Incorporation of nutyl froups into chlorinated diamond surface carbons by orgainc rastins at ambient tempertature

Article abstract of DOI:10.1039/a707905b

Hydrogenated diamond powder has been chlorinated by a radical reaction using sulfuryl chloride in chloroform at 50 °C. The chlorinated diamond was then treated with n-, sec- and teri-butyllithium in tetrahydrofuran at 30 °C for 4 h, and butyl groups were incorporated onto the surface. The modified diamond powder was characterized by diffuse reflectance IR Fouriertransformed (DRIFT) spectroscopy. The surface substitueras were decomposed by flash pyrolysis in a nitrogen flow at temperatures between 255 and 1040 °C and essentially all organic fragments were recovered. When the pyrolysis temperature was increased, the total amount of recovered carbons gradually approached a constant value. The fraction of butylated surface carbons to the total surface carbons was calculated based on pyrolysis products obtained at 1040 °C and was 0.055 for nbutylation, 0.040 for sec-butylation and 0.047 for ;ert-butylation.

Full text of DOI:10.1039/a707905b

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Incorporation of butyl groups into chlorinated diamond surface
carbons by organic reactions at ambient temperature
Takeyasu Saito,a Yoshinori Ikeda,a Shin-ichi Egawa,a Katsuki Kusakabe,a
Shigeharu Morooka,a*¤ Hideaki Maeda,b Yuki Taniguchib and Yuzo Fujiwarab
a Department of Materials Physics and Chemistry, b Department of Chemistry and Biochemistry,
Graduate School of Engineering, Kyushu University, Fukuoka 812-8581, Japan
Hydrogenated diamond powder has been chlorinated by a radical reaction using sulfuryl chloride in chloroform at 50 ¡C. The
chlorinated diamond was then treated with n-, sec- and tert-butyllithium in tetrahydrofuran at 30 ¡C for 4 h, and butyl groups
were incorporated onto the surface. The modiÐed diamond powder was characterized by di†use reÑectance IR Fourier-
transformed (DRIFT) spectroscopy. The surface substituents were decomposed by Ñash pyrolysis in a nitrogen Ñow at tem-
peratures between 255 and 1040 ¡C and essentially all organic fragments were recovered. When the pyrolysis temperature was
increased, the total amount of recovered carbons gradually approached a constant value. The fraction of butylated surface
carbons to the total surface carbons was calculated based on pyrolysis products obtained at 1040 ¡C and was 0.055 for n-
butylation, 0.040 for sec-butylation and 0.047 for tert-butylation.
of diamond surfaces. Harrison et al.14 calculated the friction
1
Introduction
of a diamond (111) surface onto which methyl, ethyl or n-
propyl groups were introduced and predicted that the modi-
Ðed surface would be expected to show a lower friction
coefficient than the hydrogen-terminated diamond (111)
surface. Miyake et al.15 reported that the friction of a polished
polycrystalline diamond surface was reduced when the surface
was Ñuorinated by RF plasma-assisted CVD.
The outstanding properties of diamond and recent develop-
ments in its gas-phase synthesis indicate that it holds con-
siderable promise for use in Ðelds of tribology and
electronics.1 When diamond is synthesized by chemical
vapour deposition (CVD), CH and H are typically used as
4
2
the starting materials. Since the bonding energy of a CwCl
bond is less than that of a CwH bond,2,3 however, reactants
of carbonÈhydrogenÈhalogen systems would be preferable in
order to decrease the deposition temperature. Rudder et al.4
and Kadono et al.5 carried out radio-frequency (RF) and
As can be seen above, modiÐcations of diamond surfaces
are usually performed using dry processes. If diamond surfaces
are modiÐed by means of organic reactions at ambient tem-
perature, however, the possibility of diamond-based molecular
devices would be considerably increased.16 In an earlier
paper,17 we reported the chlorination of carbons on the
diamond surface by a radical reaction in dry chloroform and
further modiÐcation of the surface with n-butyl groups.
