Study of selectivity of metal phosphates and phosphonates in Baeyer-Villiger oxidations

Article abstract of DOI:10.1007/s10562-010-0481-2

Layered materials including metal phosphates and phosphonates have been widely investigated in several fields acting as good selective catalysts in a great number of oxidative reactions. Zirconium phosphate amorphous [Zr(HPO ₄)₂?H₂O; ZrPA], sodium exchanged zirconium phosphate amorphous [Zr(NaPO₄)₂; NaZrPA], potassium exchanged zirconium phosphate amorphous [Zr(KPO₄)₂; KZrPA], zirconium phenylphosphonate amorphous [Zr(O₃PC ₆H₅)₂; ZrPPA], zirconium carboxyethylphosphonate [Zr(O₃PCH₂CH₂COOH) ₂; ZrCEP] and aluminium carboxyethylphosphonate [Al ₃(OH)₃(O₃PCH₂CH₂CO ₂)₂?3H₂O; AlCEP] were prepared, characterized and evaluated as selective catalysts in the Baeyer-Villiger oxidation of cyclopentanone, p-methoxybenzaldehyde and 2,4,6- trimethylbenzaldehyde by hydrogen peroxide, in acetic acid. The selectivity of δ-valerolactone, p-methoxyphenol and 2,4,6-trimethylphenol have been found to be strongly related with the properties and structure of each catalyst. Graphical Abstract: The selectivity of zirconium phosphate amorphous [Zr(HPO₄)₂?H₂O; ZrPA], sodium exchanged zirconium phosphate amorphous [Zr(NaPO₄)₂; NaZrPA], potassium exchanged zirconium phosphate amorphous [Zr(KPO₄) ₂; KZrPA], zirconium phenylphosphonate amorphous [Zr(O ₃PC₆H₅)₂; ZrPPA], zirconium carboxyethylphosphonate [Zr(O₃PCH₂CH₂COOH) ₂; ZrCEP] and aluminium carboxyethylphosphonate [Al ₃(OH)₃(O₃PCH₂CH₂CO ₂)₂?3H₂O; AlCEP] was evaluated in the Baeyer-Villiger oxidation of cyclopentanone, p-methoxybenzaldehyde and 2,4,6-trimethylbenzaldehyde by hydrogen peroxide, in acetic acid. Different selectivities have been found which were correlated with the properties and structure of each compound.

Full text of DOI:10.1007/s10562-010-0481-2

Catal Lett (2011) 141:100–110
DOI 10.1007/s10562-010-0481-2
Study of Selectivity of Metal Phosphates and Phosphonates
in Baeyer–Villiger Oxidations
•
Grac¸a M. S. R. O. Rocha Teresa M. Santos
•
´
Claudia S. S. Bispo
Received: 16 August 2010 / Accepted: 22 October 2010 / Published online: 10 November 2010
Ó Springer Science+Business Media, LLC 2010
Abstract Layered materials including metal phosphates
and phosphonates have been widely investigated in several
fields acting as good selective catalysts in a great number
of oxidative reactions. Zirconium phosphate amorphous
[Zr(HPO4)2ꢀH2O; ZrPA], sodium exchanged zirconium
phosphate amorphous [Zr(NaPO4)2; NaZrPA], potassium
exchanged zirconium phosphate amorphous [Zr(KPO4)2;
KZrPA], zirconium phenylphosphonate amorphous
[Zr(O3PC6H5)2; ZrPPA], zirconium carboxyethylphospho-
nate [Zr(O3PCH2CH2COOH)2; ZrCEP] and aluminium
carboxyethylphosphonate [Al3(OH)3(O3PCH2CH2CO2)2ꢀ
3H2O; AlCEP] were prepared, characterized and evaluated
as selective catalysts in the Baeyer–Villiger oxidation of
cyclopentanone, p-methoxybenzaldehyde and 2,4,6-trim-
ethylbenzaldehyde by hydrogen peroxide, in acetic acid.
The selectivity of d-valerolactone, p-methoxyphenol and
2,4,6-trimethylphenol have been found to be strongly
related with the properties and structure of each catalyst.
1 Introduction
The Baeyer–Villiger (BV) oxidation of aromatic aldehydes
yields formate esters which often hydrolyse to the corre-
sponding phenols. Substituted phenols, and in particular
p-alkoxy derivatives, are substances of a wide range of
application in organic chemistry since they act as inter-
mediates for drugs, agrochemicals, and dyes. These
derivatives can also deactivate the ribonucleotide reductase
in tumor cells inhibiting their growth and have been
employed for melanoma treatment and applied in AIDS
therapy [1–7]. The oxidation of cyclic and linear ketones to
their respective lactones and esters, using oxidants such as
organic peroxides or peroxyoxides, alkyl hydroperoxides
or hydrogen peroxide, are very important industrial inter-
mediates finding application in polymers, pharmaceuticals
and herbicides production and as solvents [8–12].
The Baeyer–Villiger oxidation of ketones, for example,
has been performed with 30% aqueous hydrogen peroxide/
benzonitrile, using Mg/Al hydrotalcite, a well known lay-
ered material [13] and cellulose-supported dendritic Sn
complexes [14]. However, only a few reports on the oxi-
dation of aromatic aldehydes have been published, mainly
because of their poor reactivity. Nevertheless, homogenous
catalysts such as SeO2 and aryl seleninic acids have been
found to be efficient in the oxidation of aromatic aldehydes
using aqueous hydrogen peroxide [15]. Corma and his
group have been designing Sn-b zeolite and Sn-MCM-41
heterogeneous catalysts for the reaction of aromatic alde-
hydes with hydrogen peroxide, in non-halogenated solvents
such as dimethylformamide and dioxane [16–19], and they
have suggested that these catalysts activates the carbonyl
compounds instead of the hydrogen peroxide, making them
more selective. A family of porous Sn(IV) phenylphosph-
onates with layered structures, high surface area and pore
Keywords Baeyer–Villiger oxidation ꢀ Metal phosphates
and phosphonates ꢀ Selectivity
G. M. S. R. O. Rocha (&) ꢀ T. M. Santos ꢀ C. S. S. Bispo
Department of Chemistry, University of Aveiro,
Campus de Santiago, 3810-193 Aveiro, Portugal
e-mail: grrocha@ua.pt
T. M. Santos
e-mail: teresa@ua.pt
C. S. S. Bispo
e-mail: claudiabispo@ua.pt
T. M. Santos
CICECO, University of Aveiro, Campus de Santiago,
3810-193 Aveiro, Portugal
123

Study of Selectivity of Metal Phosphates and Phosphonates
101
˚
diameters in the 10–20 A range, have also been synthe-
research areas such as electrochemistry, microelectronics,
biological membranes, photochemical mechanisms and
catalysis [30]. To the best knowledge of the authors of this
paper, there is a lack of results in the research field con-
cerning the use of carboxyethylphosphonates and ion
exchanged phosphates as selective catalysts in the Baeyer–
Villiger oxidation of cyclic ketones and aromatic aldehydes
by hydrogen peroxide.
sized [20, 21] and were found to be extremely active in the
oxidation of different aromatic aldehydes, using 30%
aqueous hydrogen peroxide, particularly in the absence of
any organic solvents [22].
