Download reactions of alcohols with alkenes over an aluminum

Clays and Clay Minerals, Vol. 31, No. 2, 129-136, 1983.
REACTIONS OF ALCOHOLS WITH A L K E N E S OVER A N
A L U M I N U M - E X C H A N G E D MONTMORILLONITE
J. M. ADAMS, D. E. CLEMENT, AND S. H. GRAHAMt
Edward Davies Chemical Laboratories, University College of Wales
Aberystwyth SY23 INE, United Kingdom
Abstract The reaction of 2-methyl pent-2-ene with primary alcohols (CI-Cls) at 95~ over an Al-montmorillonite gave yields of 20-90% of ethers of the type R-O-C(CH3)2CaHT. Lower yields were produced
if secondary alcohols were employed, and tertiary alcohols gave only a trace of this ether. When a variety
of alkenes was reacted with bntan-l-ol at 95~ over a similar catalyst, no reaction occurred unless the
alkene was capable of forming a tertiary carbonium ion immediately upon protonation. In this case the
product was the tertiary ether t-R-O-nC4H9. However, at a reaction temperature of 150~ a variety of
products were formed including (1) ether by the attack of butanol on the carbonium ions produced either
directly from protonation of the alkenes or by hydride shift from such an ion, (2) alkenes by the attack of
n-C4Ha§ ions (derived from protonation and dehydration of butanol) on the alkene, (3) di-(but-1-yl) ether
by dehydration of the butanol, and (4) small amounts of alcohol by hydration of the alkene. The differences
in reactivity below and above 100~ are related directly to the amount of water present in the interlayer
space of the clay and the degree of acidity found there. Although the clay behaves as an acid catalyst, the
reactions are far cleaner (more selective) than comparable reactions catalyzed by sulfuric acid.
Key Words Alcohol, Alkene, Aluminum, Catalyst, Montmorillonite.
INTRODUCTION
An extensive study has been made of a wide range of
organic reactions catalyzed by clay minerals (see, e.g.,
Fripiat and Cruz-Cumplido, 1974; Theng, 1974; Thomas et al., 1977; Bittles et al., 1964a, 1964b, 1964c). Recently, renewed interest has been shown in the use of
natural and synthetic smectitic clays as highly selective
acid catalysts (e.g., Adams et al., 1978, 1979a, 1979b;
Ballantine et al., 1981a, 1981b). In many studies carbonium ions, formed by the protonation of the reactant
molecules, have been considered to be essential intermediates in the reactions. The protons originate from
the dissociation of interlayer water molecules coordinated to the exchangeable cations (Mortland, 1968; Fripiat and Cruz-Cumplido, 1974)--indeed the interlayer
water in smectities is known to be dissociated to a much
greater extent than bulk water (Hougardy et al., 1976;
Mortland et al., 1963; Fripiat et al., 1965; Touillaux et
a l , 1968).
At low temperatures (<100~ the reactions of alkenes over montmorillonites usually produce ethers or
alcohols, depending upon the type of alkene (Adams et
al., 1979a, 1982a), whereas at higher temperatures they
give dimers and other oligomers. Recently, Ballantine
et al. (1981b) found that the reactions of alcohols with
ion-exchanged montmorillonites give di-(alk-1-yl) ethers
at 180~ The possibility of reaction between alcohols
and alkenes over ion-exchanged montmorillonite catalysts has been explored in the case of methyl t-butyl
ether (MTBE) production from isobutene and methanol
t Deceased .
Copyright 9 1983, The Clay Minerals Society
(Bylina et al., 1980; Adams et al., 1982b) or t-butanol
and methanol (Adams et al., 1981).
In the present study we have extended this work to
the reactions of a range of alkenes and alcohols at temperatures both above and below 100~ Initially the alkene chosen was 2-methyl pent-2-ene, which is similar
to isobutene in that protonation should give a tertiary
carbonium ion. In addition, this alkene is much easier
to handle than isobutene and reaction with a range of
alcohols was attempted. A variety of alkenes was also
reacted with butan-l-ol. In all experiments an Al-exchanged montmorillonite was used as a catalyst, because this material is highly acidic (Mortland, 1968).
EXPERIMENTAL
C a t a l y s t characterization
The Wyoming bentonite used in this study (Volclay,
foundry grade, Hopkin and Williams Ltd.) was crushed,
separated from gross impurities and size graded in a cyclone before delivery. Eighty-five percent of the particles were specified as being <75/xm. The <2-/~m clay
fraction was selected by sedimentation. Cation exchange was carried out by exposing the clay to a 0.6
mole/liter solution of Al(NO3)3" 9H20 for 24 hr. The clay
was then centrifuged and resuspended in deionized
water repeatedly until a test for the exchanging salt
proved negative, after which the clay was isolated by
centrifugation, dried in an oven at 40~ and ground
finely. The cation-exchange capacity (CEC) of the isolated montmorillonite sample was found to be 70 -+ 2
meq/100 g for air-dry material by a precipitation method
described previously (Adams et al., 1981) and also by
129
130
Adams. Clement. and Graham
the conductimetric method of Mortland and Mellor
1954). These exchange capacities correspond to 1/6 AP +
per Si8020 unit.
