GLYCOL-CLEAVAGE OXIDATION OF
POLYSACCHARIDES AND MODEL COMPOUNDS
Calcium complexation of dicarboxy glucans
On the cover: Complexation of two lanthanide(III) ions by dicarboxy-^-cyclodextrin. Drawing: Mr. W.J. Jongeleen.
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V-POLYSACCHARIDES AND MODEL COMPOUNDS
Calcium complexation of dicarboxy glucans
PROEFSCHRIFT
ter verkrijging van de graad van doctor aan de Technische Universiteit Delft
op gezag van de Rector Magnificus, prof.drs. P.A. Schencl<, in het openbaar te verdedigen ten overstaan van
een commissie aangewezen door het College van Dekanen op dinsdag 31 oktober 1989 te 16.00 uur
door Michiel Floor geboren te Leiden scheikundig doctorandus
TR diss
1762
Dit proefschrift is goedgekeurd door de promotoren
Prof. dr. ir. H. van Bekkum en
Prof. dr. ir. A.P.G. Kieboom
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van volledige kennis zou iedereen bezwijken.
The investigations described in this thesis have been financially supported by the Netherlands Technology Foundation (STW) under the auspices of the Netherlands Organization for Scientific Research.
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1. INTRODUCTION
Phosphates in detergents 1 Environmental concern 2 Phosphate substitutes 4
Low molecular weight systems 5
High molecular weight systems 7
A. Zeolites 7
B. Polymeric carboxylates 9
Oxidized polysaccharides 10 Catalytic glycol-cleavage oxidation 14
Scope of the thesis 17 References and notes 19
2. ALUMINA- AND Y-ZEOLITE CATALYZED REACTION OF CYCLOHEXANOL WITH tert-BUTYL HYDROPEROXIDE
Abstract 27 Introduction 27 Experimental 28 Results and discussion 29
Type I catalysts: rearrangement of tBHP 3 0
Type II catalysts: oxidation of cyclohexanol 32
Conclusions 34 References 35
Contents
3. REDOX PROPERTIES OF CERIUM-EXCHANGED Y-ZEOLITES
Abstract 37 Introduction 37 Experimental 39 Results and discussion 40
Oxidation of zeolite NaCeY with HJ)^ 40
Oxidation of zeolite NaCeY with 0^ 44
Oxidation of pinacol with NaCe(IV)Y 46
Conclusions 49 References 49
4. HETEROPOLYANIONS AS OXIDATION CATALYSTS IN A TWO-PHASE SYSTEM
Abstract 51 Introduction 51 Experimental 52 Results and discussion 52
Conclusions 56 References 56
5. OXIDATION OF MALTODEXTRINS AND STARCH BY THE SYSTEM TUNGSTATE-HYDROGEN PEROXIDE
Abstract 59 Introduction 59 Experimental 61 Results and discussion 63
Kinetics and mechanism 63
Effect of temperature and pH 69
Effect of the chain length 69
Analysis of the precipitated reaction products 71
Conclusions 74 References and notes 74
OXIDATION OF MALTODEXTRINS AND STARCH WITH ALKALINE SODIUM HYPOCHLORITE
Abstract 77 Introduction 77 Experimental 80 Results and discussion 82
Effect of pH 82
Effect of additives 88
Calcium complexation 89
Conclusions 94 References and notes 94
HYDROGEN PEROXIDE AS CO-REACTANT IN THE CHLORITE OXIDATION OF DIALDEHYDE GLUCANS
Abstract 97 Introduction 97 Experimental 100 Results and discussion 104
Preparation of dialdehyde polysaccharides 104
Preparation of dicarboxy polysaccharides: application of
hydrogen peroxide as a co-reactant 105
Degree of polymerization of dicarboxy polysaccharides 110
Calcium complexation 111
Conclusions 118 References and notes 119
Contents
STRUCTURAL AND CONFORMATIONAL ASPECTS OF CALCIUM COMPLEXATION BY 2,3-DICARBOXY DERIVATIVES OF ^-CYCLODEXTRIN, AMYLOSE AND CELLULOSE
Abstract 123 Introduction 124 Experimental 125 Results and discussion 129
Preparation of dicarboxy polysaccharides 129
Calcium complexation 130
Conformational effects 133
1. Complexation of Ca(II) and lanthanide(III) ions by DC^CD 133
2. Complexation of Ca(II) by DCA and DCC 138
Conclusions 143 References and notes 143
CONCLUDING REMARKS
Comparison of oxidation methods 145
Environmental aspects 146 References and notes 146
SUMMARY 147
SAMENVATTING 151
DANKWOORD 155
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C H A P T E R 1
I N T R O D U C T I O N
Phosphates in detergents
Pentasodium triphosphate (NacP^^O,». (H„0)g), more commonly known as sodium tripolyphosphate (STP), has been used for over forty years as a so-called
'builder' in laundry detergents. STP plays an essential role in the washing process because of the following properties [1-4]:
- sequestration of the calcium and magnesium ions present in hard water, thus preventing the formation of insoluble salts of (anionic) surfactants and the precipitation of mineral salts on the fabric and the washing machine.
- disintegration of soil incrustations on the fabric. - dispersion of pigment soils.
- alkalinity and buffering capacity.
In addition, STP is physiologically safe and it can be produced at low cost [5].
The importance of phosphate builders is illustrated by the vast world consumption of STP (1982: 8.4-10 tons/year [4]) at a total world production of soaps, detergents and cleaners of 30-10 tons/year [6]. In Western Europe
g (1985) the annual market for cleaning products amounts to Dfl. 16-10 , with an estimated growth-rate of 4%/year [7]. The per capita detergent and cleaner consumption in Europe is about 20 kg/year [7].
Chapter 1 2
-Environmental concern
In spite of the outstanding performance and cost-effectivity of STP, its large scale application in detergents has a serious drawback: phosphates in domestic waste waters are drained via sewage plants into surface waters and contribute, among other sources (see below), to eutrophication of lakes and stagnant waters. In most cases, phosphate is the limiting nutrient for the growth of algae. In summer, when light is not the limiting factor, the high levels of phosphate allow an uncontrolled growth of algae. The anaerobic degradation of these algae in the deeper water areas, induced by a light and oxygen deficit, causes HpS development. Moreover, some algae produce toxins that effect swimmers' skin irritation and fish mortality. The eightfold increase of the total inorganic P-level of the river Rhine from 1930-1986 [8] may illustrate the gravity of the present situation.
Problems with eutrophication are not confined to lakes and rivers only, coastal seawater is also affected as is evidenced by a burst of
Chrysochromulina polylepis algae growth at Norway's west-coast in 1988 [8]. It has even been suggested that eutrophication significantly contributes to acid rain because some marine algae produce dimethyl sulfide which is photochemically converted in the atmosphere to SO^ [9].
The problems concerning eutrophication have been recognized since 1953 [10], but it was not until 1968 that Vollenweider initiated the inter-national discussion [11]. In the Netherlands Golterman called attention to the increasing eutrophication and the measures to be taken [12]. Depending on the specific situation, nitrogen or phosphorus is the growth limiting factor. It is, however, generally accepted that eutrophication is best controlled by P-reduction because (i) N is drained more diffusely and
(ii) because of the occurrence of nitrogen fixing blue-green algae [13,14]. In order to evaluate the effect of phosphate restrictions, the relative contributions of different sources should be known. In the Netherlands, the extensive studies of Olsthoorn [15-18] indicate that in 1983 approximately 26% (3.9-10 kg P) of the Dutch phosphate load to sweet surface waters originated from detergents [17] (Fig. lA). Fig. IB reveals the substantial contribution of the international rivers (Rhine and Meuse; 10-10 kg P ) . Figures for 1986 [18] indicate a 10% reduction (with respect to 1983) of the phosphate load of the Rhine (resulting from phosphate restrictions in West
16 V.
A B
Fig. 1. Phosphorus load on Dutch sweet surface waters: relative contributions from different sources (1983)[17].
A. Sources of Dutch origin (100% = 15 10 kg P/year). B. Internationa] rivers (Rhine, Meuse) included as a source
(100% = 25-10^ kg P/year).
1. international rivers including foreign industries; 2. detergents; 3. human excretion; 4. drainage from (agricultural) land; 5. Dutch
industry; 6. others.
