A palladium wall coated microcapillary reactor for use in continuous flow transfer hydrogenation

Article abstract of DOI:10.1002/adsc.201000139

Herein we describe the preparation of a novel continuous flow multi-channel microreactor in which the internal surface has been functionalised with a palladium coating, enabling its use in catalytic heterogeneous liquid-phase reactions. Simple chemical deposition techniques were used to immobilise palladium(O) on the channel wall surface of a polymeric multi-capillary extrudate made from ethylenevinyl alcohol copolymer. The Pd coating of the mi- crocapillaries has been characterised by mass spectrometry and light and electron microscopy. The functional activity of the catalytic Pd layer was tested in a series of transfer hydrogenation reactions using triethylsilane as the hydrogen source.

Full text of DOI:10.1002/adsc.201000139

FULL PAPERS
DOI: 10.1002/adsc.201000139
A Palladium Wall Coated Microcapillary Reactor for Use in
Continuous Flow Transfer Hydrogenation
Christian H. Hornung,a Bart Hallmark,a Malcolm R. Mackley,a,*
Ian R. Baxendale,b and Steven V. Leyb,*
a
Department of Chemical Engineering and Biotechnology, University of Cambridge, Pembroke St., Cambridge,
CB2 3RA, U.K.
Fax : (+44)-1223-334-796; e-mail: mrm5@cam.ac.uk
Innovative Technology Centre, Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge,
b
CB2 1EW, U.K.
Fax : (+44)-1223-336-973; e-mail: svl1000@cam.ac.uk
Received: February 21, 2010; Published online: July 7, 2010
Abstract: Herein we describe the preparation of a crocapillaries has been characterised by mass spec-
novel continuous flow multi-channel microreactor in trometry and light and electron microscopy. The
which the internal surface has been functionalised functional activity of the catalytic Pd layer was
with a palladium coating, enabling its use in catalytic tested in a series of transfer hydrogenation reactions
heterogeneous liquid-phase reactions. Simple chemi- using triethylsilane as the hydrogen source.
cal deposition techniques were used to immobilise
palladium(0) on the channel wall surface of a poly-
meric multi-capillary extrudate made from ethylene- Keywords: flow chemistry; hydrogenation; immobili-
vinyl alcohol copolymer. The Pd coating of the mi- sation; microreactors; palladium; reduction
Introduction
ratory environment and the fast adaptation of these
processes for a small production scale by simply in-
Chemical microreactors are devices containing consis- creasing the number of reactor units. In this way, the
tent dimensionally defined, fluidic pathways in the optimisation of reaction conditions can be carried out
sub-millimetre range. Many designs have a single or using a single device with a small number of microca-
multiple parallel channels with diameters between 10 pillaries, whilst the production reactor can be operat-
and 1000 mm, where the chemical reaction takes ed using multiple devices with hundreds or even thou-
place.[1–5] A major advantage of microreactor technol- sands of microcapillaries running in parallel. This so-
ogy is the very high surface area to volume ratio of called ꢀnumbering-upꢁ or ꢀscale-outꢁ requires neither
typically 10000 to 50000 m2/m3. This contrasts signifi- the redesign of reactors nor extensive optimisation
cantly with the specific surface area in conventional studies which are usually associated with the classical
reactors which is usually about 100 m2/m3 and seldom batch scale-up approach.[2] In this new research proj-
exceeds 1000 m2/m3.[6] Owing to this property, micro- ect, we have developed our microreactor system fur-
structured reactors with chemically active surfaces ther to include a catalytic palladium wall coating on
offer tangible benefits for use in heterogeneous cata- the microcapillaries in order to carry out palladium-
lytic processes. Micro- and mesoscale reactor designs promoted processes as these are of pivotal importance
for use in catalytic operations include packed bed sys- in modern synthesis projects.
