Reaction of chlorides of phosphoric, sulfonic, and carboxylic acids on solid potassium carbonate surface under PTC circumstances

Article abstract of DOI:10.1002/hc.20039

Simple syntheses of phosphoric (4) and carboxylic (6) acid anhydrides have been elaborated by means of solid potassium carbonate in phase-transfer catalytic acylation. Behavior of various acid chlorides, phosphoric (1), sulfonic (2), and carboxylic (8), have also been studied toward potassium carbonate in the presence of lipophilic quaternary ammonium salt.

Full text of DOI:10.1002/hc.20039

Heteroatom Chemistry
Volume 15, Number 6, 2004
Reaction of Chlorides of Phosphoric, Sulfonic,
and Carboxylic Acids on Solid Potassium
Carbonate Surface under PTC Circumstances
Zsuzsa M. Ja´szay,1 Imre Petneha´zy,2 and La´szlo´ To´´ke1
1Organic Chemical Technology Research Group of the Hungarian Academy of Sciences, H-1521,
Budapest, Hungary
2Department of Organic Chemical Technology, Budapest University of Technology and Economics,
H-1521, Budapest, Hungary
Received 5 April 2004; revised 9 June 2004
Wittig–Horner syntheses [3] as well as N-acylation
ABSTRACT: Simple syntheses of phosphoric (4) and
of ureas in the synthesis of carbodiimides [4].
carboxylic (6) acid anhydrides have been elaborated by
Earlier, we published our results on the prepa-
means of solid potassium carbonate in phase-transfer
ration of carboxylic esters and amides from free car-
catalytic acylation. Behavior of various acid chlo-
boxylic acids using dialkylphosphoric acid chloride 1
rides, phosphoric (1), sulfonic (2), and carboxylic (8),
(R1 = Me, Et) generated “in situ” from dialkyl phos-
have also been studied toward potassium carbonate
phite 2 (R1 = Me, Et) and carbon tetrachloride [5],
in the presence of lipophilic quaternary ammonium
or p-toluenesulfonic acid chloride 3 (R3 = 4-MeC6H4)
ꢀ
C
salt.
2004 Wiley Periodicals, Inc. Heteroatom Chem
[6], respectively, with the combination of solid,
dry potassium carbonate, and lipophilic quaternary
ammonium salt, such as benzyltriethylammonium
chloride (TEBAC).
15:447–450, 2004; Published online in Wiley InterScience
(www.interscience.wiley.com). DOI 10.1002/hc.20039
We found that in both methods a side prod-
uct, tetraalkylpyrophosphate 4 (R1 = Me, Et) and the
potassium salt of sulfonic acid 5 (R3 = 4-MeC6H4),
respectively, were formed.
To find the reason for the formation of these
“side products” we continued the research work, and
as a result of this effort we succeeded in develop-
ing a simple way to make available the tetraalkyl
(aryl) pyrophosphates 4, as well as a new method
for the preparation of carboxylic acid anhydrides 6.
The present article gives an account of this research.
INTRODUCTION
Solid potassium carbonate has become a popular
reagent in phase-transfer catalytic reactions and ap-
plied as dry material, in the absence of water, when
water sensitive substrates are involved. It also has
the advantage of being milder, promoting fewer hy-
drolytic reactions than, e.g., solid potassium hydrox-
ide or potassium tert-butoxide does. Among the ex-
amples in which solid potassium carbonate has been
applied as a base are Michael reaction [1], C- and N-
alkylations [2], preparation of amino acids [1a,2c],
RESULTS AND DISCUSSIONS
Correspondence to: Z. M. Ja´szay; e-mail: Zjaszay@mail.bme.hu.
Contract grant sponsor: National Research Foundation of
Hungary.
Preparation of Pyrophosphates 4
In the first set of experiments, we put together di-
Contract grant number: OTKA grant no. T-038103.
c
ꢀ
2004 Wiley Periodicals, Inc.
ethyl chlorophosphate 1 (R1 = Et), solid potassium
447

