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Organic Derivatives of Mica-type Layer-Silicates.

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carbon is isolated as a red oil but has low thermal stability and is susceptible to autoxidation. On catalytic
hydrogenation under mild conditions, it absorbs three
moles of hydrogen to form the previously reported compound s-hydrindacene (8.5) [501. Bromination of sindacene to give hexabromo-s-hydrindacene(86) is also
associated with a transition of the quinonoid system
(84) to the energeticallyfavored benzenoid system of s
hydrindacene (85).
s-Indacene (84), which is closely related to the still unreported compound pentalene [7], is a nonalternating
hydrocarbon(like heptalen 1511) with twelvesc-electrons.
In agreement with theoretical considerations, s-indacene
behaves more like a cyclopolyolefinthan a nonbenzenoid “aromatic” system.
Conclusion
Discussions of “aromatic character” have resulted in
recent years in fruitful theoretical proposals and in the
synthesis of numerous nonbenzenoid cyclic conjugated
[SO] R. T. Arnold and E. Rondesivedr, J. Amer. chem. Soc. 67,1265
(1945).
15 I ]H.J. Dauben and D. J. Bertelli, I. Amer. chem. SOC.83,4659
(1961).
systems. Despitesystematicand critical attack from both
the theoreticaland experimentalstandpoint, the concept
of “aromatic character” still remains to be precisely defined. The blurred boundary between distinctly olefinic
and classical “aromatic” systems makes interpretation
of the phenomenon difficult,and hard and fast divisions
are meaningless. Nevertheless, the cyclic conjugation,
electrondzlocalizationenergy, and chemical reacti rity of
any given compoundhave proved to be useful criteriafor
investigation of the relationships between its constitution and “aromatic character.” This has been confirmed
by the results reported in the present paper. By considering the fulvenes and several carbo- and heterocyclic
systems derived from them as examples, the existence of
some relationships between fine structure and chemical
behavior in benzenoid and nonbenzoid compounds has
been indicated. Furthermore, the great variety of reactivities of cross-conjugatedsystems has been demonstrated.
Sincere thanks are due to Prof. K. Ziegler, Prof.0.
Bayer, the Fonds der Chrmischen Industrie, the Deutsche
Forschungsgemeinschafr, Farbenfabriken Bayer, the Badische Anilin- und Soda-Fabrik, and Degussa for their
generous support of our investigations.
Received. November 14th, 1962 [A 266/76 1 9
Organic Derivatives of Mica-Type Layer-Silicates
BY PROF. DR. ARMIN W E I S
INSTITUT m R ANORGANISCHE CHEMIE DER UNIVERSITAT HEIDELBERG (GERMANY)
Dedicated to Prof.Dr. Ulrich Hofmann on the occasion of his 60th birthday
Mica-type layer-silicates such as montmorillonite and vermiculite are capable of exchanging
their cations for other (including organic) cations, just like the zeolites. These derivatives
swell in a variety of liquids. This paper presents a survey of the structures of organic
derivatives of mica-type layer-silicatesand illustrates some possibilities for their industrial
utilization.
Introduction
One-dimensional intracrystalline swelling of the clay
mineral montmorillonitewas discovered just thirty years
ago by U.Hofmann, Endell, and Wilm [l]. Since then,
the phenomenon has been repeatedly reinvestigated [2].
[l] U.Hofmnn, K. Endell, and D. Wilm,Z. Kristallogr., Mineralog. Petrogr. Abt. A 86, 340 (1933); Angew. Chem. 47, 539
(1934).
[2]In this connection, see K. Jasmund: Die Tonminerale. 2nd
Edit., Verlag Chemie, Weinheim 1955; P. F. Kerr and P. K.
Hamilton: Reference Clay Minerals. Amer. Petrol. Inst. Research
Project 49 (1949); G. Brown: The X-Ray Identification and Ctystal Structuresof Clay Minerals. Mineralogical Soc., London 1961:
R. C. Muckenzie: The Differential Thermal Investigations on
Clays. Mineralog. Soc., London 1957; R. E. Grim: Clay Mineralogy, McGraw-Hill, London 1953; R. E. Grim: Applied Clay
Mineralogy. McGraw-Hill, London 1962; M. Dkribdrd and A.
Esme: L a Bentonite. 3rd Edit., Dunod, Paris 1952.
134
This intensive research on montmorillonite is due
primarily to its industrial utilization as a binder for
molding sand, its uses in oil well drilling and in the
production of catalysts, and its importance as a model
substance in swelling studies 13.1. In the past ten years,
organic derivatives of montmorillonite have been developed and employed in the manufacture of thixotropic lacquers, thermostable lubricants, emulsion
stabilizers, etc. [4].
In mica-type layer-silicates of composition represented
by the limiting formulae
[3] U.Hofmann, Angew. Chem. 68, 53 (1956).
[4]0.P. Muller, J. W. Jordm, and J. I. Brancaro. Official Digest
Federation Paint and Varnish Production Clubs No. 294, 451
(1949); E. P. Pererson and 0. P. Muller, US-Patent 2531825
(1950);J. W. Jordan, US-Patent 2531440 (1950); E. A. Hauser,
US-Patent 2531427 (1950): L. W. Carter, J. G. Hendricks, and
D. S. Bolly, US-Patent 2531396 (1950).
Angew. Chem. internat. mit. I Vol. 2 (1963) I No.3
zeolite-type cation exchange can occur, whereby the
Mf ions can be exchanged for other cations, including
organic ones. With the exception of saturated
hydrocarbons, any solvent molecules may be introduced as swelling agent Y. The quantity of swelling
agent can be varied over a wide range. Sincethe quantity
x of monovalent cations per (Si, Al)sOlo structuralunit,
i.e. the charge on the layer structure, may also vary,
the result is an extraordinarily large variety of possible
compounds; so far, about 9O00 organic derivatives of
montmorillonite have been prepared. The properties
of these derivativessometimes vary systematically in the
sense of homologous series; at other times, unexpected
properties appear.
tion is permissiblewhen water i s used as swelling agent.
Hem the maximum percentage deviation is only f 7 %
in the various stages of swelling of montmorillonite [9].
Glycol and glycerol are incorporated especially strongly
[lo]. Determination of the uptake of glycol or glycerol
has proved to be a simple and rcliable gravimetric
method for determiningthe montmorillonitz content of
mixtures [Il, 121. Sugars are also strongly bonded, if
Ca2f or Sr2+ is present [131.
Normal solvated complexes with interplanar spacingsof
15.9-19.4 A are formed from sodium montmorillonite
with anhydrous pyridine, a-picoline, or other aromatic
nitrogenous bases [14]. In addition, water is absorbed
in discrete stagesfrom aqueous nitrogenous bases. There
are two such hydrate stages in the case of pyridine, and
as many as five in the case of a-picoline [151; see Table 1.