F o r all experiments pre-weighed Al-exchanged samples were equilibrated for 36-48 hr over a saturated LiC1
solution at 30~ this salt solution produces an atmosphere of constant 12% RH and consistently gave a fixed
water content in the interlamellar space of the clay. The
reproducibility of the clay water content is important
because the acidity of interlayer water is a function of
the amount of such water present (Mortland. 1968), and
the product of reactions catalyzed by montmorillonites
have likewise been shown to be dependent upon this
content of water (e.g., Adams et al.. 1979a). Thermogravimetric analysis showed that the clay samples contained 4.2 • 10 -3 moles H20/g clay. i.e.. 3.0 water molecules/ unit cell.
Gas-liquid chromatography and
mass spectrometry
Gas-liquid chromatography (GLC) was used to monitor the purity of reactants and to analyze the reaction
products. Glass columns, 0.25-inch internal diameter,
were packed with 10% polyethylene glycol 20 M. with
2% silver nitrate supported on acid-washed silanized
Chromosorb G. F o r the identification of reaction products a gas-liquid chromatograph coupled to an A E I MS
30 mass spectrometer was used with a DS 50 S microprocessor.
Reaction conditions
Teflon-lined brass vessels were employed for the reactions carried out at 95~ stainless steel vessels were
used at 150~ These containers were charged with either
1.0 g or 0.5 g (12% RH) of Al-exchanged clay together
with the appropriate alkene and alcohol and n-hexane
solvent. The vessels were sealed, placed in thermostatted oil baths, and stirred magnetically.
RESULTS
Reaction o f 2.methyl pent-2-ene
with alcohols
Reactions of 2-methyl pent-2-ene were carried out in
Teflon-lined vessels at 95~ for 5 hr with 1 g of Al-clay
(12% RH) and 12.5 mmole of the pentene and the appropriate alcohol; 3 cm 3 of n-hexane was used as solvent. Reasonable yields (20-:40%, Table !) of t-ether,
i.e., 2-alkoxy 2-methyl pentane, were obtained by the
acid-catalyzed reaction of 2-methyl pent-2-ene with all
straight-chain alcohols (Figure 1) With carbon chain
lengths from C.~ to C28. With methanol the reaction was
much more efficient and a larger ( - 9 0 % ) yield was ob.
served. Here a small quantity of 2-methyl pentan-2-ol
was produced from the hydration of the parent alkene,
and a small quantity of MeOMe was formed from the
methanol; as was found previously in the formation of
Clays and Cla~ Minerals
§ +
CH
i.to,' wr
CHf=CH-C2H..H§
HH
I'c-CH2C2Hs
,o
zO
+ROH[-ROH
//
+HzO
H+
CH3
\
'
uO-CH2C2H
CH3
. [H3
R'O,-C-CH2C2H
5
H
-H9 J[.H9
CHa
HO-r
CHs
2- methyl pentan-2-ol
,OH3
R-O-C-CH2C2H
CH3
2-methyl-2-alkoxy pentane
Figure 1. Mechanism for the acid-catalyzed reaction of
2-methyl pent-2-ene with alcohols (Al-montmorillonite catalyst).
methyl t-butyl ether when using a clay catalyst (Bylina
et al.. 1980: Adams et al.. 1981b). At this temperature
methanol is the only alcohol to form a di-alkyl ether.
whereas Ballantine et al. (198 lb) showed that at higher
temperatures di(alk-l-yl) ethers can be synthesized from
n-alcohols using clay catalysts.
The ethers produced were identified by GLC-MS
cracking patterns. Generally the yield of the tertiary alcohol, 2-methyl pentan-2-ol, was between 0.8 and 1.2
mole, which is less than that which could have been
produced if all of the interlayer water originally in the
clay had been consumed (4.2 mmole). No dimers of
2-methyl pent-2-ene were found in any reaction at 95~
whereas in a comparable reactions involving methanol
and 2-methyl propene, Adams et al. (1982b) reported
the production of dimers of the reactant alkene. Where
secondary alcohols were used as reactants, the yield of
the appropriate tertiary ether was less than with primary alcohols, and a tertiary alcohol led to a negligible
yield of ether.
These results indicate that there is no limit to the size
of n-alcohols that can react to give t-ethers (up to C18);
the lower yields obtained with secondary and tertiary
alcohols are probably due to the increase in steric
hindrance around the hydroxyl group which prevented
the tertiary carbonium ion (produced by protonation of
the alkene) and the alcohol from approaching each other in a manner suitable for ether formation. The yield
of 2-methyl pentan-2-ol is greater when secondary or
tertiary alcohols are used rather than primary alcohols
because the ether formation is restricted by steric
hindrance; there are, therefore, more pronotated al-
Vol. 31, No. 2, 1983
Alcohol-alkene reactions on A!-montmorillonite
Table 1. Yields of tertiary hexyl ethers (R-O-C(CH~)2C~HT)
and the tertiary alcohol 2-methyl pentan-2-ol using various
alcohols.
