Photoacid generators (PAGs) based on N-acyl-N-phenylhydroxylamines for carboxylic and sulfonic acids

Article abstract of DOI:10.1016/j.tet.2011.03.049

Simple and efficient photoacid generators (PAGs) for carboxylic and sulfonic acids based on N-acyl-N-phenylhydroxylamines have been demonstrated. Irradiation of o-carboxylates and thermally rearranged o-arenesulfonates of N-acyl-N-phenylhydroxylamines using UV light (≥254 nm) in aqueous methanolic solution resulted in efficient generation of carboxylic and sulfonic acids, respectively. The carboxylic acid generation ability of N-acyl-N- phenylhydroxylamines was found to be dependent on their N-acyl substituents. Further, polymer bearing o-arenesulfonates of N-acyl-N-phenylhydroxylamine was synthesized and demonstrated as PAG for sulfonic acids.

Full text of DOI:10.1016/j.tet.2011.03.049

Tetrahedron 67 (2011) 3733e3742
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Photoacid generators (PAGs) based on N-acyl-N-phenylhydroxylamines
for carboxylic and sulfonic acids
*
*
Mohammed Ikbal, Avijit Jana, N.D. Pradeep Singh , Rakesh Banerjee, Dibakar Dhara
Department of Chemistry, Indian Institute of Technology Kharagpur, Kharagpur 721302, West Bengal, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Simple and efficient photoacid generators (PAGs) for carboxylic and sulfonic acids based on N-acyl-
N-phenylhydroxylamines have been demonstrated. Irradiation of o-carboxylates and thermally re-
arranged o-arenesulfonates of N-acyl-N-phenylhydroxylamines using UV light (ꢀ254 nm) in aqueous
methanolic solution resulted in efficient generation of carboxylic and sulfonic acids, respectively. The
carboxylic acid generation ability of N-acyl-N-phenylhydroxylamines was found to be dependent on
their N-acyl substituents. Further, polymer bearing o-arenesulfonates of N-acyl-N-phenylhydroxylamine
was synthesized and demonstrated as PAG for sulfonic acids.
Received 1 November 2010
Received in revised form 28 February 2011
Accepted 17 March 2011
Available online 30 March 2011
Keywords:
N-Acyl-N-phenylhydroxylamine
Photoacid generator
Homolytic cleavage
Carboxylic acid
Ó 2011 Elsevier Ltd. All rights reserved.
Sulfonic acid
1. Introduction
sulfonic acids by photoinduced homolytic NeO bond cleavage led
us to explore N,O-diacyl-N-phenylhydroxylamines.
The growing demand to generate photoresist materials with
high resolution1 and high sensitivity2 for lithography have sparkled
the interest in photoacid generators (PAGs).3,4 PAGs can be classi-
fied into two group’s namely ionic and non-ionic type.5 Non-ionic
PAGs have gained much attention over ionic type due to its wide
Considerable research has been undertaken to understand the
mechanistic mode of NeO bond cleavage of N,O-diacyl-N-phenyl-
hydroxylamines in connection to its photoaroyloxy rearrange-
ment.19 Sakurai and his co-workers19 showed that direct photolysis
of N,O-diacyl-N-phenylhydroxylamines undergoes efficient homo-
lytic NeO bond cleavage from its singlet excited state to form 1,3 and
1,5 aroyloxy rearranged products via ‘in-cage’ reaction of aroyloxyl
and amido radicals, along with fragmentation products, such as
arenecarboxanilide, carboxylic acid and hydrocarbons through
‘cage-escape’ reaction of the above said radicals. Interestingly, the
same group further showed that photolysis of N,O-diacyl-N-phe-
nylhydroxylamines in hydrogen donor solvents produced largely
fragmentation products (carboxylic acid and carboxanilide) via ef-
ficient hydrogen atom abstractions by aroyloxyl and amido radicals
from the solvent by cage escape mechanism.19,20 Considering the
above result to produce carboxylic acids as a major product in
hydrogen donor solvents, together with our recent research interest
on exploring the applications of homolytic NeO bond cleavage of
N,O-diacyl-N-phenylhydroxylamines,21 made us to investigate N,O-
diacyl-N-phenylhydroxylamines as PAGs.
range of solubility in organic solvents and in polymer films.6
A
variety of non-ionic PAGs have been reported for the generation of
sulfonic acids,7,8 carboxylic acids,9 phosphoric acids10 and hydro-
gen halides.11,12
In the past years, significant progress has been made in the field
of photoinduced cleavage of NeO bond due to its potential appli-
cations in the areas like radical generation,13 protecting groups for
biological molecules,14 photopolymerisation15 and also for the
synthesis of several biologically important heterocyclic com-
pounds.16 In recent times, homolytic cleavage of the weak NeO
bond by direct or sensitized photolysis shows growing interest in
the area of PAGs. So far, only certain sulfonate esters derived from
N-hydroxyamides,17 N-hydroxyimides3 and few imino sulfonates18
were reported to generate sulfonic acids on photolysis via homo-
lytic NeO bond cleavage. Hence, in search of simple organic mol-
ecules, which can act as efficient PAGs for both carboxylic and
Herein, we report o-carboxylates and thermally rearranged
o-arenesulfonates of N-acyl-N-phenylhydroxylamines as simple
and efficient PAGs for carboxylic and sulfonic acids, respectively.
The synthesis and the characterization of the PAGs were discussed.
The generation of carboxylic and sulfonic acids was achieved by
irradiating their corresponding PAGs using UV light (ꢀ254 nm). The
* Corresponding authors. Tel.: þ91 3222 282324; fax: þ91 3222 282252; e-mail
addresses: ndpradeep@chem.iitkgp.ernet.in (N.D.P. Singh), dibakar@chem.
iitkgp.ernet.in (D. Dhara).
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.03.049

3734
M. Ikbal et al. / Tetrahedron 67 (2011) 3733e3742
Table 2
effect of different N-acyl substituents on the acid generation ability
of the PAGs was investigated. Further, we also synthesized poly-
mers bearing o-arenesulfonyloxyanilide and showed that irradia-
tion of these polymers in thin films resulted in the generation of
sulfonic acids.
