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 ASYMMETRIC MONO(2-CYANOETHYL)TRIORGANOPHOSPHONIUM SALT, PROCESS FOR ITS SYNTHESIS AND ITS USE AS AN ELECTROLYTE COMPOUND, AS A LUBRICANT AND LUBRICANT ADDITIVE, AS A GAS CAPTURE AGENT, 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 process and its use as an electrolyte compound, as a lubricant and lubricant additive, as a gas capture agent, as a solvent for catalysis and as a surface modification agent by Click Chemistry.

Field of 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 that involves the alkylation of an asymmetric triorganophosphine with a (2-cyanoethyl) chain. This synthesis uses a non-aromatic triorganophosphine that 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 that obtains a mixture of by-products that 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 _PH3 (toxic, flammable and extremely sensitive to oxidation) or phosphorus trichloride _PCl3 and this leads to a mixture of mixed primary, secondary and tertiary phosphines that are difficult to control.

Current synthesis processes do not allow this asymmetric triorganophosphine precursor to be easily obtained.

Current synthesis processes do not allow the elimination of traces of phosphine oxides and phosphorus by-products, which results in poor purity of the synthesized product.

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

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

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

There is a real need for a new family of asymmetric mono(2-cyanoethyl)triorganophosphonium compounds with different non-aromatic substituents and a synthesis process that can produce high-purity products that are compatible with industrial scale.

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

(I)

in which

X ^- is selected from fluoroalkyl phosphates, fluoroalkyl phosphinates, fluoroalkyl phosphonates, acetates, triflates, imides, amides, methanides, borates, phosphates, sulfonimides or aluminates;

R1, R2 and R3 are different from each other and independently selected 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 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.

The invention also relates to a dimer of (2-cyanoethyl)phosphonium salt 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 a lubricant additive, 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, 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 a better desolvation of Lithium ions as well as a strong interaction with the surfaces and gives the possibility of being grafted on the surfaces. These new salts are asymmetric, 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 for different interaction with surfaces and bis(trifluoromethanesulfonyl)imide (FSI) salts have lower melting points.

The method according to the invention has several advantages.

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

Second, the synthesis precursors are inexpensive and air stable, and the synthesis intermediates are of low toxicity.

Third, the reactions involved are not very sensitive to oxygen.

Fourth, the synthesis process allows for the independent selection of the three non-aromatic organic groups that replace the (2-cyanoethyl)triorganophosphonium salt.

Fifth, the synthesis process allows obtaining high purity (2-cyanoethyl)triorganophosphonium salts.

Sixth, the process allows an industrializable synthesis route.

DETAILED DESCRIPTION OF THE INVENTION

A first object of the invention concerns a new family of phosphonium salts of formula (I)

(I)

in which

X ^- is selected from fluoroalkyl phosphates, fluoroalkyl phosphinates, fluoroalkyl phosphonates, acetates, triflates, imides, amides, methanides, borates, phosphates, sulfonimides or aluminates;

R1, R2 and R3 are different from each other and independently selected 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 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.

Hydrogen atoms can therefore be partially substituted as long as the molecule is stable.

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

The term "alkenyl" means an alkyl group, as defined above, comprising at least one C=C double bond.

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

In a more particularly preferred embodiment, R1 is selected from a C1-C10 alkyl in which the hydrogen atoms may 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 selected from methyl or C1-C4 alkyl in which the hydrogen atoms may be substituted by fluorine, _-CF3 , ether, alkyl, perfluorinated alkyl, silyl, siloxy, sulfoxide, nitrile, thioether or combinations thereof; and R2 is C1-C10 alkyl in which the hydrogen atoms may be substituted by fluorine, _-CF3 , ether, alkyl, perfluorinated alkyl, silyl, siloxy, sulfoxide, nitrile, thioether or combinations thereof; and even more preferably, R2 is chosen from methyl, ethyl, propyl, isobutyl, n- butyl, or allyl; and of which R3 is preferably chosen from C1-C10 alkyl and even more preferably from 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 selected from FSI or TFSI.

The preferred embodiments as to the choice of the anion X ^- set out above can be combined with the preferred embodiments as to the choice of the groups R1, R2 and R3 set out previously.

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

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

(II)

in which

Z is chosen from C1-C20 alkyl diradicals 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;

X ^- is selected from fluoroalkyl phosphates, fluoroalkyl phosphinates, fluoroalkyl phosphonates, acetates, triflates, imides, amides, methanides, borates, phosphates, sulfonimides or aluminates;

R2 and R3 are different from each other and independently selected 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; provided that R2 and R3 are different from a CH ₂ -CH ₂ -CN chain.

