Kinetics of dehydrohalogenation of N-chloro-3-azabicyclo[3,3,0]octane in alkaline medium. NMR and ES/MS evidence of the dimerization of 3-azabicyclo[3,3,0]oct-2-ene

Article abstract of DOI:10.1002/(SICI)1097-4601(1998)30:2<129::AID-KIN4>3.0.CO;2-U

The formation of 3-azabicyclo[3,3,0]oct-2-ene in the course of the synthesis of N-amino-3-azabicyclo[3,3,0]octane using the Raschig process results from the following two consecutive reactions: chlorine transfer between the monochloramine and the 3-azabicyclo[3,3,0]octane followed by a dehydrohalogenation of the substituted haloamine. The kinetics of the reaction were studied by HPLC and UV as a function of temperature (15 to 44°C), and the concentrations of NaOH (0.1 to 1 M) and the chlorinated derivative (1 to 4 × 10^-3 M). The reaction is bimolecular (k = 103 × 10^-6 M^-1 s^-1; ΔH^0# = 89kJ mol^-1; and ΔS^0# = -33.6 J mol^-1 K^-1) and has an E2 mechanism. The spectral data of 3-azabicyclo[3,3,0]oct-2-ene were determined. IR, NMR, and ES/MS analysis show dimerization of the water-soluble monomer into a white insoluble dimer.

Full text of DOI:10.1002/(SICI)1097-4601(1998)30:2<129::AID-KIN4>3.0.CO;2-U

Kinetics of
Dehydrohalogenation
of N-Chloro-3-
Azabicyclo[3,3,0]Octane in
Alkaline Medium. NMR and
ES/MS Evidence of the
Dimerization of 3-
Azabicyclo[3,3,0]Oct-2-Ene
M. ELKHATIB, L. PEYROT, J. P. SCHARFF, H. DELALU
Laboratoire d’Energe´tique et Synthe`se Inorganique, UPRES A CNRS 5079, Universite´ Claude Bernard Lyon I, Baˆtiment
731, 43 Boulevard du 11 novembre 1918, 69622 Villeurbanne cedex, France
Received 21 February 1997; accepted 19 May 1997
ABSTRACT: The formation of 3-azabicyclo[3,3,0]oct-2-ene in the course of the synthesis of N-
amino-3-azabicyclo[3,3,0]octane using the Raschig process results from the following two con-
secutive reactions: chlorine transfer between the monochloramine and the 3-azabicy-
clo[3,3,0]octane followed by a dehydrohalogenation of the substituted haloamine. The kinetics
of the reaction were studied by HPLC and UV as a function of temperature (15 to 44ЊC), and
the concentrations of NaOH (0.1 to 1 M) and the chlorinated derivative (1 to 4 ϫ 10Ϫ3 M).
6
1
The reaction is bimolecular (k ϭ 103 ϫ 10Ϫ MϪ sϪ1; ⌬H0# ϭ 89 kJ molϪ1; and ⌬S0#
ϭ
Ϫ33.6 J molϪ KϪ1) and has an E2 mechanism. The spectral data of 3-azabicyclo[3,3,0]oct-2-
ene were determined. IR, NMR, and ES/MS analysis show dimerization of the water-soluble
monomer into a white insoluble dimer. ᭧ 1998 John Wiley & Sons, Inc. Int J Chem Kinet:
30: 129–136, 1998.
1
INTRODUCTION
of asymmetric bicyclic hydrazines, in particular N-
amino-3-azabicyclo[3,3,0]octane 1 (NAZA):
This work concerns the reactivity of chloramine with
mono- and di-substituted amines when using the Ras-
chig process, shown in reaction (1), for the synthesis
RRЈNH ϩ NH2Cl !: RRЈNNH2 ϩ HCl (1)
Where R, RЈ ϭ H, alkyl, aryl, and alicyclic.
During the synthesis of this molecule and under
certain pH conditions, one can observe the forma-
Correspondence to: H. Delalu
᭧ 1998 John Wiley & Sons, Inc.
CCC 0538-8066/98/020129-08