Germany and Switzerland). In contrast, due to a 1 0 % increased human P-secretion and a 2 2 % rise in detergent use in the Netherlands, the overall phosphorus accumulation in Dutch surface waters increased from 1983-1985 (from 24-27-10^ to 26-29-10^ kg P ) . It should be noted that the accumulation of phosphorus in agricultural land amounts to 100-10 kg/year which may give rise to serious future problems. In addition, the fertilizer industry produces a significant amount of phosphate waste but this hardly contaminates sweet surface waters as the effluents are drained close to the sea.
By appointment of November 1987, the Rhine-delta countries agreed to reduce the phosphorus load by 5 0 % in 1995. Possible measures for phosphate reduction of domestic origin include:
* Prevention: - Local or central softening of tap water (ion-exchange or precipitation of Ca(II) and Mg(II) ions by the addition of alkal i and C O - ) .
Chapter 1 4
-* Substitution: - Development of substitutes for STP (see below).
* Removal: - Biological phosphate removal in the second stage of sewage plants by phosphate incorporating Acinetobacter species [19].
- Precipitation of phosphates in the third stage of sewage plants by the addition of Fe{III) or Al(III) salts. Interestingly, controlled precipitation of calcium phosphate can also be effected on a grafting material by the addition of calcium hydroxide [20,21]. This precipitate can be used as a raw material for the phosphates industry.
(Phosphate removal at sewage plants has the advantage of reducing the phosphorus load from both detergent and human secretion origin (50% of effluent P to surface waters.) Measures against non-household P-sources should include restrictions in manure production by the bio-industry and reduction of the effluents from the fertilizer industry.
In the Netherlands, as the result of a voluntary agreement, 40-50% of the detergents has been phosphate-free since December 1988, a further reduction aims at zero-phosphate in 1990. Moreover, the Dutch Government agreed to stimulate third-stage phosphate removal at sewage plants in order to attain the 50% decrease in 1995 of the phosphate load in the Rhine delta as required by the international agreement [22,23]. Moreover, manure-restricting legislation is in progress [24].
The regulations of some other countries are summarized in Table I.
Phosphate substitutes
The restrictions for the use of STP induced the development of alternative builder systems by the detergent industry. These builders should have good sequestering properties and, for environmental acceptation, preferably consist of the elements C, H and 0 together with the counter-ions Na and K and should be readily biodegradable. For these reasons, organic polycarboxylates, both of low and high molecular weight, have been studied most extensively.
22 Table I. Actual phosphate limits in detergents (as STP)
country Austria West Germany Italy Norway Switzerland Netherlands Japan Canada limit % 22 22 4 12 0 22 0 17 9 effective status 01-01-1987 01-01-1984 31-03-1988 01-01-1986 01-07-1986 01-12-1987 1990 01-01-1978 regulation regulation regulation regulation regulation voluntary agreement voluntary agreement 01-01-1973 regulation
U.S.A., varying e.g.
New York, Indiana 0 Florida, Maine 35
1973 1972
regulation regulation
Low molecular weight systems
An impressive range of ether carboxylates has been studied [25,26]. In these systems both carboxylate and ether (or acetal) oxygens are involved in complexation giving a relatively stable complex with calcium ions. The most
important ether carboxylates (Fig. 2) are carboxymethyl oxysuccinate [27] (CMOS) and carboxymethyl tartronate [28] (CMT). They were, however, never commercialized, presumably because of relatively poor cost performance. More recent developments include oxydisuccinate [29] (ODS) and adducts of maleic acid to propylene glycol [30] (PGDS, propylene glycol disuccinate), to glycerol [31] (GTS, glycerol trisuccinate) and to tartaric acid [32] (TDS, tartrate disuccinate).
In spite of its poor builder performance compared to STP, sodium citrate (Fig. 2) is widely used in USA liquid detergents due to its safety and environmental acceptability [33].
Chapter 1 6
-COO" -COO" H , C - C O O " I I ^ HC—O —CH^ —COO" HC — O - C H j —COO" HC —COO"
COO" O I H C - C O O " I H j C — C O O " CMOS CMT ODS H,C —COO" H,C—COO" H,C —COO"
' l ' l ^ HC—COO" HC—COO" HC —COO"
I I I O O O
I I I ;—CH CH, H C - C O O "
I I H I CH, HC —O—C — C H , —COO" HC—COO"
I ' I I ' I O CH, COO" O I I ' I HC —COO" O HC —COO' I I I H , C - C O O " HC—COO" H,C —COO" ' I ^ HjC—COO" PGDS GTS TDS COO" CH, —COO" COO"
I I I CH, N — C H , — C O O " HCOH I I I H O - C — C O O " CH, —COO" HOCH I I CH, HCOH I I COO" HCOH I COO" citrate N T A glucarate
Fig. 2. Structures of some low molecular weight polycarboxylate builders.
Sodium nitrilotriacetate (NTA, Kig. 2) combines excellent Ca(II) complexing properties with a much disputed safety record. NTA was introduced successfully in the late 1960's but its USA use declined in the 70's because of safety testing results claiming carcinogenity, non-biodegradability and mobilization of heavy metals from sewage or river sludge by chelation [34].
Recent studies [35-37], however, contradict the early safety reports and at present NTA is increasingly used as a builder [38] (USA: banned only in New York; Canada: no restriction; Europe: maximum yearly use e.g. the Netherlands: 5500 tons/year, Switzerland: 5% limit).
Sodium carbonate, in combination with sodium silicate as a corrosion inhibitor, has been used at high levels in phosphate-ban areas in the USA. However, serious incrustation on the fabric and the washing machine could not be avoided. To circumvent this problem, AKZO developed a two-component "washing-bag" containing a mixture of carboxylic acids in the first and a carbonate-silicate-surfactant mixture in the second compartment [39]. During the washing cycle the acids are released at low temperature, they remove the calcium carbonate precipitate remaining from a previous wash. At higher temperature the second compartment opens, starting the actual washing process and leaving behind a new calcium carbonate deposit (to be removed in the next wash).
Mixtures of glucarate (Fig. 2) and borate are promising from an environmental point of view but the performance of this system was recently reported [40] not to come up to earlier expectations.
Liquid detergent formulations enjoy an increasing popularity. These systems contain a soap (e.g. sodium oleate) as the major component which acts both as a builder (by precipitation of its Ca(II) salt) and as a surfactant, together with alkylbenzene sulfonates and non-ionic surfactants (alcohol ethoxylates).
High molecular weight systems A. Zeolites
The most important phosphate substitute is zeolite NaA. This water-insoluble inorganic alumino-silicate exchanges Na(I) for Ca(II) (and, to a lesser extent, Mg(II)) during the washing process [41-45]. Zeolite NaA was 3 introduced in the late 1970's, its production capacity in 1985 was 440-10 tons/year, which is expected to be tripled by 1990 [45]. For satisfactory performance, zeolite NaA requires a so-called co-builder, applied in less-than-stoichiometric amounts. Two types of co-builder can be discerned: - carrier: A soluble complexing agent, e.g. NTA or citrate, adsorbs onto
Ca(II) containing precipitates and subsequently desorbs as its Ca(II) complex. Upon dissociation, the latter exchanges the
Chapter 1 8
-Ca(II) with the zeolite. In this way, Ca{II) ions that form bridges between soil and fiber are also removed [44,47-49]. - dispersant: A polymeric carboxylate (e.g. polyacrylic acid, see below) or
a phosphonate exhibits a so-called threshold effect by slowing down crystal-growth, thus preventing the formation of deposits and precipitates (incrustations) on the fabric [25,50-56]. The dispersants are present at only 0.5-3% weight fractions in detergents and are therefore generally referred to as additives.
Depending on the phosphate restrictions detergent formulations may contain 0-40% STP in combination with zeolite NaA and co-builder(s). Some typical European builder formulations are given in Table II [57,58]. Extensive studies demonstrated the environmental safety of zeolite NaA [59]. However, the performance of zeolite containing detergents is considered to be somewhat lower than that of STP-based products [57].
Table II. Typical compositions of builder systems in European detergent J7
formulations"
builder STP zeolite NTA polycarboxylate
% % % % All STP systems Binary systems STP/zeolite STP/NTA STP/polycarboxylate zeolite/NTA zeolite/polycarboxylate Ternary systems STP/zeolite/NTA STP/zeolite/polycarboxylate STP/NTA/polycarboxyl ate zeolite/NTA/polycarboxylate 20-40 15-30 15-30 15-30 -15-25 15-25 15-25 -15-30 -25-40 30-40 15-25 15-25 -20-35 -3-6 -3-6 -3-6 -3-6 3-6 -0.5-3 -0.5-3 -0.5-3 0.5-3 0.5-3
B. Polymeric carboxylates
The effect of anionic polymers as antiredeposition agents is well known. They make surfaces more hydrophylic, thus preventing the redeposition of detached soil. For many years, cellulose ether carboxylates (especially carboxymethyl cellulose) have been formulated at levels of up to 2% for this purpose [50].
