Mild synthesis of mesoporous silica supported ruthenium nanoparticles as heterogeneous catalysts in oxidative Wittig coupling reactions

Article abstract of DOI:10.1039/c3cy00773a

A new efficient approach for the in situ synthesis of anchored ruthenium nanoparticles (RuNP) in three different kinds of mesoporous silica materials, MCM-41, SBA-15 and HMS, has been developed. Solids have been synthesized under very mild conditions from RuCl₃·H₂O salt reduced in one hour at room temperature in the mesoporous silicas previously grafted with aminopropyltriethoxysilane (APTES). Well-dispersed ruthenium nanoparticles, with an average size of 3 nm, anchored into the silica network by the APTES were obtained. These materials, with a molar ratio of Si/Ru = 40, were found to be catalytically active and selective in the alcohol oxidation-Wittig olefination. Interestingly, while the reaction occurs from the alcohol, control experiments suggest that the aldehyde (the common Wittig substrate) is not involved. The Royal Society of Chemistry.

Full text of DOI:10.1039/c3cy00773a

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Mild synthesis of mesoporous silica supported
ruthenium nanoparticles as heterogeneous
catalysts in oxidative Wittig coupling reactions†
a
Cite this: Catal. Sci. Technol., 2014,
4, 435
Adela I. Carrillo,a Luciana C. Schmidt,a M. Luisa Marínab and Juan C. Scaiano
*
A new efficient approach for the in situ synthesis of anchored ruthenium nanoparticles (RuNP) in
three different kinds of mesoporous silica materials, MCM-41, SBA-15 and HMS, has been developed.
Solids have been synthesized under very mild conditions from RuCl3·H2O salt reduced in one hour
at room temperature in the mesoporous silicas previously grafted with aminopropyltriethoxysilane
(APTES). Well-dispersed ruthenium nanoparticles, with an average size of 3 nm, anchored into the silica
network by the APTES were obtained. These materials, with a molar ratio of Si/Ru = 40, were found
to be catalytically active and selective in the alcohol oxidation–Wittig olefination. Interestingly, while
the reaction occurs from the alcohol, control experiments suggest that the aldehyde (the common
Wittig substrate) is not involved.
Received 4th October 2013,
Accepted 4th November 2013
DOI: 10.1039/c3cy00773a
www.rsc.org/catalysis
reaction media, potentially leading to a decrease in the
catalytic activity of the material. To overcome this issue,
Introduction
The development of sustainable routes for the large scale pro-
duction of fine chemicals, i.e., cost-effective and environmen-
tally friendly, is one of the major current concerns at the
industrial level.1 The use of supported metal nanoparticles
allows the combination of increased efficiency from nanopar-
ticle catalysts, with the advantages of heterogeneous supports,
leading to a ‘green catalytic process’, with higher selectivity
and conversion and easy catalyst recovery.2
The design of the catalyst is the key step in the develop-
ment of a sustainable catalytic reaction. Among the most cru-
cial issues in the preparation of a nanocatalyst is avoiding
agglomeration of the nanoparticles as well as leaching from
the active sites of the support; this can be achieved by
anchoring the nanoparticles to the support surface.
Mesoporous silicas such as MCM-41 are attractive catalyst
supports because they present high surface areas where the
active sites can be highly dispersed. Different strategies have
been successfully employed to introduce catalytic active sites
into mesoporous silicas including ion exchange, chemical
vapor deposition or impregnation.3,4 However, the interaction
between the active site and the support is frequently very
weak. This may cause leaching of the active sites into the
more recently co-condensation or chemical grafting methods
to covalently bond the active species into mesoporous
materials are being reported. For example, the
co-condensation method has been used to incorporate palla-
dium nanoparticles into a silica matrix by functionalizing the
nanoparticles with alkoxysilanes and then co-polymerizing
them with tetraethoxysilanes in the presence of cationic
surfactants via base-catalyzed hydrolysis.5 Recently, the
synthesis of a hybrid mesoporous material with a molybde-
num complex covalently attached was reported6 by using
either post synthesis grafting or co-condensation approaches.
