Rapid and facile solvent-free mechanosynthesis in a cell lysis mill: Preparation and mechanochemical complexation of aminobenzoquinones

Article abstract of DOI:10.1039/c4ce00328d

A cell lysis mill, typically used for the breakdown of biological structures in microbiological and biochemical studies, was used as a tool for rapid, solvent-free and general synthesis of short- and long-chain substituted zwitterionic meta- and para-amin

Full text of DOI:10.1039/c4ce00328d

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Rapid and facile solvent-free mechanosynthesis in
a cell lysis mill: preparation and mechanochemical
complexation of aminobenzoquinones†
Cite this: CrystEngComm, 2014, 16,
7180
a
a
a
b
b
Received 15th February 2014,
Accepted 12th June 2014
*
Yuan Fang, Nadime Salamé, Simon Woo, D. Scott Bohle, Tomislav Friščić
a
*
and Louis A. Cuccia
DOI: 10.1039/c4ce00328d
www.rsc.org/crystengcomm
A cell lysis mill, typically used for the breakdown of biological
structures in microbiological and biochemical studies, was used as
a tool for rapid, solvent-free and general synthesis of short- and long-
chain substituted zwitterionic meta- and para-aminobenzoquinones,
never previously prepared under solvent-free conditions. Rapid agi-
tation and self-heating in the lysis mill enabled thermally-demanding
reactions without external solvent, providing yields comparable to
those obtained by conventional solution chemistry, ball milling
and melt chemistry. The lysis mill is also suitable for coordination-
based reactions, demonstrated by the mechanosynthesis of a
mononuclear Ni(II) meta-benzoquinonemonoimine complex.
readily form extended networks on surfaces, where their large
intrinsic dipoles allow the alteration of static dipoles on sur-
faces and the creation of conductive molecular films.10,12,13
We have recently reported the charge-assisted hydrogen
bond-directed self-assembly of an amphiphilic zwitterionic
quinonemonoimine (C18m, Scheme 1) at the liquid–solid
interface investigated using scanning tunnelling microscopy.14
Whereas the synthesis of para- and meta-aminobenzoquinones
Quinonoid compounds are ubiquitous in many areas of
chemistry and biochemistry, and stable quinonoids are
normally derived from ortho- and para-benzoquinones
(Fig. 1a, I and II, respectively).1,2 Aminobenzoquinones have
been widely explored for biological applications, especially in
medicinal chemistry due to anticancer and antimalarial
properties.3–5 The first synthesis of
a novel stable
meta-benzoquinone zwitterion (Fig. 1a, III), was reported in
2002 by the Braunstein group.6 The unique structural and
physical properties of this benzoquinonemonoimine have
attracted much attention, with X-ray structural analysis
revealing a formal zwitterion composed of two separate
charged subunits.7,8 In 2005, a simple one-pot route to III
was developed via a transamination reaction, which enabled
the introduction of diverse functionalities onto the quino-
noid core.9 The resulting quinonoids show rich organic,7
supramolecular10 and coordination chemistry,8,9,11 and
a Department of Chemistry & Biochemistry, FRQNT Center for Self-Assembled
Chemical Structures, Concordia University, 7141 Sherbrooke St. W, Montréal,
Canada H4B 1R6. E-mail: louis.cuccia@concordia.ca
b Department of Chemistry and FRQNT Center for Self-Assembled Chemical Structures
McGill University, 801 Sherbrooke St. W., Montréal, H3A 0B8, Canada.
E-mail: tomislav.friscic@mcgill.ca
† Electronic supplementary information (ESI) available: Detailed synthesis and
characterization of all compounds is described in the ESI. CCDC 1005686. For
ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/
c4ce00328d
Fig. 1 (a) Schematic representations of ortho-benzoquinone (I),
para-benzoquinone (II), and diamino-meta-benzoquinone (III) and (b) a
laboratory cell lysis mill (FastPrep®-24 from MP-Biomedicals) in
operation.