tems, catalytic wall reactors, flow reactors containing
microporous media, such as monolithic structures and tion of a catalytic wall microreactor through immobi-
other chemically functionalised devices.[6–15]
lisation of Pd on the walls of polymer channels with a
This paper reports a novel process for the prepara-
We have been developing microreactor concepts mean capillary diameter of 146 mm using a series of
around multi-channelled polymer devices for use in aqueous preparative flow steps. The general proce-
chemical synthesis and have presented these results in dure was modified from previous protocols for immo-
previous publications.[16,17] The design and flexibility bilising Pd within monolithic structures or on
of these modular constructs facilitates both develop- beads.[11,15,18–20] The reactor system presented herein
ment of new synthesis routes within a research labo- contrasts traditional polystyrene or silica solid sup-
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A Palladium Wall Coated Microcapillary Reactor for Use in Continuous Flow Transfer Hydrogenation
ports, which have a granular, bead or gel form,[7,20–24] simple polyvinyl alcohol (PVA), which has been used
as it consists of multiple capillaries manufactured in previous studies.[29] The EVOH capillary structures
from ethylene-vinyl alcohol (EVOH). The capillary are stable to water and alcohols and have a good gen-
geometry provides a known flow profile, which can be eral resistance to many other organic solvents includ-
easily characterised and modelled, and does not suffer ing dichloromethane and tetrahydrofuran. The thick-
from channelling problems that are typically observed ness of the EVOH-MCFs was 0.6 mm, their width was
in packed bed systems. Due to the small capillary di- 6.9 mm and they had a mean capillary diameter of
ameters, the microreactor also offers a uniform tem- 146 mm. For these diameters, and the chosen process
perature profile[25] giving a fast thermal response and flow rates, the flow within each capillary is laminar.[25]
consequently facile control over its temperature.
Lengths of MCF were coiled in a double spiral con-
figuration to form reusable reactor cartridges, termed
microcapillary flow discs (MFDs).[16] These discs had
a capillary length of 10 to 15 m with an associated re-
action volume of 3.2 to 4.8 mL. They proved suitable
to carry out liquid-phase organic synthesis enabling
reaction times of between a few minutes and several
Results and Discussion
Preparation of Palladium-Microcapillary Reactors
The disc-shaped microreactors[16] were fabricated hours. The double spiral configuration allows for both
from a flat polymer film in which arrays of parallel the inlet and outlet of the reactor to be positioned on
capillaries are embedded; this structure, termed mi- the outer edge of the MFD. The reaction mixture
crocapillary film (MCF), is manufactured by a poly- enters the disc tangentially at the circumference, pro-
mer extrusion process, which is described in detail in gresses concentrically to the centre and subsequently
previous publications.[26,27]
from the centre back to the circumference, where it
In the MCF manufacturing process, a polymer melt exits the disc at the outlet. The connection between
is extruded over an array of injectors that are placed an MFD and standard microfluidic tubing or pumping
near the exit of a rectangular die.[26] The injectors are devices was achieved using standard microfluidic fit-
connected to an air inlet at ambient conditions and tings and tubing and a highly solvent-resistant epoxy
the flow of polymer melt over the injectors causes air resin (Robnor Resins PX439XS), described in more
to be entrained into the polymer, thus forming an detail in previous work.[17,29]
array of continuous, linear capillaries. The extrudate
The surface functionalisation of MFDs was carried
leaving the die passes either through a quench bath out in four subsequent wet chemical steps under con-
or over a set of chilled rollers to solidify the polymer tinuous flow conditions. Each of these steps used a
melt. The quenched extrudate is then drawn away simple set-up whereby a premade stock solution was
from the process by means of a haul-off device. pumped through the MFD via an HPLC pump
Changing the quench and haul-off conditions enables (Knauer Smartline 100), in either a single pass or a
the capillary diameters and film dimensions to be al- recycling loop procedure. In the first of these steps,
tered by a significant amount. For the work reported 1M sodium hydroxide (NaOH) solution was recycled
below, MCFs were extruded from ethylene-vinyl alco- in a loop for several hours. This was to ensure that
hol (EVAL F101B, vinyl alcohol content: 68%)[28] at the hydroxy groups were fully unmasked and the
standard extrusion conditions. EVOH is a copolymer polymer would reach its maximum functionalistion
containing pendant hydroxy groups which can be potential. After this initial conditioning step, the disc
used for post-extrusion surface functionalisation was treated with a solution of N-trimethoxysilylprop-
(Figure 1).
