Bergaya F. Handbook of Clay Science

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Table 10.2.1. Types and examples of Brønsted acid-catalysed reactions on clay minerals

Reaction type Example Catalyst Reference

Deuterium exchange Deuteration of b-ketoesters,

b-diketones, pyrrole, indoles

Clays containing interlayer D

O Rao et al. (1989)

Ether formation and cleavage Alkenes+primary alcohols M

-clays Adams et al. (1983b), Ballantine et al.

(1984a)

Substituted alkenes,

butadiene+alcohols

Cation-exchanged clays Adams et al. (1983a)

Isobutene+methanol to form MTBE M

-clays Adams et al. (1981, 1982, 1986),

Bylina et al. (1980)

Primary alcohols to 1,1

-ethers Al

-or Fe

-clays Habib et al. (1988)

Deprotection of tetrahydropyranyl

ethers to give alcohols and phenols

K10 in methanol Li et al.(1999)

Cholesteryl ethers from alcohols or

phenols with cholesterol

K10 Lu et al. (1998)

Preparation of silyl ethers from

alcohols or phenols with

hexamethyldisilazane and their

desilylation

K10 then K10 methanol to remove Zhang et al. (1998)

Alkylene oxides+alcohols to form

hydroxyalkylated ether products

Bentonites or Group 11 or 12 cation-

exchanged clays

Kapustin et al. (1986), Fujita et al.

(1987a)

Ester and lactone formation Alkenes, chloroalkanes or alcohols

react with carboxylic acids to make

esters

Acid-treated clays Ballantine et al. (1984b), Gregory

et al. (1983) , Atkins (1986), BASF

(1963)

Ketenes+alcohols to esters Acid activated clays BASF (1971)

Alcohols, phenols, thiols acetylated

with acetic anhydride

K10 or KSF Li and Li (1998)

Isobutene+diethyl keto-malonate

gives g-lactones (ene reaction)

Acid-treated clays Roudier and Foucaud (1986)

Formation of amides and peptides Tert-alcohols and nitriles form

substituted amides (Ritter reaction)

-montmorillonite O’Neil (1982)

Amines are acetylated with acetic

anhydride

K10 or KSF Li and Li (1998)

Esters and ammonia can give amides

and nitriles

K10 Wali et al. (1998)

Amino acid adenylates give

polypeptides

Montmorillonites Katchalsky and Ailam (1967),

Paecht-Horowitz (1977), Paecht-

Horowitz, et al. (1970)

(continued on next page )

Chapter 10.2: Clay Minerals as Catalysts548

Table 10.2.1 (Continued )

Reaction type Example Catalyst Reference

Reactions dependent on protection,

deprotection or activation of

carbonyl groups

Acetal formation from carbonyls and

alcohols

Cation-exchanged montmorillonites,

Filtrol 24 or

dodecatungstophosphoric acid on

(K10, Su

d Chemie)

Tateiwa et al. (1995), Li et al. (1997a) ,

Yadav and Pujari (1999)

Ketals (incl. cyclic) from 1,2-diols or

epoxides

Acid-treated or cation-exchanged

clays

Conan et al. (1976), Su

d Chemie

(1961)

Diols and enol ethers form acetals

and ketals

Montmorillonite Vu Moc and Maitte (1979)

Acetals and ketals from

trialkylorthoformates and carbonyls

Acid-treated clay Taylor and Chaing (1977)

Dithianes, thioacetals, thioketals

from ketones or aldehydes and thiols

Acid-treated clay (KSF, Su

d Chemie) Labiad and Villemin (1989)

1,1

-Diacetates from aldehydes and

acetic anhydride

or Zn

-montmorillonite Zhang et al. (1997a), Jankovic and

Komadel (2000), Nagy et al. (2002)

Deprotect 1,1

-diacetates K10 Li et al. (1997b)

Enamines from sec-amines and

ketones

Acid-treated or cation-exchanged

montmorillonites

nig et al. (1962), Dewan et al.

