A safe and efficient procedure to prepare alkyl and alkoxyalkyl chlorides and dichlorides by catalytic decomposition of the corresponding alkyl and alkoxyalkyl chloroformates and bischloroformates with hexabutylguanidinium chloride

Article abstract of DOI:10.1081/SCC-100000525

Small amounts of hexabutylguanidinium chloride (0.01 mol%) decomposes pure chloroformates or bischloroformates with different lengths of carbon chains by a semicontinuous process to diminish run-away risk, leading to chloride compounds with high yield and purity.

Full text of DOI:10.1081/SCC-100000525

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A SAFE AND EFFICIENT PROCEDURE TO PREPARE
ALKYL AND ALKOXYALKYL CHLORIDES AND
DICHLORIDES BY CATALYTIC DECOMPOSITION OF
THE CORRESPONDING ALKYL AND ALKOXYALKYL
CHLOROFORMATES AND BISCHLOROFORMATES WITH
HEXABUTYLGUANIDINIUM CHLORIDE
Frédéric Violleau a , Sophie Thiébaud b , Elisabeth Borredon a & Pierre Le Gars c
a Laboratoire de Chimie Agro-industrielle, Ecole Nationale Supérieure des Ingénieurs
en Arts Chimiques et Technologiques de Toulouse, Institut National Polytechnique de
Toulouse, UMR 1010 INRA-INPT, 118, route de Narbonne, Toulouse Cedex 4, 31077,
France
b Laboratoire de Chimie Agro-industrielle, Ecole Nationale Supérieure des Ingénieurs
en Arts Chimiques et Technologiques de Toulouse, Institut National Polytechnique de
Toulouse, UMR 1010 INRA-INPT, 118, route de Narbonne, Toulouse Cedex 4, 31077,
France
c SNPE, Chemin de la loge, Toulouse Cedex, 31078, France
Version of record first published: 09 Nov 2006.
To cite this article: Frédéric Violleau, Sophie Thiébaud, Elisabeth Borredon & Pierre Le Gars (2001): A SAFE
AND EFFICIENT PROCEDURE TO PREPARE ALKYL AND ALKOXYALKYL CHLORIDES AND DICHLORIDES BY CATALYTIC
DECOMPOSITION OF THE CORRESPONDING ALKYL AND ALKOXYALKYL CHLOROFORMATES AND BISCHLOROFORMATES WITH
HEXABUTYLGUANIDINIUM CHLORIDE, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 31:3, 367-373
To link to this article: http://dx.doi.org/10.1081/SCC-100000525
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SYNTHETIC COMMUNICATIONS, 31(3), 367–373 (2001)
A SAFE AND EFFICIENT PROCEDURE TO
PREPARE ALKYL AND ALKOXYALKYL
CHLORIDES AND DICHLORIDES BY
CATALYTIC DECOMPOSITION OF THE
CORRESPONDING ALKYL AND
ALKOXYALKYL CHLOROFORMATES
AND BISCHLOROFORMATES WITH
HEXABUTYLGUANIDINIUM CHLORIDE
Fre´de´ric Violleau,1 Sophie Thie´baud,1,∗ Elisabeth
Borredon,1 and Pierre Le Gars2
1Laboratoire de Chimie Agro-industrielle, UMR 1010
INRA-INPT, Ecole Nationale Supe´rieure des Inge´nieurs en
Arts Chimiques et Technologiques de Toulouse, Institut
National Polytechnique de Toulouse, 118, route de
Narbonne, 31077 Toulouse Cedex 4, France
2SNPE, Chemin de la loge, 31078 Toulouse Cedex, France
ABSTRACT
Smallamountsofhexabutylguanidiniumchloride(0.01mol%)
decomposes pure chloroformates or bischloroformates with differ-
ent lengths of carbon chains by a semicontinuous process to dimin-
ish run-away risk, leading to chloride compounds with high yield
and purity.
∗Corresponding author.
367
Copyright ꢀ 2001 by Marcel Dekker, Inc.
www.dekker.com
C

