The evaporation study of silicon-containing ionic liquid

Accepted Manuscript Research paper The evaporation study of silicon-containing ionic liquid Norbert S. Chilingarov, Artem A. Medvedev, Grigoriy S. Deyko, Leonid M. Kustov, Elena A. Chernikova, Lev M. Glukhov, Marina V. Polyakova, Vitaliy A. Ioutsi, Vitaliy Yu. Markov, Lev N. Sidorov PII: DOI: Reference:

S0009-2614(16)30305-0 http://dx.doi.org/10.1016/j.cplett.2016.05.015 CPLETT 33855

To appear in:

Chemical Physics Letters

Received Date: Accepted Date:

8 April 2016 7 May 2016

Please cite this article as: N.S. Chilingarov, A.A. Medvedev, G.S. Deyko, L.M. Kustov, E.A. Chernikova, L.M. Glukhov, M.V. Polyakova, V.A. Ioutsi, V.Y. Markov, L.N. Sidorov, The evaporation study of silicon-containing ionic liquid, Chemical Physics Letters (2016), doi: http://dx.doi.org/10.1016/j.cplett.2016.05.015

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The evaporation study of silicon-containing ionic liquid Norbert S. Chilingarov a, Artem A. Medvedev a, Grigoriy S. Deyko a, Leonid M. Kustov a,b, Elena A. Chernikova b, Lev M. Glukhov b, Marina V. Polyakova a, Vitaliy A. Ioutsia, Vitaliy Yu. Markov* a, Lev N. Sidorova a

Chemistry Department, M.V. Lomonosov Moscow State University, Leninskie Gory 1-3, 119991 Moscow, Russia, [email protected] b

N.D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Leninskiy avenue 47, 119991 Moscow, Russia, [email protected]

ABSTRACT 1,2-dimethyl-3-(1´,1´,3´,3´-tetramethyl-3´-phenyldisiloxanyl)methylimidazolium bis(trifluoromethanesulfonyl)amide ([PhC5OSi2 MMIm+][Tf2N−]) is the first silicon-containing ionic liquid which was characterized with the vaporization enthalpy, (138.5±1.8) kJ·mol−1, and saturated vapor pressure, ln(p/Pa)= −(16656±219)/(T/K)+(30.69±0.92). This compound is an unique ionic liquid giving ions, retaining both cationic and anionic portions, in the electron impact ionization (EI) mass spectrum.

Keywords: ionic liquid, vaporization enthalpy, vapor pressure, mass spectrum, Knudsen cell, ions, fragments

Supplementary Information (SI) attached (see Supl1.docx)

INTRODUCTION Ionic liquids ([Cat +][An−]) demonstrate great potential for practical use as materials for ion generation in various ionic techniques, non-volatile heat-transfer agents, ionic solvents in electrochemistry, surfactants, lubricants, reagents and catalysts in chemical synthesis. Ionic liquids with an organosilicon substituent are expected to possess unique physical properties beneficial for their applications. By a present moment the density, viscosity, conductivity and glass transition temperatures have been measured for some of them.[1−3] The introduction of a

*

Correspondence to Dr. Sc. V. Yu. Markov, Chemistry Department, M.V. Lomonosov Moscow State University, Leninskie Gory 1-3, 119991 Moscow, Russia, tel: +7 4959395373, fax: +7 4959391240, e-mail: [email protected]

siloxane fragment instead of an aliphatic one in the cation brings about a lower viscosity at a higher molar mass.[1−2] The intermolecular interaction, molecular dynamics and electronic structure of some silicon-containing ionic liquids have been also studied.[1, 4] In practice, the realization of the aforesaid perspectives requires that the thermodynamic characteristics of ionic liquids be available, those for vaporization are most intriguing. For a long time, ionic liquids were believed to decompose before reaching vaporization temperatures, but in 2005 some interesting exceptions were found.[5] Up to now the vaporization enthalpy and saturated vapor pressure

have

been

determined

only

for

alkylimidazolium

bis(trifluoromethanesulfonyl)amides.[6−19] Data on the evaporation of ionic liquids with organosilicon moieties are completely absent. Here we first report on the vaporization enthalpy and

saturated

vapor

pressure

phenyldisiloxanyl)methylimidazolium

of

1,2-dimethyl-3-(1´,1´,3´,3´-tetramethyl-3´-

bis(trifluoromethanesulfonyl)amide

([Cat +]=

[PhC5OSi2MMIm+], 1, [An−]=[Tf2N−]).