(1995)

Deprotection of acetals to aldehydes K10 Li and Li (1997)

Removal of acetal, silyl and 4,4

dimethoxytrityl protecting groups

from carbohydrate and nucleoside

hydroxyl groups

Clay in aqueous methanol Asakura et al. (1996)

Oximes can be cleaved to aldehydes

or ketones

Bentonite Alvarez et al. (1987)

Aldoximes can be dehydrated to

nitriles

Acid-treated clay KSF Meshram (1992)

Semicarbazones can be cleaved to

aldehydes or ketones

Bentonite+acid or supported

reagents such as clayfen

Cano et al. (1988)

Cyclic anhydride formation a, o-dicarboxylic acids can be

converted to cyclic anhydrides under

very mild conditions

- montmorillonite or microwave

plus acid-treated clay KSF

Graham et al. (1974), Villemin et al.

(1993)

(continued on next page )

10.2.3. Summary of Catalytic Activity 549

Table 10.2.1 (Continued )

Reaction type Example Catalyst Reference

Formation of heterocyclics Primary amines+1,4–diketones form

pyrroles

Acid-treated clay (K10) Texier-Boullet et al. (1986)

Piperonyl alcohol gives

trimethylendioxyortho-cyclophane

A bentonitic earth, Tonsil Actisil FF Miranda et al. (1999)

Phenylhydrazine+ketones give

2-substituted indoles

Microwave plus acid-treated clay

KSF

Villemin et al. (1989)

Pyrrole+benzaldehyde give

meso–tetraphenylporphyrin

Montmorillonite Geier et al. (2000), Geier and Lindsey

(2002)

Tetrahydroquinolines from aromatic

amines, aromatic aldehydes and

cyclopentadiene

Bieliaca bentonite or KSF

montmorillonite

Sartori et al. (2001), Ballini et al.

(2000)

Dihydropyrimidines from aldehydes,

b-dicarbonyls and urea

Solventless, KSF montmorillonite or

in water

Ballini et al. (2000) Bigi et al. (1999)

Chromenes KSF montmorillonite Ballini et al. (2000)

Malononitriles and 1,2–aminoalcohol

gives 2–oxazolines which on

hydrolysis give 2,2-dialkyl-3-

aminopropanoic acids

Natural kaolinitic clay Jnaneshwara et al. (1998, 1999)

Phenols and ketones or aldehydes

give 2,2- or 2–substituted

1,3–benzodioxoles

montmorillonite KSF or K10 Li et al. (1998a)

Pechmann condensation of phenols

with ethyl acetoacetate give

coumarins

montmorillonite Li et al. (1998b)

2-Methyl-8-ethylquinoline from

ethylene glycol and excess

2-ethylaniline

In vapour phase over K10

montmorillonite

Campanati et al. (1997)

(continued on next page )

Chapter 10.2: Clay Minerals as Catalysts550

Table 10.2.1 (Continued )

Reaction type Example Catalyst Reference

Rearrangement reactions 1,2-Diols undergo pinacol

rearrangements to form

2–hydroxyketones rather than

dehydration products

1,2-Diols intercalated in

montmorillonite

Gutierrez and Ruiz-Hitzky (1987),

Gutierrez et al. (1988)

4,4-Dialkylcholest-5-enes undergo

backbone rearrangement to (20R)-

and (20R)-4,4-dialkyl-5b,14b-

dimethyl-18,19-dinor-8a,9b,10-

cholest-13(17)-enes

K10 Duan et al. (1999)

Allyl phenyl ethers to o– allyl phenols Montmorillonite Dauben et al. (1990)

Alkyl phenyl ethers to 4–alkyl

phenols

Cation-exchanged montmorillonites Tateiwa et al. (1994)

Claisen orthoester rearrangements Microwave plus acid-treated clay

(KSF, Su

d Chemie)

Huber and Jones (1992)

a-Pinene rearranges to camphene,

limonene and tricyclene

Acid-treated clays; cation-exchanged

clays; polyaminocation-exchanged

clay

Kullaj (1989), Besun et al. (2002),

Breen and Moronta (2001), Breen

(1999), Breen and Watson (1998)