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Table 1 Synthesis of 4,6-di(alkylamino)-m-quinonesa b c
,
,
Alkylamine
Entry Product Reaction type Time (min) (equiv.)
Yield (%)
1
2
3
4
5
6
7
8
C4m
A
A
B
B
C
C
D
A
A
B
B
C
C
D
A
A
B
B
C
C
D
120
120
10
10
60
60
10
120
120
10
10
60
60
10
120
120
10
10
60
4
7
4
7
4
7
10
4
7
4
7
4
7
8
4
7
4
7
4
7
7
79
88
83
86
80
89
92
70
74
79
85
81
86
84
75
80
70
90
83
87
69
Scheme 1 General reaction for the synthesis of 4,6-di(alkylamino)-m-
quinones.
C12m
C18m
in solution is well established, such processes require polar
solvents and extended reaction times.3,4,9,15 Presumably, a
facile and rapid synthesis would make such compounds
more readily accessible for potential applications in materials
science and synthetic chemistry. We now demonstrate how a
cell lysis mill (Fig. 1b),16–18 a tool designed for the breakdown
of bacterial cell walls in biochemical and microbiological
research, can be adapted for rapid and solvent-free synthesis
of meta- and para-aminobenzoquinones. To the best of our
knowledge, this is the first demonstration of solvent-free
synthesis19–24 of aminobenzoquinones.
9
10
11
12
13
14
15
16
17
18
19
20
21
60
10
In order to evaluate the efficiency of lysis mill methodology
with respect to conventional solution synthesis of 4,6-di
(alkylamino)-m-quinones, we first conducted the synthesis of
C4m, C12m and C18m in solution. We followed a previously
reported procedure8,9 involving the reaction of 4,6-diaminoresorcinol
dihydrochloride (1, Scheme 1) with excess alkylamine using
methanol as a solvent most compatible with long-, as well as
short-chain alkylamines. The reactions were conducted using
either a 1 : 4 or a 1 : 7 ratio of 1 to the alkylamine. After two
hours stirring at room temperature the products were iso-
lated in typical yields >70%, following rotary evaporation
and centrifugal chromatography (Table 1, entries 1, 2, 8, 9,
15, and 16).9‡ In this procedure, two equivalents of the
alkylamine are required to neutralise the HCl salt and the
remaining alkylamine drives the reversible reaction towards
the desired product. Whereas this reaction is reminiscent of
Schiff base condensations of aldehydes and amines, known
to be accessible by solvent-free chemistry and mechano-
chemistry, we note that it involves three steps: deprotonation
of 1, aerobic oxidation to form C0m, and the exchange of
amine ligands.25–28
In an attempt to use the lysis mill (Scheme 1) as a means
to eliminate the use of solvents and reduce reaction times, a
stoichiometric amount (4 eq.) or an excess (7 eq.) of an
alkylamine and 1 were added to a 2 mL screw cap Eppendorf
tube (lysis tube). The tube was loaded with ceramic grinding
media to a specific height (vide infra) and shaken in a cell
lysis mill for 10 minutes, after which the reaction mixture
became dark green (for C18m) or dark red/purple (for C12m
and C4m) indicating that the reaction had taken place. Crude
reaction mixtures were purified by centrifugal chromatography
to provide products in high yields (>80%, Table 1, entries 3, 4,
10, 11, 17, and 18).‡ The products were characterised by 1H and
13C NMR, as well as powder X-ray diffraction (see ESI†). Prelimi-
nary attempts to structurally characterise the synthesised
compounds gave crystals of C12m of sufficient quality for a
a
Reaction conditions: A: conventional solution synthesis in
methanol (C4m) and ethanol (C12m and C18m); B: lysis mill; C: ball
b
c
mill; D: melt. Pre-heated in oven at 45 °C for 20 min. Monitoring
the solution reactions by TLC indicates that the maximum
conversion in solution is achieved after ca. 12 hours. Detailed
procedures provided in the ESI.
