Phosphonium-phosphates/thiophosphates: Ionic liquids or liquid ion pairs? NMR spectroscopic classification

Article abstract of DOI:10.1016/j.tetlet.2017.05.031

Structurally unique ionic liquids phosphonium-phosphate and phosphonium-thiophosphate, having both phosphorus based counter ions, in which the anionic part is represented by di-aryl phosphate or di-aryl thiophosphate and cations been tetraalkylphosphonium groups, behave differently in terms of their NMR behaviour. While phosphonium-phosphates show significant changes in its ¹H, ¹³C and ³¹P NMR chemical shifts vis. á vis. corresponding chemical shifts for a physical mixture of tetraalkylphosphonium bromide and di-aryl phosphate, phosphonium-thiophosphates behave almost similarly in terms of NMR with their synthetic precursors, hence indicating phosphate-phosphonium interaction has a significant covalent component resembling more to a liquid ion pair while thiophosphate-phosphonium interaction is principally ionic in nature. Translational diffusion behavior studied by PFGSE-NMR experiments and ionic conductivities of these ionic liquids in chloroform solution corroborated the hypothesis. The effect of variable alkyl chain length in phosphonium cation is effectively observed in the extent of ion association. Results of this study may provide insight into the solution state behavior of these ionic liquids, would help to classify those in terms of their strength of ion association and thus potential application thereof.

Full text of DOI:10.1016/j.tetlet.2017.05.031

Tetrahedron Letters 58 (2017) 2460–2464
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Phosphonium-phosphates/thiophosphates: Ionic liquids or liquid ion
pairs? NMR spectroscopic classification
⇑
Sujit Mondal , Tanmay Mandal, Meeta Sharma, Ravindra Kumar, Ajay K. Arora,
Veena Bansal, J. Christopher, G.S. Kapur
Indian Oil Corporation Limited, R&D Centre, Sector-13, Faridabad 121007, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Structurally unique ionic liquids phosphonium-phosphate and phosphonium-thiophosphate, having both
phosphorus based counter ions, in which the anionic part is represented by di-aryl phosphate or di-aryl
thiophosphate and cations been tetraalkylphosphonium groups, behave differently in terms of their NMR
Received 7 April 2017
Revised 7 May 2017
Accepted 11 May 2017
Available online 12 May 2017
1
13
31
behaviour. While phosphonium-phosphates show significant changes in its H, C and P NMR chemical
shifts vis. á vis. corresponding chemical shifts for a physical mixture of tetraalkylphosphonium bromide
and di-aryl phosphate, phosphonium-thiophosphates behave almost similarly in terms of NMR with their
synthetic precursors, hence indicating phosphate-phosphonium interaction has a significant covalent
component resembling more to a liquid ion pair while thiophosphate-phosphonium interaction is prin-
cipally ionic in nature. Translational diffusion behavior studied by PFGSE-NMR experiments and ionic
conductivities of these ionic liquids in chloroform solution corroborated the hypothesis. The effect of
variable alkyl chain length in phosphonium cation is effectively observed in the extent of ion association.
Results of this study may provide insight into the solution state behavior of these ionic liquids, would
help to classify those in terms of their strength of ion association and thus potential application thereof.
Ó 2017 Elsevier Ltd. All rights reserved.
Keywords:
NMR
DOSY NMR
Ionic liquid
Ion association
Liquid ion pair
Phosphonium phosphate
Phosphonium thiophosphate
Introduction
It has been demonstrated that tetraalkylphosphonium cation
based ILs are thermally more stable than their tetraalkylammo-
1
5
Ionic liquids (ILs) have been used as green solvents, primarily
not only as a replacement of conventional media in chemical pro-
cesses but also for its unique properties to mimic the media in liv-
ing systems, thus providing specially designed environmentally
nium counterparts, but very few study have been reported on
1
0
phosphonium phosphate and phosphonium thiophosphate ILs.
