Accelerating effects of N-aryl-N′,N′-dialkyl ureas on epoxy-dicyandiamide curing system

Article abstract of DOI:10.1002/pola.24329

This report focuses on epoxy-dicyandiamide (DICY) curing system accelerated by N-aryl-N′,N′-dialkyl urea, aiming at clarifying the accelerating mechanism and the relationship between accelerating effect and molecular structure of the accelerators. Nine N-aryl-N′,N′-dialkyl ureas were synthesized and investigated with measurements of differential scanning calorimetry, thermo gravimetric/differential thermal analysis and NMR spectroscopy. The results revealed that the ureas released the corresponding secondary amines by the thermal dissociation in the presence of epoxide, which led to the formation of tertiary amines that catalyze the addition reaction of DICY to epoxide. Moreover, a tendency that the ureas able to release more compact amines exhibited higher acceleration effects was discovered.

Full text of DOI:10.1002/pola.24329

Accelerating Effects of N-Aryl-N0,N0-dialkyl Ureas on
Epoxy-Dicyandiamide Curing System
XIANG DONG LIU,1,2 MIKA KIMURA,2 ATSUSHI SUDO,2 TAKESHI ENDO2
1Key Laboratory of Advanced Textile Materials and Manufacturing Technology, Ministry of Education, College of Materials and
Textile, Zhejiang Sci-Tech University, Xiasha Higher Education Zone, Hangzhou 310018, People’s Republic of China
2Molecular Engineering Institute, Kinki University, Kayanomori, Iizuka 820-8555, Japan
Received 5 April 2010; accepted 18 August 2010
DOI: 10.1002/pola.24329
Published online 1 October 2010 in Wiley Online Library (wileyonlinelibrary.com).
ABSTRACT: This report focuses on epoxy-dicyandiamide (DICY)
curing system accelerated by N-aryl-N0,N0-dialkyl urea, aiming
at clarifying the accelerating mechanism and the relationship
between accelerating effect and molecular structure of the
accelerators. Nine N-aryl-N0,N0-dialkyl ureas were synthesized
and investigated with measurements of differential scanning
calorimetry, thermo gravimetric/differential thermal analysis
and NMR spectroscopy. The results revealed that the ureas
released the corresponding secondary amines by the thermal
dissociation in the presence of epoxide, which led to the for-
mation of tertiary amines that catalyze the addition reaction of
DICY to epoxide. Moreover, a tendency that the ureas able to
release more compact amines exhibited higher acceleration
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effects was discovered. 2010 Wiley Periodicals, Inc. J Polym
Sci Part A: Polym Chem 48: 5298–5305, 2010
KEYWORDS: accelerator; cure; dicyandiamide; epoxy resin; N-
aryl-N0,N0-disubstituted urea; urea derivatives
INTRODUCTION Dicyandiamide (DICY) has been used as a
heating latency hardener for epoxy resins for a long time
since early 1960s.1,2 It has been widely introduced into
many industrial purposes such as laminates, prepregs, coat-
ings, and adhesives.3–16 DICY is a solid powder with a lim-
ited solubility in epoxy resins at ambient temperature,17,18
resulting in the stability of the corresponding formulations
at ambient tempeꢀrature and the efficient hardening at
approximately 190 C, which is very near to the DICY’s melt
point. In contrast, with addition of N-aryl-N0,N0-dialkyl ureas
such as N,N-dimethyl-N0-phenylurea (fenuron), N-(4-chloro-
phenyl)-N0,N0-dimethylurea (monouron), and N-(3,4-dichloro-
phenyl)-N0,N0-dimethylurea (diuron), epoxy-DICY systems can
be cured at temperatures lower than 140 ꢀC,19 and thus
they have been widely used for epoxy-DICY curing systems
in many products with an industrial scale.
membered cyclic urethane with releasing dimethylamine
[Scheme 1(c)].24,25 The three mechanisms all agreed on the
point that the resulting dimethylamine plays an important
role in the acceleration of epoxy-DICY system.
