2 1 4 G. BROWN, R. GREENE-KELLY AND K.
NORRISH during the formation of the clay chloride may perhaps attack the mineral However, our montmorillonite chloride was transformed by water to a hydrogen clay which had the same exchange capacity as the starting material. OH-groups attached to A1 are not able to form such organic derivatives as the clay minerals described by us.
Aluminium hydroxides did not react with the organic reagents used.
(5) We did not prepare other halogenides. To introduce heavy atoms into the organic groups will be of great interest. These de- rivatives may also be helpful for electron diffraction study.
(6) The consumption of organic reagents seems to show that they can prenetrate between the clay particles. Likewise the dispersion of the derivatives in organic solvents makes this highly probable. We hope to show more conclusively by X-ray and infra-red absorption that the reaction really takes place between the crystal layers.
(7) Experiments published in the literature prove that silanols may be totally esterified. Simultaneously a condensation between two
Si--OH groups of different molecules may occur.
(8) Finally, silica gel also reacts under the conditions studied but it has only a small cation exchange capacity and will therefore react only to a small extent. I do not think that silica gel impurity can explain our results. Amorphous as well as crystalline material may form organic derivatives. Perhaps our reactions take place pre- ferentially at irregularities of the crystal lattice which cannot be shown by X-ray methods.
O R G A N I C D E R I V A T I V E S O F
M O N T M O R I L L O N I T E
BY G.
R. GREENE-KELLY and K.
Rothamsted
Experimental Station.
Read 2nd November, 1951
Introduction.
The supposed analogy between hydrogen montmorillonite and a weak organic acid has encouraged several investigators, notably
Berger I and Deuel ~, a, 4, to attempt to esterify the exchange positions using standard organo-chemical methods.
In our opinion the experimental evidence so far presented to establish the course and extent of the esterification reaction is incon- clusive. Thus Berger 1 determined the methoxyl content of the pro- duct obtained by treating dry hydrogen montmorillonite with dia- zomethane in ether without showing that sorbed methyl alcohol was absent. This omission is particularly relevant when Berger states that he dried his starting material at 150~ Data on the dehydration

ORGANIC DERIVATIVES OF MONTMORILLONITE 215 of hydrogen montmorillonite has shown that under these conditions
Berger's sample probably contained more than 2% sorbed water.
Taking into account the difficulty o f washing montmoriUonite free of methyl alcohol, this a m o u n t o f water would be sufficient to hydrolyse enough diazomethane to account for the observed methoxyl contents.
Deuel prepared m a n y o f his derivatives from a montmorillonite chloride prepared from montmorillonite and thionyl chloride. I f this chloride is formed it is probable that it is very sensitive to traces o f water and hydrolysis would give hydrogen montmoriUonite cf. organochloro silanes~.
Deuel has characterised his derivatives by determining decreases in exchange capacity after reaction. However, conventional exchange capacity determinations on previously dried hydrogen montmoril- lonite :give low and unreliable results, and hence Deuel's results for the degree o f esterification m a y be seriously overestimated.
Table I.
Sample*
Sodium montmorillonite, dried, exchanged with Ba~+ (pH 7)
BaZ+ determined as BaSO4 .. . . .
Sodium montmorillonite exchanged with"trie~yiaminehydro" chloride (pH 5); total nitrogen determined on the sample ....
Wet hydrogen montmorillonite titrated to pH 7
Hydrogen montmorillonite dried from alcohol, dispersed and titrated to pH 7 ....
Dry hydrogen montmorilionite iaeated'to 9O~ in water for three hours before titration ....
Hydrogen montmorillonite, dried~"then'exchanged wiih warm triethlyamine hydrochloride for long periods; total nitrogen determined . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Exchange
Capacity
1Tl.e,]
100 gins.
90
9O
72
4I
55
84
Montmorillonite used was a very fine fraction of Wyoming bentonite washed with the appropriate chloride and then washed free of excess salt with water and alcohol. 0.1 N HC1 was used for preparing H+ mont- morillonite.
Again in determining the extent o f formation o f the m o n o - p r o p y - lene glycol ester, Deuel determined the glycol after saponification without showing that sorbed glycol was absent from the preparation.
Montmorillonite Esters.
In view o f the undoubted importance of the esterification reaction, should it indeed take place, we have investigated a number o f esters prepared by Deuel and sent to our department for examination.
Those investigated were the methyl, ethyl and propyl esters preparexl by treating montmorillonite chloride with the corresponding alcohol'; the mono-ethylene glycol ester prepared f r o m hydrogen montmoril-

