Preparation of artificial urushi via an environmentally benign process

Article abstract of DOI:10.1246/bcsj.74.1067

"Artificial urushi" has been developed by laccase-catalyzed curing of new urushiol analogues. The analogues were designed and conveniently synthesized by regioselective acylation of phenol derivatives having a primary alcohol with unsaturated fatty acids using lipase as catalyst. The curing of the catechol derivative having a linolenoyl group proceeded in the presence of acetone powder from Chinese urushi, yielding the crosslinked film ("artificial urushi") with high hardness and gloss surface, which are comparable with those of natural urushi coating. The analogues obtained from vanillyl alcohol were also cured. FT-IR monitoring of the curing showed that the crosslinking mechanism was similar to that of the natural urushi. The curing of the urushiol analogues in the presence of starch-urea phosphate took place to give the artificial urushi consisting exclusively of synthetic compounds.

Full text of DOI:10.1246/bcsj.74.1067

c. Jpn.
© 2001 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 74, 1067—1073 (2001) 1067
e Chemical
ciety of Ja-
n
e Chemical
ciety of Ja-
n
Preparation of Artificial Urushi via an Environmentally Benign Process
Preparation of Artificial Urushi
R. Ikeda et al.
Ryohei Ikeda,# Hozumi Tanaka,† Hiroshi Oyabu,†† Hiroshi Uyama,††† and Shiro Kobayashi*,†††
Joint Research Center for Precision Polymerization (JRCPP)-Japan Chemical Innovation Institute (JCII),
Higashi 1-1, Tsukuba, 305-8565
01
67
73
†Toyo Ink Mfg. Co., Ltd., 27, Wadai, Tsukuba, Ibaraki, 300-4247
SJA8
09-2673
320
††Kyoto Municipal Institute of Industrial Research, 17 Chudojiminami-cho, Shimogyo-ku, Kyoto 600-8813
†††Department of Materials Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 606-8501
ptember
(Received September 14, 2000)
00
01
“Artificial urushi” has been developed by laccase-catalyzed curing of new urushiol analogues. The analogues were
designed and conveniently synthesized by regioselective acylation of phenol derivatives having a primary alcohol with
unsaturated fatty acids using lipase as catalyst. The curing of the catechol derivative having a linolenoyl group proceed-
ed in the presence of acetone powder from Chinese urushi, yielding the crosslinked film (“artificial urushi”) with high
hardness and gloss surface, which are comparable with those of natural urushi coating. The analogues obtained from va-
nillyl alcohol were also cured. FT-IR monitoring of the curing showed that the crosslinking mechanism was similar to
that of the natural urushi. The curing of the urushiol analogues in the presence of starch–urea phosphate took place to
give the artificial urushi consisting exclusively of synthetic compounds.
As “japan” implies the meaning of “a lacquer or varnish giv-
ing a hard, glossy finish” and/or “objects decorated and lac-
quered in the Japanese style”, urushi wares have been devel-
oped as one of the most typical symbols of Japanese art and
many of such wares have also been used for daily needs.1
Urushi coating exhibits excellent toughness and brilliance for a
long period, even longer than one thousand years in some cas-
es; such coating is prepared from sap of Japanese lacquer tree
(Rhus vernicifera).2–5 In the early days of this century, pio-
Chart 1.
neering works by Majima revealed the structure of main im-
portant components in urushi, “urushiols”. Urushiol is a cate-
attempted.13 This is mainly due to the difficulty in preparation
of urushiols.
chol derivative having unsaturated hydrocarbon chains mainly
with 1–3 double bonds at 3- or 4-position of catechol.6–11 Typ-
ical urushiols are shown as follows (Chart 1).
There has been much interest in polymerizations catalyzed
by enzymes (“enzymatic polymerizations”) as a new method-
ology of polymer synthesis.14–18 Recently, enzymatic synthesis
of polyphenols has received much attention as an alternative of
conventional phenolic resins (novolaks and resols),19 since var-
ious phenols are enzymatically polymerized under mild reac-
tion conditions without using toxic formaldehyde by conve-
nient procedures to produce a new class of polyphenols
consisting of a mixture of phenylene and oxyphenylene
units.20–24 The coupling selectivity (regioselectivity) could be
controlled by changing the solvent composition, yielding a
DMF-soluble polyphenol from non-substituted phenol.25,26 In
the oxidative polymerization of phenols having an unsaturated
polymerizable group, peroxidase catalysis induced the
chemoselective polymerization, yielding the polyphenols bear-
ing the polymerizable group in the side chain.27–29
Crosslinking of urushiols takes place slowly with laccase
catalysis involving sophisticated procedures under air to pro-
duce an insoluble polymeric film of urushi, normally taking
more than one month for complete crosslinking. The film for-
mation is supposed to be accomplished mainly by a laccase-
catalyzed oxidative coupling of the phenol moiety of the
urushiol and a subsequent autoxidation of unsaturated alkyl
chains.11,12
Urushi can be regarded as the sole example of practical nat-
ural paints utilizing in vitro enzymatic catalysis for hardening.