Herein, our investigation on epoxy-DICY system described
was focused on the acceleration effects by N-aryl-N0,N0-dia-
lkyl ureas, because a more thorough understanding about it
is important not only in the control over the curing process
but also in designing new accelerators with desirable capa-
bilities. This report will characterize and compare nine N-
aryl-N0,N0-dialkyl ureas (Fig. 1), which were synthesized from
the corresponding amines and isocyanates, aiming to clarify
the correlation between their molecular structures and the
corresponding accelerating effects and to find out a common
mechanism that governs the urea-promoted epoxy-DICY sys-
tem. Differential scanning calorimetry (DSC), thermo gravi-
metric/differential thermal analysis (TG/DTA), and NMR
were used to examine the accelerating behavior.
Among these excellent accelerators, monouron has been well
investigated.20–24 At least three mechanisms for its accelera-
tion effect on the epoxy-DICY system have been proposed
(Scheme 1): In the first mechanism [Scheme 1(a)], monouron
is regarded as a isocyanate-blocked amine that can release
dimethylamine by thermal dissociation.20–22 The liberated
amine could either enhance the reactivity of DICY or react
with epoxide. The second mechanism was reported by Son
and Weber23 in which DICY can attack to monouron to pro-
duce dimethylamine [Scheme 1(b)]. In the third mechanism,
monouron reacts with epoxide to form the corresponding 5-
RESULTS AND DISCUSSION
Dependence of Accelerating Behavior on Structure of
N-Aryl-N0,N0-disubstituted Urea
In this investigation, DSC was conveniently used to monitor
the curing reactions. The formulations werꢁe1heated in a DSC
instrument at a heating rate of 5 ꢀC min to observe the
resulting exothermic peak.26–29 Both the corresponding onset
Correspondence to: T. Endo (E-mail: tendo@me-henkel.fuk.kindai.ac.jp)
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SCHEME 1 Proposed mechanisms of
secondary amine produced from the
parent urea.
FIGURE 1 Nine N-aryl-N0,N0-dia-
lkyl ureas used in this study.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
TABLE 1 DSC Characteristics of DGEBA/DICY System in the
Presence of Ureasa
TABLE 2 DSC Characteristics of DGEBA/DICY System in the
Presence of Aminesa
DSC-Onset
Temperature,
Tonset (ꢀC)
DSC-Peak Top
Temperature,
Tpeak top (ꢀC)
DSC-Onset
DSC-Peak Top
Temperature, Temperature,
Tonset (ꢀC)
Urea
Amine
Tpeak top (ꢀC)
Without urea
182
139
139
139
160
158
167
149
152
180
193
146
147
147
168
172
181
161
165
189
Diethylamine
Di(n-propyl)amine
Di(n-butyl)amine
Pyrrolidine
158
164
166
124
147
167
174
178
139
157
188
1
2
3
4
5
6
7
8
9
a
Piperidine
2,2,6,6-Tetramethyl-piperidine 181
a
Heating rate: 5 ꢀC minꢁ1; [DGEBA]0/[DICY]0/[amine]0 ¼ 3.5/1/0.08.
aryl-N0,N0-disubstituted urea would be the actual activator
for promoting the epoxy-DICY curing system.
Heating rate: 5 ꢀC minꢁ1; [DGEBA]/[DICY]/[Urea] ¼ 3.5/1/0.08; Tp
peak temperature; TO ¼ onset temperature.