Montmorillonite Derivatives with Exchangeable
Inorganic Cations and Neutral Organic Molecules
Montmorillonite consists of two-dimensionally infinite
macroanions electrostatically bonded by the cations
located between them [I, 5,6]. The energy required for
swelling, i.e., for increasing the distances between the
layers by separation of the positive and negative charges,
is provided by hydration or solvationof the cations and
the anion layers. Since solvation energies are generally
substantially lower than hydration energies, only molecules of substances that have high dielectric constants
or the ability to form hydrogen bridges can be intercalated. The number of montmorillonite derivatives of
this kind is therefore limited.
Intercalated neutral molecules can be exchanged by
suspending the montmorillonite derivative in another
liquid. Since no additional swelling is required for the
exchange, and the distancebetween the layers sometimes
even decreases, a series of further derivatives may be
produced in this manner [7,8].
Most of the bonds, with which these compounds are
held in montmorillonite, are very weak. If an attempt
is made to remove a constituent adhering to the surface, liquid also escapes from the interior of the crystal.
Therefore, stoichiometric relationships are still not
clearly established. Approximate values may be computed from the magnitude of the basal plane spacing
if it is assumed that the difference between the density of
the intercalated substance within the swollen compound
and its density in the free state is negligible. This assump
[5] C. E. Marshall, Z . Kristallogr. Mineralog. Petrogr. Abt. A
91,433 (1935).
[a] W. Noll, Chem. d. Erde 10, 129 (1936).
[7] W . F. Bradley, I. Amer. chem. Soc. 67, 975 (1945); Amer.
Mineralogist 30, 704 (1945); Nature (London) 154, 577 (1944);
157, 159 (1946).
[8] D, M. C. McEwan, Nature (London) 154, 577 (1944); 157,
159 (1946); Trans. Farad. SOC. 44. 349 (1948); G. F. Waker,
Nature (London) 166,695 (1950); G. W. Brindley and M.Ruston.
Amer. Mineralogist 43, 627 (1958); R. W. Hoffmannand G. W.
Brindley, Geochim. cosmochim. Acta (London) ZO, 15 (1960).
Angew. Chem. internat. Edit. I Vol. 2 (1963) I NO.3
Water content
of the suspension
fluid [%I
&pal
0
2
5
10
15
20
25
30
35
19.4 and 14.8 [*I
diffuse [**I
di8u.w [**I
15.9
21.9
21.9
23.3
23.3
23.3
diffuse [**I
40
50
plane spacing [A]
pyridine
diffuse [**I
dimuse [**I
diffuse [**I
29.3
29.3
I
a-piwfiw
25.1
21.9
21.9
diffuse [**I
31.8
33.8
[*I On intercalation from a solution of pyridine in alkanca.
I**]
,,Diffuse” implies that tbe (001) interferences am broadened and
occur in irregularsequence, f
.c different interlayer spacings are mixed in
a random m a n w .
Unexpected derivatives with neutral, colored chelate
complexes are formed if the exchangeable cations between the silicak sheets react with organic components
capable of forming complexes, e.g. Mg ions with
quinalizarine, or Ni ions with diacetyldioxime [16]. In
-.
..
191 W. P. Bradley, Nature (London) 183, 1614 (1959); R. C.
Mackenzie, ibid. 183, 1615 (1959); 181. 334 (1958); C.P. De wit
and P.L. Arens: Trans. 4th Int. Congr. Soil Sci. Amsterdam 1959.
Vol. 2, p. 59; D. T.Oakes, Clays and Clay Minerals 5 , 4 6 (1958);
C. T. Deeds and H. v. Olphen, Adv. Chem. Set. 33, 332 (1961).
[lo] W. F. Bradley, R. A. Rowland, E. J. Weiss, and C. E. Weaver,
Clays and Clay Minerals 5, 348 (1958); C. E. Weaver, ibid. 5.
348 (1958).
[Ill R. S. Dyaland S. B. HenaWcks, Soil Sci. 69,421 (1950); C.A.
Bower and F. B. Gschwend, Soil Sci. Amer. Proceed. 16, 342
(1952); P. J. S. Bryone, Clays and Clay Minerals 2, 241 (1954);
G. W. Kunze, ibid. 3, 88 (1955).
[I21 E. B. Kinter and S. Diamond, <’lays and Clay Minerals 5,
318,334 (1958).
1131 W. W. Emerson, Nature (London) 186,573 (1960).
[I41 R. Greenc-Kelley,Trans. Farad. SOC. 51,412 (1955).
[I51 H. v. Olphen and C. T. Deeds, Nature (London) 194. 176
(1962); R. Greene-Kelley, Clay Min. Bull. 2, 226 (1955); Nature
(London) 184, 181 (1959).
[I61 A. We&s and U. Hofmann, Z. Naturfomh. 66,405 (1951).
135
this case., hydronium ions balance the negative charges
of the silicate layers [17].
Montmorillonite with Intercalated Organic Cations
Onium ions such as ammonium, phosphonium, sulfonium, or oxonium ions may replace the inorganic
cations [18-221. This substitution occurs especially well
with n-alkylammonium ions. The longer the n-alkyl
chain, the steeper the exchange isotherm corresponding
to increased bond strength [23]. Equilibrium is achieved
after only a fewhours for lowcharged montmorillonites,
but requires up to 14 months for highly charged material
[24]. Surprisingly, with the latter, attainment of equilibrium takes less time with long-chain, i.e. larger ions
than with short-chain ones; this behavior is consistent
with the mechanism for change of lattice sites within
the interior of the crystal.
The bonding strengths of the alkyl compounds decrease.
sharply in the series RNH3+, R2NH2+, and R3NH+.
Quaternary alkylammonium ions R4N+ behave quite
differently: Asymmetrical ions, such as trimethylcetyl
or dimethyl-di-n-octadecylammoniumions, must be
classified among the primary ammonium ions, whereas
symmetrical ions, on the other hand, rank behind the
secondary ammonium ions. Because of the bulkiness of
the groups: the bonding strengths of R2NH2+, RsNH+,
and symmetrical &N+ also decrease rapidly with increasing charge of the montmorillonite layers. The
behavior of sulfonium and oxonium ions is similar to
that of R3NH+.
The exchange capacity for organic cations is, generally
speaking, much the same as for small inorganic ions;
this value is never exceeded (251. An excess of alkylammonium salt can, of course, be taken up in place of the swelling
agent, giving a t times an appearance of higher exchange
capacities. The exchange capacity is more limited in highly
charged silicates, because here the organic cations can no
longer be accommodated between the densely packed layers
1261.
Intercalation of n-Alkylammonium Ions
On intercalation of n-alkylammonium ions, the resulting distance between the silicate layers depends
upon the length of the alkyl chain and the layer charge.
[17] A. Weiss, Ph.D. Thesis, Technische Hochschule Dannstadt,
1953.
[I81 C. R. Smith,J. Amer. chem. SOC.56,1561 (1934); US-Patent
2033856 (1936).