The film-forming of urushiol proceeds under air at room tem-
perature without organic solvents, and hence, urushi coating
system can be regarded as an environmentally benign process,
which is more and more required for future coating industry.
However, few modeling studies of urushi have been scarcely
Very recently, we have preliminarily reported design, syn-
thesis, and enzymatic curing of new urushiol analogues (4 and
5) to produce an “artificial urushi”.30 This modeling is the first
example on the single-step synthesis of urushi-like cured film
# Toyo Ink Mfg. Co., Ltd., Wadai, Tsukuba, Ibaraki, 300-4247,
Japan.

1068 Bull. Chem. Soc. Jpn., 74, No. 6 (2001)
Preparation of Artificial Urushi
5.32 (2H, m, –CHꢁCH–), 6.60–6.73 (3H, m, Ar), 8.98 (2H, br,
ArOH); FT-IR (KBr) 3373 (O–H), 3004, 2924, 2853 (C–H), 1706
(CꢁO), 1607, 1519, 1446 (CꢁC of Ar), 1289, 1190 (C–O),
864, 811, 718 cmꢀ1 (C–H of Ar).
from monomeric phenol derivatives (urushiol analogues),
which do not possess the rash-causing properties. This study
deals with comprehensive results of preparation of the artificial
urushi.
[4-(cis,cis-9,12-Octadecadienoyloxy)methyl]catechol (4b):
1
Yield ꢁ 39%; H NMR (DMSO-d6) δ 0.85 (3H, t, J ꢁ 7.3 Hz,
Experimental
CH3),1.27(14H,br,–CCH2C–), 1.50 (2H, m, –C(ꢁO)CH2CH2C–),
2.01 (4H, br, –CHꢁCHCH2C–), 2.28 (2H, t, J ꢁ 7.3 Hz,
–C(ꢁO)CH2C), 2.73 (2H, m, –CHꢁCHCH2CHꢁCH–), 4.88 (2H,
s, ArCH2O), 5.32 (4H, m, –CHꢁCH–), 6.60–6.73 (3H, m, Ar),
8.94 (2H, br, ArOH); FT-IR (KBr) 3377 (O–H), 3010, 2928, 2855
(C–H), 1704 (CꢁO), 1613, 1522, 1448 (CꢁC of Ar), 1289, 1190
(C–O), 866, 811, 723 cmꢀ1 (C–H of Ar).
Materials. Laccase derived from Pycnoporus coccineus was
purchased from Koken Co. (Tokyo). Pseudomonas cepacia lipase
was purchased from Amano Pharmaceutical Co. (Aichi). The so-
called “acetone powder” (AP) was obtained by pouring Chinese
urushi sap into a large amount of acetone.31 The resulting powder
had no laccase activity. Starch-urea phosphate was provided from
Nippi Inc. (Tokyo). Vanillyl alcohol (2), unsaturated fatty acids
(3), other reagents, and solvents were commercially available and
were used without further purifications.
