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 Procédés, Université Claude Bernard Lyon 1, UMR CNRS 5179, Bâtiment 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 /[NH2 Cl]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. C 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 331–344, 2011

INTRODUCTION candidate for the satellite propulsion system. Indeed,

its specific impulsion is of the same order as that of
2-Hydroxyethylhydrazine (HEH) is currently used as a hydrazine (273 s for HEH and 283 s for hydrazine), but
precursor in the pharmaceutical industry [1]; it is also its saturated vapor pressure is much smaller (1.33 Pa
used in the cosmetics, agrochemical and photographic for HEH and 1.89 × 103 Pa for hydrazine). This is very
industries. However, the most promising application is important because hydrazine and its derivatives are
the aerospace industry [2,3] because it will be a good 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
Correspondence to: V. Pasquet; e-mail: veronique.pasquet@
univ-lyon1.fr. salts and their applications as ergols or explosives. The
c 2011 Wiley Periodicals, Inc. different salts are as follows:
332 GOUTELLE ET AL.

[HO-CH2 -CH2 -NH2 -NH+ −

2 ][X ]

HO-CH2 -CH2 -NH-NH2 + mHX −→ or

−
[HO-CH2 -CH2 -NH2 -NH2+
3 ][X ]2

with HX = HNO3 , HClO4 , HN(NO2 )2 , HC(NO2 )3

m = 1, 2

Since that time, the interest in this molecule has The Apparatus and Experimental Protocol
remained relevant.
The apparatus was composed of two parts: The upper
In a previous paper [4], HEH was synthesized by
part consisted of a double-walled cylindrical bulb with
alkylation of N2 H4 with 2-chloroethanol (CletOH)
a capacity of 200 mL in which a temperature sensor was
with or without a strong base. Another widely used
introduced. A wide diameter needle valve at the base of
method is the Raschig process. However, it has two
the bulb ensured that the liquid flowed rapidly. The bulb
main disadvantages: low reagent concentrations, espe-
was connected to the lower part which was a thermo-
cially chloramine, and a large number of secondary
static reactor with a capacity of 500 mL. Several inlets
reactions. On the other hand, it has several advantages:
allowed the introduction of nitrogen into the reactor,
the reaction is carried out in water, the reagents are
taking samples and measuring temperature. Agitation
less pollutant and expensive, and the process does not
was ensured by using a magnetic stirring bar. The bulb
use highly toxic reagents such as carcinogenic nitrate
and the reactor were kept at constant temperature by
and nitroso derivatives, thereby preserving the envi-
using a Julabo cryo-thermostat.
ronment. Thus, the aim of this paper is to describe
The ethanolamine (EA) or HEH solution (50 mL)
HEH synthesis by using the Raschig process and its
was introduced under nitrogen into the reactor, whereas
advantages and then compare the two methods.
the NH2 Cl 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.
EXPERIMENTAL

Reagents Analyses
Ethanolamine (99% purity) was provided by Aldrich, The different reactions involved in the system
and ammonia in aqueous solution (32%) was provided EA/NH2 Cl were studied by ultraviolet (UV) either
by Prolabo. The solutions of sodium hypochlorite at directly or by HPLC (high performance liquid chro-
48◦ chlorometry were provided by ELF-ATOCHEM, matography). The reaction products were character-
kept at 5◦ C, and systematically analyzed before use. ized by coupled GC–MS (gas chromatography–mass
Monochloramine (NH2 Cl) is not commercially spectrometry).
available so it was prepared at −10◦ C by reacting The different tests were carried out at pH 12.89 and
sodium hypochlorite (25 mL, 48◦ chlorometry) with T = 25◦ C, in a reductive medium for HEH concentra-
a mixed ammonia solution NH3 /NH4 Cl (25 mL, 3.6 tions between 8 and 40 × 10−3 M.
M/2.38 M) in the presence of ethyl ether (40 mL). For
the kinetic studies, NH2 Cl was purified by successive UV Spectrometry. A CARY 100 dual beam spectrom-
extractions with water and then stored at 5◦ C in ethyl eter from VARIAN was used (quartz cells from 1 to
ether to keep it stable. The aqueous solutions were ob- 10 mm light pathway), linked to a data acquisition sys-
tained just before use by reextraction from the ether tem. This device can perform repetitive spectrum scans
phase. The residual solvent and ammonia traces were between 900 and 180 nm, programmable as a function
eliminated by vacuum treatment. At this stage of prepa- of time, measure absorbance at each wavelength, and
ration, the NH2 Cl concentration was between 0.1 and superpose and add curves.
0.15 M.
The other reagents and salts used in this study HPLC Analysis. Five milliliters of the synthesis so-
(NaOH, NH4 Cl, Na2 HPO4 , KH2 PO4 , etc.) were prod- lution was taken and added to the same volume of
ucts for analysis at +99% (reagents from Prolabo RP, ethyl ether. After mixing, the solution separated itself
Merck, Aldrich, etc.). into two phases and the upper phase was extracted and
Water was purified by using an ion exchange resin. conditioned at a temperature of 0◦ C. The two reagents

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)
analyzed. An Agilent 1100 chromatograph with a bar
1.4
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 1.2
was used for basic injections. The mobile phase was
a mixture of 95% water/5% acetonitrile. The volume λ=λmax=243nm
of the manual injection loop was 20 μL, and the flow 1
rate was 0.5 mL/min. The wavelengths measured by
the bar iodine detector were established at λ = 200,
0.8
243, 254 nm.