Density, viscosity and conductivity of few commercial
tetraalkylphosphonium ILs have been studied by Vaughan et al.16
Studies on sweetener anions such as saccharinate, acesulfamate
and cyclamate to achieve a range of phosphonium ILs have been
1
–3
benign reaction system.
It is well documented that the chemical
and physical properties of ILs can be tuned by varying the size and
structure of the component ions.4 Room temperature ILs (RTILs)
in which the inorganic anions are replaced by large organic anions
have been gaining considerable attention as they represent a dif-
–8
17
18
described by Davis Jr. and co-workers , and Pernak et al. Con-
cept of intermediate compounds between true ionic liquids and
true molecular liquids has been appropriately described by Angell
1
9
9
ferent class of compounds between true ‘‘molecular” and true
and co-workers and Fraser et al. with a focus on their electrical
transport properties in terms of deviation from Walden plot. They
concluded that these phosphonium ILs with sweetener, charge dif-
fused anions are strongly ion-paired or ion-associated, thus lie
between true ‘‘molecular” and true ‘‘ionic” liquids. It has been
9
‘
‘ionic” liquids. Unlike most other conventional ILs that have very
low solubility in nonpolar fluids, this class of compounds are fully
miscible with various hydrocarbon oils, show special properties
such as antiwear, antioxidant, antiscuffing when blended with
lubricating oils, potential dispersive media for nano-catalyst,
media in electrochemical devices such as rechargeable lithium bat-
teries, fuel cells, electrochemical capacitors, and photo-electro-
9
shown that for tetraalkylphosphonium ILs with sweetener organic
anions, the ion association increases with increasing alkyl chain
length in the phosphonium cation keeping the anion intact. Also
symmetrical anionic donor has greater ion association
than unsymmetrical donor with same phosphonium cation.9
Effect of structures, especially of variable alkyl chain length in
phosphonium moiety on various transport properties of aprotic
9
–14
chemical solar cells and benign solvents for organic chemistry.
⇑
Corresponding author.
E-mail address: mondals3@indianoil.in (S. Mondal).
http://dx.doi.org/10.1016/j.tetlet.2017.05.031
040-4039/Ó 2017 Elsevier Ltd. All rights reserved.
0

S. Mondal et al. / Tetrahedron Letters 58 (2017) 2460–2464
2461
heterocyclic anion (AHA)-phosphonium ILs has recently been dis-
cussed by Liyuan Sun et al.20 Increase in interactive forces between
the ions with increasing alkyl chain length in the phosphonium
cation was one of their conclusions. They also concluded that the
macroscopic properties of RTILs are a combined result of both
the electrostatic interactions among the ionic species and the van
der Waals forces. Transport properties and aggregation behaviour
of various kind of imidazolium ILs in dilute non aqueous solution
have most recently been studied by Cade et al.14 They have con-
cluded that maximum average solute radii, thus the extent of
aggregation of these ILs, followed an order where chloroform lies
3 6 5 2 2
at the top among four solvents studied, viz. CHCl , C H Cl, CH Cl
and THF.
Nuclear magnetic resonance (NMR) spectroscopy has revolu-
tionized the world of chemistry, biochemistry, material science,
biology and even the medical sciences by virtue of its pragmatic
and multifaceted applications, especially in terms of characterizing
molecules-deducing simple to exceptionally complex structures,
and predicting properties of materials. In spite of its vast domain
of application, NMR, especially solution state NMR has limitations
predicating weaker intra- and intermolecular interactions, like van
der-Waals, dipole-dipole, anisotropic interactions, weak H-bonds,
cation-anion electrostatic interactions or ion association etc., pri-
marily, because in solution these forces generally get overpowered
by relatively stronger solvation energy and other interactions. Rea-
son being that the ion association in neat compounds may not be
observed or studied in solution could thus be well explained.