Synthesis of 4-(Hydroxymethyl)catechol (1). To a disper-
sion of 3,4-dihydroxybenzaldehyde (15 g, 0.109 mol) in 70 mL of
ethanol, was added sodium tetrahydroborate (3.0 g, 0.079 mol) in
120 mL of water at 0 ˚C. After 3,4-dihydroxybenzaldehyde be-
came completely soluble in the solvent, the reaction mixture was
kept at room temperature for 30 min. The solution was adjusted to
pH 3–4 by addition of dilute hydrochloric acid and then concen-
trated under reduced pressure. Sodium chloride was added until
the solution became saturated and then the products were extract-
ed with diethyl ether. The organic layer was washed with water
and dried over anhydrous magnesium sulfate. The solution was
concentrated under reduced pressure and the mixture was subject-
ed to recrystallization using a mixture of diethyl ether/1,2-dichlo-
roethane at ꢀ20 ˚C. The resulting crystal was collected by filtra-
tion and dried in vacuo to give 9.9 g of 4-(hydroxymethyl)catechol
1 (yield 65%). 1H NMR (DMSO-d6) δ 4.3 (2H, d, J ꢁ 5.2 Hz,
ArCH2O), 4.89 (1H, t, J ꢁ 5.6 Hz, CH2OH), 6.52–6.72 (3H, m,
Ar), 8.66 (1H, s, ArOH), 8.76 (1H, s, ArOH); FT-IR (KBr) 3369
(O–H), 1606, 1527 (CꢁC of Ar), 1203, 1159, 1122 cmꢀ1 (C–O);
mp 123–128 ˚C (ref. 137 ˚C).32
Enzymatic Synthesis of Urushiol Analogues. A typical pro-
cedure was as follows. A mixture of 2 (3.1 g, 20 mmol), 3b (2.8 g,
10 mmol), and crude lipase (10 g) in a mixture of 90 mL of isopro-
pyl ether and 10 mL of tetrahydrofuran was heated at 60 ˚C under
gentle stirring. After 240 h, the enzyme was removed by filtration
and the filtrate was poured into water. The organic layer was sep-
arated and further washed twice with water. The organic solution
was dried over anhydrous sodium sulfate and the solvent was
evaporated under reduced pressure. Remaining 2 was removed by
recrystallization to give 3.4 g of 2-methoxy-[4-(cis,cis-9,12-octa-
decadienoyloxy)methyl]phenol (5b) (yield 81%). 1H NMR (DM-
SO-d6) δ 0.85 (3H, t, J ꢁ 6.9 Hz, CH3), 1.26 (14H, br, –CCH2C–),
1.52 (2H, m, –C(ꢁO)CH2CH2C–), 2.01(4H, m, –CHꢁCHCH2C–),
2.29 (2H, t, J ꢁ 7.3 Hz, –C(ꢁO)CH2C), 2.73 (2H, m, –CHꢁCH-
CH2CHꢁCH–), 3.75 (3H, s, OCH3), 4.95 (2H, s, ArCH2O), 5.32
(4H, m, –CHꢁCH–), 6.73–6.91 (3H, m, Ar), 9.06 (1H, br, ArOH);
FT-IR (KBr) 3444 (O–H), 3007, 2925, 2853 (C–H), 1735
(CꢁO), 1606, 1517, 1460 (CꢁC of Ar), 1273, 1157, 1035 (C–O),
850, 816, 796, 720 cmꢀ1 (C–H of Ar).
[4-(cis,cis,cis-9,12,15-Octadecatrienoyloxy)methyl]catechol
(4c): Yield ꢁ 46%; 1H NMR (DMSO-d6) δ 0.92 (3H, t, J ꢁ 7.3
Hz, CH3), 1.24 (8H, br, –CCH2C–), 1.51 (2H, m, –C(ꢁO)CH2-
CH2C–), 2.03 (4H, br, –CHꢁCHCH2C–), 2.28 (2H, t, J ꢁ 7.3 Hz,
–C(ꢁO)CH2C), 2.77 (4H, m, –CHꢁCHCH2CHꢁCH–), 4.88 (2H,
s, ArCH2O), 5.32 (6H, m, –CHꢁCH–), 6.60–6.73 (3H, m, Ar),
8.94 (2H, br, ArOH); FT-IR (KBr) 3386 (O–H), 3008, 2930, 2855
(C–H), 1705 (CꢁO), 1612, 1523, 1449 (CꢁC of Ar), 1292, 1190,
1114 (C–O), 856, 813, 725 cmꢀ1 (C–H of Ar).
2-Methoxy-[4-(cis-9-octadecenoyloxy)methyl]phenol (5a):
1
Yield ꢁ 87%; H NMR (DMSO-d6) δ 0.85 (3H, t, J ꢁ 7.2 Hz,
CH3),1.23(20H,br,–CCH2C–),1.51(2H, m, –C(ꢁO)CH2CH2C–),
2.01 (2H, br, –CHꢁCHCH2C–), 2.29 (2H, t, J ꢁ 7.3 Hz,
–C(ꢁO)CH2C), 3.75 (3H, s, OCH3), 4.95 (2H, s, ArCH2O), 5.33
(2H, m, –CHꢁCH–), 6.73–6.91 (3H, m, Ar), 9.06 (1H, br, ArOH);
FT-IR (KBr) 3443 (O–H), 3004, 2924, 2853 (C–H), 1732
(CꢁO), 1606, 1517, 1463 (CꢁC of Ar), 1275, 1157, 1035 (C–O),
850, 816, 796, 720 cmꢀ1 (C–H of Ar).