Synthetic yield, UV/vis and photolysis data of the carboxylate esters of N-acetyl-N-
phenylhydroxylamine (3aeh)
Entry Carboxylate Synthetic UV/vis
yielda (%)
Photogeneration of
carboxylic acids
l
(nm)b log 3c Time
Yielde
Quantum
(min.)d (RCO2H) yield (
f)
f
1
2
3
4
5
6
7
8
3ag
3b
90
91
90
92
90
95
90
93
230
277
246
243
261
298
243
246
4.17
4.31
4.27 120
4.29 100
4.24
4.57
4.20 110
4.22 140
60
90
91
90
95
95
93
95
92
85
0.042
0.028
0.022
0.026
0.051
0.088
0.023
0.017
2. Results and discussion
3cg
3dg
3eg
3f
2.1. Carboxylates of N-acyl-N-phenylhydroxylamines as PAGs
for carboxylic acids
50
30
3gg
3hg
2.1.1. Synthesis of carboxylates of N-acetyl-N-phenylhydroxylamine
(3aeh). We have synthesized carboxylate esters of N-acetyl-N-phe-
nylhydroxylamine (3aeh) as outlined in Scheme 1. The carboxylates
were synthesized, initially by carrying out N-acetylation of N-phe-
nylhydroxylamine (1) with acetyl chloride in presence of NaHCO3 in
a
b
c
d
e
f
Based on isolated yield.
Maximum absorption wavelength.
Molar absorption coefficient.
Time for photolysis.
Photolysis yield based on HPLC.
Quantum yield for the generation of various carboxylic acids at room temper-
dry DCM at
0
ꢁC to yield N-acetyl-N-phenylhydroxylamine
(2).22Treatment of 2 with various acid chlorides in presence of trie-
thylamine in dry DCM resulted in quantative yield of carboxylates of
N-acetyl-N-phenylhydroxylamine (3aeh, Table 2). All the carboxyl-
ates were characterized by 1H,13C NMR, IR and mass spectral analysis.
ature (error limit within ꢂ5%).
g
Carboxylates for which the photoproducts were isolated and compared with
authentic samples.
CH3COCl, NaHCO3
OH
R1COCl, Et3N
OH
O
O
O
DCM, 0 oC
DCM, 0 oC
N
N
N
COR1
H
H3C
H3C
1
2
3a-h
R1 = CH2C6H5 (3a), C2H2C6H5 (3b), C6H5 (3c), p-MeC6H4 (3d), p-MeOC6H4 (3e),
p-EtO(m-MeO)C6H3 (3f), p-ClC6H4 (3g), p-NO2C6H4 (3h).
Scheme 1. Synthesis of carboxylate esters of N-acetyl-N-phenylhydroxylamine.
2.2. Photolysis of carboxylate esters of N-acetyl-N-
phenylhydroxylamine (3aeh) to form carboxylic acids
Hence, we irradiated the carboxylate esters of N-acetyl-N-phe-
nylhydroxylamine (3aeh) in MeOH/H2O (9:1) solution and we
found the corresponding carboxylic acids to be generated in nearly
quantative yield as summarized in Table 2. In each case the pho-
tolysis was stopped when conversion reached at least 95% (as in-
dicated by HPLC). For the carboxylates indicated in Table 2, their
photoproducts (carboxylic acid and acetanilide) were isolated and
characterized by 1H NMR spectra with corresponding authentic
samples. Quantum yield for the generation of various carboxylic
acids were found to be in the range of 0.017e0.088 using valer-
ophenone as an actinometer.23
As a representative example, we have shown in Fig. 1a HPLC
analysis of photolyzed 3d. The HPLC data clearly shows the de-
pletion of the peak at tR 17.48 min with increase in irradiation time,
indicating the photodecomposition of the carboxylate (3d). On the
other hand, we noticed gradual increase of two new major peaks at
tR 5.76 min and tR 10.03 min corresponding to the photoproducts
p-toluic acid and acetanilide, respectively.
In order to compare the efficiency of photorelease from various
solutions of carboxylates, The compound 3a, 3c, 3e, and 3h
(0.05 mM) in MeOH/H2O (9:1) were irradiated using light above
254 nm and the course of the reaction was monitored by HPLC at
regular interval of time. The Fig. 1b shows appearance of the
carboxylic acids with respect to irradiation time. We notice that
these carboxylates generates the corresponding carboxylic acids
(ꢀ85%) within 140 min of irradiation. In particular, aromatic car-
boxylic acids with electron donating substituent were generated
more efficiently compared to aromatic carboxylic acids with
electron withdrawing substituent (for example, p-methoxy ben-
zoic acid was formed almost three times more efficiently com-
pared to p-nitro benzoic acid).
Initially, we investigated the photolysis of carboxylate (3c) in
methanolic solution using a 125-W medium pressure Hg lamp with
quartz sleeve and we found homolytic NeO bond cleavage occurred
to produce benzoic acid and acetanilide in good yields. This ob-
servation encouraged us to find the best solvent system for the
efficient generation of carboxylic acids in high yield. We carried out
the photolysis of 3c (0.05 mM) in various solvents including
methanol (MeOH), acetonitrile (ACN), tetrahydrofuran (THF),
MeOH/H2O (9:1) and ACN/H2O (9:1) for 2 h and the results are
tabulated in Table 1.
Table 1
Photolysis of carboxylate (3c) in various solvents
b
Entry
Solvent system
% of Acid generateda
Quantum yield (f)
1
2
3
4
5
MeOH
ACN
THF
ACN/H2O (9:1)
MeOH/H2O (9:1)
80
70
75
75
95
0.019
0.016
0.017
0.017
0.022
a
Photolysis yield based on HPLC.
Quantum yield for the generation of benzoic acid at room temperature (error
b
limit within ꢂ5%).
Among the above solvents, we found carboxylate (3c) gener-
ated benzoic acid in relatively high quantum yield and chemical
yield in MeOH/H2O (9:1) compared to other solvents used for the
study.

M. Ikbal et al. / Tetrahedron 67 (2011) 3733e3742
3735
Fig. 1. a. HPLC data of photolysis of ester 3d at regular interval of time: (a) 0 min (b) 25 min (c) 50 min (d) 75 min (e) 100 min (f) std p-toluic acid (g) std acetanilide. b. Comparison
of efficiency for photoinduced formation of various carboxylic acids from respective carboxylates (3a, 3c, 3e and 3h) at regular interval of photo irradiation.
2.3. Mechanism for the photogeneration of carboxylic acids
p-toluic esters of N-acyl-N-phenylhydroxylamines (4aec) as de-
scribed in Scheme 3.