130
ELKHATIB ET AL.
tion of several by-products, in particular 3,4-diaza-
bicyclo[4,3,0]non-2-ene 2, N,NЈ-azo-3-azabicy-
clo[3,3,0]octane 3, and 3-aza-bicyclo[3,3,0]oct-2-ene
4 which precipitates in the form of a white solid.
N
NNH2
NH
1
2
Figure 1 Mass spectrum of 3-azabicyclo[3,3,0]oct-2-ene
by direct injection (70 eV).
NN"NN
N
3
4
This hypothesis has been reported in the literature of
analogous compounds, but comprehensive quantifi-
cation of the phenomena involved has never been per-
formed.
The first two of these were the object of previous in-
vestigations [1–4]. The present study has the objective
of researching the mechanism of the formation of 4
and of determining the kinetic parameters in order to
define the optimal synthesis conditions. The most sim-
ple reaction scheme would consist of a direct dehy-
drogenation of 3-azabicyclo[3,3,0]octane (AZA) to
form imine:
RESULTS AND DISCUSSION
With the goal of verifying the above hypothesis con-
cerning the formation of imine in the course of the
synthesis of NAZA, preliminary identification at-
tempts were effected in concentrated media.
NH
N dehydrogenation
Experiments performed in the laboratory in the pres-
ence of oxygen or of monochloramine exclude this
route as a source of 4. Analysis of the reaction mixture
during the preparation of hydrazine reveals the exis-
tence of small quantities of an organohaloamine 5, N-
chloro-3-azabicyclo[3,3,0]octane (ClAZA). In these
conditions, imine would result from the following two
consecutive reactions: chlorine exchange between the
chloramine and 3-aza-bicyclo[3,3,0]octane [5–11]
followed by a dehydrohalogenation [12–27] of the
substituted haloamine (reactions 2 and 3):
ϩ
NH2 ϩ NH2Cl
ϩ
NCl ϩ NH4
(2)
5
NCl ϩ NaOH
Figure 2 13C NMR spectrum at t ϭ 0 of 3-azabicy-
N ϩ NaCl ϩ H2O (3)
clo[3,3,0]oct-2-ene after dissolution of the dimer in CDCl3.

KINETICS OF DEHYDROHALOGENATION
131
Characterization of 3-Azabicyclo[3,3,0]Oct-
2-Ene
These results allow us to postulate the existence of a
monomer in aqueous solution which then precipitates
in dimeric form. In order to confirm this hypothesis,
multinuclear NMR analysis were undertaken imme-
The reaction of dehydrohalogenation of ClAZA was
conducted by introducing into a 500 mL reactor 40 g
NaOH (1 mol), 2.33 g anhydrous AZA (0.021 mol),
and 10 mL sodium hypochlorite (0.02 mol). Initially
one obtains an emulsion that gradually disappears. At
the end of the reaction, the white precipitate formed is
filtered, washed several times with water, and dried
under reduced pressure.
diately after dissolution of the dimer in CDCl3.
13
Figure 2 presents the
NMR spectrum at time
C
t ϭ 0 of the solubilized compound. One can observe
seven peaks that each correspond to two carbon atoms,
implicating the existence of a symmetry element. Fol-
lowing the spectra as a function of time shows the
appearance of seven new peaks (Fig. 3) representing
the monomeric structure. Increase in temperature
drives the disappearance of the dimer in favor of the
monomer.
The direct injection mass spectrum is presented in
Figure 1. The molecular ion obtained (Mϩ ϭ 109) and
the isotopic study of the ion fragments lead to an em-
pirical formula of C7H11N. Elemental analysis of the
product shows good agreement between calculated
and experimental percentages (C: 0.065%; H:
Ϫ0.20%; N: 0.155%). The UV spectrum obtained af-
ter dissolution of 4 in basic solutions exhibits an ab-
sorption at ␭ ϭ 225 nm with a molar extinction
Furthermore, in order to clarify the form of the im-
ine in the reaction mixture,
were treated by
100 mL
2 mL deuterated chloroform containing 1% tetrame-
thylsilane. The 1H and 13C NMR spectra of the organic
phase shows that the benchmark signals are superim-
posed over those caused by the dissociation of the
solid. DEPT analysis of the monomeric and dimeric
forms reveals the presence of two and three peaks,
respectively, corresponding to methyne carbons (CH).
1
1
coefficient ⑀ ϭ 172 MϪ cmϪ .
The IR analysis of the white powder surprisingly
shows an absence of the band due to the C"N stretch.
Figure 3 13C NMR spectrum of imine in CDCl3 as a function of time: equilibrium between monomeric (m) and dimeric (d)
forms.