2-Methoxy-[4-(cis,cis,cis-9,12,15-octadecatrienoyloxy)me-
1
thyl]phenol (5c): Yield ꢁ 80%; H NMR (DMSO-d6) δ 0.92
(3H, t, J ꢁ 7.8 Hz, CH3), 1.29 (8H, br, –CCH2C–), 1.52 (2H, m,
–C(ꢁO)CH2CH2C–), 2.03 (4H, br, –CHꢁCHCH2C–), 2.30 (2H, t,
J ꢁ 7.3 Hz, –C(ꢁO)CH2C), 2.77 (4H, m, –CHꢁCHCH2-
CHꢁCH–), 3.75 (3H, s, OCH3), 4.95 (2H, s, ArCH2O), 5.33 (6H,
m, –CHꢁCH–), 6.73–6.91 (3H, m, Ar), 9.06 (1H, br, ArOH); FT-
IR (KBr) 3446 (O–H), 3009, 2927, 2854 (C–H), 1734
(CꢁO), 1606, 1517, 1463 (CꢁC of Ar), 1275, 1229, 1157, 1035
(C–O), 851, 818, 796, 720 cmꢀ1 (C–H of Ar).
Enzymatic Curing of Urushiol Analogues.
A typical run
was as follows. A mixture of an urushiol analogue (0.20 g), lacca-
se solution (0.030 mL, 4.5 ꢂ 104 units), and acetone powder (0.15
g) was coated using a film applicator with slit thickness of 50 µm
on a glass plate and kept in 80% humidity at 30 ˚C for 24 h.
Measurements. 1H NMR and IR spectra were recorded on a
300 MHz Varian BB300 and Perkin-Elmer Paragon 1000 spec-
trometers, respectively. Film hardness was evaluated by a Fis-
cherscope H100VS microhardness tester with test force of 1 mN
(Helmut Fischer). Gloss value of films was measured at 60˚ by a
Minolta CM-3610d gloss meter. Pyrolysis GC-MS measurement
was carried out using a Frontier Lab PY-2010D vertical micro fur-
nace-type pyrolyzer, a Hewlett-Packard HP 6890 gas chromato-
graph and a JEOL Automass II spectrometer. The pyrolysis was
carried out at 500 ˚C. The GC analysis was performed using a
Frontier Lab PY-1 column kept at 40 ˚C and subsequently heated
at 20 ˚C/min rate to 330 ˚C. Dynamic viscoelasticity was mea-
sured using a Toyo Baldwin Rheovibron DDV-II-EA with fre-
quency of 3.5 Hz at a heating rate of 1 ˚C minꢀ1. DSC measure-
ments were made at a 10 ˚C minꢀ1 heating rate under nitrogen
using a Mac Science DSC-3200S differential scanning calorimeter
Similarly, 4a–4c, 5a, and 5c were synthesized. As for 4a–4c,
these analogues were purified by silica-gel chromatography (elu-
ent: hexane/ethyl acetate ꢁ 77/23 (vol%)). [4-(cis-9-Octade-
cenoyloxy)methyl]catechol (4a): Yield ꢁ 39%; 1H NMR (DMSO-
d6) δ 0.85 (3H, t, J ꢁ 6.8 Hz, CH3), 1.28 (20H, br, –CCH2C–),
1.50(2H,m, –C(ꢁO)CH2CH2C–), 2.00(2H, br, –CHꢁCHCH2C–),
2.17 (2H, t, J ꢁ 7.6 Hz, –C(ꢁO)CH2C), 4.90 (2H, s, ArCH2O),

R. Ikeda et al.
Bull. Chem. Soc. Jpn., 74, No. 6 (2001) 1069
calibrated with an indium reference standard. TG analysis was
performed using a Mac Science TG-DTA-2000S apparatus for
thermogravimetry/differential thermal analysis at a heating rate of
presence of acetone powder (AP, containing mainly polysac-
charides and glycoproteins) with 80% humidity at 30 ˚C for 24
h. AP, an acetone-insoluble part of the urushi sap, is a third
component of the sap in addition to an urushil and laccase.
This third component is believed to act as emulsifier of oily
urushiol and aqueous laccase solution. The curing of 4b, 4c,
5b, and 5c, which possessed more than 2 carbon–carbon dou-
ble bonds, took place to give a film insoluble in organic sol-
vents and water. On the other hand, 4a and 5a were not cured.
In the curing without laccase (control experiment), the film
formation was not observed. These data indicate that the
present curing took place via the enzymatic catalysis and that
two or three unsaturated groups in the side chain were required
for the hardening. The hardening of 4 proceeded faster than
that of 5. This may be due to the formation of unstable o-
quinone intermediates from 4.
The curing of 4 was monitored by using a dynamic micro-
hardness tester (Fig. 1). At the initial stage of the curing of 4c,
the curing proceeded very slowly. After two weeks, the hard-
ness value suddenly increased. Later, the value gradually in-
creased to reach ca. 150 N mmꢀ2 after 5 weeks. The pencil
scratch hardness39,40 of the sample after 15 days was H, which
is hard enough for practical uses. The gloss value of the film
surface was more than 100. These data are comparable to
those of natural urushi coating, indicating the formation of the
brilliant film with the high gloss surface from the urushiol ana-
logues. On the other hand, the curing of 4b produced a soft
film with the hardness less than 5 N mmꢀ2 after 6 weeks.
