FR3141939A1 - NON-AROMATIC ASYMMETRICAL MONO(2-CYANOETHYL)TRIORGANOPHOSPHONIUM SALT, ITS SYNTHESIS PROCESS AND ITS USE AS AN ELECTROLYTE COMPOUND, AS A LUBRICANT AND LUBRICANT ADDITIVE, AS A GAS CAPTURE AGENT, IN AS A SOLVENT FOR CATALYSIS AND AS A SURFACE MODIFICATION AGENT BY CLICK CHEMISTRY - Google Patents

Abstract

The present invention relates to a non-aromatic asymmetric mono(2-cyanoethyl)triorganophosphonium salt, its synthesis method and its use as an electrolyte compound, as a lubricant and lubricant additive, as a capture agent gas, as a solvent for catalysis and as a surface modification agent by Chimie Click.

Description

NON-AROMATIC ASYMMETRICAL MONO(2-CYANOETHYL)TRIORGANOPHOSPHONIUM SALT, ITS SYNTHESIS PROCESS AND ITS USE AS AN ELECTROLYTE COMPOUND, AS A LUBRICANT AND LUBRICANT ADDITIVE, AS A GAS CAPTURE AGENT, IN AS A SOLVENT FOR CATALYSIS AND AS A SURFACE MODIFICATION AGENT BY CLICK CHEMISTRY

The present invention relates to a non-aromatic asymmetric mono(2-cyanoethyl)triorganophosphonium salt, its synthesis method and its use as an electrolyte compound, as a lubricant and lubricant additive, as a capture agent gas, as a solvent for catalysis and as a surface modification agent by Chimie Click.

Field of the invention

The synthesis of ionic compounds derived from tris(2-cyanoethyl)phosphine leads to the formation of compounds belonging to the family of phosphonium salts substituted by a single chain (2-cyanoethyl) and three different non-aromatic substituents.

The prior art describes a current synthesis technology which involves the alkylation of an asymmetric triorganophosphine with a (2-cyanoethyl) chain. This synthesis uses a non-aromatic triorganophoshine which can be flammable, toxic and is particularly sensitive to air oxidation.

Air-Stable Trialkylphosphonium Salts: Simple, Practical, and Versatile Replacements for Air-Sensitive Trialkylphosphines . Applications in Stoichiometric and Catalytic Processes. Org. Lett. 2001, 3, 4295–4298 describes a process which obtains a mixture of secondary products which are difficult to separate from the desired product.

Vlád, G.; Richter, FU; Horváth, IT Synthesis of Fluorous Trialkyl Phosphines with the Complete Exclusion of PH3. Tetrahedron Letters 2005 , 46 (49), 8605–8608 describes a synthesis from phosphorus trihydride PH ₃ (toxic, flammable and extremely sensitive to oxidation) or phosphorus trichloride PCl ₃ and this leads to a mixture of phosphines mixed primary, secondary and tertiary sectors which are difficult to control.

Current synthesis processes do not make it easy to obtain this asymmetric triorganophosphine precursor.

Current synthesis processes do not make it possible to eliminate traces of phosphine oxides and phosphorus side products, which leads to poor purity of the synthesized product.

For these reasons, state-of-the-art synthesis processes are not compatible with manufacturing on an industrial scale.

In addition, the tris(2-cyanoethyl)phosphonium of the prior art are phosphonium salts containing a single 2-cyanoethyl chain and three identical non-aromatic substituents.

DE102008021271 describes a mono(2-cyanoethyl)trialkylphosphonium salt therefore having three identical substituents.

There is a real need for a new family of asymmetric mono(2-cyanoethyl)triorganophosphonium having different non-aromatic substituents and for a synthesis process making it possible to obtain products of high purity and compatible on an industrial scale.