An alternative method to perform the selective oxidation
of cyclopentanone, p-methoxybenzaldehyde and 2,4,6-
trimethylbenzaldehyde involves the use of metal phos-
phates or phosphonates, possessing layered or pillared
structures. Metal phosphates and phosphonates can be
obtained at low temperatures, in aqueous media, using soft
chemical routes and their preparation is quite accessible if
the correct phosphonic acids are available. High yields and
short reaction times, easy recovery of the catalyst and the
possibility to perform reactions in solvent-free conditions
are important aspects that make these heterogeneous cat-
alysts interesting from the economical as well as from the
environmental points of view. Due to their particular
physical and chemical properties and high versatility, in the
last 40 years, this class of inorganic and inorganic–organic
compounds have been captivating the attention of many
researchers involved in heterogeneous catalysis [23–28].
Nowadays, a large number of metal phosphates and phos-
phonates of the a- and c-type are known [24, 25, 28–30].
The general interest in the chemistry of metal phosphates
and phosphonates is mainly due to their unusual compo-
sitional and structural diversity, varying from 1-D
arrangements to 3-D microporous frameworks, passing by
the most common layered networks. The versatility of
these layered metal compounds can be well illustrated by
the proton exchange with cations in the interlayer region or
by the replacement of the hydroxyl groups attached to the
phosphorus atoms of a-Zr(HPO4)2ꢀH2O by organic groups.
Several ion exchanged phosphates have been obtained with
different acid/base properties. Protons can be exchanged at
different rates depending on the size and on the hydration
degree of the cations. Large and highly hydrated cations
have been exchanged using precursors with high interlayer
distances [25, 31, 32]. It is possible to vary the properties of
the phosphonates from neutral (e.g. P–CH3) or weakly
acidic (e.g. P–CH2COOH) to strong acidic (e.g. P–C6H4
SO3H) or, even to basic compounds (e.g. P–C2H4NH2).
Large organic groups (R) can be attached to the a-layers of
the phosphates and phosphonates if their dimensions are
compensated by the introduction of small organic groups
(R0; R0 being H, OH or CH3) in order to obtain mixed
compounds of general formula Zr(RPO3)2-X(R0PO3)X
[33, 34].
The promising properties of the metal phosphates and
phosphonates, encourage our interest towards the evalua-
tion of their selective ability in the oxidation reactions of
cyclopentanone, p-methoxybenzaldehyde and 2,4,6-trim-
ethylbenzaldehyde by hydrogen peroxide, with glacial
acetic acid, with the objective of obtaining exclusively,
d-valerolactone, p-methoxyphenol and 2,4,6-trimethylphe-
nol, in good yields. The selective capacity of zirconium
phosphate amorphous (ZrPA), sodium exchanged zirco-
nium phosphate amorphous (NaZrPA), potassium exchan-
ged zirconium phosphate amorphous (KZrPA), zirconium
phenylphosphonate amorphous (ZrPPA), zirconium car-
boxyethylphosphonate (ZrCEP) and aluminium carbo-
xyethylphosphonate (AlCEP) have been the main objective
considered in this study.
2 Experimental
2.1 Characterisation of the Catalysts and Reaction
Products
The metal phosphates and phosphonates prepared in this
work, already described in the literature, were characterized
by comparison with their published spectroscopic data. The
oxidation reaction products were identified by comparison
with authentic samples or by spectroscopic analysis. Infra-
red spectra of solid samples, in KBr disks, were recorded on
a Perkin-Elmer 1720-X Infrared Fourier-Transform Spec-
trometer. A Bruker RFS 100/S was used to record Raman
spectra and a Bruker MSL 400P spectrometer to measure
solid-state 31P MAS NMR and 13C CP MAS NMR spectra,
where chemical shifts were quoted in ppm from 85%
phosphoric acid and glycine, respectively. The conditions
were as follows: (i) nuclear magnetic resonance magic
angle spinning (NMR-MAS), recycle delay = 60 s; pulse
length = 3 ls; spinning rate = 12–15 kHz; (ii) nuclear
magnetic resonance cross polarization (NMR-CP), recycle
delay = 5 s; spinning rate = 8–10 kHz; 90° pulses =
3.5 ls; contact time = 1.5 ms. Thermogravimetric analy-
ses were performed on a TGA Shimadzu, model 50, under
N2 flow (10 °C/min, from 298 up to 973 K). The amount
of the exchanged metal cations was determined by induc-
tively coupled plasma—optical emission spectroscopy
using a Jobin–Yvon JY 70 plus instrument. A Gemini
Good results have been obtained with amorphous and
layered zirconium phosphates [35–37], ion exchanged
zirconium phosphates [38–41] and sulfophenylphospho-
nates [42, 43] in a variety of organic reactions. The
importance of these systems has also been recognized in
123

102
G. M. S. R. O. Rocha et al.
II-2370-Surface Area Analyser was used to determine sur-
face areas, by the BET nitrogen sorption method. The
degassing was done at 100 °C for more than 2 h; equili-
bration time = 5 s; saturation pressure = 763.170 mmHg;
evacuation rate = 300.0 mmHg/min and evacuation
time = 1.0 min. The X-ray powder diffraction patterns
were collected on a Philips X’Pert MPD diffractometer
in geometry Bragg–Brentanno, with radiation of k =
40 mL). The resulting suspension was stirred at room
temperature for 10 min and an aqueous solution of sodium
hydroxide (0.2 M, 36 mL) was slowly added dropwise.
After stirring for 3 h at room temperature, the resulting
solid was filtered out and washed with small amounts of
deionised water until the pH of the filtrate dropped from 12
to 8. The white solid obtained was dried at 70 °C for 24 h
yielding 0.88 g of sodium exchanged zirconium phosphate
amorphous.
˚
1.5406 A (40 kV; 50 mA). The powder patterns were
recorded between 3.5 and 198 in 2h, with a step size of 0.048
and a counting time of 20 s per step.
Quantity of Na? found per gram of solid: 86.9 mg.
Determined specific surface area (BET): 39.0 m2 g-1
.
