A greener synthetic protocol for the preparation of carbodiimide

Article abstract of DOI:10.1016/j.tetlet.2009.12.017

A new and facile preparation of symmetrical and unsymmetrical 1,3-diaryl and aryl-alkyl carbodiimides via a dehydrosulfurisation of their corresponding thioureas is described. Herein, the classical method of oxidative desulfurisation of thiourea to carbodiimide involving toxic heavy metal oxides (HgO) has been replaced with an easily available, cost-effective and environmentally benign reagent, iodine. Simple reaction conditions, easy purification of the products and high yields are important attributes of the present methodology and perhaps the best alternative from a green chemistry perspective. The only limitation to this method however, is in the preparation of 1,3-dialkyl substituted carbodiimide.

Full text of DOI:10.1016/j.tetlet.2009.12.017

Tetrahedron Letters 51 (2010) 1019–1021
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Tetrahedron Letters
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A greener synthetic protocol for the preparation of carbodiimide
*
Abdur Rezzak Ali, Harisadhan Ghosh, Bhisma K. Patel
Department of Chemistry, Indian Institute of Technology, Guwahati 781 039, Assam, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A new and facile preparation of symmetrical and unsymmetrical 1,3-diaryl and aryl-alkyl carbodiimides
via a dehydrosulfurisation of their corresponding thioureas is described. Herein, the classical method of
oxidative desulfurisation of thiourea to carbodiimide involving toxic heavy metal oxides (HgO) has been
replaced with an easily available, cost-effective and environmentally benign reagent, iodine. Simple reac-
tion conditions, easy purification of the products and high yields are important attributes of the present
methodology and perhaps the best alternative from a green chemistry perspective. The only limitation to
this method however, is in the preparation of 1,3-dialkyl substituted carbodiimide.
Received 20 October 2009
Revised 2 December 2009
Accepted 4 December 2009
Available online 11 December 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Carbodiimides rank as one of the most important class of re-
agent in synthetic organic chemistry, which are widely used as
synthetic intermediates. They have found several applications such
as synthesis of nucleotides, peptides and heterocycles, oxidation
with dimethyl sulfoxide, permease inhibitors, polymer stabilisers,
cycloaddition reactions etc.1 The importance of carbodiimides
can be judged from the earliest review by Khorana1a and subse-
quent three reviews1b–d where various methods of their prepara-
tion, properties and uses have been extensively discussed.
Carbodiimides are normally constructed from a preformed NÀCÀN
skeleton, addition of N to CÀN and a N+C+N approach.1a–d Syn-
thetic methods for carbodiimides employed before the year 1981
are covered in the above four reviews. Subsequent methods
adopted also, falls into the above three categories which can again
be broadly classified as, (i) thermolysis-decarboxylation of isocya-
nates,2 (ii) dehydration of ureas3 and (iii) dehydrosulfurisation of
thioureas.4 Following the N+CÀN type approach, it has been pre-
pared by the condensation of an amine and an isonitrile in the
nature of the reagents used. In spite of its known toxicity, yellow
mercuric oxide (HgO) has remained as the most frequently used re-
agent till date.1a
We have been working on various aspects of green chemistry.6
Our recent success on hypervalent iodine(III) mediated desulfurisa-
tion of dithiocarbamate salts to isothiocyanates further leading to
heterocycles7a and cyanamides7b and the similar success using
molecular iodine8 prompted us to attempt an iodine mediated des-
ulfurisation of 1,3-disubstituted thiourea for the preparation of car-
bodiimide. This approach is similar to the earlier desulfurisation
strategy, where treatment of the 1,3-disubstituted thiourea with
diacetoxyiodobenzene (DIB) gave carbodiimide as the intermediate
which reacted with the liberated acetate from DIB giving N-acylated
urea.7c In the absence of any external nucleophile, it should be pos-
sible to stop the reaction at the carbodiimide stage. When 1,3-diphe-
nyl thiourea 1 (1 equiv) was treated with iodine (1.1 equiv) in the
presence of a base, triethylamine (2 equiv) in ethyl acetate in an
ice-cold condition, carbodiimide 1a was obtained in good yield.11
Among the various solvents tested, such as ethyl acetate, acetoni-
presence of oxygen and iodine using
a
palladium catalyst.5
Although a large number of processes are available in the litera-
ture, there are limitations to these methods. Some of the draw-
backs associated are the use of expensive palladium catalyst and
strongly oxidising vanadium and phosphorous based reagents.