yl-N,N,N-trimethylammonium chloride. Here the disc
The selected resin contains a high ethylene content was heated to 408C for 3 h using a reactor heater
such that it remains resistant to polar solvents, unlike system (Cambridge Disc Microreactor, Lamina Di-
Figure 1. Wall surface functionalisation of microcapillaries inside EVOH-MFDs; right: general reaction scheme; left: sche-
matic drawing of functionalised capillary.
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Scheme 1. Wall surface functionalisation of microcapillaries inside EVOH-MFDs in four preparation steps.
ACHTUNGTRENNUNG
electrics),[30] while the solution was recycled through preparation sequence starting from the conditioning
the disc. Afterwards an aqueous solution of Na2PdCl4 step with NaOH, the third sample was prepared only
was pumped through the disc followed by an aqueous with Na2PdCl4 solution and NaBH4. This comparative
solution of NaBH4, both in a single pass. The Pd(II) experiment was conducted in order to investigate the
salt was trapped onto the polymer surface via anion effect of the silane ion exchange surface capping on
exchange at the silyl linker, and subsequent treatment the respective capturing of Na2PdCl4. As can be seen,
with NaBH4 reduced it to form a Pd(0) precipitate, the first two samples have a ~9 times higher Pd load-
which immediately coloured the MFD black. Similar ing, which leads to the conclusion that the Pd salt is
procedures, stabilising Pd particles with quaternary mainly immobilised on the surface via the proposed
ammonium salts have been reported by Reetz anion exchange mechanism. Control experiments with
et al.[31,32] All steps except the silylation step were car- untreated MCFs established a value of 0.06 mg Pd/g
ried out at room temperature and were followed by a MCF. When comparing the first two samples, which
short washing protocol. This procedure presents a have identical preparation protocols, but differ in the
modification of previous protocols,[11,18] which were MCF section that was analysed, it can be concluded
used for the immobilisation of Pd on monolithic struc- that the coating shows non-uniformity over the cross
tures.
section of the MCF. The first sample consisted of a
Scheme 1 shows the preparation sequence from the short strip of MCF containing all 19 channels, the
untreated EVOH disc to the catalytically active Pd second sample was taken from the central section
microreactor. Figure 2 shows a microscope image of only (middle 11 channels; see Table 1). As the central
an MCF cross section, a side view of a typical MCF, channels in most MCF extrudates are slightly larger
an MCF connector and MFDs before and after Pd than the outer ones (mean capillary variation 5.6%),
coating.
they also experience a higher flow rate fraction.[25]
Consequently, more Pd is deposited in the central ca-
pillaries compared to the outer capillaries, although
the difference is small. Based on these results, the
total amount of Pd per disc equates to 0.31–0.47 mg.
Light microscope images were taken of MCF cross
Characterisation of Pd-Microcapillary Reactors
A series of analysis methods were used in order to
characterise the Pd coating on the channel walls as sections before and after Pd coating; these are shown
well as the durability and usability of the polymer in Figure 3.
disc for continuous flow catalytic processes.
The image after treatment with Pd (Figure 3, right)
Initially, the amount of Pd per gram or metre of mi- distinctly shows a dark brown ring originating at the
crocapillary film was determined by inductively cou- capillary wall and diffusing into the surrounding plas-
pled plasma mass spectroscopy (ICP-MS); these re- tic. At closer inspection, it was confirmed that the in-
sults are shown in Table 1. For this analysis, small tensity of the colouration is at a maximum at the ca-
strips of MCF were first dissolved in concentrated pillary wall and gradually drops with distance. The ap-
nitric acid and the solutions obtained were subse- parent width of this ring was measured to be 30 to
quently diluted with water (Milli-Q) prior to the spec- 38 mm. It was observed that the intensity of these
troscopy measurements.
rings was not uniform across the 19 capillaries in the
The results derived from the three MCF samples cross section, with the central capillaries being stained
prepared under different conditions are interesting. darker than those situated at the edges (see discussion
Whilst the first two samples underwent the entire above).