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368
VIOLLEAU ET AL.
R1OCOCl
R1Cl + CO2
chloroformate
ClOCOR2OCOCl ClR2Cl + 2 CO2
bischloroformate
R1, R2 : alkyl or alkoxyalkyl group
Scheme 1.
Alkyl chlorides and dichlorides are largely used to prepare herbicides and
drugs (1–5). They are generally prepared by decomposition of the corresponding
chloroformates or bischloroformates in the presence or not of a catalyst
(Sch. 1).
Without a catalyst, these exothermic reactions of decomposition (6) lead to
the formation of many by-products (olefin (7) or rearranged alkyl chlorides (8)).
This does not occur in the presence of catalysts (e.g., amides (9) and the tertiary
amines or their hydrochlorides (10–12)). In this case, the reaction is carried out
with large quantities of catalyst (up to 43 mol%).
Othercatalysts, suchasphosphoniumorquaternaryammoniumsalts(13,14),
which are thermally unstable, lose their activity during the reaction and cannot be
recycled.
Recently, Foulon et al. (15) used a hexasubstitued guanidinium salt (hy-
drochlorate of hexabutylguanidinium chloride: HBGC · HCl), which is thermally
stable, to decompose small quantities (1 mmol) of monochloroformates with
short carbon chains (≤8) at 100◦C and with 0.5% of catalyst in the presence
of monochlorobenzene as solvent. In this case, the kinetics of the reaction is
fast.
Preliminary experiments were carried out by using Foulon’s conditions
to the decomposition of a more significant quantity (10 mmol) of n-octyl
chloroformate. It was found that violent and very exothermic reactions were
produced, even in the case of chloroformate with longer carbon chains (R1 =
CH3(CH2)9) or bischloroformate (R2 = (CH2)8). The reduction to 0.01% of the
quantity of catalyst was not successful to control the decomposition of the n-octyl
chloroformate.
Such results led us to modify these experimental conditions so that they
could be applicable to the decomposition of large quantities of mono and bischlo-
roformates. Reactions were carried out in absence of organic solvent to facilitate
synthesis scale transfer. Variable length of carbon chain (between 4 and 18) was
also considered.

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HEXABUTYLGUANIDINIUM CHLORIDE
Table 1. Thermogravimetric Analysis of the Chloroformates and
369
Bischloroformates Studied
Products
Decomposition Temp. (◦C)
ClOCO(CH2)4OCOCl
ClOCO(CH2)6OCOCl
ClOCO(CH2)8OCOCl
ClOCO(CH2)10OCOCl
ClOCO(CH2)12OCOCl
142
142
150
165
170
O(CH2CH2OCOCl)2
(CH2OCH2CH2OCOCl)2
O(CH2CH2OCH2CH2OCOCl)2
143
160
163
CH3(CH2)15OCOCl
CH3(CH2)17OCOCl
160
163
RESULTS AND DISCUSSION
Thestudiedchloroformatesorbischloroformateswerefirstsynthesizedwith-
out catalyst and solvent by reaction of corresponding alcohol with phosgene (16).
In order to avoid the formation of by-products by thermal decomposition of
chloroformates and bischloroformates (7,8), we first determined their decomposi-
tion temperatures by thermogravimetric analysis (Table 1).
Table 1 shows that, for compounds belonging to the same family, the longer
the alkyl or alkoxyalkyl chain is, the more thermally stable the chloroformate
or bischloroformate becomes. For all the studied compounds, the decomposition
temperatures are equal to or higher than 142◦C. Thus, maximum temperature of
the reaction should not exceed 140◦C if catalytic decomposition is desired (instead
of thermal degradation).
In order to avoid the violence of the reaction observed with Foulon’s con-
ditions, chloroformates and bischloroformates were introduced gradually into the
reactor containing a catalyst: HBGC · HCl (0.01 mol%/total amount of chlorofor-
mates and bischloroformates), which was previously dissolved in chloroformate
(1000 g/g catalyst). In the case of the decomposition of butyl 1,4-bischloroformate
and bis(ethyl 2-chloroformate)ether, the catalyst was dissolved in the correspond-
ing chlorinated compound (1000 g/g catalyst) because the decomposition of these
bischloroformates is fast and violent. The chloroformate feed rate was varied so
that the reaction temperature was kept between 110 and 115◦C. However, total
reaction time was fixed to 4 h. Results obtained at the end of various reactions are
shown in Table 2.

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VIOLLEAU ET AL.
Table 2. Catalytic Decomposition of Chloroformate or Bischloroformate in the Presence
of HBGC·HCl (0.01 mol%)
Chloroformate’s
R1 and R2 Groups
Products Other Than
Feed Time Yielda (%) Puritya (%) Chloridesb
R1
–
c
–
(CH2)4
2:50
91
97
Carbonate and
polycarbonate
Chloroformate
Chloroformate
Small amount of
carbonate and
polycarbonate
Carbonate and
polycarbonate
No impurity
Small amount of
carbonate and
polycarbonate
Carbonate and
polycarbonate
–
–
–
–
–
(CH2)6
(CH2)8
2:30
2:00
1:00
93
94
97
98
96
>99
–
(CH2)10
–
–
(CH2)12
0:20
88
92
c
–
O(CH2)2
2:00
2:30
91
97
>99
>99
–
(CH2OCH2CH2)2
–
O(CH2CH2OCH2CH2)2
R2
1:50
81
87
–
–
CH3(CH2)15
CH3(CH2)17
0:50
0:20
92
90
97
94
Chloroformate
No impurity
aAnalysis of crude reaction medium by CPG by internal calibration.
bAnalysis by IR; chloroformate (νco ≈ 1780 cm−1); carbonate (νco ≈ 1750 cm−1).
cThe HBGC · HCl is dissolved in the chlorinated compound and not in chloroformate.
The shorter the carbon chain of R1 or R2 is, the longer the substrate feed
takes. The decomposition kinetics is very fast for the compounds bearing short
carbon chains (15) (≤8) and obliges to decrease the feed rate to limit the heat
generation. The mechanism being a SN2 one (15), the nucleophilic attack of the
–
chloride ion of catalyst on the α carbon of the O(CO)Cl function would be
easier and faster for these small molecules. The viscosity of the reaction medium
increases with the length of R1 and R2 which is unfavorable to the diffusion of the
catalyst molecules leading to a decrease of yield. This fact was especially marked
for R1 = (CH2)12, O(CH2CHOCH2CH2)2 and R2 = CH3(CH2)17.
Other compounds yielded chlorinated derivatives in more than 90% with
purity higher than 96%. In all the cases, yield values were minimized because
of a stripping of the chlorinated compound by CO2 during the reaction. The by-
products present in small quantities (carbonates or polycarbonates) arose from the
secondary reactions between catalyst and the chloroformate or bischloroformate
(15) (Sch. 2).