Based on the literature precedence,24 mechanism for the pho-
togeneration of carboxylic acid is outlined in Scheme 2. After initial
excitation of the carboxylate to its singlet excited state, it undergoes
homolytic NeO bond cleavage to generate carboxyl and acetanilide
radical pair. The above generated radical pair, escapes from the cage
and subsequently abstracts hydrogen from the solvent to produce
the corresponding carboxylic acid (5) and acetanilide (4).
In order to compare the efficiency of photogeneration of p-toluic
acid by different N-acyl substituent PAGs, 0.05 mM solution of PAGs
(3d, 6aec) in MeOH/H2O (9:1) were irradiated using light source of
ꢀ254 nm for 50 min and the photolysis was monitored by HPLC at
regular interval of time. Based on HPLC data for each PAGs, the
natural logarithm of the concentration of p-toluic acid generated
(lnC) versus irradiated time was plotted. We observed a linear
correlation for the generation of p-toluic acid, which suggested
a first order reaction, obtained by linear least square methodology
for a straight line (Fig. 2).
2.4. Effect of N-acyl substituents on the acid generation
ability of PAGs
The quantum yield (f) for the generation of p-toluic acid by
PAGs (Table 3), indicate that N-acyl substituents have pronounced
effect on the acid generation ability of PAGs. We noticed that with
To investigate the effect of different N-acyl substituents on the
acid generation ability of PAGs, we synthesized PAGs based on
O
O
O
R1
>
hν 254 nm
N
R1COOH
+
NH
+
N
O
R1
MeOH-H2O
O
H3C
H3C
O
H3C
O
3a-h
4
5
Scheme 2. Mechanism for the photogeneration of carboxylic acids.
CH3
RCOCl, NaHCO3
DCM, 0 oC
p-CH3C6H4COCl, Et3N
OH
OH
O
O
DCM, 0 oC
N
H
N
N
O
R
R
O
6a-c
1
2a-c
R = C6H5 (6a), p-MeoC6H4 (6b), p-NO2C6H4 (6c).
Scheme 3. Synthesis of p-toluic esters of N-acyl-N-phenylhydroxylamines (6aec).

3736
M. Ikbal et al. / Tetrahedron 67 (2011) 3733e3742
2.8
2.4
2.0
1.6
1.2
0.8
0.4
0.0
3. N-Acyl-N-phenylhydroxylamines as PAGs for sulfonic acids
3d
6a
6b
6c
The photoinduced generation of strong acids, such as sulfonic
acids is essentially important since they afford high sensitivity re-
sists.28 Hence we investigated the application of N-acyl-N-phenyl-
hydroxylamines as PAGs for sulfonic acids.
3.1. Synthesis of o-arenesulfonyloxyacetanilide (8aef) and o-
arenesulfonyloxybenzanilide (10aee)
We synthesized two series of o-arenesulfonyloxyanilide as
outlined in Scheme 4. The series-1 consists of o-arenesulfonylox-
yacetanilides and the series-2 has o-arenesulfonyloxybenzanilides.
The sulfonates of series-1 were synthesized by carrying out
N-acetylation of N-phenylhydroxylamine (1) to yield N-acetyl-N-
phenylhydroxylamine (2). However, treatment of 2 with various
sulfonyl chlorides in presence of Et3N in dry DCM at 0 ꢁC resulted in
thermally unstable N-sulfonyl-N-acetyl-N-phenylhydroxylamines
(7aef), which then efficiently rearranged to form o-arenesulfonates
of N-acetyl-N-phenylhydroxylamine in excellent yields29 (Table 4,
8aef). Similarly in the case of series-2, N-phenylhydroxylamine (1)
was benzoylated and then treated with various sulfonyl chlorides to
yield rearranged o-arenesulfonyloxybenzanilide (Table 4, 10aee).
0
10
20
30
40
50
Time (min)
Fig. 2. Concentration of p-toluic acid (lnC) versus irradiation time for the PAGs (3d,
6aec).
Table 3
Synthetic yield, UV/vis and photolysis data of PAGs (3d, 6aec)
3.2. Irradiation of o-arenesulfonyloxyacetanilides (8aef) and
o-arenesulfonyloxybenzanilides (10aee) for the generation of
sulfonic acids
PAGs Synthetic yielda (%) UV/vis
(nm)b log 3c Yieldd (R1CO2H) Quantum yield (
f)
Photogeneration of p-toluic acid
e
l
3d
6a
6b
6c
92
85
91
90
243
245
242
245
4.29 65
4.54 90
4.55 60
4.62 95
0.036
0.050
0.039
0.053
Irradiation of the methanolic solution of sulfonates (8aef,
10aee) using the similar procedure as described for the generation
of carboxylic acids (Section 2.2), resulted in efficient SeO bond
cleavage to generate their corresponding sulfonic acids in high yield
(Scheme 5, Table 4). The photolysis was monitored using 1H NMR
spectroscopy and the reaction was stopped when the conversion
reached about 95%. In all the cases, sulfonic acid was isolated as the
only significant photoproduct along with o-hydroxyacetanilide or
o-hydroxybenzanilide (11). As anticipated, the o-arenesulfonylox-
ybenzanilide (10aee, Table 4, entries 7e11) generated sulfonic
acids more efficiently with higher quantum yield compared to o-
arenesulfonyloxyacetanilide (8aef, Table 4, entries 1e6).
a
Based on isolated yield.
Maximum absorption wavelength.
Molar absorption coefficient.
Photolysis yield based on HPLC.
Quantum yield for the generation of p-toluic acid at room temperature (error
b
c
d
e
limit within ꢂ5%).
increased electron withdrawing group on the N-acyl substituents of
PAGs, quantum yield (f) for the generation of p-toluic acid in-
creases. Since, stronger electron withdrawing acyl substituent sta-
As a representative example, we have shown in Fig. 3a the 1H
NMR spectra of sulfonate (10d) at regular interval of irradiation.