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A Palladium Wall Coated Microcapillary Reactor for Use in Continuous Flow Transfer Hydrogenation
Figure 2. a) Microscope image of an MCF cross section made from EVOH, containing 19 capillaries; b) side view of a single
length of MCF; c) MCF connector components; d) EVOH-MFD before and e) after functionalisation and reduction to
Pd(0).
Table 1. Pd content in MCF extrudate determined by ICP-MS, samples prepared with different protocols.
Sample
NaOH/silane/Pd/NaBH4 all channels[a] NaOH/silane/Pd/NaBH4 MCF centre[b] Pd/NaBH4 all channels[a]
mg Pd/g MCF
mg Pd/m MCF 30.89
8.01
8.38
32.33
0.91
3.53
[a]
Sample consisted of short MCF strip containing all 19 channels:
.
[b]
Sample taken from central section of short MCF strip, discarding outer four channels at each side:
.
Scanning electron microscopy (SEM) was used to mal image quality, a series of MCF samples (before
investigate the surface morphology of the capillary and after Pd loading) were prepared with gold sputter
walls and detect the location of Pd deposits. For opti- coating; for energy dispersive X-ray spectroscopy
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Figure 3. Light microscope images of EVOH-MCF channels before (left) and after (right) Pd-coating.
(EDS) MCF samples were prepared with a carbon
The images taken of the untreated sample show a
coating. Before the sputter process, both sample sets uniformly smooth capillary wall surface (Figure 4 a
were prepared by freeze fracturing, which enabled mi- and c), while the Pd-EVOH sample shows irregulari-
croscope access to the channel walls. Hereby, a small ties and a different wall surface morphology (Figure 4
section of MCF was dipped into liquid nitrogen fol- b and d). Larger sections of the capillary wall appear
lowed by fracturing on a solid metal block while to have undergone a leaching process where parts of
frozen. The aim was to split the sample at a fracture the polymer have been either displaced or certain
plane with a short angle with respect to the centre voiding has occurred (Figure 4 b). These areas are be-
line of the channels, such that the electron beam lieved to have contained amorphous phases which
could be focused on the capillary wall. Figure 4 shows have been attacked by one or several of the stock sol-
a selection of SEM images of the gold coated samples utions used during preparation. Interestingly, it was
at two different magnifications (top and bottom row), observed that following treatment with NaOH and
one before (left column) and one after (right column) the silane solution at 408C, the MCF became notice-
Pd treatment.
ACHTUNGTRENaNUGN bly softer. However, this softening did not noticeably
Figure 4. SEM images of EVOH-MCF before (a and c) and after (b and d) Pd loading, low magnification (a and b) and high
magnification of channel wall surface (c and d).
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A Palladium Wall Coated Microcapillary Reactor for Use in Continuous Flow Transfer Hydrogenation
affect the systemꢁs overall structural integrity. The mer matrix. This can be rationalised through the dif-
images of the channel wall at high magnification show fusive nature of the polymer composite that allows
small hairline cracks and deposits on the polymer sur- the priming solutions of activators and then palladium
face (Figure 4 d) after Pd loading, whilst before, the to permeate to a certain extent into the resin struc-
surface appears regular and homogeneous (Figure 4 ture. Furthermore, it would appear that the coating
c). It would appear that the chemical treatment does process results in some non-uniformity along the
change the capillary wall surface and results in small length of the capillaries as well as the cross section of
cracks in the nanometre range as well as larger irregu- the MCF capillaries. This can also be explained in
lar areas. It was not possible to determine the size of terms of the effective residence time and resulting ex-
Pd particles deposited on the channel walls from posure of each section of the capillary to the reacting
these SEM images, however, the relatively uniform solutions.
