Synthesis of hydroxyethylhydrazine by the Raschig process and comparison with synthesis by the alkylation process

Article abstract of DOI:10.1002/kin.20559

The Raschig synthesis of hydroxyethylhydrazine (HEH) is studied, that is, the reaction of monochloramine on ethanolamine. The formation of HEH is monitored by UV spectrometry, and the influence of temperature and pH is studied. The primary reaction is an SN₂-type mechanism, whereas the main secondary reaction is the oxidation of HEH by monochloramine. This reaction is also monitored by UV spectrometry, and the oxidation product is identified by GC-MS analysis, showing the formation of hydroxyethylhydrazone. The reaction mechanisms and the rate constants were determined, and the results permit establishing the main reactions occurring during HEH synthesis. These reactions were validated in a concentrated medium, with the systematic study of the influence of the molar ratio p ([HEH]₀/[NH₂Cl] ₀) and the final sodium hydroxide concentration and temperature. A comparison is made with the other synthesis process already published, that is, the alkylation of hydrazine by either chloroethanol or epoxide.

Full text of DOI:10.1002/kin.20559

Synthesis of
Hydroxyethylhydrazine by
the Raschig Process and
Comparison with Synthesis
by the Alkylation Process
V. GOUTELLE, V. PASQUET, A. EL HAJJ, A. J. BOUGRINE, H. DELALU
Laboratoire Hydrazines et Proce´de´s, Universite´ Claude Bernard Lyon 1, UMR CNRS 5179, Baˆtiment Berthollet, 22 Avenue
Gaston Berger, F-69622 Villeurbanne Cedex, France
Received 18 May 2010; revised 16 November 2010, 22 February 2011; accepted 26 February 2011
DOI 10.1002/kin.20559
Published online 27 April 2011 in Wiley Online Library (wileyonlinelibrary.com).
ABSTRACT: The Raschig synthesis of hydroxyethylhydrazine (HEH) is studied, that is, the reac-
tion of monochloramine on ethanolamine. The formation of HEH is monitored by UV spectrom-
etry, and the influence of temperature and pH is studied. The primary reaction is an SN2-type
mechanism, whereas the main secondary reaction is the oxidation of HEH by monochloramine.
This reaction is also monitored by UV spectrometry, and the oxidation product is identified by
GC–MS analysis, showing the formation of hydroxyethylhydrazone. The reaction mechanisms
and the rate constants were determined, and the results permit establishing the main reactions
occurring during HEH synthesis. These reactions were validated in a concentrated medium,
with the systematic study of the influence of the molar ratio p ([HEH]0/[NH2Cl]0) and the
final sodium hydroxide concentration and temperature. A comparison is made with the other
synthesis process already published, that is, the alkylation of hydrazine by either chloroethanol
or epoxide. ꢀ 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 331–344, 2011
C
candidate for the satellite propulsion system. Indeed,
its specific impulsion is of the same order as that of
hydrazine (273 s for HEH and 283 s for hydrazine), but
its saturated vapor pressure is much smaller (1.33 Pa
for HEH and 1.89 × 103 Pa for hydrazine). This is very
important because hydrazine and its derivatives are
toxic molecules. In consequence, studies were carried
out by different laboratories and in 2001, the U.S. Air
Force took out a patent [3] for the preparation of HEH
salts and their applications as ergols or explosives. The
different salts are as follows:
INTRODUCTION
2-Hydroxyethylhydrazine (HEH) is currently used as a
precursor in the pharmaceutical industry [1]; it is also
used in the cosmetics, agrochemical and photographic
industries. However, the most promising application is
the aerospace industry [2,3] because it will be a good
Correspondence to: V. Pasquet; e-mail: veronique.pasquet@
univ-lyon1.fr.
c
ꢀ
2011 Wiley Periodicals, Inc.

332
GOUTELLE ET AL.
[HO-CH2-CH2-NH2-NH+2 ][X−]
or
HO-CH2-CH2-NH-NH2 + mHX −→
[HO-CH2-CH2-NH2-NH23+][X−]2
with HX = HNO3, HClO4, HN(NO2)2, HC(NO2)3
m = 1, 2
The Apparatus and Experimental Protocol
Since that time, the interest in this molecule has
remained relevant.
The apparatus was composed of two parts: The upper
part consisted of a double-walled cylindrical bulb with
a capacity of 200 mL in which a temperature sensor was
introduced. A wide diameter needle valve at the base of
the bulb ensured that the liquid flowed rapidly. The bulb
was connected to the lower part which was a thermo-
static reactor with a capacity of 500 mL. Several inlets
allowed the introduction of nitrogen into the reactor,
taking samples and measuring temperature. Agitation
was ensured by using a magnetic stirring bar. The bulb
and the reactor were kept at constant temperature by
using a Julabo cryo-thermostat.
The ethanolamine (EA) or HEH solution (50 mL)
was introduced under nitrogen into the reactor, whereas
the NH2Cl solution (50 mL) was introduced into the
upper part. When the temperature was homogeneous,
the reagents were mixed together and samples were
taken under nitrogen.
In a previous paper [4], HEH was synthesized by
alkylation of N2H4 with 2-chloroethanol (CletOH)
with or without a strong base. Another widely used
method is the Raschig process. However, it has two
main disadvantages: low reagent concentrations, espe-
cially chloramine, and a large number of secondary
reactions. On the other hand, it has several advantages:
the reaction is carried out in water, the reagents are
less pollutant and expensive, and the process does not
use highly toxic reagents such as carcinogenic nitrate
and nitroso derivatives, thereby preserving the envi-
ronment. Thus, the aim of this paper is to describe
HEH synthesis by using the Raschig process and its
advantages and then compare the two methods.