From the 1H NMR spectra we observed signal at 2.38 ppm corre-
sponding to the methyl group of sulfonate decreases with
bilizes generated acyl aminyl radicals.25e27
C6H5COCl, NaHCO3
CH3COCl, NaHCO3
HO
OH
OH
O
DCM, 0 oC
N
N
H
DCM, 0 oC
N
O
CH3
C6H5
2
1
2a
R2SO2Cl DCM, 0 oC
Et3N
R3SO2Cl DCM, 0 oC
Et3N
NHCOC6H5
H3COCHN
rearrangment
rt
rearrangment
rt
O
O
O
O
R2O2S
N
N
SO2R3
OSO2R3
Series-2
R2O2SO
Series-1
CH3
7a-f
C6H5
9a-e
R2 = CH3 (8a),
C4H9 (8b),
R3 = CH3 (10a),
C4H9 (10b),
C6H5 (8c),
C6H5 (10c),
p-CH3C6H4 (8d),
o-NO2C6H4 (8e),
p-NO2C6H4 (8f).
p-CH3C6H4 (10d),
o-NO2C6H4 (10e).
Scheme 4. Synthesis of o-arenesulfonyloxyacetanilides (8aef) and o-arenesulfonyloxybenzanilides (10aee).

M. Ikbal et al. / Tetrahedron 67 (2011) 3733e3742
3737
Table 4
Synthetic yield, UV/vis and photolysis data of the o-arenesulfonyloxyacetanilide (8aef) and o-arenesulfonyloxybenzanilide (10aee)
Entry
Sulfonate
Synthetic yielda (%)
UV/vis
(nm)b
Photogeneration of sulfonic acids
f
l
log 3c
Time (min.)d
Yielde (RSO3H)
Quantum yield (f)
1
2
3
4
5
6
7
8
8a
8b
8c
8d
8e
8f
10a
10b
10c
10d
10e
83
80
91
90
85
90
85
80
91
90
82
236
237
246
227
240
241
249
245
246
242
250
4.05
4.12
4.08
4.47
4.21
4.38
4.05
4.12
4.08
4.47
4.21
45
60
90
50
75
100
35
45
40
50
45
95
85
90
93
90
90
95
92
90
90
95
0.058
0.039
0.027
0.051
0.033
0.025
0.075
0.057
0.062
0.050
0.058
9
10
11
a
Based on isolated yield.
b
c
d
e
f
Maximum absorption wavelength.
Molar absorption coefficient.
Time for photolysis.
Photolysis yield based on 1H NMR.
Quantum yield for the generation of various sulfonic acids at room temperature (error limit within ꢂ5%).
bearing o-arenesulfonyloxyanilide as PAG for sulfonic acids, since
they can be used as photoresist materials for lithography.
NHCOR
OH
NHCOR
>
hν 254 nm
R2/R3SO3H
+
MeOH-H2O
OSO2R2/R3
4.1. Synthesis of monomer o-(styrenesulfonoxy) acetanilide
(SSAI)
8a-f or 10a-e
11
12a-f or 13a-e
Scheme 5. Photogeneration of sulfonic acids from o-arenesulfonyloxyanilide.
The monomer o-(styrenesulfonoxy) acetanilide (16) was syn-
thesized by treating p-styrenesulfonyl chloride30 (14) with
Fig. 3. a. 1H NMR spectra of sulfonate (10d) at regular interval of irradiation. b. Change of pH on photolysis of sulfonate esters (8aee) at regular interval of irradiation.
irradiation time, indicating the photodecomposition of 10d. On the
other hand, we can notice gradual increase of a signal at 2.35 ppm
corresponding to the methyl peak of p-toluic sulfonic acid with
increase in irradiation time. In addition, we also observed gradual
appearance of a broad singlet at 4.38 ppm of eOH proton, which
disappeared on D2O exchange confirming the formation of p-toluic
sulfonic acid.
Furthermore, the generation of sulfonic acids from their corre-
sponding sulfonates (8aee) was also studied by monitoring the pH
change of the photolysate at regular interval of irradiation (Fig. 3b).
N-hydroxyacetanilide (2) in presence of Et3N in dry DCM under
nitrogen atmosphere as outlined in Scheme 6.
4.2. Synthesis of o-(styrenesulfonoxy)
acetanilideemethylmethcrylate (SSAIeMMA) and
o-styrenesulfonyloxy acetanilideelauryl acrylate (SSAIeLA)
polymers
Polymerization was carried out by free radical method using
AIBN as an initiator.31 The monomer o-(styrenesulfonoxy) acetani-
lide (16) and methylmethcrylate (MMA) (17) or lauryl acrylate (LA)
(18) were dissolved in THF and AIBN was added (molar ratio of
monomer: AIBN was 200:1) under nitrogen atmosphere. The re-
action mixture was heated at 80 ꢁC for 3 h to yield the corresponding
polymers SSAIeMMA (19) and SSAIeLA (20) (Scheme 7).
4. Polymers derived from o-arenesulfonyloxyacetanilide as
sulfonic acid generators
After successfully demonstrating o-arenesulfonyloxyanilides as
PAGs for sulfonic acids, we were interested to develop polymers

3738
M. Ikbal et al. / Tetrahedron 67 (2011) 3733e3742
O
S
O
O
DCM, 0 °C
Et3N
O
S
O
rearrangment
rt
O
O
OH
O
N
+
N
ClO2S
NHCOCH3
H3C
H3C
16
2
14
15
Scheme 6. Synthesis of monomer o-(styrenesulfonyloxy) acetanilide.
R4
CH2 CH CH2
n
C
C O
O
m
R5
S
R4
AIBN, DMF
80 oC
O
O
O
O
S
+
O
O
O
R5
NHCOCH3
O
NH
H3C
O
(19) SSAI-MMA, R4 = CH3, R5 = CH3
(20) SSAI-LA, R4 = H, R5 = (CH2)11CH3
(17) MMA R4, R5 =CH3
(18) LA R4 = H, R5 = (CH2)11CH3
16
Scheme 7. Synthesis of polymer SSAIeMMA and SSAIeLA.
4.3. Characterisation of the polymers
The FTIR spectra (Fig. 5a) indicated photodecomposition of
polymer films (SSAIeMMA) on irradiation at 254 nm. We noticed
the peak at 1375, 1195 and 1180 cmꢄ1
SO2) due to aminosulfonate
unit decreases on irradiation, indicating the photodecomposition of
the polymer. The above fact was also noticed in the UV/vis spectra
from the decrease in the absorbance around 250 nm, which cor-
responds to aminosulfonate unit (for UV/vis spectra see
Supplementary data).
