionic complexes
[22], and indicates that the O–Sn chemical bond is more po-
lar in radical (III). This is also supported by significantly
lower value of hyperfine interaction constant with tin iso-
topes, aSn-117 ꢃ aSn-119 = 6.0 G. It may seem possible that
the ESR spectrum in Fig. 1c represent a dynamic rather
than a static spectrum due to migration of the Sn atom be-
tween two oxygen atoms of the paramagnetic ligand. How-
ever, in contrast to radical (II), the ESR spectrum of
radical (III) is temperature independent and indicates the
absence of the migration of the Sn atom in this radical.
In Fig. 1d, we present the ESR spectrum recorded after
we added an excess amount of (PhO)2P(O)Cl to the solu-
tion containing radical (III). In this ESR spectrum a septet
structure due to hyperfine interaction with 2 equiv. chlorine
atoms is seen, aCl = 0.6 G . This shows the placement of
one more chlorine atom in the Sn coordination sphere
and the formation of 3,6-di-tert-butyl-2-trichlorostannyl-
oxyphenoxide, SQSnCl3, radical (IV),
ð7Þ
At higher temperatures in toluene the ESR spectrum of this
radical shows hyperfine interaction with all three chlorine
atoms due to intramolecular rotation of SnCl3 group. In
some solvents, where solvent molecules L are able to coor-
dinate Sn atom, radical (IV) can have two types of octahe-
dral structures [20],
ð8Þ
Octahedra of the type A were observed in tetrahydrofuran
(THF) and liquid phosphates of the general formula
P(O)(OR)3, while octahedra of the type B were observed in
dimethyl formamide, acetonitrile, and tertiary amines [20].
In the presence of LiCl along with crown-ether in toluene,
radical (IV) forms octahedral radical–anion complex [20],
ð9Þ
ð6Þ
The Sn atom is symmetrically located between two oxygen
atoms, since aH,4 = aH,5 = 3.70 G. Smaller value of
aSn-117 ꢃ aSn-119 = 6.0 G again confirms more polar O–Sn
chemical bond.
Radical (IV) has been previously studied in Refs. [20,23].
This radical can be directly obtained by the reaction of 3,6-
di-tert-butyl-ortho-semiquinone radical anion with tin tet-
rachloride SnCl4. Depending on the solvent and tempera-
ture, the ESR spectrum of radical (IV) shows hyperfine
interaction due to either one, two or three chlorine atoms.
In toluene at room temperature the ESR spectrum of rad-
ical (IV) shows hyperfine interaction due to only one chlo-
rine atom suggesting the tetragonal–pyramidal structure,
The parameters of the ESR spectrum in Fig. 1d are exactly
the same as for the octahedral radical–anion complex
above [20], and represents radical (IV) in (PhO)2P(O)Cl
solvent. This is confirmed by ESR spectra shown in
Fig. 2. In Fig. 2a, we present the ESR spectrum of radical
(IV) in toluene obtained by the direct reaction of 3,6-di-
tert-butyl-ortho-semiquinone radical anion with tin tetra-
chloride SnCl4. After vaporization of the toluene solvent
from the ESR tube in vacuum, we dissolved radical (IV)

R.R. Rakhimov et al. / Inorganica Chimica Acta 360 (2007) 3033–3039
3037
This complex is unstable, and transformation of the ESR
spectrum from Fig. 2b and c shows that the original
(PhO)2P(O)Cl solvent compound transforms to a dechlori-
nated phosphate P(O)R3, so that radical SQSnCl3 forms a
stable adduct SQSnCl3ꢁ ꢁ ꢁP(O)R3 with octahedral structure
of the type A. This transformation and the sequence of
transformations from radical (I) to radical (IV) suggests
the formation of diphenyl-phosphoryl radical (PhO)2Pꢀ(O),
which was not observed during the solution dechlorination
process. This radical could have reacted with 3,6-di-tert-
butyl-ortho-semiquinone ligand by addition to the aro-
matic system of the ligand or to its oxygen atom. In solu-
tions, however, we have not observed any additional
radical products containing the phosphoryl group. Follow-
ing the dechlorination reaction, the (PhO)2Pꢀ(O) radical
and phenyl radical Phꢀ may recombine and form phospho-
nate P(O)(OPh)2Ph or other similar diamagnetic products.