EXPERIMENTAL
Reagents
Analyses
Ethanolamine (99% purity) was provided by Aldrich,
and ammonia in aqueous solution (32%) was provided
by Prolabo. The solutions of sodium hypochlorite at
48◦ chlorometry were provided by ELF-ATOCHEM,
kept at 5◦C, and systematically analyzed before use.
Monochloramine (NH2Cl) is not commercially
available so it was prepared at −10◦C by reacting
sodium hypochlorite (25 mL, 48◦ chlorometry) with
a mixed ammonia solution NH3/NH4Cl (25 mL, 3.6
M/2.38 M) in the presence of ethyl ether (40 mL). For
the kinetic studies, NH2Cl was purified by successive
extractions with water and then stored at 5◦C in ethyl
ether to keep it stable. The aqueous solutions were ob-
tained just before use by reextraction from the ether
phase. The residual solvent and ammonia traces were
eliminated by vacuum treatment. At this stage of prepa-
ration, the NH2Cl concentration was between 0.1 and
0.15 M.
The different reactions involved in the system
EA/NH2Cl were studied by ultraviolet (UV) either
directly or by HPLC (high performance liquid chro-
matography). The reaction products were character-
ized by coupled GC–MS (gas chromatography–mass
spectrometry).
The different tests were carried out at pH 12.89 and
T = 25◦C, in a reductive medium for HEH concentra-
tions between 8 and 40 × 10−3 M.
UV Spectrometry. A CARY 100 dual beam spectrom-
eter from VARIAN was used (quartz cells from 1 to
10 mm light pathway), linked to a data acquisition sys-
tem. This device can perform repetitive spectrum scans
between 900 and 180 nm, programmable as a function
of time, measure absorbance at each wavelength, and
superpose and add curves.
The other reagents and salts used in this study
(NaOH, NH4Cl, Na2HPO4, KH2PO4, etc.) were prod-
ucts for analysis at +99% (reagents from Prolabo RP,
Merck, Aldrich, etc.).
HPLC Analysis. Five milliliters of the synthesis so-
lution was taken and added to the same volume of
ethyl ether. After mixing, the solution separated itself
into two phases and the upper phase was extracted and
conditioned at a temperature of 0◦C. The two reagents
Water was purified by using an ion exchange resin.
International Journal of Chemical Kinetics DOI 10.1002/kin

SYNTHESIS OF HYDROXYETHYLHYDRAZINE BY THE RASCHIG PROCESS
333
were isolated in each phase after which the sample was
Absorbance (D)
1.4
analyzed. An Agilent 1100 chromatograph with a bar
iodine detector was used with an Eclipse ODS XDB-
C8 column (grafted phase octadecylsilane) of 150 mm
length and 3 mm diameter (dp = 5 μm). A precolumn
was used for basic injections. The mobile phase was
a mixture of 95% water/5% acetonitrile. The volume
of the manual injection loop was 20 μL, and the flow
rate was 0.5 mL/min. The wavelengths measured by
the bar iodine detector were established at λ = 200,
243, 254 nm.
1.2
1
λ=λmax=243nm
0.8
0.6
0.4
0.2
GC–MS. The samples were analyzed with a 5970
spectrometer from Agilent Technologies, equipped
with a quadrupole analyzer, and the molecules were
ionized by electronic impact (70 eV). The ionic frag-
ments were identified according to their mass/charge
(m/z) ratio. The GC–MS analyses were performed
with an HP-5MS trace analysis column (30 m, 250 μm,
df = 0.25 μm).
time/min
1000
0
0
500
RESULTS AND DISCUSSION
Figure 1 Variation of the absorbance with time at λ =
243 nm, T = 25◦C, p = 21.4, pH 12.89.
Kinetics of HEH Formation by the Reaction
of Monochloramine on Ethanolamine
HEH formation kinetics was initially monitored at a
temperature of 25◦C and a pH of 12.89 (0.1 M NaOH).
Excess EA was used to limit the secondary reactions.
These experimental conditions are in accordance with
the constraints imposed by the Raschig synthesis:
NH2Cl was separately prepared from sodium
hypochlorite and ammonia:
by monitoring the NH2Cl concentration. The spectrum
of a reaction mixture at different times is complex
and involves several steps. Initially, the absorbance of
NH2Cl decreases and shifts to a higher wavelength.
The absorbance does not tend toward zero, but toward
a value that depends on the initial conditions. At the end
of the reaction, a new absorption peak appears. It in-
creases slowly and shifts to lower wavelengths. These
results can be expressed quantitatively when monitor-
ing the variation of the absorbance with time at λ =
243 nm (Fig. 1). After a continuous decrease to about
37%, the curve stabilizes and then increases again. The
anomaly observed at the end of the reaction is due to
interference between the absorption peak of NH2Cl,
which decreases, and the increase of a peak related to a
chromophore product “P” that is not due to the forma-
tion of HEH, the latter failing to provide any peak un-
der UV spectrometry. The absence of isobestic points
(dDλ/dt = 0) excludes any stoichiometric relation be-
tween NH2Cl and P. Consequently, the formation of P
is subsequent to the NH2Cl/EA reaction. It must re-
sult from an interaction between HEH and one of the
two reagents, namely NH2Cl. This interpretation will
be further confirmed by an exhaustive study of HEH
oxidation by NH2Cl. Indeed, interference is null at the
beginning of the reaction, but increases with the de-
gree of conversion. UV spectrometry then permits the
NH4Cl
OCl− + NH3 −→ NH2Cl + OH−
Then it was used as a reagent to form HEH:
NH2Cl + HO-(CH2)2-NH2
k1
−→ HO-(CH2)2-NH-NH2 + Cl− + H2O
OH−
k2
NH2Cl + OH− −→ NH2OH + Cl−
These two reactions, formation of HEH from NH2Cl
and hydrolysis of NH2Cl, are simultaneous.