GC-FID was performed in a Varian Star 3900 chro-
matograph with hydrogen as the carrier gas (55 cm/s) and
GC–MS analyses using a Finnigan Trace GC/MS (Thermo
Quest CE instruments) with helium as the carrier gas
(35 cm/s). In both cases, SPB-5 fused silica Supelco cap-
illary columns with 30 m 9 0.25 mm of internal diameter
and 0.25 lm film thickness have been used. The chro-
matographic conditions for the evaluation of cyclopenta-
none reactions were as follows: initial temperature, 40 °C;
temperature rate, 15 °C/min; final temperature, 220 °C;
injector temperature, 250 °C; detector temperature,
250 °C. The chromatographic conditions for the evaluation
of p-methoxybenzaldehyde and 2,4,6-trimethylbenzalde-
hyde reactions were as follows: initial temperature, 80 °C;
temperature rate, 10 °C/min; final temperature, 220 °C;
injector temperature, 250 °C; detector temperature,
250 °C.
2.2.2 Potassium Exchanged Zirconium Phosphate
Amorphous (KZrPA) [46]
Two aqueous solutions of potassium hydroxide (1 M,
50 mL) and potassium chloride (1 M, 50 mL) were added
to zirconium phosphate amorphous (6.9 g, 21.6 mmol).
After 24 h of slow stirring at room temperature, aqueous
potassium chloride (1 M; 7 mL) and potassium hydroxide
(1 M; 7 mL) were added. The heterogeneous solution was
further stirred for 6 days. The solid was filtered out,
washed with aqueous potassium hydrogenophosphate
(1 M; 20 mL) and dried at room temperature for 2 days.
The resulting solid was further dried at 190 °C for 24 h
yielding 6.5 g of potassium exchanged zirconium phos-
phate amorphous.
Quantity of K? found per gram of solid: 163 mg.
Determined specific surface area (BET): 7.1 m2 g-1
Cyclopentanone, p-methoxybenzaldehyde, 2,4,6-trim-
ethylbenzaldehyde, zirconyl chloride octahydrate, phenyl-
phosphonic acid and 2-carboxyethylphosphonic acid were
purchased from Aldrich. All other chemicals and solvents
were obtained from commercial sources and used as
received or distilled and dried using standard procedures,
whenever necessary.
.
2.2.3 Zirconium Phenylphosphonate Amorphous (ZrPPA)
[45]
A solution of zirconyl chloride (3.9 g, 11.46 mmol) in
water (30 mL) was slowly added, with stirring, to an
aqueous solution of phenylphosphonic acid (3.0 g,
19 mmol) at room temperature. A white suspension formed
immediately and, after filtration, the resulting solid was air-
dried for 24 h and further dried at 65 °C in vacuum for
72 h to yield 3.4 g of zirconium phenylphosphonate
amorphous.
High resolution solid-state 31P MAS NMR spectrum,
d = -4.87 ppm (main peak); broad peak between 13.00
and -8.00 ppm centred at 2.13 ppm. Infrared spectrum
(IR), tmax 3055 (m, CH, aromatic), 1438 (m, C=C, phenyl),
1156 (s, P–C), 748 and 692 (m, phenyl) cm-1. Determined
specific surface area (BET): 40.6 m2 g-1. Thermogravi-
metric analysis (TGA): a plateau was observed up to
450 °C. Above that temperature, the sharp weight loss
observed at 540 °C is assigned to the oxidation of the
phenyl groups and to dehydration to yield zirconium
pyrophosphate.
2.2 Synthesis of Metal Phosphates and Phosphonates
Zirconium phosphate amorphous (ZrPA) was prepared as
previously described in the literature [44]. Sodium
exchanged zirconium phosphate amorphous (NaZrPA),
potassium exchanged zirconium phosphate amorphous
(KZrPA), zirconium phenylphosphonate amorphous
(ZrPPA), zirconium carboxyethylphosphonate (ZrCEP)
and aluminium carboxyethylphosphonate (AlCEP) were
prepared as described below.
2.2.1 Sodium Exchanged Zirconium Phosphate
Amorphous (NaZrPA) [45]
Zirconium phosphate amorphous (1 g, 3.13 mmol) was
added to an aqueous solution of sodium chloride (0.5 M,
123

Study of Selectivity of Metal Phosphates and Phosphonates
103
(s, COO-) cm-1. Thermogravimetric analysis (TGA): the
initial weight loss between room temperature and 310 °C,
10.9%, is due to the loss of three interlayered water mol-
ecules. The second weight loss, between 310 and 650 °C,
28.8%, is due to the dehydroxylation process and to the
combustion of the organic moieties. XRD diffractogram:
2.2.4 Zirconium Carboxyethylphosphonate (ZrCEP)
Semicrysralline [47]
A 25 mL three-necked flask fitted with a reflux condenser,
stirrer, thermometer, and heating mantle were charged with
21.8 mL of aqueous 38% 2-carboxyethylphosphonic acid
(11.1 g) and 25 mL of H2O. Stirring was commenced, and
9.2 g of ZrOCl2, in 10 mL of water were added. Immediately
a white precipitate was formed. Water (17 mL) was added to
fluidize the slurry, and the temperature was raised in order to
maintain a gentle reflux for 15 h. The final slurry was cooled
to room temperature, and a white solid, isolated by filtration,
was washed with water, acetone, and diethyl ether. The solid
product was dried at 110 °C till constant weight (12.1 g).
Infrared spectrum (IR), tmax 3600–2500 (br, OH), 1700
(s, C = O), 1432 (m, P-CH2) 1292 (s, C = O), 1045 (s,
˚
d = 7.89 A.
2.3 Oxidation of Substrates with Hydrogen Peroxide
in Glacial Acetic Acid in the Absence
of the Catalysts
Cyclopentanone, p-methoxybenzaldehyde and 2,4,6-trim-
ethylbenzaldehyde (2.00 mmol) were dissolved in glacial
acetic acid (4 mL) and heated to 45 °C. Aqueous hydrogen
peroxide solution (30%, w/w; 8.00 mmol) was slowly
added via a peristaltic pump. The reaction mixtures were
analysed every hour by gas chromatography (GC) until 6 h
of reaction, and again after 24 h. The reaction products
were identified by mass spectrometry (MS). The results are
presented in Tables 1, 2 and 3. In all cases, at regular
intervals, an aliquot was taken directly from the reaction
mixture with a microsyringe and directly injected into the
GC or GC–MS equipment for analysis of starting materials
and products. The percentage of each compound in the
reaction mixtures was estimated directly from the corre-
sponding peak areas.
PO3) cm-1. XRD d = 12.9 A. 13C CP MAS NMR
˚
d(COOH) 180.9 ppm, d(CH2) 28.0 ppm. 31P MAS NMR
d = 12.4 ppm. Thermogravimetric analysis (TGA): until
200 °C any weight loss was observed. The first weight loss
occured in the region of 200–450 °C, -21.7%, followed by
a second weight loss between 450 and 1150 °C, -11.2%.