132
ELKHATIB ET AL.
T ϭ 25ЊC, the solubility limit of the chlorinated deriv-
ative is 10Ϫ2 M. At 1 M NaOH, the limit is no more
than 4 ϫ 10Ϫ3 M. GC analysis is not suitable because
N-chloro-3-azabicyclo[3,3,0]octane partially decom-
poses in the injector. Preliminary tries have shown that
AZA/ClAZA interaction is negligible under the con-
ditions of the study. The reaction kinetics were fol-
lowed simultaneously by HPLC and UV spectropho-
tometry.
Order and Stoichiometry
The measurements were carried out at 25ЊC over a
NaOH concentration interval of 0.1 to 1 M. The
ClAZA contents were fixed between 1 and 4 ϫ
10Ϫ3 M in order to avoid phase demixtion. The HPLC
chromatograms recorded at different times on a mix-
ture initially 4.02 ϫ 10Ϫ3 M in 5 and 0.25 M in NaOH
show a decrease in the chlorinated derivative peak at
tR ϭ 6.56 mn and the formation of a second peak at
tR ϭ 4.02 mn characteristic of the imine.
Figure 4 Mass spectrum of 3-azabicyclo[3,3,0]oct-2-ene
Figure 5 presents, as an example, the evolution of
the UV spectrum as a function of temperature. One
can observe the decrease of the haloamine absorption
band at ␭ ϭ 257 nm and, correlatively, the appearance
by ES/MS at 35 eV. Existence of two peaks corresponding
ϩ
to monomeric (M ϭ 109) and dimeric (Mϩ ϭ 218) forms.
Examination of the chemical shifts suggests the fol-
lowing structure:
N
2
N
N
The direct injection mass spectrum (Mϩ ϭ 109) does
not allow unambiguous determination because the di-
meric imine dissociates under the analysis conditions.
Because of its lability, nondestructive characterization
by ES/MS spectroscopy was undertaken at 35 eV. Fig-
ure 4 shows the presence of two peaks situated at
Mϩ ϭ 109 and Mϩ ϭ 218, which definitely proves the
dimerization of 3-azabicyclo[3,3,0]oct-2-ene. Ther-
modynamic and X-ray diffraction studies are in pro-
gress in order to determine the complete structure of
this new molecule.
Kinetics of Formation of 3-
Azabicyclo[3,3,0]Oct-2-Ene
One of the difficulties of the kinetic study results from
the low solubility of ClAZA and the imine in water.
To follow the reaction in one phase, it is necessary to
use low concentrations. For example, at pH ϭ 7 and
Figure 5 Dehydrohalogenation of N-chloro-3-azabicy-
clo[3,3,0]octane. UV absorption spectra of ClAZA
(257 nm) and imine (225 nm) with time.