channel wall surface after coating and the absence of
Melting point experiments of untreated EVOH-
larger metallic deposits suggests that the particles are MCF on a Perkin–Elmer Pyres-1 differential scanning
in the nanometre range. This agrees with the litera- calorimeter (DSC) were carried out in order to inves-
ture, such as Nikbin et al., 2007 (particle size: 5 to tigate the stability of the polymer, EVAL F101B at
50 nm)[18] or Mennecke et al., 2008 (particle size: 1 to elevated temperatures (Figure 6). This information
10 nm),[15] where similar depositing procedures have was important as initial flow experiments at 80 to
been applied. Both these systems are based on poly- 1008C resulted in softening of the polymer and burst-
mer monoliths which enabled the observation of the ing of the capillaries (see Experimental Section).
Pd particles using transmission electron microscopy
(TEM), which could not be adopted in the same way and cooling (lower) curves for an untreated EVOH-
for our polymer capillary system. MCF sample between 50 and 2508C. It can be ob-
Figure 5 shows a typical spectrum taken from SEM- served that the main melting region lies in the area of
EDS experiments with carbon coated samples. 1878C, which agrees well with the manufacturer infor-
The graph in Figure 6 shows the heating (upper)
This spectrum shown in Figure 5 was taken at the mation of 1838C.[28] However, a small peak can also
capillary wall surface and indicates the presence of Pd be observed around 1258C, which could correspond
and chloride next to strong carbon and oxygen signals, to a secondary melting region. This behaviour can be
which result from the EVOH polymer. The signal in- explained by the copolymeric nature of EVOH, which
tensity varied between the channels with maximum is polymerised from two different monomers: ethyl-
values of up to 5 wt% for Pd and 8 wt% for chloride. ene and vinyl alcohol. Previous experiments with
The chloride residues remain from the synthesis of polyethylene MFDs (LLDPE NG5056E), which have
the Pd-MFDs introduced from the silane and a melting region around 1208C (similar to the ob-
Na2PdCl4. In some spectra, an additional signal for served secondary melting region of EVOH), have
low levels of sodium (Na) could also be detected. A shown softening at relatively low temperatures of 60
total of 49 spectra at different positions over several to 708C when in contact with organic solvents. A
channels were taken and in 70% of them Pd was de- small irregularity in the heating curve of EVOH at
tected, while control samples before functionalistion
did not show any Pd signals.
In summary, the results obtained from SEM-EDS,
ICP-MS and light microscopy indicate that Pd is de-
posited on the microcapillary wall surface and also
penetrates to some extent into the surrounding poly-
Figure 6. Differential scanning calorimetry results of un-
treated EVOH-MCF showing main (1878C) and secondary
Figure 5. SEM-EDS spectrum of the capillary wall surface in
a Pd-coated EVOH-MCF.
(1258C) melting regent.
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668C can also be seen. These observations lead to the fully carried out, including the reduction of carbonyl
conclusion that the ethylene content of EVOH results groups to alcohols, imines and nitro-groups to amines,
in a softening of the polymer around 60 to 708C, as well as carbon-carbon double and triple bonds.
which is significantly lower than the melting point of Figure 7 shows the experimental set-up and the gener-
1838C, and was not expected initially. Consequently, al reaction scheme using the example of a carbonyl
reaction systems at lower temperatures were investi- reduction, while Table 2 lists several reaction exam-
gated.
ples together with the corresponding conversions.