¼
Polymerization of Epoxide Using Urea as an Initiator in
the Absence of DICY
Generally, the nucleophilicity of ureas is quite low compared
to that of amines. Therefore, it would be rather difficult to
expect that the ureas themselves can initiate the polymeriza-
tion of epoxide as shown in Scheme 1(c); however, if the
ureas can undergo the thermal dissociation to generate the
corresponding amines and there is epoxide but no DICY com-
ponent, these amines would be able to attack epoxide and
initiate its polymerization. Based on this consideration, mix-
tures of diglycidyl ether of bisphenol A (DGEBA) and ureas
([DGEBA]0/[urea]0 ¼ 2/1) were prepared and their curing
reactions were studied by DSC in a dynamic scan mode with
a heating rate at 5 ꢀC minꢁ1. As a result, in all cases, clear
exothermic peaks were observed, implying that the polymer-
ization proceeded. The peak temperatures (Tep) and the
onset temperatures (Teo) are shown in Table 3, which
revealed two important points: (1) When the three ureas 1,
2, and 3 having difference in terms of electron density on
the isocyanate-derived aromatic part were used, there was
no significant difference in the resulting acceleration effects.
and peak top temperatures (Tonset and Tpeak top, respectively)
are summarized in Table 1.
For the three curing reactions using N-aryl-N0,N0-dimethyl
ureas 1, 2, and 3, quite similar Tonset and Tpeak
values
top
were obtained to indicate that the functional groups substi-
tuting on the phenyl group had only a negligible effect on
the acceleration ability. In contrast, the alkyl groups had a
significant influence on the acceleration as evidenced by the
completely different peak temperatures observed by using
urea 1 and 4–9. As bulkiness of alkyl group increased in the
order of methyl, ethyl, n-propyl, and n-butyl, Tpeak
tem-
top
perature became higher accordingly. Another interesting as-
pect that was discovered for the first time by this research
was that the ureas derived from cyclic amines exhibited
good acceleration effects. For example, the acceleration
effects of ureas 7 and 8 derived from cyclic amines (¼ pyr-
rolidine and piperidine) were much higher than those of
N,N-diethyl-, N,N-di-n-propyl- and N,N-butyl-ureas, suggesting
that the compactness of these cyclic structures was advanta-
geous for exhibiting high acceleration effect.
We next examined acceleration effects by the secondary
amines used as the precursor of the ureas 4–9. Dimethyl-
amine was not studied because of the difficulty in mixing it
into the epoxy formulation due to its high volatility. DSC-
heat evolution profiles were measured at a heating rate of 5
ꢀC minꢁ1, and the corresponding onset and peak top temper-
atures (Tonset and Tpeak top, respectively) are shown in Table
2. We found a clear dependence of the acceleration effects
on bulkiness of the amines: less bulkiness was favorable for
the higher effect, and particularly, cyclic amines such as pyr-
rolidine and piperidine exhibited high activities. This tend-
ency was quite similar to that found in the epoxy/DICY/urea
system as discussed above. As shown in Figure 2, the results
described in Tables 1 and 2 were correlated well, as the lin-
ear correlation coefficient was greater than 0.84. These
results implied that the secondary amine released from a N-
FIGURE 2 Correlation plot of DSC peak temperatures of DICY/
DGEBA systems accelerated by secondary amines versus those
by ureas.
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TABLE 3 DSC Characteristics of the Ureas Mixed with DGEBAa
[Scheme 2(a)]. However, in the presence of epoxide, the iso-
cyanate can react with it irreversibly to give the correspond-
ing cyclic urethane A, and the amine can react with epoxide
irreversibly to give the corresponding adduct B having
hydroxyl and tertiary amino moieties. In the epoxy/urea for-
mulation (without DICY), the tertiary amine quaternarized
by the epoxide to induce the ring-opening polymerization of
the epoxide was clarified by the NMR-analysis [Scheme
2(b)]. On the other hand, in the presence of DICY, the terti-
ary amine B can abstract a proton from DICY to convert it
into a more nucleophilic anionic species that can react with
epoxide more easily at lower temperature [Scheme 2(c)].
Because the reaction of DICY with epoxy also produces terti-
ary amines,1,4,30–33 the acceleration of N-aryl-N0,N0-disubsti-
tuted urea, in other word, is a trigger reaction, which can
cause the epoxy-DICY system to undergo an autocatalytic
process.