single crystal X-ray diffraction experiment.§ Structure deter-
mination revealed the crystals, grown from methanol, are a
methanol solvate of C12m (Fig. 2a). The crystals are built up
of hydrogen-bonded chains containing two types of supramo-
lecular synthons: the R44(14) motifs involving two molecules
of C12m and two molecules of methanol, as well as homo-
dimeric R22(10) motifs formed between neighboring C12m
molecules (Fig. 2b). Each R44(14) ring synthon consists of two
N–H⋯O hydrogen bonds (N⋯O distance: 2.82 Å), involving
C12m as the hydrogen bond donor and the methanol molecule
as the acceptor, and two O–H⋯O hydrogen bonds involving
the methanol hydroxyl moiety as the donor and a C12m oxygen
atom as the acceptor (O⋯O distance 2.72 Å). The R22(10) ring
synthons consist of two N–H⋯O hydrogen bonds (N⋯O
distance: 2.92 Å). The resulting hydrogen-bonded chains
propagate along the crystallographic b-direction and are
juxtaposed to form layers in the crystallographic (103) plane
(Fig. 2c). Formation of a layered structure is consistent with
the expected tendency of alkyl-substituted aminobenzoquinones
to form self-assembled layers on surfaces.14
Each of the two alkyl chains on a C12m molecule adopts a
different geometry due to a difference in the conformations
of methylene groups attached closest to the aminobenzo-
quinone core. While one of the alkyl chains (C7–C18) is lin-
ear, with all methylene groups adopting
a staggered
conformation, the other one (C19–C30) adopts a kinked
structure due to the partially eclipsed conformations of the
first three methylene groups in the chain (Fig. 2a).
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Fig. 3 Lysis tube temperature after 1 minute of agitation in the lysis
mill operating at 6.0 m s−1 as a function of bead height.
experiments, the temperature of the steel jars did not
increase significantly after 1 h milling. Therefore, we consid-
ered that, in spite of the mechanical input, the lower temper-
ature was insufficient to overcome the activation barrier to
convert the C0m intermediate to the final product. We then
attempted the ball milling synthesis of C18m in a steel jar
pre-heated to 45 °C for 20 min prior to milling. After 1 h mill-
ing the crude product was dark green and the formation of
C18m was confirmed by thin layer chromatography (TLC)
and solution 1H NMR analysis (Table 1, entries 19 and 20,
see ESI† for details of characterisation). Ball milling synthesis
of C12m and C4m did not require heat (Table 1, entries 5, 6,
12, and 13), probably due to the lower melting points of
n-dodecylamine and n-butylamine (28 °C and −49 °C, respec-
tively), compared to n-octadecylamine (52 °C).29
At this point, we speculated if the herein investigated
mechanochemical reactions are mediated by a liquid phase,
as demonstrated for a number of organic and supramolecular
mechanochemical processes.20,27,30–35 We attempted a simple
melt reaction for the synthesis of C18m by mixing the reactant
1 with excess octadecylamine. The two powders were ground
together using a mortar and pestle for 2 min, with no signifi-
cant color change. The mixture was then heated at 70 °C
for 10 min. As soon as the octadecylamine melted, a color
change from white to dark green was observed and product
formation was confirmed by TLC and 1H NMR (Table 1,
entry 21). Thus, the transamination reaction to prepare zwit-
terionic meta-benzoquinones can proceed in the melt. In the
case of C18m, only the melting of the octadecylamine was
necessary. This was further confirmed with the synthesis of
C4m and C12m (Table 1, entries 7 and 14). When the reaction
was attempted using 4,6-diaminoresorcinol dihydrochloride
and n-butylamine, a liquid at room temperature, no heat was
required for the reaction to proceed. As soon as both starting
materials were combined, the transparent reaction mixture
became red indicating the formation of product (Table 1,
Fig. 2 (a) ORTEP representation of the asymmetric unit in the solvate
C12m·methanol; (b) the assembly of C12m and methanol molecules
into hydrogen-bonded chains, with designated hydrogen-bonded
synthons and (c) the assembly of hydrogen-bonded chains in the
structure of methanol solvate of C12m into layers parallel to the (103)
crystallographic planes.