The invention relates to a new family of phosphonium salts of formula (I)

(I)

in which

^-

R1, R2 and R3 are different from each other and independently chosen from a C1-C20 alkyl, a C3-C6 cycloalkyl, a C2-C20 alkenyl, a C5-C8 cycloalkenyl, a C2-C20 alkynyl, a vinylbenzyl group; in which the hydrogen atoms can be substituted by a fluorine, a -CF ₃ , an ether, an alkyl group, a fluorinated alkyl group, a silyl group, a siloxy group, a sulfoxide group, a nitrile group, a thioether group or their combinations; on the condition that R1, R2 and R3 are different from a CH ₂ -CH ₂ -CN chain.

The invention also relates to a (2-cyanoethyl)phosphonium salt dimer as well as the process for the synthesis of this family of compounds and the use of this family of compounds as an electrolyte compound, as an additive of lubricant, as a lubricant, as a gas capture agent and as a catalysis solvent and as a surface modification agent by Click Chemistry.

Advantages of the invention

The invention proposes a new family of (2-cyanoethyl)phosphonium salts comprising a single (2-cyanoethyl) chain. These compounds have the advantage of being of high purity.

Phosphonium salts comprising a single chain (2-cyanoethyl) are very interesting. Indeed, the dipole moment and the dielectric constant of the ionic liquid of these compounds are increased compared to phosphonium salts not having a nitrile function. The presence of a chain (2-cyanoethyl) allows better desolvation of Lithium ions as well as strong interaction with surfaces and gives the possibility of being grafted onto surfaces. These new salts are asymmetrical, which allows them to have a low crystallization point and therefore to be compatible with uses over wider temperature ranges. In addition, the fact of carrying only one chain (2-cyanoethyl) and 3 non-aromatic substituents makes it possible to obtain low viscosity compounds.

Compared to their ammonium counterparts, the softer phosphorus atom allows different interaction with surfaces and bis(trifluoromethanesulfonyl)imide (FSI) salts have lower melting points.

The process according to the invention has several advantages.

Firstly, the solvents used are low-toxic products that are safe for the environment because they are called “green”.

Second, the synthesis precursors are inexpensive and stable in air and the synthesis intermediates are low toxic.

Third, the reactions carried out are not very sensitive to oxygen.

Fourth, the synthesis process makes it possible to independently choose the three non-aromatic organic groups which replace the (2-cyanoethyl)triorganophosphonium salt.

Fifth, the synthesis process can obtain high purity (2-cyanoethyl)triorganophosphonium salts.

Sixth, the process allows for an industrializable synthesis route.

DETAILED DESCRIPTION OF THE INVENTION

A first subject of the invention relates to a new family of phosphonium salts of formula (I)

(I)

in which

^-

R1, R2 and R3 are different from each other and independently chosen from a C1-C20 alkyl, a C3-C6 cycloalkyl, a C2-C20 alkenyl, a C5-C8 cycloalkenyl, a C2-C20 alkynyl, a vinylbenzyl group; in which the hydrogen atoms can be substituted by a fluorine, a -CF ₃ , an ether, an alkyl group, a fluorinated alkyl group, a silyl group, a siloxy group, a sulfoxide group, a nitrile group, a thioether group or their combinations; on the condition that R1, R2 and R3 are different from a CH ₂ -CH ₂ -CN chain.

The hydrogen atoms can therefore be partly substituted as long as the molecule is stable.

The term "alkyl" designates a saturated aliphatic radical, linear or branched, having the indicated number of carbon atoms. The alkyl moiety may be straight or branched chain.

The term “alkenyl” designates an alkyl group, as defined above, comprising at least one C=C double bond.

The term "alkynyl" designates an alkyl group, as defined above, comprising at least one C≡C triple bond. The term "cycloalkyl" designates a set of saturated or partially unsaturated, monocyclic, bicyclic, bridged polycyclic or spiro rings. Monocyclic rings include, for example, cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl rings.