GC–MS. The samples were analyzed with a 5970 0.6

spectrometer from Agilent Technologies, equipped
with a quadrupole analyzer, and the molecules were
ionized by electronic impact (70 eV). The ionic frag- 0.4
ments were identified according to their mass/charge
(m/z) ratio. The GC–MS analyses were performed 0.2
with an HP-5MS trace analysis column (30 m, 250 μm,
df = 0.25 μm). time/min
0
0 500 1000
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
by monitoring the NH2 Cl concentration. The spectrum
temperature of 25◦ C and a pH of 12.89 (0.1 M NaOH).
of a reaction mixture at different times is complex
Excess EA was used to limit the secondary reactions.
and involves several steps. Initially, the absorbance of
These experimental conditions are in accordance with
NH2 Cl decreases and shifts to a higher wavelength.
the constraints imposed by the Raschig synthesis:
The absorbance does not tend toward zero, but toward
NH2 Cl was separately prepared from sodium
a value that depends on the initial conditions. At the end
hypochlorite and ammonia:
of the reaction, a new absorption peak appears. It in-
NH4 Cl
creases slowly and shifts to lower wavelengths. These
OCl− + NH3 −→ NH2 Cl + OH− results can be expressed quantitatively when monitor-
ing the variation of the absorbance with time at λ =
Then it was used as a reagent to form HEH: 243 nm (Fig. 1). After a continuous decrease to about
37%, the curve stabilizes and then increases again. The
NH2 Cl + HO-(CH2 )2 -NH2 anomaly observed at the end of the reaction is due to
k1 interference between the absorption peak of NH2 Cl,
−→
−
HO-(CH2 )2 -NH-NH2 + Cl− + H2 O which decreases, and the increase of a peak related to a
OH
chromophore product “P” that is not due to the forma-
k2
NH2 Cl + OH− −→ NH2 OH + Cl− tion of HEH, the latter failing to provide any peak un-
der UV spectrometry. The absence of isobestic points
These two reactions, formation of HEH from NH2 Cl (dDλ /dt = 0) excludes any stoichiometric relation be-
and hydrolysis of NH2 Cl, are simultaneous. tween NH2 Cl and P. Consequently, the formation of P
Because of the high value of the reaction constants, is subsequent to the NH2 Cl/EA reaction. It must re-
the experiments were carried out in a diluted medium, sult from an interaction between HEH and one of the
using reagent concentrations between 10−3 and 10−2 two reagents, namely NH2 Cl. This interpretation will
M. The ionic strength of the medium was imposed by be further confirmed by an exhaustive study of HEH
the NaOH concentration (0.1–1 M). Under these con- oxidation by NH2 Cl. Indeed, interference is null at the
ditions, the kinetic parameters of the reaction between beginning of the reaction, but increases with the de-
NH2 Cl and EA were determined by UV spectrometry, gree of conversion. UV spectrometry then permits the

International Journal of Chemical Kinetics DOI 10.1002/kin

334 GOUTELLE ET AL.

Table I Determination of the Kinetic Parameters of the Reaction between NH2 Cl and EA (T = 25◦ C, [NaOH] = 0.1 M)
T (◦ C) [EA]0 (10−2 M) [NH2 Cl]0 (10−3 M) p = [EA]0 /[NH2 Cl]0 k1 (10−1 M−1 min−1 ) R2
25 2.2 2.8 7.9 1.62 0.999
25 2.6 2.8 9.2 1.61 0.998
25 3.2 2.9 11.2 1.62 0.999
25 4.8 2.9 16.2 1.62 0.998
25 6.1 2.9 21.4 1.61 0.993