Supported ruthenium catalysts, mostly obtained by
impregnation, have emerged as a new family of versatile
catalysts for different chemical reactions. In fact, they have
been employed in industrial processes for the synthesis of paraf-
fins,7 methanation of CO8 or in the hydrogenation of benzene
to cyclohexane.9 Supported ruthenium nanoparticles (SRuNP)
have been found to have very good catalytic activity towards the
synthesis of ammonia10 or hydrogenation of monoaromatics.11
In the present work, we take advantage of the activity of
RuNP and mesoporous silica to prepare three new hybrid
materials and explore their catalytic properties. The one-pot
alcohol oxidation–Wittig reaction producing α,β-unsaturated
esters was chosen to test the catalytic activity of the materials
as it is the most commonly used method for the synthesis of
alkenes12 and a process where catalytic routes would be
important.13 The new materials showed good catalytic activity
in the Wittig olefination of benzyl alcohols.14 The most inter-
esting point was that reaction occurs without the intermediacy
a Department of Chemistry and Centre for Catalysis Research and Innovation,
University of Ottawa, 10 Marie Curie, Ottawa, K1N 6N5, Canada.
E-mail: scaiano@photo.chem.uottawa.ca
b Instituto Universitario Mixto de Tecnología Química (UPV-CSIC), Universitat
Politècnica de València. Avenida de los Naranjos s/n, 46022 Valencia, Spain
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
c3cy00773a
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of free aldehyde and with a high selectivity for the E product.
These new solids have been prepared by initially grafting
APTES onto the surface of MCM-41, SBA-15 or HMS type silicas.
Then aqueous RuCl3 was stirred in the presence of the solids
leading to covalently bonded RuNP that were fully character-
ized by BET surface area, pore size distribution, X-ray diffrac-
tion (XRD), transmission electron microscopy (TEM), X-ray
photoelectron spectroscopy (XPS) and inductively coupled
plasma mass spectrometry (ICP).
Experimental
Most of the experimental details are supplied as ESI,† with
only a few key details included here.
Preparation of SRuNP
First, 1.5 g of mesoporous silica solid, MCM-41,6 SBA-1515 or
HMS16 (prepared according to already published methods,
see more details in the ESI†) was dehydrated in an oven at
473 K for 2 h. Then, 50 mL of anhydrous toluene was added
to the activated materials and this mixture was stirred for 1 h
in order to obtain a homogeneous dispersion followed by the
addition of 0.5 mL APTES and refluxed overnight. Finally, the
white solid (silica–APTES) obtained was filtered, washed with
fresh toluene and acetone and air-dried.
Second, ruthenium chloride (RuCl3·xH2O, 9 mg) was
added to an aqueous mixture (110 mL) of the corresponding
silica–APTES material (1.5 g). After stirring for 1 h at room
temperature, the grey solids obtained were filtered and
washed several times with water to remove the unreacted salt.
The air-dried new SRuNP (2.3–2.5 wt% Ru, ICP determined)
were denoted as Ru@MCM, Ru@SBA and Ru@HMS.
Fig. 1 Low angle XRD patterns of pure silicas: MCM-41 (top), SBA-15
(middle) and HMS (bottom) and their corresponding SRuNP materials.
Catalysis tests
The catalysis tests were performed using the new mesoporous
mesostructure was shown.16 Fig. 2 also reveals that RuNP are
confined and highly dispersed into the channels of the
mesoporous silica and confirms that these materials main-
tain the 2D-hexagonal mesopore arrangement of the pure
MCM-41. The SBA-15 family of materials showed three well-
defined peaks at 2θ values between 1 and 8° (Fig. 1, middle)
that can be indexed as (100), (110) and (200) Bragg reflec-
tions, typical of hexagonal (p6mm) SBA-15.18 In these mate-
rials, both the intensity and resolution of the peaks are not
decreased by anchoring RuNP, probably because the size
of the RuNP (ca. 3 nm) does not affect the pores of SBA-15
silica materials. Typically,
a mixture of benzyl alcohol
(0.1 mL, 1.0 mmol), methyl (triphenylphosphoranylidene)acetate
(334 mg, 1.0 mmol) and 50 mg of SRuNP (1.2 mol% Ru) in
2 mL of toluene was stirred for 24 h at 80 °C under an oxygen
atmosphere. The yields were determined by GC–MS after filtra-
tion and addition of 1,1′-binaphthyl as an internal standard.