1

EXPERIMENTAL A sample of [PhC5OSi 2MMIm+][Tf2N−] was synthesized by the reaction of 1,2dimethylimidazole with 1,1,3,3-tetramethyl-1-chloromethyl-3-phenyldisiloxane (SI, S1) followed

by

an

ion

exchange

reaction

with

lithium

bis(trifluoromethanesulfonyl)amide.[2] [PhC5OSi2MMIm+][Tf2N−] C18H27F6N3O5S2 Si2. Calcd. (%): C, 36.05; H, 4.54; F, 19.01; N, 7.01; O, 13.34; S, 10.69; Si, 9.37. Found (%): C, 35.96; H, 4.61; F, 19.00; N, 6.95; S, 10.66; Si, 9.41. 1H NMR (300 MHz, DMSO-d6). (ppm): 0.15 (6H, s, OSi(CH3)2Ph), 0.29 (6H, s, CH2Si(CH3 )2O), 2.46 (3H, s, CCH3 ), 3.70 (3H, s, NCH3 ), 3.83 (2H, s, NCH2 Si), 7.37−7.49 (6H, m, Ph + C(5)H(Im)), 7.62 (1H, br. s, C(4)H(Im)). MALDI mass spectra (> 1%), positive

ion

mode:

[PhC5OSi2MMIm+]

(100%),

[PhC7O2Si3MMIm+]

(1.4%),

{[MMIMCH2Si(Me)2(OSi(Me)2)2CH2MMIm][Tf2N]}+ (3.3%); negative ion mode: [Tf2N−] (100%). HRMS (electrospray), positive ion mode: found 319.1656, calcd. for C 16H27N2OSi2 (Cat+)

319.1656.

[PhC 7O2Si3MMIm+] +

and

{[MMIMCH2Si(Me)2(OSi(Me)2)2CH2MMIm][Tf2N]} peaks correspond to impurities (SI, S2).

A Knudsen Effusion Mass Spectrometry (KEMS) with electron impact ionization (EI) was applied to study the vaporization of [PhC5OSi2MMIm+][Tf2N−], the electron energy being 75 eV. The experimental setup was constructed on the base of a commercial MI1201 magnetic sector device and detailed elsewhere [19−20]. The stainless steel effusion cell (orifice diameter 0.35 mm, channel length 0.15 mm) had an effective evaporation/effusion area ratio > 6103. Matrix-assisted laser desorption/ionization (MALDI) mass spectra were acquired using the Bruker AutoFlex II reflector time-of-flight mass spectrometer equipped with an N2 laser (337 nm, 2.5 ns pulse). Trans-2-[3-(4-tert-butylphenyl)-2-methyl-2propenylidene]malononitrile (DCTB, ≥98%, Sigma-Aldrich) was chosen as a matrix, matrix-to-analyte molar ratio being more than 100/1. High resolution mass spectra (HRMS), including collision induced dissociation (CID) spectra, were acquired using AB Sciex TripleTOF 5600+ instrument, DuoSpray ion source (electrospray ionization mode), acetonitrile (LiCrosolv, LC-MS grade) solvent, concentration of analyte ~ 0.1 ng/ml.

RESULTS AND DISCUSSION The EI mass spectrum of [PhC5OSi2MMIm+][Tf2N−] is presented as Table 1 and Fig. 1 (mass range 515−605). In addition to [Cat +] (most prominent), its fragments, double charged {[Cat]−Me}2+, and impurity ion [PhC 7O2Si3MMIm+], there were ions {[Cat][An]−Ph}+, {[Cat][An]−H−2Me}+,

{[Cat][An]−Me}+

and

{[Cat][An]−H}+

which

arose

from

{[Cat][An]}•+ by the loss of small neutral pieces of the cation portion while retaining the entire anionic one.† The presence of similar ions in EI mass spectra of ionic liquids has not been reported previously. The high resolution mass spectrum (HRMS) of the collision induced dissociation (CID) (Fig.2) of [Cat +], generated by electrospray ionization, demonstrated a large number of peaks, including peaks which were present in the EI mass spectrum and assigned to the fragments of [Cat+]. Thus, there are two channels of decay of [PhC5OSi2MMIm+]: the complete or partial breaking of a substituent and the loss of a neutral fragment involving imidazolium moiety. Both obey the even-electron rule typical for cations of ionic liquids [19, 21]. EI mass spectra remained unchanged while varying the temperature. MALDI mass spectra and IR spectra of [PhC5OSi2MMIm+][Tf2N−] (SI, S3 and S4) did not undergo any changes after evaporation experiments. Therefore, the evaporation of [PhC 5OSi2MMIm+][Tf2N−] occurs congruently. Its vaporization enthalpy was obtained by least squares fitting (LSF) of the ln(I[Cat+]T) versus T-1 datasets, seven runs being performed (SI, S5). The results are presented in

†

"−" sign in a chemical formula of ion indicates that a neutral peace, standing after it, was lost.