The use of halogenated solvents, strong alkaline condition, the
requirement of specialised reaction conditions, elevated tempera-
ture and longer reaction times are other drawbacks. Further, most
of the reported methods for the preparation of carbodiimides are
associated with the formation of urea, isothiocyanate and guani-
dine byproducts and the polymerisation, particularly for aromatic
carbodiimides. Some of the reported methods, though interesting,
are of no preparative value, because of the expensive and toxic
Et3N
Et3N
N
H
N
H
N
H
N
I2 / Et3N
I-.+NHEt3
I-.+NHEt3
Ar
Ar
I
Ar
S
+
S
I2
S
I
I
H
N
Ar
N
C
N
Ar
+
+
N
S
Ar
* Corresponding author. Tel.: +91 361 2582307; fax: +91 361 2690762.
E-mail address: patel@iitg.ernet.in (B.K. Patel).
Scheme 1. Plausible mechanism for the formation of carbodiimide from 1,3-
disubstituted thiourea.
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.12.017

1020
A. R. Ali et al. / Tetrahedron Letters 51 (2010) 1019–1021
Table 1
Preparation of carbodiimide from 1,3-disubstituted thiourea and iodinea
Substrate
Productb
S
I2 / Et3N
R1
R2
R1
N
N
R2
C
N
N
H
H
R1
R2
Yield (%)c
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
C6H5–
C6H5–
1a
2a
3a
4a
5a
6a
7a
8a
86
93
88
76
73
70
72
94
58
68
81
82
90
85
67
p-CH3C6H4-
o,p-(CH3)2C6H3-
p-OCH3C6H4-
o-OCH3C6H4–
p-CIC6H4–
p-BrC6H4–
C6H5–
C6H5–
C6H5–
C6H5–
C6H5–
p-CH3C6H4–
o,p-(CH3)2C6H3–
p-OCH3C6H4–
o-OCH3C6H4–
p-CIC6H4–
p-BrC6H4–
p-CH3C6H4–
o,o’-(CH3)2C6H3–
o-CIC6H4–
m-NO2C6H4–
p-BrC6H4–
9a
10a
11a
12a
13a
14a
15a
p-CH3C6H4–
C6H5–
C6H5–
p-CIC6H4–
C6H11
–
m,p-(OMe)2C6H3CH2CH2–
a
b
c
Reaction were monitored by TLC.
Confirmed by IR, 1H, and 13C NMR.12
Isolated yield.
trile, dichloromethane, toluene and THF, ethyl acetate was found to
be the most efficient solvent giving the highest yield. The reaction
when performed at 0–5 °C gives better yields with fewer side prod-
ucts which otherwise is associated with a number of side products
when carried out at room temperature. Further, a portion-wise addi-
tion of iodine over a period of 10–15 min furnished better yields
compared to the addition in one go.
The proposed mechanism for the formation of carbodiimide is
shown in Scheme 1. This is supported by the isolation of precipitated
elemental sulfur. The requirement of 2 equiv of base triethylamine is
essential for this reaction. It may be noted here that 1,3-diarylthiou-
rea on treatment with iodine in the absence of triethylamine under-
goes oxidative cyclisation to yield benzothiazole exclusively
(Scheme 1).
To demonstrate the versatility of this methodology we synthes-
ised a series of symmetrical and unsymmetrical 1,3-diaryl as well
as aryl–alkyl thioureas which were subjected to a treatment with io-
dine and triethylamine in ethyl acetate. As can be seen from Table 1,
symmetrical thioureas containing electron-donating groups at o-
and p- positions or both the positions 2–5, all gave their correspond-
ing carbodiimides 2a–5a in good to excellent yields (73–93%). This
methodology was found to be equally efficient even when moder-
ately electron-withdrawing substituents such as chloro 6 or bromo
7 groups are attached to the aromatic ring.