Results
Catalyst characterization
Fig. 1 compares the X-ray diffraction patterns of MCM-41, SBA-15
and HMS before and after their functionalization with anchored
RuNP. In the patterns of MCM-41 type materials (Fig. 1, top), a
dominant (100) peak with small (110) and (200) reflections is
normally attributed to the 2D-hexagonal structure (p6mm).17
Aminosilane grafting into MCM-41 and further incorporation
of RuNP caused a considerable decrease in the XRD intensity.
TEM images of the SRuNP are shown in Fig. 2. Ru@MCM
and Ru@SBA reveal the hexagonal mesoporous arrangement
typical for these materials, even after incorporation of RuNP,
while in the case of Ru@HMS a disordered and wormhole
Fig. 2 TEM images of the hybrid materials Ru@MCM (left), Ru@SBA
(center) and Ru@HMS (right).
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(ca. 9 nm). HMS and Ru@HMS patterns show a single low-angle
diffraction peak characteristic of a wormhole framework.19
The new hybrid materials exhibited type IV isotherms with
a distinctive nitrogen uptake due to the capillary condensa-
tion of nitrogen inside the mesopores (Fig. 3).3 Further, each
material showed its characteristic features; for instance,
MCM-41 solids showed a sharp increase in the adsorbed vol-
ume at P/P0 = 0.2–0.4 because of the 2–3 nm diameter
pores.20 Otherwise, SBA-15 type materials showed an abrupt
step at higher relative pressures (P/P0 = 0.6–0.8) as expected
for bigger pore size silicas.18 Finally, HMS solids did not
show an abrupt step in their isotherm profiles due to the
broad pore size distributions.3 Table 1 summarizes BJH pore
size distributions calculated from the adsorption branches of
the isotherms and BET surface areas of the new solids.
As expected, in all cases both the pore diameter and the sur-
face area decreased after the incorporation of the anchored
RuNP into the mesopores.
Additional efforts were made to characterize the oxidation
state of the SRuNP. Since the XRD experiments were incon-
clusive, XPS was performed on the all new materials, includ-
ing the MCM–APTES that was used as the standard. According
to the XPS spectra (Fig. 4) (Ru 3d5/2 at 280.4 eV, and Ru 3p3/2
at 462.0 eV, respectively), the ruthenium particles were at least
partially in a zero oxidation state in accordance with the litera-
ture, although other states are also likely to be found.21
ester methyl cinnamate (Scheme 1). This suggests that, in con-
trast with the literature example, our catalysts can yield Wittig
products without free aldehyde mediation.
The reaction does not occur without using SRuNP (Table 2,
entry 1) or when only the support is used as the catalyst
(Table 2, entry 2). In a control experiment, the reaction was
performed using aldehyde, instead of alcohol. This reaction
was essentially complete after 3 h at 80 °C (1 mmol benzalde-
hyde, 1 mmol ylide and 1.2% mol Ru@MCM under O2); not
surprisingly the catalyst is not required when the reagent is
the aldehyde.
The effects of organic solvent, temperature, time of reac-
tion, atmosphere, and Ru% on yield and stereoselectivity
were investigated using Ru@MCM, as shown in Table 2.
Higher conversions were obtained when non-polar sol-
vents such as toluene and CCl4 were used. Very low yield was
obtained when DMF was used (Table 2, entry 5). While using
THF, no conversion was achieved even under reflux for 18 h
(Table 2, entry 6). Increasing the temperature from 80 to 110 °C
did not result in an increase in the conversion (Table 2,
entries 4 and 7). When the reaction was performed under air,
the byproduct benzyl cinnamate was obtained together with a
similar yield of the desired methyl cinnamate (Table 2, entry 9),
whereas, under N2, very little reaction was observed even after
increasing the temperature (Table 2, entry 8). When the percent-
age of Ru was increased up to 1.2% the conversion enhanced
up to 70% after 24 h; nevertheless, quantitative conversion
could be obtained after 48 h (Table 2, entries 10 and 11).
From the data in Table 2, the reaction leads always to the
E-methyl cinnamate as the preferred isomer. Further, in
order to evaluate the scope of this reaction, different primary
alcohols were used as shown in Table 3.
Finally, the nature of the silica support as well as the recy-
clability in the reaction of the benzyl alcohol with methyl
(triphenylphosphoranylidene)acetate was tested (Table 4).
MCM-41 and SBA-15 type silica showed the same conversion.