In the current work of NMR spectroscopic characterization of
various kind of tetraalkylphosphonium diaryl phosphate (PP) and
diaryl thiophosphate (PTP) ILs it has been discovered that few ILs
show stronger ion association, even in solution and can be termed
as liquid ion pair. The ion association was studied by solution state
NMR, and confirmed along with 1D 1H and C NMR by diffusion
ordered spectroscopy (1D & 2D DOSY).21 The hypothesis thus pro-
posed by studying the NMR behaviour of theses ILs was also cor-
roborated by their transport properties.
Fig. 2. Partial 1H NMR Spectrum of (A) Diaryl Phospahate 2a and (B) IL-1.
dent (Fig. 3). Though a significant alteration in the pattern of the
aromatic protons and carbons observed in the formation of PP, a
dramatic upfield shift for H4 and downfield shift for C1 have been
phenomenal. The extent of upfield shift for H4 and downfield shift
1
13
for C1 in their corresponding H and C NMR spectra with
different phosphonium cations have been tabulated in Table 1.
Interestingly the effect of the alkyl chain length in the
tetraalkylphosphonium group has been transmitted to the aro-
matic protons and carbons indicating the presence of possible
ion association in these PPs. It can be argued that increasing the
13
alkyl chain length in phosphonium cations is associated with
greater change in chemical shifts, as evident by both 1H and
13
C
NMR, thus have greater ion association. It is worthy to mention
1
here that this effect is being reflected equivalently in both
H
1
3
and C NMR and was not accounted by mere deprotonation of acid
a as confirmed by studying a dilute solution of its potassium salt.
2
Result and discussion
Significant downfield shift in the signals of methylene protons
attached to the phosphorus atom of the phosphonium moiety as
well as all other methylene and methyl signals of butyl groups
have been observed indicating the effect of shielding aromatic ring
current on nearby phosphonium substituents. This perhaps proves
the concept of associated ion pair that the anion resides very close
Numerous PP and PTP (Fig. 1) with variable alkyl chain in the
22
phosphonium ions were synthesized (see Supporting informa-
tion) and systematically investigated by solution state NMR in
order to establish their structures and possible ion association in
them in solution. It has been noticed that 1H NMR spectra for PP
and an equi-molar physical mixture of the two reacting compo-
9
to the cationic centre , in this case in solution as well. Changes in
the chemical shifts occur near to the vicinity of the ionic centre
indicated possible strong ion paring in PP. The effect of change in
nents-tetraalkylphosphonium bromide and diaryl phosphate has
1
1
13
a little differences in the chemical shifts in their respective
H
chemical shift values in H and C NMR in formation of IL does
not depend on the concentration of the ILs in solution, and also
independent of temperature up to 50 °C.
3
1
1
and P NMR spectra. However, spectral pattern in their H NMR,
especially, at the aromatic region-phenol ring protons has a dra-
1
3
matic shift (Fig. 2). C NMR analysis showed interesting observa-
tions- shift in several of the signals of the phenol ring carbons in
the product PP vis. á vis. reacting diaryl phosphate have been evi-
In order to understand the effect of alkyl chain length in the
phosphonium moiety on the extent of ion association in relative
quantitative terms a parameter degree of ion association in chloro-
form solution (rIA) for PPs has been defined with respect to a
hypothetical zwitterions type compound ZI (Fig. 4) with complete
covalent bonds among two oxygen and two phosphorus atoms. The
O
P
O
R
O
P
O
R
1
3
Br
C chemical shift values for this hypothetical compound have
n-Bu
P
R'
3
HX
O
n-Bu
P
R'
X
O
+
3
13
been observed using ChemDraw Ultra 12.0 version. The C1
C
1
value of this hypothetical compound by ChemDraw Ultra 12.0
was found to be 157.1 ppm. The corresponding C chemical shift
R' = C15
H
31 = [P4,4,4,15] (1a)
13
R
R
=
=
=
=
C
C
C
C
14
H
H
29 = [P4,4,4,14] (1b)
21 = [P4,4,4,10] (1c) 2a, X = O
2b, X = S
ILs; X = O = [P4,4,4,Y] [OOP(OAr)
2
] (PP)
value for 2a was recorded 150.6 ppm. The former value was con-
sidered for 100% associated ions while the later with zero ion asso-
ciation. The relative degree of ion association was thus estimated
for all PPs and has been tabulated in Table 1. It is clearly evident
that the ion association increases with increasing alkyl chain
10
H
H
13 = [P4,4,4,6] (1d)
= [P4,4,4,4] (1e)
X = S = [P4,4,4,Z] [SOP(OAr) ] (PTP)
2
6
4
9
R = C15H
31
Y = 15, 14, 10, 6, 4; Z = 15, 10, 6, 5, 4
IL-1, 2, 3, 4,
5 ; IL-6, 7, 8, 9,10
[
P
4,4,4,15] denotes tributyl (4) pentadecyl (15) phsophonium and so on...