Alcohol (ROH)
CH3OH
C2H~OH
n-C3HrOH
n-C4H9OH
n-CsH,,OH
n-C,H,3OH
n-C4HlzOH
n-CsH,rOH
n-C~-I~9OH
n-C,0H~,OH
n-C12H25OH
n-C14H29OH
n-C1~H33OH
n-C18H37OH
CH3CH(OH)CH3
CHz-CH2.
I
)CHOH
CHe-CH2~
(CH3)3COH
R-O-C(CH:32
C:Mflmmole
2 methyl
pentan-2-ol/
mmole
11,32
3.0
3.5
4.8
3.7
3.8
3.9
4.7
4.0
3.7
3.3
3.2
2.5
2.4
0.71
1.2
0.8
0.8
1.1
0.75
0.9
0.8
1.1
0.4
1.0
0.9
1
I
1
1.87
0.86
1.1
0.07
2.6
1 1 g Al-clay (12% RH) + 12.5 mmole 2 methyl pent-2-ene
+ 12.5 mmole ROH + 3 cm3 n-hexane (5 hr, 95~
2 This value is based on the loss of methanol and gives the
total of this ether and a small amount of MeOMe,
kene molecules available for hydration and subsequent
conversion to alcohol by loss of a proton.
R e a c t i o n o f b u t a n - l - o l with a l k e n e s
A series of alkenes--some of which gave secondary
carbonium ions on protonation and some which gave
tertiary carbonium ions--were reacted with butan-1-ol
in the presence of Al-clay at 95~ and 150~ in sealed
vessels. The alkenes used were: 2-methyl pent-l-ene,
2-methyl hept- 1-ene, 4-methyl pent- 1-ene, cis 4-methyl
pent-2-ene, trans 4-methyl pent-2-ene, 3,3-dimethyl but1-ene, hex-l-ene, and hex-2-ene. For all experiments,
0.5 g Al-clay (12% RH) was reacted with 6.25 mmole
alkene, 6.25 mmole butan-l-ol, and 1.5 cm 3 n-hexane
solvents for 5 hr at 95~ and 150~
The reactions catalyzed by the clay at 95~ gave rise
to new products (t-ethers and t-alcohols) only in those
reactions where the alkene was able to give a tertiary
carbonium ion immediately upon protonation (Table 2).
The alkenes which could give only primary or secondary carbonium ions on protonation did not yield new
products.
At 150~ all of the alkenes studied reacted to give a
range of products (Table 3), although the GLC trace
was far cleaner than in those reactions catalyzed by
concentrated acid. At this higher temperature some din-butyl ether was produced (Figure 2) from the butanI-ol, as observed by Bal!antine et al. (198 la, 198 lb). In
addition, each alkene reacted with butyl carbonium ions
131
CH3CH2CH2CH20H~ CH3CH2CH2CH2-O\
-H
H
_H~O~~
"H20
CH
+atkene/y"
L§
3"CH CH CH
+
egCH2
a 2 2~H3/"/
CH~CHoCH~CHoOCH~CH~CH~CHo
J Z Z Zi
L Z. z
CH3+
_H.L H
c~,C-CH2CH2CH3
(~H2,~),~ ~ .
CHq
CH3CH2CH2CH2OCH2CH2CH2CH
3
u§
\
di-n-buty[ ether
~H2
-CH2CH2%\ CH9
CH
~,CH~
CGH9
0
variety of
\Jr
ru Cm otkenes
/'-, ~.u,2un3 ,,,
!H2
C~H9
Figure 2, Diagrammatic representation of production and
possible reaction pathways of butyl carbonium ions generated
in the montmorillonitte.
(produced by protonation and subsequent loss of water
from the butanol) to g i v e a C10 carbonium ion which
then lost a proton to g i v e a C10 alkene (Figure 2). The
synthesis of di-(alk-l-yl) ethers from alcohols using a
clay catalyst has been reported previously by Ballantine et al. (1981b), but in previous work involving the
reaction of alkan-l-ols with hex-l-ene no mention was
made of any ethers or alkenes arising from the reaction
of the reactant alkene with a carbonium ion derived from
the alcohol, the sole product of the reaction being
1-alkyl 2-hexyl ether and the 1-alkyl 3-hexyl ether (Ballantine et al., 1981a).
In all experiments carried out in the present study at
150~ the alkenes reacted with the butanol to give iso:
meric ether products. The reactions involving the methyl
Table 2. Summary of results for the reaction of various alkenes with butan-l-o! at 95~ in sealed vessels. 1
Alkene
t-ethers
Other
ethers
Tertiary
alcohols
2-methyl pent-l-ene
2-methyl hept-l-ene
1.74
1.40
---
0.45
0,32
Dimers
of
alkene. BuOH
---
4.51
4.85
Note that the following alkenes did not react under these
conditions: 4-methyl pent-l-ene, cis 4-methyl pent-2-ene, trans
4-methyl pent-2-ene, 3,3-dimethyl but-l-ene, hex-l-ene, hex2-ene. Values in millimoles.