After the successful preparation of various symmetrical carbodii-
mides, we tested this strategy on some unsymmetrical 1,3-disubsti-
tuted thioureas. Unsymmetrical substrate, 1-phenyl-3-p-tolyl
thiourea 8 afforded corresponding carbodiimide 8a in high yield
(94%) but 1-(2,6-dimethylphenyl)-3-phenylthiourea 9 gave much
lower yield (58%) of the product 9a. The lesser yield in the latter
may possibly be due to the steric crowding imparted by the two
bulky methyl substituents from the adjacent ortho positions which
perhaps prevented the deprotonation by the hindered triethylamine
base. Again, starting with 1-(2-chlorophenyl)-3-phenylthiourea 10,
the corresponding carbodiimide 10a was obtained in satisfactory
yield. In the case of thiourea 11 the conversion to carbodiimide
11a was found to be excellent (81%). Other unsymmetrical thioureas
12–15 gave good to satisfactory yields of their corresponding carbo-
diimides 12a–15a as shown in Table 1. It may be noted that sub-
strates 14 and 15 are unsymmetrical thioureas having an aryl
group on one side and an alkyl pendant on the other. When we ap-
plied this protocol to bis-alkyl thioureas such as 1,3-dic-
yclohexylthiourea, the method was not very successful in giving a
number of side products. Earlier, we had observed a pKa dependent
regioselectivity for unsymmetrical thioureas.6a,9 On the basis of
our previous observations6a,8,9 and mechanism proposed in
Scheme 1, we have reasoned that this has to do with the acidity of
the aliphatic amine protons attached to the thiourea. The acidity of
the aromatic amines(pKa in the range 3.8–5.6) are expected to be en-
hanced further when attached to the thiourea and are thus suffi-
ciently acidic to be abstracted by triethylamine base (pKa 10.78).
On the other hand, the cyclohexylamine (pKa 10.66), even when at-
tached to the thiourea is probably not sufficiently acidic to be ab-
stracted by triethylamine base and particularly so when two
subsequent deprotection are to take place. This explains why the
method is not feasible for the synthesis of 1,3-dialkyl substituted
carbodiimide and is thus unsuccessful in synthesising the useful re-
agent dicyclohexylcarbodiimide (DCC). Indeed this is perhaps the
only drawback associated with this methodology compared to the
reported procedures.
In summary, we have developed a general, economical and
environmentally acceptable method for the preparation of carbo-
diimides from their corresponding 1,3-disubstituted thioureas. In
comparison to the reported methods for the preparation of carbo-
diimides, our procedure is perhaps the simplest and most conve-
nient and thus has industrial implication.
Acknowledgements
B.K.P. acknowledges support of this research from DST, New
Delhi, (SR/S1/OC-15/2006) and CSIR, 01(2270)/08/EMR-II. H.G.
thanks the CSIR for fellowships. Thanks are due to CIF IIT Guwahati
for NMR spectra.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tetlet.2009.12.017.

A. R. Ali et al. / Tetrahedron Letters 51 (2010) 1019–1021
1021
1,3-Di(o-methoxyphenyl)carbodiimide 5a: white solid; mp 71.5–72.5 °C; (Lit.7c
72–76 °C); 1H NMR (400 MHz, CDCl3): d 3.85 (s, 6H, 2 Â CH3), 6.90 (m, 4H), 7.14
(m, 4H). 13C NMR (CDCl3, 100 MHz): d 56.2, 111.5, 121.1, 125.2, 126.0, 128.1,
137.6, 154.1. IR (KBr): 2938 (w), 2138 (s), 2102 (s), 1492 (m), 1454 (w), 1257
(m), 1024 (w), 754 (m) cmÀ1. HRMS (ESI): MH+, found 255.2929, C15H15N2O2
requires 255.2957. Calcd for C15H14N2O2 (254.28): C, 70.85; H, 5.55; N, 11.02.
Found: C, 70.81; H, 5.65; N, 11.00.
References and notes
1. (a) Khorana, H. G. Chem. Rev. 1953, 53, 145; (b) Kurzer, F.; Douraghi-Zadeh, K.
