Alkyl β-oxoalkanesulfonates: Synthesis and structure of methyl aroylmethanesulfonates

Article abstract of DOI:10.1134/S1070363213030092

A number of new methyl esters of para-substituted benzoylmethanesulfonic acids was synthesized. An ability of both esters and salts to tautomeric transformations was examined. The esters were found to undergo an acid cleavage in alkaline medium.

Full text of DOI:10.1134/S1070363213030092

ISSN 1070-3632, Russian Journal of General Chemistry, 2013, Vol. 83, No. 3, pp. 462–465. © Pleiades Publishing, Ltd., 2013.
Original Russian Text © T.P. Efimova, E.S. Lipina, N.V. Kuz’mina, 2013, published in Zhurnal Obshchei Khimii, 2013, Vol. 83, No. 3, pp. 408–412.
Alkyl β-Oxoalkanesulfonates: Synthesis and Structure
of Methyl Aroylmethanesulfonates
T. P. Efimova, E. S. Lipina, and N. V. Kuz’mina
Herzen Russian State Pedagogical University, Moyka emb. 48, St. Petersburg, 191186 Russia
e-mail: kohrgpu@yandex.ru
Received October 25, 2012
Abstract―A number of new methyl esters of para-substituted benzoylmethanesulfonic acids was synthesized.
An ability of both esters and salts to tautomeric transformations was examined. The esters were found to
undergo an acid cleavage in alkaline medium.
DOI: 10.1134/S1070363213030092
Previously we have proposed a new general
synthetic method for methyl esters of β-oxoalkane-
sulfonic acids via the reaction of acetyl- and
benzoylmethanesulfonic acids with diazomethane [1].
In this work we synthesized a series of new methyl
esters of p-substituted benzoylmethanesulfonic acids
Ib–IIIb and investigated their ability to tautomeric
transformations and to the cleavage in an alkaline
medium. The esters Ib–IIb were also obtained in
another way: through the reaction of the previously
unknown corresponding acid chlorides with methanol.
Earlier only the salts of these sulfonic acids were
described, and their chemical behavior was not studied
[2].
18oC
X−C6H4−C−CH2−SO2Cl
+ CH3OH
O
X−C6H4−C−CH2−SO3CH3
Ic, IIIc
−60oC
−N2
O
X−C6H4−C−CH2−SO3H + CH2N2
Ib−IIIb
O
Iа, IIа
X = p-CH3 (I), p-OCH3 (II), p-Cl (III).
As in the case of the previously studied benzoyl-
of benzoylmethanesulfonate [1], in the UV and
1H NMR spectra of the esters Ib–IIIb the presence of
enol form was not detected regardless of the solvent
polarity. However, like the carboxylic analogs, the
studied esters decolorize a bromine methanol solution
while standing and react with an excess of
diazomethane like the enolized β-oxosulfones [3] to
form methyl esters IV, V.
methanesulfonate [1], the analysis of the spectral
characteristics of the presented acids and their esters
suggests a high CH-acidity of both classes of com-
pounds, which exceed those of the structurally similar
β-oxocarboxylic acids and their esters (Table 1).
β-Oxocarboxylic acids esters are classical objects
of studying the keto-enol tautomerism. As in the case
0oC
X−C6H4−C=CH−SO3CH3
X−C6H4−C−CH2−SO3CH3 + CH2N2
−N2
OCH3
O
X = Cl (IV), OCH3 (V)
IIIb, IIb
462

ALKYL β-OXOALKANESULFONATES
463
Table 1. Physicochemical characteristics of aroylmethanesulfonic acids and their esters Ia,Ib–IIIa,IIIb
p-XC6H4−C−CH2−SO3Y
O
IR spectrum, ν, cm–1
1Н NMR spectruma, δН, ppm (J, Hz)
Comp. no.