In a more particularly preferred embodiment, R1 is chosen from a C1-C10 alkyl in which the hydrogen atoms can be substituted by a fluorine, a -CF ₃ , an ether, an alkyl group, a perfluorinated alkyl group, a silyl group, a siloxy, a sulfoxide, a nitrile, a thioether or combinations thereof;

Even more preferably, R1 is chosen from a methyl or a C1-C4 alkyl in which the hydrogen atoms can be substituted by a fluorine, a -CF ₃ , an ether, an alkyl group, a perfluorinated alkyl group, a silyl group, a siloxy group, a sulfoxide group, a nitrile group, a thioether group or combinations thereof; and R2 is a C1-C10 alkyl in which the hydrogen atoms can be substituted by a fluorine, a -CF ₃ , an ether, an alkyl group, a perfluorinated alkyl group, a silyl group, a siloxy group, a group sulfoxide, a nitrile group, a thioether group or combinations thereof; and even more preferably, R2 is chosen from methyl, ethyl, propyl, iso-butyl, n -butyl, or allyl; and of which R3 is preferably chosen from a C1-C10 alkyl and even more preferably from a C1-C4 alkyl.

In ^a preferred embodiment, , fluorosulfonyl(trifluoromethanesulfonyl)imide, bis(oxalato)borate, difluorobis(oxalato)borate, acetate, N-ethyl-N-methyl-functionalized sulfonimide, (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imide, (methanesulfonyl)(trifluoromethanesulfonyl)imide.

In an even more preferred embodiment, X ^- is chosen from FSI or TFSI.

The preferred ^embodiments regarding the choice of the anion

A second object of the invention is the phosphonium salt in dimer form.

The phosphonium salt dimer is represented by formula (II),

(II)

in which

Z is chosen from C1-C20 alkyl di-radicals of the –(CH ₂ )n– type which may comprise one or more ethers or which may comprise one or more chains of the –CH ₂ –Y–CH ₂ – type with Y=S , SO or SO2; preferably the alkyl diradical is an ethyl, propyl, butyl or pentyl diradical;

^-

R2 and R3 are different from each other and independently chosen from a C1-C20 alkyl, a C3-C6 cycloalkyl, a C2-C20 alkenyl, a C5-C8 cycloalkenyl, a C2-C20 alkynyl, a vinylbenzyl group; in which the hydrogen atoms may be substituted by a fluorine, a -CF ₃ , an ether, an alkyl group, a perfluorinated alkyl, a silyl, a siloxy, a sulfoxide, a nitrile, a thioether or combinations thereof; on the condition that R2 and R3 are different from a CH ₂ -CH ₂ -CN chain.

A third object of the invention is a process for synthesizing the family of phosphonium salts defined above.

When the salt is a monomer, the process includes the following steps:

a) Mixing an alkaline alkoxide solution with a solution of tetrakis(hydroxymethyl)phosphonium chloride (THPC) or with a solution of tetrakis(hydroxymethyl)phosphonium sulfate (THPS) to obtain mixture A

b) Filtration of mixture A

c) Mixing the filtrate obtained in step b) with acrylonitrile

d) Filtration of the mixture obtained in step c) to obtain the precipitate formed from tris(2-cyanoethyl)phosphine (TCP)

e) Addition followed by the mixture of an electrophile R3Y of which Y can be a halide or an OTf (triflate) or an OTs (tosylate) and of which R3 is chosen from a C1-C20 alkyl group, a C3-C6 cycloalkyl, a C2-C20 alkenyl, a C5-C8 cycloalkenyl, a C2-C20 alkynyl, a vinylbenzyl group; in which the hydrogen atoms can be substituted by a fluorine, a -CF ₃ , an ether, an alkyl group, a fluorinated alkyl group, a silyl group, a siloxy group, a sulfoxide group, a nitrile group, a thioether group or their combinations with a solution of TCP obtained in step d) in a solvent

f) Filtration followed by drying of the mixture obtained in step e) to obtain the precipitate formed from tris(2-cyanoethyl)phosphonium salt

g) Mixing an alkaline alkoxide solution with the salt obtained in step f) in alcohol to obtain mixture B