[I91 5'. B. HerUiricks, J. physic. Chem. 45,65 (1941).
(201 H. Erbring and H.Lehmann, Kolloid-Z. 107,201 (1944).
[2Oa] R. E. Grim, H. W. Allaway, and F. L Cuthbert, J. h e r .
ceram. Soc. 30,137 (1947).
[tl] E. A. Hauser and J. W.Jordan, J. physic. Colloid Chem. 53,
294 (1950).
[U]
J. W.Jordan, Mineral. Mag. 28,598 (1949).
[23] A. Weissand E. Michel, Z. anorg. allg. Chem.296,313(1958).
[24] A. Weiss, Z. anorg. allg. Chem. 297, 258 (1958).
[25] A. Welss, Clays and Clay Minerals 10, in the press (1962).
[26) A. Weiss, Z. anorg. allg. Chem. 299.92 (1959); A. Weiss and
1. Kantner, Z. Naturfoorsch. 166,804 (1960).
136
With increasing length of the alkyl chain, this distance
increases alternately by a greater or lesser amount depending on whether the resulting number of carbon
atoms in the intercalated chain is even or odd [Z271;
,
see Figure 1. This m s n s that the alkyl chains can be
25
J
Fig. 1. IncreaJing basal plane spacings on intercalation of n-alkylammonium ions with increasingly long alkyl chains
(batavite specimen from KropfmOhlc near Passau,Germany);
x in Formula (b) 0.67.
Ordinate: basal plane spacing [A]
Abscissa: number of carbon a t o m in alkyl chain
-
present neither in the form of a statistical coil nor with
their longitudinal axes parallel or perpendicular to the
silicate layers.
If the alkyl chains were perpendicular (Fig. 2e), the interlayer distance would have to increase by approximately
1.26 A per carbon atom. However, the average increase in
Figure 1 is only 1.04 A (=..1.26 Asin 56'). Thus, the true
arrangement of the alkyl chains must correspond to the
schematic representation shown in Fig. 2c or d. For reason
of clarity, however, the planar cis-trans-configuration is
shown in Fig. 2d which is less favored from the energy
standpoint.
Figure 2 c or d clearly shows the pronounced stepwise changes
in the interplanar distance encountered when the alkyl chain
is lengthened. According to Figure 1, on passing from a n
odd to the next higher even number of carbon atoms, the
interplanar distance increases by 2.0-2.1 A, but on passing
from a n even to the next higher odd number, the increase is
only 0.0-0.1 A. The value of 2.0-2.1 &C atom exceeds the
length of a single C-C bond (= 1.54 A). The additional
distance originates from the coordination of the terminal
CH3 group with the six-membered SiO ring. According to
Figure 2c, one would expect the greatest variation in the
interlayer distance to occur on transition from an even to
a n odd number of carbon atoms. The opposite is in fact
observed because the terminal CH3 group may dip into the
six-membered SiO ring only when there is an even number
of carbon atoms. On transition to an odd number of carbon
atoms, the distance betwwn the silicate layers must increase
by the entire van der Waals radius of a CH3 group.
The fact that CH3 groups can penetrate far into the sixmembered SiO ring has been shown in investigations of
methylammonium montmorillonites by Rowland and J. E.
Weiss [28]; here the basal plane spacing attained 12.5 A.
This value is some 3 A greater than the thickness of the silia t e layer and 2.0-2.5 A greater than the basal spacing
in NH4 montmorillonite.
On replacing the methylammonium with the ethylammonium cation, the basal plane spacing becomes
I271 A. Weiss, A. Mehler, and U.Hofmann, Z. Naturforsch. 116,
341,435 (1956).
[28] R. A. Rowland and J. E. Weiss, Clays and Clay Minerals 10,
(1962), in the press.
Angew. Chcm. internut. Edit. I Vol. 2 (1963) I No.3
about 2.0A larger. If the alkyl chain is made even
longer, the increase in the interplanar distance begins
to depend also on the charge on the layer [29]. In
a
-
pound; with a still lower chargc density (x 0.33), it remains practically unchanged at 13-14 A from the ethyl
to the n-decylammonium derivative. The first increase
is observed with the n-dodecylammonium compound.
With an interlayer distance of 13-14 A, there is a free
space available, with a height of 4-5 A; this is equal to
the van der Waals diameter of the chain. Evidently,
when the layer charge is low, the alkyl chains remain
flat, until the layers are densely covered (Fig. 2a). As
the charge density is increased, the chains begin increasingly to slip over one another (Fig. 2b) and stand more
erect, until finally the arrangements in Fig. 2c or d are
achieved. These arrangements are especially favored,
because the hydrogen atoms of the RNH3+ group are
able to form hydrogen bonds to the oxygen atoms of
the six-membered SiO rings without distortion of their
valence angle. A one-dimensional Fourier synthesisfor
an n-hexylammonium derivative yields N-Ha
distances of 2.85 A at the most, whcreas for the NH4+ compound, it gives distances of 3.18 A [30].
m . 0
cl
Zi
The relationship between length of the alkyl chain, basal
plane spacing and charge density (Fig. 3) may be used to
determine the charge on the layers of montmorillonoids[31].
Moreover, the montmorillonite may even be present in a
mixture of other minerals. The distances between the silicate
sheets may, of course, be affected by any preliminary treatment [25]. It is therefore necessary to carry out such work
under standardizedconditions.
e
ma
Fig. 2. Arrangements of alkylammonium ions in mica-type
layer-dlicates with different layer charges.
a) Very low charge
b) Medium charge.
c) Preferred arrangement with the formation of three hydrogen bonds
per RNHs+ ion and with rrons,bans-configuration.
d) As c) but with cls.trans-configuration (for reason of clarity the
energetically unfavorable, planar cis,rrans-configuration ia shown
here).
e) High charge.
Hatched areas: silicate layers.'
highly charged silicate layers (x in Formula (b) cu. l.O),
the basal plane spacing increases, starting with the ethyl
compound; if a somewhat lower charge density (x -0.66)
is present, it increases beginning with the n-butyl com[29] A. Weiss, Chem. Ber. 91, 487 (1958); A. Mehler, Ph.D.
Thesis, Technische Hochschule Darmstadt, 1956; C. T. Cowun
and D. White,Trans Farad. Soc. 54,691 (1958).
Angew. Chem. internal. Edit. I Vul. 2 (1963) I No.3
0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
lam
Fig. 3. Relationship of basal plane spaciii&s to the charge on the layers
in unswollen n-alkylammonium derivatives of mica-typc layer-s&atsr:
Curve I: intercalation of n-Cl8H37NH3'.
Curve 11: intercalation of ~ - C ~ ~ H Z S N H ~ ~
Curve 111: intercalation of n-GHlaNHP
Curve IV: intercalation of n-C&NH3+
Tho dashed linca indicate bsslll plane spacings for unstable
arrangements.
ordinate: basal plane spacings [A]
Abscisra: layer charge, = x in Formula (a) or (b)
Apart from its role in determiningthe exchange capacity of
montmorillonoids, the value of thc charge density has additional technological importance. Diffuse ionic double layers
[30] A. Weiss, E. Michef. and A. Weiss in: Hydrogen Bonding.