However, the e†ect of nucleophiles on substitution yields was
not fully investigated. In the present study, diamond powder
was chlorinated by organic reactions in the liquid phase. The
resulting chlorinated diamond surfaces were then butylated
with n-, sec- and tert-butyllithium at 30 ¡C. The surface cover-
age by butyl groups was evaluated by pyrolysing the modiÐed
diamond at various temperatures, followed by recovery of the
pyrolysis products.
microwave plasma-assisted CVDs using mixtures of CF and
4
H . Maeda et al.6 also investigated the kinetics of the growth
2
of diamond using mixtures of hydrocarbons, Ñuorocarbons
and hydrogen. Frenklach et al.7 found that chlorine was
capable of abstracting residual hydrogen atoms from poly-
cyclic aromatic compounds. Hong et al.2 succeeded in synthe-
sizing diamond at 380 ¡C by employing a hot-Ðlament CVD
method using CCl and H . Pan et al.8 investigated the e†ect
4
2
of chlorine on the formation of diamond by thermal CVD on
a platinum substrate. The use of chlorine allowed the sub-
strate temperature to be reduced by ca. 150 ¡C while main-
taining the original growth rate without chlorine. Patterson et
al.9 reported that diamond was formed at 250È750 ¡C by ther-
mally excited CVD in a tubular reactor using halocarbons.
Tsang et al.10 claimed that chlorine, which was added to a
hot-Ðlament CVD reactor, enhanced the abstraction of surface
hydrogen rather than activating gas-phase reactions. Ando et
al.11 reported that Ñuorine abstracted hydrogen on the
diamond surface at [10 ¡C and reacted with CxO bonds at
temperatures [100 ¡C. The diamond surface was fully Ñuori-
nated at 500 ¡C. They also reported that hydrogen atoms on
the diamond surface were chlorinated at moderate tem-
peratures.12 Miller et al.13 found that UV irradiation from an
Hg lamp enhanced the chlorination of the hydrogenated
diamond surface.
2
Experimental
Fine diamond particles, less than 0.5 lm in diameter, (Tomei
Diamond Co., Japan) were washed in a heated acid mixture
(H SO ÈHNO ) and were then used as the substrate. The
2
4
3
surface area was determined to be 21.0 m2 g~1 by nitrogen
adsorption at [196 ¡C using a BET unit (Shimadzu, Micro-
meritics ASAP 2000). The equivalent diameter was calculated
to be 40.6 nm. Fig. 1(a) shows the reaction scheme for chlorin-
ation and oxidation of diamond. The diamond powder was
Ðrst hydrogenated in hydrogen at 900 ¡C for 4 h. After hydro-
genation, the powder (0.1 g) was suspended in a solution of
2,2@-azobisisobutyronitrile (AIBN, 50 mg), sulfuryl chloride
(0.01 mol) and anhydrous chloroform (10 ml) at 50 ¡C in an
atmosphere of argon. AIBN was added as a radical initiator
and sulfuryl chloride served as the chlorinating agent. The
chlorinated diamond was sensitive to moisture, even at room
temperature, giving an oxidized diamond surface. In order to
The above results suggest that halogens react with hydro-
gen atoms on the diamond surface at moderate temperatures,
and that this technique has applications for the modiÐcation
¤ E-mail: smorotcf=mbox.nc.kyushu-u.ac.jp
J. Chem. Soc., Faraday T rans., 1998, 94(7), 929È932
929

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No CwCl stretching at 800È600 cm~1 was observed for the
oxidized sample.
Ando et al.20 measured the weight gain of a hydrogenated
diamond powder after gas-phase chlorination at 250 ¡C and
concluded that the weight gain was equivalent to 52È60% of
that calculated, assuming that all surface carbons were substi-
tuted with chlorine. They further evaluated the degree of oxi-
dation of chlorinated diamond by exposing the sample to
ambient atmospheric conditions for periods of 5È180 min.
Since they observed no peaks for CwH and CwCl and
observed only peaks corresponding to CwOwC and CxO,
they concluded that the chlorine which had been bonded to
diamond was completely oxidized at room temperature. In the
present study, no changes in the DRIFT spectrum were
observed after the hydrogenated diamond was exposed to
water vapour at 500 ¡C. The CwH peaks in spectrum (a) com-
pletely disappeared after chlorination and oxidation. The
CxO and CwOwC peaks, therefore, were formed by oxida-
tion of CwCl bonds. Thus, the fraction of the chlorinated
surface carbon atoms may be considered to be as high as that
reported by Ando et al.20
Fig. 1 Reaction schemes on diamond surface: (a) chlorination;
(b) alkylation
evaluate the degree of chlorination, therefore, the chlorinated
diamond was intentionally oxidized, as indicated in Fig. 1(a),
and CwOH and CwOwC absorbances of the oxidized
diamond surface were determined by DRIFT spectroscopy
(Perkin, Paragon 1000).