h) Drying of mixture B

i) Addition followed by the mixture of an electrophile R2Y of which Y can be a halide or OTf (triflate) or OTs (tosylate) and of which R2 is chosen from the group consisting of a C1-C20 alkyl, a C3-C6 cycloalkyl , a C2-C20 alkenyl, a C5-C8 cycloalkenyl, a C2-C20 alkynyl, a vinylbenzyl group; in which the hydrogen atoms can be substituted by a fluorine, a -CF ₃ , an ether, an alkyl group, a fluorinated alkyl group, a silyl group, a siloxy group, a sulfoxide group, a nitrile group, a thioether group or their combinations; to a solution of the bis(2-cyanoethyl)phosphine obtained in step h) in a solvent

j) Filtration followed by drying of the mixture obtained in step i) to obtain the precipitate formed from bis(2-cyanoethyl)phosphonium salt

k) Mixing an alkaline alkoxide solution with the salt obtained in step j) in alcohol to obtain mixture C

l) Drying of mixture C

m) Addition followed by the mixture of an electrophile R1Y of which Y can be a halide or OTf (triflate) or OTs (tosylate) and of which R1 is chosen from the group consisting of a C1-C20 alkyl, a C3-C6 cycloalkyl , a C2-C20 alkenyl, a C5-C8 cycloalkenyl, a C2-C20 alkynyl, a vinylbenzyl group; in which the hydrogen atoms can be substituted by a fluorine, a -CF ₃ , an ether, an alkyl group, a fluorinated alkyl group, a silyl group, a siloxy group, a sulfoxide group, a nitrile group, a thioether group or their combinations; to a solution of the (2-cyanoethyl)phosphine obtained in step l) in a solvent

n) Filtration followed by drying of the mixture obtained in step m) to obtain the precipitate formed from (2-cyanoethyl)phosphonium salt

o) Ionic metathesis of the salt obtained in step n) in a solvent to obtain mixture D

p) Decantation, separation/filtration and drying of mixture D in order to obtain the (2-cyanoethyl)phosphonium salt PR1R2R3(2CN)X

When the salt is a dimer, the process comprises the following steps:

a) Mixing an alkaline alkoxide solution with a solution of tetrakis(hydroxymethyl)phosphonium chloride (THPC) or with a solution of tetrakis(hydroxymethyl)phosphonium sulfate (THPS) to obtain mixture A

b) Filtration of mixture A

c) Mixing the filtrate obtained in step b) with acrylonitrile

d) Filtration of the mixture obtained in step c) to obtain the precipitate formed from tris(2-cyanoethyl)phosphine (TCP)

e) Addition followed by the mixture of an electrophile R3Y of which Y can be a halide or an OTf (triflate) or an OTs (tosylate) and of which R3 is chosen from a C1-C20 alkyl group, a C3-C6 cycloalkyl, a C2-C20 alkenyl, a C5-C8 cycloalkenyl, a C2-C20 alkynyl, a vinylbenzyl group; in which the hydrogen atoms can be substituted by a fluorine, a -CF ₃ , an ether, an alkyl group, a fluorinated alkyl group, a silyl group, a siloxy group, a sulfoxide group, a nitrile group, a thioether group or their combinations with a solution of TCP obtained in step d) in a solvent

f) Filtration followed by drying of the mixture obtained in step e) to obtain the precipitate formed from tris(2-cyanoethyl)phosphonium salt

g) Mixing an alkaline alkoxide solution with the salt obtained in step f) in alcohol to obtain mixture B

h) Drying of mixture B

i) Addition followed by the mixture of an electrophile R2Y of which Y can be a halide or OTf (triflate) or OTs (tosylate) and of which R2 is chosen from the group consisting of a C1-C20 alkyl, a C3-C6 cycloalkyl , a C2-C20 alkenyl, a C5-C8 cycloalkenyl, a C2-C20 alkynyl, a vinylbenzyl group; in which the hydrogen atoms can be substituted by a fluorine, a -CF ₃ , an ether, an alkyl group, a fluorinated alkyl group, a silyl group, a siloxy group, a sulfoxide group, a nitrile group, a thioether group or their combinations; to a solution of the bis(2-cyanoethyl)phosphine obtained in step h) in a solvent