Because of the high value of the reaction constants,
the experiments were carried out in a diluted medium,
using reagent concentrations between 10−3 and 10−2
M. The ionic strength of the medium was imposed by
the NaOH concentration (0.1–1 M). Under these con-
ditions, the kinetic parameters of the reaction between
NH2Cl and EA were determined by UV spectrometry,
International Journal of Chemical Kinetics DOI 10.1002/kin

334
GOUTELLE ET AL.
Table I Determination of the Kinetic Parameters of the Reaction between NH2Cl and EA (T = 25◦C, [NaOH] = 0.1 M)
T (◦C)
[EA]0 (10−2 M)
[NH2Cl]0 (10−3 M)
p = [EA]0/[NH2Cl]0
k1 (10−1 M−1 min−1
)
R2
25
25
25
25
25
2.2
2.6
3.2
4.8
6.1
2.8
2.8
2.9
2.9
2.9
7.9
9.2
11.2
16.2
21.4
1.62
1.61
1.62
1.62
1.61
0.999
0.998
0.999
0.998
0.993
precise determination of the rate laws from the NH2Cl
concentration–time curves, limiting the measurement
to the half time of the reaction.
leads to the following equation:
1
[NH2Cl]0 [EA]
ln
[EA]0 − [NH2Cl]0 [EA]0 [NH2Cl]
= k1t (3)
The Rate Laws. The rate of NH2Cl disappearance is
expressed by the relation (1) according to the two reac-
tions described above: formation of HEH from NH2Cl
and hydrolysis of NH2Cl.
The plot ln A/([EA]0− [NH2Cl]0) = f (t), with A =
[NH2Cl]0 [EA]/[EA]0 [NH2Cl] at 25◦C, pH 12.89, and
a molar ratio p = [EA]/[NH2Cl] = 11.2, is linear.
The straight line obtained goes through the origin with
a slope equal to 1.62 × 10−1 L mol−1 min−1 and a
correlation coefficient R2 = 0.999.
d[NH2Cl]
−
= ν1k1 [NH2Cl]α [EA]β
+ k2 [NH2Cl] [OH−]
dt
(1)
A similar treatment was carried out for a series of
mixtures of different reagent compositions, to verify
invariability k1 at a fixed pH and temperature. The
uncertainty of measurement is about 5% for k1 and
the other kinetic parameters determined in this paper.
The results are presented in Table I.
where ν1 is the stoichiometry coefficient and k1, α,
β, respectively, the rate constant of the reaction com-
pared to NH2Cl and the partial orders compared to the
reagents. The second term is related to NH2Cl hydrol-
ysis, which can be neglected under the experimental
conditions studied (pH < 13).
The kinetic parameters were determined by integra-
tion, by considering α = β = 1. Under these condi-
tions, the NH2Cl concentration was determined from
the absorbance at λ = 243 nm at each instant.
The values obtained are almost constant considering
the experimental errors. Thus, at T = 25◦C and pH
12.89, the average value of k1 is 1.62 × 10−1 L mol−1
min−1
.
Influence of pH. Concerning the Raschig process, an
increase in medium alkalinity generally leads to an
increase in the reaction rate. A systematic study was
carried out for HEH for a concentration of NaOH be-
tween 0.1 and 1 M. The pH values were calculated
by using the works of Akerlof and Kegeles [5,6] con-
cerning the determination of activity coefficients in
concentrated solutions. The tests were carried out for
a constant concentration of NH2Cl (∼2.9 × 10−3 M)
and EA (∼60 × 10−3 M).
Dλ(t)
[NH2Cl] =
εl
(ε = 4581 mol−1cm−1; l = 1 cm)
(2)
For unity stoichiometry (ν = 1), the instantaneous con-
centration of EA was deduced by the formula
[EA] = [EA]0 − [NH2Cl]
The application of the same analytical method leads
to an almost twofold increase in k1 (2.38 × 10−1 M−1
min−1 at pH 14). However, these values require a cor-
rection because NH2Cl hydrolysis cannot be neglected
under the experimental conditions studied. This reac-
tion was studied by Anbar and Yagil [7]. It follows
a kinetic law of order 2 compared to the reagents
(k2 = 62 × 10−6 M−1 s−1 or 3.72 × 10−3 M−1 min−1 at
T = 25◦C).
where [EA]0 represents the amine concentration at
t = 0.
By representing the initial NH2Cl concentration by
[NH2Cl]0, the integration of relation (1),
ꢀ
ꢀ
[NH2Cl]
t
d[NH2 Cl]
−
= k1
dt
[NH2Cl]([EA]0 − [NH2 Cl])
[NH2Cl]0
0
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SYNTHESIS OF HYDROXYETHYLHYDRAZINE BY THE RASCHIG PROCESS
335
Table II Influence of pH on the Hydrazine Formation Constant k1 and Its Corrected Value ϕ0 (T = 25◦C)
pH
[EA]0 (10−2 M)
[NH2Cl]0 (10−3 M)
p = [EA]0/[NH2Cl]0
k1 (10−1 M−1 min−1
)
ϕ0 (10−1 M−1 min−1
)
12.9
13.2
13.6
13.8
6.1
6.0
6.1
6.0
2.9
2.9
2.9
2.8
21.4
21.0
21.5
21.4
1.61
1.71
2.04
2.38
1.55
1.59
1.65
1.76
Under these conditions, we can write
d[NH2Cl]
The plot ln k1 = f(1/T) gives a straight line with a
slope –Ea/R and a y-intercept ln A1. This corresponds
to the activation energy and to the Arrhenius factor:
−
= [NH2Cl](k1[EA]0 + k2[OH−]0)
dt
k1 = 3.06 × 107 exp(−57.5/RT)
= ϕ0[NH2Cl]
(k−1 in M−1 s−1, Ea1 in kJ mol−1
)
To ensure sufficient excess EA and during the first
moments of the reaction (isolation method), the term
between brackets can be considered as constant.