10.5 g Al-clay (12% RH)+ 6.25-mmole alkene + 6.25
mmole butan-l-ol + 1.5 cm3n-hexane (5 hr, 95~
132
Clays and Clay Minerals
Adams, Clement, and Graham
o vQriety 01CIO alkenes
e x t e n t to w h i c h h y d r i d e shift o c c u r r e d . T h e r a t i o o f 2m e t h y l 4 - b u t o x y p e n t a n e to 2 - m e t h y l 3 - b u t o x y p e n t a n e
CH H +
CH +
CH3
+
\
~CH3-c+-cH2CH2CH3 ~CH-C-CHCH
3
3~CH-CH-CHCH
3
~'CHCH2CH-CH2-Ct+Hg c o u l d n o t b e d e t e r m i n e d f r o m G L C a n a l y s i s b e c a u s e
CGHgCH2 ~
CH3 C~H% ~'~+nC
t h e s e c o m p o u n d s give u n r e s o l v a b l e o v e r l a p p i n g p e a k s .
CH3 [.nC/H;
H o w e v e r , G L C - M S d a t a i n d i c a t e d t h a t t h e p e a k in
CH3 m
CH~ H "
CH~ H
CH3"C~ '/gH~
q u e s t i o n was t h e r e s u l t o f t w o e t h e r s since m o l e c u l a r
;~-~H2~H3
~Zc~c ,H
CH'3 CH2 CH2
CH2
CH3 H ~
CH3 H "CH3
f r a g m e n t s h a v i n g m/e 45 f r o m t h e 4 - b u t o x y e t h e r a n d
2-methyl pent-l- c~L-methyl
trans G-methyl
t.-methylgent-l-erie
m/e 59 a n d 73 f r o m t h e 3 - b u t o x y e t h e r were p r e s e n t .
ene pent-2-ene penl-2-ene
1
A s i n d i c a t e d in T a b l e 3a, 2 - m e t h y l p e n t - l - e n e g a v e
+H+
~
*H+
predominantly the t-ether, 2-methyl 2-butoxypentane,
CH3 +
+---~
CH3 + "~^rR.L CH3
*
"
+
~.'C-CH2CH2CH
3
~CHCHCH2CH3
~CHCH2CHCH3 m CH3/cHCH2CHCH3
w h e r e a s t h e r e m a i n i n g s u b s t i t u t e d p e n t e n e s g a v e mixCH3
CH3
)
CH3
\
CH3
tures of 2-methyl 3 - b u t o x y a n d 2-methyl 4 - b u t o x y e t h e r s
[.nC/+H90H
|+nC/HgOH
H_H~nCIH90H
with m i n o r a m o u n t s of 2 - m e t h y l 2 - b u t o x y p e n t a n e . I t
should be noted that on hydration 2-methyl pent- l-ene
,3
,3
,3
CH3-C-CH~CH2CH3 CH -CH-CH-CHCH
CH3-CH-CH2-CHCH3
gave only 2-methyl pentan-2-ol, a t-alcohol, w h e r e a s the
i
3 b ~3
o
o t h e r m e t h y l p e n t e n e s g a v e t w o s e c o n d a r y alcohols.
Ct,H9
Ct,Hg
CLHg
2 - m e t h y l h e p t - l - e n e (Table 3b) b e h a v e d similarly to
Figure 3. Diagram showing the various n-butyl ethers and
2 - m e t h y l p e n t - l - e n e e x c e p t t h a t t h e r e was slightly less
C~0 alkenes that can be derived from reactions involving the C12 ( c o m p a r e d w i t h Cio) a l k e n e p r o d u c e d b y t h e reacisomeric methyl pentenes and n-butanol.
tion of a b u t y l c a r b o n i u m ion w i t h the 2 - m e t h y l h e p t - l erie.
p e n t e n e s give v a r i o u s a m o u n t s o f 2 - m e t h y l 3-butoxyOf the two isomeric hexenes, hex-l-ene gave the
pentane, 3-methyl 4-butoxypentane, and 2-methyl
g r e a t e r yield of e t h e r w i t h t h e m a j o r p r o d u c t b e i n g t h e
2 - b u t o x y p e n t a n e (Figure 3) d e p e n d i n g u p o n t h e posi1-butyl 2-hexyl e t h e r ( T a b l e 3c). T h i s e t h e r w a s protion o f p r o t o n a t i o n o f t h e a l k e n e in q u e s t i o n a n d t h e d u c e d f r o m t h e s e c o n d a r y c a r b o n i u m ion f o r m e d di-
T-H"
~\c~c~H3
Table 3.
(a)
Alkene
(methyl
pentenes)
(b)
Alkene
(c)
(d)
Alkene
Alkene
"~
Summary of results for the reaction of various alkenes with butan-l-ol at 150~ in sealed vessels.