Chem. Rev. 1967, 67, 107; (c) Williams, A.; Ibrahim, I. T. Chem. Rev. 1981, 81,
589; (d) Mikolajczyk, M.; Kielbasinski, P. Tetrahedron 1981, 32, 233; (e) Lv, X.;
Bao, W. J. Org. Chem. 2009, 74, 5618; (f) Zhang, W.-X.; Li, D.; Wang, Z.; Xi, Z.
Organometallics 2009, 28, 882; (g) Olimpieri, F.; Volonterio, A.; Zanda, M. Synlett
2008, 882.
2. Thermolysis-decarboxylation of isocyanates: (a) Bryan, J. C.; Rheingold, A. L.;
Geib, S. J.; Mayer, J. M. J. Am. Chem. Soc. 1987, 109, 2826; (b) Deeming, A. J.;
Hardcastle, K.; Fuchita, Y.; Henrick, K.; McPartlin, M. J. Chem. Soc., Dalton 1986,
2259; (c) Rahman, A. K. F.; Nicholas, K. M. Tetrehedron Lett. 2007, 48, 6002; (d)
Barbaro, G.; Battaglia, A.; Giorgianni, P.; Guerrini, A.; Scconi, G. J. Org. Chem.
1995, 60, 6032; (e) Tang, J.; Mohan, T.; Verkade, J. G. J. Org. Chem. 1994, 59,
4931.
3. Dehydration of ureas: (a) Fell, J. B.; Coppola, G. M. Synth. Commun. 1999, 25, 43;
(b) Hessel, E. T.; Jones, W. D. Organometallics 1992, 11, 1496; (c) Schlama, T.;
Gouverneur, V.; Mioskowski, C. Tetrahedron Lett. 1996, 37, 7047; (d) Zhang, M.;
Vedantham, P.; Flynn, D. L.; Hanson, P. R. J. Org. Chem. 2004, 69, 8340.
4. Dehydrosulfurization of thioureas: (a) Kim, S.; Yi, K. Y. Tetrahedron Lett. 1986,
27, 1925; (b) Kim, S.; Yi, K. Y. J. Org. Chem. 1986, 51, 2613; (c) Isobe, T.;
Ishikawa, T. J. Org. Chem. 1999, 64, 6984.
1,3-Di(p-chlorophenyl)carbodiimide 6a: white solid; mp 51–52 °C; (Lit.10a 54–
57 °C); 1H NMR (400 MHz, CDCl3): d 7.09 (d, 4H, J = 8.8 Hz), 7.29 (d, 4H, J = 8.8
Hz). 13C NMR (CDCl3, 100 MHz): d 125.7, 129.9, 131.5, 134.8, 136.8. IR (KBr):
2924 (w), 2166 (s), 2137 (s), 1485 (s), 1209 (m), 1091 (s), 834 (s) cmÀ1. Calcd
for C13H8Cl2N2 (263.12): C, 59.34; H, 3.06; N, 10.65. Found: C, 59.33; H, 3.02; N,
10.59.