Pergamon Press,London 1959, p. 495.
[31] A. Welss and I. Kuntner, Z. Nulurforsch. I6b. 804 (1960).
137
can be formed from monovalent inorganic ions only at charge
densities below about 0.55. Under these conditions, the eltrostatic repulsion of the diffuse ionic double layers takes
the place of the electrostatic attraction between the cations
and the silicate anions [32,33]. Thus, in water, swelling
can progress until separation of the material into individual
silicate sheets occurs.
Swelling of n-Alkylammonium Montmorillonitea
in Water and Electrolyte Solutions
With the exclusion of a few still unexplained exceptions
[34], n-alkylammonium ions in montmorillonite do not
build diffuse ionic double layers with water, since the
alkyl groups are hydrophobic and the N-H...O hydrogen bridges with the silicate sheets are too strong. The
swelling of n-alkylammoniummontmorillonitesin water
is therefore completely different from that of unaltered
montmorillonite. When the alkyl chains are short, no
I
I
i
--
i
m
i
6
I
I
I
I
8
10
12
14
swelling takes place. Surprisingly, however, n-alkylammonium montmorillonites with longer alkyl chains
do swell, although here stronger hydrophobism is actually to be expected. Figure 4 shows that a relationship
exists between the charge density, the length of the alkyl
chain, and the swelling in water.
It is interesting that the samples become increasingly
hydrophobic and organophilic to the same extent as
their tendencies to intracrystalline swelling with water
increase. Thus, when such samples are shaken with a
toluenelwater mixture, for example, montmorillonite
derivatives with short alkyl chains are extracted into
the aqueous phase, while the long-chain derivatives,
which are capable of swelling in water, pass quantitatively into the toluene [35].
The swelling behavior in electrolyte solutions is also
unexpected. If inorganic cations are intercalated between the silicate layers, the basal plane spacings are
decreased when an electrolyte is added to the aqueous
swelling agent [33]. The electrolyte limits the extension
of the diffuse ionic double layers and correspondingly
decreases the electrostatic repulsion. However, in the
case of montmorillonite derivatives with long-chain nalkylammonium ions, the interplanar distances increase when an electrolyte is dissolved in the swelling
agent [25].
Swelling of n-Alkylammonium Montmorillonites
in n-Alkyl Compounds
Fig. 4. Relationship between the length of the alkyl chain. the layer
charge x. and the swelling power of n-alkylammonium
montmorilloniteain water:
Curve I: x in Formula (a) or (b) = 0.55
Curve 11: x in Formula (a) or (b) = 0.66
Curve 111: x in Formula (a) or (b) = 0.42
Curve 1V: x in Formula (a) or (b) = 0.33
Ordinate: basal plane spacing in water [A]
Abscissa: number of carbon atoms in the alkyl chain.
Swelling adopts a much simpler pattern in nonaqueous
liquids than in water or aqueous electrolytes. In nalkyl alcohols or n-alkylamines 1251 of the same chain
length as the intercalated n-alkylammonium ion, the
charge density has no longer any effect on the interplanar
distances (Table 2). No difference appears even in the
number and sharpness of the (001) interferences.
Table 2. B a d plane spacing of n-alkylammonium derivatives of mica-type layer-silicates after swelling in n-alkyl alcohols
or n-alkylaminea with alkyl chains of equal lengtha.
Intercalated:
Mica-type layer-silicate
Swelling agent:
~GHIIOH
from Hector, Calif.,
(USA)
MontmoriUonitefrom
Geisanheim (Germany)
Vermiculite from
KropfmlLhIe (Germany)
Mite from
Sarospatak (Hungary)
Muscovite from Norwaj
Biotite from
Monroe, N.Y. (USA)
25.53
A
Swelling agent: Swelling agent: Swelling agent: Swelling agent:
n-CloHZlOH.
n-CaH1,N H2
~ - G H I I N H z n-CsH170H
25.69 A
30.11 A
30.32 A
37.4
A
37.8 A
29.98 A
36.9
A
37.1 A
37.1
A
37.6
26.01 A
26.0s
A
29.91 A
A
25.84
A
30.32
25.68 A
25.94
A
29.h A
29.96
A
25.4s A
25.62
29.9,
A
36.7
A
36.9
A
25.63
A
A
29.91 A
A
30.24 A
37.1
A
37.3
A
25.6
25.38
30.04
A
A
(321 A. Webs,G. Koch, and U.Hofmann, Ber. dtsch. keram. Ges.
32, 12 (1955).
(331 A. Weiss, Chem. Ber. 91,487 (1958).
[34] G. F. Walker, Nature (London) 187, 312 (1960); W. G.
Garrett and G. F.Walker, Clays and Clay Minerals 9, (1962), in
the pms.
138
Zwelling agent:
n-CloH21NH2
30.51 A
36.9 A
A
37.2 A
The similar behavior of the minerals montmorillonite,
vermiculite,and the micas (Table 2) is due to the stoichiometry of thec‘clathrate”compounds(Table3).Thesum of
the number of n-alkylammoniumions and the molecules
(351 A. W e b , Angew. Chem. 73, 549 (1961).
Angew. Chem. internal. Wit. I Vol. 2 (1963)
I No. 3
Swelling agent Y
Hectorite from
Hector, Calif.
(USA)
n-CdH90H
to
n-ClsH310H
1.75(1.82)
Montmorillonite Montmorillonite
from Geisenfrom Cyprus
heim (Germany)
1.67(1.74)
1
Beidellia from
(Germany)
1
6:: .1
Saponite from Butavite from
Groschlatten- KropfmOhle
grOn (Germany) (Cicrmany)
Unterrupsrolh
0.58
;.42(1.50)
1
0.57
1.43(1.50)
I
3@
.:l )
lromNorway
I
0.92
1.08(1.10)
to
~-CIRH~NHZ
0.57
n-Ct,H,sCHO
1.75( I .77)
1
1.60(1.63)
I
n-C3H7COOH
to
n-Cl7HlsCOOH
0.25
ca. 1.75
0.33
ca. 1.66
ca. 1.60
1
of swelling liquid per (Si,AI)4010 unit is nearly the same
in all mica-type silicates, and amounts to 2.00-2.07, if
compounds with unbranched alkyl chains are used as
swelling agents. This number is largely independent of
the nature of the functional groups, as the results of
experimenti with alcohols, amines, aldehydes, nitriles,
carboxamides, and carboxylic acids have shown. Additional neutral molecules evidently fill the vacant
cation positions in low-charged montmorillonites.
In all of these “clathrate” compounds, the alkylammonium ions and the molecules of swellingfluid are arranged
in a bimolecularlayer between the silicateanions(Fig. 5).