Next, we investigated the synthesis in a laboratory ball
mill, using the synthesis of C18m as the first model reaction.
After 60 minutes milling the reaction mixture became brown-
ish red, i.e. different than in the lysis mill. The colour was
found to be due to C0m (Scheme 1), an intermediate on the
route to the target zwitterionic meta-aminoquinone, formed
by deprotonation of 1. The formation of C0m indicates that
the reaction in the ball mill is not limited by deprotonation
or aerobic oxidation steps, but by the amine exchange reac-
tion. While searching for an explanation for the difference in
reactivity between the lysis mill and the ball mill, we noted
that the temperature of the lysis tube after 1 min agitation
varied significantly between different experiments. Moreover,
higher yields were obtained in hotter tubes, while cooler
tubes resulted in notable quantities of C0m. Presumably, the
principal factor behind such temperature variations was the
number of beads in the tube, i.e. the “bead height”. This was
subsequently verified by measuring the temperature of the
tube contents as a function of bead height after 1 min agita-
tion (at 6.0 m s−1), by inserting a thermocouple into the
ceramic beads. The results, shown in Fig. 3, confirm that the
bead height has a considerable effect on the temperature of
the vial contents, with a maximum measured temperature of
ca. 70 °C after 1 min for a bead height of 70% of the tube
height. Too many or not enough ceramic beads reduced the
temperature increase, presumably due to a lower overall
number of collisions between the beads or less efficient con-
version of kinetic energy into heat. In the ball milling
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entry 7). The melt reactions, however, required the use of
excess liquid amine in order to facilitate stirring. In the end,
we conclude that the combination of vigorous agitation and
frictional heating in the lysis mill enables the simple and
rapid synthesis of m-aminobenzoquinones without external
solvents or excess reagents.
The formation of (C18m)2Ni was confirmed by mass spec-
trometry (see ESI†). For the reaction with nickel acetate, a
distinct odor of acetic acid by-product was detected upon
opening the reaction tube. The reaction was also successful
with a standard ball mill apparatus. After grinding the
reagents together for 2 h, comparable yields of the desired
product were obtained (Table 2, entries 5 and 6).
Mechanosynthesis by manual grinding or ball milling has
become particularly popular for making metal–organic mate-
rials, held together by coordination bonds.36–38 In order to
verify the applicability of the lysis mill for such reactions, we
explored the synthesis of a mononuclear complex of nickel
with one of the prepared aminoquinones, (C18m)2Ni (Scheme 2).
The conventional solution-based reaction was carried out
overnight in refluxing toluene using a 1 : 1 ratio of C18m
and nickel(II) acetate tetrahydrate, Ni(OAc)2·4H2O (Table 2,
entry 1).39 These conditions were based on those reported for
the synthesis of a related compound, (C4m)2Ni, with shorter
alkyl chains, using nickel(II) acetylacetonate, Ni(acac)2 (using
a C4m : Ni(acac)2 ratio of 2 : 1). However, we successfully
substituted the more expensive Ni(acac)2 reagent used in
the solution synthesis with Ni(OAc)2·4H2O. In particular, the
cost of Ni(acac)2 (CAD$ 1297 mol−1) greatly exceeds the cost
of Ni(OAc)2·4H2O of comparable purity (CAD$ 45 mol−1).¶
We also considered using the even less expensive nickel(II)
hydroxide, Ni(OH)2 (CAD$ 21 mol−1), which also offered a fur-
ther advantage of producing water as the only by-product.‖
However, due to its low solubility, Ni(OH)2 is not a reagent of
choice in solution reactions (Table 2, entry 2). For mechano-
chemical syntheses carried out with the lysis mill, reagent
solubility is no longer expected to be a relevant factor.40
Indeed, Ni(OAc)2·4H2O or Ni(OH)2 react with C18m in the
lysis mill to give 85% and 80% yield of the (C18m)2Ni com-
plex, respectively, after 20 shaking cycles (Table 2, entries 3, 4).