The bimolecular constant k1 can be written as
from which the enthalpy and the entropy can be de-
duced:
ꢀH10# = Ea1 − RT ; ꢀS10# = R ln(A1h/ekBT ) (5)
ϕ0 − k2[OH−]0
k1 =
(4)
[EA]0
where kB and h represent the Boltzmann constant
and the Planck universal constant, respectively (kB =
1.380 × 10−23 J K−1; h = 6.623 × 10−34 J s).
The results for both treatments are reported in Table II.
After correction, we noted a moderate increase in the
reaction rate. Therefore, it is not useful to carry out the
synthesis in a very alkaline medium.
This gives ꢀH10# = 55.0 kJ mol−1 and ꢀS10#
=
−110 J K−1 mol−1. The uncertainty of measurement
is about 6% for these thermodynamic values.
Mechanistic Aspect. The HEH formation mechanism
is of the SN2-type. The limiting step corresponds to
a nucleophilic attack of the electron doublet of the
nitrogen from the amine on the weakly electropositive
site of the nitrogen of the chlorinated derivative. Proton
elimination is instantaneous.
Influence of Temperature. The influence of tempera-
ture was studied between 15 and 45◦C for NH2Cl and
EA concentrations equal to 2.8 × 10−3 and 60 × 10−3
M, respectively. The variation of k1 versus temperature
obeys Arrhenius’ law (Fig. 2).
1/T /K-1
0.0035
-4
+
+
_
0.0031
0.0032
0.0033
0.0034
HO-(CH2)2-NH2
+
NH2-Cl
[H2N-NH2-(CH2)2-OH] Cl
H2N-NH-(CH2)2-OH
+ HCl
y = -6912.7x + 17.237
R2 = 0.9995
-5
The rate of HEH formation, controlled by the limit-
ing step, is bimolecular and thus agrees with the kinetic
results. Its value is linked to the nucleophilicity of the
amine, its degree of substitution, and its electronic en-
vironment. Table III gives the rate constants of the
different hydrazines evaluated in the laboratory. This
table shows that the ratio of the rate constants kf of
the primary, secondary, and tertiary amines compared
to N2H4 are equal to 65, 800, and 2000, respectively,
thus equivalent to those observed in the case of the
Hofmann reactions (reaction of NH3 and amines on
the halogenated carbonated derivatives).
-6
-7
ln k1
Figure
2 Determination of activation energy Ea1.
[NH2Cl]0 = 2.8 × 10−3 M, [EA]0 = 60 × 10−3 M,
[NaOH]0 = 0.1 M.
The rate constant of HEH formation is about
two times lower than its monosubstituted homologue
International Journal of Chemical Kinetics DOI 10.1002/kin

336
GOUTELLE ET AL.
Table III Influence of Amine Nucleophilicity on the Hydrazine Formation Constant kf (pH 13 and T = 25◦C)
Amine
Substitution Degree
Hydrazine Formed
kf (M−1 s−1
)
T (◦C)
Reference
NH3
0
1
1
2
N2H4
0.09 × 10−3
5.09 × 10−3
2.7 × 10−3
72 × 10−3
27.5
25
25
25
25
[12]
[13]
CH3NH2
HO(CH2)2NH2
(CH3)2NH
C7H12NH
C5H10NH
(CH3)3N
CH3NHNH2
HO(CH2)2NHNH2
(CH3)2NNH2
C7H12NNH2
C5H10NNH2
(CH3)3NNH2
[14]
[15]
[16]
[12]
2 (cyclic)
2 (cyclic)
3
45.5 × 10−3
56 × 10−3
25
27.5
205 × 10−3
(monomethylhydrazine CH3NHNH2). This result is
due to the electroattractive effect of the terminal hy-
droxyl.
At pH ≤ 12.89, k1 is practically constant, whereas it
increases progressively at pH ≥12.89. Anbar and Yagil
[8] first established that the catalytic effect of OH− ions
The UV analysis (Fig. 3) shows two consecutive
reaction processes: First, the decrease in the NH2Cl
peak at λ = 243 nm is limited by the increase of a
chromogen peak “D” that gives an isobestic point at
λ1 = 290 nm and a pseudoisobestic point at λ2 =
234 nm. These two points mean that the disappearance
of NH2Cl and the formation of D are simultaneous.
could be explained considering the partial dissociation
of NH2Cl into chloramide NHCl− ion (pKaNH Cl
=
2
k3
18). They compared the relative rates of the reaction of
ammonia, mono-, di-, and triamine in alkaline medium
with NH2Cl. These rates increase sharply with the
degree of amine substitution. On the contrary, they
noted the absence of any diminution of the rate when
NH2Cl was substituted. Previous works of our lab-
oratory [9,10] confirmed these results and permitted
establishing the following reaction scheme:
ν1NH2Cl+ν2HEH −→ ν3D
After a longer period, UV analysis showed that the ab-
sorption bands do not pass through the isobestic points
and that, finally, a new isobestic point appears at λ3 =
247 nm. At this point, only two products were present
in the medium, D, and a new peak F at λ = 224 nm. The
NH2Cl was totallyconsumed. The chromogenproducts
D and F are linked together by the relation
NH2Cl + HO-(CH2)2-NH2
→ HO-(CH2)2-NH-NH2 + HCl
NH2Cl ꢀ NHCl− + H+
k4
ν3D −→ ν4F
To characterize the two processes, GC–MS analyses
were carried out. The initial concentrations for NH2Cl,
HEH, and NaOH were equal to 0.1, 0.11, and 0.5 M,
respectively, which corresponds to HEH/NH2Cl, and
NaOH/NH2Cl ratios almost equal to 1.1 and 5.