Molecular weights and the polydispersity of the polymers
SSAIeMMA (19) and SSAIeLA (20) were recorded by gel permeation
chromatography (GPC) and the results are tabulated in Table 5. GPC
was carried out at ambient temperature using a Viscotek-GPC sys-
tem equipped with two GMH HR-H non polar organic columns in
series. Tetrahydrofuran was used as an eluant at a flow rate of 1 ml/
min. Polystyrene standards in the Mn range of 955e37,15,000 was
used for calibrations (Fig. 4).
(n
On the other hand, the generation of sulfonic acid by the poly-
mer films was confirmed by using acid-catalyzed polysiloxane
Table 5
Polymerization conditions and characterization of polymer
a
Compound
Sample name
SSAI
MMA (gm)
LA (gm)
AIBN (gm)
Mw
Mw/Mn
19
SSAIeMMA copolymer
0.75
0.238
d
0.002
18,432
1.95
(2.365 mmol)
0.75
(2.365 mmol)
0.75
(2.375 mmol)
d
(0.012 mmol)
0.002
(0.012 mmol)
0.002
20
21
SSAIeLA copolymer
0.568
(2.363 mmol)
d
13,339
10,859
1.86
1.74
Homo polymer
d
(2.365 mmol)
(0.012 mmol)
a
Measured against polystyrene standards.
Further the polymers were also characterized by UV, IR and 1H
NMR spectroscopy.
formation technique.32 From the FTIR spectra (Fig. 5b) we can no-
tice changes of irradiated film before and after treatment with
methyltriethoxysilane (MTEOS). The appearance of new peaks at
780 (SieCH3), 900 (SieOH), 1000e1200 (SieOeSi) and 3200e3500
(SieOH) on the irradiated film shows the formation of silanol,
which indicates hydrolysation of MTEOS under humid condition by
the newly generated sulfonic acids.
4.4. Photogeneration of sulfonic acid from polymers
To investigate the polymers as PAG, the SSAIeMMA (19) poly-
mer was spin coated onto silicon wafers using a headway research
spinner (Spin Coating Unit SCU 2005). The photoresist films were
then baked at 90 ꢁC for 5 min in an oven. The film thicknesses
were measured with a dektak-150 film thickness measurement
5. Conclusions
We have showed simple carboxylates of N-acyl-N-phenyl-
hydroxylamines to act as efficient PAGs for carboxylic acids. We
demonstrated that by altering the N-acyl substituents, the acid
generation ability of N-acyl-N-phenylhydroxylamines can be easily
tuned. Furthermore, o-arenesulfonates of N-acyl-N-phenyl-
hydroxylamines (rearranged product) and the polymers bearing o-
arenesulfonyl N-acyl phenylhydroxylamines were demonstrated as
PAG for sulfonic acids.
gauge and were in the range of 0.5e0.8
mm. Irradiation of the
polymer thin films at 254 nm by the use of low pressure Hg lamp
(The
incident
photon
flux
(I0)
at
254
nm
is
1.8ꢃ1017 photon sꢄ1 cmꢄ2) at room temperature in air resulted in
homolytic SeO bond cleavage followed by hydrogen abstraction
from the residual solvent in the film or polymer molecule leading
to the generation of sulfonic acids.

M. Ikbal et al. / Tetrahedron 67 (2011) 3733e3742
3739
200
150
100
50
equipped with two GMH HR-H non polar organic columns in series.
Photolysis of all the ester were carried out using 125 W medium
pressure mercury lamp supplied by SAIC (India).
W ITH LA
Mw/Mn = 1.855
HOMO POLYMER
Mw/Mn= 1.74
6.2. General procedure for the synthesis of carboxylate esters
of N-acetyl-N-phenylhydroxylamine (3aeh)
W ITH MMA
Mw/Mn = 1.945
RI
0
To the N-acetyl-N-phenylhydroxylamine (500 mg, 3.31 mmol) in
dry DCM, acid chloride (3.98 mmol), was added, to the reaction
mixture Et3N (0.92 ml, 6.61 mmol) was slowly added over a period
of 5 min at 0 ꢁC. The reaction mixture was stirred for further 12 h at
room temperature. After the completion of the reaction (as in-
dicated by TLC), it was quenched by ice cold water, diluted with
DCM. The organic layer was separated, dried over Na2SO4 and the
solvent was removed under vacuum.
-50
-100
-150
16
17
18
19
20
21
Retention volume(ml)
6.2.1. O-Phenylethanoyl-N-phenyl-acetohydroxamic acid (3a). The
crude product was purified by column chromatography (20% ethyl
acetate/hexane) to give the title compound 3a (90%) as brown
Fig. 4. GPC chromatogram of HOMO polymer of SSAI (21) and copolymers SSAIeMMA
(19) and SSAIeLA (20).
Fig. 5. a. FTIR spectral change of SSAIeMMA film on irradiation at 254 nm. Film thickness: 0.2 mm. b. FTIR spectral change of the SSAIeMMA film before (red) and after (black)
treatment with MTEOS vapour for 20 min. Film thickness: 0.2
mm.
6. Experimental section
liquid; Rf (30% ethyl acetate/hexane) 0.45; FTIR (neat) nmax (cmꢄ1):
1648, 1793; 1H NMR (CDCl3, 200 MHZ)
: 2.01 (s, 3H), 3.78 (s, 2H),
7.29e7.32 (m, 5H), 7.39 (m, 5H); 13C NMR (CDCl3, 100 MHz)
d
6.1. General
d:
21.3, 38.5, 127.5, 128.7 (2C), 129.2 (4C), 129.6 (4C), 139.1, 168.4,
168.6; MS m/z: 292 (72%, MNaþ), 270 (100%, MHþ), 214 (18%);
HRMS (ESþ) calcd for C16H16NO3 [MþHþ] 270.1125, found
270.1128.