Mechanochemistry was also successful in the synthesis
of the analogous para-compounds. Conventionally, 2,5-di
(alkylamino)-1,4-benzoquinones are synthesized by mixing
1,4-benzoquinone and an alkylamine in a 3 : 2 ratio in solu-
tion and stirring at room temperature for several hours
(Table 3, entries 1, 5, and 9).4,5,15 The additional two equiva-
lents of benzoquinone serve to oxidize reaction intermediates
back to the quinone oxidation state (Scheme 3). In this reac-
tion, a colour change was apparent as soon as the reagents
came into contact, and was even observed when the reagents
were simply kept in close proximity. To visualize this phe-
nomenon, benzoquinone and octadecylamine were placed in
separate vials within a sealed jar (see ESI† Fig. S1). Upon
aging, the initially white octadecylamine turned from slightly
brown-orange (after several hours) to light brown (after 1 day)
and, finally to dark brown (after 1 week). Analysis of the dark
brown powder using TLC revealed the formation of C18p. It is
likely that the high vapor pressure of benzoquinone facilitates
the contact between the two reactants.
In that way the synthesis of p-aminoquinones is analogous
to the solvent-free and mechanochemical syntheses of two-
and three-component cocrystals of p-benzoquinone investi-
gated by the groups of Kuroda and of Rastogi.41–43 Next,
we attempted to enhance the mixing of reagents by milling.
The reagents were placed in a 2 mL lysis tube loaded with
ceramic beads to 3/4 of the tube height. The tube was shaken
at 6.0 m s−1 in the lysis mill for 5 shaking cycles (Table 3,
entries 2, 6, 10). The colour of the reaction mixture changed
to black in less than 1 minute. Comparable reaction yields
were also obtained in a ball mill after 7 min milling (Table 3,
entries 3, 7 and 11). As with the meta-compounds, the synthe-
sis also proceeds in the melt, by heating the reaction mixture
to 70 °C for 5 minutes (Table 3, entries 4, 8 and 12). The mix-
ture turned black immediately upon melting of the
alkylamine and, in the synthesis of C4p (Table 3, entry 4),
white vapour was also observed upon the addition of liquid
Scheme 2 General reaction for the synthesis of 4,6-di(alkylamino)-m-
aminoquinone monometallic complexes.
Table 2 Synthesis of bis[4-(octadecylamino)-2-(octadecylimino)-5-oxo-1,4-cyclohexadienolato]nickel (C18m)2Ni under different reaction conditionsa
Entry
Reaction typea
Time (min)
Alkylamine (equiv.)
Yield (%)
1
2
3
4
5
6
A
A
B
B
C
C
720
720
20
20
120
120
C18m : nickel acetate, 1 : 1
C18m : nickel hydroxide, 1 : 1
C18m : nickel acetate, 1 : 1
C18m : nickel hydroxide, 1 : 1
C18m : nickel acetate, 1 : 1
C18m : nickel hydroxide, 1 : 1
69
10
85
80
71
70
a
Reaction conditions: reaction type A, conventional solvent synthesis in refluxing toluene; type B, lysis mill; type C, ball mill. Detailed
procedures provided in the ESI.
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the solid-state assembly of corresponding coordination com-
plexes, while offering increased flexibility in reactant choice.
Acknowledgements
We acknowledge the NSERC Discovery Grant, FRQNT Nouveaux
Chercheurs Grant, Canada Foundation for Innovation Leader's
Opportunity Fund, and FRQNT Centre for Self-Assembled
Chemical Structures for financial support of this research.