The benefits of polyacrylates and copolymers have been recognized as early as 1934 [50] but their incorporation into detergent formulations became important with the development of zeolite-built systems. As mentioned already, the polymeric carboxylates enhance the performance of these detergents by acting as a dispersant. Many polycarboxylates have been studied, both with a carbon backbone and with a polyether or polyacetal structure (Fig. 3 ) . The only polymers that have acquired any significance
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polycarboxylate precursor-E ^"^-^^ 1
I - n COO" polyacrylQte -P CH, —CH ^ - P CH —CH^-COO" ^-COO" ^-COO" polyacrylQte - maleate OH COO" pol y h y d r o x y o c r y late -P O - C H ^ COO" p o l y g l y o x y l a t e acrylic acid
acrylic acid+maleic anhydride CICHj—CHCI —COOH
2,3-dichloropropionic acid CHO—COOR
glyoxylic acid esters
Fig. 3. Structures of some high molecular weight polycarboxylate builders and their precursors.
Chapter 1 10
-[50] are polyhydroxyacrylates, copolymers of methyl vinyl ether and maleic acid and, to a much larger extent, polyacrylates and copolymers of acrylic acid and maleic anhydride.
Crystal growth inhibition by polymers is attributed to adsorptive stabilization of amorphous and colloidal aggregates of inorganic calcium salts e.g. calcium carbonate [61-63]. For effective inhibition the distance between the negatively charged polyelectrolyte groups should correspond to the distance between Ca(II) ions in the crystal lattice. For example, in polyacrylate the distance between COO" groups is 0.5 nm, which is equal to that between Ca(II) ions in CaSO.-2 aq and in CaCO, [64]. The strong adsorption of polyelectrolytes on growth sites inhibits crystal growth. In addition, the polyelectrolyte electric field might affect the ion diffusion to the crystal surface [65].
The precipitation of Ca(II) salts of anionic surfactants (e.g. dodecyl sulfate) was found to be inhibited by polyacrylic acid by complexation of Ca(II) ions and not by adsorption to growth sites of the crystals, which is in contrast with the situation for inorganic salts [66].
Thus, an effective polyelectrolyte co-builder should have both good Ca(II)-sequestering and crystal growth inhibiting properties. The optimum constitution of polyelectrolytes may depend considerably on the detergent formulation [67]. Generally, copolymers of acrylic acid and maleic anhydride (R = 50-70-10 ) show optimal performance for incrustation inhibition [50].
These copolymers of acrylic and maleic acid have been reported to be physiologically harmless [50] but they are only poorly biodegradable [68]. In sewage treatment plants the polyelectrolytes are largely precipitated as insoluble salts or adsorbed onto the sludge [68]. Thus, although surface waters are hardly contaminated, these non-degradable polyelectrolytes pollute sewage sludge. For this reason, the development of (bio-)degradable polyelectrolyte detergent additives is of considerable importance.
Polyhydroxyacrylic [69] and polyglyoxylic acids [70,71] have been developed as biodegradable dispersants in detergents but were not commercialized.
Oxidized polysaccharides
Carbohydrates may serve as an alternative feedstock for the preparation of polycarboxylic acids because (i) carbohydrates are inexpensive renewable
materials and (ii) carbohydrate-derived products are expected to be readily (bio-)degradable via hydrolysis of the acid-labile acetal bonds.
An effective Ca(II) complexing polysaccharide is obtained from the C„,C,-glycol-cleavage oxidation of the glucose units in I,4-D-glucans (e.g. starch) to a Cp,C,-dicarboxy polyglucoside [72-77] (Fig. 4 ) .
_l n O H O ooc\ COO" I O' m
Fig. 4. Glycol-cleavage oxidation of starch to Cp,C.,-dicarboxy starch.
As to the background of the good Ca(II) complexation exhibited by the Cp.Cn-glycol-cleaved 1,4-D-glucans it should be noted that they can be regarded as a polymer containing substituted oxydiacetate units (ODA, "OOC-C-O-C-COO"). At our laboratory, W/ewen/iu/zen et al. [78,79] showed that the ODA moiety is a structural unit which favours Ca(II) complexation. Both in the crystalline state and in solution [80] ODA adopts a planar W-shaped conformation upon (tridentate) Ca(II) complexation involving the ether and carboxylate oxygens. Nieuwenhuizen et al. [81] studied the Ca(II) complexation of glycol-cleaved maltodextrins (partly depolymerized starches) and starch as a function of the degree of polymerization (DP). A tenfold increase of the complexation constant was observed going from DP 5 to DP 15. It was concluded that at a DP > 10 cooperation of non-neighbouring ODA units occurred, creating very effective (hexadentate) complexing sites which are by far superior to monomeric ODA molecules. The formation of helix structures was tentatively proposed.
Because of their good Ca(II) complexing properties the application of C-iCj-dicarboxy maltodextrins and starches as a co-builder in detergents seems very attractive. They are stable at the alkaline pH of the washing process but are degraded under the acidic (pH 4-5) waste water conditions, as is to be expected from their polyacetal structure (Fig. 5 [82]); the resulting mono- and oligomeric fragments will be readily biodegradable.
Chapter 1 12
-i 1 1 1 1 1 1 1 0 4 8 12 16 20 24 28
t(h)
Fig. 5. Hydrolysis of C^jCydicarboxy starch (10 mg/ml) as a function of the pH at 353 K [82] (% polymeric dicarboxy starch is defined as the fraction with DP > 2).
pH 2 (•); pH 3 (o); pH 4 (K); pH 5 (i); pH 7 (w); pH 9 (a).
The required C-.C,-glycol-cleavage oxidation can be effected either in one step by the application of alkaline hypochlorite [83,84] or in two steps by cleaving the Cp,C.,-diol with periodate [85-88] followed by chlorite oxidation of the resulting dialdehyde to a dicarboxylate [89-91] (Fig. 6 ) . Generally, the two step procedure is preferred since it yields dicarboxy polysaccharides with higher selectivity and carboxyl content than the oxidation with hypochlorite.
A major obstacle for the large-scale introduction of dicarboxy starches in detergents is their expensive method of preparation via the two step glycol-cleavage oxidation with periodate and chlorite. However, the periodate oxidation can be performed economically by chemical (hypochlorite [92,93]) or electrochemical [94-96] regeneration of the iodate formed. Indeed, dialdehyde starch has been produced in the 1950's and 70's by Miles (USA) and Carl it (Japan), with applications as wet-strength improver in the paper industry [97,98]. Gradually, the product has been replaced by lower
regeneration lOi.HjO OH O ^ O H c \ CHO I O ' 3 0 c r ^ 3C|-2 H * H j O 6 C I O i OH "OOC COO"
Fig. 6. Glycol-cleavage oxidations of starch to Cp,C^-dicarboxy starch.
cost synthetic resins and the production was abandoned. However, recent publications still consider dialdehyde starch an attractive product [98-101] and increased demand might encourage its production again. Thus, starting from dialdehyde starch the second step, chlorite oxidation, remains to be improved for the efficient preparation of dicarboxy starches. The major drawback of this oxidation is the ineffective use of the oxidant; though one equivalent of chlorite is formally required for the oxidation of an aldehyde group, three equivalents are actually consumed, due to the formation of the toxic chlorine dioxide gas as a side reaction:
R-CHO + ClO^ HOCl + 2 CIO
2
-> R-COO" + HOCl -> 2 C102 + c r + HO"
Another approach would be the development of an alternative, preferably catalytic, one-step procedure for the glycol-cleavage oxidation of starch to dicarboxy starch.
Chapter 1 14
-Catalytic glycol-cleavage oxidation
A survey of the methods available for the catalytic oxidation of glycols to dicarboxylic acids is given in Table III. In order to be potentially attractive for oxidation of polysaccharides the oxidation methods should at least fulfil the following practical requirements:
1. selective glycol-cleavage.
2. aqueous, or mixed aqueous-organic solvent at pH 2-11 (solubility and stability of substrate and product).