KINETICS OF DEHYDROHALOGENATION
133
Table I Dehydrohalogenation of N-Chloro-3-Azabicyclo[3,3,0]Octane in Alkaline Medium: Stoichiometry Imine/
ClAZA
Time
(mn)
[ClAZA] ϫ 103
␦[ClAZA] ϫ 103
[imine] ϫ 103
(M)
(M)
(M)
[imine]/␦[ClAZA]
25
97
3.86
3.43
2.96
2.43
2.02
1.67
1.37
1.10
0.82
0.61
0.32
0.16
0.59
1.06
1.59
2.00
2.35
2.65
2.92
3.20
3.41
3.70
–
–
0.59
1.05
1.62
2.08
2.36
2.63
2.88
3.11
3.43
3.71
1.007
0.992
1.022
1.039
1.004
0.992
0.986
0.972
1.005
1.003
199
329
467
564
695
829
1009
1197
1619
of the characteristic band of 4 at ␭ ϭ 225 nm. One
note an isosbestic point at ␭ ϭ 232 nm, proving that
only these two compounds coexist in the reaction me-
dium and that they are linked by a stoichiometric re-
lation.
rhenius law. The curve Log k ϭ f(1/T) is a line of
slope ϪE/R and ordinate at the origin Log A
(r2 ϭ 0.999). E and A represent the energy and the
activation energy of the reaction, respectively
1
(E en kcal molϪ ).
Table I shows that ClAZA/imine ratio is constant
and close to unity. Figure 6 shows the variations of
ClAZA and imine concentrations with respect to time.
Under these conditions, the rate of organohaloamine
disappearance is obtained from the equation:
␤
Ϫd[C7H12NCl]/dt ϭ k[C7H12NCl]␣[HOϪ]0
The kinetic parameters were determined by Ostwald
method. To evaluate ␣, we performed three series of
measurements corresponding to a constant concentra-
tion of 0.25 M NaOH and to ClAZA concentrations
going from
1
to 4.02 ϫ 10Ϫ3 M. The curves
Log[ClAZA]0/[ClAZA] ϭ f(t) are in all cases straight
␤
lines (␣ ϭ 1) of the same slope ␸ ϭ k[HOϪ]0 . The
value of ␤ was determined under the same temperature
conditions with a constant concentration of 2 ϫ
10Ϫ3 M in 5 and NaOH strengths between 0.1 and
␤
1 M. Log ␸ ϭ f(Log[HOϪ]0 ) is
a line passing
through the origin Log k and of slope ␤ ϭ 1 (r2 ϭ
0.999). The overall results are summarized in Table
II. In consequence, the bimolecular rate constant of
the reaction at T ϭ 25ЊC is equal to k ϭ 103 ϫ
6
1
1
10Ϫ6 (Ϯ3 ϫ 10Ϫ ) MϪ sϪ .
Influence of Temperature
The temperature influence was studied between 15 and
44.4ЊC for NaOH and C7H12NCl concentrations of
0.25 M and 4 ϫ 10Ϫ3 M, respectively. The variation
of k as a function of temperature agrees with the Ar-
Figure 6 Kinetics of N-chloro-3-azabicyclo[3,3,0]octane/
NaOH reaction. Variation of imine and ClAZA concentra-
tions as
a
function of time ([ClAZA] ϭ 4.06 ϫ
Ϫ3
10 M; [NaOH] ϭ 0.25 M; and T ϭ 25ЊC).

134
ELKHATIB ET AL.
Table II Kinetics of Dehydrohalogenation of N-Chloro-3-Azabicyclo[3,3,0]-Octane.
Determination of the Bimolecular Rate Constant k at T ϭ 25ЊC
Ϫ
1
Ϫ
Ϫ1
[ClAZA] ϫ 103(M)
[NaOH](M)
␸ ϫ 106(s
)
k ϫ 106(M 1 s
)
1.01
2.02
4.02
2.03
2.05
2.04
2.02
0.25
0.25
0.25
0.10
0.50
0.75
1.00
25.2
26.0
25.5
10.3
51.5
78.0
105.0
101
104
102
103
103
104
105
1
1
k ϭ 2.95 ϫ 1011 exp(Ϫ21.9/RT) MϪ sϪ
nation of which the mechanism could be the follow-
ing:
From these one can determine the reaction entropy and
activation enthalpy:
N
Cl ϩ ϪHO
Ah
⌬H0# ϭ E Ϫ RT; ⌬S0# ϭ R Log
(5)
ekBT
H
where kB and h are the Boltzmann and Planck con-
1
N
Cl
stants, respectively (kB ϭ 1.380 ϫ 10Ϫ23 J KϪ ; h ϭ
6.623 ϫ 10Ϫ34 J s). The quantities (5) have the follow-
ing numerical values.
H
ϪOH
⌬H0# ϭ 89(Ϯ6) kJ molϪ ;
1
1
1
⌬S0# ϭ Ϫ33.6(Ϯ3.5) J molϪ KϪ
N ϩ ClϪ ϩ H2O
Mechanistic Aspects
The existence of an isosbestic point indicates synchro-
nization between the disappearance of ClAZA and the
formation of imine. Therefore, the reaction does not
pass through a stable intermediate. According to AN-
BAR and YAGIL [15], in the case of dimethylchlor-
amine, the reaction should pass through dimethylhy-
droxylamine (SN2 mechanism) that then dehydrates
to form N-methylmethanimine:
The hydrogen in vicinal position to the nitrogen
atom has acidic character due to the inductive effect
of the chlorine atom. When exposed to a strong base
the proton is removed with simultaneous elimination
of chlorine.
In conclusion, the present study describes the syn-
thesis and characterization of a new molecule, 3-aza-
bicyclo[3,3,0]oct-2-ene, that dimerizes to form a white
solid. The application of the Raschig process to the
synthesis of bicyclic hydrazines requires very strict
operating conditions in order to avoid the precipitation
of the dimer. This work underscores the necessity of
operating in strongly alkaline medium to neutralize the
transient formation of organohaloamine as a precursor
of the imine. However, this operating condition pres-
ents the disadvantage of requiring a heterogeneous
medium and of diminishing the hydrazine yield on ac-
count of the hydrolysis of the monochloramine to hy-
droxylamine. A global kinetic model taking all of the
interactions into account is forthcoming.
(CH3)2NCl ϩ NaOH !: (CH3)2NOH ϩ NaCl
(CH3)2NOH !: CH3N"CH2 ϩ H2O
Laboratory trials investigating dimethylhydroxylam-
ine reactivity show that it is stable and can therefore
not be the origin of the imine. Also, an interaction
between dimethylchloramine and dimethylhydroxy-
lamine is excluded because that leads to liberation of
gas and other products.
The formation of imine thus results from one single
elementary process that corresponds to an E2 elimi-