DSC-Onset
Temperature,
Tonset (ꢀC)
DSC-Peak Top
Temperature,
Tpeak top (ꢀC)
Urea
Without urea
182
129
128
131
165
176
184
149
160
185
193
146
146
149
192
197
200
172
178
192
1
2
3
4
5
6
7
8
9
a
Heating rate: 5 ꢀC minꢁ1; [DGEBA]0/[urea]0 ¼ 3.5/1.
The results in the present investigations also evidenced that
the urea having sterically less hindered amine-derived moi-
ety exhibited higher acceleration effect. This tendency is in
good accordance with an idea that the reaction rate of the
amine released by the thermal dissociation of the urea with
epoxide would be a critical factor to determine the accelera-
tion effect. Because epoxy with a nucleophile proceeds to a
typical SN2 mechanism, the addition reaction of the second-
ary amine to epoxide must be strongly affected by steric hin-
drance with a general rule that small structures are favor-
If the acceleration effect was brought about by the nucleo-
philic attack of urea to epoxide as proposed in the ref. 24,
the acceleration effect of 3 should be higher than that of 2
because of the higher electron density of 3 than that of 2.
(2) Similarly to the epoxy/DICY/urea system, in this epoxy/
urea system, bulkiness of the amine-derived part dominated
the acceleration effect, i.e., less bulky amine-derived part was
favorable for higher acceleration effect. As shown in Figure
3, there were highly correlated relationships between the
DSC-peak top temperature of the epoxy/DICY/urea system
and that of the epoxy/urea system.
able for nucleophilic substitution. This would be
a
reasonable explanation for the tendency that small N-aryl-
N0,N0-disubstituted ureas exhibited higher acceleration effects
on the epoxy-DICY system. The ureas 1–3, which had a com-
mon dimethylamine-derived moiety and different substituent
groups on the phenyl rings, exhibited quite similar accelera-
tion effects, presumably because the systems were governed
by steric factors related to the amine moiety rather than
electronic factors caused from the substituent groups on the
phenyl rings.
To confirm that the real initiator for the polymerization was
not the urea but the amine that was released from the urea,
the reactions of ureas 1, 3, 4, and 7 with glycidyl phenyl
ether (GPE) ([GPE]0/[urea]0 ¼ 1/1) were carried out at 140
ꢀC for 4 h, and the resulting products were analyzed by 13C
NMR spectroscopy (Fig. 4). Similar to the study with using
urea 2 has been already reported,24 the spectrum of the
reaction mixture of 1 and GPE revealed no signal at 49.7
ppm for the oxirane ring, confirming the complete consump-
tion of GPE [Fig. 4(a)], while a signal attributable to a qua-
ternary ammonium moiety was observed at 45.2 ppm. This
quaternary ammonium moiety would be formed by (1) the
addition reaction of dimethyl amine (released from 1) and
GPE to give the corresponding tertiary amino group and (2)
the quaternization of the tertiary amino group by GPE. The
same signal was observed in the spectrum [Fig. 4(b)] for the
reaction mixture of urea 3 and GPE, suggesting that dimethyl
amine released from 3 triggered the same reaction sequence.
When urea 4 was used, unconsumed GPE was detected to
support the low activity of 4, which was in good agreement
with the results of the investigations with DSC. NMR analysis
of the reaction mixture of urea 7 and GPE indicated the cor-
responding quaternarized pyrrolidine moiety clearly.
These investigations with DSC and NMR gave a possible ex-
planation for the acceleration mechanisms (Scheme 2). The
thermal dissociation of the urea is reversible, and thus the
isocyanate and amine can react to give the urea again
FIGURE 3 Correlation plot of DSC peak temperatures of
DGEBA/urea systems mixed with DICY versus those without
DICY.
EFFECTS OF N-ARYL-N0,N0-DIALKYL UREAS, LIU ET AL.
