A safe synthesis of symmetrical carbonates from alkyl halides and tetraethylammonium carbonate

Article abstract of DOI:10.1081/SCC-120003611

A safe and mild procedure for the synthesis of organic carbonates from alkyl halides and tetraethylammonium carbonate (TEAC) is described. This method avoids the use of classical toxic and harmful chemicals like phosgene and carbon monoxide and works unde

Full text of DOI:10.1081/SCC-120003611

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A SAFE SYNTHESIS OF SYMMETRICAL CARBONATES
FROM ALKYL HALIDES AND TETRAETHYLAMMONIUM
CARBONATE
Vittoria Mucciante a , Leucio Rossi a , Marta Feroci b & Giovanni Sotgiu c
a Departimento di Chimica, Ingegneria Chimica e Materiali , Università degli Studi ,
Monteluco di Roio, L’Aquila, I-67040, Italy
b Dipartimento di ICMMPM , Università degli Studi‘La Sapienza’ , Via del Castro Laurenziano
7, Roma, I-00161, Italy
c Dipartimento di Ingegneria Elettronica , Università di Roma Tre , Via Vasca Navale 84,
Roma, I-00146, Italy
Published online: 16 Aug 2006.
To cite this article: Vittoria Mucciante , Leucio Rossi , Marta Feroci & Giovanni Sotgiu (2002) A SAFE SYNTHESIS OF
SYMMETRICAL CARBONATES FROM ALKYL HALIDES AND TETRAETHYLAMMONIUM CARBONATE, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 32:8, 1205-1210, DOI: 10.1081/SCC-120003611
To link to this article: http://dx.doi.org/10.1081/SCC-120003611
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SYNTHETIC COMMUNICATIONS, 32(8), 1205–1210 (2002)
A SAFE SYNTHESIS OF SYMMETRICAL
CARBONATES FROM ALKYL HALIDES
AND TETRAETHYLAMMONIUM
CARBONATE
Vittoria Mucciante,1 Leucio Rossi,1,
*
Marta Feroci,2 and Giovanni Sotgiu3
1Departimento di Chimica, Ingegneria Chimica e
Materiali, Universita degli Studi,
Monteluco di Roio, I-67040, L’Aquila, Italy
2Dipartimento di ICMMPM, Universita degli Studi
‘La Sapienza’, Via del Castro Laurenziano 7,
I-00161, Roma, Italy
3Dipartimento di Ingegneria Elettronica,
Universita di Roma Tre, Via Vasca Navale 84,
I-00146, Roma, Italy
ABSTRACT
A safe and mild procedure for the synthesis of organic carbo-
nates from alkyl halides and tetraethylammonium carbonate
(TEAC) is described. This method avoids the use of classical
toxic and harmful chemicals like phosgene and carbon
monoxide and works under very mild reaction conditions.
An electrochemically-generated derivative of carbon dioxide
*Corresponding author.
1205
Copyright & 2002 by Marcel Dekker, Inc.
www.dekker.com

1206
MUCCIANTE ET AL.
(a cheap and abundant carbon source) was used as the main
reagent (TEAC).
INTRODUCTION
Dialkyl carbonates are useful substrates for a variety of industrial
and synthetic applications. They found wide use as solvents and inter-
mediates for the synthesis of several pharmaceuticals, plastics, lubricants,
herbicides and pesticides. The traditional syntheses of these compounds
require toxic and harmful chemicals like phosgene, pyridine and carbon
monoxide, so the development of new methodologies employing safe and
clean reagents has been extensively studied in the last decade.1,2
Recently we found that unsymmetrical organic carbonates can be
obtained, in quite good yields, by reaction of primary and secondary alco-
hols with tetraethylammonium carbonate (TEAC)3 or tetraethylammonium
peroxodicarbonates (TEAPC).4 Both methods avoid hazardous reagents
and are based on the electrochemical conversion of a cheap, abundant
and harmless compound like carbon dioxide in derivatives showing carbox-
ylating properties.
In this communication we report a safe and mild method for the syn-
thesis of symmetrical dialkyl carbonates by reaction of alkyl halides with
TEAC at room temperature in acetonitrile.
RESULTS AND DISCUSSION
The use of alkyl halides as starting materials for the synthesis of
carbonates was first reported by Dehmlow5 and Cella.6 Both methods con-
sist of an alkylation of alkali-metal carbonates and hydrogen carbonates
performed by alkyl halides under phase transfer catalysis (PTC) conditions
at high temperature (100–150ꢀC).
Starting from these considerations we performed the reaction of dif-
ferent alkyl halides 1 in the presence of electrochemically generated TEAC 2
so as to obtain symmetric carbonates 3, avoiding PTC and working under
very mild reaction conditions (Scheme 1).
In order to optimise the reaction conditions, 3-phenylpropyl bromide
(scheme 1 R¼Ph(CH2)3 and X¼Br) was used as a model compound and
different molar ratios RX : TEAC were tested. A complete report of the
results obtained is shown in Table 1. A side reaction encountered in the
preparation of carbonates through this process is the formation of alcohols.