1H NMR (200 MHz) spectra were recorded on a BRUKER-AC
200 MHz spectrometer. Chemical shifts are reported in parts per
million from tetramethylsilane with the solvent resonance as the
internal standard (deuterochloroform: 7.26 ppm). Data are repor-
ted as follows: chemical shifts, multiplicity (s¼singlet, d¼doublet,
t¼triplet, q¼quartet, dd¼doublet of doublet, m¼multiplet), cou-
pling constant (Hz). 13C NMR (50 MHz) spectra were recorded on
a BRUKER-AC 200 MHz Spectrometer with complete proton
decoupling. Chemical shifts are reported in ppm from tetrame-
thylsilane with the solvent resonance as the internal standard
(deuterochloroform: 77.0 ppm). Chromatographic purification was
done with 60e120 mesh silica gel (Merck). For reaction monitoring,
precoated silica gel 60 F254 TLC sheets (Merck) were used. UV/vis
absorption spectra were recorded on a Shimadzu UV-2450 UV/vis
spectrophotometer. FTIR spectra were recorded on a PerkineElmer
RXI spectrometer. High-resolution mass spectra (HRMS) were
recorded using LCT micro mass spectrometer. HPLC was performed
using Shimadzu Prominence (LC 20 AT) liquid chromatography on
a C18 column (4.5 mmꢃ250 mm) with a UV/vis detector. GPC was
carried out at ambient temperature using a Vistek-GPC system
6.2.2. O-Cinnamoyl-N-phenyl-acetohydroxamic acid (3b). The dark
yellow crude product on purification by column chromatography
(30% ethyl acetate/hexane) resulted the title compound 3b (91%) as
pale yellow solid; Rf (30% ethyl acetate/hexane) 0.54; mp:
65e67 ꢁC; FTIR (KBr) nmax (cmꢄ1): 1699, 1763; 1H NMR (CDCl3,
200 MHz)
d
: 2.13 (m, 3H), 6.53 (d, 1H, J¼16 Hz), 7.26e7.43 (m, 6H),
7.51e7.56 (m, 4H), 7.86 (d, 1H, J¼16 Hz); 13C NMR (CDCl3, 100 MHz)
d: 21.5, 113.2,128.3 (4C),128.9 (4C),129.3, 131.6, 133.6, 139.4, 148.50,
164.1, 164.3; MS m/z: 305 (19%), 304 (80%, MNaþ), 282 (100%, MHþ),
214 (35%); HRMS (ESþ) calcd for C17H16NO3 [MþHþ] 282.1125,
found 282.1127.
6.2.3. O-Benzoyl-N-phenyl-acetohydroxamic acid (3c). The crude
product was purified bycolumn chromatography (30% ethyl acetate/
hexane) to give the title compound 3c (90%) as brown liquid; Rf (40%
ethyl acetate/hexane) 0.50; FTIR (neat) nmax (cmꢄ1): 1687, 1757; 1H

3740
M. Ikbal et al. / Tetrahedron 67 (2011) 3733e3742
NMR (CDCl3, 200 MHz)
d
: 2.17 (m, 3H), 7.37e7.50 (m, 5H), 7.57 (d, 2H,
was separated, dried over Na2SO4 and the solvent was removed
under vacuum.
J¼8 Hz), 7.63 (m, 1H), 8.11 (d, 2H, J¼7.6 Hz); 13C NMR (CDCl3,
100 MHz) d: 21.6,128.7 (2C),129.3 (4C),129.7 (4C) 134.2,139.4,164.0,
164.3; MS m/z: 278 (100%, MNaþ), 256 (42%, MHþ), 214 (19%); HRMS
(ESþ) calcd for C15H14NO3 [MþHþ] 256.0968, found 256.0971.
6.3.1. O-(4-Methylbenzoyl)-N-phenyl-benzohydroxamicacid (6a). N-
Benzoyl-N-phenylhydroxylamine (250 mg, 1.17 mmol) reacts with
(272 mg, 1.77 mmol) of p-methyl benzoyl chloride in presence of
Et3N (0.23 ml, 2.34 mmol) as base to give the crude product. The
dark yellow crude product on purification by column chromatog-
raphy (30% ethyl acetate/hexane) gives title compound 6a (85%) as
white solid; Rf (40% ethyl acetate/hexane) 0.42; mp: 120e121 ꢁC;
6.2.4. O-(4-Methylbenzoyl)-N-phenyl-acetohydroxamic acid (3d). On
purification of crude product by column chromatography (40% ethyl
acetate/hexane) gives title compound 3d (92%) as light brown solid;
Rf (30% ethyl acetate/hexane) 0.35; mp: 53e55 ꢁC; FTIR (KBr) nmax
(cmꢄ1): 1690, 1755; 1H NMR (CDCl3, 200 MHz)
d: 2.16 (m, 3H), 2.42
FTIR (KBr) nmax (cmꢄ1): 1683, 1762; 1H NMR (CDCl3, 200 MHz)
d:
(s, 3H), 7.30e7.42 (m, 5H), 7.55 (d, 2H, J¼2.8 Hz), 7.90 (d, 2H,
2.35 (m, 3H), 7.18e7.31 (m, 8H), 7.40 (d, 2H, J¼1.6 Hz), 7.59 (d, 2H,
J¼8.4 Hz); 13C NMR (CDCl3, 100 MHz)
d: 21.5, 21.7, 123.8, 129.0, 129.2
J¼6.4 Hz), 7.94 (d, 2H, J¼8.2 Hz); 13C NMR (CDCl3, 50 MHz)
d: 21.7,
(4), 130.0 (4C), 139.4, 145.3, 164.0, 164.1; HRMS (ESþ) calcd for
124.1, 126.4 (2C), 127.2 (2C), 128.1 (2C), 128.7 (3C), 129.1 (2C), 129.4
(2C), 131.0, 133.5, 140.7, 145.1, 164.2, 167.2; HRMS (ESþ) calcd for
C21H18NO3 [MþHþ] 332.1281, found 332.1285.
C16H16NO3 [MþHþ] 270.1125, found 270.1129.
6.2.5. O-(4-Methoxybenzoyl)-N-phenyl-acetohydroxamic acid (3e).
The compound 3e (90%) was obtained as pale yellow solid on puri-
fication of the crude product through column chromatography (40%
ethyl acetate/hexane); Rf (20% ethyl acetate/hexane) 0.25; mp:
65e67 ꢁC; FTIR (KBr) nmax (cmꢄ1): 1692, 1750; 1H NMR (CDCl3,
6.3.2. O-(4-Methylbenzoyl)-N-phenyl-4-methoxybenzohydroxamic
acid (6b). By the reaction of (210 mg, 0.86 mmol) of p-methoxy-N-
benzoyl-N-phenylhydroxylamine with (200 mg, 1.29 mmol) of p-
methyl benzoyl chloride in presence of Et3N (0.16 ml, 1.15 mmol)
gives the light brown crude product, onpurification of crude product
by column chromatography (40% ethyl acetate/hexane) gives the
title compound 6b (91%) as white solid; Rf (30% ethyl acetate/hex-
ane) 0.41; mp: 85e87 ꢁC; FTIR (KBr) nmax (cmꢄ1): 1673, 1758; 1H
200 MHz)
d
: 2.16 (m, 3H), 3.87 (s, 3H), 6.95 (d, 2H, J¼9.0 Hz),
7.38e7.55 (m, 3H), 7.58 (d, 2H, J¼1.8 Hz), 8.06 (d, 2H, J¼2 Hz); 13C
NMR (CDCl3, 100 MHz) d: 21.6, 55.5, 114.1, 118.8, 129.2 (4C), 132.3
(4C), 139.5, 145.5, 163.7, 164.4; HRMS (ESþ) calcd for C16H16NO4
[MþHþ] 286.1074, found 286.1078.