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FIGURE 4 NMR spectra of GPE
heated at 140 ꢀC in the presence
of urea 1 (a), 3 (b), 4 (c), and 7 (d).
Thermal Dissociation of N-Aryl-N0,N0-disubstituted Urea
As discussed above, (1) the thermal dissociation of urea that
gives the corresponding secondary amine and (2) its reaction
with epoxide to form the corresponding tertiary amine
would be the core of the acceleration effect. To investigate
the thermal dissociation behaviors of the ureas in the epoxy
formulations, these ureas were dissolved in 2,2-bis(4-butoxy-
phenyl)propane (BBPP), a nonreactive model compound sim-
ulating DGEBA, and were heated in a DSC instrument to
monitor the thermal dissociation of the ureas. Table 4 shows
the resulting onset (Tdo) and peak (Tdp) temperatures of the
heat evolution profiles. Interestingly, there was not a clear
correlation between these thermal dissociation behaviors
and the acceleration effects that were shown in Table 1. For
example, the dissociation temperatures of 4 and 5 that can
potentially release diethylamine and di-n-propylamine,
respectively, were lower than that of the dimethylamine-
derived urea 1; however, their acceleration effects were
much less than that of 1. In addition, despite the high disso-
ciation temperatures, 7 and 8 exhibited high acceleration
effects comparable to that of 1. Urea 9 having the sterically
hindered structure dissociates at the lowest temperature
among the ureas investigated herein; however, its accelera-
tion effect was quite poor. These results implied that the
most important factor would be the reactivity of the released
amine that depends on its steric factor, rather than the disso-
ciation process.
Reactivity of Urea with DICY
Herein, we investigated the effect of the presence of DICY on
the thermal dissociation behaviors of the ureas. The ureas,
DICY, and BBPP were mixed ([urea]0/ [DICY]0/[BBPP]0 ¼ 1/
2/2) and heated in a DSC instrument up to 260 ꢀC. As a
result, the heat evolution peaks due to the thermal dissocia-
tion of the ureas were observed, and the corresponding
onset temperatures and peak top temperatures were quite
similar to those observed in the absence of DICY, implying
that the presence of DICY has only a negligible effect on the
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Synthesis of N-Aryl-N0,N0-dialkyl Ureas (1–9)
The synthesis of N,N-dimethyl-N0-phenylurea (1) is described
as a typical procedure: To a solution of dimethylamine (2.5
g, 0.55 mmol) in toluene (10 mL), phenylisocyanate (5.9 g,
0.50 mmol) was added slowly. The mixture was heated at 80
ꢀC for 1 h, cooled to room temperature, and concentrated
under reduced pressure. The residual solid was crystallized
from a mixed solvent of toluene and hexane [10 mL, 7/3 (v/
v)], filtered, and dried under vacuum to obtain 1 as a white
powder.
Yield 95%: mp 136 ꢀC; 1H NMR 7.30–7.40, 7.04, 6.31, 3.05;
13C NMR 155.9, 139.0, 128.8, 123.0, 120.0, 36.8; IR 3350,
1658, 1598, 1539, 1492, 1375, 1309, 1246, 1186, 881, 756,
695 cmꢁ1
.
N-(4-Chlorophenyl)-N0,N0-dimethylurea (2) was synthesized
by the reaction of 4-chlorophenylisocyante with dimethyl-
amine according to the typical procedure, and obtained as
white powder.
1
Yield ¼ 96%; mp 172 C; H NMR 7.24–7.36, 6.31, 3.01; 13C
ꢀ
NMR 155.6, 140.5, 128.4, 121.5, 119.8, 36.8; IR 3302, 1645,
1592, 1498, 1402, 1378, 1248, 1190, 1088, 1013, 900, 834,
SCHEME 2 Possible reaction pathways involved in the epoxy/
756, 656 cmꢁ1
.
DICY/urea system.