j) Filtration followed by drying of the mixture obtained in step i) to obtain the precipitate formed from bis(2-cyanoethyl)phosphonium salt

k) Mixing an alkaline alkoxide solution with the salt obtained in step j) in alcohol to obtain mixture C

l) Drying of mixture C

m) Addition followed by the mixture of an electrophile YZY of which Y can be a halide or OTf (triflate) or OTs (tosylate) and of which Z is chosen from di-radical C1-C20 alkyls of type –(CH ₂ )n – which may include one or more ethers or which may include one or more sequences of type –CH ₂ –Y–CH ₂ – with Y=S, SO or SO2; preferably the alkyl diradical is an ethyl, propyl, butyl or pentyl diradical; in which the hydrogen atoms can be substituted by a fluorine, a -CF ₃ , an ether, an alkyl group, a fluorinated alkyl group, a silyl group, a siloxy group, a sulfoxide group, a nitrile group, a thioether group or their combinations; to a solution of the (2-cyanoethyl)phosphine obtained in step l) in a solvent

n) Filtration followed by drying of the mixture obtained in step m) to obtain the precipitate formed from (2-cyanoethyl)phosphonium dimer salt

o) Ionic metathesis of the salt obtained in step n) in a solvent to obtain mixture D

p) Decantation, separation/filtration and drying of mixture D in order to obtain the (2-cyanoethyl)phosphonium dimer salt (XPR2R3(2CN)) ₂ Z

A fourth object of the invention is the use of the family of phosphonium salts defined by formulas (I) and (II) as an electrolyte compound.

A fifth object of the invention is the use of the family of phosphonium salts defined by formulas (I) and (II) as a gas capture agent.

A sixth object of the invention is the use of the family of phosphonium salts defined by formulas (I) and (II) as a surface modification agent by Chimie Click.

A seventh object of the invention is the use of the family of phosphonium salts defined by formulas (I) and (II) as a solvent for catalysis.

An eighth object of the invention is the use of the family of phosphonium salts defined by formulas (I) and (II) as a lubricant and as a lubricant additive.

BRIEF DESCRIPTION OF THE FIGURES

: General diagram of the synthesis process

: 1H NMR spectrum of (2-cyanoethyl)ethylmethylpropylphosphonium bis(fluorosulfonyl)imide P123(2CN)FSI

: 19F NMR spectrum of (2-cyanoethyl)ethylmethylpropylphosphonium bis(fluorosulfonyl)imide P123(2CN)FSI

: 31P NMR spectrum of (2-cyanoethyl)ethylmethylpropylphosphonium bis(fluorosulfonyl)imide P123(2CN)FSI

: Graph showing the discharge capacities and coulombic efficiencies of whole cells (LMNO//Graphite) with and without the compound (2-cyanoethyl)ethylmethylpropylphosphonium bis(fluorosulfonyl)imide P123(2CN)FSI at a C rate of 0.5 C between 2 V at 5 V compared to Li+/Li at 25 °C.

EXAMPLE 1: (2- cyanoethyl) ethylmethylpropylphosphonium bis( fluorosulfonyl )imide P123(2CN)FSI