Figure 2 shows FT-IR spectra of the cured films of 4c with
different reaction times. Intensity changes of characteristic
10 ˚C minꢀ1 in an argon flow rate of 200 mL minꢀ1
.
Results and Discussion
Design and Lipase-Catalyzed Synthesis of Urushiol Ana-
logues. Novel urushiol analogues (4 and 5), in which the un-
saturated group is connected with the phenolic group through
an ester linkage, were designed and synthesized via facile pro-
cedures (Scheme 1); the analogues were prepared by a lipase-
catalyzed esterification of phenols having a primary alcohol (1
or 2) with unsaturated fatty acids of different number of double
bonds (3). In conventional acylations of compounds having
more than two kinds of hydroxy groups, it is often difficult to
achieve the regioselective esterification.33 In the case of our
new approach, however, the analogues were obtained by one or
two reaction steps from commercially available reagents,
whereas urushiol synthesis involved multi-step reaction path-
ways mainly owing to the difficulty of the direct introduction
of the unsaturated group onto the phenolic aromatics; protec-
tion and deprotection of the phenol moiety are often re-
quired.34–36
We have paid much attention to selective catalysis of lipase
toward acylation between an aliphatic alcohol and a phenolic
alcohol and used Pseudomonas cepacia lipase as catalyst for
the esterification of 1 or 2 with acid 3. By using an excess of
phenolic substrates (1 or 2), the acid was quantitatively reacted
to give oily products 4 and 5 with purity of ca. 95% in moder-
1
ate yields (see, experimental). In H NMR spectrum of the
product, a peak at δ 4.3 due to the methylene protons bonded
to the aromatic moiety was completely shifted to one at ca. 4.9,
whose integrated area was two-thirds as large as that of the
peak at δ 0.9 due to the terminal methyl protons of the higher
fatty acids. These data indicate that the primary aliphatic alco-
hol has been regioselectively acylated to give urushiol ana-
logues (4 or 5).
Enzymatic Curing of Urushiol Analogues Using Acetone
Powder. In this study, laccase derived from Pycnoporus coc-
cineus was used; it was highly active for the oxidative poly-
merization of 2,6-dimethylphenol and syringic acid to give
poly(oxy-1,4-phenylene).37,38 Laccase belongs to an oxi-
doreductase having a copper-protein moiety as active site.14
The laccase-catalyzed curing of 4 and 5 was performed in the
Fig. 1.
Time course in hardening of artificial urushi films
from 4b and 4c by using Fischer microhardness tester: (ꢀ)
4b with 2.3 ꢂ 105 units of laccase per 1 g of the substrate
in the presence of AP; (ꢁ) 4c with 2.3 ꢂ 105 units of lac-
case per 1 g of the substrate in the presence of AP; (ꢂ) 4b
with 7.5 ꢂ 104 units of laccase per 1 g of the substrate in
the presence of SP; (ꢃ) 4b with 1.5 ꢂ 105 units of laccase
per 1 g of the substrate in the presence of SP; (✸) 4c with
7.5 ꢂ 104 units of laccase per 1 g of the substrate in the
presence of SP.
Scheme 1.

1070 Bull. Chem. Soc. Jpn., 74, No. 6 (2001)
Preparation of Artificial Urushi
peaks using a peak at 2856 cmꢀ1 due to C–H vibration of the
terminal methyl group as standard are shown in Fig. 3. In the
curing of 4c, a peak at 3010 cmꢀ1 ascribed to C–H vibration of
the unsaturated group in the side chain rapidly decreased in the
period from 10 to 20 days (Fig. 3C); such behaviors might be
correlated with those of the hardness (Fig. 1). On the other
hand, a slight decrease of the peak was observed in the case of
4b.
For both 4b and 4c, a peak at 990 cmꢀ1 due to C–H vibra-
tion of the conjugated trans group newly appeared. The inten-
sity rapidly increased at the initial curing stage and afterward
became constant (Fig. 3B). Formation of a new peak at 970
cmꢀ1 ascribed to that of the non-conjugated trans bond was
also observed. In case of 4c, the peak slightly increased at the
initial stage and a sudden increase was seen after 10 days (Fig.
3A). These behaviors were similar to those of hardening of
natural urushi. As to 4b, the peak intensity slightly increased
as a function of the time.
Fig. 2.
Monitoring of the enzymatic curing of 4c in the
presence of AP using FT-IR spectroscopy.
Fig. 3.