SYNTHESIS OF SYMMETRICAL CARBONATES
1207
Scheme 1.
Table 1. Reaction of 3-Phenylpropyl Bromide (1.0mmol) and TEAC via Scheme 1
Under Different Reaction Conditions
Reaction Products (mmol)
TEAC
Entry (mmol)
RXa
(mmol)
Temperature Yieldb
ROCO2R
ROH
(ꢀC)
(%)
1
2
3
4
5
6
7
8
9
0.25
0.40
0.50
0.60
0.68
0.75
1.00
1.25
0.60
0.60
0.60
0.60
0.15
0.17
0.20
0.20
0.20
0.22
0.22
0.20
0.20
–
0.14
0.27
0.28
0.29
0.39
0.49
0.53
0.51
0.34
–
0.46
0.37
0.21
0.05
0.11
–
–
–
–
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
80
30
34
40
40
40
44
44
40
40
10
11c
12d
1.00
0.29
0.05
ꢁ20–
r.t.
r.t.
0.20
0.27
0.29
0.36
40
54
aUnreacted halide recovered at the end of the reaction; bYield calculated considering
c
the amount of alkyl halide 1 converted in carbonate; DMF was used as solvent;
dReaction time of seven days.
These products appear to be the result of decarboxylation of the intermedi-
ate monoalkylated carbonate salt.
As shown in the table, symmetrical carbonate and alcohol yields are
strongly dependent upon the amount of tetraethylammonium carbonate
used. An increase of TEAC causes a direct increase in the formation of
carbonate; on the other hand, the quantity of alcohol obtained at the end
of the reaction also increases to the detriment of the alkyl halides potentially
recoverable from the reaction mixture. It is obvious that we need to reach a
compromise among the amounts of carbonate and alcohol (undesirable)
obtained in the reaction. We chose a ratio alkyl halide/TEAC of 1 : 0.6 so
as to get better yields without obtaining large quantity of alcohol and with the
possibility of recovering the unreacted alkyl halides for further reactions. In
addition, reaction times show a remarkable influence on the reaction yield;