precise determination of the rate laws from the NH2 Cl leads to the following equation:
concentration–time curves, limiting the measurement
to the half time of the reaction.
1 [NH2 Cl]0 [EA]
ln = k1 t (3)
[EA]0 − [NH2 Cl]0 [EA]0 [NH2 Cl]
The Rate Laws. The rate of NH2 Cl disappearance is
expressed by the relation (1) according to the two reac-
tions described above: formation of HEH from NH2 Cl The plot ln A/([EA]0 − [NH2 Cl]0 ) = f (t), with A =
and hydrolysis of NH2 Cl. [NH2 Cl]0 [EA]/[EA]0 [NH2 Cl] at 25◦ C, pH 12.89, and
a molar ratio p = [EA]/[NH2 Cl] = 11.2, is linear.
d[NH2 Cl] The straight line obtained goes through the origin with
− = ν1 k1 [NH2 Cl]α [EA]β a slope equal to 1.62 × 10−1 L mol−1 min−1 and a
dt
correlation coefficient R 2 = 0.999.
+ k2 [NH2 Cl] [OH− ] (1) A similar treatment was carried out for a series of
mixtures of different reagent compositions, to verify
where ν1 is the stoichiometry coefficient and k1 , α, invariability k1 at a fixed pH and temperature. The
β, respectively, the rate constant of the reaction com- uncertainty of measurement is about 5% for k1 and
pared to NH2 Cl and the partial orders compared to the the other kinetic parameters determined in this paper.
reagents. The second term is related to NH2 Cl hydrol- The results are presented in Table I.
ysis, which can be neglected under the experimental The values obtained are almost constant considering
conditions studied (pH < 13). the experimental errors. Thus, at T = 25◦ C and pH
The kinetic parameters were determined by integra- 12.89, the average value of k1 is 1.62 × 10−1 L mol−1
tion, by considering α = β = 1. Under these condi- min−1 .
tions, the NH2 Cl concentration was determined from
the absorbance at λ = 243 nm at each instant.
Influence of pH. Concerning the Raschig process, an
Dλ (t) increase in medium alkalinity generally leads to an
[NH2 Cl] =
εl increase in the reaction rate. A systematic study was
(ε = 4581 mol−1 cm−1 ; l = 1 cm) (2) 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-
For unity stoichiometry (ν = 1), the instantaneous con- cerning the determination of activity coefficients in
centration of EA was deduced by the formula concentrated solutions. The tests were carried out for
a constant concentration of NH2 Cl (∼2.9 × 10−3 M)
[EA] = [EA]0 − [NH2 Cl] and EA (∼60 × 10−3 M).
The application of the same analytical method leads
to an almost twofold increase in k1 (2.38 × 10−1 M−1
where [EA]0 represents the amine concentration at
min−1 at pH 14). However, these values require a cor-
t = 0.
rection because NH2 Cl hydrolysis cannot be neglected
By representing the initial NH2 Cl concentration by
under the experimental conditions studied. This reac-
[NH2 Cl]0 , the integration of relation (1),
tion was studied by Anbar and Yagil [7]. It follows
  a kinetic law of order 2 compared to the reagents
[NH2 Cl]
d[NH2 Cl] t
(k2 = 62 × 10−6 M−1 s−1 or 3.72 × 10−3 M−1 min−1 at
− = k1 dt
[NH2 Cl]0 [NH2 Cl]([EA]0 − [NH2 Cl]) 0 T = 25◦ C).

International Journal of Chemical Kinetics DOI 10.1002/kin

 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) [NH2 Cl]0 (10−3 M) p = [EA]0 /[NH2 Cl]0 k1 (10−1 M−1 min−1 ) ϕ0 (10−1 M−1 min−1 )
12.9 6.1 2.9 21.4 1.61 1.55
13.2 6.0 2.9 21.0 1.71 1.59
13.6 6.1 2.9 21.5 2.04 1.65
13.8 6.0 2.8 21.4 2.38 1.76

Under these conditions, we can write The plot ln k1 = f(1/T) gives a straight line with a
slope –Ea /R and a y-intercept ln A1 . This corresponds
d[NH2 Cl] to the activation energy and to the Arrhenius factor:
− = [NH2 Cl](k1 [EA]0 + k2 [OH− ]0 )
dt
= ϕ0 [NH2 Cl] k1 = 3.06 × 107 exp(−57.5/RT)
(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 from which the enthalpy and the entropy can be de-
between brackets can be considered as constant. duced:
The bimolecular constant k1 can be written as
H10# = Ea1 − RT ; S10# = R ln(A1 h/ekB T ) (5)
ϕ0 − k2 [OH − ]0
k1 = (4)
[EA] 0 where kB and h represent the Boltzmann constant
and the Planck universal constant, respectively (kB =
The results for both treatments are reported in Table II.
1.380 × 10−23 J K−1 ; h = 6.623 × 10−34 J s).
After correction, we noted a moderate increase in the
This gives H10# = 55.0 kJ mol−1 and S10# =
reaction rate. Therefore, it is not useful to carry out the
−110 J K −1 mol−1 . The uncertainty of measurement
synthesis in a very alkaline medium.
is about 6% for these thermodynamic values.
Influence of Temperature. The influence of tempera- Mechanistic Aspect. The HEH formation mechanism
ture was studied between 15 and 45◦ C for NH2 Cl and is of the SN2 -type. The limiting step corresponds to
EA concentrations equal to 2.8 × 10−3 and 60 × 10−3 a nucleophilic attack of the electron doublet of the
M, respectively. The variation of k1 versus temperature nitrogen from the amine on the weakly electropositive
obeys Arrhenius’ law (Fig. 2). site of the nitrogen of the chlorinated derivative. Proton
elimination is instantaneous.
-1
1/T /K
-4 +
+ _
0.0031 0.0032 0.0033 0.0034 0.0035
HO-(CH2)2-NH2 + NH2-Cl [H2N-NH2-(CH2)2-OH] Cl