We have also investigated a solution reaction of
sodium 3,6-di-tert-butyl-ortho-semiquinone SQNa with
(PhO)2P(O)Cl in methanol and THF. The ESR analysis
of this system showed only rapid and complete disappear-
ance of the ESR spectrum of 3,6-di-tert-butyl-ortho-semi-
quinone radical anion, with no observation of new
paramagnetic products. Sodium chloride was identified as
one of the reaction products. Again, in solution no new sta-
ble radical products were observed, although the formation
of sodium chloride may indicate the formation of the
(PhO)2Pꢀ(O) radical in the initial act of the reaction.
To stabilize the intermediate products of the reaction,
we tried to see if the reaction between 3,6-di-tert-butyl-
ortho-semiquinone radical anion and (PhO)2P(O)Cl can
proceed in solid phase with mechanochemical activation
at low temperature, 77 K in liquid nitrogen. We first found
that sodium 3,6-di-tert-butyl-ortho-semiquinone radical–
anion complex can be obtained by mechanochemical treat-
ment of a solid mixture of 3,6-di-tert-butyl-ortho-quinone
and NaOH, as described in Section 2. After 10 min of
mechanochemical treatment of this mixture at 77 K, we
observed a singlet ESR spectrum with the g-factor value
g = 2.002 and the linewidth D = 12 G. After dissolving
the reaction products in THF at room temperature we
obtained the ESR spectrum of sodium 3,6-di-tert-butyl-
ortho-semiquinone radical–anion complex SQNa, with
aH,4 = aH,5 = 3.47 G and aNa = 0.57 G (hyperfine interac-
tion due to 23Na, nuclear spin I = 3/2). Therefore, we con-
clude that sodium 3,6-di-tert-butyl-ortho-semiquinone
radical–anion complex is formed during cryo-mechano-
chemical reaction between 3,6-di-tert-butyl-ortho-quinone
and NaOH. In the second step of mechanochemical treat-
ment, we added frozen at 77 K solution of (PhO)2P(O)Cl.
Then the reaction mixture of sodium 3,6-di-tert-
butyl-ortho-semiquinone radical–anion complex and
(PhO)2P(O)Cl was exposed to mechanochemical treatment
at 77 K for 10 min. The ESR spectrum of the reaction
products at 77 K is shown in Fig. 3. The single line in the
center of the spectrum corresponds to the remaining
sodium 3,6-di-tert-butyl-ortho-semiquinone radical–anion
a
b
c
3430
3440
3450
Magnetic Field, G
Fig. 2. ESR spectra of the SQSnCl3 radical (IV): (a) in toluene; (b) in
(PhO)2P(O)Cl solvent, initial ESR spectrum of unstable radical–anion
complex (V); (c) final ESR spectrum that shows the formation of a stable
adduct SQSnCl3ꢁ ꢁ ꢁP(O)R3 with octahedral structure of the type A.
in (PhO)2P(O)Cl solvent and obtained the ESR spectrum
shown in Fig. 2b, which is exactly the same as the ESR
spectrum obtained by the sequence of transformations of
radical (I) in the presence of (PhO)2P(O)Cl.
It is important to note that intensities of experimental
ESR spectra in Figs. 1d and 2b are orders of values lower
than the intensities of the ESR spectra for precursor radi-
cals (I)–(III). We found that the ESR spectrum in Fig. 2b
disappears within couple of hours and final ESR spectrum
of the sample is shown in Fig. 2c. It implies that the low
intensity ESR spectra in Figs. 1d and 2b may represent
steady-state concentration of an intermediate form of the
radical (IV) in (PhO)2P(O)Cl solvent.