448 Ja´szay et al.
(R1 = Me) [7], and cannot be used for the prepara-
tion of tetraphenyl pyrophosphate 4 (R1 = Ph). The
usual way of its preparation involves the reaction
of diphenyl chlorophosphate and phosphoric acid
diphenyl ester in the presence of pyridine [10].
It is also known from the literature that forma-
tion of tetraethyl pyrophosphate can be observed
from diethyl phosphoryl chloride without adding wa-
ter by means of solid potassium hydroxide [11] or by
using an acetic acid pyridine mixture [12]. In [11] the
hydroxyl anion serves as nucleophile, in [12] water
is formed from one molecule of acetate anion and
one molecule of acetic acid, while in our PTC experi-
ments the formation of the pyrophosphates proceeds
on the surface of the potassium carbonate producing
potassium chloride and carbon dioxide.
carbonate, and TEBAC in dry toluene, and found that
the total amount of 1 was transformed to tetraethyl
pyrophosphate 4 (R1 = Et). As the reaction was ac-
companied by carbon dioxide evolution, we had
to suppose that a part of 1 underwent a transfor-
mation with potassium carbonate providing diethyl
phosphoric acid potassium salt 7 (R1 = Et), which
was acylated in a fast reaction by 1 (R1 = Et) still
present. It is important to mention that this trans-
formation cannot be originated from the hydrolysis
of 1(R1 = Et) caused by the adherent water being al-
ways present even on the freshly dried potassium
carbonate surface. A number of experiments were
carried out with potassium carbonate adherent dif-
ferent amount of water to the surface of the solid, and
it was found that the influence of the water content
on the phosphoryl chloride hydrolysis was almost
negligible.
In the next set of experiments, we used diethyl
phosphite 2 (R1 = Et) and carbon tetrachloride gen-
erating 1 (R1 = Et) “in situ” in Atherton–Todd oxida-
tive chlorination, and found that the formation of 4
(R1 = Et) is also nearly quantitative. The pyrophos-
phate forming reaction proved to be general, all the
examined phosphites 2 (R1 = alkyl, aralkyl, phenyl)
provided the desired 4 in clean form and in good
yield (Scheme 1, Table 1).
It must be noted that in contrast with our method
none of the numerous procedures available in the
literature are generally applicable for the prepa-
ration of phosphoric acid anhydrides. The known
method resulting in tetramethyl pyrophosphate
gives this product only in poor yield, because of its
tendency toward decomposition [7]. Though, several
methods are known for the preparation of the stable
pyrophosphates, which involve the controlled partial
hydrolysis of dialkyl phosphoryl chloride prepared in
the previous step [7], or generated “in situ” [8,9] in
the presence of water and organic or inorganic base.
These methods give poor yields in the preparation
of the more sensitive tetramethyl pyrophosphate 4
Preparation of Carboxylic Anhydrides 6
As a consequence of the experiments presented
above, it was imperative to check the behavior of
the mixture of carboxylic acid chlorides 8 with dry
potassium carbonate and lipophilic quaternary salt
in toluene. We found that a fast reaction proceeded
with benzoyl chloride 8 (R2 = Ph) in hot toluene so-
lution giving benzoic acid anhydride 6 in practically
quantitative yield. The reaction proved to be general
also for the preparation of various types of anhy-
drides (Scheme 2, Table 2).
Because of the simplicity, our method seems to
be superior to other PTC methods starting from acid
chlorides, such as that of Plusquellec [18], which
uses aqueous sodium hydroxide as a base, and that
of Wang, which applies solid sodium or potassium
hydrocarbonate and either Co/Pd complex catalyst
[13], or ultrasound [19].
Formation of Sulfonic Acid Potassium salt
on Solid Potassium Carbonate
It was also noticed that p-toluenesulfonic acid chlo-
ride 3 (R3 = 4-MeC6H4) was consumed in the pres-
ence of solid potassium carbonate and TEBAC
in hot toluene resulting in the formation of the
potassium salt of p-toluenesulfonic acid 5 (R3 =
4-MeC6H4) (Scheme 3). As one can expect, the
same result was obtained when benzenesulfonyl
chloride 3 (R3 = Ph), or p-bromobenzenesulfonyl
chloride 3 (R3 = 4-BrC6H4) was used instead of p-
toluenesulfonyl chloride in the reaction mixture. It
is important to note that methanesulfonyl chloride 3
(R3 = Me) also gives the appropriate potassium salt,
but in a much faster reaction.
The main difference, as the side product quality
is concerned using sulfonic acid chloride instead of
SCHEME 1