y = -6912.7x + 17.237 H2N-NH-(CH2)2-OH + HCl

-5 R2 = 0.9995
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-
-6 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 N2 H4 are equal to 65, 800, and 2000, respectively,
-7 thus equivalent to those observed in the case of the
ln k1 Hofmann reactions (reaction of NH3 and amines on
Figure 2 Determination of activation energy Ea1 . the halogenated carbonated derivatives).
[NH2 Cl]0 = 2.8 × 10−3 M, [EA]0 = 60 × 10−3 M, The rate constant of HEH formation is about
[NaOH]0 = 0.1 M. 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 N2 H4 0.09 × 10−3 27.5 [12]
CH3 NH2 1 CH3 NHNH2 5.09 × 10−3 25 [13]
HO(CH2 )2 NH2 1 HO(CH2 )2 NHNH2 2.7 × 10−3 25
(CH3 )2 NH 2 (CH3 )2 NNH2 72 × 10−3 25 [14]
C7 H12 NH 2 (cyclic) C7 H12 NNH2 45.5 × 10−3 25 [15]
C5 H10 NH 2 (cyclic) C5 H10 NNH2 56 × 10−3 25 [16]
(CH3 )3 N 3 (CH3 )3 NNH2 205 × 10−3 27.5 [12]

(monomethylhydrazine CH3 NHNH2 ). This result is The UV analysis (Fig. 3) shows two consecutive
due to the electroattractive effect of the terminal hy- reaction processes: First, the decrease in the NH2 Cl
droxyl. peak at λ = 243 nm is limited by the increase of a
At pH ≤ 12.89, k1 is practically constant, whereas it chromogen peak “D” that gives an isobestic point at
increases progressively at pH ≥12.89. Anbar and Yagil λ1 = 290 nm and a pseudoisobestic point at λ2 =
[8] first established that the catalytic effect of OH− ions 234 nm. These two points mean that the disappearance
could be explained considering the partial dissociation of NH2 Cl and the formation of D are simultaneous.
of NH2 Cl into chloramide NHCl− ion (pKaNH2 Cl =
18). They compared the relative rates of the reaction of k3
ν1 NH2 Cl+ν2 HEH −→ ν3 D
ammonia, mono-, di-, and triamine in alkaline medium
with NH2 Cl. These rates increase sharply with the After a longer period, UV analysis showed that the ab-
degree of amine substitution. On the contrary, they sorption bands do not pass through the isobestic points
noted the absence of any diminution of the rate when and that, finally, a new isobestic point appears at λ3 =
NH2 Cl was substituted. Previous works of our lab- 247 nm. At this point, only two products were present
oratory [9,10] confirmed these results and permitted in the medium, D, and a new peak F at λ = 224 nm. The
establishing the following reaction scheme: NH2 Cl was totally consumed. The chromogen products
D and F are linked together by the relation
NH2 Cl + HO-(CH2 )2 -NH2
k4
ν3 D −→ ν4 F
→ HO-(CH2 )2 -NH-NH2 + HCl
NH2 Cl  NHCl− + H+ To characterize the two processes, GC–MS analyses
were carried out. The initial concentrations for NH2 Cl,
HO-(CH2 )2 -NH2 + NHCl− HEH, and NaOH were equal to 0.1, 0.11, and 0.5 M,
→ HO-(CH2 )2 -NH-NH2 + Cl− (6) respectively, which corresponds to HEH/NH2 Cl, and
NaOH/NH2 Cl ratios almost equal to 1.1 and 5.
The concentrations were a little higher than the re-
This reaction scheme is in accordance with the fact that
action medium, to obtain sufficient sensitivity for the
NH2 Cl reacts with trimethylamine to give a salt and, as
analyses.
this reaction is also catalyzed by the OH− ions [8–11],
After 10 min reaction, the GC–MS spectrum shows
we obtain
that residual HEH was observed at t2 = 4.8 min and
a bulky peak located at t1 = 3 min corresponds to the
(CH3 )3 N + NH2 Cl → (CH3 )3 NNH+
2 Cl
−
reaction product. GC–MS analysis gives a mass of m/z
(basic catalysis) = 74 for this product. Also, the fragmentation analysis
gives the formula

Kinetics of HEH Oxidation by NH2 Cl HO-CH2 -CH = N-NH2

Characterization of the Products. The reaction sys- that is, the hydroxyethylhydrazone. Its functional
tem HEH/NH2 Cl was studied either by UV or by group corresponds to the UV peak of product F at
HPLC, and the reaction products were characterized λ = 224 nm.
by GC–MS. In addition, the experiments were carried
out at pH 12.89 and T = 25◦ C and for HEH concen- Reaction Mechanisms. By analogy with the phe-
trations between 8 and 40 × 10−3 M. nomena observed in our laboratory in the case

International Journal of Chemical Kinetics DOI 10.1002/kin

 SYNTHESIS OF HYDROXYETHYLHYDRAZINE BY THE RASCHIG PROCESS 337

Figure 3 UV spectra for a reaction mixture HEH + NH2 Cl at 25◦ C. [HEH]0 = 40 × 10−3 M; [NH2 Cl]0 = 1.6 × 10−3 M;
[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 - In aqueous medium, the diazene can be considered

aminoaza-3-bicyclo[3,3,0]octane and N -aminopi- as an alkaline compound capable of trapping protons
peridine (NAP), the first step corresponds to the for- according to the following acid–base balance:
mation of diazene (aminonitrene):