KINETICS OF DEHYDROHALOGENATION
135
EXPERIMENTAL PART
Reactants
molar extinction coefficient is consistent with those
observed for secondary chloramines [29].
3-azabicyclo[3,3,0]oct-2-ene is prepared at ambient
temperature in concentrated solution by the action of
NaOH on a ClAZA solution. The reaction is slow and
takes several days. The white precipitate formed is
separated, washed, and dried. Its purity was deter-
mined by GC (99.9%).
Reactants and salts used were reagent grade products
of Prolabo RP and Aldrich. The water used was treated
by passage through an ion exchange resin then twice
distilled in a silice apparatus, deoxygenated, and
stored under nitrogen.
3-azabicyclo[3,3,0]octane is not commercially
available. It is prepared starting from an acidic solu-
tion of AZA sulfate (16%) obtained from ORIL SA.
After neutralization, the mixture is distilled at
760 torr. One obtains at the head of the column a het-
eroazeotropic solution (bp ϭ 98.4ЊC) titrating 29.8%
in amine. Treatment with NaOH followed by redistil-
lation under vacuum leads to the 99.9% pure product
(GC).
N-chloro-3-azabicyclo[3,3,0]octane is obtained
quantitatively by chlorination of 3-azabicyclo-
[3,3,0]octane (1–2% excess AZA) by hypochlorite
ion (reaction 4).
Apparatus
Ultraviolet spectra were obtained with a CARY 1E
double beam spectrometer with 1 cm pathlengh quartz
cells. HPLC analysis were carried out on a BECK-
MAN 421A chromatograph equipped with a UV de-
tector of variable wavelength. The column was a
250 ϫ 4.6 mm ODS (dp ϭ 5 ␮m) and the mobile
phase was H2O/CH3OH (22%/78% v/v) with a flow
rate of 1 mL mnϪ . NMR data were obtained with a
1
high resolution BRUKER AM300 spectrometer at
300 MHz for 1H and 75 MHz for 13C. All NMR anal-
ysis were recorded in CDCl3 solution. Chemical shifts
are given in ␦ values (ppm) against Si(CH3)4 as the
internal standard. IR spectra were measured with a
BECKMAN 842 instrument with CsI cells.
NH ϩ ClOϪ
MS analysis were performed on DELSI NERMAG
apparatus consisting of a GC chromatograph and an
electron impact (70 eV) mass spectrometer. The chro-
matographic separation was done on a 30 m long
NCl ϩ HOϪ
(4)
DB17 capillary column (50% phenyl). The analytical
1
Thus, upon combining equal volumes (100 mL) of
NaOCl (60 ϫ 10Ϫ3 M) and amine (62 ϫ 10Ϫ3 M) so-
lutions at room temperature, the solution phase sepa-
rates to give a pale yellow oil phase. This product,
slightly soluble in water, decomposes at 70ЊC during
distillation by liberating a gas and depositing carbon.
Hexane extraction followed by cryogenic transfer
leads to a liquid that immediately degrades. It is there-
fore prepared in situ under quasistoichiometric con-
ditions.
conditions follow: Helium ϭ 2 mL mnϪ , Tinj.
ϭ
250ЊC, and Tcol. ϭ 60ЊC/200ЊC (8ЊC mnϪ ). The ES/
MS spectra were performed using a HP electrospray
59987A linked with a HP 5989A mass spectrometer.
This technique requires preliminary extraction with
methanol and the addition of acetic acid until the ali-
quot reaches 1%. The mixture is then introduced to the
1
chamber by injection with a flow rate of 2 ␮L mnϪ
1
and the spectrum is obtained at 35 eV.
Because of its instability in the pure state and its
thermodegradability, the mass spectrum was realized
by ES/MS. One can observe two intense peaks of mass
146 and 148 (32% relative abundance) that are char-
acteristic of the presence of chlorine 37 and 35 iso-
topes. This result was confirmed by the ion fragment
of m/e ϭ 111 that corresponds to the loss of a Cl atom.
The spectral data of 5 were determined in aqueous
medium after preliminary determination by iodometry
[28]. This compound alternatively was prepared by the
direct action of a chloramine solution on protonated
AZA at pH ϭ 8 and T ϭ 25ЊC (reaction 2). The two
methods lead to identical UV and mass spectra. The
Procedure and Analysis
It consists of two thermostated vessels of borosilicate
glass, one on top of the other and joined by a conical
fitting. Each one contains one of the two reactants. The
lower reactor (200 mL), contains a magnetic stirrer
and has inlets to allow the measurement of temperature
and removal of aliquots for analysis. The upper cylin-
drical vessel (100 mL), is blocked at its base by a solid
machined stopper (17 mm i.d.) fastened to a control
rod. This setup allows the rapid introduction of the
ampoule contents into the reactor, and therefore a pre-
cise definition of the start of the reaction. The HPLC