1208
MUCCIANTE ET AL.
Table 2. Reaction of Different Alkyl Halides with TEAC Under Optimised
Reaction Conditions.a Carbonates Produced via Scheme 1
Reaction Products (mmol)
RXb
(mmol)
Yieldc
(%)
Entry
R
X
ROCO2R
ROH
1
2
3
4
5
6
7
8
9
Ph(CH2)3
Ph(CH2)3
Ph(CH2)3
Ph(CH2)2
PhCH2
I
0.21
–
0.13
0.11
0.29
0.10
0.21
0.35
0.38
0.35
–
0.40
0.74
0.05
0.48
0.12
0.10
0.36
0.12
–
42
–
Cl
OTs
I
Br
Br
Br
0.21
0.19
0.22
0.27
0.13
0.20
0.10
42
38
44
54
26
40
20
Ph(CH3)CH
Ph2CH(CH2)2
PhCH¼CHCH2 Br
CH2CH2 Br
aMolar ratio halide/TEAC 1 : 0.6, r.t. CN3CN; bUnreacted halide recovered at the
end of the reaction; cYield calculated considering the amount of alkyl halide 1
converted in carbonate; dReaction carried out with 1,2-dibromoethane; a molar
ratio halide/TEAC of 1 : 1.2 was used.
extending the reaction time up to seven days increase the amount of carbo-
nate obtained from 40to 54% (Entry 12). Considering the temperature, no
reaction was observed at ꢁ20ꢀC (Entry 10), while raising the temperature to
80ꢀC did not produce relevant improvements in the reaction yield (Entry 9).
Using the optimized reaction conditions (Entry 4), the reaction
was tested on different alkyl halides in order to evaluate potential differences
in reactivity. Results are reported in Table 2. 3-Phenylpropyl iodide and
tosylate did not show substantial differences when compared to the corre-
sponding bromide (Entries 1 and 3), but the chloride did not react at all
(Entry 2). When an a,o-dibromide was used, the corresponding cyclic car-
bonate was obtained but only in 20% of yield (Entry 11).
CONCLUSION
In conclusion this simple and safe method represents a valuable alter-
native to the methods up to now reported. Although reaction yields are only
moderate, the procedure utilizes a safe and clean derivative of carbon
dioxide and works in very mild medium, avoiding both toxic and harmful
reagents and harsh reaction conditions.

SYNTHESIS OF SYMMETRICAL CARBONATES
1209
EXPERIMENTAL
General
TLC analyses were performed on Merck kiesegel 60F254 plates. Flash
chromatography was carried out on Merck silica gel (230–400 mesh). 1H and
13C NMR were determined at 200 and 50.3 MHz respectively with a Bruker
AC200 instrument using CDCl3 as an internal standard. Dry acetonitrile
(Lab-scan, anhydroscan) was used as received. Alkyl halides 1 are commer-
cially available and were used as received.
Reaction of Alkyl Halides with TEAC: General Procedure (3)
A solution (20ml) of MeCN–Et 4NClO4 (0.1 mol dmꢁ3), with continu-
ous CO2 bubbling, was electrolysed (divided cell, Pt anode, 0ꢀC) over a Cu
cathode at a potential of ꢁ 2.1 V (vs. SCE). At the end of electrolysis
(1.2 F molꢁ1) the halide was added and the reaction was stirred overnight.
After removal of the solvent, flash chromatography afforded the desired
carbonate.
Carbonates in Table 2 Entries 1–6, 9 are commercial or well-known
compounds; product assignment was determinated by 1H-NMR, 13C-NMR
and elemental analysis compared to authentic materials or literature
assignments.
Carbonic acid bis-(3,3-diphenyl-propyl) ester: 1H NMR (CDCl3,
200 MHz) d; 7.34–7.15 (m, 20H, Ar); 4.14–4.04 (m, 6H, OCH2, CHPh2);
2.43 (q, 4H, J ¼ 6.0Hz, C H2CH). 13C NMR (CDCl3, 50.3 MHz) d: 160.8,
155.0, 128.3, 127.8, 126.4, 66.2, 47.2, 34.3. Anal. calcd for C31H30O3: C,
82.64; H, 6.71. Found: C, 82.52; H, 6.78.
Carbonic acid bis-(3-phenyl-allyl) ester: 1H NMR (CDCl3, 200 MHz) d;
7.41–7.23 (m, 10H, Ar); 6.68 (d, 2H, J ¼ 15.9 Hz, PhCH¼); 6.29 (dt, 2H,
J ¼ 6.3, 15.9 Hz, CH2CH¼); 4.80(dd, 4H, J ¼ 1.0, 6.3 Hz, OCH2). 13C NMR
(CDCl3, 50.3 MHz) d: 154.9, 136.0 134.8, 128.5, 128.1, 126.6, 122.4, 68.4.
Anal. calcd for C19H18O3: C, 77.53; H, 6.16. Found: C, 77.41; H, 6.12.
ACKNOWLEDGMENTS
This work was supported by grants from M.U.R.S.T. and C.N.R.
(Italy).

1210
MUCCIANTE ET AL.
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Received in the Netherlands May 16, 2001