N-methyl-N-nitrosoaniline (I)

undergoes Fischer rearrangement to

N–methyl-4-nitrosoaniline

K10 or KSF montmorillonite Kannan et al. (1997)

Electrophilic aromatic substitution

reactions

2-(Triﬂuoromethyl)aniline gives

dimers and oligomers

Cation-exchanged KSF or K10 Kowalska et al. (2001)

Phenylacetylene reacts with

p–toluidine or p-anisidine to give the

corresponding

2,6–bis(1–phenylvinyl)anilines

KSF Arienti et al. (1997)

10.2.3. Summary of Catalytic Activity 551

pre-biotic synthesis of RNA type oligonucleotides from activated nucleotides (Tessis

et al., 1995; Ding et al., 1996; Ertem and Ferris, 1997; Prabahar and Ferris, 1997;

Sawai et al., 1997; Ertem and Ferris, 1998; Ferris, 1999; Kawamura and Ferris, 1999;

Porter et al., 1999; Ertem et al., 2000; Wang and Ferris, 2001; Ferris, 2002).

Clay minerals (montmorillonite, beidellite, illite and vermiculite) were compared

for the hydrolysis of ﬁve carbamate pesticides: carbosulfan, carbofuran, aldicarb,

pirimicarb and chlorpropham (Wei et al., 2001 ). Montmorillonite has the strongest

inﬂuence on the hydrolysis of these carbamates. Similarly, the phosphorous con-

taining pesticides chlorpyrifos-methyl, oxon, and paraoxon are hydrolysed by mont-

morillonite and kaolinite (Smolen and Stone, 1998).

The unusual product p-nitrosodiphenylamine is formed from N-phenylhydroxyla-

mine in the presence of K10 or cation-exchange d K10 rather than the typical

Bamberger products, aminophenols (Naicker et al., 1998).

B. Lewis Acid Catalysis

It was shown, for example, by the thermal desorption of ammonia (Matsuda et al.,

1988) and the changes in the IR spectrum of pyridine adsorbed on clay minerals

(e.g., Breen et al., 1987) that as the clay mineral is dehydrated with increasing

temperature, its Lewis acidity becomes more important than its Brønsted acidity.

Several of the reactions listed below have complex mechanisms, but Lewis activity is

thought to be crucial (Table 10.2.2).

In 1930, clays were ﬁrst used as catalysts for cracking petroleum (Franz et al.,

1959). At 300 1C, the efﬁciency and stability of montmorillonite catalysts was much

improved by acid activation (Thomas et al., 1950). Nonetheless, there is a theme in

reactions of this type for the catalysts not to be resistant enough to the hydrothermal

treatment needed for oxidation of coke (catalyst regeneration) which builds up in

catalyst pores (Ballantine, 1986). Thus there was a trend towards use of zeolites,

though PILC derivatives are promising.

C. Redox Reactions

Redox reactions are associated with transition metals either substituted in the oc-

tahedral or tetrahedral sheets of the clay mineral or those introduced as exchange-

able cations between the clay mineral layers. We summarise the situation for

oxidation reactions in Tables 10.2.3 and 10.2.4.

Several smectite-based materials were also been found to be efﬁcacious for ox-

idation when used in concert with hydrogen peroxide, t-butyl hydroperoxide or

iodosylbenzene.

Sodium hypochlorite or potassium persulphate epoxidise 1-hexene preferentially

over cyclic alkenes when catalysed by M(salen) complexes (M ¼ Mn(III), Ni(II);

salen ¼ bis-(salicylidene)ethylenediamine) adsorbed onto mo ntmorillonite or zeolite

Y(Chatterjee and Mitra, 1999). Iodosylbenzene and a chiral Mn(salen) complex on a

Chapter 10.2: Clay Minerals as Catalysts552

(continued on next page )

Table 10.2.2. Types and examples of Lewis acid catalysed reactions on clay minerals

Reaction type Example Catalyst Reference

Catalytic cracking and

isomerisation

Long-chain cracking to short-

chain alkanes

Pillared clays Lahav et al. (1978), Endo

et al. (1980)

Isomerisation of n-alkanes to

iso–alkanes

TM-exchanged clays See, e.g., Chevron Research

(1972, 1973)