Time course of relative FT-IR peak intensity in the enzymatic curing of 4b (ꢁ) and 4c (ꢀ) employing AP as a third com-
ponent with use of intensity of a peak at 2856 cmꢀ1 as standard: (A) 970 cmꢀ1; (B) 990 cmꢀ1; (C) 3010 cmꢀ1; (D) 3400 cmꢀ1
.

R. Ikeda et al.
Bull. Chem. Soc. Jpn., 74, No. 6 (2001) 1071
The broad peak at 3400 cmꢀ1 due to O–H vibration (Fig.
3D) showed a rapid decrease at the initial stage. This is proba-
bly owing to the evaporation of water contained in the enzyme
solution and the oxidative coupling of the phenol moiety of 4
(Scheme 2). Afterwards, the peak gradually increased, sug-
gesting that the autoxidation of the unsaturated group in the
side chain takes place.11 The change of the peak intensity of 4c
was much larger than that of 4b.
than that using AP as the third component. The hardness was
improved by adding more laccase; the hardness value of the
film from 4b attained 30 N mmꢀ2 after 10 weeks. Interesting-
ly, the curing of 4b in the presence of SP produced the
crosslinked film with relatively good hardness; only a soft film
was obtained by curing of 4b in the presence of AP.
Characterization of Artificial Urushi. Pyrolysis
gas
chromatography-mass (GC-MS) is very useful for structural
analysis of crosslinked polymers such as phenolic polymers
and natural urushi.28,42–44 Figure 4 shows pyrolysis GC-MS
spectra of natural urushi film and the cured product from 4c
obtained by using AP as the third component. The samples
were decomposed at 500 ˚C. In the spectrum of natural urushi
at m/z ꢁ 108, 10 peaks due to alkylphenols with carbon num-
ber of the side chain from 1 to 10 were clearly observed; such
alkylphenols are formed by the cleavage of C–O bonds (Chart
2). Although these peaks at m/z ꢁ 108 were also observed in
Furthermore, the urushiol quinone was detected at the initial
curing stage from the appearance of a new peak at 1650 cmꢀ1
.
Similar behaviors were observed in the curing of natural
urushiols, indicating that the present curing of 4 proceeds via
the oxidative coupling of the phenol moiety of 4 and the subse-
quent autoxidation of the unsaturated group in the side chain.11
In relation to the laccase catalysis, iron-protoporphyrin-type
oxidoreductases, horseradish and soybean peroxidases, were
examined for the present system. However, under similar reac-
tion conditions, these peroxidases did not induce the crosslink-
ing of urushiol analogues.
Enzymatic Curing of Urushiol Analogues Using Starch–
Urea Phosphate as Third Component. Recently, starch-
urea phosphate (SP), a synthetic material, has been reported to
be highly effective as the third component for in vitro enzy-
matic curing of urushiols.41 Here, the laccase-catalyzed curing
of 4 was examined in the presence of SP, which is a substitute
of AP, the natural sap component (Fig. 1). In the same enzyme
amount, the hardness of the film obtained from 4c was larger
than that from 4b; however, the hardness was much smaller
Fig. 4.
Pyrolysis GC-MS chromatographs of (A) natural
urushi coating and (B) the enzymatically cured products
from 4c obtained in the presence of AP.
Scheme 2.

1072 Bull. Chem. Soc. Jpn., 74, No. 6 (2001)
Preparation of Artificial Urushi
Chart 2.
sured sample. The smooth trace of tan δ means the homoge-
neous structure of the present cured film, suggesting good mis-
cibility between the urushiol analogue and AP. Similar traces
were observed in the sample prepared by using SP as the third
component (Fig. 5B). These dynamic elastic behaviors of the
artificial urushi were very similar to those of natural urushi
(Fig. 5C). For both artificial and natural urushi films, there
was a small change of E′ in the wide range of temperature.
These behaviors of the urushi fims were quite characteristic
since big change of E′ by changing the measured temperature
Chart 3.
is often observed in the case of industrial coating materials.3,45–
the spectrum of the artificial urushi, the peak pattern was dif-
ferent from that of the natural urushi and the peak intensity
was very small. Considering the structure of 4, which possess-
es an ester group connected with phenolic and unsaturated
alkyl groups, these peaks are formed by cleavage of the C–C
coupling products (Chart 3A); the decomposition of the C–O
oligomers does not afford the peaks ascribed to longer alky-
lphenols (Chart 3B). These data suggest the formation of the
coupling units between the aromatics and unsaturated alkyl
group in the curing of 4 in a similar manner to that of the natu-
ral urushi.