Х
Y
SO3
C=O
1680
Ar
Solvent
CH2
Ar
X
CH3
H
1200
1060
1580
(CD3)2SO
4.42 s
7.28 d
7.93 d
(J 4)
2.47 s
Ia
Ibа
IIа
CH3
OCH3
OCH3
Cl
CH3
H
1370
1180
1680
1680
1675
1680
1685
1600
1580
CDCl3
4.59 s
4.41 s
4.85 s
4.48 s
4.61 s
7.11 d
7.69 d
(J 4)
2.34 s
3.79 s
3.83 s
–
1200
1060
(CD3)2SO
CDCl3
6.86 d
7.89 d
(J 5)
IIbа
IIIа
IIIbа
CH3
Н
1370
1180
1590
1570
6.90 d
7.85 d
(J 5)
1200
1060
1570
1580
(CD3)2SO
CDCl3
7.72 d
8.19 d
(J 4)
Cl
CH3
1370
1180
7.44 d
7.91 d
(J 4)
–
a
In the 1Н NMR spectra of compounds Ib–IIIb the signal of the protons of the methyl group of the SO3CH3 moiety was found as a singlet
in the region of 3.89–3.90 ppm.
Methyl aroylmethanesulphonates are well soluble
presence of alkali: The signal of the methylene protons
at 5 ppm disappears and the signal of the vinyl protons
appears at 7.64 ppm. According to the UV spectra, this
enolization is reversible: The acidification of an
alkaline solution leads to disappearance of the
absorption of enolate form and to an increase in the
absorption of the oxoform (Table 2). Like the
alkaline aqueous solutions. According to the spectral
data, they form salts of the enolate structure (Table 2).
In alkaline solution methyl aroylmethane-sulfonates
1
are fully enolized as evidenced by the H NMR and
1
UV spectroscopy. According to the H NMR spectra,
the enolization of esters Ib–IIIb is observed in the
X−C6H4−C−O− + CH3SO3−
O
OH−
slowly
(e)
−OH (−OR), (a)
−OH,
X−C6H4−C−CH2−SO3CH3
X−C6H4−C=CH−SO3CH3
Δ, (c)
H+, (b)
O−
O
Ib−IIIb
−OH, (c)
H+, (d)
X−C6H4−C−CH2−SO3H
X−C6H4−C=CH−SO3−
O−
O
Iа, IIIа
(a) 5% NaOH solution (aq.) or NaOH in CH3OH–CHCl3; (b) acidification of the alkaline solution of ester; (c) 20% NaOH
solution (aq.); (d) HCl; (e) 5% NaOH solution (aq.).
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464
EFIMOVA et al.
Table 2. The 1Н NMR and UV spectral data of methyl aroylmethanesulfonates Ib–IIIb in different media
p-XC6H4−C−CH2−SO3CH3
O
1Н NMR spectrum, δН, ppm (J, Hz)
Comp.
Х
UV spectrum, λmax, nm (ε)а
no.
solvent
CDCl3
СH3
CH2
=CH
–
Ar
X
CH3
4.38 s 5.08 s
7.68 d
8.20 d
(J 8)
2.83 s
70% C2H5OH, 30% H2O – 265 (1500)
NaOHb – 231.5 (11700), 284 (12000)
HCld – 265 (13000)
Ib
NaOD–CD3ODc 3.40 s
–
7.63 s 7.43 d
7.85 d
2.61 s
(J 8)
OCH3 CDCl3
4.36 s 5.03 s
–
7.38 d
8.28 d
(J 9)
4.26 s 70% С2H5OH, 30% H2O – 226 (8000), 291 (16000)
NaOHb – 245 (10000), 287 (16000)
HCld – 226 (7200), 292 (14400)
3.96 s
IIb
NaOD–CD3OD 4.06 s
–
7.64 s 7.11 d
7.91 d
(J 9)
Cl
CDCl3
4.38 s 5.13 s
–
7.88 d
8.31 d
(J 8)
–
–
70% С2H5OH, 30% H2O – 263 (16000)
NaOHb – 234 (12800), 288 (10000)
HCld – 264 (14250)
IIIb
NaOD–CD3OD 3.95 s
–
7.64 s 7.51 d
7.79 d
(J 8)
a
UV spectrum of salts, λmах, nm (ε): 20% NaOH–80% H2O, 231 (6550), 278 (4040) (Ia); 228 (10000), 290 (7100) (IIIa); HCl, 266 (6000)
(Ia); 265 (14000) (IIIa). b The solid alkali was added to a water–alcohol solution. c An alcoholic alkali solution was added to CDCl3
solution. d The acidification of alkaline solution.