Dehydration and

isomerisation of alcohols,

e.g., 1-hexanol to 2- and

3–hexenes

Clays Musaev et al. (1986)

Methanol and Syn-gas

conversions

Methanol to C

–C

alkenes Ce-clays; Zr–PILC Toyo Soda (1983), Burch and

Warburton (1986)

Methanol to methyl formate Cu-TFSM Morikawa et al. (1982)

Syn gas to alkene/alkane mix

–C

)

TM-exchanged clays NL Industries (1977)

Friedel-Crafts alkylation and

acylation of aromatics

Phenol alkylation with

alkenes, branched alkenes,

substituted styrenes,

cycloalkenes and polyalkenes

Cation-exchanged or acid-

treated clays

Chivadze and Khakhnelidze

(1987), Imanari et al. (1987),

Takagi and Naruse (1989)

Aniline alkylated by alkenes Cation-exchanged or acid-

treated montmorillonite, Ce-

exchanged Al pillared SWy-2

Shigeshiro et al. (1987),

Bacskai and Valerias (1988),

Narayanan and Deshpande

(2000)

Unactivated aromatic and

heteroaromatic hydrocarbons

alkylated by halides, alcohols

and alkenes

Cation-exchanged clays, K10

and PILCs.

Hassan et al. (1985), Laszlo

and Mathy (1987), Natekar

and Samant (1995),

Narayanan and Deshpande

(2000), Li et al. (1998) Clark

and Mesher (1995)

10.2.3. Summary of Catalytic Activity 553

Table 10.2.2 (Continued )

Reaction type Example Catalyst Reference

Acylation of benzo-15-crown-

5 ether with acetyl chloride

gives 4

-acetyl-benzo-15-

crown-5

Best with Sn exchanged K10 Biro et al. (2000)

Acylation of aromatic

hydrocarbons with carboxylic

acids

Cation-exchanged

montmorillonite

Chiche et al. (1987)

Other electrophilic aromatic

substitution reactions

Nitration of aromatics Nitric acid and cation-

exchanged clay

Bakke and Liaskan (1979),

Sato et al. (1989)

Chlorination of toluene Clay Pitchumani et al. (1993)

Reduction of mutagenicity of

benzopyrenes by methyl

transfer

Acid-activated clay or

pillared clay

Roy et al.(1999)

Methylation of

alkylnaphthalenes with

hexamethylbenzene as a

model for natural occurrence

of methylnaphthalenes in

crude oil

Al-montmorillonite Bastow et al. (2000)

Rearrangements Citronellal to menthone and

isomenthone

Al/Fe-pillared clay at 80 1C Cramarossa et al. (2001)

Citronellal to pulegol and

isopulegol

Al/Fe-pillared clay at room

temperature

Cramarossa et al. (2001)

Chapter 10.2: Clay Minerals as Catalysts554

montmorillonite showed slightly decreas ed enantioselectivi ty compared to free so-

lution epoxidation (Fraile et al., 1998).

Alkanethiols undergo facile anti-Markovnikov addition to styrene over K10-

montmorillonite and cation-exchanged clay minerals by way of a radical mechanism

to form sulphides (Kannan and Pitchumani, 1997). Surfactant PILC minerals were

found to be remarkably selective at suppressing side reactions. Iron cations in mica

or talc can produce a conducting polymer of anilinium dodecylbenzenesulphonate,

which encapsulates the clay particle (Segal et al., 2000; Jia et al., 2002 ). The prep-

aration of a zirconia-pillared montmorillo nite was made more effective by ultra-

sonication during adsorption of the polyhydroxyzirconium cation (Awate et al.,

2001). The Zr-PILC was very effective for the hydroxylation of phenol.

Few reduction reactions mediated by clay minerals alone were reported. One example

is the acid-treated clay-catalysed reduction of nitroarenes to anilines with hydrazine

Table 10.2.3. Examples of clay-catalysed redox reactions

Substrate (A)/(P)



Product Clay Reference

Allylic alcohols A Ketones Ni

-F-containing

synthetic mica

Fujita et al.