Storage modulus (E′) and dissipation factor (tan δ) of the
cured films from 4c, as a function of temperature, are shown in
Fig. 5. In case of the sample obtained in the presence of AP af-
ter drying for 5 months, the glass transition temperature was
observed at 102 ˚C (Fig. 5A). From the increase of E′ in the
region of high temperature, it is suggested that the unreacted
unsaturated carbon-carbon double bonds remained in the mea-
47
Thermal properties of the cured film from 4c obtained using
AP as the third component were also evaluated by using differ-
ential scanning calorimetry (DSC) and thermogravimetry
(TG). In the first DSC scan measured under nitrogen, endo-
thermic and exothermic peaks were observed at 67 and 150 ˚C,
respectively. The latter is probably due to the crosslinking of
the unreacted unsaturated group in the side chain. In the TG
measurement under nitrogen, the cured film gradually decom-
posed and the temperatures at 5 and 10 wt% loss were 180 and
230 ˚C, respectively. Similar DSC and TG data were found in
the natural urushi film.48
Conclusion
In conclusion, “artificial urushi” has been developed by en-
zymatic crosslinking of new urushiol analogues, which were
designed and synthesized by lipase-catalyzed regioselective
Fig. 5.
Dynamic viscoelasticity of (A) artificial urushi obtained from 4c in the presence of AP; (B) that from 4b in the presence of
SP, and (C) natural urushi.

R. Ikeda et al.
Bull. Chem. Soc. Jpn., 74, No. 6 (2001) 1073
(1999).
21 P. Wang and J. S. Dordick, Macromolecules, 31, 941
(1998).
22 H. Tonami, H. Uyama, S. Kobayashi, K. Rettig, and H.
Ritter, Macromol. Chem. Phys., 200, 1998 (1999).
23 H. Tonami, H. Uyama, S. Kobayashi, and M. Kubota, Mac-
romol. Chem. Phys., 200, 2365 (1999).
24 M. H. Reihmann and H. Ritter, Macromol. Chem. Phys.,
201, 798 (2000).
25 T. Oguchi, S. Tawaki, H. Uyama, and S. Kobayashi, Mac-
romol. Rapid Commun., 20, 401 (1999).
acylation with facile procedures. These compounds were
cured in the presence of commercially available laccase cata-
lyst under mild reaction conditions without use of organic sol-
vents to produce the crosslinked polymeric film with high
gloss surface and good elastic properties. In case of the com-
bination of the urushiol analogue and starch–urea phosphate,
the artificial urushi was prepared from exclusively synthetic
compounds. Therefore, the present method has large potential
for a future environmentally-benign process of polymer coat-
ing, giving an example system of green polymer chemistry.49–53
26 T. Oguchi, S. Tawaki, H. Uyama, and S. Kobayashi, Bull.
Chem. Soc. Jpn., 73, 1389 (2000).
27 H. Uyama, C. Lohavisavapanich, R. Ikeda, and S.
Kobayashi, Macromolecules, 31, 554 (1998).
28 R. Ikeda, H. Tanaka, H. Uyama, and S. Kobayashi, Polym.
J., 32, 589 (2000).
This work was supported by a Grant-in-Aid for Specially
Promoted Research (No. 08102002) from the Ministry of Edu-
cation, Science, Sports and Culture, and from NEDO for the
project on Technology for Novel High-Functional Materials in
Industrial Science and Technology Frontier Program, AIST.
29 H. Tonami, H. Uyama, S. Kobayashi, T. Fujita, Y. Taguchi,
and K. Osada, Biomacromolecules, 1, 149 (2000).
30 S. Kobayashi, R. Ikeda, H. Oyabu, H. Tanaka, and H.
Uyama, Chem. Lett., 2000, 1214.
References
1
“Webster’s New World Dictionary of the American Lan-
guage,” ed by D. B. Guralink, 2nd ed, The World Publishing Co.,
New York (1970), p. 754.
31 JIS K-5950-1979.
2
B. V. Rague, “A History of Japanese Lacquer Work,” Uni-
versity of Toronto Press, Toronto (1976).
J. Kumanotani, “Polymer Application of Renewable Re-
32 K. W. Rosenmund and T. Boehm, Arch Pharm., 264, 448
(1926).
33 J. Otera, Chem. Rev., 93, 1449 (1993).
34 J. H. P. Tyman, Chem. Soc. Rev., 8, 499 (1979).
35 M. V. Sargent and S. Wangchareontrakul, J. Chem. Soc.,
Perkin Trans. 1, 1990, 1429.
3
source Materials,” ed by C. E. Carraher and L. H. Sperling, Ple-
num Press, New York (1983), pp. 225–248.
4
O. Vogl and J. D. Mitchell, J. Macromol. Sci. Pure Appl.
Chem., A33, 1581 (1996).