unsubstituted benzoylmethanesulfonate ester [1], esters
Ib–IIIb in the course of time undergo acid cleavage as
evidenced by the preparative isolation of the para-
substituted benzoic acids in a yield of >90%. The
decomposition rate depends on the nature of the
substituents in benzene ring. According to the UV
spectra (absorption intensity changes with time in the
series OCH3, H, Cl), the half-life decreases regularly
(Table 3). This result, as well as the presence of an
isobestic point in the electron spectra of esters IIb,
IIIb taken over time is consistent with the assumption
that the ketone form of β-oxocarboxylic esters
undergoes the same acid cleavage.
Table 3. Change in UV spectra of methyl benzoylmethane-
sulfonate IIb and methyl aroylmethanesulfonate IIIb due to
the acid cleavage in 5% NaOH (aq.)
Aroylmethanesulfonic acids salts are also capable
of enolization, but under more rigid conditions (20%
alkaline aqueous solution). Unlike ester enolates, the
generated dianions are stable and decompose only
when boiled to form the decpmposition products, which
are identified as the para-substituted benzoic acids.
p-XC6H4−C−CH2−SO3CH3
O
Comp.
X
λmах, nm (ε) Half period τ, min λmах, nm (ε)
no.
EXPERIMENTAL
H
224 (9200)
278 (8500)
150
210
60
223.5 (8100)
278 (4200)
IIb
1
The Н NMR spectra were registered on a Tesla
BS-487C spectrometer (80 MHz). The IR spectra were
recorded on a UR-20 spectrometer from CDCl3
solution or mullin mineral oil. Electronic spectra were
recorded on a Specord M-40 spectrophotometer. The
individuality of the compounds obtained and the
OCH3 248 (10000)
285 (16000)
248 (11000)
280 (8000)
Cl
233 (11000)
283 (9600)
234 (11000)
281 (4600)
IIIb
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ALKYL β-OXOALKANESULFONATES
465
reaction progress were monitored by thin layer
chromatography (TLC) on Silufol UV-254 plates
eluting with a hexane–acetone mixture (1:2) and
detecting with UV irradiation (254 nm). Synthesis of
β-oxoalkanesulfonic acids Ia–IIIa was performed
according to [2] via the sulfonation of fatty aromatic
ketones obtained by acylating the corresponding
benzene derivatives according to [4].
71°C (CHCl3). Found, %: C 46.29; H 4.09. C9H9ClO3S.
Calculated, %: C 46.45; H 3.87.
Methyl 2-methoxy-(p-chlorostyryl)sulfonate (IV).
To a solution of 0.72 g of methyl p-chlorobenzoyl-
methanesulfonate IIIb in a mixture of 12 ml of
anhydrous ether and 3 ml of anhydrous methanol was
slowly added 11 ml of solution of diazomethane in
diethyl ether (c 0.00097 mol/ml) with cooling to 0–5°C
and stirring. Then, diethyl ether was distilled off, and
the residue was chromatographed on a silica gel
eluting with benzene. Yield 0.283 g (37%), oily
substance. IR spectrum, ν, cm–1: 1610 (С=С) 1590
Methyl p-chlorobenzoylmethanesulfonate (IIIb).
a. To a suspension of 5 g of p-chlorobenzoylmethane-
sulfonic acid in 30 ml of anhydrous ether was slowly
added 30 ml of diazomethane in diethyl ether (c
0.00097 mol/ml) with cooling to –60°C and stirring.
Then the temperature of the reaction mixture was
gradually increased to 25°C. Diethyl ether was re-
moved, and the residue was recrystallized from CCl4.