The concentrations were a little higher than the re-
action medium, to obtain sufficient sensitivity for the
analyses.
After 10 min reaction, the GC–MS spectrum shows
that residual HEH was observed at t2 = 4.8 min and
a bulky peak located at t1 = 3 min corresponds to the
reaction product. GC–MS analysis gives a mass of m/z
= 74 for this product. Also, the fragmentation analysis
gives the formula
HO-(CH2)2-NH2 + NHCl−
→ HO-(CH2)2-NH-NH2 + Cl−
(6)
This reaction scheme is in accordance with the fact that
NH2Cl reacts with trimethylamine to give a salt and, as
this reaction is also catalyzed by the OH− ions [8–11],
we obtain
(CH3)3N + NH2Cl → (CH3)3NNH+2 Cl−
(basic catalysis)
HO-CH2-CH = N-NH2
Kinetics of HEH Oxidation by NH2Cl
that is, the hydroxyethylhydrazone. Its functional
group corresponds to the UV peak of product F at
λ = 224 nm.
Characterization of the Products. The reaction sys-
tem HEH/NH2Cl was studied either by UV or by
HPLC, and the reaction products were characterized
by GC–MS. In addition, the experiments were carried
out at pH 12.89 and T = 25◦C and for HEH concen-
trations between 8 and 40 × 10−3 M.
Reaction Mechanisms. By analogy with the phe-
nomena observed in our laboratory in the case
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SYNTHESIS OF HYDROXYETHYLHYDRAZINE BY THE RASCHIG PROCESS
337
Figure 3 UV spectra for a reaction mixture HEH + NH2Cl at 25◦C. [HEH]0 = 40 × 10−3M; [NH2Cl]0 = 1.6 × 10−3M;
[NaOH]0 = 0.1M. The first trace was recorded at 2 min and then at every 5 min. [Color figure can be viewed in the online issue,
which is available at wileyonlinelibrary.com.]
of unsymmetrical dimethylhydrazine (UDMH), N-
aminoaza-3-bicyclo[3,3,0]octane and N-aminopi-
peridine (NAP), the first step corresponds to the for-
mation of diazene (aminonitrene):
In aqueous medium, the diazene can be considered
as an alkaline compound capable of trapping protons
according to the following acid–base balance:
+
+
HO-(CH ) -NH = − +H O ꢁ HO-(CH ) -NH
HO-(CH2)2-NH-NH2 + NH2Cl
N
2
2 2
2 2
+
−→ HO-(CH ) -NH = − +NH Cl
k3
= N-H + OH−
N
2
4
2
This is the result of the two following oxidation–
reduction reactions:
In alkaline medium, the equilibrium shifts toward the
neutral entity. In this configuration, since the hydrogen
atom linked to the quaternary nitrogen is “acid,” it is
easily extracted in alkaline medium, leading to an azo
compound that rearranges itself immediately by dy-
namic isomerism to give a hydrazone with a molecular
HO-(CH2)2-NH-NH2
+
→ HO-(CH ) -NH = − +2H++2e−
N
2 2
NH2Cl + 2H++2e− → NH4Cl
International Journal of Chemical Kinetics DOI 10.1002/kin

338
GOUTELLE ET AL.
weight of 74:
Yield ρΝ (%)
80
HO-(CH2)2-N = NH ↔ HO-CH2-CH = N-NH2
70
60
50
40
30
20
10
Rate Laws. The previous results show that the oxida-
tion mechanism of HEH by NH2Cl can be described
by the following two reactions:
NH2Cl + HO-(CH2)2-NH-NH2
−
−→ HO-(CH ) -+ H = +NH + Cl− + H O
k3
N
N
3
2
2 2
OH−
−
HO-(CH ) -+ H =
N
N
2 2
k4
calculation
−→ HO-CH2-CH = NH-NH2
cacul
experimental
expÈrimental
The second process, that is, the rearrangement of
diazene/hydrazone does not control the HEH yield as it
is consecutive. Therefore, only the kinetic parameters
of the aminonitrene formation were determined. The
rate laws were established at pH 12.89 and T = 25◦C.
A specific method was developed to monitor the
chlorinated compound analytically. It consists of ex-
tracting NH2Cl by demixion with a solvent, namely
diethylether. The chlorinated compound is then sepa-
rated and analyzed by HPLC equipped with a UV de-
tector. By using this method, the hydroxylated deriva-
tives that have good affinity with water can be isolated
in the aqueous phase. At the same time, the interac-
tion is blocked in the solvent as no organic reagent is
present.
0
0
p
5
10
15
20
25
Figure 4 Evolution yield of HEH in a concentrated
medium with reagent ratio p ([NAOH]f = 0, 3 M; T =
25◦C; k1 exp = 1.62 × 10−1 M−1 min−1; k2 exp = 2.62 M−1
min−1; k3 = 3.72 × 10−3 M−1 min−1).
The kinetic parameters were determined by integra-
tion using the same methods as described previously:
d[NH2Cl]
r3 = −
The plot
= ν3 k3[NH2Cl]α[HEH]β
dt
The initial concentrations were between 1.7 × 10−3
and 2 × 10−3 M for NH2Cl and between 8 × 10−3 and
40 × 10−3 M for HEH (4.5 ≤ [HEH]0/[NH2Cl]0 ≤
24).