A solution of NaOH is added to a solution of THPC in a solvent with stirring. Then the acrylonitrile is added. The reaction medium is filtered in order to recover the precipitate formed (TCP). Phosphine TCP is dissolved in a solvent and iodomethane is added with stirring. The mixture obtained is filtered and dried in order to recover the tris(2-cyanoethyl)methylphosphonium iodide salt. An alkaline alkoxide solution is added to a suspension of tris(2-cyanoethyl)methylphosphonium iodide salt in alcohol with stirring. The reaction medium is evaporated resulting in crude bis(2-cyanoethyl)methylphosphine. To a solution of this phosphine in a solvent, bromoethane is added with stirring. After filtration, the solid obtained is purified to obtain the bis(2-cyanoethyl)ethylmethylphosphonium bromide salt. An alkaline alkoxide solution is added to a suspension of bis(2-cyanoethyl)ethylmethylphosphonium bromide salt in alcohol with stirring. The medium is evaporated under vacuum resulting in a crude mixture of (2-cyanoethyl)ethylmethylphosphine. To a solution of this crude phosphine in a solvent, iodopropane is added with stirring. After filtration, the solid obtained is purified to obtain the iodide salt of (2-cyanoethyl)ethylmethylpropylphosphonium. In a solvent, (2-cyanoethyl)ethyldimethylphosphonium iodide is added in suspension with LiFSI while stirring. The liquid obtained is purified to obtain the (2-cyanoethyl)ethylmethylpropylphosphonium bis(fluorosulfonyl)imide salt.

Figures 2, 3 and 4 show that (2-cyanoethyl)ethylmethylpropylphosphonium bis(fluorosulfonyl)imide P123(2CN)FSI was synthesized. FTIR (cm ^-1 ) (pure) 2985, 2924, 2253, 1373, 1173, 1099, 829, 732, 567. ¹ H NMR (CD ₃ CN, 500.11 MHz) d (ppm) 2.75 (dt, 2H, J = 13.1, 7.7 Hz), 2.51 (dt, 2H, J = 13.2, 7.7 Hz), 2.23 – 2.10 (m, 4H), 1.78 (d, 3H, J = 13.7 Hz), 1.63 – 1.53 (m, 2H), 1.20 (dt, 3H, J = 19.5, 7.7 Hz), 1.07 (td, 3H, J = 7.2, 1.3 Hz). ³¹ P NMR (CD ₃ CN, 202.45 MHz) d (ppm) 34.9. ¹⁹ F NMR (CD ₃ CN, 470.57 MHz) d (ppm) 51.42. Ionic purity (IC): 99.99%. Crystal temperature < -80 °C.

EXAMPLE 2: P r e repairing a battery lmno //graphite with and without compound [P123(2CN) FSI] and load and dump of the pile

In a glove box under an inert atmosphere (Argon) with a water and O ₂ content less than 1 ppm, the lithium salt LiFSI (0.936 g) is dissolved in the ionic liquid PYR13FSI (6.045 g) to obtain the desired concentration, a (2-cyanoethyl)ethylmethylpropylphosphonium compound P123(2CN)FSI (0.154 g) is then added and mixed to obtain a homogeneous electrolyte solution.

Table 1 below groups together the different cathode/anode/electrolyte combinations tested in a battery.

Positive Electrode - Ability Negative Electrode - Ability Electrolytes LMNO – 1.1mAh/cm² Graphite – 1.4 mAh/cm² 1M LiFSI in PYR13FSI + 0.0628 mol/kg P123(2CN)FSI LMNO – 1.1mAh/cm² Graphite – 1.4 mAh/cm² 1M LiFSI in PYR13FSI

Table 1: LMNO cathode/Graphite anode/electrolyte combinations tested in battery.

The batteries were tested in galvanostatic cycling from 2 to 5 V at a C rate of 0.5 C in a climatic chamber at 25 °C.

Electrolyte C-rate
(Number of cycles) Charging capacity (mAh/g) Discharge capacity (mAh/g) Efficiency (%) 1M LiFSI in PYR13FSI + 0.063 mol/kg P123(2CN)FSI 0.5C
( ^1st cycle) 105.85 105.34 99.51 1M LiFSI in PYR13FSI + 0.063 mol/kg P123(2CN)FSI 0.5C
( ^246th cycle) 98.48 98.17 99.68 1M LiFSI in PYR13FSI + 0.063 mol/kg P123(2CN)FSI 0.5C
( ^478th cycle) 89.09 88.80 99.68 1M LiFSI in PYR13FSI 0.5C
( ^1st cycle) 107.99 107.45 99.51 1M LiFSI in PYR13FSI 0.5C
( ^246th cycle) 93.64 93.33 99.67

Table 2 : Characteristics of batteries with an LMNO//Graphite system at 0.5 C with and without P123(2CN)FSI compound.