3. inexpensive and non-polluting oxidant e.g. oxygen, hydrogen peroxide, tert-butyl hydroperoxide or sodium hypochlorite.
4. easy separation of product and catalyst.
By comparison of the practical conditions of the methods in Table III with the above criteria, the potential applicability of the method for catalytic glycol-cleavage of polysaccharides can be evaluated.
Cerium(IV) seems an attractive oxidant; entries 4 and 5 illustrate its selective action on polysaccharides in spite of the low pH of the reaction medium. Glycol-cleavage oxidation by Ce(IV) involves mono- or bidentate
[125] coordination with the hydroxyl groups, followed by a one-electron oxidation to give an intermediate radical which is oxidized by a second Ce(IV) ion [102,103] (Fig. 7 ) . For an efficient procedure, reoxidation of the Ce(III) formed is essential. This can be performed in situ by electrochemical means (entry 3) or ex situ, for example by hydrogen peroxide [126-128] or hypochlorite [129].
HO OH ^ HO OjTCe'* O
\—OH+Ce'^ ^ \ = 0 + H*+Ce"'
Table III. Survey of methods available for catalytic glycol-cleavage oxidation.
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1,2 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. -diol^ aromatic aliphatic aliphatic cellulose dextran aliphatic aliphatic aliphatic aliphatic aliphatic aliphatic aliphatic aliphatic starch aliphatic aliphatic aliphatic aliphatic aliphatic aromatic aromatic product^ 2 ArCHO 2 RCHO 2 RCHO di-CHO di-COOH RCOOH^ 2 RCOOH 2 RCOOH 2 RCOOH 2 RCOOH 2 RCHO 2 RCOOH 2 RCOOH di-COOH 2 RCOOH 2 RCOOH 2 RCOOH 2 RCHO^ 2 RCOOH 2 ArCHO 2 ArCHO catalyst/oxidant Ce(IV)^ Ce(IV)^ Ce(III), electr. Ce{IV)^ CellV)*^ Co(II), O2 Co(II), AcOOH Co(II), O2 + AcOOH Ru(VIIl), AcOOH Ru(VIII), NaOCl Ru{VlII), H2O2 Pb^RUyO^^ O2 Ag{0)/Ag(I), O2 Ag(0)/Ag(I), 03/02^ (NH4)6MO7024, H2O2 NajWOi/HjPO,, H2O2 PW12OIÓ ^ H2O2 C-anode, electr. Ni-anode, electr. Cr-porphyrin, N-oxide Fe-porphyrin, O2 conditions H2O, pH 1, 323 K H2O, pH 0-1 no solvent H2O, pH 0 H2O, pH 0-1 benzonitrile, 373 K propyl acetate, 323 K butyl acetate, 323 K H2O/HOAC, 333 K H2O, pH 11 HjO/acetone, 320 K H2O, pH > 13 H2O, pH > 13 H2O, pH > 13 H2O/THF, 328 K H2O, pH 2-4 H20/t-BuOH, 354 K methanol H2O, pH 13 CH3CN CH2CI2 ref 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 119 120 121 122 124" Aromatic: Ar(CHOH)(CHOH)Ar, with Ar R(CHOH)(CHOH)R, with R
T
(substituted) phenyl; aliphatic: (substituted) alkyl. Typical reaction conditions, is ambient unless otherwise indicated. Ce(IV) applied stoichiometri-cally. Usually mixtures of the aldehyde and the carboxylic acid are
e f obtained. Typical analysis: x = 2.62, y = 1.38, z = 6.50. Mith
co-catalyst Co(II) or Pd(0) reoxidation with oxygen is claimed. " As tris-(cetylpyridinium) salt. Largely isolated as dimethyl acetal.
Chapter 1 16
-The cobalt(II) catalyzed systems are attractive for the oxidation of aliphatic v;c-diols but are expected to give aspecific oxidation and degradation with the polyfunctional carbohydrates. Moreover, efficient Co(II) catalysis requires anhydrous solvents [107]. The ruthenium(VlII)-based systems will also not give selective glycol-cleavage in the presence of other functional groups (e.g. primary hydroxyls are preferentially oxidized [130]).
The selective glycol-cleavage oxidation of oligo- and polysaccharides to dicarboxy derivatives using the silver/silver(I) oxide reagent (entry 14), optimistically claimed by Lamberti and Kogan [115], was shown at our laboratory [131] to yield only monomeric (hydroxy-)carboxylic acids, probably resulting from alkaline degradation in the strongly basic medium of the oxidation (pH 13).
The peroxotungstate species formed in solutions of tungstates or tungsten heteropolyacids upon addition of H-Op (Fig. 8) seem to be very attractive oxidants because (i) they are active in aqueous medium at pH 2-4 [117,118], (ii) they effect selective oxidation of secondary alcohols in the presence of primary hydroxyl groups [116,119], (Hi) they use H-0- as the primary
Fig. 8. Example of a peroxo tungstophosphate species: tetra(diperoxo-tungsto)phosphate , as crystallized from an aqueous solution of HpOp, HJ/0. and H^PO. by the addition of tetrahexylammonium chloride
oxidant and (iv) they can be easily separated from aqueous solution, e.g. as quaternary ammonium salts.
Although of no practical importance, interesting examples of electrochemical glycol-cleavages and biomimetic systems (using porphyrins as cytochrome P-450 analoga) have been included in Table III [122-124].
Thus, of all methods for catalytic glycol-cleavage known so far, only oxidations using Ce(IV) or peroxotungstate-based systems seem to be of practical importance with respect to polysaccharide oxidations.
Scope of this thesis
Dicarboxy starches, prepared by the glycol-cleavage oxidation of maltodextrins and starch are excellent calcium(II) sequestering agents, with potential application as a phosphate substitute in detergents. However, the production of dicarboxy starch via the conventional two-step procedure, involving periodate and chlorite as the oxidants, is economically unattractive.
This thesis describes the exploration of alternative routes for the preparation of dicarboxy starch. The first part of the thesis deals with the oxidation of cyclohexanol and aliphatic sec-l,2-diols as model compounds for the Cp,C,-diol moiety of a glucose unit (Chapters 2-4). The second part describes the oxidation and Ca(II) complexation of maltodextrins, starch and some other polysaccharides (Chapters 5-8). A survey of the systems studied is given in Fig. 9. Part of the work described has been published [133-139] and patented [140].
Cerium(IV) has been recognized (see Table III) as a potentially attractive catalyst for glycol-cleavage oxidations, provided the Ce(III) formed can be regenerated by a readily available and non-polluting oxidant. For convenient work-up and regeneration, the Ce(IV) should be immobilized. Therefore, the possible use of cerium(III)-exchanged Y-zeolites as catalysts has been investigated for the oxidation of the model compounds cyclohexanol and 2,3-dimethyl-2,3-butanediol (Chapters 2 and 3 ) .
Since peroxotungstate species have also been considered as attractive glycol-cleaving oxidants, the scope and limitations of tungsten
hetero-Chapter 1 18 -OH o z o a. O u Q O 2 OH OH I I H,C—C—C —CH, ' I I ' CH3CH3
O a
H j O j / O j OHC
COOH COON X o (J ^ CE > . < O I - Q I W I complexationFig. 9. Survey of the oxidation reactions described in this thesis. Numbers refer to the Chapters.
polyanions and peroxotungstates using hydrogen peroxide as the oxidant have been evaluated (Chapters 4 and 5 ) .
In addition to a re-examination of the one-step oxidation of maltodextrins and starch by the use of sodium hypochlorite under controlled conditions (Chapter 6 ) , a new and advantageous two-step oxidation procedure has been developed using hydrogen peroxide as an inexpensive co-reactant in the chlorite oxidation of dialdehyde starch (Chapter 7 ) . The dicarboxy starches were obtained in excellent yields and showed superior
Ca(II)-complexing properties.
The conformational effects upon Ca(II)-complexation by dicarboxy polysaccharides are discussed in Chapter 8.
A brief evaluation of the practical implications of the application of dicarboxy polysaccharides as phosphate substitutes and the economic aspects of the various oxidation methods concludes the thesis.
References and notes
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Chapter 1 20
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42. P. Berth, G. Jacobi, E. Schmadel, M.J. Schwuger and C.H. Krauch, Angew. Chem. 87, 115 (1975).