N-(4-Methoxyphenyl)-N0,N0-dimethylurea (3) was synthesized
by the reaction of 4-methoxyphenylisocyanate and dimethyl-
amine according to the typical procedure and was obtained
as white powder.
thermal dissociation. In addition, the ureas and DICY were
mixed and heated at 140 ꢀC for 2 h, and the mixtures were
analyzed by NMR; however, there was no noticeable change
in the spectra, to suggest that the mechanism involving
direct attack of DICY to urea to produce amine can be
neglected.
Yield ¼ 92%; mp 132 ꢀC; 1H NMR 3.03, 3.79, 6.19, 6.86,
7.26–7.29; 13C NMR 156.3, 155.7, 132.0, 129.4, 122.4, 55.4,
36.3; IR 3308, 2940, 1645, 1515, 1377, 1295, 1239, 1174,
1033, 832, 756, 571 cmꢁ1
.
N,N-Diethyl-N0-phenylurea (4) was synthesized by the reac-
tion of phenylisocyanate and diethylamine according to the
typical procedure and was obtained as white powder.
EXPERIMENTAL
Materials
DICY (particle size <6 lm) was purchased from Degussa AG
(Marl, Germany). Glycidyl phenyl ether (GPE) was purchased
from Wako Pure Chemical Industries (Osaka, Japan) and
purified by distillation over calcium hydride before use. SiO2
particle (99.8% SiO2 content, 12-nm average particle size),
an antisagging agent for epoxy/DICY mixture, was purchased
from Nippon Aerosil (Tokyo, Japan). DGEBA and all the
amines used in the present study were purchased from To-
kyo Chemical Industry (Tokyo, Japan) and used as received.
1
ꢀ
Yield ¼ 89%; mp 87 C; H NMR 1.20–1.26, 3.34–3.41, 6.24,
7.01, 7.30–7.40; 13C NMR 154.5, 139.3, 128.5, 122.5, 119.8,
TABLE 4 Dissociation Temperatures of Ureas in BBPP
Measured by DSCa
DSC-Onset
DSC-Peak Top
Temperature for
Dissociation, Td-onset (ꢀC)
Temperature for
Dissociation, Td-peak top (ꢀC)
Measurements
Urea
Differential scanning calorimetric (DSC) analysis was per-
formed with an Extra6000 DSC instrument, with using a
sample (5–15 mg) sealed in an aluminum pan, under nitro-
gen atmosphere at the heating rate of 5 ꢀC minꢁ1, and
recorded by collecting the data every 0.2 s. Thermal gravi-
metric (TG) analysis was performed with an Extra6000 TG/
DTA instrument under the conditions similar to those for
DSC. 1H and 13C NMR spectra were recorded with JEOL k-
300 with tetramethylsilane as an internal standard; the d
and J values are given in ppm and Hz, respectively. IR spec-
trum was recorded with a JASCO FT/IR-460 Plus spectrome-
1
2
3
4
5
6
7
8
9
a
167
181
173
143
152
172
188
173
61
216
276
212
192
205
201
267
223
67
ter, and the wave-numbers are given in cmꢁ1
.
Heating rate: 5 ꢀC minꢁ1; [BBPP]0/[Urea]0 ¼ 3.5/1.
EFFECTS OF N-ARYL-N0,N0-DIALKYL UREAS, LIU ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
41.3, 13.7; IR 3311, 2982, 2936, 1641, 1541, 1447, 1303,
Synthesis of 2,2-Bis(4-butoxyphenyl)propane
1249, 1170, 1030, 873, 753, 696 cmꢁ1
.
To a solution of bisphenol A (5.7 g, 25 mmol) and 1-iodobu-
tane (12.0 g, 65 mmol) in acetone (100 mL), potassium car-
bonate (13.8 g, 100 mmol) was added. The resulting suspen-
sion was heated with refluxing for 5 h, cooled to room
temperature, and concentrated under reduced pressure.
From the resulting residue, BBPP was isolated by distillation
with using a Kugel Rohr apparatus in 91% yield.