2-methyl
2-butoxy
pentane
2-methyl
3-butoxy
pentaneand
2-methyl
4-butoxy
pentane
2-methyl
C~oalkenes pentan-2-ol
Secondary
alcohols
Di-n-butyl
ether
Dimerof
alkene
Butan-l-ol
0.4
0.08
2.05
0.17
--
0.35
1.46
3.02
0.11
1.5
0.12
--
0.07
0.25
--
4.02
0.28
1 .46
0.53
--
0.1
0.28
--
3.32
O. 18
0.74
0.41
--
O. I
0.32
--
4.28
2-rrtethyl
2-butoxy
heptane
Other ethers
from BuOH +
alkene
C,2 alkene
Di-n-butyl
ether
Dimerof
alkene
Butan-1-ol
0.41
--
0.36
--
4.22
2-butoxy
hexane
3-butoxy
hexane
C~0alkenes
Hexan-3-ol
Di-n-butyl
ether
Dimerof
alkene
Butan-1-ol
2.33
0.46
0.04
0.06
0.02
0.34
--
2.74
I. 18
0.79
0.02
0.06
0.04
0.62
--
3.02
2,2-di-methyl
3-butoxy
butane
2-methyl
2-butoxy
3-methyl
butane
C,0 alkene
Di-n-butyl
ether
Dimerof
alkene
Butan-1-ol
0.19
0~04
0.23
--
5.39
0.17
0.9
2-methyl
heptan-2-ol
0.12
hexan-2-ol
2,3-di-methyl
butan-2-ol
0.08
Secondary
alcohols
--
Secondary
alcohols
--
0.5 g Al-clay (12% RH) + 6.25 mmole alkene + 6.25 mmole butan-l-ol + 1.5 cm 3 n-hexane (5 hr, 150~
quoted are in mmoles of product.
All quantities
Vol. 31, No. 2, 1983
Alcohol-alkene reactions on Al-montmorillonite
rectly by protonation rather than the alternative carbonium ion which would be produced by a hydride shift
and which would generate 1-butyl 3-hexyl ether. With
hex-2-ene, relatively more 1-butyl 3-hexyl ether was
produced because the carbonium ion required to give
both the 2-hexyl and 3-hexyl ethers was generated directly from protonation of the alkene.
F o r 2,2-dimethyl but-l-ene the yield of all products
was lower than with the remaining alkenes (Table 3).
Two isomeric ethers were produced from the reaction
with butan-1-ol, one of which is 2,2-dimethyl 3-butoxybutane formed by protonation of the double bond of the
alkene followed by attack of the alcohol and loss of a
proton. The secondary carbonium ion produced, however, undergoes a Wagner-Meerwein rearrangement
(Fieser and Fieser, 1961) with migration of a methyl
group to give a more stable carbonium ion CH3CH(CH3)+C(CHa)~. GLC/MS data indicated that this
process did indeed occur to give 2,3-dimethyl 3-butoxybutane. Furthermore the alcohol produced in the reaction was that derived from the tertiary carbonium ion
given by this Wagner-Meerwein rearrangement.
Reactions in the interlayer space
The reaction of alcohol and alkene molecules could,
in principle, take place in solution, on the clay surface,
or in the interlayer space of the clay catalyst. In control
experiments made without clay catalyst, no reaction
occurred. In a second set of experiments using A1Cla,
together with the alcohol and alkene, none of the materials produced by the clay catalyzed reactions were
found. The compounds 2-methyl pent-l-ene and cis
4-methyl pent-2-ene were also used for control experiments where they were stirred for 3 hr with equimolar
amounts of butan-1-ol and concentrated sulfuric acid.
G L C analysis of the organic reaction products indicated a low conversion of butanol together with a broad
envelope of unresolvable peaks which consisted of alcohols, ethers, alkenes, and other polymerization and
breakdown products of the alkene. It is apparent that
the reactions must take place on the external surface of
the clay particles, or in the interlayer space, or both.
The Al-clay equilibrated at 12% RH had a basal spacing of 15.4 ,~. On immersion of this clay in 2-methyl
pent-2-ene and hexan- 1-ol the spacing increased to 15.9
A and 17.9 A, respectively. When the clay was immersed in a mixture of this alkene and alcohol, the spacing increased to 17.9/~ and remained there after heating
to 95 ~ and 150~ for 5 hr. Although both types of reactant molecules obviously had access to the interlayer
space during the reaction, these data do not necessarily
prove that reaction took place there.
A collapsed Al-clay was produced by heating at 500~
for 48 hr: reactions carried out using this material as a
catalyst were compared with those using the normal,
uncollapsed, clay (the reaction used was 2-methyl pent1-ene + butan-l-ol). At 95~ the normal clay gave
133
t-ether and t-alcohol products (Table 2), as did the collapsed clay, but the yield was only about 25% of that
for the normal clay. At 150~ the normal clay gave dimers of the reactant alkene and other ethers in addition
to the t-ether and t-alcohol (Table 3a). The collapsed
clay, however, gave a reduced yield of the t-ether and
t-alcohol, but other products were not detected.
These results suggest that two types of sites may be
involved in these reactions. First, a surface site may
exist where carbonium ions can react with oxygenated
species, such as the alcohol and water, but not with hydrocarbons. Second, the carbonium ions can react in
the interlayer region with hydrocarbons to give dimers,
etc. Moreover, these two sites would probably differ in
acidity, with the interlayer site being more acidic. It is
not completely clear whether the carbonium ions themselves can be formed on the surface and in the interlayer
space, or only at one of these sites with subsequent migration to the reaction site.