43. M.J. Schwuger, H.G. Smolka and C.P. Kurzendörfer, Tenside Deterg. 13, 305 (1976).
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45. H. Andree, P. Krings, H. Upadek and H. Verbeek, "Proceedings of the Second World Conference on Detergents", Montreux, A.R. Baldwin, ed.. The American Oil Chemists' Society (1987), p. 148.
47. H.G. Smolka and M.J. Schwuger, Tenside Deterg. 14, 222 (1977). 48. P. Berth, J. Am. Oil Chem. Soc. 55, 52 (1978).
49. M.S. Nieuwenhuizen, A.H.E.F. Ebaid, M. van Duin, A.P.G. Kieboom and
H. van Bekkum, Tenside Deterg. 21, 221 (1984).
50. W.J. Mirth, "Proceedings of the Second World Conference on Detergents", Montreux, A.R. Baldwin, ed.. The American Oil Chemists' Society (1987), p. 138.
51. E.A. Matzner, M.M. Crutchfield, R.P. Langguth and R.D. Swish, Tenside Deterg. 10, 239 (1973).
52. J.F. Schaffer and R.T. Uoodhams, Tenside Deterg. 16, 82 (1977). 53. H.D. Nagerl and H. Roesler, Vom Wasser 54, 121 (1980).
54. C.P. Kurzendörfer, M. Liphard, U. von Rybinski and M.J. Schwuger, Stud. Surf. Sci. Catal. 28, 1009 (1986).
55. J. Grosse and H.-D. Nielen, Seife-Oele-Fette-Wachse 112, 39 (1986). 56. J. Perner and H.-U. Neumann, Tenside Deterg. 24, 334 (1987).
57. R. Gresser, "Proceedings of the Second World Conference on Detergents", Montreux, A.R. Baldwin, ed., The American Oil Chemists' Society (1987), p. 153.
58. For a recent report on total detergent composition see:
B.F. Greek and P.L. Layman, Chem. Eng. News Jan. 1989, p. 29.
59. Umweltbundesamt (Berlin, W. Germany), Materialien 4/79, "Die Prüfung des Umweltverhaltens von Natrium-Aluminium-Silikat Zeolith A als
Phosphatersatzstoff Wasch- und Reinigungsmitteln", E. Schmidt, Berlin (1979).
Chapter 1 22
-60. Ger. Pat. 690.951 and 697.945 (1934).
61. E.R. McCartney and A.E. Alexander, J. Colloid Sci. 13, 383 (1958). 62. J.f Crawford and B.R. Smith, J. Colloid Interface Sci. 21, 623 (1966). 63. F.V. yUliams and R.A. Rührwein, J. Am. Chem. Soc. 79, 4898 (1957). 54. S. Sarig and F. Shifrin, Seawater Desalination, Natl Counc. Res. Dev.,
150 (1975).
65. B.R. Smith and A.E. Alexander, J. Colloid Interface Sci. 34, 81 (1970). 66. R.S. Lee and I.D. Robb, J. Chem. S o c , Faraday Trans. I 75, 2126 (1979). 67. J. Perner and W. Trieselt, Tenside Deterg. 18, 239 (1981).
58. For a review on toxicology and biodegradability of polycarboxylic acids see: M. Hunter, D.M.A. da Motta Marques, J.N. Lester and R. Perry, Environ. Techn. Lett. 9, 3 (1988).
69. Y. Abe, S. Matsumura, Y. Masago, M. Hashimoto, T. Miura and K. Sakai, Yukagaku 34, 202 (1985).
70. W.f. Gledhill and V.U. Saeger, J. Ind. Microbiol. 2, 97 (1987). 71. U.S. Pat. US 4.600.750 (1986) and Eur. Pat. Appl. EP 169.826 (1986);
CA 105, 192210 and 135984 (1986), respectively. 72. U.S. Pat. 3.629.121 (1971).
73. Ger. Often. 2.053.273 (1971).
74. CA. Uilham, T.A. McGuire, A.M. Mark and C.L. Mehltretter, J. Am. Oil Chem. Soc. 47, 522 (1970).
75. Brit. Pat. 1.330.122 and 1.330.123 (1973). 76. Ger. Often. 2.436.843 (1976).
77. M. Diamantoglou, H. Magerlein and R. Zielke, Tenside Deterg. 14, 250 (1977).
78. M.S. Nieuwenhuizen, A.P.G. Kieboom and H. van Bekkum, J. Am. Oil Chem. Soc. 60, 120 (1983).
79. M.S. Nieuwenhuizen, A.P.G. Kieboom and H. van Bekkum, Tenside Deterg. 22, 247 (1985).
80. V.A. Uchtman and R.P. Oertel, J. Am. Chem. Soc. 95, 1802 (1973). 81. M.S. Nieuwenhuizen, A.P.G. Kieboom and H. van Bekkum, Starch 37, 192
(1985).
82. M. Bongard and M. Floor, this thesis, Chapter 7. Interestingly, the acid-catalyzed hydrolysis is faster at pH 3-5 than at pH 2. A similar dependence of the rate of hydrolysis on the pH has been found for acidic polysaccharides like pectic and alginic acid, and is ascribed to
or intramolecular nucleophilic attack of carboxylate groups:
0. Smidsr0d, A. Haug and B. Larsen, Acta Chim. Scand. 20, 1026 (1955). 83. R.L. Uhistler, R. Schweiger and S. Kazeniac, J. Am. Chem. Soc. 78, 4704
(1956).
84. R.L. Uhistler and R. Schweiger, J. Am. Chem. Soc. 79, 5450 (1957). 85. E.L. Jackson and C.S. Hudson, J. Am. Chem. Soc. 59, 2049 (1937). 86. J.U. Sloan, B.J. Hofreiter, R.L. Mellies and I.A. Uolff, Ind. Eng.
Chem. 49, 350 (1957).
87. G. Tegge, Starch 12, 321 (1960).
88. C.L. Mehltretter, Starch 15, 313 (1963).
89. B.T. Hofreiter, I.A. Uolff and C.L. Mehltretter, J. Am. Chem. Soc. 79,6467 (1957).
90. U.S. Pat. 2.894.945 (1959). 91. Dutch Pat. 70.12380 (1970).
92. T.A. McGuire and C.L. Mehltretter, Starch 23, 42 (1971).
93. W.M. Hearon, F.L. Cheng and J.F. Uitte, Appl. Polym. Symp. 28, 77 (1975).
94. U.S. Pat. 2.830.941 (1958).
95. V.F. Pfeifer, V.E. Sohns, H.F. Conway, E.B. Lancaster, S. Dabic and E.L. Griffin Jr, Ind. Eng. Chem. 52, 201 (1950).
95. J.A. Radley ed., "Starch Production Technology", Appl. Sci., Barking, (1975), p. 423.
97. U.S. Pat. 3.052.703 and 3.057.088 (1952). 98. C.L. Mehltretter, Starch 37, 294 (1985).
99. J.P. Varma and R.S. Khisti, Chem. Eng. World 10, Sect. 1, 117 (1975). 100. G. Tegge and H. Mayer, Getreide, Mehl Brot 38, 85 (1984).
101. M.M. Baizer, "Proc. Bio-Expo 1985", Butterworth, Stoneham, Mass., 1986, p. 341.
102. U.S. Trahanovski, J.R. Gilmore and P.C. Heaton, J. Org. Chem. 38, 750 (1973).
103. H.L. Hintz and D.C. Johnson, J. Org. Chem. 32, 555 (1957). 104. East Ger. Pat. DD 248.815 (1987); CA 109, 148884 (1988).
105. C.R. Pottenger and D.C. Johnson, J. Polym. Sci A-1 8, 301 (1970). 106. R.K. Samal, S.C. Satrusallya, P.K. Sahoo, S.S. Ray and S.N. Nayak,
Colloid Polym. Sci. 262, 939 (1984).
107. G. de Vries and A. Schors, Tetrahedron Lett. 54, 5689 (1968). 108. Ger. Offen. DE 2.035.558 (1972); CA 76, 72034 (1972).
Chapter 1 24
-109. Ger. Offen. DE 2.144.015, 2.052.815 and 2.106.913 (1972); CA 77, 4929, 33963 and 151493 (1972), respectively.