HO-(CH2 )2 -NH-NH2 + NH2 Cl + − +

HO-(CH2 )2 -NH = N +H2 O  HO-(CH2 )2 -NH
k3 + −
−→ HO-(CH2 )2 -NH = N +NH4 Cl = N-H + OH−

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
HO-(CH2 )2 -NH-NH2
atom linked to the quaternary nitrogen is “acid,” it is
+ − easily extracted in alkaline medium, leading to an azo
→ HO-(CH2 )2 -NH = N +2H+ +2e−
compound that rearranges itself immediately by dy-
NH2 Cl + 2H+ +2e− → NH4 Cl namic isomerism to give a hydrazone with a molecular

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
Rate Laws. The previous results show that the oxida-
tion mechanism of HEH by NH2 Cl can be described 60
by the following two reactions:
50
NH2 Cl + HO-(CH2 )2 -NH-NH2
k3 + −
−→
−
HO-(CH2 )2 -N H = N +NH3 + Cl− + H2 O 40
OH
+ − 30
HO-(CH2 )2 -N H = N
k4
−→ HO-CH2 -CH = NH-NH2 20 calculation
cacul
experimental
expÈrimental

The second process, that is, the rearrangement of 10

diazene/hydrazone does not control the HEH yield as it

is consecutive. Therefore, only the kinetic parameters 0
p
0 5 10 15 20 25
of the aminonitrene formation were determined. The
rate laws were established at pH 12.89 and T = 25◦ C. Figure 4 Evolution yield of HEH in a concentrated
A specific method was developed to monitor the medium with reagent ratio p ([NAOH]f = 0, 3 M; T =
chlorinated compound analytically. It consists of ex- 25◦ C; k1 exp = 1.62 × 10−1 M−1 min−1 ; k2 exp = 2.62 M−1
tracting NH2 Cl by demixion with a solvent, namely min−1 ; k3 = 3.72 × 10−3 M−1 min−1 ).
diethylether. The chlorinated compound is then sepa-
rated and analyzed by HPLC equipped with a UV de- The kinetic parameters were determined by integra-
tector. By using this method, the hydroxylated deriva- tion using the same methods as described previously:
tives that have good affinity with water can be isolated
in the aqueous phase. At the same time, the interac- d[NH2 Cl]
r3 = − = ν3 k3 [NH2 Cl]α [HEH]β
tion is blocked in the solvent as no organic reagent is dt
present.
The initial concentrations were between 1.7 × 10−3 The plot
and 2 × 10−3 M for NH2 Cl and between 8 × 10−3 and  
40 × 10−3 M for HEH (4.5 ≤ [HEH]0 /[NH2 Cl]0 ≤ 1 [NH2 Cl]0 [HEH]
ln = f (t)
24). [HEH]0 − [NH2 Cl]0 [HEH]0 [NH2 Cl]
Table IV and Fig. 4 show the variation of the NH2 Cl
concentration as a function of time for initial concen- is linear up to the end of the reaction with a correlation
trations of 1.7 × 10−3 M for NH2 Cl and 40 × 10−3 M coefficient of 0.996. Consequently, NH2 Cl does not
for HEH. participate in a secondary reaction process; in fact the

Table IV Evolution of Rate Constant k3 with Time

Time (min) [NH2 Cl] (10−3 M) ln A ln A/([HEH]0 – [NH2 Cl]0 ) k3 (M−1 min−1 )
1 1.54 0.08 2.14 2.14
1 1.56 0.07 1.72 1.72
6 0.99 0.51 13.21 2.40
6 1.00 0.49 12.89 2.34
16 0.33 1.6 41.82 2.70
16 0.31 1.66 43.27 2.79
31 0.08 2.99 78.06 2.52
31 0.08 3.03 79.00 2.55
47 0.02 4.29 111.97 2.38
47 0.02 4.25 110.86 2.36

T = 25◦ C, [NH2 Cl]0 = 1.7 × 10−3 M, [HEH]0 = 40 × 10−3 M, [NaOH] = 0.1 M with A = ([NH2 Cl]0 × [HEH])/([HEH]0 × [NH2 Cl]).

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 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
CH3 NH2 1 CH3 NHNH2 5.09 × 10−3 25 [13]
HO-(CH2 )2 -NH2 1 HO-(CH2 )2 -NH-NH2 2.66 × 10−3 25 This work

Hydrazine Substitution Degree Intermediary Product kd (M−1 s−1 ) T (◦ C) Reference