Fig. 1(b) shows the reaction scheme for the butylation reac-
tions. After chlorination, the solution was exhaustively evapo-
rated, and a solution of n-, sec- or tert-butyllithium in
tetrahydrofuran (THF) was introduced into the Ñask contain-
ing the chlorinated diamond, without exposure to air. The
butylation was carried out by stirring the suspension at 30 ¡C
for 4 h under an argon atmosphere. The reaction was then
terminated by adding water to the solution. The powder was
then repeatedly washed with THF and water to remove LiCl
and other by-products, and the treated powder was then char-
acterized by DRIFT spectroscopy.
Butyl groups incorporated on the diamond surface were
decomposed using a Curie-point pyrolyser (Japan Analytical
Ind., JHP22). A 5È7 mg portion of each sample was wrapped
with a pyrofoil possessing Curie temperatures of 255, 358, 590,
764 and 1040 ¡C, and was inductively heated at a rate of ca.
3000 ¡C s~1 in a stream of nitrogen. The pyrolysis was main-
tained for 5 s at each Curie temperature, and all gaseous pro-
3.2 Butylation of chlorinated diamond surface
Fig. 3 shows a DRIFT spectrum of the chlorinated diamond
powder after treatment with n-butyllithium for 4 h. Peaks cor-
responding to CwH stretching at 2958 cm~1 and CwH
deformation at 1454, 1378 and 1327 cm~1 were increased as a
result of alkylation, suggesting that chlorine was replaced by
an n-butyl group. Weak peaks at ca. 2200 and 1700È1600
cm~1 were presumed to be assigned to alkyne and alkene,
respectively, but this formation mechanism was not eluci-
dated. An intense peak at 1350È1000 cm~1 and a broad peak
in the range 3600È2800 cm~1, assigned to CwOwC and
OwH groups, respectively, appeared as a result of reaction
between the remaining chlorine and water, when the sample
was exposed to water.
Fig. 4 shows a DRIFT spectrum of the diamond powder
treated with sec-butyllithium for 4 h. Again, peaks corre-
sponding to CwH deformation at 1411 and 1358 cm~1
increased, suggesting the introduction of sec-butyl groups.
Peaks assigned to CwOwC and OwH groups also appeared.
Fig. 5 shows a DRIFT spectrum for the case of tert-
butyllithium. Peaks corresponding to CwH stretching
appeared, and weak peaks corresponding to CwH deforma-
tion appeared. This suggests that tert-butyl groups, which
contain three methyl groups and no methylene group, were
introduced.
ducts were recovered and determined using
chromatograph.
a
gas
3
Results and Discussion
3.1 Chlorination of hydrogenated diamond surface
Fig. 2(a) and (b) show DRIFT spectra of the diamond
powders, which had been hydrogenated and then chlorinated
at 50 ¡C for 8 h and then further oxidized by exposure to
water. The assignments of hydrogen chemisorbed on the
diamond M100N and M111N surfaces have been investigated18,19
as cited previously.17 Spectrum (a), without chlorination,
shows peaks at 2930 and 2835 cm~1, which are assigned to
CwH groups on the diamond M100N and M111N surfaces,
respectively. Spectrum (b), of the chlorinated and oxidized
diamond, shows a peak at 1350È1000 cm~1, which is assigned
to a CwOwC ether group, and a peak at 1693 cm~1, which is
assigned to a CxO group. A broad peak at 3400È2800 cm~1
is assigned to OwH groups formed by reaction with water.
3.3 Product distribution in the Ñash pyrolysis of butylated
diamond surfaces
Fig. 6 shows the e†ect of pyrolysis temperature on product
distributions for the n-butylated diamond. The major organic
products were methane, ethylene, ethane, propylene, propane,
Fig. 2 DRIFT spectra of chlorinated and then oxidized diamond:
(a) without chlorination, (b) chlorinated for 8 h
Fig. 3 DRIFT spectrum of a chlorinated diamond powder treated
with n-butyllithium for 4 h
930
J. Chem. Soc., Faraday T rans., 1998, V ol. 94

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surfaces, respectively.22 The number of hydrogenated surface
carbon atoms depends on the surface structure. If the
diamond powder, having a total surface area of 21.0 m2 g~1,
possesses only the M100N or M111N surface, the number of
hydrogenated surface carbons is 5.5 or 6.4 ] 10~4 mol g~1,
respectively. If the M100N and M111N faces appear equally, the
number of hydrogenated surface carbon atoms is 5.95 ] 10~4
mol g~1. The number of butyl groups recovered by the Ñash
pyrolysis are converted to fractions of n-butylated surface
carbons by dividing by the number of hydrogenated surface
carbons. As shown in Fig. 8, the calculated values show an
asymptote of 0.055, which is approximated by the value at a
pyrolysis temperature of 1040 ¡C.