4 9
length in the phosphonium cation (rIA = 20.0 for R = C H and
Fig. 1. Phosphonium Bromides, Diaryl Phosphates, PP and PTP Studied.

2
462
S. Mondal et al. / Tetrahedron Letters 58 (2017) 2460–2464
Fig. 3. Partial 13C NMR Spectrum of (A) IL-1 and (B) Diaryl Phospahate 2a.
Table 1
Degree of Ion Association (
In case of diaryl thiophosphates PTP there has been surprising
1
13
r
): Effect of Alkyl Chain Length (R) on
r
.
silence in the behavior of both H and C NMR- no change in pat-
1
13
IA* (by 13C)
r
tern in H NMR or chemical shift values in C NMR signals in for-
mation of ionic liquids have been observed. The only change
associated with the formation of product PTP is significant down-
field shift in the signals of methylene protons attached to the phos-
phorus atom in the phosphonium moiety with respect to the same
in its parent phosphonium salt. The said methylene protons
showed marginal upfield shift to 2.42 ppm in IL-6 and 2.40 ppm
in IL-7 to significant upfield shift to 2.24 ppm in IL-8 from corre-
sponding value ꢀ2.45–2.47 ppm in the free phosphonium bro-
mides (see Supporting information). The significantly large-sized
R=
Chemical Shift (d)
1H (H4)
13C (C1)
C
C
C
C
C
15
14
10
H
H
H
31 (IL-1)
29 (IL-2)
21 (IL-3)
6.76
6.78
6.78
6.82
6.87
153.9
153.7
153.5
152.7
151.9
50.8
47.7
44.6
32.3
20.0
6
H13 (IL-4)
4
H
9
(IL-5)
*
estimated values; repeatability in d ±0.05 (13C) ±0.02 ( H) ppm.
1
–
thiophosphate anion having the S donor might not fit in the catio-
1
28.4
117.4
50.6
125.5
120.7
1
29.9
113.1
157.1
nic cavity of phosphonium cation giving rise insignificant ion asso-
1
17.6 128.4
R'
31
Bu
P
O
O
R'
ciation. As expected no significant alteration for P chemical shift
Bu
Bu
δ+
1
22.2
H
145.2
1
43.1
13.8
O
1
Bu Bu
O
O
P
O
C1
4
119.4
1
δ−
153.9
1
P
O
Bu
P
has been noticed in the formation of thiophosphate ionic liquids-
the values remained at d 53.0 ppm for thiophosphate and d
32.9 ppm for phosphonium phosphorus; both for PTPs and their
precursors diaryl thiophosphate and phosphonium salts.
P
O
OAr
143.7
R'
20.4
HO
R
OAr
a (DAP)
OAr
ILs
C
15
H
31
2
ZI
For R= C15H
31
1
00
Presence of strong ion association in IL-1 has been unambigu-
ously confirmed while the constituent ions, the tetraalkylphospho-
nium and diaryl phosphate diffuse together in chloroform at a
Relative Degree of Ion Association, σ
x (δIL-δDAP)
IA=
ZI = 157.1; δDAP = 150.6; DAP = Di-aryl phosphate (2a)
(δZI-δDAP
)
δ
À10
À10
2
significantly slower rate at 4.9 Â 10
m /s than its precursors-
Fig. 4. Degree of Ion Association (r).