All these mass losses are due to the combustion of the
organic moieties of the compound.
2.2.5 Aluminium Carboxyethylphosphonate (AlCEP) [48]
The experimental procedure for the 1:1 M ratio synthesis
was: 20 mL of an aqueous solution containing 1.2175 g
(3.25 mmol) of Al(NO3)3ꢀ9H2O was added to 20 mL of an
aqueous solution containing 0.50 g (3.25 mmol) of
2-carboxyethylphosphonic acid, under stirring at room
temperature. As the initial pH of the resulting mixture was
1.70 it was raised till pH 5.0 by adding dropwise a 10%
NaOH aqueous solution. The formed suspension was
heated in a Teflon-lined autoclave at 150 °C for 3 days and
a white polycrystalline solid was obtained, which was
washed with water and acetone and dried at 60 °C.
2.4 Oxidation of Substrates with Hydrogen Peroxide
in Glacial Acetic Acid in the Presence
of the Catalysts
Cyclopentanone, p-methoxybenzaldehyde and 2,4,6-trim-
ethylbenzaldehyde (2.00 mmol) were dissolved in glacial
acetic acid (4 mL), the catalyst was added (0.10 g) and the
mixture was heated at 45 °C. Aqueous hydrogen peroxide
solution (30%, w/w; 8.00 mmol) was slowly added via a
peristaltic pump. The reaction mixtures were analysed
every hour by GC until 6 h of reaction, and again after
24 h. The reaction products were identified by MS. The
Infrared spectrum (IR), tmax 3657–3448 (s, OH), 3050
(br, HOH), 2900 (w, C–H), 1620 (s, HOH and CO), 1455
Table 1 Cyclopentanone oxidation with hydrogen peroxide catalysed by metal phosphates and phosphonates, in glacial acetic acida
Solids
ZrPA (%) ZrPPA (%) ZrCEP (%) AlCEP (%) KZrPA (%) NaZrPA (%) Blank (%)
Selectivity of 1
72.0
10.0
–
72.0
7.0
80.0
5.0
75.0
13.0
8.0
86.0
10.0
–
85.0
10.0
–
64.0
11.0
16.0
9.0
Selectivity of 5-hydroxypentanoic acid
Selectivity of dicyclopentylidenediperoxide
Selectivity of 5-acetoxypentanoic acid
Conversion of cyclopentanoneb
a
4.0
4.0
18.0
76.0
17.0
37.0
11.0
47.0
4.0
4.0
5.0
51.0
49.0
49.0
55.0
Results after 24 h of reaction time. Reaction conditions are all similar and are described in Sect. 2
b
Based on gas chromatographic peak areas
123

104
G. M. S. R. O. Rocha et al.
Table 2 p-Methoxybenzaldehyde oxidation with hydrogen peroxide catalysed by metal phosphates and phosphonates, in glacial acetic acida
Solids
ZrPA (%) ZrPPA (%) ZrCEP (%) AlCEP (%) KZrPA (%) NaZrPA (%) Blank (%)
Selectivity of 2
67.0
100
–
83.0
17.0
93.0
53.0
47.0
97.0
100
–
100
–
–
Selectivity of p-methoxyphenyl formate 33.0
Conversion of p-methoxybenzaldehydeb 93.0
100
98.0
91.0
97.0
75.0
a
Results after 6 h of reaction. Reaction conditions are all similar and are described in Sect. 2
Based on gas chromatographic peak areas
b
Table 3 2,4,6-Trimethylbenzaldehyde oxidation with hydrogen peroxide catalysed by metal phosphates and phosphonates, in glacial acetic
acida
Solids
ZrPA (%) ZrPPA (%) ZrCEP (%) AlCEP (%) KZrPA (%) NaZrPA (%) Blank (%)
Selectivity of 3
14.0
86.0
25.0
75.0
22.0
78.0
21.0
79.0
29.0
71.0
35.0
65.0
10.0
90.0
Selectivity of 2,4,6-trimethylphenyl formate
Conversion of 2,4,6-trimethylbenzaldehydeb 100
100
100
100
100
100
100
a
Results after 24 h of reaction. Reaction conditions are all similar and are described in Sect. 2
Based on gas chromatographic peak areas
b
Table 4 MS (EI) of the oxidation reactions products
Products
MS (EI) m/z (relative intensity, %)
d-Valerolactone
101 (2%), 100 (28%), 56 (56%), 55 (29%), 42 (100%), 41 (65%), 28 (45%)
101 (2%), 73 (15%), 60 (100%), 45 (35%), 42 (70%)
5-Hydroxypentanoic acid
5-Acetoxypentanoic acid
Dicyclopentylidenediperoxide
p-Methoxyphenol
100 (57%), 99 (45%), 70 (27%), 55 (53%), 54 (25%), 43 (100%), 42 (30%), 41 (29%)
101 (60%), 84 (100%), 56 (41%), 45 (5%), 42 (20%)
124 (75%), 109 (100%), 95 (5%), 81 (70%), 65 (10%), 53 (30%), 39 (10%)
152 (27%), 124 (87%), 109 (100%), 95 (5%), 81 (39%), 63 (7%), 53 (12%), 39 (5%)
136 (100%), 121 (93%), 91 (29%), 77 (13%), 65 (10%)
p-Methoxyphenyl formate
2,4,6-Trimethylphenol
2,4,6-Trimethylphenyl formate
164 (78%), 136 (89%), 120 (100%), 91 (39%), 77 (22%), 65 (14%)
results are also presented in Tables 1, 2 and 3. In all cases,
at regular intervals, an aliquot was taken directly from the
reaction mixture with a microsyringe and directly injected
into the GC or GC–MS equipment for analysis of starting
materials and products. The percentage of each compound
in the reaction mixtures was estimated directly from the
corresponding peak areas.
trimethylbenzaldehyde, considering several metal phos-
phates and phosphonates with different characteristics and
properties.
Metal phosphates are well known as strong inorganic
solid acids and much of their catalytic activity has been
attributed to the Brønsted acidity of the interlayered
hydroxyl groups and Lewis acidity of the metal centre. On
the other hand, metal phosphonates are a class of inor-
ganic–organic hybrid materials, characterized by the pres-
ence of covalent bonds between the inorganic and organic
moieties. The main research effort in the metal phosphate
and phosphonate field was initially directed towards com-
pounds with tetravalent metal cations, but now a wide
variety of divalent and trivalent metals have also been
reported [49–52].
In Table 4 the reaction products obtained in all the
oxidation reactions described above are summarized,
together with the corresponding mass spectra peaks
(identified molecular ions).