36 T. Miyakoshi, H. Kobuchi, N. Niimura, and Y. Yoshihiro,
Bull. Chem. Soc. Jpn., 64, 2560 (1991).
37 R. Ikeda, H. Uyama, and S. Kobayashi, Macromolecules,
29, 3053 (1996).
38 R. Ikeda, J. Sugihara, H. Uyama, and S. Kobayashi, Mac-
romolecules, 29, 8072 (1996).
5
6
7
8
9
D. M. Snyder, J. Chem. Educ., 66, 977 (1989).
R. Majima, Ber. Dtsch. Chem. Ges., 42B, 1418 (1909).
R. Majima, Ber. Dtsch. Chem. Ges., 45B, 2727 (1912).
R. Majima, Ber. Dtsch. Chem. Ges., 55B, 172 (1922).
R. Majima, Ber. Dtsch. Chem. Ges., 55B, 191 (1922).
10 M. Kasamori, M. Sakamoto, K. Awazu, T. Ichikawa, and T.
Egashira, “The Polymeric Materials Encyclopedia,” ed by J. C.
Salamone, CRC Press, Boca Raton (1996), pp. 3499–3504.
11 J. Kumanotani, “The Polymeric Materials Encyclopedia,”
ed by J. C. Salamone, CRC Press, Boca Raton (1996), pp. 4835–
4842.
12 R. Oshima, Y. Yamauchi, C. Watanabe, and J. Kumanotani,
J. Org. Chem., 50, 2613 (1985).
13 M. Terada, H. Oyabu, and Y. Aso, J. Jpn. Soc. Colour Mat-
er., 67, 681 (1994).
39 P. R. Guevin, Jr., J. Coat. Technol., 67, 61 (1995).
40 JIS K-5400.
41 H. Oyabu, M. Terada, Y. Aso, and Y. Oda, J. Jpn. Soc. Co-
lour Mater., 68, 729 (1995).
42 M. Blazso, J. Anal. Appl. Pyrolysis, 19, 251 (1991).
43 N. Niimura, T. Miyakoshi, J. Onodera, and T. Higuchi, J.
Anal. Appl. Pyrolysis, 37, 199 (1996).
44 T. P. Wampler, G. A. Bishea, and W. J. Simonsick, J. Anal.
Appl. Pyrolysis, 40-41, 79 (1997).
45 T. Kuwata, J. Kumanotani, and S. Kazama, Bull. Chem.
Soc. Jpn., 34, 1678 (1961).
46 L. W. Chen and J. Kumanotani, J. Appl. Polym. Sci., 9,
2785 (1965).
14 S. Kobayashi, S. Shoda, and H. Uyama, “Catalysis in Pre-
cision Polymerization,” ed by S. Kobayashi, John Wiley & Sons,
Chichester (1997), Chap. 8.
15 H. Ritter, “Desk Reference of Functional Polymers, Syn-
theses and Applications,” ed by R. Arshady, American Chemical
Society, Washington (1997), pp. 103–113.
16 R. A. Gross, D. L. Kaplan, and G. Swift (eds), ACS Symp.
Ser., 684 (1998).
17 S. Kobayashi and H. Uyama, “Materials Science and Tech-
nology—Synthesis of Polymers,” ed by A.-D. Schlüter, Wiley-
VCH, Weinheim (1998), Chap. 16.
18 S. Kobayashi, J. Polym. Sci., Polym. Chem. Ed., 37, 3041
(1999).
47 L. W. Chen and J. Kumanotani, J. Appl. Polym. Sci., 9,
3519 (1965).
48 T. Ogawa, J. Jpn. Soc. Colour Mater., 63, 71 (1990).
49 S. Kobayashi, High Polymers, Jpn., 48, 124 (1999).
50 H. Higashimura, M. Kubota, A. Shiga, K. Fujisawa, Y.
Moro-oka, H. Uyama, and S. Kobayashi, Macromolecules, 33,
1986 (2000).
51 J. Sakamoto, J. Sugiyama, S. Kimura, T. Imai, T. Itoh, T.
Watanabe, and S. Kobayashi, Macromolecules, 33, 4155 (2000).
52 S. Kobayashi, H. Uyama, and T. Takamoto, Biomacromole-
cules, 1, 3 (2000).
19 P. W. Kopf, “Encyclopedia of Polymer Science and Engi-
neering,” 2nd ed, John Wiley & Sons, New York (1986), Vol. 11,
pp. 45–95.
53 R. Ikeda, H. Tanaka, H. Uyama, and S. Kobayashi, Macro-
mol. Rapid Commun., 21, 496 (2000).
20 H. Uyama and S. Kobayashi, CHEMTECH, 29(10), 22