Nevertheless, Ru@MCM material was more selective toward
the E-methyl cinnamate isomer. This may reflect the smaller
pore size of the MCM type silica, i.e., 3 nm, against the 9 nm
pore size of the SBA-15 type silica. Moreover, HMS solids
showed lower conversions due to their porosity disorder.
With regard to the recyclability, all the catalysts conserved
50%–60% of their original activity upon second use (Table 4).
Although the mechanism of the alcohol oxidation–Wittig
olefination has not been investigated in detail in the
absence of the methyl (triphenylphosphoranylidene)acetate,
the benzaldehyde was not detected when the reaction of the
catalyst and alcohol was attempted. On the other hand, as
expected, the reaction between the aldehyde and the methyl
(triphenylphosphoranylidene)acetate proceeded without the
presence of the catalyst (vide supra).
Catalytic activity: alcohol oxidation–Wittig olefination
Embedded ruthenium nanoparticles in aluminum oxyhydroxide
have been reported as catalysts for the one-pot alcohol oxida-
tion–Wittig reaction producing α,β-unsaturated esters.14 In
this report, the overall reaction is mediated by the aldehyde.
This reaction was selected as a test to evaluate the activity of
the new catalysts.
Interestingly, we were unable to oxidize benzyl alcohol to
benzaldehyde using SRuNP in toluene at 80 °C under an oxy-
gen atmosphere (with or without added Ph3PO); however, in
the presence of methyl (triphenylphosphoranylidene)acetate, the
reaction proceeded with the formation of the α,β-unsaturated
Discussion
Metal nanoparticles are usually prepared by reduction of the
aqueous salt in the presence of a protective agent to prevent
Fig. 3 Nitrogen adsorption–desorption isotherms of the synthesized
materials: MCM-41, Ru@MCM, SBA-15, Ru@SBA, HMS, and Ru@HMS.
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Table 1 Textural properties and ruthenium loading of the new catalysts
dBpJH,a (nm)
ABET (m2 g−1
)
VBpJH,c (cc g−1
)
Metal loading wt%d
b
Sample
MCM-41
Ru@MCM
SBA-15
Ru@SBA
HMS
3.0
2.4
9.0
8.7
2.0
2.0–4.0
995
740
785
430
700
190
1.1
0.7
1.2
0.8
0.7
0.4
—
2.3
—
2.5
—
2.3
Ru@HMS
a
b
Average mesopore diameters were estimated from the adsorption branch of the nitrogen isotherm using the BJH method. The BET surface
c
area was estimated by multipoint BET method using the adsorption data in the relative pressure (P/P0) range of 0.05–0.30. Mesopore volume
from the isotherms at the relative pressure of 0.8. Ruthenium amount determined by ICP analysis.
d
Table
3 Reaction of different primary alcohols with methyl
(triphenylphosphoranylidene)acetatea
#
1
Alcohol
Product
Product yield %b E/Z ratiob
32 : 1
99
2
3
4
75
57
45
18 : 1
6 : 1
Fig. 4 XPS spectra showing the C1s, Ru 3d5/2 and Ru3p3/2 regions of
Ru@MCM (red) and MCM–APTES (green).
10 : 1
Scheme 1 Alcohol oxidation–Wittig olefination.
5
40
65
2 : 1
aggregation. Literature reports indicate that RuNP could be
obtained using polyols as reductants and PVP as stabilizer
under microwave heating22 or simply refluxing.23 On the
other hand, amines have been reported as useful reducing
agents in the formation of AuNPs from HAuCl4, acting also
as protecting agents.24 Here, we have demonstrated that the
two concepts can be applied to the synthesis of new hybrid
heterogeneous materials based on RuNP. In fact, APTES
anchored to the surface of MCM-41, SBA-15 or HMS silicas
acted as both a reducing and protecting agent. The developed
6
—
a
Primary
alcohol
(0.1
mL,
1.0
mmol),
methyl
(triphenylphosphoranylidene)acetate (334 mg, 1.0 mmol) and 1.2 mol%
of Ru@MCM in 2 mL of toluene, under an oxygen atmosphere for 24 h.
b
The product yields were determined by gas chromatography using
1,1′-binaphthyl as internal standard, error <5%.