2
the diaryl phosphate 2a at 8.2 Â 10
m /s and tetraalkylphos-
À10
2
phonium bromide [P4,4,4,15]Br at 9.4 Â 10
m /s under identical
conditions (Fig. 5). On the other hand constituent of thiophosphate
r
IA = 50.8 for R = C15H31). It is necessary to mention that in spite of
13
ionic liquid IL-6 shows differential diffusion coefficients of
limitation, ChemDraw prediction of C chemical shift values for 2a
matches almost exactly with that of the experimental values and
the use of ZI is purely for a comparative purpose- the absolute
change in chemical shift values were merely normalized against
a hypothetical ZI.
À10
2
À10
2
2
.7 Â 10
m /s for thiophosphate and 3.5 Â 10
m /s for phos-
phonium cation. Relatively slower diffusion for thiophosphate as
well as for tetraalkylphosphonium cation can be attributed to the
larger size of thiophosphate and presence of a weak ion association
between them (Fig. 6). While compared to free phosphonium bro-
mide [P4,4,4,15]Br, the significant lower translational diffusion coef-
ficient for the phosphonium cation in IL-6 could also be attributed
to the presence of strong hydrophobic interaction (van der
The 31P NMR chemical shifts for phosphates vary from d
À10.4 ppm in IL-1 to À12.7 in IL-5 while the phosphonium phos-
phorous was found to be remained consistent at d 32.9 ppm for
all of them. The corresponding 31P chemical shifts for diaryl phos-
2
0
Waals) between the substituents of phosphonium cation and
phosphate anion. The diffusion coefficients for various kinds of
phate and tetraalkylphosphonium bromides were found to be at d
À9.8 and 32.9 ppm respectively.

S. Mondal et al. / Tetrahedron Letters 58 (2017) 2460–2464
2463
Fig. 5. 1H DOSY NMR Spectra of (A) Equimolar Mixture of 2a and [P4,4,4,15]Br and (B) IL-1 (Temp = 25 °C, Conc. = 0.039–0.040 M).
Fig. 6. 1H DOSY NMR Spectrum of IL-6 (Temp = 25 °C, Conc. = 0.043 M).
protons in IL-1, IL-3, IL-6, IL-7 and an equimolar mixture of 2a and
4,4,4,15]Br have been derived by 1D DOSY curve fitting analysis
and tabulated in the Supporting information. It is interesting to
notice that the diffusion coefficients for most of the protons (in
both phosphonium and phosphate parts) in IL-1 as well as in IL-
solutions have been studied. The selection of equimolar chloroform
[
P
solution (of ꢀ0.06 and 0.04 M) for each case has been in the line as
1
4
reported in literature and in order to make both diffusion and
conductivity analyses comparable. The result is summarized in
9
Table 2. As expected the conductivities for bromides vary from
3
have been found to be close enough-it was concluded that they
diffuse together with strongly contact ion paired forms. However
in IL-6 and IL-7 characteristic protons for phosphonium and thio-
phosphate moieties show significantly differential diffusion coeffi-
cients that they appear to be distinct moieties in solution or behave
like solvent separated ion pairs. Effect of temperature and concen-
tration on the diffusion behaviour have also been studied and
described in the Supporting information. The rate of diffusion
increases almost linearly with increasing temperature. However,
the similar diffusion coefficient values for protons characteristic
to phosphonium and phosphate moieties in PP ILs indicated intact
ion association over a range of temperature from 25 to 50 °C
Table 2
Transport Properties of Various Ionic Liquids.