1
I
I
I
0.40
0.58
ca. 1.42
0.57
a. 1.43
0.67
ca. 1.33
0.92
ca. 1.08
Since only about 23 of surfacearea are available for
each (Si,Al)4010 unit, and since a fully extended nalkyl chain in crystallinecompounds requires 18-21 ,@,
the alkyl chains must be very densely packed here, with
their longitudinalaxes perpendicularto thesilicatelayer;
this is confirmed by the basal plane spacings measured
[251.
These results are consistent with the fact that when the
molar ratio of n-alkylammonium ions to n-alkyl alcohol
is 1.0, the basal spacing is determined only by the sum
of the carbon atoms in the alkyl chains of the cation
and the alcohol. The same is observed with uranyl compounds which arecapable of swelling, c.g. M+(UO2PO4),
M+(UO~ASO~),
and M+(UO2VO4)[36].
The maximum intercalatable qunnlity is most readily determined by means of thermogravimetric analysis. If the samples are triturated in the course of the thermal analysis, a
m
Fig. 5. Arrangement of n-alkylammonium ions and of n-alkyl
compounds intercalated as swelling agents between silicate layers
(hatched area!+). The total (n-alkylammoniumions plus molecules of
n-alkyl compound) = 2.00 to 2.07 per (Si, Al)4Olo unit. Here, an n-alkyl
alcohol is drawn as an example of a swelling agent.
Angew. Chem. internat. Edit. I Vd. 2 (1963) I No.3
[36]A . Weiss, K. H a d , and U.Hoftriunn, Z. Naturforsch. 126,
351 (1957).
139
metastable intermediate stage can be obtained in which the
sum of the n-alkylammonium ions and the neutral n-alkyl
compounds per (Si, A1)4010 unit lies between 1.6and 1.75.
In this case., the sheet separation (Le. basal plane spacing
minus the thickness of the silicate anion) is smallerbya
factor of sin 56' than in themost highly swollensamples.This
may be explained by the arrangement of the alkyl chains
shown in Fig 6.
Swelling of n-Alkylammonium Montmorillonites
in Hydrocarbons
Saturated hydrocarbons cannot be intercalated into nalkylammonium montmorillonites. On the other hand,
alkenes and arol"Xltic
are absorbed
vigorously, even when present at very high dilution in
saturated hydrocarbons. The resulting basal plane
spacings are, however, not readily explainable in all
cases. The aromatic rings arrange themselves parallel to
the silicatelayers, insofar as the steric conditionspermit.
Swelling of n-Alkylammonium Montmorillonites
in Compounds with Branched Alkyl Chains
With regard to swelling in compounds containing
branched alkyl chains, such as ethers, esters, ketones,
and similar compounds, the relationships are especially
unclear. Besides the size and the form of the intercalated molecules, the position of the polar group also
plays a role in their orientation within the interior of
the crystal. The polar group is almost always in a
position in direct contact with the silicate layer, so that
the arrangementsformed have various packing densities,
depending on the molecular shape. Thus, stoichiometric
relationshipscannot be estimated simply by calculation
from the volume of the free molecules. It is especially
perplexing that, owing to their effect on the hydrogen
Di- and Trialkylammonium Montmorillonites
Montmorillonites with unsymmetrical cations, such as
methyl-n-dodecylammonium, hydroxyethyl-n - decylammonium, or di-(hydroxyethy1)-a-decylammonium,
have properties similar to those of the n-alkylammonium
montmorillonites. With large, symmetrical di- and trialkylammonium ions, however, the situation is quite
complicated even in unswollen samples because, as a
result of the bulky structure of'these cations, cavities
open to the exterior are formed in the montmorillonite.
These cavities can be filled with gasesor liquids of small
molecular size, as occufs in molecular sieves, with no
apparent change in the lattice dimensions.
Montmorillonites with Quaternary
Alkylammonium Ions
No peculiarities appear on intercalation of small quaternary alkylammonium ions. The products swell only
slightly in water and in most nonaqueous liquids [38].
Gas& can be absorbed in a zeolitetype exchange, with
no change in the basal plane spacings 1391.
Materials of this kind are therefore suited for special
gaschromatographicseparations [40].
Because of their colloidal chemical properties, derivatives with unsymmetrical ions, such as trimethyl-nhexadecylammonium or dimethyldi-n-octadecylammonium ions, are of special importance. These derivatives
are the chief constituents of the commercial Bentones
C 3 4 and C38@. These montmorillonites form thixotropic gels with high contents of liquid with the majority
of slightly polar liquids, excluding saturated hydrocarbons (Table 4) [41].
Table 4. Volumea of thixotropic golr of alkylamrnonium montmorillonito in various fluida.
Volume of thixotropic gels roquiring 6 seconds for golation (dliquid/3 g of montmorillonite)
Suspension fluid
[~-CI~HZSNH~I+[n-CisH37NH31+dorivative
derivative
methanol
ocetcme
othyl methyl k m n o
cyclohoxmono
diethyl other
toluene
nitrobemno
'
17.7
27.0
lS.6
39.3
[~-CI~H~~N(CH~)~I+derivative
~
129
12.0
18.0
12.3
23.6
18.3
34.5
18.0
23.1
16.5
324
35.7
46.5
92.4
bonds, molecules with strongly negative groups cause
the preferably prone alkyl chains of n-alkylammonium
sheet separation
to stand erect and thereby
that has no direct relationship to their dimensions.
From aqueous solutionspolar organic compounds are preferably incorporated. Alkylammonium montmorillonites might
therefore conceivably be used for wastewater purilication.
Cowan [37] has reported on quantitative experiments on the
removal of phenols.
[37] C. T.Cowan, Clays and Clay Minerals 10 (1962), in the press.
140
~~~
8.1
21.6
29.4
24.0
43.5
41.7
>I 2 0
11.7
20. I
23.1
27.0
la9
29.7
89.1
Even very limited additions of these raise the viscosity
of toluene and other solvents considerably (Fig. 7) [42].
[38] A. Weiss, Z. anorg. allg. Chem. 299,92 (1959).
[39] R. M . Barrer and D . M. M c k o d , Trans. Farad. Soc. 50,
980 (1954); R. M. Barref and J - s. s. R e w , ibid. 53, 1253 (1957).
[MI D. White. Nature (London) 179, 1075 (1957).
[41] J. W. Jordan, J. physic. Colloid. Chem. 53,294 (1950); J. W.
Jordan, B. J. Hook, and C. M. Finlayson, ibid. 54, 1196 (1950);
A. Mehler, Ph.D. Thesis, Technische Hochschule Darmstadt,
1956; W. Zmmel, Ph.D. Thesis, Technische Hochschule Darmstadt, 1960.
