Langmuir 1992,8, 1688-1689
1688
Notes Solid-state Reaction of Phenethylammonium Chloride and Al-Exchanged Clays As Followed by Cross-Polarization/Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy Shelton Bank' and Gabriel Ofori-Oki Department of Chemistry, State University of New York at Albany, Albany, New York 12222 Received January 24, 1992. In Final Form: March 30, 1992
Solid-solid reactions are thought to occur according to the so-called topochemical factor' and molecular loosening.2a The topochemical factor can be stated as '...reactions in the solid state occur with a minimum amount of atomic or molecular movement." Molecular loosening and the attendant nucleation are commonly associated with crystal defects, and indeed 'crystal defects play a substantial role in determining the rate of reactions in the solid The nature of clay structure, that is, having a myriad of defects in an ordered structure, would suggest many possibilities for solid-solid reactions. Moreover, clays have expanded layers with many edges and unoccupied sites available for ion migration. We3 and others4 have found that this kind of metal ion motion in solid clays is rapid on the NMR time scale and that cross-polarization/magic angle spinning nuclear magnetic resonance (CPMAS NMR) spectroscopy is an ideal method for identification and characterization. 13C CPMAS NMR has also been used to follow proton-electronreactions in the solid system quinone-hydr~quinone.~We describe in this paper the use of CPMAS NMR to identify a proton transfer and ion migration in a solid amine-clay mixture. The 13C CPMAS NMR spectrum of phenethylammonium chloride gives rise to an aromatic region with a line width of 171 Hz and is described adequately as the ipso carbon cleanly separated from the other five carbons. The 13CCPMAS NMR spectrum of the phenethylammonium ion, when ion exchanged on select clays, has line widths on the order of 400Hz, and the region is a complex envelope of multiple chemically-shifted species. While an increase in line width is expected for an adsorbed material on a surface, there is a significant differential broadening in the aromatic region compared to the aliphatic region as shown in Figure lb. This broadening is considered to be the result of motionally restricted rotation of the aromatic ring leading to differences in the chemical shifts of the two ortho and the two meta carbons. The line widths and chemical shift differences give the resulting spectrum for the ion-exchanged material and lead to a considerably broader aromatic signal (Table I). These same spectral differences were reported for the benzyltriethylammonium ion when the solid bromide and the ion-exchanged
. . 160
140
120
100
80
60
40
20
0
PPY
Figure 1. 13C CPMAS NMR spectra with 1-ms contact time of (A) phenethylammoniumchloride, (B)phenethylammoniumion
exchanged on Hectorite, (C)ground mixture of solid phenethylammonium chloride and Hectorite. Line broadening of 25 Hz was applied to all spectra. Table I. Line Widths. of '42 Aromatic Carbons of Ammonium Cationsb phenethylammonium cation benzyltriethylammonium cation Clb) Lap ion exch Hector ion exch Cl(e)/Hector Cl(s)/Lap
171 380 400 400 400
Br(s)c Lap ion exchc Br(s)/Lap
140 450
140
Hertz. Abbreviations used: solid, e; Laponite, Lap; Hectorite, Hector; ion exchanged, ion exch. Ground solids are Separated by a slant. Reference 6. (I
(1) Cohen, M. D.; Schmidt, G. M. J. J. Chem. SOC. 1964, 1996. (2) (a) Paul, I. C.; Curtin, D. Y. Acc. Chem. Res. 1973,6,217. (b) Bym, S. R. Solid State Chemistry ofDrugs; Academic Press: New York, 1982. (3) Bank, S.; Bank, J. F.; Ellis, P. D. J. Phys. Chem. 1989, 93, 4847. (4) (a) Weiss, C. A., Jr.; Altaner, S. P.; Kirkpatrick, R. J. Geochem. Cosmochim. Acta 1990,54, 1655. (b) Laperches, C. V.; Lambert, J. F.; Frost, R.; Fripiat, J. J. J.Phys. Chem. 1990, 90,8821. ( 5 ) Scheffer, J. R.; Wong, Y. F.; Patil, A. 0.; Curtin, D. Y.; Paul, I. C. J.Am. Chem. SOC. 1985, 107, 4898.
..
~. - .
.
material on Laponite were measured.6 Related results of restricted motion have been obtained for o-xylene, but not p-xylene, in ZSM-5 catalyst? When the two solids phenethylammonium chloride and Al-exchanged Hectorite (or Laponite) are mixed and 0 1992 American Chemical Society
Notes
Langmuir, Vol. 8,No. 6,1992 1689
ground with a mortar and pestle for several minutes, the resulting mixture gives rise to an NMR spectrum (Figure IC)identical to that of the ion-exchanged material (Figure l b ) and not that of pure phenethylammonium chloride (Figure la). The phenethylammonium ion now occupies sites in the clay structure in which rotational averaging of the ortho and meta carbons is not possible (Table I). For this process to occur, the phenethylammonium ion that was associated with the chloride ion must now be associated with the clay anion and occupy an inner clay site. This suggests that proton transfer and subsequent ion migration indicated by eq 1 have occurred.
times.g In this regard the layered clay structure likely contributes to the facility of ion motion occurring via the unoccupied sites. Since these vacancies are probably far more numerous and random than the defect sites in solids, the ion migration in clays is faster. This rapid proton transfer and ion migration in clay structures may have some bearing on processes occurring in environmental situations. For example, the use of claylined beds for the storage of hazardous materials might be vulnerable to solid-state reaction and migration. Additionally, acid rain in areas surrounding lakes could contribute to contamination by solid-state proton transfer and ion migration.