À1
IL
Conductivity (mS cm , at 25 °C)
0
.06 M Solution in CHCl
3
0.04 M Solution in CHCl
3
[P4,4,4,15]Br
26.1
28.4
37.9
38.9
42.4
42.8
4.7
12.3
28.4
13.1
18.9
30.6
11.3
12.3
16.6
16.8
18.8
18.9
2.5
6.4
13.8
6.2
[P4,4,4,14]Br
[P4,4,4,10]Br
[P4,4,4,6]Br
[P4,4,4,5]Br
[P4,4,4,4]Br
IL-1
IL-3
IL-4
IL-6
(Table 5S). It is worth mentioning that at higher concentration both
the components (anion and cation) in PTP get slowed down and
diffuse together instead of at differential rates in dilute solution
IL-7
IL-8
8.1
15.0
à
(Table 6S).
The ionic conductivities of various tetraalkylphosphonium bro-
mides and PP/PTP ionic liquids as dilute equimolar chloroform
Repeatability in conductivity measurement: RSD = 0.04–0.11 (three different
readings for each measurement).

2
464
S. Mondal et al. / Tetrahedron Letters 58 (2017) 2460–2464
3. Inamuddin AM. (eds.) Green Solvents II: Properties and Applications of Ionic
2
6.1 mS/cm for [P4,4,4,15]Br to 42.8 mS/cm for [P4,4,4,4]Br replicating
Liquids, Dordrecht, 2012, Springer Science+Business Media. (ii) Rogers RD,
Seddon KR. (eds.) Ionic Liquids as Green Solvents, Washington, DC., 2003,
American Chemical Society.
the association in solution as well. For ionic liquid IL-1, IL-3, and
IL-4 the conductivities have been found to be 4.7, 12.3 and
2
8.4 mS/cm respectively. These large variations in the conductivi-
4. Welton T. Chem Rev. 1999;99:2071–2084.
5
6
.
.
Wasserscheid P, Keim W. Angew Chem Int Ed. 2000;39:3772–3789.
Thomas MF, Li L-L, Handley-Pendleton JM, van der Lelie D, Dunn JJ, Wishart JF.
Bioresour Technol. 2011;102:11200–11203.
ties could not be attributed only on the variation in their sizes;
the stronger ion association with increasing alkyl chain also plays
a significant role. For ionic liquids IL-1 and IL-6 the conductivities
have been found to be 4.7 and 13.1 mS/cm respectively. It can be
assumed that much diffuse, bulkier thiophosphate anion of IL-6
would move slower than phosphate anion in IL-1 for equimolar
solutions and should thus provide higher conductivity for IL-1. Like
diffusion studies the conductivities of these two ILs show a reverse
trend- higher electrical conductivities for bulkier ions. Thus pres-
ence of significant ion association in IL-1 and absence of it in IL-
7. Froschauer C, Hummel M, Laus G, et al. Biomacromolecules.
012;13:1973–1980.
2
8
9
.
.
Zhao D, Li H, Zhang J, et al. Carbohr Polym. 2012;87:1490–1494.
Fraser KJ, Izgorodina EI, Forsyth M, Scott JL, MacFarlane DR. Chem Commun.
2007;3817–3819. and the reference thereof.
1
0. Sun J, Howlett PC, MacFrarlane DR, Lin J, Forsyth M. Electrochim Acta.
008;54:254–260.
1. Totolin V, Minami I, Gabler C, Brenner J, Dörr N. Tribol Lett. 2014;53:421–433.
2
1
12. Zhou Y, Dyck J, Graham TW, Luo H, Leonard DN, Qu J. Langmuir.
014;30:13301–13311.
2
1
1
3. Jalkh J, Leroux YR, Lagrost C, Hapiot P. J Phys Chem C. 2014;118:28640–28646.
4. Cade EA, Petenuci III J, Hoffmann MM. ChemPhysChem. 2016;17:520–529. and
the references therein.
6
could be attributed. Similarly while compared the conductivities
between IL-3 and IL-7 (12.3 and 18.9 mS/cm respectively) and
between IL-4 and IL-8 (28.4 and 30.6 mS/cm respectively) they cor-
roborated our hypothesis that the constituent ions in PPs are sig-
nificantly associated while that of in PTPs are solvent separated.