Table 2 Reaction of benzyl alcohol with methyl (triphenylphosphoranylidene)acetatea
#
Catalyst (mol%)
Solvent
Conditions time
Conv.b (%)
Product yieldc (%)
E/Z ratiod
1
2
3
4
5
6
7
8
None
MCM–APTES
Toluene
Toluene
CCl4
Toluene
DMF
80 °C, O2/18 h
80 °C, O2/18 h
80 °C, O2/18 h
80 °C, O2/18 h
80 °C, O2/18 h
Reflux/18 h
110 °C, O2/18 h
110 °C, N2/18 h
80 °C, air/18 h
80 °C, O2/24 h
80 °C, O2/48 h
0
0
32
49
12
0
34
10
48
70
100
—
—
27
49
12
—
31
—
—
0.4
0.4
0.4
0.4
0.4
0.4
0.4
1.2
1.2
Not quantified
11 : 1
11 : 1
—
10 : 1
Not quantified
11 : 1
17 : 1
THF
Toluene
Toluene
Toluene
Toluene
Toluene
Not quantified
9
10
11
40d
61
81
16 : 1
a
Benzyl alcohol (0.1 mL, 1.0 mmol), methyl (triphenylphosphoranylidene)acetate (334 mg, 1.0 mmol) and the state amount of Ru@MCM in
b
c
2 mL of solvent. Quantification of unreacted benzyl alcohol. The product methyl cinnamate was determined by GC using 1,1′-binaphthyl as
the internal standard, error <5%. d Together with benzyl cinnamate product of transesterification.
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Table 4 Recyclability of SRuNP in the reaction of the benzyl alcohol
with methyl (triphenylphosphoranylidene)acetate
From the data shown in Table 2, the reaction leads always
to the E-methyl cinnamate as the preferred isomer. Higher
conversions were obtained when non-polar solvents such as
toluene and CCl4 were used. A very low yield was obtained
when DMF (Table 2, entry 5) was used. While using THF, no
conversion was achieved even under reflux for 18 h (Table 2,
entry 6). Increasing the temperature from 80 to 110 °C did
not result in an increase in the conversion (Table 2, entries 4
and 7). When the reaction was performed under air, the
byproduct benzyl cinnamate was obtained together with a
similar yield of the desired methyl cinnamate (Table 2,
entry 9), whereas under N2, almost no reaction took place,
even after increasing the temperature (Table 2, entry 8).
When the percentage of Ru was increased up to 1.2%, the
conversion increased up to 70% after 24 h; nevertheless,
quantitative conversion could be obtained after 48 h (Table 2,
entries 10 and 11). Blank experiments showed that the reac-
tion does not occur without SRuNP (Table 2, entry 1) or when
only the support was tested as a possible catalyst (Table 2,
entry 2).
Table 3 shows that the steric hindrance plays an impor-
tant role in the yield and selectivity of the reaction. The OMe
substituent was evaluated in the ortho, meta and para posi-
tions of benzyl alcohol. When the OMe substituent was in
para position, the donating effect of the substituent achieved
quantitative conversion and excellent selectivity as shown by
the E/Z ratio. However, the yield and selectivity decreased as
steric hindrance increased (Table 3, entries 2 and 3). Even
more, the very sterically hindered anthracene-9-methanol
gave the desired product in only 40% yield the E/Z ratio being
as low as 2 : 1 (Table 3, entry 5). The effect of an electron-
withdrawing group in the para position decreases the yield
and the E/Z ratio (Table 3, entry 4). In addition, in Table 3,
entry 6, the ester was obtained, but eventually the alkene was
hydrogenated to afford the saturated product, in accordance
with previous results using [Ir(COD)Cl]2.33 Table 4 showed
that MCM-41 and SBA-15 type silica showed the same conver-
sion. Nevertheless, Ru@MCM material was more selective
toward the E-methylcinnamate isomer. This may reflect the
smaller pore size of the MCM type silica, i.e., 3 nm, against
the 9 nm for SBA-15 type silica. Moreover, HMS solids
showed lower conversions presumably due to their reduced
accessible volume; it is common for metal to reduce the
available volume, but the effect of ruthenium seems to be
Catalyst
Conversion (%)
E/Z ratio
% reuse
Ru@MCM
Ru@SBA
Ru@HMS
70.0
70.0
55.0
17 : 1
11 : 1
17 : 1
50
60
60
protocol is simple and mild since stirring for just 1 hour at
room temperature was enough to reduce the Ru(III) salt and
incorporate the resulting RuNP into the mesoporous silica
solids. The properties of the materials obtained, Ru@MCM,
Ru@SBA and Ru@HMS include defined particle size and
narrow distribution.25 TEM images (Fig. 2) showed that RuNP
are embedded into the pores of the solids, thus inhibiting
the agglomeration of the nanoparticles and the subsequent
loss of activity. Incorporating the RuNP into the silica mesopores
led to the expected decrease of the surface of the final solid.