1,3-Di(p-bromophenyl)carbodiimide 7a: white solid; mp 69–70 °C; (Lit.10c 69–
71 °C); 1H NMR (400 MHz, CDCl3): d 7.04 (d, 4H, J = 8.8 Hz), 7.45 (d, 4H,
J = 8.8 Hz). 13C NMR (CDCl3, 100 MHz): d 119.1, 126.0, 132.8, 134.6, 137.2. IR
(KBr): 2159 (w), 2159 (s), 2116 (s), 1578 (w), 1480 (m), 1209 (m), 1069 (w),
1009 (w), 822 (s) cmÀ1. Calcd for C13H8Br2N2 (352.03): C, 44.36; H, 2.29; N,
7.96. Found: 44.39; H, 2.33; N, 7.90.
Phenyl-p-tolyl-carbodiimide 8a: clourless liquid (Lit.10d liquid); 1H NMR
(400 MHz, CDCl3) d 2.33 (s, 3H, CH3), 7.09 (m, 7H), 7.28 (m, 2H); 13C NMR
(CDCl3, 100 MHz) d 20.7, 123.7, 123.8, 125.3, 129.3, 129.9, 135.1, 135.2, 135.3,
138.4. IR (KBr) 2921 (w), 2129 (s), 2104 (s), 1594 (m), 1519 (w), 1494 (m), 1281
(w), 1206 (m), 816 (m) cmÀ1. Calcd for C14H12N2 (208.26): C, 80.74; H, 5.81; N,
13.45. Found: C, 80.71; H, 5.78; N, 13.49.
5. Pri-Bar, I.; Schwartz, J. Chem. Commun. 1997, 347.
6. (a) Yella, R.; Ghosh, H.; Patel, B. K. Green Chem. 2008, 10, 1307; (b) Murru, S.;
Patel, B. K.; Bras, J. L.; Muzart, J. J. Org. Chem. 2009, 74, 2217; (c) Palsuledesai, C.
C.; Murru, S.; Sahoo, S. K.; Patel, B. K. Org. Lett. 2009, 11, 3382; (d) Murru, S.;
Ghosh, H.; Sahoo, S. K.; Patel, B. K. Org. Lett. 2009, 11, 4254; (e) Murru, S.;
Mondal, P.; Yella, R.; Patel, B. K. Eur. J. Org. Chem. 2009, 5406; (f) Ghosh, H.;
Patel, B. K. Org. Biomol. Chem. 2010, doi:10.1039/B917096k.
7. (a) Ghosh, H.; Yella, R.; Nath, J.; Patel, B. K. Eur. J. Org. Chem. 2008, 6189; (b)
Ghosh, H.; Yella, R.; Ali, A. R.; Sahoo, S. K.; Patel, B. K. Tetrahedron Lett. 2009, 50,
2407; (c) Singh, C. B.; Ghosh, H.; Murru, S.; Patel, B. K. J. Org. Chem. 2008, 73,
2924.
(2,6-Dimethyl-phenyl)-phenyl-carbodiimide 9a: yellowish liquid; 1H NMR
(400 MHz, CDCl3): d 2.38 (s, 6H, 2 Â CH3), 6.98 (m, 3H). 7.08–7.17 (m, 3H),
7.29 (m, 2H). 13C NMR (CDCl3, 100 MHz): d 19.2, 123.9, 124.9, 125.3, 128.4,
129.6, 131.7, 133.0, 135.1, 140.0. IR (KBr): 2917 (w), 2151 (s), 2120 (m), 1590
(w), 1474 (w), 1198 (w), 754 (w) cmÀ1. Calcd for C15H14N2 (222.29): C, 81.05;
H, 6.35; N, 12.60. Found: C, 81.10; H, 6.38; N, 12.61.
(2-Chloro-phenyl)-phenyl-carbodiimide 10a: clourless liquid (Lit.10d liquid); 1H
NMR (400 MHz, CDCl3): d 7.06 (m, 1H), 7.17 (m, 5H), 7.33 (m, 3H). 13C NMR
(CDCl3, 100 MHz): d 124.4, 125.7, 125.8, 126.4, 127.7, 129.6, 130.1, 133.0,
135.9, 138.0. IR (KBr): 2907 (w), 2145 (s), 2103 (s), 1584 (m), 1481 (m), 1215
(m), 1051 (w), 751 (m) cmÀ1. Calcd for C13H9ClN2 (228.68): C, 68.28; H, 3.97; N,
12.25. Found: C, 68.30; H, 3.98; N, 12.24.
8. (a) Nath, J.; Ghosh, H.; Yella, R.; Patel, B. K. Eur. J. Org. Chem. 2009, 1849; (b)
Nath, J.; Patel, B. K.; Jamir, L.; Sinha, U. B.; Satyanarayana, K. V. V. V. Green Chem.
2009, 11, 1503.
9. Murru, S.; Singh, C. B.; Kavala, V.; Patel, B. K. Tetrahedron 2008, 64, 1931.
10. (a) Rahman, A. K. F.; Nicholas, K. M. Tetrahedron Lett. 2007, 48, 6002; (b)
Molina, P.; Alajarin, M.; Arques, A. Synthesis 1982, 596; (c) Hunig, S.; Lehmann,
H.; Grimmer, G. Liebigs Ann. Chem. 1953, 579, 77; (d) Katritzky, A. R.; Nie, P.-L.;
Dondoni, A.; Tassi, D. Synth. Commun. 1977, 7, 387.