1421 J. W. Jordan and F. J . WiNiams, Kolloid-Z. 137,40 (1954).
Angew. Chem.internut. m i t . I Vol. 2 (1963) I No. 3
This property has led to the utilization of montmorillonites with quaternary alkylammonium ions in the
production of thixotropic lacquers and thermostable
lubricants. In mixtures containing mainly polar liquids,
rn
200
400
600
800
Pig. 7. Relationship between the viscosity of some suspensions of
dimethyldi-n-xtadecylammonium montmorillonite in toluene and the
rotation speed of the rotor in a Stormer viscosimeter.
0-0-0
S%ssolid
X-X-JI
6%dd
7 % solid
8% solid
o-0-0
9%solid
Ordinate: vkosity [cp]
Abscissa: rotation specd [rpm]
A-A-A
0-0-0
n-octadecylammoniummontmorillonites (@BentoneC
18) are preferred. The intensive gel formation of these
onium montmorillonites is always associated with the
presence of traces of water [43]. The water molecules
evidently interlink the platelike montmorillonitecrystals
by hydrogen bridges to form wide-mesh frameworks
(edge-to-edge linkage) [MI.
Fig. 8. Arrangement of alkylen~~.diammonium
ions in the most
hehly swollen state of mica-type silicatar
a) Alkylene chains with even numbers of carbon atoms.
b) Alkylene chains with odd numbers of carbon atoms.
Hatched areaa: silicate sheets.
Although the basal plane spacing in the most highly swollen state is independent of the charge density, in the dry
state, it is strongly influenced by the charge. When the
charge density is low, the chains lie flat; when it is higher,
they are coiled into a correspondingly denser packing. In the
swelling process, the volume of the swelling agent intercalated
is independent of its nature, being constant for any given
charge density of the silicate layers. As the charge density
increases, there is an increasingly greater limitation on the
shape and size of the molecules: the alkylene chains spread
the sheets apart like rigid columns. The higher the charge
density, the more closely these columns are packed together
and the more limited is the space which the swelling fluid can
occupy (Table 5).
Table 5. Calculated and observed basal plane spacings of batavite
with intercalated alkylenc-a.w-diammonium ions.
B ~ Splane
~ I spacinga [A]
Montmorillonites with Alkylene-a,o-diammonium
Ions
dried at
Cation
60°C
+H~N-(CH~)X-NH~+ and
0.1 mm
Hg
The swelling properties of mica-type layer-silicates
loaded with alkylene-a,o-diammonium ions depend
largely upon the number of carbon atoms in the alkylene
chain. If this number is even, the two NH3+ groups are
in direct contact with both the adjacent anion layers.
With a cis-trans chain that is helical or inclined at 56 O,
all six N-hydrogen atoms can form hydrogen bonds
(Fig. 8a) [45]. The basal plane spacing that corresponds
to this arrangement should therefore provide an upper
limit to the swelling, since at least two hydrogen bridges
per ion must be broken in order to exceed this distance [33].
If the alkylenechain contains an odd number of carbon
atoms, further swelling will cease when the extended
chains stand perpendicular to the anion sheets (Fig.
8b). Further swelling would require separation of the
positive and negative charges.
[43] V. R. Damerell and E. Mflberger, Nature (London) 178.200
(1956); A. Weiss and W.Immel in U.Hofmann: Internat. Kongr.
fur grenzflilchenaktive Stoffe. Mainzer Universitilts-Druckerei,
Vol. I1 B, p. 669.
[44] A . Weiss, Acta Rheolog., in the pnss.
(451 A. Weiss and E. Michel, Z. anorg. allg. chsm. 306, 278
(1 960).
Angew. Chem. internat. Edit. I Yo!. 2 (1963) I No. 3
x=
0
2
4
6
8
10
I2
under
maximum
swelling
calculated lor the
arrangementsin:
--
Pig.80
10.0
12.6
15. I
10.0
12.3
12.9
15.8
17.7
17.2
17.6
19.4
21.5
23.8
12.3
12.8
13.9
17.1
17.4
12.8
17.4
20.0
21.8
25.4
17.3
I Fig.8b
11.5
12.9
15.0
17.1
19.1
21.2
23.3
15.0
17.9
20.4
22.9
25.4
Intercalation of Alkaloid Cations
Alkaloid cations are very strongly bound by mica-type
layer-silicates[46]. Thus, they are absorbed from even
very dilute solutions. When there is enough excess
montmorillonite, i.e. as long as the alkaloid cations
remain loosely packed within the montmorillonite, the
equilibrium concentration of many alkaloids in the
(461 A . Weiss, I. Koch, G. Caring, and A. Schreiber, unpublished
reSUlt.9.
141
(area occupied per molecule = 46-50 k,
thickness = 8.1-8.6
A, molar volume = 373 to 430 A3, molar volume calculated
from molecular weight and density = 377 A3) [46].
solution falls below the limit of detectability. However,
quantitative cation exchange is possible only when the
sheet charge is low.
8
The intracrystalline swelling capacity is largely blocked by
alkaloid cations. With nicotine, however, the intercalation
compound still swells in water. On the other hand, zeolitic
uptake of liquid is always possible whenever closest packing
of the cations does not occur.
Intercalation of Amino Acids and Proteins
Amino Acids, peptides, and proteins can also be intercalated into mica-type layer-silicates[47].At low pH values, proteins are exchanged almost quantitatively. With
increasing pH values, thc number of cationic positions
in the protein drops, and the exchange becomes incomplete [48].The reaction with protamines proceeds
especially readily (Table 6). Here the swelling capacity
is probably determined largely by the guanido groups;
the formation of hydrogen bridges from these to the
silicate sheets is promoted by the symmetry relationships. This is also indicated by investigations with pure
guanidine and aminoguanidine montmorillonites [49].
Albumins, globulins, and prolamines are also intercalated. With serum globulins, the protein seems to
penetrate the lattice to only about 20-30 A from the
Pig. 9. Relationship between the cation exchanger capacity and the
magnitude of the equivalent surtace area in mica-typo layer-silicates.
Calculated exchange capacity without steric hindrance.
Calculated exchange capacity for a cation with an m a of 50 Az.
A Exchange capacity determined for codeine cations.
Ordinate: quantity of exchangeable cations (moq./IOOg)
Abscissa: equivalent surface area (A*/unit charge).
__......
Table 6. Cotion exchange in mica-type layer-silicates with proteins (salmine from herring sperm)
Equivalent surface.arca pH during exchange
of silicate ion
[Azlunit charge]
initial
final
value
value
Mica-type layer-silicate
Montmorillonite
from
Geisenheim (Germany)
calculated determined
2.5
4.6
8.7
11.2
12.1
2.7
5.9
8.0
8.5
11.4
218
218
218
252
488
222
248
262
267
266
14.8
15.7
15.9
16.9
16.9
17.1
. 17.7
18.0
18.4
18.3
Nontronite
from Grube Ficht
(Gamany)
60
2.5
4.6
8.7
11.2
12.1
2.1
3.9
7.2
7.7
11.4
263
263
263
303
588
258
250
250
272
285
15.3
15.9
16.1
17.5
17.5
18.0
19.0
18.9
19.3
20.3
Beidellite
from Unterrupsroth
(Germany)
57
2.5
4.6
8.7
2.7
5.4
8.3
10.0
11.9
316
316
316
363
706
263
258
289
283
386
15.5
17.0
17.3
17.3
17.3
18.8
19.8
I
11.2
12.1
Figure 9 summarizes the calculated and the observed relationships between the exchange capacity and the charge
density. Here the equivalent surface area (Az/unit charge)
replacep thecharge density inequivalents per (Si, A1)4010unit.
