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Dimerization of Carbodiimides.

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Dimerization of Carbodiimides 111
stable indefinitely at room temperature, but when warmed
decompose partly into the monomers. Thus in the mass
spectrum of (40) one observes the molecular ion and fragBy K. Hartke and F. Rossbuch [*I 121
ments with mass numbers greater than that of the monomer
only when the evaporation temperature is low. Moreover,
Aliphatic carbodiimides react readily with alkylating agents
some di-n-propylcarbodiimide is detectable by I R spectrosuch as dimethyl sulfate. If equivalent amounts of the two
scopy in the fresh distillate of (4b) but disappears after a few
compounds are mixed and kept at room temperature without
days.
a solvent being present, the v-N=C-N stretching vibration
of diisopropylcarbodiimide disappears in 5 days, of di-nAromatic carbodiimides also dimerize, within a few minutes,
propylcarbodiimide in 30 h, and of diethylcarbodiimide in
o n addition of 0.5 molar equivalent of anhydrous tetrafluoro16 h. N M R spectra indicate in each case reaction of two
boric acid in anhydrous methylene chloride; however, they
molar equivalents of carbodiimide with one of dimethyl
afford in this reaction substituted quinazolinium salts of
sulfate to yield N-alkyl-N-methyl-l,3-dialkyl-2-alkylimino- structure ( 5 ) , from which the 3-aryl-2-arylamino-4-aryl1,3-diazetidine-4-iminium methyl sulfates ( I ) .
iminoquinazolines (6) [(6u), m.p. 181-185 OC[51, yield 85
(6b), m.p. 246 "C, yield 82 %I, are obtained by means of
bases.
2 R-N=C=N-R + (CH3)2S04
2 R - C & I - N = C = N - C & - R + HBF4
x;
B
1
The salts (1) are isolated as oils; they are soluble in water
NIC6H4- R
and on addition of an excess of aqueous sodium hydroxide
are at once hydrolyzed to N,N',N"-trialkyl-N-(N-alkyl-NmethyIcarbamoy1)guanidines (
2
)
, which, being sparingly
The structure (6) was proved by IR, N M R , and mass spectral
soluble, are then precipitated. Compound (2a) is crystalline,
results. The compound (6a) was previously prepared by
has m.p. 102-103°C, is formed in 81 % yield, and has a
M c C o y (1897) from chloro-N,N'-diphenylformamidinium
molecular weight 286 (acidimetric); in the I R spectrum
chloride by means of aluminum chloride [61.
(KBr) v N H 2.99 p. v C 0 6.09 p, vC=N 6.22 p. and in the
Received: November 28, 1967
[Z 660 IE]
N M R spectrum (CDC13) doublets at 1.10 ppm [3 C(CH&]
German version: Angew. Chern. 80,83 (1968)
and 1.29 ppm [l C(CH&], a singlet at 2.68 ppm (1 N-CH3),
and a broad singlet at 3.4 ppm (NH). The compounds (Zb)
[*] Prof. Dr. K. Hartke and F. Rossbach
and (2c) are liquid and have not yet been obtained analytiInstitut fur Pharmazeutische Chernie und
cally pure.
Lebensmittelchemie der Universitat
355 Marburg, Marbacher Weg 6 (Germany)
A n analogous dimerization of aliphatic carbodiimides t o
salts of structure (3) is observed on admixture with 0.5 molar
[l] Part 9 of Carbodiimides. - Part 8: K. Hurtke, Arch. Pharrnaz. 300, 766 (1967).
equivalent of anhydrous ethereal tetrafluoroboric acid (31 in
121 We thank the Deutsche Forschungsgemeinschaft and the
anhydrous methylene chloride. IR spectroscopic studies
Verband der Chemischen Industrie for financial support of this
showed that the reaction is complete within only a few
work, and Dr. Zuhorszky, Marburg, and Varian AG., Zurich,
minutes at room temperature.
for measurement of the mass spectra.
[ 3 ] Preparation: K . Hufner, A. Stephan, and C. Bernhard, Liebigs
Ann. Chem. 650,57 (1961);U. Hurder, E . Pfeil, and K.-F. Zenner,
Chem. Ber. 97, 516 (1964).
[4] The only observation is by F. Zetzsche and A. Fredrieh, Ber.
dtsch. chem. Ges. 73, 1114 (1940), who isolated a crystalline
substance in low yield from the polymeric distillation residue of
dibenzylcarbodiimide; on the basis of an N analysis and a not
very accurate cryoscopic molecular-weight determination they
ascribed to this product a 1,3-diazetidine structure.
[5] Compound (6u) melts partially at 171 "C, resolidifies, and
remelts unsharply at 181-1 85 "C.
[6] H . N . McCoy, Ber. dtsch. chem. Ges. 30, 1090 (1897); the
structure was clarified by degradation [ H . N . McCoy, ibid. 30,
1682 (1897)J.
The salts ( 3 ) were not isolated but were converted into the
1,3-dialkyl-2,4-bis(aIkylimino)-1,3-diazetidines( 4 ) by cautious neutralization with aqueous sodium hydroxide or by
Preparation of Halogeno- and Acetatofiltration through a column of basic A1203 [(4u): m.p. 52OC,
yield 90 %. ( 4 b ) : b.p. 90 "Cj0.05 torr, yield 70 %. ( 4 c ) : m.p.
organoplumbates(1v)111
122.5 "C, yield 95 %I. The structure ( 4 ) was proved by
elemental analysis and spectroscopic data: e.g., for (4u) :
By F. Huber and E . ScltOnafinger[*I
molecular weight 252 (acidimetric), 252 (mass spectrometric);
I R (KBr) vC=N 5.96 p; N M R (CC14) doublets at 1.12 ppm
A large proportion of the covalent bond energy in the total
free energy of the relevant system[2.31 is an important
[2 C(CH&] and 1.29 ppm [2 C(CH3)zI. Dimeric aliphatic
condition for the possibility of synthesis, and for the stability,
carbodiimides were previously almost unknown [41. They are
72
Angew. Chem. internal. Edif. Vol. 7 (1968) No. I
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