Yield 2.13 g (41%), mp 85–87°C. Found, %: C 43.50,
H 3.67. C9H9ClO4S. Calculated, %: C 43.46, H 3.62.
1
(Ar), 1160, 1360 (SO3). Н NMR spectrum, δН, ppm:
3.66 s (3Н, OCH3), 3.81 s (3Н, SO3CH3), 5.79 s (1Н,
CH=), 7.34 m (4Нarom). Found, %: C 45.84; Н 4.27.
C10H11ClO4S. Calculated, %: C 45.71; Н 4.19.
Methyl 2-methoxy-(p-methoxystyryl) sulfonate
(V) was prepared similarly from 0.8 g of methyl p-
methoxybenzoylmethanesulfonate IIb. Yield 0.335 g
b. A mixture of 1.5 g of p-chlorobenzoylmethane-
sulfonyl chloride IIIc and 4 ml of methanol was kept
for 1 h at 18°C and then cooled to 0°C. The pre-
cipitated crystals were filtered off and dried in air.
Yield 1.21 g (83%), mp 85–87°C (CCl4).
1
(40%), oily substance. Н NMR spectrum, δН, ppm:
3.69 s (3Н, OCH3), 3.76 s (3Н, OCH3) 3.83 s (3Н,
SO3CH3), 5.68 s (1Н, CH=), 6.83 d, 7.26 d (4Нarom).
Found, %: C 51.24; Н 5.56. C11H14O5S. Calculated, %:
C 51.16; Н 5.43
Methyl p-methoxybenzoylmethanesulfonate (IIb)
was prepared similarly from 5 g of p-methoxybenzoyl-
methanesulfonic acid IIa. Yield 1.97 g (37%), mp
133–135°C (CCl4). Found, %: C 52.55; H 5.50.
C10H12O5S. Calculated, %: C 49.18; H 4.09.
Decomposition of p-chlorobenzoylmethanesulfonic
acid (IIIa). A solution of 2 g of IIIa in 10 ml of 20%
NaOH aqueous solution was heated for 5 h. After
cooling to room temperature, the reaction mixture was
acidified with hydrochloric acid to pH 1, the formed
crystalline p-chlorobenzoic acid was filtered off. Yield
1.33 g (98%).
Methyl p-methylbenzoylmethanesulfonate (Ib)
was prepared similarly from 1 g of p-methylbenzoyl-
methanesulfonyl chloride Ic. Yield 0.75 g (77%), mp
71–73°C (CCl4). Found, %: C 52.63; H 5.26.
C10H12O4S. Calculated, %: C 52.75; H 5.50.
Decomposition of p-methylbenzoylmethanesulfonic
acid Ia was performed similarly.
p-Chlorobenzoylmethanesulfonyl chloride (IIIc).
A mixture of 27 g of p-chlorobenzoylmethanesulfonic
acid IIIa and 20 ml of PCl3 was heated for 14 h on a
water bath. Then, an excess of PCl3 was removed, and
the residue was recrystallized from СHCl3. Yield 12.70 g
(43%), mp 79–83°C. Found, %: C 38.09, H 2.49.
C8H6Cl2O3S. Calculated, %: C 37.94, H 2.37.
REFERENCES
1. Efimova, T.P., Lipina, E.S., Berkova, G.A., and
Pozdnyakov, V.P., Zh. Org. Khim., 1996, vol. 32,
no. 10, p. 1473.
2. Terent’ev, A.P., Potapov, V.M., and Dem’yanovich, V.M.,
Zh. Obshch. Khim., 1959, vol. 29, no. 3, p. 949.
3. Arnone, A., Brano, P., Caviechino, G., and Frigerio, M.,
Tetrahedron Lett., 1992, vol. 33, no. 38, p. 5609.
4. Bekker, H. and Berger, V., Organikum (Organicum),
p-Methylbenzoylmethanesulfonyl chloride (Ic)
was prepared similarly from 15 g of p- methylbenzoyl-
methanesulfonic acid Ia. Yield 3.1 g (19%), mp 65–
Moscow: Mir, 1982, vol. 1, p. 456.
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