Table 2 and show the discharge capacity as a function of cycle number of both systems, with and without (2-cyanoethyl)ethylmethylpropylphosphonium salt compound.

In the electrolyte without P123(2CN)FSI compound, the discharge capacity of the first cycle at a charge and discharge rate of 0.5 C is slightly higher than with the (2-cyanoethyl)ethylmethylpropylphosphonium compound (respectively 107.45 mAh /g and 105.34 mAh/g). But regarding cyclability, the capacity of the system containing the compound P123(2CN)FSI is more stable during cycles. Indeed, taking into account the first 246 cycles, the loss of discharge capacity for the system without the compound P123(2CN)FSI is 13.14% compared to 6.81% for that containing the compound (2-cyanoethyl)ethylmethylpropylphosphonium .

Capacity retention is better for the system containing the P123(2CN)FSI compound.

Claims (12)

(2-cyanoethyl)phosphonium salts represented by formula (I):
(I)
in which
^-
R1, R2 and R3 are different from each other and independently chosen from a C1-C20 alkyl, a C3-C6 cycloalkyl, a C2-C20 alkenyl, a C5-C8 cycloalkenyl, a C2-C20 alkynyl, a vinylbenzyl group; in which the hydrogen atoms can be substituted by a fluorine, a -CF ₃ , an ether, an alkyl group, a fluorinated alkyl group, a silyl group, a siloxy group, a sulfoxide group, a nitrile group, a thioether group or their combinations; provided that R1, R2 and R3 are different from a CH ₂ -CH ₂ -CN chain. Phosphonium salt according to claim 1 in which R1, R2 and R3 are different from each other and chosen independently from a C1-C10 alkyl in which the hydrogen atoms can be substituted by a fluorine, a -CF ₃ , an ether, an alkyl group, a fluorinated alkyl group, a silyl group, a siloxy group, a sulfoxide group, a nitrile group, a thioether group or combinations thereof; provided that R1, R2 and R3 are different from a CH ₂ -CH ₂ -CN chain. Phosphonium salt according to claim 2 in which R1, R2 and R3 are different from each other and chosen from a methyl or a C1-C4 alkyl in which the hydrogen atoms can be substituted by a fluorine, a -CF ₃ , a ether, an alkyl group, a fluorinated alkyl group, a silyl group, a siloxy group, a sulfoxide group, a nitrile group, a thioether group or combinations thereof; provided that R1, R2 and R3 are different from a CH ₂ -CH ₂ -CN chain. Phosphonium salt according to any one of claims 1 to 3 in which the anion is chosen from bis(fluorosulfonyl)imide (FSI), bis(trifluoromethanesulfonyl)imide (TFSI), tetrafluoroborate, hexafluorophosphate, dicyanamide, triflate, 4.5 -dicyano-2-(trifluoromethyl)imidazolate, fluorosulfonyl(trifluoromethanesulfonyl)imide, bis(oxalato)borate, difluorobis(oxalato)borate, acetate, N-ethyl-N-methyl-functionalized sulfonimide, (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imide, ( methanesulfonyl)(trifluoromethanesulfonyl)imide, (difluoromethanesulfonyl)(fluoromethanesulfonyl)imide, (methanesulfonyl)(fluoromethanesulfonyl)imide. Phosphonium salt according to claim 4 in which the anion X ^- is chosen from FSI or TFSI. Phosphonium salt according to one of claims 1 to 5, the (2-cyanoethyl)phosphonium salt of which is in the form of a dimer. Process for synthesizing a phosphonium salt as defined in one of claims 1 to 5 comprising the following steps:
a) Mixing an alkaline alkoxide solution with a solution of tetrakis(hydroxymethyl)phosphonium chloride (THPC) or with a solution of tetrakis(hydroxymethyl)phosphonium sulfate (THPS) to obtain mixture A