(3-Nitro-phenyl)-phenyl-carbodiimide 11a: yellowish liquid; 1H NMR (400 MHz,
CDCl3): d 7.23 (m, 3H), 7.36 (m, 2H), 7.49 (m, 2H), 8.02 (m, 1H). 13C NMR
(CDCl3, 100 MHz): d 119.2, 120.3, 124.7, 126.6, 129.8, 130.2, 130.4, 133.8,
136.8, 140.8, 149.2. IR (KBr): 2140 (s), 2104 (m), 1638 (w), 1526 (w), 1349 (w),
1208 (w), 751 (s) cmÀ1. Calcd for C13H9N3O2 (239.23): C, 65.27; H, 3.79; N,
17.56. Found: C, 65.33; H, 3.75; N, 17.55.
11. General procedure for preparation of 1,3-diphenyl carbodiimide 1a10a from 1,3-
diphenyl thiourea 1: To
a
stirred and ice-cooled solution of 1,3-
(4-Bromophenyl)-phenyl-carbodiimide 12a: oily liquid; 1H NMR (400 MHz,
CDCl3): d 7.00 (d, 2H, J = 8.0 Hz), 7.15 (m, 3H), 7.29 (m, 2H), 7.38 (d, 2H,
J = 8.00 Hz). 13C NMR (CDCl3, 100 MHz): d 118.8, 124.5, 125.9, 126.0, 129.7,
132.7, 134.9, 137.8, 137.9. IR (KBr): 3063 (w), 2137 (s), 2101 (s), 1595 (w),
1582 (m), 1485 (m), 1206 (m), 1069 (w), 825 (m), 755 (m) cmÀ1. Calcd for
C13H9BrN2 (273.13): C, 57.17; H, 3.32; N, 10.26. Found: C, 57.21; H, 3.29; N,
10.27.
diphenylthiourea
triethylamine (556
1
l
(457 mg, 2 mmol) in ethyl acetate (5 mL), was added
L, 4 mmol). To this was added iodine (558 mg, 2.2 mmol)
portion-wise over a period of 30 min. A light yellow colour precipitate of sulfur
started separating out during this period. The precipitated sulfur was filtered,
the organic layer evaporated and then extracted with hexane (2 Â 15 mL). The
solution was concentrated under reduced pressure and purified by eluting
through a short column of silica gel (100% hexane) to give 1a (334 mg, 86%).
Oily liquid; 1H NMR (400 MHz, CDCl3): d 7.18 (m, 6H), 7.31 (m, 4H). 13C NMR
(CDCl3, 100 MHz): d 124.4, 125.8, 129.7, 135.5, 138.5. IR (KBr): 2936 (w), 2139
(s), 2105 (m), 1588 (w), 1487 (m), 1202 (w), 757 (w). Calcd for C13H10N2
(194.23): C, 80.39; H, 5.19; N, 14.42. Found: C, 80.45; H, 5.21; N, 14.38.
12. Spectral data of compounds:
(4-Chloro-phenyl)-p-tolyl-carbodiimide 13a: yellowish liquid; 1H NMR
(400 MHz, CDCl3) d 2.30 (s, 3H, CH3), 7.07 (m, 6H), 7.23 (m, 2H). 13C NMR
(CDCl3, 100 MHz) d 21.1, 124.2, 125.4, 129.7, 130.3, 130.8, 135.1, 135.3, 135.9,
137.7. IR (KBr) 2921 (w), 2135 (s), 2108 (s), 1591 (w), 1492 (m), 1209 (m), 1093
(w), 828 (m), 816 (m) cmÀ1. Calcd for C14H11ClN2 (242.70): C, 69.28; H, 4.57; N,
11.54. Found: C, 69.28; H, 4.54; N, 11.52.
1,3-Di(p-tolyl)carbodiimide 2a: white solid; mp 57–58 °C (Lit10b 55–58 °C); 1H
NMR (400 MHz, CDCl3): d 2.31 (s, 6H, 2 Â CH3), 7.05 (d, 4H, J = 8.4 Hz), 7.10 (d,
4H, J = 8.4 Hz). 13C NMR (CDCl3, 100 MHz): d 21.1, 124.0, 130.2, 135.4, 135.9,
136.1. IR (KBr): 2922 (w), 2761 (w), 2678 (w), 2137 (s), 2108 (s), 1607 (w),
1504 (m), 1209 (w), 814 (m) cmÀ1. Calcd for C15H14N2 (222.29): C, 81.05; H,
6.35; N, 12.60. Found: C, 81.11; H, 6.32; N, 12.58.