N-Phenyl-N0,N0-di(n-propyl)urea (5) was synthesized by the
reaction of phenylisocyanate and di(n-propyl)amine accord-
ing to the typical procedure and was obtained as white
powder.
1
ꢀ
Yield ¼ 86%; mp 71 C; H NMR 0.98, 1.71, 3.28, 6.27, 7.02,
7.29–7.40; 13C NMR 154.3, 139.1, 128.7, 122.4, 120.0, 51.3,
23.7, 13.8; IR 3323, 2965, 2874, 1645, 1597, 1544, 1500,
1H NMR 7.14, 6.80, 3.95, 1.70–1.80, 1.63, 1.42–1.56, 0.97;
13C NMR 155.7, 141.7, 126.4, 112.5, 66.3, 40.4, 30.2, 18.0,
12.6; IR 3096, 3031, 1602, 1495, 1389, 1245, 765, 612
1449, 1317, 1242, 1174, 1105, 892, 756, 696 cmꢁ1
.
N,N-Di(n-butyl)-N0-phenylurea (6) was synthesized by the
reaction of phenylisocyanate and di(n-butyl)amine according
to the typical procedure and was obtained as white powder.
cmꢁ1
.
CONCLUSIONS
1
ꢀ
Our data provide further evidence that the secondary amine
released from N-aryl-N0,N0-disubstituted urea plays a very
important role for accelerating cure reactions between DICY
and epoxide. In the heating mixture of N-aryl-N0,N0-disubsti-
tuted urea, DICY and epoxy, a reasonable mechanism is that
the secondary amine is produced by thermal dissociation of
the urea with presence of epoxy rather than by other paths.
The secondary amine further reacts with epoxy to produce
tertiary amine and quaternary ammonium salt, causing the
epoxy-DICY system to undergo an autocatalytic process. As
the steric hindrance in the addition reactions to oxirane car-
bons, compact N-aryl-N0,N0-disubstituted ureas commonly
give a strong acceleration for the epoxy-DICY system. These
results not only are of importance in the control over the
cure process but also have high significance in designing of
new accelerator with desirable capabilities.
Yield ¼ 88%; mp 84 C; H NMR 0.98, 1.42, 1.65, 3.31, 6.26,
7.05, 7.32–7.40; 13C NMR 154.6, 139.8, 129.0, 122.6, 120.1,
49.5, 33.2, 22.6, 15.8; IR 3299, 2960, 2872, 1640, 1535,
1449, 1408, 1320, 1245, 1225, 1112, 886, 755, 700 cmꢁ1
.
Pyrrolidine-1-carboxylic acid phenylamide (7) was synthe-
sized by the reaction of phenylisocyanate and pyrrolidine
according to the typical procedure and was obtained as
white powder.
Yield ¼ 91%; mp 135 ꢀC; 1H NMR 1.99, 3.48, 6.17, 7.03,
7.29–7.44; 13C NMR 154.2, 139.1, 128.3, 122.2, 119.6, 45.3,
25.0; IR 3301, 2975, 2876, 1648, 1596, 1541, 1444, 1386,
1243, 1075, 883, 763, 694 cmꢁ1
.
Piperidine-1-carboxylic acid phenylamide (8) was synthe-
sized by the reaction of phenylisocyanate and piperidine
according to the typical procedure and was obtained as
white powder.
Yield ¼ 94%; mp 160 ꢀC; 1H NMR 1.65, 3.48, 6.39, 7.03,
7.29–7.38; 13C NMR 154.5, 139.0, 128.2, 122.4, 120.1, 49.5,
30.1, 24.3; IR 3300, 2928, 2858, 1632, 1543, 1500, 1451,
1420, 1353, 1305, 1245, 1133, 1030, 955, 907, 876, 757,
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EFFECTS OF N-ARYL-N0,N0-DIALKYL UREAS, LIU ET AL.
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