3 Results and Discussion
The work described in this contribution analyses and
correlates the selectivities obtained on the oxidation
of cyclopentanone, p-methoxybenzaldehyde and 2,4,6-
In our work, the metal phosphates and phosphonates
synthesised included the zirconium phosphate amorphous
(ZrPA), sodium exchanged zirconium phosphate amorphous
123

Study of Selectivity of Metal Phosphates and Phosphonates
105
(NaZrPA), potassium exchanged zirconium phosphate amor-
phous (KZrPA), zirconium phenylphosphonate amorphous
(ZrPPA), zirconium carboxyethylphosphonate (ZrCEP) and
aluminium carboxyethylphosphonate (AlCEP). These sol-
ids were evaluated for their selective skills on the oxidation
of cyclopentanone, p-methoxybenzaldehyde and 2,4,6-
trimethylbenzaldehyde.
MS as being 5-hydroxypentanoic acid. Using acetic acid
two different by-products were formed which were iden-
tified by MS as 5-hydroxypentanoic acid (4) and 5-acet-
oxypentanoic acid (6), as expected. The retention time of
5-hydroxypentanoic acid and 5-acetoxypentanoic acid
obtained in the above reactions have shown the same
retention times of two of the by-products obtained in our
previous reactions described in Sects. 2.3 and 2.4. The third
by-product, resulting from the reaction of cyclopentanone
in acidic media with two molecules of hydrogen peroxide,
was also identified by MS as dicyclopentylidenediperoxide.
In Table 1, in the absence of a metal phosphate or
phosphonate, 55.0% of conversion of cyclopentanone into
the products is depicted, with a selectivity of 64.0% for
d-valerolactone, and 11.0, 16.0 and 9.0% for 5-hydroxy-
pentanoic acid, dicyclopentylidenediperoxide and 5-acet-
oxypentanoic acid, respectively. With all the catalysts, good
selectivities of d-valerolactone were obtained and low
yields of 5-hydroxypentanoic acid, 5-acetoxypentanoic acid
and dicyclopentylidenediperoxide were detected. In the
particular case of NaZrPA, KZrPA and ZrPA no dicyclo-
pentylidenediperoxide was formed. It appears important to
notice that, although the conversion of cyclopentanone in
the blank reaction is 55.0%, the selectivity of the target
product is the lowest of all set of results.
Our studies started by examining the cyclopentanone
oxidation, in the absence and in the presence of metal
phosphates or phosphonates, by hydrogen peroxide, in
glacial acetic acid. The possible formation of peroxyacetic
acid, in these systems, had already been investigated in a
previous work, in which the rate of peroxyacetic acid
formation was examined in the absence and in the presence
of some metal(IV) phosphates [53]. Considering its for-
mation, there is a strong possibility that the cyclopentanone
oxidation follows an acid catalysed ‘‘ionic’’ mechanism.
The oxidation steps of the cyclopentanone may be sum-
marised considering an initial formation of d-valerolactone
(1), followed by its acidic cleavage to produce 5-hy-
droxypentanoic acid (4). As it is known, in acidic condi-
tions, the cyclopentanone can also react with two
molecules of hydrogen peroxide with the formation of
dicyclopentylidenediperoxide (5). Furthermore, the pres-
ence of acetic acid also favours the production of 5-acet-
oxypentanoic acid (6) (Scheme 1).
The oxidation of p-methoxybenzaldehyde and 2,4,6-
trimethylbenzaldehyde was also performed in the absence
and in the presence of metal phosphates or phosphonates,
with aqueous hydrogen peroxide, in glacial acetic acid.
Like in the majority of the Baeyer–Villiger oxidations of
aldehydes, the aimed product is the phenol rather than the
formate ester. Since the formate esters are formed in the
first step of the reactions, the catalysts used in these studies
should be able to perform the Baeyer–Villiger reactions in
the presence of water, while catalysing rapidly the hydro-
lysis of the ester formed previously. With both substrates,
the oxidation proceeded to give the respective formate
esters (p-methoxyphenyl formate and 2,4,6-trimethyl-
phenyl formate) along with the corresponding phenols, in
different yields (Tables 2 and 3).
The reaction products were identified by GC and char-
acterized by MS. d-Valerolactone was identified by com-
parison with the retention time, in the GC column, of a
commercial sample and confirmed by MS. The identifica-
tion of two of the by-products referred above (4 and 6)
were elucidated using two additional reactions performed
with d-valerolactone in aqueous media. In one of them,
acidification with hydrochloric acid was provided, and in
the other acetic acid was used with the same purpose. In the
first case (with HCl) the product formed was identified by
O
O
O
O
O
O
H2O2 , AcOH
T = 45 ºC
O
+
The stages of the oxidation reaction of p-methoxy-
benzaldehyde may be summarised as the initial formation
of p-methoxyphenyl formate (7) followed by hydrolysis, in
order to produce p-methoxyphenol (2) (Scheme 2). The
reaction products were identified and characterized by GC
and MS, respectively. p-Methoxyphenol was identified by
comparison with the retention time, in the GC column, of a
commercial sample and confirmed by its mass spectrum.
p-Methoxyphenyl formate was identified by MS.
(1)
(5)
H+ / H2O
HO
OH
O
O
(4)
+
O
In the absence of a metal phosphate or phosphonate,
75.0% of conversion of p-methoxybenzaldehyde into
p-methoxyphenyl formate was found, and any p-methoxy-
phenol was formed (Table 2). But with ZrPK, ZrPNa and
HO
O
(6)
Scheme 1 Baeyer–Villiger oxidation of cyclopentanone
123

106
G. M. S. R. O. Rocha et al.
H
Scheme 2 Baeyer–Villiger
oxidation of p-
methoxybenzaldehyde
CHO
O
OH
H2O2, AcOH
+
°
O
T = 45 C
H3CO
H3CO
H3CO
(7)
(2)
H2O
ZrPPA, 100% selectivity of p-methoxyphenol was obtained.
With the other catalysts good conversions of p-methoxy-
benzaldehyde and selectivities of p-methoxyphenol were
also reached. The results shown in Table 2 are referred to
6 h of reaction time because after this time interval and with
some of our catalysts (KZrPA, NaZrPA and ZrPPA), 100%
of selectivity of 2 was already reached.
2,4,6-trimethylphenyl formate and 10.0% of 2,4,6-tri-
methylphenol were found. With ZrCEP, AlCEP and ZrPPA
high selectivities of 2,4,6-trimethylphenol were obtained
although the best results were achieved with ZrPK and
ZrPNa. After 24 h of reaction, 100% of conversion of
2,4,6-trimethylbenzaldehyde was reached, with all the
catalysts.
Similarly, the oxidation of 2,4,6-trimethylbenzaldehyde
proceeded with the initial formation of 2,4,6-trimethyl-
phenyl formate (8), which was further hydrolysed to 2,4,6-
trimethylphenol (3) (Scheme 3). The products of this
reaction were also identified and characterized by GC and
MS, respectively. 2,4,6-Trimethylphenol was identified by
comparison with the retention time, in the GC column, of a
commercial sample and confirmed by its mass spectrum.