Cyclohexyl-phenyl-carbodiimide 14a: yellowish liquid (Lit.4a liquid); 1H NMR
(400 MHz, CDCl3): d 1.20–1.37 (m, 3H), 1.42–1.56 (m, 3H), 1.75 (m, 2H), 1.98
(m, 2H), 3.44 (m, 1H), 7.07 (m, 3H), 7.26 (m, 2H). 13C NMR (CDCl3, 100 MHz): d
24.4, 25.4, 35.0, 56.7, 123.4, 124.6, 129.4, 136.3, 141.0. IR (KBr): 2931 (m), 2855
(w), 2129 (s), 2049 (w), 1595 (m), 1500 (w), 1152 (m), 755 (m) cmÀ1. Calcd for
C13H16N2 (200.28): C, 77.96; H, 8.05; N, 13.99. Found: C, 77.98; H, 8.01; N,
13.95.
1,3-Di(2,4-dimethylphenyl)carbodiimide 3a: white solid; mp 71.5–72.5 °C; 1H
NMR (400 MHz, CDCl3): d 2.32 (s, 6H, 2 Â CH3), 2.36 (s, 3H, 2 Â CH3), 6.95–7.11
(m, 6H). 13C NMR (CDCl3, 100 MHz): d 18.1, 20.8, 124.0, 127.4, 131.4, 131.9,
133.8, 134.5, 134.7. IR (KBr): 2920 (w), 2142 (s), 2116 (s), 1496 (m), 1209 (m),
1119 (w), 811 (w) cmÀ1. Calcd for C17H18N2 (250.34): C, 81.56; H, 7.25; N,
11.19. Found: C, 81.54; H, 7.28; N, 11.23.
[2-(3,4-Dimethoxy-phenyl)-ethyl]-phenyl-carbodiimide 15a: yellowish liquid; 1H
NMR (400 MHz, CDCl3): d 2.92 (t, 2H, J = 6.8 Hz, NCH2), 3.64 (t, 2H, J = 6.8 Hz,
ArCH2), 3.80 (s, 3H, CH3), 3.82 (s, 3H, CH3), 6.75 (m, 3H), 6.86 (d, 2H, J = 7.2 Hz),
7.06 (t, 1H, J = 7.2 Hz), 7.21 (t, 2H, J = 8.0 Hz). 13C NMR (CDCl3, 100 MHz): d
37.2, 48.1, 55.8, 55.9, 111.5, 112.2, 120.9, 123.6, 124.6, 129.2, 130.8, 136.4,
140.3, 147.9, 149.0. IR (KBr): 2936 (m), 2834 (w), 2125 (s), 1592 (m), 1505 (m),
1463 (w), 1261 (m), 1237 (m), 1028 (m), 804 (w), 760 (m) cmÀ1. Calcd for
C17H18N2O2 (282.34): C, 72.32; H, 6.43; N, 9.92. Found: C, 72.36; H, 6.41; N,
9.94.
1,3-Di(p-methoxyphenyl)carbodiimide 4a: oily liquid; (Lit.2c mp 52–53 °C); 1H
NMR (400 MHz, CDCl3): d 3.7 (s, 6H), 6.82 (d, 4H, J = 8.0 Hz), 7.08 (d, 2H,
J = 8.0 Hz). 13C NMR (CDCl3, 100 MHz): d 55.5, 114.8, 125.1, 131.3, 136.5, 157.4.
IR (KBr): 2927 (w), 2126 (s), 2105 (s), 1501 (s), 1245 (m), 828 (w), 764 (s) cmÀ1
.
Calcd for C15H14N2O2 (254.28): C, 70.85; H, 5.55; N, 11.02. Found: C, 70.88; H,
5.61; N, 11.08.