ꢁ
ꢂ
1
[NH2Cl]0[HEH]
[HEH]0[NH2Cl]
ln
= f (t)
[HEH]0 − [NH2Cl]0
Table IV and Fig. 4 show the variation of the NH2Cl
concentration as a function of time for initial concen-
trations of 1.7 × 10−3 M for NH2Cl and 40 × 10−3 M
for HEH.
is linear up to the end of the reaction with a correlation
coefficient of 0.996. Consequently, NH2Cl does not
participate in a secondary reaction process; in fact the
Table IV Evolution of Rate Constant k3 with Time
Time (min)
[NH2Cl] (10−3 M)
ln A
ln A/([HEH]0 – [NH2Cl]0)
k3 (M−1 min−1
)
1
1
6
6
16
16
31
31
47
47
1.54
1.56
0.99
1.00
0.33
0.31
0.08
0.08
0.02
0.02
0.08
0.07
0.51
0.49
1.6
1.66
2.99
3.03
4.29
4.25
2.14
1.72
2.14
1.72
2.40
2.34
2.70
2.79
2.52
2.55
2.38
2.36
13.21
12.89
41.82
43.27
78.06
79.00
111.97
110.86
T = 25◦C, [NH2Cl]0 = 1.7 × 10−3 M, [HEH]0 = 40 × 10−3 M, [NaOH] = 0.1 M with A = ([NH2Cl]0 × [HEH])/([HEH]0 × [NH2Cl]).
International Journal of Chemical Kinetics DOI 10.1002/kin

SYNTHESIS OF HYDROXYETHYLHYDRAZINE BY THE RASCHIG PROCESS
339
Table V Formation and Oxidation Constants of MMH and HEH, pH 12.89
Amine
Substitution Degree
Product Formed
kf (M−1 s−1
)
T (◦C)
Reference
CH3NH2
HO-(CH2)2-NH2
1
1
CH3NHNH2
HO-(CH2)2-NH-NH2
5.09 × 10−3
25
25
[13]
This work
2.66 × 10−3
Hydrazine
Substitution Degree
Intermediary Product
kd (M−1 s−1
)
T (◦C)
Reference
CH3NHNH2
HO-(CH2)2-NH-NH2
1
1
CH3N+H=N−
2.27 × 10−2
4.37 × 10−2
25
25
[13]
This work
HO-(CH2)2-N+H=N−
reaction is composed of two consecutive reactions that
explain the isobestic points.
Formulation of a Kinetic Model
In view of the previous results, the main reactions de-
termining the rate of HEH synthesis by the Raschig
process are
The linear plots obtained at 25◦C for a NaOH con-
centration of 0.1 M (pH 12.89) and different initial
concentrations of HEH and NH2Cl, permit establish-
ing the kinetic parameters of the reaction between HEH
and NH2Cl:
NH2Cl + HO-(CH2)2-NH2
ν3 = α = β = 1 and k3 = 2.62 L mol−1 min−1
k1
−→ HO-(CH2)2-NH-NH2 + H2O + Cl−
(7)
(8)
Table V compares the bimolecular kinetic constants
of formation and degradation for two hydrazines with
a substitution degree equal to unity: monomethylhy-
drazine (MMH) and HEH.
OH−
k2
NH2Cl + OH− −→ NH2OH + Cl−
HO-(CH2)2-NH-NH2 + NH2Cl
At 25◦C and pH 12.89, ratio kd/kf is less favorable
for HEH. It is necessary to operate under nonstoichio-
metric conditions, that is, with a large amount of excess
EA to limit the contact time between NH2Cl and HEH.
+
−
k3
−→ HO-(CH ) -NH = +NH+ + Cl−
(9)
N
2 2
4
+
−
HO-(CH ) -NH =
N
2 2
k4
Influence of the Temperature. The influence of the
temperature was studied at pH 12.89, between 15 and
35◦C for constant concentrations of NH2Cl and HEH
equal to 2 × 10−3 and 40 × 10−3 M, respectively
(p =[HEH]0/[NH2Cl]0 ≈ 20) (Table VI). A plot ln
k3 = f(1/T) leads to the Arrhenius relation (Ea3 in
kJ mol−1):
−→ HO-CH2-CH = N-NH2
(10)
Reaction (7) is the useful step of the synthesis. It is
a bimolecular reaction, and its order is equal to one
compared to each reagent. The second reaction (8) is
the hydrolysis of the chlorinated derivative. As soon
as HEH is formed, it is partially oxidized by NH2Cl
to give an aminonitrene (9) that rearranges itself into
hydroxyethylhydrazone (10).
k3 = 7.95 × 106 exp(−47.7/RT )
(k3 in M−1 s−1,Ea3 in kJ mol−1
)
The enthalpy and the entropy are as follows:
The determination of the residence times in the re-
actor and of the rate of synthesis as a function of initial
reagent concentrations and temperature is linked to the
ꢀH30# = 45.2 kJ mol−1; ꢀ S30# = −121 J K−1 mol−1
Table VI Influence of Temperature on Oxidation Constant k3
T (◦C)
[HEH]0 (10−2 M)
[NH2Cl]0 (10−3 M)
p = [HEH]0/[NH2Cl]0
k3 (M−1 min−1
)
R2
15
20
20
25
25
35
4.0
4.1
4.2
4.0
4.0
4.0
2.0
2.1
2.1
1.7
2.0
2.0
20.0
19.1
20
24.0
20
1.09
1.37
1.36
2.48
2.50
3.76
0.998
0.983
0.989
0.996
0.991
0.982
20.0
[NaOH] = 0.1 M.