2,4,6-Trimethylphenyl formate was identified by MS.
As shown in Table 3, in the absence of a metal phos-
phate or phosphonate, 100% of conversion of 2,4,6-
trimethylbenzaldehyde and a selectivity of 90.0% of
A correlation between the results shown in Tables 1, 2
and 3 and the structure of the solids used in our study was
attempted, and the details are discussed in the next
considerations.
3.1 Zirconium Phosphate Amorphous
ZrPA (Fig. 1a) is one of the most studied metal(IV)
phosphates and it is well known for its strong acidic
properties, either due to the hydroxyl groups in the inter-
layers or to the zirconium metal centres in the layers
H3C
CH3
CH3
Scheme 3 Baeyer–Villiger
oxidation of 2,4,6-
trimethylbenzaldehyde
H
CHO
CH3
O
OH
H2O2, AcOH
+
°
O
T = 45 C
CH3
H3C
CH3
H3C
H3C
(8)
(3)
H2O
(B)
(A)
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
= Zr
=P
=O
Fig. 1 Schematic representation of zirconium phosphate (a) and zirconium phenylphosphonate (b)
123

Study of Selectivity of Metal Phosphates and Phosphonates
107
˚
[28, 34]. The interlayer distance is 7.56 A and the layer
which forces the interlayer space to increase from 7.56 to
˚
14.7 A, with the Zr atoms in the centre of the plane, in a
thickness, calculated as the shortest distance between the
centres of the oxygen atoms of the P–OH groups present on
near hexagonal array arrangement. The Zr metal centres
are bridged by the phosphonate oxygen atoms in much the
same way as in ZrPA. Zirconium phenylphosphonate
amorphous has 1.07 mmol/g available acidic sites in the
less acidic region and like ZrPA, in the stronger acidic
region this polymeric compound has no available
acidic sites [45]. However, despite this solid having more
acidic sites in the less acidic region than ZrPA, the yields
of 5-hydroxypentanoic acid (4) and 5-acetoxypentanoic
acid (6) produced together are similar to the results
achieved with ZrPA (Table 1). The difference relies on the
bigger selectivity of 6 relatively to 4. It is possible that the
intermediate 4 is not formed in a high yield because
the distance between the layers permit its easier access to
the active sites of ZrPPA and its consequent conversion
into 6 justifying the bigger selectivity of the latter com-
˚
the opposite sides of one layer, is 6.3 A. The distance
between adjacent P–OH groups on one side of the layer is
˚
5.3 A then the ‘‘free area’’ around each phosphate group is
˚
24 A. The arrangement of the pendent phosphate groups
creates six-sided cavities, each one containing a water
molecule in the interlayer region. These water molecules
form a hydrogen bonding network with the P–OH groups
belonging to one of the sides of the layer. The active
hydroxyl groups of ZrPA play an important role in heter-
ogeneous catalysis because they can be easily reached by
subtracts. As described in the literature, the acidic strength
of our type of solid is directly related to values of H0 (the
Hammett acidity function), meaning a certain number of
acidic sites available in the structure of the catalysts. For
ZrPA, there are two types of sites with remarkably different
acid strengths. In the less acidic region, the number of
acidic sites is 0.124 mmol/g of solid, but in the strong
acidic region no available acid sites were found [45].
From data in Table 1 it can be confirmed that, accord-
ingly to the properties described for ZrPA, some 5-hy-
droxypentanoic acid (4) and 5-acetoxypentanoic acid (6)
were formed but any dicyclopentylidenediperoxide (5) was
detected. Probably the interlayer distance of this solid
prevents the formation of this last bulky compound 5.
Relatively to the p-methoxybenzaldehyde and 2,4,6-trim-
ethylbenzaldehyde, good conversions of these substrates
and good selectivities of the corresponding phenols were
found (Tables 2 and 3). However, 2,4,6-trimethylphenol
(3) is obtained in a lower yield than p-methoxyphenol (2).
The acid hydrolysis of the p-methoxyphenyl formate is
favoured due to the presence of the methoxy group. The
methoxy group being a stronger activating substituent will
stabilize by resonance the formate while facilitating the
protonation of the carboxylic group and the subsequent
formation of the tetrahedral intermediate. Once formed, the
tetrahedral intermediate may revert to the starting materials
or continue onwards to the products. In the second stage of
the ester hydrolysis, the tetrahedral intermediate dissociates
to the phenol and to a carboxylic acid. It is also possible
that the 2,4,6-trimethylphenyl formate (8) being bulkier
than the p-methoxyphenyl formate (7), consequently have a
lower capacity to access the active sites of ZrPA, in order
to be further hydrolysed to the corresponding phenol.
˚
pound. The 14.7 A distance between interlayers and the
acidity of ZrPPA also allows the formation of some
quantity of dicyclopentylidenediperoxide (5). Good con-
versions of p-methoxybenzaldehyde and 2,4,6-trimethyl-
benzaldehyde were recorded as well as good selectivities of
the corresponding phenols (Tables 2 and 3). These results
were expected because the intermediate formate species
will be able to approach the interlayers of ZrPPA and
consequently will be much more available to be hydrolysed
to the corresponding phenols.
3.3 Sodium and Potassium Exchanged Zirconium
Phosphate Amorphous
The protons of zirconium phosphate amorphous are easily
exchanged with sodium and potassium cations to give the
sodium exchanged zirconium phosphate amorphous
(NaZrPA) and the potassium exchanged zirconium phos-
phate amorphous (KZrPA), respectively. The interlayer
˚
distance of NaZrPA and KZrPA is 9.8 and 10.7 A,
respectively. These phosphates show more basic charac-
teristics than the zirconium phosphate amorphous, due the
presence of the Na? and K? cations. The environment
created by NaZrPA and KZrPA may favour the hydrolysis
of the formates, since in basic media the reactions are
irreversible, contrarily to the acidic hydrolysis mechanism,
which is reversible. The low yields of 5-hydroxypentanoic
acid and 5-acetoxypentanoic acid and the absence of
dicyclopentylidenediperoxide in the final products (see
Table 1) can be justified by the features of NaZrPA and
KZrPA. With these two last solids the selectivities of
d-valerolactone were the best of our set of solids. The best
selectivities of p-methoxyphenol and 2,4,6-trimethylphenol
were also achieved with those two solids along with good
3.2 Zirconium Phenyphosphonate Amorphous
Zirconium phenyphosphonate amorphous is prepared from
aqueous solutions of zirconyl chloride and phenyphos-
phonic acid. In the ZrPPA (Fig. 1b) all the hydroxyl groups
in the interlayers have been substituted for phenyl groups,
123

108
G. M. S. R. O. Rocha et al.
conversions of p-methoxybenzaldehyde and 2,4,6-trimeth-
ylbenzaldehyde (Tables 2 and 3).