As it was noticed above, the ESR spectrum of radical
(IV) in P(O)(OR)3 solvents reveals hyperfine interaction
only with one chlorine atom. The fact that in (PhO)2P(O)Cl
solvent we observe hyperfine interaction with two chlorine
atoms, indicates that radical (IV) forms a radical–anion
complex with (PhO)2P(O)Cl structurally similar to the
complex with LiCl [20],
ð10Þ

3038
R.R. Rakhimov et al. / Inorganica Chimica Acta 360 (2007) 3033–3039
complex, while the doublet ESR spectrum with a splitting
of about 50 G corresponds to a new paramagnetic product.
Only the presence of phosphorus atom in this paramag-
netic product can explain such a large hyperfine interaction
constant (31P, nuclear spin I = 1/2). The value of aP ꢃ 50 G
is typical for adducts of phosphoryl radicals with 3,6-di-
tert-butyl-ortho-quinone [17], when phosphoryl radicals
attack the carbon atom in the 4th position of the aromatic
system,
aP
3280
3320
3360
3400
3440
ð11Þ
Magnetic Field, G
Hyperfine interaction constants due to protons of the aro-
matic system in these types of radicals is 610 G [17], and can-
not be resolved within larger line broadening of the ESR
spectrum in Fig. 3. The formation of such adduct during
the mechanochemical process can be represented as
Fig. 3. ESR spectrum of the products of cryo-mechanochemical reaction
between SQNa and (PhO)2P(O)Cl at 77 K. A doublet with the hyperfine
splitting aP ꢃ 50 G is due to the radical (VI). A single ESR line is due to
SQNa.
dechlorination. In our future work we plan to study the
kinetics of all solution dechlorination reactions (4)–(6)
described above, and report it in a separate paper. Our
present data on solution reactions already show that
dechlorination of diphenyl chlorophosphate by tin 3,6-di-
tert-butyl-ortho-semiquinone complexes can be achieved
by using small initial amounts of tin complex. Observation
of an intermediate complex (V), and its transformation to
final radical (IV) with the type A octahedral structure with
L = P(O)R3 implies catalytic mechanism of dechlorination
reaction.
ð12Þ
Cryo-mechanochemical dechlorination of diphenyl chlo-
rophosphate
by
3,6-di-tert-butyl-ortho-semiquinone
deserves special attention. Deactivation of organophospho-
rus chemical warfare compounds at low temperatures is a
challenging problem [5,24], due to limited solubility of
the compounds at cold-weather operations. When toxic liq-
uids such as chlorophosphates are being decomposed
below their freezing point, the low-temperature solid state
chemical reactions may be less harmful. Therefore, mecha-
nochemical approach to decompose organophosphorus
compounds can provide new environmentally friendly
decontamination methods.
We found that radical (VI) is unstable at room tem-
perature both in solid phase and in toluene solution,
since we were not able to record any ESR spectra after
the mechanochemical reaction products were warmed
up from 77 K to room temperature. Therefore, instability
of the radical adduct (VI) makes it impossible to observe
phosphoryl radicals during thermal dechlorination reac-
tions in solutions. It should be noted that radical (VI)
cannot be obtained by mechanochemical treatment of
the mixture of Q and (PhO)2P(O)Cl, i.e. it is 3,6-di-
tert-butyl-ortho-semiquinone radical anion that decom-
poses the chlorophosphate molecule.
Acknowledgements
Financial support for this work was provided by the US
Army Research Office, Grant W911NF-05-10470. Two of
the authors, R.B. and S.A.P gratefully acknowledge sup-
port for graduate (R.B.) and undergraduate (S.A.P.) re-
search assistantships provided under this grant at
Norfolk State University. J.S.H gratefully acknowledges
the support from Texas A&M University at Qatar.
4. Conclusions
Tin and sodium 3,6-di-tert-butyl-ortho-semiquinones
decompose diphenyl chlorophosphate by means of its

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