136
ELKHATIB ET AL.
analysis of the chlorinated derivative does not present
any difficulty as the molecule contains a chromophore
and a sufficiently high absorption coefficient. This
contrasts with compound 4, which absorbs more
weakly and at a wavelength of 225 nm. Direct injec-
tion of the basic aliquot does not allow the imine ev-
olution to be monitored with sufficient sensitivity.
To alleviate these difficulties, we extracted the re-
action mixture into hexane. This operation presents a
double advantage. It allows us to quench the reaction
by separating the reactants of different polarities and
to concentrate the products in an organic phase by a
volume effect. Under these conditions, the concentra-
tion of compound i in the aqueous phase is calculated
from the equation:
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23. A. Scho¨nberg, R. Moubasher, M. Z. Barakat, J. Chem.
Soc., 2504 (1951).
The imine and ClAZA solutions were analysed by
UV spectrophotometry. Due to spectral interference,
the optical measurements were taken at two wave-
lengths ␭ ϭ 225 nm and ␭ ϭ 280 nm. The imine
1
2
absorption at ␭ being zero, the concentrations of 4
2
and 5 were calculated from the following equations
(l ϭ 1 cm):
24. S. W. Fox, M. W. Bullock, J. Amer. Chem. Soc., 73,
2754 (1951).
25. R. C. Petterson, U. Grzeskowiak, J. Org. Chem., 24,
1414 (1959).
A(␭1, t)
[ClAZA] ϭ
␭
1
⑀
ClAZA
␭
␭
2
26. P. Kovacic, M. K. Lowery, J. Org. Chem., 34, 911
(1969).
27. C. M. Sharts, J. Org. Chem., 33, 1008 (1968).
28. W. Markwald, M. Willie, Ber., 56, 1319 (1923).
29. M. Ferriol, J. Gazet, R. Rizk-Ouaini, Anal. Chim. Acta,
231, 161 (1990).
1
[A(␭2, t)⑀ClAZA Ϫ ⑀ClAZA A(␭1, t)]
[Imine] ϭ
␭
1
␭
1
⑀
⑀
lmine
ClAZA
where ⑀Imine ϭ 172 MϪ cmϪ , ⑀ClAZA ϭ 118 MϪ
cmϪ et ⑀ClAZA ϭ 209 MϪ cmϪ .
␭
1
1
1
␭
1
1
1
␭
2
1
1