This value indicates the surface area on the anion layer
available for one monovalent cation 1331. In the absence of
steric hindrance, the exchange capacity should increase
hyperbolically as the equivalent surface diminishes. If,
however, the value of the equivalent surface area drops
below’the surface area required by the exchangeable cation,
the final exchange capacity must decrease, unless an arrangement in a bimolecular layer is possible. Since, at the same
time, the basal plane spacing and hence the third dimension
of the exchanged cation can also be determined, the shape of
large cations that are not easily deformed can be ascertained
in this fashion. This method yields good results for codeine
142
Amount of bonded
protein [mg/g of layersilicate]
20.1
20.I
20.2
outer edge of the silicate crystal. Albumins spread out
between the silicate layers. The basal plane spacing
of 14.5-15.0 A makes it clear that, at the most, a sheet
thickness of 5.5-6.0A is available for the extended
protein [16,50].Gelatine can be bound in two arrangements, with basal spacings of about 15A and about
[47] L. E. Ensminger and J . E. Gieseking. Soil Science 48, 467
(1939); 51,125 (1941); 53,205 (1942); A. We&s and U.Hofmann,
Z. Naturforsch. 66,405 (1951).
[48] A. Weiss and G. Koch, 1’h.D. Thesis, Technische Hochschule
Darmstadt, 1960.
[49] C. W.Beck and G. Brunton, Clays and Clay Minerals 8,22
(1 960).
[SO] 0. Talibudeen, Trans. Farad. Soc. 51,582 (1955).
Angew. Chem. internat. Edit. I Vol. 2 (1963) I No.3
18 A, respectively 1511. Tobacco mosaic virus is not
taken up by layer-silicates[52].
Neutral or basic amino acids are bound as cations [MI.
In the weakly acid or neutral pH range, they may also
be intercalated as neutral molecules replacing the swelling agent, if inorganic cations are bound at the same
time [53,54]. Both variants differ in interlayer distances,
quantity of amino acids bound, and swelling in water.
Amino acids intercalated as neutral molecules are displaced by large quantities of water.
Organic Derivatives of Mica-Type Layer-Silicates
in Petroleum Deposits and their Surroundings
[61,62]. Only the Si-OH groups lying at the edge of the
prism faces can react. Their number is limited and depends
on the diameter of the montmorillonite crystal [24]. Since the
predominant part of the surface of the platelike montmorillonite crystals is made up by basal planes, changes in the surface properties such as occur with Si02 are not observed 1631.
Catalytic Reactions in Mica-Type Layer-Silicates
Chemical reactionsoccur in the layers betweenthe silicate
anions that do not take place under similar conditions
in free solutions. For example, if their aromatic rings
lie parallel to the silicate sheets, intercalated arylammonium ions are oxidized by atmospheric oxygen. The
type of product formed dependson the charge density of
the silicate anion. Thus, with a low charge (x approx.
0.33), aniline is oxidized to a red ion, with a somewhat
higher charge (x = approx. 0.55) to a bluish purple ion,
and with a still higher charge, finally, to aniline black
1641. The oxidation products are displaced from the
silicate lattice by alkaline solutions. They can be obtained in pure form by extraction with ether.
In all cases,the oxidizing agent is atmospheric oxygen,
which diffuses through the hollows between the arylammonium ions. The high oxidation potential is
probably related to a strong deformation of the electron
shell by the silicate layers. As Simon has established,
molecular oxygen loses its pammagnetic properties in
the narrow passages within the zeolite. mineral chabazite
-
Mica-type layer-silicateswith unusual basal plane spacings containing organic compounds occur in petroleum
deposits and their surroundings [55]. The oil in oil
shales appears to be stored deep within the interior of
montmorilloniteminerals 1561.It is conjecturedthat such
montmorilloniteminerals have played an essential part
in the genesis of petroleum deposits 1573. Perhaps this
part was limited to the storage or transport of petroleum. However, it may have been in direct connection
with petroleum formation, since mixtures of aliphatic,
cyclic, and aromatic hydrocarbons are formed when
oxygen is excluded during thermal decomposition of
organic dzrivatives of montmorillonite minerals [58].
The high nitrogen contents of such mica-type layersilicates in the vicinity of petroleum deposits explains
the hitherto baffling deficit in the elemental balance.
This nitrogen is partly bound in putrescine and cadaverine montmorillonites, which are also found in
nearly pure form [59].
Moatmorillonite Derivatives with Si -C
Si -0 -C-Bonds
- and
For the sake of completeness, some mention should also be
made of the work performed by Deuel and his colleagues
[60] on montmorillonite derivatives with Si-C and Si-0-C
bonds. The hypothesis that a cation exchange capacity corre
sponding to the quantity of reactive Si-OH groups exists
in the H-form of montmorillonite could not be confirmed
[51] 0. Talibudeen,Nature (London) 166,236 (1950).
[52] A. D. McLuren and G. H. Peterson, Nature (London) 192,
960 (1961).
[53] G. F. Walker and W. G. Garrett, Nature (London) 191,1389
(1 96 I).
[54] 0. Sieskind, C. R. hebd. Seances Acad. Sci. 250,2392 (1960).
1551 I. D. Sedlefskii and S. M. Yusupova. Dokl. Akad. Nauk
SSSR 46, 27 (1945).
[56] W. Immel, Ph.D. Thesis, Technische Hochschule Darmtadt,
1960.
[57] C. E. Weaver, Clays and Clay Minerals 8,214 (1960).
[58] A . WeisJ and G. Rolof, unpublished results.
[59] A. Weiss and €
Srrunz,
I
. in the press.
[MI H. Deuel, G. Huber, and R. Iberg, Helv. chim. Acta 33,1229
(1950); H.Deuel, Clay Min. Bull. I, 205 (1952); see also E. A.
Hauser and J. Alexander, Colloid. Chem. 7.431 (1951).
Angew. Chem. infernat. Hit. I Vol. 2 (1963)
No.3
WI.
Oxidation of aromatic diamine derivatives yields semiquinones [66]. The deep color of these products attracted
interest long ago, and it has sincc served as the basis of a
rapid test for the presence of montmorillonite in mineral
mixtures [67]. The formation of semiquinones, however, is
not a specific reaction. Other silicates with large surfaces,
such as kaolinite, also give a positive test [68].