CH3 NHNH2 1 CH3 N+ H=N− 2.27 × 10−2 25 [13]
HO-(CH2 )2 -NH-NH2 1 HO-(CH2 )2 -N+ H=N− 4.37 × 10−2 25 This work

reaction is composed of two consecutive reactions that Formulation of a Kinetic Model

explain the isobestic points.
In view of the previous results, the main reactions de-
The linear plots obtained at 25◦ C for a NaOH con-
termining the rate of HEH synthesis by the Raschig
centration of 0.1 M (pH 12.89) and different initial
process are
concentrations of HEH and NH2 Cl, permit establish-
ing the kinetic parameters of the reaction between HEH
and NH2 Cl:
ν3 = α = β = 1 and k3 = 2.62 L mol−1 min−1 NH2 Cl + HO-(CH2 )2 -NH2
k1
Table V compares the bimolecular kinetic constants −→
−
HO-(CH2 )2 -NH-NH2 + H2 O + Cl− (7)
OH
of formation and degradation for two hydrazines with
k2
a substitution degree equal to unity: monomethylhy- NH2 Cl + OH− −→ NH2 OH + Cl− (8)
drazine (MMH) and HEH.
At 25◦ C and pH 12.89, ratio kd /kf is less favorable HO-(CH2 )2 -NH-NH2 + NH2 Cl
for HEH. It is necessary to operate under nonstoichio- k3 + −
−→ HO-(CH2 )2 -NH = N +NH+
4 + Cl
−
(9)
metric conditions, that is, with a large amount of excess
EA to limit the contact time between NH2 Cl and HEH. + −
HO-(CH2 )2 -NH = N
Influence of the Temperature. The influence of the k4
−→ HO-CH2 -CH = N-NH2 (10)
temperature was studied at pH 12.89, between 15 and
35◦ C for constant concentrations of NH2 Cl and HEH
equal to 2 × 10−3 and 40 × 10−3 M, respectively
(p =[HEH]0 /[NH2 Cl]0 ≈ 20) (Table VI). A plot ln Reaction (7) is the useful step of the synthesis. It is
k3 = f(1/T) leads to the Arrhenius relation (Ea3 in a bimolecular reaction, and its order is equal to one
kJ mol−1 ): compared to each reagent. The second reaction (8) is
the hydrolysis of the chlorinated derivative. As soon
k3 = 7.95 × 106 exp(−47.7/RT ) as HEH is formed, it is partially oxidized by NH2 Cl
(k3 in M−1 s−1 ,Ea3 in kJ mol−1 ) to give an aminonitrene (9) that rearranges itself into
hydroxyethylhydrazone (10).
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
H30# = 45.2 kJ mol−1 ;  S30# = −121 J K−1 mol−1 reagent concentrations and temperature is linked to the

Table VI Influence of Temperature on Oxidation Constant k3

T (◦ C) [HEH]0 (10−2 M) [NH2 Cl]0 (10−3 M) p = [HEH]0 /[NH2 Cl]0 k3 (M−1 min−1 ) R2
15 4.0 2.0 20.0 1.09 0.998
20 4.1 2.1 19.1 1.37 0.983
20 4.2 2.1 20 1.36 0.989
25 4.0 1.7 24.0 2.48 0.996
25 4.0 2.0 20 2.50 0.991
35 4.0 2.0 20.0 3.76 0.982
[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
dx reagents, and at t = ∞, noted Di (i = 2–5).
= −k1 a x − k3 u x − k2 xb0
dt To achieve this, the volumes of NH2 Cl and EA to
da be injected are designated by VN and VA , respectively:
= −k1 a x
dt
B1
du VN = 1000 mL, VA = 103 × p ×
= k1 a x − k3 u x CA
dt
df where subscript A represents an EA solution with mass
= k3 u x
dt composition WA :