Products 3a to 3d were obtained with high conver-
sions of greater than 95%. Substrate 1f, which con-
tained both a carbon-carbon double bond and a car-
bonyl group, resulted in a mixture of two products,
Pd-Catalysed Transfer Hydrogenation
Transfer hydrogenations are commonly used in organ- namely the fully reduced alcohol 3g and the partially
ic synthesis[33] as well as in industrial processes, where reduced aldehyde 3f. Using pure MeOH as solvent,
the use of gaseous hydrogen (H2) is undesirable either the double-bond reduction had a conversion of 93%
because of inconvenience, safety or cost. A large- and the carbonyl reduction 75%. No partially reduced
scale example is coal liquefaction using hydrogen alcohol was detected and the remaining 7% were re-
donor solvents such as tetralin.[34] In this paper, a turned as unreacted starting material. Substrate 1e
transfer hydrogenation using triethylsilane as the hy- showed a poor solubility in pure MeOH, and thus sol-
drogen donor was chosen, as this can be carried out vent mixtures with isopropyl alcohol (i-PrOH) or tol-
at room temperature. This case study was based on uene were used in higher dilutions than the other sub-
work by Mandal and McMurray, who used a palladi- strates. The observed lower conversions are believed
um on charcoal catalyst in suspension in batch reduc- to be a result of the solvent mixture rather than the
tion reactions.[35]
inherent activity of the substrate. The range of differ-
A simple experimental configuration was used to ent substrates shows the versatility of the reactor
perform this reaction at room temperature, whereby a system and its efficiency for heterogeneous catalytic
solution of 0.5 to 2 mmol substrate (1) and 10 equiva- reactions. Leaching of Pd during reaction was mini-
lents of triethylsilane (2) in methanol (MeOH) was mal as any amount of catalyst in the product was
pumped via an HPLC pump through the reactor at below the detection limit for the investigated reaction
0.1 mLminÀ1 in a single pass (see Figure 7). Upon scale (0.5 to 2 mmol of substrate). Furthermore, the
first entry of substrate into the microcapillaries, for- reactor discs could be used several times without a
mation of small gas bubbles was noticed, which in- noticeable loss of catalytic activity. The reduction of
creased over time to a fully developed gas-liquid slug 1e after ten repeated reactions in the same disc
flow at steady-state conditions. The formation of gas- showed similar conversion (~3% less) when com-
eous H2 during the reaction, resulting in a two phase pared to a fresh disc.
flow, was believed to be beneficial for mixing inside
A detailed description of the reaction protocol is
the capillaries, thus ensuring that the reaction mixture given in the Experimental Section for one example,
was in good contact with the catalytic wall. With this namely the reduction of acetophenone (1a) to 1-phe-
procedure, a series of reduction reactions was success- nylethanol (3a).
Figure 7. Flow diagram and reaction scheme of transfer hydrogenation reactions in Pd-MFDs, using an HPLC pump.
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A Palladium Wall Coated Microcapillary Reactor for Use in Continuous Flow Transfer Hydrogenation
Table 2. Transfer hydrogenation in Pd-MFDs using triethyl-
tent quantified to be 31 mg Pd/m MCF by ICP-MS. It
would appear that this value is higher than the theo-
retical estimation for a Pd monolayer on the surface.
Coated EVOH also appears to have nano-cracks and
there is some evidence pointing towards Pd penetrat-
ing into the polymer support.
silane.[a]
We anticipate that, with similar experimental proto-
cols, it should be possible to immobilise other catalyti-
cally active transition metals such as gold, nickel or
copper onto MFD microcapillary walls. The upper
temperature limit of EVOH of around 60 to 708C
however, confines the range of applications of discs
made from this particular polymer. So far, MCFs
have been extruded from a wide range of different
thermoplastic polymers, including highly solvent- and
temperature-resistant fluorinated polymers.[17,30] These
extrudates easily withstand temperatures of 1508C
but cannot be functionalised in the same way as
EVOH. Future work will be dedicated to finding a
melt-extrudable polymer, which combines both the
ability to immobilise catalytic materials or other func-
tional groups and high thermal stability.