110. Ger. Offen. ÜE 2.106.307 (1972); CA 77, 151485 (1972).
111. S. Uolfe, S.K. Hasan and J.R. Campbell, J. Chem. S o c , Chem. Commun., 1420 (1970).
112. Jpn. Pat. 80.102.528 (1980); CA 94, 46774 (1981). 113. T.R. Felthouse, J. Am. Chem. Soc. 109, 7566 (1987). 114. J. Kubias, Collect. Czech. Chem. Commun. 31, 1665 (1966). 115. v. Lambert! and 5.L. Kogan, U.S. Pat. 3.873.614 (1975). 116. B.M. Trost and Y. Masuyama, Isr. J. Chem. 24, 134 (1984). 117. C. Venturello and M. Ricci, J. Org. Chem. 51, 1599 (1986).
118. Eur. Pat. Appl. 123.495 and 122.804 (1984); CA 102, 78375 and 95256 (1985), respectively.
119. Y. Ishii, K. Yamawaki, T. Ura, H. Yamada, T. Yoshida and M. Ogawa, J. Org. Chem. 53, 3587 (1988).
120. T. Shono, Y. Matsumura, T. Hashimoto, K. Hibino, H. Hamaguchi and
T. Aoki, J. Am. Chem. Soc. 97, 2546 (1975). 121. H. Ruholl and H.J. Schafer, Synthesis, 55 (1988).
122. R.I. Murray and S.G. Sligar, J. Am. Chem. Soc. 107, 2186 (1985). 123. T. Okamoto, K. Sasaki, M. Shimada and S. Oka, J. Chem. S o c , Chem.
Commun., 381 (1985).
124. T. Okamoto, K. Sasaki and S. Oka, J. Am. Chem. Soc. 110, 1187 (1988). 125. Note: With 1,2-diols bidentate complexation is preferred, but no
prerequisite for oxidation as is evidenced by the similar rates of cleavage for glycols and their monomethyl ethers: J.S. Littler and W.A
yaters, J. Chem. Soc. 2767 (1960).
126. Pol. Pat. 62463 (1971); CA 75, 142386 (1971). 127. Eur. Pat. 93.627 (1983); CA 100, 50664 (1984).
128. H. Firouzabadi and N. Iranpoor, Synth. Commun. 14, 875 (1984). 129. A.A. Ivakin, Zh. Prikl. Khim. 35, 245 (1967); CA 56, 15119 (1962). 130. E.S. Gore, Plat. Met. Rev. 27, 111 (1983).
131. M.S. Nieuwenhuizen, unpublished results from this laboratory.
132. C. Venturello, R. d'Aloisio, J.C.J. Bart and M. Ricci, J. Mol. Catal. 32, 107 (1985).
133. H. Floor, A.P.G. Kieboom and H. van Bekkum, Reel. Trav. Chim. Pays-Bas 107, 362 (1988).
134. M. Floor, A.P.G. Kieboom and H. van Bekkum, Reel. Trav. Chim. Pays-Bas, 108, 128 (1989).
135. M. Schwegler, M. Floor and H. van Bekkum, Tetrahedron Lett. 29, 823 (1988).
136. M. Floor, K.M. Schenk, A.P.G. Kieboom and H. van Bekkum, Starch, in press.
137. M. Floor, A.P.G. Kieboom and H. van Bekkum, Starch, submitted for publication.
138. M. Floor, L.P.M. Hofsteede, ».P.J. Groenland, L.A.Th. Verhaar,
A.P.G. Kieboom and H. van Bekkum, Reel. Trav. Chim. Pays-Bas, in press. 139. M. Floor, J.H. Koek, F.L.M. Smeets, R.E. Niemantsverdriet, J.A. Peters,
H. van Bekkum and A.P.G. Kieboom, Carbohydr. Res., submitted for publication.
140. M. Floor, A.P.G. Kieboom and H. van Bekkum, Dutch Pat. Appl. NL 88.02907 (1988).
CHAPTER 2
ALUMINA- AND Y-ZEOLITE CATALYZED REACTION OF CYCLOHEXANOL WITH tert-BUTYL HYDROPEROXIDE *
Abstract
The use of 7-alumina and exchanged Y-zeolites as catalysts in the liquid-phase oxidation of cyclohexanol by tert-butyl hydroperoxide (tBHP) has been studied. With 7-alumina cyclohexanone is formed, whereas the zeolites NaCeY and NaLaY give cyclohexyl formate as the main product. This compound is thought to originate from a zeolite-mediated rearrangement of tBHP to acetone and methanol, oxidation of methanol to formic acid and electrophilic addition of formic acid to cyclohexene (formed in situ from cyclohexanol).
Introduction
For the transformation of a secondary alcohol into the corresponding carbonyl compound a large number of stoichiometric transition metal oxidants is available. However, from an economical and environmental point of view, there is a need for alternative catalytic oxidation processes. These should make use of readily available and non-polluting oxygen donors, such as tert-butyl hydroperoxide (tBHP) and hydrogen peroxide, in combination with a catalyst. In the past decade, several examples of such
*
M. Floor, A.P.G. Kieboom and H. van Bekkum, Reel. Trav. Chim. Pays-Bas 107, 362 (1988).
Chapter 2 28
-transition-metal-catalyzed alcohol oxidations have been reported [1-5]. Application of a heterogeneous catalyst is attractive with respect to the work-up procedure and recovery of the catalyst. Kanemoto et al. [6] reported a heterogeneous catalytic analogue of Ce(IV) and Cr(VI) reagents using Ce(IV)- or Cr{VI)-impregnated Nafion-K ion-exchange resins and tBHP to oxidize secondary alcohols.
This chapter describes the potential of heterogeneous inorganic catalysts in the oxidation of a secondary alcohol by tBHP. The catalytic activities of a Ce-exchanged Y-zeolite (as an inorganic analogue of the Ce-Nafion resin) and 7-alumina (known to be active in alcohol oxidation under Oppenauer conditions [7]) have been compared using cyclohexanol as the model secondary alcohol.
Experimental
Materials
Zeolite NaY was obtained from Union Carbide (type SK 40). NaY was exchanged at 293 K (24 h) with 0.033 M aqueous metal chloride solution to yield zeolites denoted as NaMY-70. The percentage of Na ions exchanged for metal ion M as determined by X-ray fluorescence spectroscopy of the
2
exchanged zeolite was 70%. Y-Alumina (Sprj = 200 m /g) was obtained from Akzo Chemie (Amsterdam, The Netherlands). The catalysts were activated
(16 h) in air (zeolites, 673 K) or N2 (7-alumina, 473-1073 K ) .
tBHP was obtained as a 70% aqueous solution from Janssen Chimica (Beerse, Belgium). Benzene was chosen as solvent since it is not susceptible to oxidation by tBHP [8]. A 4.0 M anhydrous solution of tBHP in benzene was obtained by azeotropic distillation and was stored over zeolite KA [9]. Cyclohexyl formate was prepared according to the literature [10]. Other reagents and solvents were analytical-grade commercial products and were used without prior purification.
Adsorption experiments
The competitive adsorption of reactants and products onto zeolite NaCeY-70 was performed by adding a solution of the substrates to the calcined zeolite at 277 K. Adsorption was monitored by GC analysis (vide infra).
Reaction conditions and analysis
tBHP (10-40 mmole) and cyclohexanol (3.5 mmole) dissolved in benzene (25 ml) were added to the calcined catalyst (1.0-2.5 g) at 353 K with stirring under reflux. Samples were withdrawn at appropriate intervals and immediately analyzed by GC (50 m capillary CP Sil5; internal standard ethylbenzene). Qualitative analysis of formic acid was performed by HPLC
(Biorad HPX-87H, 0.01 M trifluoroacetic acid, 333 K) of an aqueous extract of the reaction mixture. At the end of the reaction, any product remaining on the catalyst was desorbed by addition of methanol/water (80:20 v/v, 4 m l ) .
Results and discussion
The oxidation of cyclohexanol in the presence of 7-alumina was performed using a tBHP/cyclohexanol ratio of 3:1. The zeolite catalyzed reaction consumed more tBHP and was performed at an 11:1 ratio. Two types of catalytic activity can be observed and the results are summarized in Tables I and II. A general picture of the reactions observed is shown in Fig. I.
CHO I
o 0 0
Ó
Ó-Ó
NaCeY. NaLaY, NaHY N B u O O H
NaCeY, NaLoY
O
Fig. 1. Reactions of cyclohexanol (with tBHP) on y-alumina, NaCeY, NaLaY and NaHY.