DISCUSSION
The dramatic differences in the products formed by
reactions at 95 ~ and 150~ were probably due to loss of
interlamellar water from the clay on heating at 150~
As dehydration proceeds, the water remaining in the
clay becomes more polarized by the A1 cations and the
proton donation ability is improved (Mortland, 1968).
At 95~ protonation of the alkene took place only when
a stable tertiary carbonium ion could be formed, whereas by 150~ the interlamellar water became sufficiently
acidic to protonate alkenes that yielded less stable secondary carbonium ions and also sufficiently acidic to
protonate butan-l-ol. This protonated alcohol subsequently lost water to yield the primary C4H9 + carbonium ion which then reacted with other alcohol molecules (Ballantine et al., 1981b) or reacted with alkenes
to form larger alkene molecules.
If the reaction of the methyl pentenes with butan-1ol is considered, 2-methyl pent-l-ene, which is the alkene that gives the most stable and easily produced
carbonium ion, gave the lowest yield of ether but the
largest yield of C10 alkene. The yield of ether was also
significantly less at 150~ than at 95~ At 150~ the
extra high acidity in the clay enabled primary butyl carbonium ions to be formed; these ions easily attacked
the nucleophilic double bond of an alkene. This process
occurred as readily as protonation of the alkene, but the
final step in the attack of the alkene by a butyl carbonium ion was the facile loss of a proton to form a C10
alkene. This loss took place more readily than the alternative attack of a butanol molecule on a protonated
alkene regardless of any special orientation effects. At
95~ however, because only 2-methyl pent-l-ene is
protonated, the only possible reaction was that between butanol and 2-methyl pent-l-ene to produce the
t-ether. As there were no other reactive species com-
134
Adams, Clement, and Graham
CLAY
INTERLAYER& SURFACE
solvent
BuOH
EXTERNALLIO,UID
~
~
solvent
BuOH
+HZO,-H+If.*,§ 7.'
0
,~
Bu § H,.,O~===~,tp~ H,70
9
;q
Bu-(~-Bu
)
alkene
Bu* II +Bu+
9
I~
9 .,
TI_.§
{Bu§
~
Bu-O-Bu
~
".,I
alkene
~
l
,+
(Bu+ ~lkene)
//
~
.~
~. alkene§ +
""
#,
__.,(alJn[e§§
"
BuOH~+N§ §247
9
Bu-O-alkyl ether ,,
~interlayer water ~
, (alke e+H +)
~'~(Bu§
-various isomers
r
r
J
' Bu-O-alkyi ether.
-- variouS
isomers
"~H./.O
~.~
,#
hydride or
methyl shift /
d
(alke e,H +}
-H +
alke] ~e'I'
//
/
~, J,.- 9 aikene 9
Figure 4. Representation of the distribution of reactants and
products between the interlayer region of the montmorillonite
and the external liquid. (* denotes isomer of reactant alkene.)
peting for the alkene molecules a reasonable yield of
t-ether was achieved.
For the isomeric hexenes the yields of the butoxy ether
were greater than with the other alkenes, probably due
to the fact that only secondary carbonium ions were
involved in the reaction, with correspondingly little stetic hindrance. On the other hand, 2,2-dimethyl but-1ene is a branched molecule which effectively protects
the double bond from attack; low yields were observed
for all products.
In the production of di-(but-l-yl) ether it would be
expected that because this ether is more basic than butan-1-ol itself, it would be instantly protonated and rehydrated by the interlamellar water giving butan-l-ol.
However, due to the high reaction temperature, the
water formed on production of the ether was rapidly
lost from the interlamellar space of the clay and, hence,
Clays and Clay Minerals
a significant amount of di-(but-l-yl) ether was produced. As evidence of competition it was noted that, in
reactions involving similar alkenes, good yields of di(but-1-yl) ether were formed when lower yields of the
ether derived from alcohol/alkene reactions were obtained and vice versa.
The final yields of the various products of these reactions were dependent upon the reactivity of the alkene, and also upon the distribution of products and
reactants between the clay and the surrounding medium. The representation of the various equilibria in the
clay/external medium system is relatively complex
(Figure 4) and is even more complicated if the various
equilibria between the liquid medium surrounding the
clay and the vapor phase existing above the clay/liquid
mixture are taken into account. Experimental distribution coefficients for these equilibria are not at present
available, and the network of interconnecting equilibria
is not therefore mathematically tractable at the present
time.
In summary, the Al-montmorillonitestudied here behaved in many ways as a solid source of protons, but
the range of products is smaller than that given by a
liquid acid catalyst. This relative selectivity probably
results from the stereochemical constraints necessary
to fit the organic molecules between the layers or on the
surface of the clay.
ACKNOWLEDGMENTS
We thank the Science and Engineering Research
Council for a studentship to D.E.C, and the Royal Society for support.