Another reaction is the proteolytic action of highly
charged mica-type layer-silicate$with exchangeable hydronium ions. At low sheet charges, proteins are bound
reversibly by cation exchangc reactions; at higher
charge densitiesonthesilicatelayers,theproteinsaresplit
into peptides and amino acids. The fragments from this
cleavage are less strongly bound within the interior of
the crystal than unaffected protein cations.
[all G. Brown, R. Greene-Kelley,and K. Norrish. Clay Min. Bull.
I , 205 (1952).
[62] R. Schwarz and If. W. Hennicke. Z . anorg. allg. Chem. 283,
346 (1956).
1631 In this connection, see U.Hofmunn, Ber. dtsch. keram. Ges.
39,272 (1962).
[64] A. Weiss, I. Kunfner, M. Eckel, C. Hofmann, and E. Michel,
Beitdge Silikoseforsch. Sonderband .1,45 (1960).
[65] I. Ahuroniand F. Simon, 2.physik. Chem. (B)4,175 (1929).
[66] Ch. G. Dodd and S. Ray, Clays and Clay Minerals 8, 237
(1960).
[67] E. A. Hauser and M . B. Leggeff,J. Amer. chem. SOC. 62,
1811 (1940); S. B. Hendricks and L. I. Alexander, Amer. Soc.
Agron J. 32,455 (1940); H. Weil-Mulherbeand J. Weiss, J. chem.
SOC..(London) 1948,2164; R. C. Miulmz and M.E. King, Proc.
Amer. Soc. Test. Mater 51, 1213 (1951); W. W.Hamblefon and
G. G. Dodd, Ewn. Geology 48, 131 (1953); Ch. G. Dodd, Clays
and Clay Technology,Calif. Div. of Mines Bull. 169, 105 (155).
[68] J. Endell, R. Zorn, and U.Hofmmn, Angew. Chem. 54,376
(1941).
143
The nonspecific acid hydrolysis of proteins in aqueous
solution becomes a subtratespecific reaction within
layer silicates that are capable of swelling. The specificity depends, on the one hand, on the number and
distribution of the negative charges in the silicate sheet,
and, on the other, on the number and distribution of the
c-amino- and guanido groups in the protein. Plausible
conceptions can be
for
menon as well [a].
Investigations with these enzyme
models are, however, made difficultby the fact that they
are only slightly stable in the hydronium form, and, on
storage, partial decompositioninto a form containinghydroxoaluminum and magnesium cations occurs [69,70].
Received. October 15th. 1962
[A 259173 1El
[69] A. Weiss, Z . anorg. allg. Chcm. 297,232 (1958).
[70] U.Hofmunn and K. Friilicryf, 2.anorg. allg. Chem. 307,187
(1960).
(Halogenomethy1)pyridines and (Halogenomethyl)quinolines
BY DR. W.MATHES A N D DR. H.SCHmY
WISSENSCHAFT'LICHES LABORATORIUM DER DR. F. RASCHIG GMBH.,
(GERMANY)
LUDWIGSHAFEN AM -IN
Hitherto, 2- and 4-trihalogenomethyl-pyridinesand -quinolines were the only compoundv of
this type readily accessible by direct halogenation with free halogen. The particulurly
important and highly reactive monohalogenomethyl compounh had to be prepared by
roundabout means, except in special cases. In the present article, a method is &scribed,for
direct monochlorination of 2-methyl groups in heterocyclic bases on a technical scale. A
review is also given of the preparation and properties of (halogenomethy1)pyridines uncl
(halogenomethy1)quinolines.
I. Halogenation of Methylpyridines and
Methylquinolines with Elemental Chlorine
and Bromine
In the benzene series, chlorination and bromination of
methyl groups takes a very clear course in most cases,
and the mono-, di-, or trihalogenomethylcompound can
each be prepared (e.g. from toluene), depending on the
experimental conditions used. On the other hand,
halogenation of methyl groups in the pyridine and
quinoline series is beset with difficulties. The reactivity
of any methyl group in these compounds is dependent
upon its position relative to the nitrogen of the ring.
1. Known Methods
Dehnel [I] obtained the very unstable compound 3-bromomethylpyridine (1) by heating 3-methylpyridine in concentrated hydrochloric acid to 15OOC with bromine in a
sealed tube; however he did not mure a pure specimen.
Druhowzal[2] obtained 2-bromomethylpyridine from 2methylpyridine using a modification of this method by
heating the base in carbon tetrachloride and concentrated
sulfuric acid at 160 "Cin a scaled tube; again the pure compound was not isolated.
c1
[I] E. Dehne/, Ber. dtsch. chem. Ges. 33,3498 (1900).
[2] F. Drahowzuf, Mh. Chemie 82,794 (1951).
144
Mono- and dihalogenomethyl compounds can be prepared
by rearrangement at high tcmpetatures of the hydrobromideperbromides of 5-, 6-, 7- or 8-methylquinolines, i.e. isomers
with the methyl group in the crrbocyclic ring 13-51.
Sell [6] obtained 2-trichloromethyl-3,4,5-trichloropyridine (3) together with 2-trichloromethyl-3,5-dichloropyridine from 2-methy I pyridine hydrochloride at
105-1 10 OC. Similar results were obtained by McBee,
Hass and Hodnert 171, who chlorinated 2-methylpyridine, 2,4-lutidine, 2,dlutidine, and 2,4,dcollidine
at increasing temperaturn (50 to 180 "C)in the presence
of a little water. All the methyl groups (in positions a
and y to the nitrogen of the pyridine ring) were chlorinated to trichloromethyl groups. Besides these trichloromethylpyridines, several trichloromethyl compounds of
type (31, which are chlorinated to a large extent in the
ring, were also present in the reaction mixture. Formation of these by-products can be avoided by carrying
out the halogenation in acetic acid in the presence of an
alkali-metal acetate. This procedure was first used by
K6nigs [8] for brominating 8-nitro-4-methylquinoline.
Hammick et al. [9-121 developed the method further.
--_[3] J.Howltzand W.Schwenk. Ber.dtsch.chem.Ges.38,1280(1905).
[4] J. Howftzand P.NJther, I3er. dtsch. chem.Ges. 39,2705(1906).
[S] J. Howltz and J. PhNipp, Liebigs Ann. Chem. 396,23 (1913).
[6] W. J. Sefl, J. chem. SOC.(London) 87,799 (1905).
[7] E. T. McBee, H. B. Haw, and E. M. Hodnett, Ind. Engng.
Chem. 39,389 (1947).
[8] W.Koenigs, Ber. dtsch. chem. Ges. 31,2364 (1898).
[9] D. L. Hummick, J. chem. Soc. (London) 1923,2882.
[lo] D. L. Hummick. J. chem. Soc. (London) 1926, 1302.
[It] P.Dysonand D.L.Hamrttick,J.chern.Soc.(London)1939,781.
[12] B. R. Brown, D. L. Hummick, and B. H. Thewlis, J. chem.
Soc. (London) 1951,I145.
Angew. Chem. internat. Edit. I Yol. 2 (1963)
1 No. 3
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