Chapter 2 30
-Type I catalysts: rearrangement of tBHP
With NaCeY-70 as the catalyst, cyclohexanol was transformed into cyclohexanone and cyclohexyl formate as the major products (Table I). tBHP was not only reduced to tert-butanol, but also rearranged to acetone and methanol. Di-tert-butyl peroxide and formic acid (HPLC) were also formed. Evolution of oxygen was not observed.
There was no involvement of the Ce(III)/Ce(IV) redox couple in the rearrangement of tBHP on NaCeY-70, since (i) the NaLaY-70-catalyzed oxidation resembles that of NaCeY while La(III) has no higher oxidation state and (ii) no Ce(IV) was detected in a tBHP-treated NaCe(III)Y-70 zeolite (Fe(II) titration of hydrolyzed zeolite). With NaHY, formation of cyclohexyl formate was also observed. In contrast, non-exchanged NaY yielded cyclohexanone with moderate selectivity and no cyclohexyl formate was observed.
The adsorption strength of reactants and products was found to follow the
Table I. Reaction of tBHP with cyclohexanol using zeolite catalysts (Type I)\
catalyst cyclohexanol tBHP selectivity to selectivity to other conv. cyclohexanone cyclohexyl formate products'"
% % NaCeY-70 NaLaY-70 NaHY-70 NaY NaCoY-70 conv. % 44 47 20 32 39 conv. % 87 100 49 17 100 cyclohex % 30 19 35 67 28 51 70 10 0 0 19 11 55 33 72
tBHP (40 mmole) and cyclohexanol (3.5 mmole) in benzene (25 ml) were added to the catalyst (2.5 g, activated at 673 K, 16 h, air) at 353 K; reaction time 8 h. Selectivity based on cyclohexanol converted. Cyclohexanol-derived products, characterized as tert-butyl- and tert-butoxy-substituted cyclohexanols and cyclohexanones and tert-butyl cyclohexyl ether.
Rl
II
I ]
I
II
II
I
I
sequence tBHP > cyclohexanol > cyclohexanone > cyclohexyl formate. This indicates that the reactants will continuously replace the products formed during the reaction.
The rearrangement of tBHP and the formation of cyclohexyl formate with NaCeY, NaLaY or NaHY is ascribed to strong Bronsted acid sites formed in these zeolites during calcination [11]. The following sequence of steps leading to the formation of cyclohexyl formate is proposed:
- tBHP undergoes a zeolite-acid-catalyzed rearrangement to acetone and methanol (Fig. 2 ) ;
- methanol is oxidized (by the excess tBHP) to formic acid; - cyclohexanol is dehydrated to cyclohexene;
- electrophilic addition of formic acid to cyclohexene gives cyclohexyl formate.
The overall reaction is shown in Fig. 3.
H 1 ^ ^ A l - " ^ O ^ ^ 0 1 1 CH3 1 H H C 3 — C - O C H 3 1 ® OH ° A V ° -0 ^ ^ -0 1 1 CH3 CH3 C — 0 -1 CH3 OH H C 3 -0 ' 1 CH3 1 © - C - O - p O H j \^ ^ CH3 A V ° -" ^ 0 1 H 0 ^ ^ 0 C H , H-p 0 II — C -- C H CH3 HCo — C — O C H , ° A V ° -0 - ^ -0 1 1 3 . CH3OH H j O , - H *
Fig. 2. Zeolite-acid-catalyzed rearrangement of tBHP.
CHO
OH o
3 / - B u O O H ^ • C H , C O C H , • 2 f - B u O H • 2 H , 0
Fig. 3. Overall equation for the reaction of cyclohexanol with tBHP to give cyclohexyl formate.
Chapter 2 32
-Acid-catalyzed rearrangement of tBHP has been reported previously. In 96% H^SO., acetone and methyl hydrogensulfate are the only reaction products [12]. In acetonitrile with HCIO., acetone, methanol and di-tert-butyl peroxide are formed [13]. tBHP reacts with 58% H^SO. to give 70% di-tert-butyl peroxide together with bis(tert-di-tert-butylperoxy)methane (formaldehyde bis(tert-butylperoxyacetal) [14]). A comparable, zeolite induced, rearrange-ment of cumene hydroperoxide has also been reported; phenol and acetone are formed on zeolite beta (Si/Al = 30) at 450 K [15], or on NaCaY at 393 K [16].
Since formaldehyde can be formed by oxidation of the methanol arising in the tBHP rearrangement [14], further oxidation to formic acid should be possible. Indeed, we have found formic acid, methanol, acetone, tert-butanol and di-tert-butyl peroxide as decomposition products of tBHP on NaCeY.
Bronsted-acid-catalyzed [17] dehydration of cyclohexanol to cyclohexene (in the absence of tBHP) was found to occur readily on NaCeY and NaLaY (80 and 100% conversion after 24 h, 100% selectivity to cyclohexene). In a separate experiment, the reaction of cyclohexanol or cyclohexene with formic acid with NaCeY as catalyst to yield cyclohexyl formate was shown to be quantitative and fast.
Comparison of NaCeY, NaLaY and NaHY with NaCoY provides further evidence for the heterolytic mechanism of formation of cyclohexyl formate on the Brönsted acid zeolites. With NaCoY, no cyclohexyl formate is formed. On this zeolite, tBHP is catalytically decomposed via a homolytic pathway involving Co(II)/Co(III) redox cycles (with formation of tert-butanol, water and oxygen [18]).
Thus, in contrast with the Ce-Nafion resin based system [6], catalytic activity of NaCeY is dominated by its acidic character.
Type II catalysts: oxidation of cyclohexanol
With 7-alumina as the catalyst, selective oxidation of cyclohexanol to cyclohexanone occurred and tBHP was reduced to tert-butanol (Table II). Dehydrated zeolite KA was added in order to adsorb the water formed during the reaction and thus to prevent deactivation of the catalyst [7]. The deactivating effect of water is shown by the increased cyclohexanol conversion on alumina upon KA addition and by the lower activity of 7-alumina in the presence of water (Table II, entries 3,4 and 5 ) . Zeolite KA
Table II. Reaction of tBHP with cyclohexanol using -^-alumina as the catalyst (Type II)\
entry catalyst activation cyclohexanol tBHP selectivity to temperature conversion conversion cyclohexanone
K % % % 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. _ zeolite T-AI2O3 7-AI2O3 7-AI2O3 7-AI2O3 7-AI2O3 7-AI2O3 7-AI2O3 7-AI2O3 KA + + + + + + + H20'^ KA KA^ KA KA KA KA _ 673 673 673 673 673 473 673 873 1073 3 4 29 37 69 58 62 69 68 79 3 7 20 34 42 38 40 42 50 65 >95 >95 96 96 94 94 96 94 95 92
^ tBHP (10.5 mmole) and cyclohexanol (3.5 mmole) in benzene (25 ml) were added to the catalyst (1.0 g y-alumina activated at 473-1073 K, 16 h, W J and/or zeolite KA powder (1.0 g, activated at 673 K, 16 h, air) at 353 K;
b c reaction time 8 h. Selectivity based on cyclohexanol converted. 50 ill
water/g -y-alumina. Reused catalyst (after activation at 673 K, 16 h, air).
itself was hardly active as a catalyst (entry 2 ) . A reaction time exceeding 8 h gave additional formation of tert-butyl- and tert-butoxy-substituted cyclohexanols and cyclohexanones. An increased cyclohexanol conversion was obtained when the 7-alumina activation temperature increased from 473 to 1073 K (entries 7-10).
Oxidation of secondary alcohols catalyzed by 7-alumina (with trichloro-acetaldehyde or benzaldehyde as the hydrogen acceptor) has been described by
Posner et al. [7]. The reaction presumably proceeds according to a mechanism related to the Oppenauer oxidation. The oxidation of cyclohexanol by tBHP on 7-alumina may also involve an alkoxyaluminum intermediate with tBHP acting
Chapter 2 - 34
as the hydrogen acceptor. We have found that aluminum isopropylate is also catalyticaHy active in the reaction of cyclohexanol with tBHP [19]. A tentative mechanism, involving dehydroxylated alumina as the catalyticaHy active site, is shown in Fig. 4. A similar mechanism has been proposed for the transfer hydrogenation of ketones on 7-alumina [20,21].
The deactivation of the catalyst by water can be explained as adsorption of water on a dehydroxylated alumina surface site. This process is clearly reversible since regeneration of 7-alumina at 673 K restored its original activity (entry 6 ) . Reuse of the catalyst is therefore possible.