It is interesting to mention that diluting the solution from 0.06 M
to 0.04 M is associated with decrease in conductivities to less than
half for most of the cases. This dramatic effect of dilution on con-
ductivity in low dielectric solvent can be attributed to the breakage
of supramolecular networks (present at higher concentration) and
formation of higher charged aggregates leading to low
15. Wooster TJ, Johanson KM, Fraser KJ, Macfarlane DR, Scott JL. Green Chem.
006;8:691–696.
2
1
1
6. Vaughan JW, Dreisinger D, Haggins J. ECS Trans. 2006;2:381–392.
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1
2
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21. Cohen Y, Avram L, Frish L. Angew Chem Int Ed. 2005;44:520–554.
J
2
13
31
2
2. Detail 1H, C & P NMR and mass spectral data for few of the synthesized ILs:
Tributyl pentadecyl phosphonium bis(3-pentadecylphenyl)phosphate (IL-1): 1
NMR (500 MHz in CDCl , d ppm relative to TMS): 0.88 (t, J = 7 Hz, 9H), 0.91 (t,
J = 7 Hz, 9H), 1.20–1.34 (m, 70H), 1.38–1.48 (m, 16H), 1.53–1.58 (m, 4H), 2.26–
H
3
1
4
conductivity.
2
.38 (m, 8H), 2.49 (t, J = 7.5 Hz, 4H), 6.76 (d, J = 7 Hz, 2H), 7.00–7.10 (m, 6H);
C NMR (125.7 MHz in CDCl ): 13.46, 14.09, 18.45–18.82 (d, J = 186.0 Hz),
3
1
3
Conclusions
1
3
1
8.67–19.04 (d, J = 186.0 Hz), 21.82, 22.68, 23.79, 23.96, 29.04, 29.36, 29.71,
0.72–30.83 (d, J = 56.5 Hz), 31.41, 31.93, 35.95, 117.59, 120.37, 122.19, 128.40,
43.71, 153.89; 31P NMR (202.5 MHz, d ppm relative to 85% phosphoric acid in
Phosphonium phosphates have significant ion association. Few
phosphonium phosphates can be termed as liquid ion pair. Increas-
ing the alkyl chain length in phosphonium cation resulted in
enhanced ion association. Symmetrical anionic donor showed
stronger ion association than unsymmetrical bulkier anionic
donor. While the phosphonium cation and phosphate anion is
strongly associated, even in solution, phosphonium thiophosphate
shows weak ion association as evident by conductivity and diffu-
sion experiments.
+
water): -10.40, 32.92; FD MS calcd for M+, C27
H
58P : 413.427; found 413.397.
1
Tributyl decyl phosphonium bis(3-pentadecylphenyl)phosphate (IL-3): H NMR
(500 MHz in CDCl , d ppm relative to TMS): 0.90 (t, 9H, J = 6.5 Hz), 0.94 (t, 9H,
J = 6.8 Hz), 1.21–1.32 (m, 60H), 1.42–1.48 (m, 16H), 1.55 (m, 4H), 2.32–2.37 (m,
H), 2.51 (t, 4H, J = 8.0 Hz), 6.78 (d, J = 6.5 Hz, 2H), 7.00-7.10 (m, 6H); 13C NMR
125.7 MHz in CDCl ): 13.48, 14.10, 18.50–18.87 (d, J = 186.0 Hz), 18.71–19.09
3
8
(
3
(d, J = 191.0 Hz), 21.82–21.85 (d, J = 14.0 Hz), 22.65, 22.68, 23.76–23.8 (d,
J = 19.0 Hz), 23.85–23.97 (d, J = 59.6 Hz), 29.01, 29.27, 29.35, 29.48, 29.57,
2
1
9.66, 29.71, 30.72–30.83 (d, J = 57.0 Hz), 31.42, 31.84, 31.91, 35.94, 117.52–
17.56 (d, J = 19.1 Hz), 120.30–120.35 (d, J = 21.5 Hz), 122.14, 128.38, 143.70,
31
153.48–153.52 (d, J = 19.8 Hz); P NMR (202.5 MHz, d ppm relative to 85%
+
+
phosphoric acid in water): -10.75, 32.92; FD MS calcd for M , C22
H
48P :
3
43.348; found 343.253. cTributyl pentadecyl phosphonium bis(3-
Acknowledgments
1
3
pentadecylphenyl)thiophosphate (IL-6): H NMR (500 MHz in CDCl , d ppm
relative to TMS): 0.88 (t, 9H, J = 6.8 Hz), 0.96 (t, 9H, J = 6.0 Hz), 1.23–1.79 (m,
70H), 1.45-1.59 (m, 20H), 2.35–2.45 (m, 8H), 2.59 (t, J = 7.5 Hz, 4H), 7.02–7.05
We acknowledge the management of IOCL R&D Centre for pro-
viding state of art facilities and granting permission to publish this
paper.