O
O
C2H4
C2H4
H
O
3.4 Zirconium and Aluminium
Carboxyethylphosphonate
H
O
O
O
O
O
O
O
O
C
O
C
O
O
H2O
H2O
O
H
O
H
H2O
O
O
O
O
H
O
O
O
H O
C
2
C
O
Zirconium carboxyethylphosphonate is prepared from
aqueous solutions of zirconyl chloride and of carboxyeth-
ylphosphonic acid. In the ZrCEP all the hydroxyl groups in
the interlayers have been substituted for carboxyethyl
groups. In consequence the interlayer distance increase
O
O
O
C2H4
C2H4
C2H4
C2H4
H
O
H
O
O
O
O
O
O
O
O
O
C
C
O
O
H2O
H2O
H2O
O
H
˚
O
H
O
O
from 7.56 (ZrPA) to 12.9 A (Fig. 2). The characterization
O
H
H O
2
O
O
C
O
C
O
O
O
O
by 13NMR and IR spectra (see Sect. 2) is consistent with a
layered structure together with an hydrogen bonding
interlayer network among the carboxylic acid groups.
Aluminium carboxyethylphosphonate is prepared from
aqueous solutions of aluminium nitrate and of carboxy-
ethylphosphonic acid. This solid has a pillared layered
structure with the phosphonate and carboxyethyl groups
cross-linking the inorganic layers, to give a three-dimen-
sional structure (Fig. 3). From X-ray powder diffraction
O
C2H4
C2H4
O
O
= Al
=P
=O
Fig. 3 Schematic representation of aluminium carboxyethylphosphonate
˚
data, the average interlayer distance is 7.89 A.
pillared structure with a smaller interlayer distance. For
this reason, the d-valerolactone initially formed can go
inside of the layered structure of ZrCEP and contact with
its active sites, being cleaved into 5-hydroxypentanoic
acid. The consequent conversion of 5-hydroxypentanoic
acid to 5-acetoxypentanoic acid is observed in a higher
extension. Therefore, the formation of 5-acetoxypentanoic
acid from 5-hydroxypentanoic acid in a bigger extension is
prevented by the smaller interlayer distance and the pil-
lared structure of AlCEP (see Table 1). The characteristics
of ZrCEP and AlCEP can also justify our results with
p-methoxybenzaldehyde and 2,4,6-trimethylbenzaldehyde
(Tables 2 and 3). In the case of p-methoxybenzaldehyde,
with ZrCEP, the corresponding phenol was formed with
good selectivity. However, it is possible that the structure
of AlCEP prevents the approach of the p-methoxyphenyl
formate to the active sites of the catalyst and the selectivity
of the corresponding phenol is observed in a lower exten-
sion. The oxidation of 2,4,6-trimethylbenzaldehyde occurs
in a similar extension, with both ZrCEP or AlCEP.
The weak acid properties of the two above solids, due to
their carboxyethyl groups in the interlayers, can justify the
cleavage of d-valerolactone and also the formation of
dicyclopentylidenediperoxide (5). On the other hand, the
different yields of 5-hydroxypentanoic and 5-acetoxypen-
tanoic acids can be related with the distinct structures and
interlayer distances of ZrCEP and AlCEP. As stated above,
ZrCEP adopt a layered structure while AlCEP have a
OH
OH
OH
O
O
O
OH
O
O
O
O
HO
O
HO
O
HO
O
HO
O
OH
OH
OH
O
OH
The versatility of the metal phosphates and phospho-
nates prepared in our work were successfully used in the
Baeyer–Villiger oxidation of cyclopentanone, p-methoxy-
benzaldehyde and 2,4,6-trimethylbenzaldehyde, by hydro-
gen peroxide, in glacial acetic acid. The best solids for
cyclopentanone were NaZrPA and KZrPA, because of their
basic properties. With these solids the acid cleavage of
d-valerolactone was detected in low yields and, in addition,
no dicyclopentylidene was formed. With ZrCEP and
AlCEP, which are solids with weak acid properties, good
selectivities of d-valerolactone were also reached.
O
O
O
HO
HO
O
HO
HO
= Zr
=P
=O
Fig. 2 Schematicrepresentationofzirconiumcarboxyethylphosphonate
123

Study of Selectivity of Metal Phosphates and Phosphonates
109
In the case of p-methoxybenzaldehyde and 2,4,6-trim-
ethylbenzaldehyde the best catalytic performances were
obtained with NaZrPA and KZrPA. For both substrates, the
mechanism involved (Scheme 2, 3) and the environment
created by these solids imply that the hydrolysis of the
intermediate formate species is irreversible and the corre-
sponding phenols are formed in a large extension. With
ZrPPA, good selectivities of the phenols are also obtained.
In this last case, it was expected that the large interlayer
distance allow the approach of the intermediate formates
that will be much more available to be hydrolysed to the
corresponding phenols.
layers have a large separation. These considerations were
extensively interpreted in Sect. 3.
Acknowledgments The authors would like to thank the Chemistry
Department and CICECO (Centre for Research in Ceramics and
Composites Materials), University of Aveiro, for support.
References
1. Gharnati L, Doring M, Arnold U (2009) Curr Org Synth 6:342
2. Saito T, Hirayama T, Sakagushi S (1996) JP Patent 08151343
3. Sato T, Matsumoto H, Kakegawa T, Niino Y (1993) JP Patent
05301836
4. Nihro Y, Furukawa H, Sogawa S, Wang TC, Miyataka H, Mat-
sumoto H, Miki T, Satoh T (1994) Chem Pharm Bull 42:576
5. Wellnitz U, Potsch S, Garbe C, Lassmann G (1997) Melanoma
Res 7:288
From the detailed analysis and discussion of the above
results, it can be assumed that a optimized combination of
glacial acetic acid and metal phosphates or phosphonates,
with both basic or weak acid properties, will constitute
ideal systems to achieve best results concerning the for-
mation of d-valerolactone, p-methoxyphenol and 2,4,6-
trimethylphenol.
6. Riley PA, Cooksey CJ, Johnson CI, Land EJ, Latter AM,
Ramsden CA (1997) Eur J Cancer 33:135
¨
7. Laßmann G, Potsch S (1995) DE Patent 4344645
8. Muzart J (2006) Adv Synth Catal 348:275
9. Usui Y, Sato K (2003) Green Chem 5:373
10. Fischer J, Hoelderich WF (1999) Appl Catal A Gen 180:435
11. Ueno S, Ebitani K, Ookubo A, Kaneda K (1997) Appl Surf Sci
121:366
4 Conclusions
The results published in this paper show that the ideal
systems to achieve the best results concerning the oxidation
of cyclopentanone, p-methoxybenzaldehyde and 2,4,6-
trimethylbenzaldehyde, were reached with NaZrPA,
KZrPA, ZrCEP, AlCEP and ZrPPA, by hydrogen peroxide,
in glacial acetic acid.