Reaction of Chlorides of Phosphoric, Sulfonic, and Carboxylic Acids on Solid Potassium Carbonate Surface 449
TABLE 1 Conditions for the Preparation of Pyrophosphates 4
Yield (%)
Time (h) (Temp.)
31PNMR
δ(ppm)
Bp(◦C/mm)
or mp(◦C)
Lit. bp(◦C/mm)
or mp (◦C)
R1
Me
Et
i-Pr
PhCH2
86 1(Rt)
82 1(80)
92 3(80)
88 0.5(60)
−10.5
−13.1
−15.0
−13.0
92–94/0.3
102–106/0.02
99–102/0.05
59–61
114–116/0.5 [7]
105–109/0.03 [8]
94–99/0.02 [8]
59–61 [9]
Ph
73 1(Rt)
−25.6
165–170/0.05
150–155/10−4 [10]
phosphoric acid chloride, is that the sulfonic acid
anion being “harder” and less nucleophilic than the
phosphate anion that cannot be acylated, while the
phosphate anion is converted to pyrophosphate.
EXPERIMENTAL
31P NMR spectra were taken by a Bruker DRX-500
spectrometer using 85% H3PO4 as external standard,
all in CDCl3 solution. The GC measurements were
performed on a Packerd-802 chromatograph using
a silylated glass column packed with Chromosorb G
impregnated with 5% QF1 silicon oil. A column tem-
perature of 210◦C was used with hydrogen as a car-
rier gas and a thermal conductivity detector. The aro-
matic sulfonyl chlorides were freshly recrystallized.
The toluene was dried on sodium. The potassium
carbonate was powdered and dried at 350◦C prior to
use.
Conclusion
Contrary to the above-mentioned phosphoric [11,12]
and carboxylic [13,18] anhydride-forming methods
in our PTC experiments, neither potassium hydrox-
ide nor acetate nucleophile was present in the re-
action mixture. Therefore to interpret the reaction
of dialkylphosphoric 1, carboxylic 8, and sulfonic 3
acid chlorides with solid potassium carbonate given
in Schemes 1, 2, and 3, we have to suppose that it
is the nucleophilic character of the carbonate an-
ion, which is responsible for the formation of the
intermediate of carbonic acid and sulfonic (9), phos-
phoric (10), and carboxylic acid (11), respectively
(Scheme 4).
The structure of the intermediate has to involve
a pentacoordinated sulfur (9) and phosphorus atom
(10) in the case of sulfonyl chloride and phospho-
ryl chloride, respectively, while a tetrahedral carbon
(11) in the case of carboxylic acid chlorides. Stabi-
lization of the intermediates can occur by the an-
hydride C O bond fission to afford potassium salt of
the appropriate sulfonic, phosphoric, and carboxylic
acid, carbon dioxide and potassium chloride. The
phosphoric and carboxylic acid salts are acylated in
the bulk to furnish products 4 and 6, respectively.
Based on the results collected by Makosza [20] and
subsequently for solid potassium carbonate and qua-
ternary onium salt in PTC systems by Sasson [21],we
suppose that it is the interface where the formation
of 9, 10, and 11 might proceed.
General Procedure for the Preparation
of Pyrophosphates 4
The toluene solution (10 mL) of dialkyl or diphenyl
phosphite 2 (20 mmol) was added to a stirred mix-
ture of solid potassium carbonate (5.53 g, 40 mmol),
TEBAC (0.22 g, 1.0 mmol), CCl4 (20 mL, 200 mmol),
and toluene (20 mL), and the reaction mixture main-
tained at the given temperature and for the given
time (see Table 1). The solid was filtered off and
washed with toluene (5 mL). The solvent was evap-
orated and the residue was distilled, or crystallized
TABLE 2 Conditions for the Preparation of Carboxylic Acid
Anhydrides 6
Mp. (◦C)
or bp.
Lit.mp.(◦C)
or Lit.bp.
(◦C/mm)
Yield (%)
R2
X
Time (h) (◦C/mm)
Ph
Cl
99
3
42–44
42–43 [13]
3,4,5(MeO)3C6H2 Cl
60
0.75
99
3
80
7
138–142 159–161 [14]
52–56 62 [15]
82–84/32 106/50 [16]
115/3 120/5 [17]
2-thienyl-
tBu
Cl
Cl
Br
CH3(Br)CH
89
6
SCHEME 2

450 Ja´szay et al.
ACKNOWLEDGMENT
The authors wish to thank Prof. Gy. Keglevich for
helpful suggestions.
SCHEME 3
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General Procedure for the Preparation
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SCHEME 4