(1987b)

2-propenyl

aromatics

A Acetophenones Cr

-Mica Kondo et al.

(1990)

Cyclohexene A Cyclohexanol and

cyclohexanone

-clays Hashimoto

et al. (1988)

Ethanol and

ether

P n.r. Uranyl-exchanged

PILCs

Suib et al.

(1986)

n.r. ¼ not required.



A ¼ aerobic oxidation; P ¼ photooxidation.

Table 10.2.4. Examples of clay-catalysed redox reactions requiring a co-reactant

Substrate Co-reagent Product Clay Reference

Phenols and

phenolic ethers

Hydrogen

peroxide

Hydroxylated

products

-beidellite Constantini

and Popa

(1989)

Allyl alcohols Hydrogen

peroxide

Epoxides V–PILC Choudary et al.

(1990)

Arylmethylenes t-butyl

peroxide

Monocarbonyl

compounds

Cr–PILC Choudary et al.

(1992)

Styrene Iodosylbenzene 1-Phenyl-l,2-

dihydroxyethane

Mn(III)- or

Fe(III)-

exchanged clay

Boricha et al.

(1999)

10.2.3. Summary of Catalytic Activity 555

(Ha n and Jang, 1990); another is the reduction of ketones and aldehydes to hydro-

carbons by triethylsilane and highly acidic clay minerals (Onaka et al., 1993).

Ghosh and Bard (1983) and Ghosh et al. (1984) ﬁrst establis hed the ﬁeld of clay-

modiﬁed electrodes in the mid-1980s. Since then unde rstanding the nature of the clay

mineral structural units and their impact on transport of a variety of electroactive

probes (anions, neutrals, small cations, large cations and compounds with distrib-

uted charge) increased (Macha and Fitch, 1998). The nature of the layered material

(i.e., size, charge, iron content, pillaring and organic tailoring) controls access to the

interlayer sites. Alumina PILC ﬁlms, made using preformed pillared structures, were

constructed on graphite electrodes (Petridis et al., 1996). The ﬁlms exhibit very good

electroactivity when immersed in solut ions containing redox active cationic specie s,

e.g., Fe(bpy)

, Os(bpy)

, Ru(NH

)

and methyl viologen. Excellent catalytic

activity was observed for the electroreduction of H

by a nontronite (SWa-1,

ferruginous smectite) clay coating on a glassy carbon electrode with incorporated

methyl viologen as mediator (Zen et al., 1996).

Electrochemical reduction of haemoglobin in assembled, stable ﬁlms of alternating

clay mineral haemoglobin layers on electrode surfaces was achieved (Zhou et al.,

2002b). The ﬁlms are deposited layer-by-layer on various solid substrates by alternate

adsorption of negatively charged clay mineral particles from their aqueous dispersions

and positively charged haemoglobin from pH 4.5 buffers. Similar clay mineral inter-

calated deposits of myoglobin, haemoglobin or horseradish peroxidase were examined

as potential electrocatalytic sensors for pollutants (Hu, 2001). Oxygen, trichloroacetic

acid, nitrite and hydrogen peroxide are catalytically reduced by all three proteins in

clay mineral ﬁlms (Zhou et al., 2002a). Hexacyanoferrate and vitamin B-12 hexacar-

boxylate intercalated into clay mineral-surfactant (cetyltrimethylammonium bromide)

ﬁlms on electrodes also show good electrocatalytic activity (Carrero and Leon, 2001).

Electro-inactive Fe(bpy)

becomes electro-catalytic for the oxidation of guanine

on binding to nontronite on a graphite surface (Ilangovan and Zen, 1999 ). Mn

exchanged montmorillonite catalyses the production of hydrogen peroxide efﬁciently

from dioxygen (or air) and hydroxylamine at pH 8.0 in aqueous solution (Hothi et

al., 1997). Oxygen can be reduced electrocatalytically at clay-modiﬁed electrodes in

the presence of tetraazamacrocyclic cobalt(III) complexes (Gobi and Ramaraj, 1998)

or platinum particles (Premkumar and Ramaraj, 1997). The Faradaic yield and the

rate of H

production are found to be higher at clay-coated electrodes than at

Nafion

-coated electrodes. During photoelectrocatalytic reductio n of oxygen at

Pt/H

-montmorillonite/[Ru(bpy)

]

electrodes, the amounts of H

produced

increase by a factor of two under light irradiation when compared to dark.