NMR (CDCl3, 200 MHz) d: 2.36 (m, 3H), 3.69 (m, 3H), 6.75 (dd, 2H,
J¼1.6, J¼8.6 Hz), 7.20e7.33 (m, 5H), 7.42 (d, 2H, J¼8.0 Hz), 7.60 (d, 2H,
6.2.6. O-(4-Ethoxy-2-methoxybenzoyl)-N-phenyl-acetohydroxamic
acid (3f). On purification of crude product by column chromatog-
raphy (40% ethyl acetate/hexane) yielded title compound 3f (95%) as
white solid; Rf (30% ethyl acetate/hexane) 0.52; mp: 90e93 ꢁC; FTIR
J¼7.4 Hz), 7.98 (d, 2H, J¼6.8 Hz); 13C NMR (CDCl3, 50 MHz)
d: 22.0,
55.4,113.7 (2C),124.4,125.5,126.7 (2C),128.3,129.4 (2C),192.6 (2C),
130.3 (2C), 131.3 (2C), 141.5, 145.3, 162.1, 164.5, 167.1; HRMS (ESþ)
calcd for C22H19NO4 [MþHþ] 362.1387, found 362.1388.
(KBr) nmax (cmꢄ1): 1683,1762; 1H NMR (CDCl3, 200 MHz)
d: 1.5 (t, 3H,
J¼6.8 Hz), 2.17 (br s, 3H), 3.98 (s, 3H), 4.17 (q, 2H, J1¼7.2, J2¼14 Hz),
6.3.3. O-(4-Methylbenzoyl)-N-phenyl-4-nitrobenzohydroxamic acid
(6c). On reaction of (150 mg, 0.58 mmol) of p-nitro-N-benzoyl-N-
phenylhydroxylamine with (0.134 mg, 0.86 mmol) of p-methyl
benzoyl chloride in presence of Et3N (0.16 ml, 1.15 mmol) produces
the crude product, then it was purified by column chromatography
(25% ethyl acetate/hexane) to give the title compound 6c (90%) as
pale yellow solid; Rf (30% ethyl acetate/hexane) 0.43; mp:
110e111 ꢁC; FTIR (KBr) nmax (cmꢄ1): 1691, 1772; 1H NMR (CDCl3,
6.90 (d, 1H, J¼8 Hz), 7.42 (m, 3H), 7.56 (m, 3H), 7.75 (d, 1H, J¼8 Hz);
13C NMR (CDCl3, 100 MHz)
d: 14.4, 21.6, 56.0, 64.5, 111.3 (2C), 112.4
(2C), 118.5, 123.4, 124.7 (2C), 129.2, 139.4, 149.0, 153.5, 164.5, 163.8;
HRMS (ESþ) calcd for C18H20NO5 [MþHþ] 330.1336, found 330.1339.
6.2.7. O-(4-Chlorobenzoyl)-N-phenyl-acetohydroxamic acid (3g). The
dark white solid compound 3g (90%) was obtained on purification of
the crude product by column chromatography (40% ethyl acetate/
hexane); Rf (50% ethyl acetate/hexane) 0.55; mp: 67e69 ꢁC; FTIR
200 MHz) d: 2.35 (m, 3H), 7.19e7.35 (m, 5H), 7.41e7.44 (m, 2H), 7.74
(d, 2H, J¼8.8 Hz), 7.90 (d, 2H, J¼7.8 Hz), 8.08 (d, 2H, J¼8.6 Hz); 13C
(KBr) nmax (cmꢄ1): 1690, 1760; 1H NMR (CDCl3, 200 MHz)
d: 2.17 (m,
NMR (CDCl3, 50 MHz) d: 21.7, 123.3 (4C), 126.4, 128.9, 129.4 (4C),
3H), 7.41e7.58 (m, 7H), 8.04 (d, 2H, J¼8.8 Hz); 13C NMR (CDCl3,
129.6 (4C), 139.6, 144.4, 145.6, 148.9, 165.2, 171.5; HRMS (ESþ) calcd
100 MHz)
d: 21.6, 125.3, 129.1 (4C), 129.5, 131.5 (4C), 139.3, 140.9,
for C20H15N2O5 [MþHþ] 363.0975, found 363.0979.
163.3, 163.5; MS m/z: 312 (50%), 290 (100%, MHþ), 214 (32%); HRMS
(ESþ) calcd for C15H13ClNO3 [MþHþ] 290.0578, found 290.0580.
6.4. Photogeneration of carboxylic acids and its quantum
yield measurement
6.2.8. O-(4-Nitrobenzoyl)-N-phenyl-acetohydroxamic acid (3h). The
compound 3h (93%) was obtained on purification of the crude
product through column chromatography (40% ethyl acetate/hex-
ane) as dark yellow solid; Rf (40% ethyl acetate/hexane) 0.50; mp:
115e117 ꢁC; FTIR (KBr) nmax (cmꢄ1): 1710, 1769; 1H NMR (CDCl3,
Carboxylates (3aeh and 6aec) (0.05 mmol) was dissolved in
MeOH/H2O (9:1), and it was irradiated using 125 W medium
pressure Hg lamp using quartz filter. In each case the photolysis was
stopped when conversion reached at least 95% (as indicated by
HPLC). After the completion of the photolysis, the solvent was re-
moved under vacuum and the photoproducts (carboxylic acids and
carboxyanilide) were separated by column chromatography using
ethyl acetate/hexane as eluant.
200 MHz) d C
: 2.13 (m, 3H), 7.29e7.59 (m, 5H), 8.24e8.33 (m, 4H); 13
NMR (CDCl3, 50 MHz) d: 21.8, 124.0 (4C), 129.9 (2C), 131.5 (3C),
132.7, 139.4, 151.3, 162.1, 162.6; HRMS (ESþ) calcd for C15H13N2O5
[MþHþ] 301.0819, found 301.0821.