216 G. BROWN, R. GREENE-KELLY AND K. NORRISH lonite a n d ethylene oxide a n d the m u s t a r d gas ester prepared f r o m sodium montmorillonite. I n all cases Deuel claimed between 80% a n d 90% esterification o f the exchange positions. T h e original material was an electrodialysed less than 2/~ fraction o f W y o m i n g bentonite with an exchange capacity given as 68 me./100 gm. I n a later paper D e u e P gives 110 me./100 gm. as the exchange capacity o f the same montmorillonite. N o explanation is given f o r this des- crepancy.
The results o f o u r chemical examination o f these samples are summarised below.
Table 2.
Material
Methyl ester ....
Propyl ester ....
Mono-ethylene glycol ester ....
Mono - ethylene glycol ester wash- ed with alcohol ....
Mustard Gas ester
Hydrogen mont- morillonite ....
% Carbon
(a)
0"64
0"35
3 "52
Exchange
Capacity m.e./100 gm.
(b)
Total Na m.e./100 gm.
(c)
78
39
10
17
10
%Loss in weight at
105~
(d)
10"8
8"9
117"9
3 "84
3 '73
0'23
26 m
10 6-9
10.7
(a) Carbon content determined by a combustion method due to Ricksonr-- modified by using oxygen instead of air. The value for the mustard gas derivative was obtained by correcting for sulphur using a carbon to sulphur ratio of 4 to 1.
(b) Exchange capacity determinations were carried out by saturating the material with Sr~+ and washing free of excess salt. The strontium was displaced with hydrochloric acid and determined spectrographically.
(c) Total sodium determined by dissolving the sample in hydrofluoric acid and determining the cations spectrographically. Only traces of potassium, calcium and magnesium were found.
(d) Per cent. loss at 105 ~ was determined on samples as received. The resultant material used for a, b and c.
T h e c a r b o n contents after deducting the c a r b o n content o f the original material are only 0.41% a n d 0-12% for the methyl and p r o p y l esters respectively. Deuel claims 82% a n d 80% esterification which should give 0-7% and 2 . 0 % carbon. T h e m o n o - g l y c o l and m u s t a r d gas esters should contain 1.4% a n d 2-9% c a r b o n respectively.
The exchange capacities are m u c h higher t h a n those found by
Deuel by titration. It is significant that the value o f 78me./100 gm. for the methyl ester was obtained by heating the solution to boiling point during the course o f the exchange process. This suggests that the other results o b t a i n e d were low due to incomplete exchange.
Exchange with a m o r e active exchanger, triethylamine hydrochloride
( p H 5), confirmed this by giving 55 me./100 gm. for the mustard gas

O R G A N I C DERIVATIVES OF M O N T M O R I L L O N I T E 217
0 " ~
B
0
;g i +
~.o
~.~. o N
,~r m ~ u
< o o
~B
~ ~
.o
- ~
0
~ . ~

218 G. BROWN, R. GREENE-KELLY AND K. NORRISH derivative. In view of the high exchange capacity of the mustard gas ester it is surprising that there were only 10 me./100 gin. total sodium present. The pH of the sample in boiled water was 3.4 and there was an appreciable amount of free chloride present, hence it might be reasonable to conclude that hydrochloric acid, set free by the hydro- lysis of mustard gas might have removed most of the exchangeable sodium.
The X-ray diffraction examination of the samples was carried out using Cu K~ radiation with a 9 em. diameter camera capable of re- cording spacings up to 30 kX. The accompanying table gives d(001) values for variously treated samples. Many of the diffraction pat- terns show an irrational series of (001) spacings indicative of varia- tions in the (001) spacings. These are denoted by It.
The most surprising feature of the above results is the lattice expansion of the esters with glycerol and water. The extent of the expansion is, except for the mono-glycol ester, exactly what would be expected for the unesterified montmorillonite. The monoglyeol ester gives a rational series of spacings with glycerol corresponding to a solution of glycerol between the layers. The most obvious solvent is ethylene glycol, d(001)=17-0 kX, formed by the hydrolysis of ethylene oxide during the esterification. This explanation is con- firmed by the presence of an irrational 16.3 kX spacing in the air dry sample.
These results seem incompatible with the alleged almost complete absence of exchange ions between the silicate layers of montmoril- lonite. Further, the esters, with the possible exception of the mustard gas derivative gave no evidence of a rational series of spacings independent of water vapour pressure as would be expected for hydrophobic esters. All the samples behaved as hydrogen montmorillonite with varying amounts of sorbed polar organic contaminants present on the internal surface.
We informed Professor Deuel of these conclusions and he was of the opinion that our samples had hydrolysed before examination.
He suggested that we should examine freshly prepared samples of the esters and also the organosilanes which contain very stable
Si--C linkages.
To study a fresh ester, we prepared the mono-propylene glycol ester from hydrogen montmorillonite and propylene oxide and determined its exchange capacity by titration. This was the same as the original hydrogen montmorillonite,
52 me./100 gm.
At our suggestion Professor Deuel supplied samples of his ethyl and phenyl organosilanes, prepared from montmorillonite chloride by Grignard and Friedel-Crafts reactions respectively.
Our results for the ethyl and phenyl derivatives are given in
Tables 4 and 5.