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Purnell, J. H., Reid, P. I., Shaman, W. Y. M., and Thomas,
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Adams, J. M., Bylina, A., and Graham, S.H. (1982a) Shape
selectivity in low temperature reactions of C6 alkenes catalyzed by a Cu2+-exchangedmontmorillonite: Clay Miner.
16, 325-332.
Adams, J. M., Clement, D. E., and Graham, S. H. (1981)
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Adams, J. M., Clement, D. E., and Graham, S. H. (1982b)
Synthesis of methyl t-butyl ether (MTBE) from methanol
and isobutene using a clay catalyst: Clays & Clay Minerals
30, 129-132.
Adams, J. M., Davies, S. E., Graham, S. H., and Thomas,
J.M. (1978) Ready production of benzophenone from diphenylethylenecatalyzed by a synthetic hectorite: J. Chem.
Soc. Chem. Comm., 930-931.
Adams, J. M., Davies, S. E., Graham, S. H., and Thomas,
J . M . (1979b) Hydrogen exchange between 9,10-dihydroanthracene and 1, l-diphenylethylene over a synthetic hectorite: J. Chem. Soc, Chem. Comm., 527-528.
Ballantine, J. A., Davies, M., Purnell, J. A., Rayanakorn, M.,
Thomas, J. M., and Williams, K.J. (1981a) Chemical conversions using sheet silicates: facile ester synthesis by direct
Vol. 31, No. 2, 1983
Alcohol-alkene reactions on Al-montmorillonite
addition of acids to alkenes: J. Chem. Soc. Chem. Comm.,
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T h o m a s , J. M., a n d Williams, K . J . (1981b) Chemical conversions using sheet silicates: novel intermolecular dehydration of alcohols to ethers and polymers: J. Chem. Soc,
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mechanism: J, Polym. Sci. Part A, 2, 1847-1862.
Bittles, J. A., Chaudhuri, A. K., and B e n s o n , S . W . (1963c)
Clay-catalyzed reactions of olefins. III. Kinetics of polymerization of styrene: J, Polym. Sci. Part A, 2, 3023-3032.
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(1980) Chemical conversions using sheet silicates: a simple
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135
H o u g a r d y , J., Stone, W. E. E., and Fripiat, J . J . (1976) N M R
study of adsorbed water. I. Molecular orientation a n d protonic motions in the two layer hydrate of sodium vermiculite: J. Chem. Phys. 64, 3840-3851.
Mortland, M. M. (1968) Protonation of c o m p o u n d s at clay
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H o l m e s , ed., Elsevier, N e w York, 691-699.
Mortland, M. M., Fripiat, J. J., C h a u s s i d o n , J., and Uytterh o e v e n , J. (1963) Interaction b e t w e e n a m m o n i a and the
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silicate intercalates: in Solid State Chemistry o f Energy
Conversion and Storage, J. B. G o o d e n o u g h and M. S, Whittingham, eds., ACS A d v a n c e s in C h e m i s t r y Series 163,
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(Received 11 February 1982; accepted 6 June 1982)
Pe31oMe--PeaKIma 2-MeTn~ nenT-2-eHa c uepanqHbIMn cnnpTaMri (C1-C18) npn TeMnepaType 95~ B
npncyTcTHnn AI-MOHTMOpn.aaOHnTa npHaoan.~a K o6pa3oBanmo 20-90% 3qbupoH T~ina R-O-C(CH3)2C3HT.
MeHbml4e KO21HHeCTBa npOH3BO~FIJII4Cb Hpn FICnOJIb3OBaHHH BTOpFIHHblX cm4pTOB. B TO BpeM,q KaK
TpeTnqabIe cnnpTbI JlaBa.an TO~bKO cJIeabI 3TOrO 3qbnpa. K o r a a pa3Hbie a.rIKeHbI pearnpoBanH c
6yTaH-1-o,qeM npH 95~ s npncyTCTBm4 noao6Horo KaTaan3aTopa, peaKul~n Be n p o n c x o a n n n ao Tex
nop, n o g a a.aKea He 6bI2I c n o c o 6 e n o6pa3OBaTb TpeTnqHoro Kap6oHHeaoro HOHa HeMeaaenHo noc:le
npOTOHI4pOBaHna. B 3TOM c a y q a e npo~yKTaM aB~a~ca TpeTI4qHbIfi ~qbI4p t - R - O - n C 4 H g . OaHaKo.