where x, a, u, and f are the concentrations of NH2 Cl,

WA × 103 × d3 1
EA, HEH, and hydrazone, respectively, at instant t. The CA = ·
initial concentrations are x = x0 , a = a0 , u = f = 0, 100 M3
and b0 stands for the initial NaOH concentration. The
fourth-order Runge–Kutta method was used to resolve Under these conditions, the NaOH solution ([NaOH]
this differential equations system. = 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 NH4 Cl (B2 )
Transfer in a Concentrated Medium and Optimiza-
and the H+ ions formed during hydrazine formation:
tion. The results obtained during the theoretical study
were validated directly in a concentrated medium by
(B2 + B1 )
using hypochlorite solutions at a high chlorometric de- VS1 = 103
gree. It is necessary to know the composition of synthe- S
sis solutions at t = 0 to predict the rate of the reaction
The second term corresponds to the amount of NaOH
when using the kinetic model. It is also necessary to
necessary to obtain the optimized value noted [OH− ]f :
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 [OH− ]f VN + VA + VS1 + VS2
VS2 =
introduced at the exit of the NH2 Cl reactor (R1 ) take S
into account the need to neutralize the residual buffer
NH+ +
4 /NH3 and the H ions provided by the reaction
The instantaneous concentrations Ci and Di are de-
duced from those equations presented in Table VII.
NH2 Cl + HO-(CH2 )2 -NH2 The results were confirmed in a concentrated
medium, by systematically studying the influence of
k1
−→ HO-(CH2 )2 -NH-NH2 + HCl (11) the molar ratio p, that of the final sodium hydroxide
concentration [OH− ]f and that of the temperature.
At the end of the reaction, the pH of the solution is The experiments were carried out using the fol-
increased to 13 to avoid a chlorine transfer reaction lowing protocol: a freshly prepared and concentrated
and profit from the pseudocatalytic effect caused by NH2 Cl solution (volume VN ) is alkalized with a vol-
the OH− ions during the reaction (11). ume VS of a 10 M NaOH solution. The NaOH/NH2 Cl
The calculation was carried out by reacting a mixture is then introduced under stirring into VA mL
concentrated solution of sodium hypochlorite at 48◦ of an EA solution at a determined temperature.
chlorometric degrees (2.14 M) at −15◦ C, with a mixed
ammonia solution NH3 /NH4 Cl (3.64 M/2.38 M). Un- Influence of the p Ratio. The experiments were car-
der these conditions, the NH2 Cl rate is almost quanti- ried out at a constant temperature of 25◦ C, at a con-
tative and the resulting solution concentration is equal stant final NaOH concentration and a constant volume
to 1.04 M (B1 ) for NH2 Cl and 0.1 M (B2 ) for NH4 Cl. of NH2 Cl (VN = 40 mL), by varying the excess amine.
The following compounds: NH2 Cl, NH4 Cl, HO- Passing from p = 5 to p = 20 involves increasing
(CH2 )2 -NH2 , NaOH, and HO-(CH2 )2 -NH-NH2 are, the yield by 33%, as shown in Fig. 4. The theoretical
respectively, represented by indices from 1 to 5. Con- curve, in agreement with the experimental results, was
sequently, the molecular weights and densities of the formulated by taking into account the variation of rate
reagents and resulting solutions are, respectively, rep- constant k1 with pH. Therefore, yield ρN is 62% for
resented by the symbols Mi and di . We wanted to cal- 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 NH2 Cl NH4 Cl EA NaOH HEH
Indices 1 2 3 4 5
103 103 B1 ×p× 103 S ×VS
Ci (t = 0) B1 VN + VA + VS B2 VN + VA + VS VN + VA + VS VN + VA + VS 0
Di (t = ∞) 0 0 C3 − C1 C4 − (C1 + C2 ) C1

Yield ρN (%) Comparison between the Different

85
Processes Studied to Synthesize HEH
80 In another paper [4], HEH was synthesized by the alky-
(a) lation of N2 H4 with 2-chloroethanol (CletOH) in the
75 presence or not of NaOH. In this first case, N2 H4 is
alkylated by ethylene oxide (CH2 OCH2 ) formed in
70 situ in the presence of NaOH, which is a strong base.
(b) These three processes (Raschig, alkylation by CletOH,
65 and alkylation by CH2 OCH2 ) can be compared.
The first reaction, bimolecular (kf ), involves a nucle-
60 ophilic reagent (amine or hydrazine) and a molecule
with an electron-deficient site (NH2 Cl, CletOH, and
55
CH2 OCH2 ).
kf
50 N + Mδ+ −→ HEH
Temperature /∞C
45 In the second step, HEH is involved in a secondary
0 20 40 60 80 100 process of consecutive parallel type (kd ).
kd 
Figure 5 Calculated evolution of the HEH yield with tem-
perature for molar ratio p = 30 (a) or p = 20 (b). HEH + Mδ+ −→ Pi
i

This implies that the operating conditions depend on

Theoretical Influence of Temperature. The influence the rate ratio between these two reactions (Vf /Vd ). kf
of temperature was studied between 10 and 90◦ C for and kd , measured during this study, are summarized
a final NaOH concentration of 0.3 M and for a ratio in Table VIII, which also indicates ratio kd /kf and the
p = 20 and 30 (Fig. 5). Increasing temperature leads corresponding activation enthalpy and entropy.
to better yields due to the enthalpy values.
HEH Reaction Mechanisms and Formation Rates.
Kinetic Profile/Residence Time. The plug-flow
The bimolecular rates are of the same order for
reactor is the most suitable reactor for limiting contact
the Raschig process and alkylation by epoxide
between the HEH and NH2 Cl formed. Figure 6 shows
(CH2 OCH2 ). This is due to the nucleophilic and elec-
the theoretical kinetic profiles in the reactor for two
trophilic power of the reagents, which compensate each
mixtures (NH2 Cl/EA/NaOH) continuously injected at
other. EA is much more nucleophilic and basic than
20 and 80◦ C for molar ratio p = 20.
N2 H4 .

HO-(CH2)2-NH2 + NH2 > Cl HEH (k = 2.61 × 10 3 L mol 1 s 1 at 25°C)

(pK a = 9,5)
+1/2 +1/2

NH2-NH2 + HEH (k = 1.71 × 10 3

L mol 1 s 1 at 25°C)
(pK a = 8,1) O

HO-(CH2)2-NH2 >> NH2-NH2 NH2 Cl << CH2OCH2

Nucleophilic power 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 [NH2 Cl]0 = 0.42 M, [EA]0 = 8.47 M. T = 80◦ C: (a) [NH2 Cl]; (b) [HEH];
(c) [hydrazone]. T = 20◦ C: (a ) [NH2 Cl]: (b ) [HEH]; (c ) [hydrazone].