(
1
m, 8H), 7.25 (t, J = 7.2 Hz, 2H); 13C NMR (125.7 MHz in CDCl
3
): 13.38, 14.00,
8.68–19.05 (d, J = 188.5 Hz), 18.89–19.27 (d, J = 188.5 Hz), 21.73–21.77 (d,
J = 19.0 Hz), 22.56, 23.66–23.70 (d, J = 19.0 Hz), 23.74–23.86 (d, J = 62.0 Hz),
8.88, 29.07, 29.23, 29.35, 29.40, 29.45, 29.53, 29.56, 30.60–30.71 (d,
J = 57.0 Hz), 31.05, 31.78, 35.55, 118.09, 120.93–120.96 (d, J = 16.7 Hz),
2
A. Supplementary data
31
1
25.58, 129.13, 144.81, 150.53–150.60 (d, J = 33.4 Hz); P NMR (202.5 MHz,
+
d ppm relative to 85% phosphoric acid in water): 32.9, 53.0; FD MS calcd for M ,
C
pentadecylphenyl)thiophosphate (IL-7): H NMR (500 MHz in CDCl , d ppm
+
H
58P : 413.427; found 413.350. 1 Tributyl decyl phosphonium bis(3-
Supplementary data (experimental details, synthesis and
27
3
1
H/13C/31P NMR spectra for ILs and precursors, COSY-HSQC spec-
relative to TMS): 0.88 (t, 9H, J = 6.8 Hz), 0.96 (t, 9H, J = 6.5 Hz), 1.21–1.32 (m,
60H), 1.48–1.59 (m, 20H), 2.34–1.42 (m, 8H), 2.59 (t, 4H, J = 7.5 Hz), 7.00-7.05
tra for IL-1, DOSY spectra for IL-3 and IL-7, Correlation curves for
diffusion measurement) associated with this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.tetlet.2017.05.
(
1
m, 8H), 7.25 (t, J = 7.5 Hz, 2H); 13C NMR (125.7 MHz in CDCl
3
): 13.57, 14.16,
8.88–19.25 (d, J = 186.0 Hz), 19.08–19.45 (d, J = 186.0 Hz), 21.94–21.97 (d,
J = 14.0 Hz), 22.70, 22.73, 23.90–23.94 (d, J = 19.0 Hz), 23.94–24.06 (d,
J = 62.0 Hz), 29.06, 29.29, 29.32, 29.38, 29.41, 29.55, 29.64, 29.73, 29.76,
0
31.
30.78–30.90 (d, J = 57.0 Hz), 31.24, 31.90, 32.0, 35.77, 118.28–118.32 (d,
J = 14.5 Hz), 121.12–121.16 (d, J = 19.0 Hz), 125.78, 129.32, 145.04, 150.72–
References
31
1
50.78 (d, J = 28.5 Hz); P NMR (202.5 MHz, d ppm relative to 85% phosphoric
+ +
acid in water): 32.9, 53.3; FD MS calcd for M , C22
H48P : 343.348; found
1
.
.
Earle MJ, Seddon KR. Pure Appl Chem. 2000;72:1391–1398.
Vishwakarma S. IJBSAC. 2014;1:1–4.
343.348.
2