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

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

(a) Mixing an alkali alcoholate solution with a tetrakis(hydroxymethyl)phosphonium chloride (THPC) solution or a tetrakis(hydroxymethyl)phosphonium sulfate (THPS) solution 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 mixing 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 combinations thereof to 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 alkali alcoholate solution with the salt obtained in step f) in alcohol to obtain mixture B

h) Drying of mixture B

i) Addition followed by mixing 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 combinations thereof; 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 alkali alcoholate solution with the salt obtained in step j) in alcohol to obtain mixture C

l) Drying of mixture C

m) Addition followed by mixing 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 combinations thereof; 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 to obtain the (2-cyanoethyl)phosphonium salt PR1R2R3(2CN)X

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

(a) Mixing an alkali alcoholate solution with a tetrakis(hydroxymethyl)phosphonium chloride (THPC) solution or a tetrakis(hydroxymethyl)phosphonium sulfate (THPS) solution 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 mixing 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 combinations thereof to 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 alkali alcoholate solution with the salt obtained in step f) in alcohol to obtain mixture B

h) Drying of mixture B

i) Addition followed by mixing 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 combinations thereof; 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 alkali alcoholate solution with the salt obtained in step j) in alcohol to obtain mixture C

l) Drying of mixture C

m) Addition followed by mixing of an electrophile YZY of which Y can be a halide or OTf (triflate) or OTs (tosylate) and of which Z is chosen from C1-C20 alkyl diradicals of the type –(CH ₂ )n– which can comprise one or more ethers or which can comprise one or more chains of the 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 combinations thereof; 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 to obtain the dimer (2-cyanoethyl)phosphonium 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 Click Chemistry.

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 discharge capacities and coulombic efficiencies of whole cells (LMNO//Graphite) with and without (2-cyanoethyl)ethylmethylpropylphosphonium bis(fluorosulfonyl)imide P123(2CN)FSI at a C rate of 0.5 C between 2 V and 5 V versus 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 acrylonitrile is added. The reaction medium is filtered to recover the precipitate formed (TCP). The TCP phosphine is dissolved in a solvent and iodomethane is added with stirring. The mixture obtained is filtered and dried to recover the tris(2-cyanoethyl)methylphosphonium iodide salt. A solution of alkaline alcoholate is added to a suspension of tris(2-cyanoethyl)methylphosphonium iodide salt in an alcohol with stirring. The reaction medium is evaporated to obtain 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 alcoholate solution is added to a suspension of bis(2-cyanoethyl)ethylmethylphosphonium bromide salt in an alcohol with stirring. The medium is evaporated under vacuum to obtain 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 (2-cyanoethyl)ethylmethylpropylphosphonium iodide salt. In a solvent, (2-cyanoethyl)ethyldimethylphosphonium iodide is added in suspension with LiFSI with 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%. T°cryst < -80 °C.

EXAMPLE 2: P r e battery preparation lmno //graphite with and without compound [P123(2CN) FSI] and charge and dump from the stack

In a glove box under an inert atmosphere (Argon) with a water and O ₂ content of 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 compound of (2-cyanoethyl)ethylmethylpropylphosphonium P123(2CN)FSI (0.154 g) is then added and mixed to obtain a homogeneous electrolyte solution.

Table 1 below lists the different cathode/anode/electrolyte combinations tested in batteries.

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 by 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 0.5 C
( ^1st cycle) 105.85 105.34 99.51 1M LiFSI in PYR13FSI + 0.063 mol/kg P123(2CN)FSI 0.5 C
( ^246th cycle) 98.48 98.17 99.68 1M LiFSI in PYR13FSI + 0.063 mol/kg P123(2CN)FSI 0.5 C
( ^478th cycle) 89.09 88.80 99.68 1M LiFSI in PYR13FSI 0.5 C
( ^1st cycle) 107.99 107.45 99.51 1M LiFSI in PYR13FSI 0.5 C
( ^246th cycle) 93.64 93.33 99.67

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

Table 2 and the show the discharge capacity as a function of the number of cycles of the two 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 concerning the cyclability, the capacity of the system containing the P123(2CN)FSI compound is more stable during the cycles. Indeed, taking into account the first 246 cycles, the loss of capacity in discharge for the system without P123(2CN)FSI compound is 13.14% against 6.81% for the one containing the (2-cyanoethyl)ethylmethylpropylphosphonium compound.

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

Claims (12)

(2-Cyanoethyl)phosphonium salts represented by the formula (I):
(I)
in which
X ^- is selected from fluoroalkyl phosphates, fluoroalkyl phosphinates, fluoroalkyl phosphonates, acetates, triflates, imides, amides, methanides, borates, phosphates, sulfonimides or aluminates;
R1, R2 and R3 are different from each other and independently selected 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 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. A phosphonium salt according to claim 1 wherein R1, R2 and R3 are different from each other and independently selected from a C1-C10 alkyl in which the hydrogen atoms may 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; with the proviso 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 , 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; with the proviso 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 selected 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 the synthesis of a phosphonium salt as defined in one of claims 1 to 5 comprising the following steps:
(a) Mixing an alkali alcoholate solution with a tetrakis(hydroxymethyl)phosphonium chloride (THPC) solution or a tetrakis(hydroxymethyl)phosphonium sulfate (THPS) solution 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 mixing 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 combinations thereof to 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 alkali alcoholate solution with the salt obtained in step f) in alcohol to obtain mixture B
h) Drying of mixture B
i) Addition followed by mixing 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 combinations thereof; 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 alkali alcoholate solution with the salt obtained in step j) in alcohol to obtain mixture C
l) Drying of mixture C
m) Addition followed by mixing 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 combinations thereof; 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 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 the phosphonium salt as defined in one of claims 1 to 6 as a gas capture agent. Use of the 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 the phosphonium salt as defined in one of claims 1 to 6 as a lubricant additive or as a lubricant.