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HEXABUTYLGUANIDINIUM CHLORIDE
371
G+Cl−
catalyst
+
R1OCOCl
chloroformate
R1O−G+
+
COCl2
G+Cl−
2 COCl2
R1O−G+
+
R1OCOCl R1O(CO)OR1
carbonate
G+O−R2O−G+
+
2 G+Cl− + ClOCOR2OCOCl
+
bischloroformate
G+O−R2O−G+
+
nClOCOR2OCOCl Cl(CO)O[R2O(CO)O]nR2O(CO)]Cl
+
2 G+Cl−
n
2
Cl(CO)O[R2O(CO)O]nR2O(CO)Cl
Cl[R2O(CO)O]nR2Cl
polycarbonate
+
2 CO2
G+Cl−
HBGC, HCl
Scheme 2.
Purity of some chlorinated derivatives can be improved by distillation of the
reaction medium.
CONCLUSION
Various chlorinated or dichlorinated derivatives with variable carbon chain
lengths were obtained with purities and yields higher than 90% by progressive
introduction of the corresponding chloroformates or bischloroformates into a re-
actor in the presence of a catalytic quantity of HBGC·HCl used as catalyst and in
absence of organic solvent. The control of the heat produced by the reaction and the
formation of secondary products allow considering the transfer of this synthesis
technique to a larger scale.
EXPERIMENTAL
TGA measurements were performed in a Setaram 92-16.18 Thermogravi-
metric Analyzer. Each sample was heated with a heating rate of 10◦C/min in an
air atmosphere up to 600◦C. IR spectra were recorded on Perkin Elmer 1600 serie
FTIR.
Yield and purity of each sample were determined by gas chromatography on
Hewlett Packard 5890 with a HP 3396A integrator using 1,2,4-trichlorobenzene
as internal standard. The capillary column (cp wax 52 CB 60 m × 0.25 mm ×
0.25 µm) was temperature-programmed from 140 to 220◦C with a heating rate of
20◦C/min. The injector and detector temperature were 220 and 250◦C, respectively.
The column head pressure was fixed at 20 psi.

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VIOLLEAU ET AL.
Alcohols and diols were Aldrich products. Phosgene and HBGC · HCL were
furnished by SNPE. Alkylchloride, alkyldichloride, and alkoxyalkyldichloride
used as standards for GC analysis were purchased from Aldrich and Fluka.
General Procedure for the Synthesis of Chloroformate and Bischloro-
formate. Phosgene (1 eq./OH function) was introduced in a reactor cooled at
−10◦C. Then, alcohol or diol (1 eq.) and phosgene (2 eq./OH) were added simul-
taneously into the reactor, maintaining the mixture temperature lower than 10◦C.
When the alcohol or diol was solid at room temperature, we had to use a heated
dropping funnel. The reaction medium was stirred for 3 h at room temperature.
Finally the excess of phosgene was removed by a stream of nitrogen through the
solution for one night.
General Procedure for the Decomposition of Chloroformate and Bis-
chloroformate. The HBGC · HCl (1 × 10−4 eq./total amount of chloroformates
and bischloroformates) was solubilized in chloroformate (or bischloroformate) or
corresponding alkyl chloride (or dichloride) (1000 g/g catalyst). The complement
of chloroformate (or bischloroformate) was added dropwise to the mixture in such
a way as to maintain the temperature lower than 115◦C and have a regular carbon
dioxide gas evolution. The reaction mixture was stirred at 120◦C for a 4-h total
reaction time.
ACKNOWLEDGMENT
The authors thank SNPE for financial and technical support of this work.
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Received in the UK February 23, 2000

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