Table 2. The averaged value, (138.5±1.8‡) kJ·mol−1, is recommended as the vaporization enthalpy of [PhC5OSi2MMIm+][Tf2N−] at the average temperature of the measurement range (= 457 K). A comparison with alkylimidazolium bis(trifluoromethanesulfonyl)amides indicated this value to lie between those for 1-octyl-3-methylimidazolium [C8MIm+], (136.8±1.0) kJ·mol−1 (387 K), and 1-decyl-3-methylimidazolium kJ·mol−1

(395

K)

[17].

The

data

for

[C10MIm+], (142.5±1.0)

1-nonyl-3-methylimidazolium

bis(trifluoromethanesulfonyl)amide [C9MIm+][Tf2 N−] was unavailable. The saturated vapor pressure of [PhC5OSi2 MMIm+][Tf2N−] was measured in two isothermal evaporation experiments at 468

and 483

K to be (6.93±0.77)10-3 and

(2.42±0.08)10-2 Pa, respectively. The experimental procedure was similar to that in work [19]; 0.9 and 3.1 mg§ were evaporated respectively at 468 and 483 K during 108 h. These values and the recommended vaporization enthalpy were used to derive the recommended temperature equation for the saturated vapor pressure (423–498 K): ln(p/Pa)= − (16656±219)/(T/K) + (30.69±0.92)

(1).

CONCLUSIONS [PhC5OSi2MMIm+][Tf2N−] is the first silicon-containing ionic liquid, the vaporization characteristics of which were determined. Moreover, by a present moment, it is an unique ionic liquid giving ions, retaining both cationic and anionic portions, in the EI mass spectrum.

ACKNOWLEDGEMENTS This research was supported by the grant of Russian Science Foundation no. 14-19-00503. The authors are grateful to Dr. Michael Temerin for fruitful discussion, and to Thermo Fisher Scientific and MS Analytica companies for providing their equipment to perform the gas chromatographic/mass

spectrometric

analysis

of

1,1,3,3-tetramethyl-1-chloromethyl-3-

phenyldisiloxane.

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TABLES Table 1 +

−

Peak list of EI mass spectrum of [PhC5OSi2 MMIm ][Tf2N ], electron energy 75 eV, [Cat+]= [PhC5OSi2 MMIm+], [An−]= [Tf2N−] Ion

m/z single isotopic

Intensity, %

{[Cat][An]−H}+

598.1

0.6

{[Cat][An]−Me}+

584.1

10.1

{[Cat][An]−2Me−H}+

568.0

0.6

{[Cat][An]−Ph}+

522.0

5.0

[PhC7O2Si3MMIm+]

393.2

0.8

[Cat+]

319.2

100

{[Cat]−CH4}

+

303.1

4

PhMe3Si2OH+

195.1

2

PhMe2Si2OCH2+

193.1

3

PhMe2Si2O+

179.0

2

{[Cat]−Me}2+

152.1

15

PhSiMe2+

135.1

3

CH2MMIm+

110.1

5

Table 2 Vaporization enthalpy of [PhC5OSi2 MMIm+][Tf2N−] as a result of LSF of ln(I[Cat+]T) versus T-1 Temperature range, K

423−498

, K

457

Averaged

Run

ρ2 for LSF

ΔvH, kJ·mol−1

1

0.999

138.3

2

0.999

138.2

3

0.998

141.1

4

0.999

135.0

5

0.998

139.1

6

0.998

137.4

7

0.998

140.2 138.5 ± 1.8

FIGURE CAPTIONS Figure 1. EI mass spectrum of [PhC5OSi2MMIm+][Tf2N−] in the mass range 515−605, temperature of Knudsen cell 513 K, electron energy 75 eV. Figure 2. High resolution CID mass spectrum (R> 40000) of [PhC5OSi2 MMIm+], generated by electrospray ionization, fragmentation energy 50 eV.

Graphical Abstract

HIGHLIGHTS

The evaporation study was first performed for silicon-containing ionic liquid. The vaporization enthalpy of silicon-containing ionic liquid is (138.5±1.8) kJ·mol−1. EI mass spectrum first showed ions retaining entire anionic portions of ionic liquid.