International Journal of Chemical Kinetics DOI 10.1002/kin

340
GOUTELLE ET AL.
resolution of the following differential equations:
culate the global composition of the reaction mixture
at t = 0, noted Ci (i = 1–5), after the injection of the
reagents, and at t = ∞, noted Di (i = 2–5).
dx
= −k1a x − k3u x − k2xb0
To achieve this, the volumes of NH2Cl and EA to
be injected are designated by VN and VA, respectively:
dt
da
= −k1 a x
dt
B1
VN = 1000 mL, VA = 103 × p ×
CA
du
= k1a x − k3u x
dt
df
where subscript A represents an EA solution with mass
composition WA:
= k3 u x
dt
where x, a, u, and f are the concentrations of NH2Cl,
EA, HEH, and hydrazone, respectively, at instant t. The
initial concentrations are x = x0, a = a0, u = f = 0,
and b0 stands for the initial NaOH concentration. The
fourth-order Runge–Kutta method was used to resolve
this differential equations system.
WA × 103 × d3
1
M3
CA =
·
100
Under these conditions, the NaOH solution ([NaOH]
= S M) to be introduced into the reactor is composed
of two terms: VS = VS1 + VS2. The first term VS1 corre-
sponds to the neutralization of the residual NH4Cl (B2)
and the H+ ions formed during hydrazine formation:
Transfer in a Concentrated Medium and Optimiza-
tion. The results obtained during the theoretical study
were validated directly in a concentrated medium by
using hypochlorite solutions at a high chlorometric de-
gree. It is necessary to know the composition of synthe-
sis solutions at t = 0 to predict the rate of the reaction
when using the kinetic model. It is also necessary to
take into account the different volumes of reagents to
be introduced, the resulting dilution and the reaction
balance. In particular, the quantities of NaOH to be
introduced at the exit of the NH2Cl reactor (R1) take
into+account the need to neutralize the residual buffer
NH4 /NH3 and the H+ ions provided by the reaction
(B2 + B1)
VS1 = 103
S
The second term corresponds to the amount of NaOH
necessary to obtain the optimized value noted [OH−]f:
ꢃ
ꢄ
[OH−]f VN + VA + VS1 + VS2
VS2 =
S
The instantaneous concentrations Ci and Di are de-
duced from those equations presented in Table VII.
The results were confirmed in a concentrated
medium, by systematically studying the influence of
the molar ratio p, that of the final sodium hydroxide
concentration [OH−]f and that of the temperature.
The experiments were carried out using the fol-
lowing protocol: a freshly prepared and concentrated
NH2Cl solution (volume VN) is alkalized with a vol-
ume VS of a 10 M NaOH solution. The NaOH/NH2Cl
mixture is then introduced under stirring into VA mL
of an EA solution at a determined temperature.
NH2Cl + HO-(CH2)2-NH2
k1
−→ HO-(CH2)2-NH-NH2 + HCl
(11)
At the end of the reaction, the pH of the solution is
increased to 13 to avoid a chlorine transfer reaction
and profit from the pseudocatalytic effect caused by
the OH− ions during the reaction (11).
The calculation was carried out by reacting a
concentrated solution of sodium hypochlorite at 48◦
chlorometric degrees (2.14 M) at −15◦C, with a mixed
ammonia solution NH3/NH4Cl (3.64 M/2.38 M). Un-
der these conditions, the NH2Cl rate is almost quanti-
tative and the resulting solution concentration is equal
to 1.04 M (B1) for NH2Cl and 0.1 M (B2) for NH4Cl.
The following compounds: NH2Cl, NH4Cl, HO-
(CH2)2-NH2, NaOH, and HO-(CH2)2-NH-NH2 are,
respectively, represented by indices from 1 to 5. Con-
sequently, the molecular weights and densities of the
reagents and resulting solutions are, respectively, rep-
resented by the symbols Mi and di. We wanted to cal-
Influence of the p Ratio. The experiments were car-
ried out at a constant temperature of 25◦C, at a con-
stant final NaOH concentration and a constant volume
of NH2Cl (VN = 40 mL), by varying the excess amine.
Passing from p = 5 to p = 20 involves increasing
the yield by 33%, as shown in Fig. 4. The theoretical
curve, in agreement with the experimental results, was
formulated by taking into account the variation of rate
constant k1 with pH. Therefore, yield ρN is 62% for
p = 20.
International Journal of Chemical Kinetics DOI 10.1002/kin

SYNTHESIS OF HYDROXYETHYLHYDRAZINE BY THE RASCHIG PROCESS
341
Table VII Instantaneous Concentrations of the Different Compounds at t = 0 and t = ∞
Compound
NH2Cl
NH4Cl
EA
NaOH
4
HEH
5
Indices
1
2
×3p× 103
103
103
B1
VN + VA + VS
S ×VS
Ci(t = 0)
B1
B2
0
C1
VN + VA + VS
VN + VA + VS
VN + VA + VS
Di(t = ∞)
0
0
C3 − C1
C4 − (C1 + C2)
Yield ρN (%)
Comparison between the Different
Processes Studied to Synthesize HEH
85
In another paper [4], HEH was synthesized by the alky-
lation of N2H4 with 2-chloroethanol (CletOH) in the
presence or not of NaOH. In this first case, N2H4 is
alkylated by ethylene oxide (CH2OCH2) formed in
situ in the presence of NaOH, which is a strong base.
These three processes (Raschig, alkylation by CletOH,
and alkylation by CH2OCH2) can be compared.
The first reaction, bimolecular (kf), involves a nucle-
ophilic reagent (amine or hydrazine) and a molecule
with an electron-deficient site (NH2Cl, CletOH, and
CH2OCH2).
80
75
70
65
60
55
50
(a)
(b)
kf
N + Mδ+ −→ HEH
Temperature /∞C
45
0
In the second step, HEH is involved in a secondary
process of consecutive parallel type (kd).