npn TeMnepaType p e a g u n n 150~ o6paaoHbma.ancb pa3HbIe npo~yI<TbI, 8K31~oqa~KI 1) 3qbI~p, no~yqeHm, ifi
BO32/efiCTBReM 6yTanoaa Ha Kap6oaaem,le aoa~,I, npon3se~enHbie ~n6o HenocpeacTSeHno nyTeM npoTonnpoBaai4,q a.rIKeHOB, yna6o nyTeM c ~ s n r a rn~pmaa n3 3Toro noHa. f23 a~qKeHbl, noYlyqeHUble BO3IIefiCTHI4eM
nonoH n-C4H9" (no~yqenHbIX nyTeM npoTonnpoaanna n ~ernapaTattnn 6yTano~I~) na arisen. (3~
an-(6yT-l-n~I) 3qbrlp nyTeM ~ern~paTalInn 6yTaHOna n (4) Hefo~bmne KO:mqeCTBa cnnpTa nyTeM
rnapaTaufifi a:iKeHa. Pa3.rn4qnbie 3HaqeHn~ peaKTnaHOCTn nI4~Ke n Hbime 100~ CBa3aHbI Henocpe~cTBeHHO C KoJInqeCTBOM BO~bI, npncyTcTByromefi s npocaofi~ax r:mnbL n cTeneHbtO KnC~OTHOCTn. XOTa
r ~ n n a Be/leT ce6~ KaK KMC31OTHblfi KaTayln3aTop, p e a ~ u n n gsaarOTCa Ha MHOFO aurae t60nee ce~IeKTnanbIMn). qeM COOTHeTCTBytO~ne peaKunm ~aTami3nposannbte cepnofi KriC~OTO.~. [E.C.]
Resiimee--Die Reaktion v o n 2-methyl-pent-2-en mit prim/iren Alkoholen [C1-C1s) bei 95~ fiber einem AlMontmorillonit ergab 20--90% A t h e r des Typs R-O-C(CHa)2CaHr. Geringere A u s b e u t e n wurden erreicht.
w e n n sekund/ire Alkohole eingesetzt wurden. Terti/ire Alkohole ergaben nur Spuren dieses )i, thers. Wenn
unterschiedliche Alkene mit Butan-1-ol bei 95~ fiber einem ~ihnlichen K a t a l y s a t o r zur Reaktion gebracht
wurden, trat keine Reaktion ein. au6er das Alken war in der Lage. ein terti/ires C a r b o n i u m - I o n unmittelbar
nach der Protonierung zu bilden. In diesem Fall war das Produkt ein terti~irer A t h e r t - R - O - n C 4 H g . Bei
einer R e a k t i o n s t e m p e r a t u r v o n 150~ wurde jedoch eine Vielzahl v o n P r o d u k t e n gebildet einschlie61ich
(1) Ather. unter der Einwirkung von Butanol a u f die Carbonium-Ionen. e n t w e d e r direkt bei der Protonierung von A l k e n e n oder durch H y d r i d v e r s c h i e b u n g von diesen Ionen. ~2) Alkene. u n t e r der Einwirkung von
n-C4H.9§
(gebildet bei tier Protonierung und Dehydrierung v o n Butanol~ a u f das Alken. (3) Di-fbutl-yl)-Ather, durch Dehydrierung v o n Butanol u n d (4) geringe M e n g e n v o n Alkohol. durch die Hydrierung
v o n Alken. Die U n t e r s c h i e d e in der Reaktivit/it u n t e r u n d fiber 100~ h/ingen direkt mit der W a s s e r m e n g e
z u s a m m e n , die in den Z w i s c h e n s c h i c h t e n des Tons v o r h a n d e n ist u n d mit der dort h e r r s c h e n d e n Acidit/it.
Obwohl der T o n als ein saurer Katalysator wirkt, sind die Reaktionen viel sauberer (selektiverl als vergleichbare Reaktionen, die d u r c h Schwefels/iure katalysiert werden. [U.W.]
136
Adams, Clement, and Graham
Clays and Clay Minerals
R6sum6---La r6action de pent-2-bne m6thyl-2 avec des alcohols primaires (C1-C1s) h 95~ sur une montmorillonite-A1 a fourni de 20-90% d'6thers du type R-O-C(CH3)zC~HT. Des rendements moindres 6taient
produits lorsque des alcohols secondaires 6taient employ6s, et des alcohols tertialres n'ont produit qu' une
trace de cet 6ther. Lorsqu' on a fair r6agir une vari6t6 d'alk~nes avec du butan-1-ol a 95~ sur un catalyste
similaire, ancune r6action ne se produisait h moins que l'alk~ne n'6tait capable de former un ion carbonium
tertiaire d6s que se passait la protonation. Dans ce cas, le produit 6tait l'6ther tertiaire t-R-O-nC4Ha. A
une temp6rature de r6action de 150~ cependant, une vari6t6 de produits on 6t6 form6s, comprenant (1)
un 6ther par l'attaque du butanol sur les ions carbonium produits soit directement par la protonation des
alk~nes soit par d~placement hydride d'un tel ion, (2) des alk~nes par l'attaque des ions n-C4H9+ (derives
de la protonation et la d6shydration du butanol) sur l'alk~ne, (3) l'6ther di-but-l-yl) par la d6sbydration du
butanol, et (4) de petites quantit6s d'alcohol par hydration de l'alk~ne. Les diff6rences de r6activit~ au
dessus et dessous 100~ sont directement apparent6es ~ la quantit6 d'eau pr6sente dans l'espace interfeuillet de l'argile et au degr6 d'acidit6 trouv6 l~t. Quoique l'argile se comporte comme un catalyste acide,
les rfiactions sont beaucoup plus propres (plus s61ectives) que des r6actions comparables catalys6es par
un acide sulphurique. [D.J.]