Thus, the situation is reversed for their electrophilic Thus kf (Raschig) ≈ kf (CH2 OCH2 ) ≈ 103 kf
homologue. (CletOH)
The N-Cl linkage of NH2 Cl is not very polarized due
to the very slight electronegative difference between
the two atoms. This explains the polarization inversion
when a hydrogen atom is replaced by an electrodonor HEH Reaction Mechanisms and Degradation and
methyl group. This substituted chloramine becomes Alkylation Rates. For identical reagent ratios, the
incapable of forming N-N linkage by reacting with HEH yields are the same for the two alkylation meth-
NH3 in an aqueous or anhydrous medium (chlorine ods (CletOH and CH2 OCH2 ). This result is not sur-
transfer mechanism in liquid ammonia). prising because the rate constants kf and kd require
the same mechanisms. This is confirmed by acti-
δ+ δ− δ− δ+
NH2 -Cl CH3 NH - Cl vation enthalpies and entropies. The absolute for-
mation rates are very different (Vf (CH2 OCH2 ) Vf
This is not the case of the epoxide, which is strongly (CletOH)), but the kf /kd ratios are almost identi-
electrophilic, due to its favorable spatial configuration cal. The adjustment variable, that is, ratio [N2 H4 ]0 /
(flat molecule, symmetry, and good site accessibility) [CH2 OCH2 ]0 or [N2 H4 ]0 /[CletOH]0 , will be low, close
and to greater carbon–oxygen polarization. to three, to obtain rates up to 80%.
The very weak value of the direct alkylation con- In the case of the Raschig process, the secondary re-
stant by CletOH in comparison with CH2 OCH2 , can be action of dialkylation is replaced by an HEH oxidation
explained by the fact that the carbon–chlorine linkage process; the reaction mechanism of which is different
is less polarized and accessible:

δ+1/2 δ+1/2
N2H4 + HEH (k = 1.71 × 10 L mol s at 25°C)
O δ

δ δ+
N2H4 + Cl-CH2-CH2-OH HEH (k = 2.18 × 10 L mol 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

kdegradation HEH /
from the formation mechanism (SN2 ). Since the bi-

kformation HEH
T = 25◦ C
molecular rate constants in favor of degradation are

13.6

0.7

0.7
equal to 14, the adjustment variable [EA]0 /[NH2 Cl]0
will be at least higher than 20.
ki at T = 25◦ C
Rate Constant

(L mol−1 s−1 )

2.61 × 10−3 CONCLUSION

3.53 × 10−2
2.18 × 10−6
1.62 × 10−6
1.71 × 10−3
1.16 × 10−3
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
(J K mol−1 )

to determine the optimal conditions of HEH

−110
−121

−102
−127
−128

formation.
Si0#

−89

A kinetic and mechanistic comparison of HEH

−1

synthesis by the Raschig process with alkyla-

tion by CletOH and the CH2 OCH2 process was
performed.
Compared with MMH, HEH synthesis by the
(kJ mol−1 )

Raschig process has two disadvantages: The nucle-

Hi0#

55.0
45.2
79.0
75.7
50.8
51.6

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
Rate Law ki = Ai e(−Eai/RT)

are in agreement with the spatial conformation of the

e(−57.7/RT )
e(−47.7/RT )
e(−81.4/RT )
e(−78.2/RT )
e(−53.3/RT )
e(−54.1/RT )

molecule promoting the interaction between the OH

(ki in M−1 s−1 and
Eai in kJ mol−1 )

end group and hydrogen atoms that are potentially

oxidizable.
Table VIII Comparison of Kinetic Data Corresponding to Each Process

3.06 × 107
7.95 × 106
4.04 × 108
8.05 × 107
3.74 × 106
3.46 × 106

BIBLIOGRAPHY

1. Schmidt, E. W. In Hydrazine and Its Derivatives: Prepa-

ration, Properties, Application, 2nd ed.; Wiley: New
2-Hydroxyethylhydrazine

2-Hydroxyethylhydrazine

2-Hydroxyethylhydrazine

York, 2001.
2. Delalu, H.; Marchand, A. J Chim Phys 1991, 88, 115–
Hydrazine (N2 H4 )

Hydrazine (N2 H4 )
Ethanolamine

127.
Nucleophilic
Reagent N

3. U.S. Air Force. U.S. Patent 6218577, 2001.

4. Goutelle, V.; Pasquet, V.; Stephan, J.; Bougrine, A. J.;
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620–640.
7. Anbar, M.; Yagil, G. J Am Chem Soc 1962, 84(10),
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Monochloramine

2-Chloroethanol

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Ethylene oxide
Reagent Mδ+
Electrophilic

1797–1803.
9. Delalu, H.; Marchand, A.; Ferriol, M.; Cohen-Adad, R.
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10. Cohen-Adad, R.; Cohen, A.; Delalu, H.; Marchand, A.;
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11. Omietanski, G. M.; Sisler, H. H. J Am Chem Soc 1956, 14. Lunn, G.; Sansone, E. B.; Keefer, L. K. J Org Chem
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International Journal of Chemical Kinetics DOI 10.1002/kin