b) Filtration of mixture A
c) Mixing the filtrate obtained in step b) with acrylonitrile
d) Filtration of the mixture obtained in step c) to obtain the precipitate formed from tris(2-cyanoethyl)phosphine (TCP)
e) Addition followed by the mixture of an electrophile R3Y of which Y can be a halide or an OTf (triflate) or an OTs (tosylate) and of which R3 is chosen from a C1-C20 alkyl group, a C3-C6 cycloalkyl, a C2-C20 alkenyl, a C5-C8 cycloalkenyl, a C2-C20 alkynyl, a vinylbenzyl group; in which the hydrogen atoms can be substituted by a fluorine, a -CF ₃ , an ether, an alkyl group, a fluorinated alkyl group, a silyl group, a siloxy group, a sulfoxide group, a nitrile group, a thioether group or their combinations with a solution of TCP obtained in step d) in a solvent
f) Filtration followed by drying of the mixture obtained in step e) to obtain the precipitate formed from tris(2-cyanoethyl)phosphonium salt
g) Mixing an alkaline alkoxide solution with the salt obtained in step f) in alcohol to obtain mixture B
h) Drying of mixture B
i) Addition followed by the mixture of an electrophile R2Y of which Y can be a halide or OTf (triflate) or OTs (tosylate) and of which R2 is chosen from the group consisting of a C1-C20 alkyl, a C3-C6 cycloalkyl , a C2-C20 alkenyl, a C5-C8 cycloalkenyl, a C2-C20 alkynyl, a vinylbenzyl group; in which the hydrogen atoms can be substituted by a fluorine, a -CF ₃ , an ether, an alkyl group, a fluorinated alkyl group, a silyl group, a siloxy group, a sulfoxide group, a nitrile group, a thioether group or their combinations; to a solution of the bis(2-cyanoethyl)phosphine obtained in step h) in a solvent
j) Filtration followed by drying of the mixture obtained in step i) to obtain the precipitate formed from bis(2-cyanoethyl)phosphonium salt
k) Mixing an alkaline alkoxide solution with the salt obtained in step j) in alcohol to obtain mixture C
l) Drying of mixture C
m) Addition followed by the mixture of an electrophile R1Y of which Y can be a halide or OTf (triflate) or OTs (tosylate) and of which R1 is chosen from the group consisting of a C1-C20 alkyl, a C3-C6 cycloalkyl , a C2-C20 alkenyl, a C5-C8 cycloalkenyl, a C2-C20 alkynyl, a vinylbenzyl group; in which the hydrogen atoms can be substituted by a fluorine, a -CF ₃ , an ether, an alkyl group, a fluorinated alkyl group, a silyl group, a siloxy group, a sulfoxide group, a nitrile group, a thioether group or their combinations; to a solution of the (2-cyanoethyl)phosphine obtained in step l) in a solvent
n) Filtration followed by drying of the mixture obtained in step m) to obtain the precipitate formed from (2-cyanoethyl)phosphonium salt
o) Ionic metathesis of the salt obtained in step n) in a solvent to obtain mixture D
p) Decantation, separation/filtration and drying of mixture D in order to obtain the (2-cyanoethyl)phosphonium salt PR1R2R3(2CN)X. Use of the phosphonium salt as defined in one of claims 1 to 6 as an electrolyte compound. Use of phosphonium salt as defined in one of claims 1 to 6 as a gas capture agent. Use of phosphonium salt as defined in one of claims 1 to 6 as a surface modification agent by “Click” chemistry. Use of the phosphonium salt as defined in one of claims 1 to 6 as a solvent for catalysis. Use of phosphonium salt as defined in one of claims 1 to 6 as a lubricant additive or as a lubricant.