ORGANIC DERIVATIVES OF MONTMORILLONITE
T a b l e 4.
219
Exchange capacity determined with triethylamine hydrochloride at pH = 5
Ethyl derivative A 82 m.e.]100 gin.
Phenyl derivative P.I
Phenyl derivative P.2
64 m.e./100 gin.
84 m.e./100 gin.
Table 5.
X-ray diffraction analysis
Ethyl derivative A
Phenyl derivative P.I
Phenyl derivative P.2
Air Dry
14.6 kX
14"6 kX Ir
14.6 kX l r
Glycerol
17.6 kX
Water Vapour
Expanded.
14"6 kX Ir No change.
14"6 kX lr No change.
The ethyl derivative was indistinguishable from hydrogen mont- morillonite. The phenyl derivatives looked more promising. At- tempts to prepare this derivative failed repeatedly but a sample similar on X-ray data to the phenyl derivative was obtained if benzene containing thiophene was used in the preparation, Qualit- ative analysis of Deuel's derivative for sulphur by sodium fusion and testing with sodium nitroprusside solution showed substantial quantities present. It was concluded that Deuel's phenyl derivative consisted of sorbed thiophene or the products o f its degradation.
Removal of Sorbed Compounds.
A c o m m o n feature of the work so far published on the formation o f esters and organosilanes is the assumption that the mineral can be easily freed from sorbed polar compounds.
Some of the reactions have been carried out with hydrogen mont- morillonite which the authors assumed to be dry. The difficulty of removing all the sorbed water from hydrogen montmorillonite does not seem to be appreciated. We have found that even after heating to 300~ for 16 hrs. it still gives 6.1% water loss on ignition, i.e., at least 0.5% sorbed water.
The common method of freeing the reaction product from sorbed polar compounds was to wash it with non-polar or weakly polar solvents. Some experiments of ours suggest that this procedure is unlikely to be effective. F o r example montmorillonite contaminated with methyl alcohol and washed six times with purified cyclohexane still gave X-ray diffraction diagrams indicating the presence of a one- layer complex with methyl alcohol. Montmorillonite containing

220 G. BROVdN~ R. GREENE-KELLY AND K. NORRISH pyridine gave an unchanged d(001) spacing (15 kX)after repeated washing with purified decahydronaphthalene for several weeks.
An alternative procedure for removing sorbed compounds is high vacuum evaporation. 7 However, even with this technique, evacuat- ing for periods at elevated temperatures may not ensure complete removal of the sorbate. A complication which may arise with this technique is the decomposition of the sorbed material on the surface during removal.
Conclusion.
We think that the experimental results so far obtained for the existence of covalently bonded groups bonded on montmorillonite are inconclusive. Very careful and critical work will be required to make progress in this difficult field.
Acknowledgements.
We are grateful to Professor Deuel for the samples of his derivatives and for helpful discussions. R.G.K. wishes to acknowledge a research grant from the A.R.C. K.N. took part in this work during the tenure of a C.S.I.R.O. (Australia) studentship.
References.
(1) Berger, G., 1941. Chem. Weekblad, 38, 42.
(2) Deuel, H., Huber, G. and Iberg, R., 1950. Helv. Chim. Acta,
33, 229.
(3) Deuel, H., 1952. Clay Minerals Bull. (preceding paper).
(4) Deuel, H., and Huber G., 1951. Helv. Chim. Acta, 34, 1697.
(5) Hardy, D . V . N . andMegson, N . J . L . , 1948. Quart. Rev., 11,30.
(6) Rickson, J. B., 1948. Analyst, 73, 268.
(7) Glaeser, R., 1950. Fourth International Congress of Soil Science
Trans. III, p. 65.
Added in Press.--Recent unpublished work by Hendricks and
Vivaldi on the reaction of diazomethane and montmorillonite has shown that considerably smaller methoxyl contents are obtained with montmorillonite dried at 300~ than Were obtained by Berger with montmorillonite dried at 150 ~ and also that there appear to be side reactions giving polymer residues on the montmorillonite.