20
40
60
80
100
Figure 5 Calculated evolution of the HEH yield with tem-
perature for molar ratio p = 30 (a) or p = 20 (b).
ꢅ
kd
HEH + Mδ+ −→
Pi
i
This implies that the operating conditions depend on
the rate ratio between these two reactions (Vf/Vd). kf
and kd, measured during this study, are summarized
in Table VIII, which also indicates ratio kd/kf and the
corresponding activation enthalpy and entropy.
Theoretical Influence of Temperature. The influence
of temperature was studied between 10 and 90◦C for
a final NaOH concentration of 0.3 M and for a ratio
p = 20 and 30 (Fig. 5). Increasing temperature leads
to better yields due to the enthalpy values.
HEH Reaction Mechanisms and Formation Rates.
The bimolecular rates are of the same order for
the Raschig process and alkylation by epoxide
(CH2OCH2). This is due to the nucleophilic and elec-
trophilic power of the reagents, which compensate each
other. EA is much more nucleophilic and basic than
N2H4.
Kinetic Profile/Residence Time. The plug-flow
reactor is the most suitable reactor for limiting contact
between the HEH and NH2Cl formed. Figure 6 shows
the theoretical kinetic profiles in the reactor for two
mixtures (NH2Cl/EA/NaOH) continuously injected at
20 and 80◦C for molar ratio p = 20.
+
HO-(CH2)2-NH2 + NH2 > Cl
HEH
HEH
(k = 2.61 × 10 3 L mol 1 s 1 at 25°C)
(pKa = 9,5)
+
1/2
+1/2
3
NH2-NH2
+
(k = 1.71 × 10 L mol 1 s 1 at 25°C)
(pKa = 8,1)
O
HO-(CH2)2-NH2 >> NH2-NH2
Nucleophilic power
NH2 Cl << CH2OCH2
Electrophilic power
International Journal of Chemical Kinetics DOI 10.1002/kin

342
GOUTELLE ET AL.
Figure 6 Kinetic profile at T = 20 and 80◦C with [NH2Cl]0 = 0.42 M, [EA]0 = 8.47 M. T = 80◦C: (a) [NH2Cl]; (b) [HEH];
(c) [hydrazone]. T = 20◦C: (aꢁ) [NH2Cl]: (bꢁ) [HEH]; (cꢁ) [hydrazone].
(CH2OCH2) ≈ 103kf
Thus, the situation is reversed for their electrophilic
homologue.
The N-Cl linkage of NH2Cl is not very polarized due
Thus
(CletOH)
kf(Raschig) ≈ kf
to the very slight electronegative difference between
the two atoms. This explains the polarization inversion
when a hydrogen atom is replaced by an electrodonor
methyl group. This substituted chloramine becomes
incapable of forming N-N linkage by reacting with
NH3 in an aqueous or anhydrous medium (chlorine
transfer mechanism in liquid ammonia).
HEH Reaction Mechanisms and Degradation and
Alkylation Rates. For identical reagent ratios, the
HEH yields are the same for the two alkylation meth-
ods (CletOH and CH2OCH2). This result is not sur-
prising because the rate constants kf and kd require
the same mechanisms. This is confirmed by acti-
vation enthalpies and entropies. The absolute for-
mation rates are very different (Vf(CH2OCH2) ꢂ Vf
(CletOH)), but the kf/kd ratios are almost identi-
cal. The adjustment variable, that is, ratio [N2H4]0/
[CH2OCH2]0 or [N2H4]0/[CletOH]0, will be low, close
to three, to obtain rates up to 80%.
δ−
δ−
δ+
δ+
H -Cl
2
CH3 NH - Cl
N
This is not the case of the epoxide, which is strongly
electrophilic, due to its favorable spatial configuration
(flat molecule, symmetry, and good site accessibility)
and to greater carbon–oxygen polarization.
The very weak value of the direct alkylation con-
stant by CletOH in comparison with CH2OCH2, can be
explained by the fact that the carbon–chlorine linkage
is less polarized and accessible:
In the case of the Raschig process, the secondary re-
action of dialkylation is replaced by an HEH oxidation
process; the reaction mechanism of which is different
δ+1/2 δ+1/2
N2H4
+
HEH
(k = 1.71 × 10 L mol
(k = 2.18 × 10 L mol
s at 25°C)
O
δ
δ δ+
N2H4 + Cl-CH2-CH2-OH
HEH
s at 25°C)
Cl-(CH2)2-OH << CH2OCH2
Electrophilic power
International Journal of Chemical Kinetics DOI 10.1002/kin

SYNTHESIS OF HYDROXYETHYLHYDRAZINE BY THE RASCHIG PROCESS
343
from the formation mechanism (SN2). Since the bi-
molecular rate constants in favor of degradation are
equal to 14, the adjustment variable [EA]0/[NH2Cl]0
will be at least higher than 20.
CONCLUSION
During this work, a separate kinetic study of for-
mation and degradation reactions permitted identify-
ing the products obtained and establishing a model
composed of
a
system of differential equa-
tions. The resolution of this model can be used
to determine the optimal conditions of HEH
formation.
A kinetic and mechanistic comparison of HEH
synthesis by the Raschig process with alkyla-
tion by CletOH and the CH2OCH2 process was
performed.
Compared with MMH, HEH synthesis by the
Raschig process has two disadvantages: The nucle-
ophilic power of the corresponding amine is lower,
and oxidation of the hydrazine is easier. These prop-
erties are linked to the electroattractive effect of the
terminal OH function. The kinetic parameters obtained
are in agreement with the spatial conformation of the
molecule promoting the interaction between the OH
end group and hydrogen atoms that are potentially
oxidizable.
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International Journal of Chemical Kinetics DOI 10.1002/kin