{.
0 -1 1 1 1 A l ' H \ -H 0. \ \ . 0 . 1 1 1 1 • " A l CH, C CH, CH, •H,0 =^ • H,0Fig. 4. Formal representation of the y-alumina catalyzed oxidation of cyclohexanol by tBHP. (Bonds linking aluminum and oxygen are represented only for the sake of convenience.)
Conclusions
- zeolites NaCeY and NaLaY transform cyclohexanol into cyclohexyl formate via acid-catalyzed rearrangement of tBHP;
- 7-alumina catalyzes the oxidation of cyclohexanol to cyclohexanone by tBHP, via a surface Oppenauer-type reaction.
R
. 1
I
1
Acknowledgement
We thank Mr Th. U. Verkroost of the Department of Mining Engineering for analyses of the zeolites.
References
1. R.A. Sheldon, J. Mol. Catal. 20, 1 (1983).
2. R.A. Sheldon, Bull. Soc. Chim. Belg. 94, 651 (1985).
3. K.B. Sharpless and T.R. Verhoeven, Aldrichimica Acta 12, 63 (1979). 4. /. Kurusu and /. Masuyama, Polyhedron 5, 289 (1985).
5. K. Kaneda, Y. Kawanishi, K. Jitsukawa and S. Teranishi, Tetrahedron Lett. 24, 5009 (1983).
6. S. Kanemoto, H. Saimoto, K. Oshima and H. Nozaki, Tetrahedron Lett. 25, 3317 (1984); Jap. Patent 60.179.148 (1985) to Mitsui Fl uorochemicals Co.; CA 104, 90958.
7. G.H. Posner, R.B. Perfetti and A.U. Runquist, Tetrahedron Lett. 39, 3499 (1976).
8. J.C. Oudejans and H. van Bekkum, J. Mol. Catal. 12, 149 (1981). 9. J.G. Hill, B.E. Rossiter and K.B. Sharpless, J. Org. Chem. 48, 3607
(1983).
10. A.I. Vogel, J. Chem. Soc. 1809 (1948).
11. D.U. Breck, "Zeolite Molecular Sieves", John Wiley and Sons, New York, 1974.
12. N.C. Deno, U.E. Billups, K.E. Kramer and R.R. Lastomirsky, J. Org. Chem. 35, 3080 (1970).
13. L.V. Petrov, V.M. Solyanikov and E.T. Denisov, Izv. Akad. Nauk Kaz. SSR, Ser. Khim. (Eng. transl.) 4, 739 (1977).
14. 7.7. Kozhukhar, V.A. Osetskaya and V.L. Mizyuk, Visn. L'viv. Politekh. Inst. 112, 16 (1977); CA 87, 183916.
15. CD. Chang and B.P. Pelrine, Eur. Pat. Appl. EP 125.066 (1984) to Mobil Oil Corporation; CA 102, 80750.
16. K-H. Bergk and F. Molf, 1. Chem. 15, 152 (1975).
17. H.G. Karge, H. Kosters and Y. Uada, "Proc. Sixth Int. Zeolite Conf.",
Chapter 2 35
-18. K-H. Bergk, F. Molf and B. Salter, J. Prakt. Chem. 321, 529 (1979). 19. M. Floor, unpublished results.
20. M.P.K. Unni, C. Sreekumar, V.S. Hariharakrishnan and C.N. Pillai, J. Catal. 53, 158 (1978).
21. A.A. Uismeyer, A.P.G. Kieboom and H. van Bekkum, Appl. Catal. 34, 189 (1987).
CHAPTER 3
REDOX PROPERTIES OF CERIUM-EXCHANGED Y-ZEOLITES *
Abstract
The oxidation of cerium{III)-exchanged zeolite NaY (exchange level 24-91%) with aqueous hydrogen peroxide and oxygen has been studied. The fraction of Ce(IV) produced decreases with increasing Ce content of the zeolites. Hydrogen peroxide is catalytically decomposed by the Ce(III)/Ce(IV) redox couple with formation of an equilibrium level of a Ce{IV)-hydroxide species. Oxidation with oxygen at temperatures higher than 400 K yields an oxycerium(IV) complex. The latter NaCe(IV)Y zeolite effects oxidative glycol-cleavage of 2,3-dimethyl-2,3-butanediol to acetone. Activation in oxygen restored its oxidizing capacity. Thus, the oxygen-activated NaCe(IV)Y zeolite is a regenerable glycol cleaving oxidant. The HpO„-oxidized NaCe(IV)Y is not active in glycol-cleavage oxidation.
Introduction
The cerium(IV) ion is a powerful oxidant [1] for the glycol-cleavage oxidation of i^/c-diols including 1,2-cyclohexanediol [2] and, of the carbohydrates, ^-cyclodextrin and cellulose [3]. The application of Ce{IV)
*
W. Floor, A.P.G. Kieboom and H. van Bekkum, Reel. Trav. Chim. Pays-Bas 108, 128 (1989).
Chapter 3 38
-reagents is however limited because of the large quantities of oxidant required. Therefore, it appeared attractive to develop an oxidation method which includes regeneration of the Ce(III) produced.
A catalytic Ce(IV)-mediated glycol-cleavage is complicated, since the pH ranges of the glycol-cleavage reaction and of the oxidation of Ce(III) in aqueous medium do not overlap (Scheme 1). As a consequence, glycol-cleavage and regeneration of Ce(IV) have to be carried out in two separate stages.
0 1 2 3 4 5 6 7 8 9 10 pH I I I \ I I I \ I \ I
glycol-cleavage by Ce(IV)
oxidation of Ce(III) by: O3 [4], S20g^7Ag^ [5], BrO,' [6], electrochem. [7] H2O2 [8,9]
MnO^" [6], O C r [10]
Scheme 1. pH range of Ce(IV) glycol-cleavage and of oxidation of Ce(III) to Ce(IV) by various oxidants.
In order to circumvent this problem we have explored an alternative route using a Ce-exchanged Y-zeolite as a regenerable oxidant. The oxidizing properties of NaCe(IV)Y, obtained after high-temperature activation of zeolite NaCe(III)Y in oxygen, are known from conversion of CO to COp [11] and of pyridine to 2,2'-bipyridine [12].
This chapter desribes the oxidation of NaCeY by 0- and H^Op, respec-tively, the latter reaction being by analogy to the homogeneous oxidation of Ce(III) by HpOp to Ce(I\/) hydroxide [8,9]. The application of the oxidized Ce(IV)-containing zeolites as oxidant for the oxidation of v;c-diols was evaluated, using the glycol-cleavage of pinacol (2,3-dimethyl-2,3-butanediol) to acetone as the model reaction. An overall view of the reactions studied is shown in Scheme 2.
H2O2 NaCe(IV)Y vacuum (773 K) NaCe(III)Y pinacol 2 acetone NaCe(III)Y O2 (473-873 K) NaCe(IV)Y vacuum (773 K) I (473-873 K) pinacol 2 acetone NaCe(III/IV)Y
Scheme 2. Summary of oxidation routes followed in this study.
Experimental
Materials
Union Carbide type SK 40 NaY (10 g) was exchanged at 293 K (24 h) with cerium(III) chloride solution (1 1; 1.7-33.0 mM) and dried (air, 373 K, 14 h) [13] to obtain zeolites NaCeY-x, where x designates the percentage of Na ions exchanged for Ce as determined by X-ray fluorescence spectroscopy of the exchanged zeolite (Table I ) . All reagents were analytical-grade commercial products and were used without prior purification.
Oxidation of NaCeY
Oxidation with H~0„: 0.50 g NaCeY (containing 24% water) was stirred with 5.0 ml 10 M H„Op (or the equivalent amount at different concentration) at 293 K, pH 5 (molar ratio H202/Ce > 50, depending on the degree of exchange). Evolution of oxygen was measured using the apparatus described in ref. 14. The oxidized zeolite was calcined (N^, 673 K, 16 h) to remove adsorbed H-O^ and H2O.
Oxidation with O^: NaCeY was oxidized in a stream of oxygen (2.5 1/h, 373-873 K, 16 h) in a tube oven.
Determination of Ce(IV): Oxidized NaCeY zeolites were hydrolyzed in teflon-lined autoclaves with 50% H^SO. (20 ml/g zeolite) at 343 K for 1 h and the resulting solutions were titrated with 0.010 M Fe(II).