Fig. 9 shows the e†ect of pyrolysis temperature on product
distributions by the Curie-point pyrolysis when sec-
butyllithium is used as the butylating reagent. The number of
carbons produced by pyrolysis was 1.7 ] 10~5, 5.2 ] 10~5,
8.4 ] 10~5 and 9.4 ] 10~5 mol g~1 at temperatures of 358,
590, 764 and 1040 ¡C, respectively. Fig. 10 shows the product
distributions for the tert-butylated diamond. When tert-
butyllithium was used, isobutane was produced selectively.
The number of carbons recovered were 4 ] 10~6, 5.6 ] 10~5,
1.07 ] 10~4 and 1.11 ] 10~4 mol g~1 at pyrolysis tem-
peratures of 358, 590, 764 and 1040 ¡C, respectively. The frac-
tions of sec- and tert-butylated carbons, calculated based on
the hydrogenated surface carbons, are also shown in Fig. 8.
Thus, the fractions of surface carbons bonded with butyl
groups, calculated from the total carbons recovered by pyrol-
ysis at 1040 ¡C, were 0.040 and 0.047 for sec-butylation and
tert-butylation, respectively.
The reactivities of the butanes used herein are controlled by
steric e†ects and the stability of the intermediates. However,
the present experiment indicates that the fractions of butyl-
bonded surface carbons are nearly the same, irrespective of the
structure of the butylation reagents. Thus, the rate-limiting
step for the butylation may be elimination of chlorine from
the surface carbon.
Fig. 4 DRIFT spectrum of a chlorinated diamond powder treated
with sec-butyllithium for 4 h
Fig. 5 DRIFT spectrum of a chlorinated diamond powder treated
with tert-butyllithium for 4 h
Fig. 6 Product distributions from n-butylated diamond powder by
pyrolysis at 358, 590, 764 and 1040 ¡C
isobutane and n-butane. No organic products were detected at
a pyrolysis temperature of 255 ¡C, suggesting that butyl
groups on the diamond surface were chemically incorporated
and not physically adsorbed. No methane was produced from
the hydrogenated samples which had not been subjected to
butylation, at all temperatures studied. Thus, the methane was
produced by the fragmentation of incorporated butyl groups
and not by cleavage of CwC bonds of the outermost surface
of the diamond. The number of carbons produced by the
pyrolysis per unit mass of diamond were 3 ] 10~6,
6.0 ] 10~5, 9.3 ] 10~5 and 1.30 ] 10~4 mol g~1 at tem-
peratures of 358, 590, 764 and 1040 ¡C, respectively. The
number of butyl groups was then calculated by dividing the
number of recovered carbon atoms by four. Matsumoto et
al.21 attempted to incorporate hydrogen, methane and ethane
onto the diamond surface by exposing the diamond surface in
an atmosphere of each compound at 1000 ¡C. They detected
hydrogen and ethane using temperature-programmed desorp-
tion (TPD) after the treatment. However, the quantities of
incorporated species were not determined. Fig. 7(a) and (b)
show the schematic structure of the diamond M100N and M111N
Fig. 7 Schematic structures of (a) M100N 2 ] 1 diamond surface;
(b) M111N diamond surface
Fig. 8 Fractions of hydrogenated surface carbons substituted by n-,
sec- and tert-butyl groups, calculated from products produced by
pyrolysis at temperatures of 358, 590, 764 and 1040 ¡C
J. Chem. Soc., Faraday T rans., 1998, V ol. 94
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ated surface carbons to the total surface carbons was calcu-
lated to be 0.055 for n-butylation, 0.040 for sec-butylation and
0.047 for tert-butylation, based on Ñash pyrolysis experiments
at 1040 ¡C. The fraction of surface carbons incorporated by
functional groups may be increased by optimizing reaction
conditions and by the careful selection of substituents.
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4
Conclusions
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Hydrogen atoms bonded to carbon atoms on the diamond
surface were chlorinated by radical reactions in chloroform,
and the chlorinated diamond was subsequently reacted with
n-, sec- or tert-butyllithium in THF at 30 ¡C for 4 h in an inert
atmosphere. The butyl groups which were incorporated onto
the diamond surface were decomposed by Ñash pyrolysis at
temperatures between 255 and 1040 ¡C. The fraction of butyl-
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Paper 7/07905B; Received 3rd November, 1997
932
J. Chem. Soc., Faraday T rans., 1998, V ol. 94