Garry Hanan and Mihaela Cibian are thanked for MS analysis
of (C18m)2Ni.
Scheme 3 General reaction for the synthesis of 2,5-di(alkylamino)-
1,4-benzoquinones.
Table 3 Synthesis of 2,5-di(alkylamino)-1,4-quinonesa
Entry
Product
Reaction type
Time (min)
Yield (%)
Notes and references
1
2
3
4
5
6
7
8
C4p
A
B
C
D
A
B
C
D
A
B
C
D
300
5
7
5
300
5
7
5
300
5
7
32
27
25
20
29
30
32
22
22
28
27
21
‡ As the separation procedures for the m- and p-aminoquinones depend strongly
on the nature of the N-substituent8,9 we opted for centrifugal chromatography as
a universal method of purification applicable to products from solution, ball
milling and lysis milling syntheses. Moreover, the herein reported compounds
are prepared for studies in surface self-assembly, which requires samples of
high purity,44 necessitating chromatographic purification regardless of the prep-
aration method.
C12p
C18p
9
§ Crystallographic and general data for C12m methanol solvate: C31H58N2O3,
10
11
12
¯
CCDC 1005686, triclinic, space group P1, a = 6.6943(6) Å, b = 15.448(2) Å, c =
15.565(2) Å, α = 94.626(1)°, β = 98.453(1)°, γ = 101.528(1)°, V = 1549.9(3) Å3, Z = 2,
R1 = 0.072, wR2 = 0.198, (for 5370 out of 7125 independent reflections with I ≥ σI).
¶ Prices based on the Sigma-Aldrich catalogue (online), 2014.
5
a
Reaction conditions: A: conventional solution synthesis in
methanol (C4m) and ethanol (C12m and C18m); B: lysis mill; C: ball
mill; D: melt. Detailed procedures provided in the ESI.
‖ The benefits of using mineral-like precursors (oxides, hydroxides, carbonates)
to metal–organic materials was previously discussed, see: (a) C. J. Adams,
M. A. Kurawa, M. Lusi and A. G. Orpen, CrystEngComm, 2008, 10, 1790–1795; (b)
T. Friščić and L. Fábián, CrystEngComm, 2009, 11, 743–745; (c) W. Yuan,
J. O'Connor and S. L. James, CrystEngComm, 2010, 12, 3515–3517.
** The work described herein used exclusively 2 mL Eppendorf tubes in a sample
holder that can accommodate 24 samples. However, in principle, the reactions
can be scaled up using 15 mL conical centrifuge tubes in a holder that can
accommodate 12 samples.
n-butylamine to benzoquinone, suggesting the reaction is suf-
ficiently exothermic to vaporize n-butylamine. After work-up,
it was determined that the yields were comparable to those
of the solution-based and mechanochemical reactions.
In summary, two families of aminobenzoquinones were
synthesized under several solvent-free reaction conditions.
Compared to conventional solvent reactions, the reaction
times are significantly reduced and, in a matter of minutes,
yields comparable to what normally takes hours in solution
can be obtained. Most importantly, the use of a lysis mill
enabled a general synthetic procedure to be applied for mak-
ing short-chain as well as long-chain N-substituted amino-
quinones. Such a general synthetic procedure is not readily
achievable in conventional solution media due to significant
differences in solubility between short- and long-chain alkyl-
substituted molecules. The reaction temperature attained
during the shaking process was found to be an important
parameter to consider when optimizing the mechano-
chemical reaction conditions. In this respect the lysis mill
provides an attractive means to conduct solvent-free reactions
that require simultaneous input of heat and mechanical
agitation.** The mechanochemical reactivity in a lysis mill
might resemble that recently reported for “vortex grinding”38
but with the added benefits of control over speed, time and
frictional heating. The lysis mill was found to be a conve-
nient tool for performing the solvent-free syntheses of m- and
p-aminoquinones on a small scale, and is also applicable for
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