Experimental Section k
I
H'
H H'
H
At
IH '
H
To demonstrate that a proton-transfer reaction was necessary for the process, we performed a similar experiment with benzyltriethylammonium bromide. Under these conditions the resulting NMR spectrum was identical to that of the solid benzyltriethylammonium bromide and distinct from that of the ion-exchanged benzyltriethylammonium ion (Table I). Therefore, reaction and ion migration did not take place. As indicated by eq 2, reaction in this case would require more than proton transfer.
0 - 0
clay-H+ +
Br-
\
N', CH2 CH3'
I
I
+
clay-
HLh-CH2CH3
-CH,CH,
I
CH
CH \2 CH3
CH3CH2Br (2)
For the proton reaction, one can envision a series of cooperative transfers of pairs of protons with identical energies followed by ion migration into the inner clay structure (eq 3). This is in line with the topochemical
-
clay-H+ + clay-Ph(CH,),NH,+ clayTh(CH,),NH,+
+ clay-H+ (3)
thesis which states that reactions in the solid state occur with a minimum amount of atomic or molecular movement. A comparable process is not possible when the ammonium ion does not have a proton as in the quaternary case. Reaction here would require significant molecular movement and is not aided by a series of isoenergetic steps in line with the topochemical factor. While the limits of reaction are still under izlvestigation, it is clear that the reaction initiated by grinding the two solids together is fast (less than 0.5 h a t room temperature). Cocrystalsare easily prepared by grinding two solids together? Solid-lid proton-transfer reactions are known but usually require higher temperatures and/or longer (6)Ocelli, M. L.; Iyer, P. S.; Sanders, J. V. Zeolites: Facta, Figures, Future. In Studies of Surface Science and Catalysis;Jacobs, P. A,, van Santen, R. A., Eds.; Elsevier: Amsterdam, 1989; Vol. 49, p 469; Chem. Abstr. 1989, 111, 220034q. (7) Nagy, J. B.;Derouane, E. G.; Resing, H. A,; Miller, G. R. J. Phys. Chem. 1983,87,833. (8)Etter, M. C. J. Phys. Chem. 1991, 95, 4601.
NMR Spectra. The solid-state 13C CPMAS spectra at 25 MHz were obtained on a modified Jeol60FX with a Chemagnetics 2.35-T magnet equipped with a Chemagnetics probe. KelF rotors were used with spinning speeds of 2.5-3.5 kHz. The single pulse sequence used a contact time of 1ms (unoptimized) and a recycle time of 4 8. The solution 13CNMR spectra were obtained at 75.5 MHz using a Varian XL300 at 7.05 T and Waltz proton decoupling. All spectra are referenced to tetramethylsilane. C~H&XI&H~NHaCl. Anhydrous HCl was passed through a solution of phenethylamine (0.3 mL, 0.0024 mol) in dry diethyl ether (20 mL) for 10 min at 0 OC. The white precipitate was filtered and dried in vacuum; yield (0.31 g, 0.002 mol) 82%.The I3CCPMAS NMR spectra had signals at 138.0 (60), 128.0 (171), 42.0 (225),and 33.5 (117) ppm. The line widths (Hz) are given in the parentheses. LaponitePhEtNHsCI Ion Exchanged. A phenethylammonium chloride solution was prepared from phenethylamine (27 mL, 0.215 mol) and a solution of concentrated HCL (18mL, 36.5 % w/w) and 50 mL of deionized water at 0 OC. The solution was added to the stirred Laponite (Laponite RD, WaverlyMineral Products Co.) suspension (1.5 g) in 150 mL of deionized water, leading to a gel. The resulting mixture was heated at 80 OC for 4 h, cooled to room temperature, and centrifuged, and the pellet was washed with deionized water (four times, 100 mL each) and dried at 75 "C for 48 h. HectoritePhEtNHsCI Ion Exchanged. The procedure followed was that above from 1.0 g of Hectorite (Source Clay Repository of the Clay Mineral Society), 100 mL of deionized water, 18 mL of phenethylamine, and 12 mL of concentrated HC1. HectoritePhEtNHaCl Ground. Al-exchanged, calcined Hectorite (0.504g) was added toPhEtNH&1(0.065 g) in a mortar and ground with a pestle for 15 min. LaponitePhEtNHaCI Ground. The procedure followedwas that above for Hectorite but with Al-exchanged Laponite (0.502 g) and PhEtNHaCl (0.065 9). HectoritePhCHzNEtaBrGround. The procedure followed was that above for Hectorite but with Al-exchanged Hectorite (0.50 g) and PhCHzNEtsBr (0.108 9). LaponitePhCHzNEtsBr Ground. The procedure followed was that above for Hectorite but with Al-exchanged Laponite (0.50 g) and PhCHzNEtsBr (0.109 g).
Acknowledgment. Acknowledgment is made to the donors of the Petroleum Research Fund, administered by the American Chemical Society, for support of this research. (9) Lin, C. T.; Siew, P. Y.; Bym, S. R. J. Chem. SOC.,Perkin Trans. 2 1978,963.