From the proof of principle reactions carried out
inside Pd-MFDs, using triethylsilane in MeOH as the
hydrogen source, it can be concluded that the catalyt-
ic Pd layer inside the microchannels is active enough
to yield excellent conversions at a reaction time of
30 min at room temperature. The gaseous hydrogen
produced during the reaction results in a two phase
gas-liquid flow inside the reactor, which is believed to
be beneficial for mixing inside the capillaries, thus en-
suring that the reaction mixture is in good contact
with the catalytic wall.
Compared to polymeric monolith structures or
packed bed columns using polymer beads, microchan-
nels with catalytic wall coatings have well defined
flow geometries, which simplifies model predictions of
fluid mechanics and heat and mass transfer processes
inside the reactor and additionally results in a poten-
tially lower pressure drop along the channel, depend-
ing on its diameter. We believe that microscale cata-
lytic wall reactors that offer a high enough catalytic
[a]
1
Conversions measured by H NMR.
Conclusions
This paper reports the preparation and evaluation of activity combined with a practical channel diameter,
novel plastic continuous flow microreactors for where diffusion lengths are minimal and convective
heteroACHTUNGTRENNUNGgeneous catalysis reactions at temperatures typ- mass transport through the channel is fast and unhin-
ically below 608C. By performing a transfer hydroge- dered, such as coated MFDs, can provide a superior
nation with Pd(0) immobilised on the capillary walls reaction environment for many heterogeneous cata-
of the disc-shaped microreactor, we demonstrated lytic reactions.
that coated microcapillary flow discs (MFDs) can be
used as reusable reactors. Each MFD was composed
of 19 parallel channels with a mean diameter of
Experimental Section
146 mm and a length of between 10 and 15 m. The
discs were manufactured from ethylene-vinyl alcohol
(EVOH) and functionalised by a series of four wet
chemical steps, resulting in a catalytic Pd coating at
the channel wall surface. The Pd coating was charac-
General Remarks
Initially we attempted to perform cross-coupling reactions
at elevated temperatures inside the Pd microcapillary reac-
terised by light and electron microscopy and its con- tors as proof of principle. First a Sonogashira-type coupling
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using benzoyl chloride and phenylacetylene at 1008C and
then a Suzuki–Miyaura coupling using 4-(methoxycarbonyl)-
phenylboronic acid and benzylbromide at 808C were investi-
gated. Unfortunately, both reactions failed owing to insuffi-
cient stability of the polymer, as channels started to buckle
and burst at the bespoke temperatures. These findings were
unexpected as the polymer used (EVAL F101B), has a de-
fined literature melting point of 1838C,[28] and so we had ini-
tially estimated the discs to be stable up to at least 100 or
1208C. Consequently, melting point experiments of EVOH-
MCFs on a differential scanning calorimeter (DSC) were
carried out (see Figure 6). These experiments enabled us to
develop a better feel for stable reaction conditions using this
polymer.
Acknowledgements
We thank the BP endowment (to SVL), the Royal Society (to
IRB) and EPSRC (to CHH) for generous financial support,
and Dr Martyn Twigg, Chief Scientist, Johnson Matthey, Roy-
ston for useful discussions.
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Firstly 50 mL of 1M aqueous NaOH solution were recycled
through the disc in a loop for 4 to 12 h at room temperature
and a flow rate of 0.5 mLminÀ1, followed by a wash with
water at 0.5 mLminÀ1 for 30 min. Then, a solution of
1029 mg N-trimethoxysilylpropyl-N,N,N-trimethylammoni-
um chloride in 30 mL acetonitrile (MeCN) and 10 mL water
at a pH between 1 and 2 was recycled through the MFD in
a loop at 0.5 mLminÀ1 and 408C for 3 h, followed by a wash
with MeCN at room temperature and 0.5 mLminÀ1 for
20 min and a wash with water at room temperature and
0.5 mLminÀ1 for 30 min. Afterwards, an aqueous solution of
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a single pass at room temperature and
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single pass at 0.3 mLminÀ1. Finally, the disc was washed
with copious amounts of water, then 20 mL of 1M aqueous
HCl solution and 20 mL of MeOH.
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