12. Kaneda K, Ueno S, Lmanaka T (1994) J Chem Soc Chem
Commun 7:797
´ ´
13. Llamas R, Jimenez-Sanchidrian C, Ruiz JR (2007) Tetrahedron
63:1435
14. Li C, Wang J, Yang Z, Hu Z, Lei Z (2007) Catal Commun 8:1202
15. Syper L (1989) Synthesis (Stuttg) 3:167
´
16. Corma A, Fornes V, Iborra S, Mifsud M, Renz M (2004) J Catal
221:67
17. Corma A, Navarro MT, Nemeth L, Renz M (2001) Chem
Commun 21:2190
18. Corma A, Nemeth LT, Renz M, Valencia S (2001) Nature
412:423
´
19. Renz M, Blasco T, Corma A, Fornes V, Jensen R, Nemeth L
(2002) Chem Eur J 8:4708
20. Huang J, Subbiah A, Pyle D, Rowland A, Smith B, Clearfield A
(2006) Chem Mater 18:5213
21. Subbiah A, Pyle D, Rowland A, Huang J, Narayanan RA,
Thiyagarajan P, Zon J, Clearfield A (2005) J Am Chem Soc
127:10826
22. Kirumakki S, Samarajeewa S, Harwell R, Mukherjee A, Herberb
RH, Clearfield A (2008) Chem Commun 43:5556
23. Alberti G, Costantino U (1991) In: Atwood JL, Davies JED, Mac
Nicol DD (eds) Inclusion compounds, vol 5. Oxford University
Press, Oxford, chap 5
Considering the formation of peroxyacetic acid in these
systems there is a strong possibility that the cyclopenta-
none oxidation follow an acid catalysed ‘‘ionic’’ mecha-
nism. The cyclopentanone oxidation starts with the
formation of d-valerolactone that can be further cleaved by
acid to give 5-hydroxypentanoic and 5-acetoxypentanoic
acids. The acidic media can also favour the formation of
some dicyclopentylidenediperoxide. The three by-products
are formed in different yields depending on the metal
phosphates and phosphonates used. The reactions per-
formed with NaZrPA and KZrPA, the solids with more
basic properties, gave the best yields of d-valerolactone.
With ZrCEP and AlCEP, which are the solids with weak
acid properties, good selectivities of d-valerolactone have
been recorded.
24. Alberti G, Casciola M, Costantino U, Vivani R (1996) Adv Mater
8:291
25. Clearfield A, Costantino U (1996) In: Alberti G, Bein T (eds)
Solid state supramolecular chemistry. Comprehensive supramo-
lecular chemistry, vol 7. Pergamon Press, New York, chap 4
26. Clearfield A (1990) Comments Inorg Chem 10:89
27. Cao G, Hong HG, Mallouk TE (1992) Accounts Chem Res
25:420427
28. Curini M, Rosati O, Costantino U (2004) Curr Org Chem 8:591
29. Vivani R, Alberti G, Costantino F (2008) Micropor Mesopor
Mater 107:58
The oxidation reactions of p-methoxybenzaldehyde and
2,4,6-trimethylbenzaldehyde also follow an ‘‘ionic’’
mechanism starting with the formation of the correspond-
ing formates which are further hydrolysed to the corre-
sponding phenols. These hydrolysis reactions were more
extensive with NaZrPA, KZrPA and ZrPPA. This can
suggest that the hydrolysis of p-methoxyphenyl formate
and 2,4,6-trimethylphenyl formate is favoured if the metal
phosphates or phosphonates have basic properties or if the
30. Sebti S, Zahouily M, Lazrek H, Mayoral J, Macquarrie D (2008)
Curr Org Chem 12:203
123

110
G. M. S. R. O. Rocha et al.
´
31. Alberti G, Costantino U, Gill JS (1976) J Inorg Nucl Chem
38:1733
41. Alvaro VFD, Johnstone RAW (2008) J Mol Catal A Chem
280:131
32. Alberti G, Bertrami R, Casciola M, Costantino U, Gupta JP
(1976) J Inorg Nucl Chem 38:843
42. Costantino U, Curini M, Marcotullio MC, Pisani E, Rosati O
(1997) Synlett 7:769
33. Clearfield A (1998) Progress in inorganic chemistry. Wiley, New
York
43. Curini M, Epifano F, Marcotullio MC, Rosati O (2001) Synlett
7:1182
34. Alberti D (1996) In: Alberti G, Bein T (eds) Solid state supra-
molecular chemistry. Comprehensive supramolecular chemistry,
vol 7. Pergamon Press, New York, chap 5
44. Stynes JA, Clearfield A (1964) J Inorg Nucl Chem 26:117
45. Pires PJC (1995) PhD Thesis, University of Liverpool, Liverpool
`
46. Fildes D, Caignaert V, Villemin D, Jaffres P (2001) Green Chem
35. Costa MCC, Jonhstone RAW, Whittaker D (1998) J Mol Catal A
Chem 129:79
3:52
47. Burwell DA, Thompson ME (1991) Chem Mater 3:730
´
´
36. La Ginestra A, Patrono P, Berardelli ML, Galli P, Ferragina C,
Massicci MA (1987) J Catal 103:346
37. Thakur D, Clearfield A (1981) J Catal 69:230
38. Curini M, Epifano F, Marcotullio MC, Rosati O, Tsadjout A
(2002) Synth Commun 32:355
48. Gomez-Alcantara MM, Cabeza A, Aranda MAG, Guagliardi A,
Mao JG, Clearfield A (2004) Solid State Sci 6:479
49. Zhang Y, Clearfield A (1992) Inorg Chem 31:2821
50. Bhardwaj C, Hu HL, Clearfield A (1993) Inorg Chem 32:4294
51. Bujoli B, Palvadeau P, Rouxel J (1990) Chem Mater 2:582
52. Wang R, Zhang Y, Hu H, Frausto RR, Clearfield A (1992) Chem
Mater 4:864
39. Curini M, Montanari F, Rosati O, Lioy E, Margarita R (2003)
Tetrahedron Lett 44:3923
40. Curini M, Epifano F, Marcotullio MC, Rosati O, Rossi M,
Tsadjout A (2000) Synth Commun 30:3181
53. Rocha GO, Johnstone RAW, Hemming BF, Pires PJC, Sankey JP
(2002) J Mol Catal A Chem 186:127
123