D. Reactions via Reactive Intermediates

-montmorillonite catalyses the condensation of glycolaldehyde to monosaccha-

rides, apparently by an aldol process (Martil and Aragon de la Cruz, 1986). Al

exchanged clay minerals catalyse the cross aldol-addition of silyl enol ethers to

Chapter 10.2: Clay Minerals as Catalysts556

carbonyl compounds or acetals (Kawai et al., 1986a, 1988a, 1988b). Similarly, silyl

ketene acetals and carbonyls give 3-silylether esters (Onaka et al., 1987). Acetals and

carbonyls can be allylated using the acid-activated clay, K10 (Kawai et al., 1986b).

Substituted salicylic aldehydes are synthesised in good yields and excellent se-

lectivities by reaction of phenols with formaldehyde over montmorillonite KSF-

triethylamine (Bigi et al., 2000). An intermediate 2-hydroxybenzaldehyde is formed

initially and this undergoes Oppenhauer oxidation with a further mole of formal-

dehyde to the salicylic aldehyde. In the absence of triethylamine the higher acidity of

the clay mineral results in mainly acetal and diphenylmethane formation instead;

while, the lower iron K10 gives just the 2-hydroxybenzaldehyde, suggesting that iron

cations aid the oxidation. Aromatic amines adsorbed on kaolini te condense with

formaldehyde to give the corres ponding diaminodiphenylmethanes (Bahul ayan et

al., 1999). Triarylmethanes are synthesised in good to excellent yield via Baeyer

condensation of aromatic aldehydes with N,N-dimethylaniline catalysed by mont-

morillonite K10 at 100 1C in the ab sence of solvent (Zhang, et al., 1997b).

Cyclohexane and morpholine in the presence of KSF under azeotropic distillation

give 1-morpholinocyclohexene which, when alkylated or acylated in situ without

isolation of the enamine, give overall yields of better or equivalent than those ob-

tained by isolation of the enamine (Hammadi and Villemin, 1996).

Dual catalysis of the Michael addition of b-diketones to a,b-unsaturated ketones by

FeCl

and NiBr

/clay was reported (Laszlo, et al., 1990). Michael adducts can also be

obtained from a,b-unsaturated esters or ketones with silyl ketene acetals or silyl enol

ethers using clay catalysts (Kawai et al., 1987, 1988a, 1988b) or from 1,3-diketones

using K10 or KSF (Soriente et al., 1999). The reactions are versatile and highly

regiospecific. 3-Unsubstituted indoles add a,b-unsaturated ketones and esters at the

3-position (Iqbal et al., 1988). 3-Methylindoles give 2-substituted products, while

3-benzylindoles give 2,3-migration of the benzyl group. Similar reactions on K10 are

improved by addition of alcohols and nitromethane as solvent (Poupaert et al., 1999).

Synthesis of alkenes via the Knoevenagel reaction from aldehydes and C-acids

(e.g., Meldrum’s acid) (Thorat et al., 1987) or malonate derivatives (Foucaud and

Bakouetila, 1987) was achieved using clays. Silylpropylethylenediamine modiﬁed

montmorillonites are weakly basic and were used for the Knoevenagel reaction

(Subba Rao and Choudary, 1991).

Certain transition metals and their cations are noted for their ability to coordinate

alkenes and generate carbenes from diazoalkanes (Wulfman et al., 1976). These can

be used for the cyclopropanation of alkenes and dienes. Cu

-montmorillonite is

effective with ethyl diazoacetate at room temperatur e (Yamagishi, 1986). Stereo

selectivity is not affected.

E. Cycloaddition Reactions

Uncatalysed Diels–Alder reactions often require extended reaction times at elevated

temperatures and pressures. Several different catalyst types shown to be effective,

10.2.3. Summary of Catalytic Activity 557