Nevertheless, 740 m2 g−1 for Ru@MCM was much higher than
the 424.7 m2 g−1 reported for the analogous heterogeneous
Ru(0) catalyst Ru/AlO(OH).26 XPS measurements performed
on the all new materials, including the MCM–APTES were con-
sistent with the presence of Ru(0). As shown in Fig. 4, the
bands at 280.4 eV and 462.0 eV can be attributed to the Ru
3d5/2 and Ru 3p3/2, respectively.21,23
Although the Wittig reaction is used worldwide as the
most common method to prepare alkenes, the mechanism
involved is still under scrutiny.12,27 In particular, ruthenium
complexes have already been reported as catalysts for the
Wittig reaction starting from alcohols through a temporarily
oxidized alcohol.28,29 On the other hand, metal nanoparticles
are not very common among the catalysts used for the one-
pot olefination starting from alcohols; in fact, only NiNPs
have been reported so far and the reaction was claimed to
proceed without a standard redox step.30,31 In this paper,
beyond preparing efficient Wittig catalysts by very mild
routes, it is worth noting that our evidence shows that the
free aldehyde does not mediate the reaction, as these cata-
lysts are unable to oxidize alcohols to the corresponding alde-
hydes. Perhaps, association of the alcohol at the ruthenium
site occurs, just as it does in the Ley–Griffith32 oxidation, but
the reaction is aborted if the Wittig reagent is not present.
The nature of the support as well as the highly dispersed
anchored RuNP may play a crucial role since embedded
RuNP in aluminum oxyhydroxide have been reported as cata-
lysts for the same reaction producing α,β-unsaturated esters
mediated by the aldehyde.14 The chemistry described here
bears some resemblance to ‘borrowing hydrogen’ type mech-
anisms;28,31,33,34 however, in this case, the aldehyde (the
product of borrowing hydrogen from an alcohol) is never iso-
lated or “free”. Further, the borrowed hydrogen is not
returned to the nascent double bond, but presumably to oxy-
gen (that is essential) to form water. The tentative mecha-
nism is depicted in Scheme 2 and shows the necessary
alcohol oxidation and the olefination as coupled processes
involving an activated alcohol on the ruthenium surface.
Scheme
2 Proposed mechanism for the alcohol oxidation–Wittig
olefination showing alcohol oxidation and olefination as coupled
processes.
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quite large compared with Fe or Co.35 With regard to the
recyclability, all the catalysts conserved 50%–60% of their
original activity upon second use.
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Conclusion
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Three new materials based on MCM-41, SBA-15 and HMS
type silica containing RuNP covalently attached to the struc-
ture have been prepared under very mild conditions; stirring
a Ru(III) salt at room temperature in the presence of the solid
grafted with APTES led to the formation of RuNP of 3 nm
average size highly dispersed into the channels of the
mesoporous silicas. The materials exhibited high catalytic
activity in the alcohol oxidation–Wittig olefination of differ-
ent benzyl alcohols. Interestingly, the reaction does not
appear to involve the intermediacy of the aldehyde, the usual
Wittig reagent.
Acknowledgements
Thanks are due to the Natural Sciences and Engineering
Council of Canada and the Canadian Foundation for Innova-
tion for their generous support. M.L. Marin thanks the
Universitat Politécnica de Valencia (Programa de Apoyo a la
Investigación y Desarrollo) for its financial support. Thanks
are due to Dr. Yun Liu for advice on XPS interpretation.
22 W. Tu and H. Liu, J. Mater. Chem., 2000, 10, 2207.
23 X. Yan, H. Liu and K. Y. Liew, J. Mater. Chem.,
2001, 11, 3387.
24 J. D. S. Newman and G. J. Blanchard, Langmuir,
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