6.3. General procedure for the synthesis of carboxylate ester
of N-acyl-N-phenylhydroxylamine (6aec)
The quantum yield of photogeneration of carboxylic acids was
analyzed by employing valerophenone as an actinometer. The
progress of the photolysis was monitored by taking 5 ml of aliquot
To the mixture of N-acyl-N-phenylhydroxylamine and p-toluic
chloride in dry DCM, Et3N was added slowly at 0 ꢁC. Then the re-
action mixture was stirred for overnight at room temperature. After
the completion of the reaction (as indicated by TLC), it was
quenched by ice cold water, diluted with DCM. The organic layer
at regular interval of time and analyzed by HPLC, using eluant
hexane/isopropanol (9:1), at a flow rate of 1 ml/min (detection:
UV 254 nm). The % of carboxylic acid generated was determined
by calculating the gradual increase in the peak area of the car-
boxylic acid.

M. Ikbal et al. / Tetrahedron 67 (2011) 3733e3742
3741
6.5. General procedure for the synthesis of
O-arenesulfonyloxyacetanilide (Series-1 8aef)
124.7, 127.7, 128.3, 131.0, 132.3, 132.5, 136.0, 137.6, 148.4, 168.4;
HRMS (ESþ) calcd for C14H13N2O6S [MþHþ] 337.0489, found
337.0490.
To the mixture of sulfonyl chloride (2.38 mmol) and N-acetyl-N-
phenylhydroxylamine (300 mg, 1.98 mmol) in dry DCM, Et3N
(0.55 ml, 3.97 mmol) was added drop by drop at 0 ꢁC. The reaction
mixture was then stirred for overnight at room temperature. After
the completion of the reaction (as indicated by TLC), it was quenched
byice cold water, diluted withDCM. Theorganic layer wasseparated,
dried over Na2SO4 and the solvent was removed under vacuum.
6.5.6. o-(4-Nitrobenzenesulfonoxy) acetanilide (8f). Theyellowsolid
compound 8f (90%) was obtained by the purification of the crude
product using column chromatography (50% ethyl acetate/hexane);
Rf (30% ethyl acetate/hexane) 0.35; mp: 120e123 ꢁC; FTIR (KBr) nmax
(cmꢄ1): 3249, 1668, 1363; 1H NMR (CDCl3, 400 MHz)
d: 2.14 (s, 3H),
6.82 (d, 1H, J¼7.2 Hz), 6.99e7.02 (m, 1H), 7.28e7.31 (m, 1H),
7.52e7.55 (m, 1H), 8.08 (d, 2H, J¼8.4 Hz), 8.16e8.18 (m, 1H), 8.41 (d,
6.5.1. o-(Methanesulfonoxy) acetanilide (8a). The dark yellow crude
solid on purification by column chromatography (40% ethyl acetate/
hexane) gives title compound 8a (83%) as light yellow solid; Rf (40%
ethyl acetate/hexane) 0.50; mp: 105e107 ꢁC; FTIR (KBr) nmax
2H, J¼8.8 Hz); 13C NMR (CDCl3, 100 MHz)
d: 24.3, 122.1, 123.9, 124.4,
124.7, 128.3, 128.8, 129.9, 130.9, 136.0, 137.6, 140.2, 151.2, 168.4; MS
m/z: 337 (100%, MHþ), 294 (85%), 214 (64%), 158 (30%); HRMS (ESþ)
calcd for C14H13N2O6S [MþHþ] 337.0489, found 337.0489.
(cmꢄ1): 3234, 1650, 1363; 1H NMR (CDCl3, 400 MHz)
d: 2.21 (s, 3H),
3.26 (s, 3H), 7.14 (t, 1H, J¼7.4 Hz), 7.27 (m, 1H), 7.32 (t, 1H, J¼8 Hz),
6.6. General procedure for the synthesis of o-
arenesulfonyloxybenzanilide (Series-2 10aee)
7.83 (br s, 1H), 8.24 (d, 1H, J¼8 Hz); 13C NMR (CDCl3, 100 MHz)
d:
24.5, 37.7, 122.5, 123.8, 124.9, 128.1, 131.0, 138.7, 168.7; MS m/z: 230
(100%, MHþ), 214 (58%), 187 (55%); HRMS (ESþ) calcd for
C9H12NO4S [MþHþ] 230.0482, found 230.0486.
To the reaction mixture of N-benzoyl N-phenyl hydroxyl amine
(400 mg, 1.88 mmol) and sulfonyl chloride (2.87 mmol) in dry DCM,
Et3N (0.52 ml, 3.75 mmol) was added drop wise at 0 ꢁC. The re-
action mixture was then stirred for 12 h at room temperature. After
the completion of the reaction (as indicated by TLC), it was
quenched by ice cold water, diluted with DCM. The organic layer
was separated, dried over Na2SO4 and the solvent was removed
under vacuum.
6.5.2. o-(Butanesulfonoxy) acetanilide (8b). The blackish crude
solid was purified using column chromatography (40% ethyl ace-
tate/hexane) gives the title compound 8b (80%) as yellow solid; Rf
(30% ethyl acetate/hexane) 0.45; mp: 75e76 ꢁC; FTIR (KBr) nmax
(cmꢄ1): 3231, 1654, 1354; 1H NMR (CDCl3, 200 MHz)
d: 1.01 (t, 3H,
J¼7.4), 1.52e1.54 (m, 2H), 1.93e2.08 (m, 2H), 2.20 (s, 3H), 3.34e3.41
(m, 2H), 7.12e7.25 (m, 2H), 7.31e7.35 (m, 1H), 7.9 (br s, 1H), 8.24 (d,
6.6.1. o-(Methanesulfonoxy) benzanilide (10a). The crude product
was purified by column chromatography (50% ethyl acetate/hex-
ane) to give the title compound 10a (85%) as white solid; Rf (30%
ethyl acetate/hexane) 0.32; mp: 115e120 ꢁC; FTIR (KBr) nmax
1H, J¼8.4 Hz); 13C NMR (CDCl3, 50 MHz)
d: 13.3, 21.3, 24.4, 25.4,
50.7, 122.7,123.7, 124.8, 127.8, 131.2,138.5, 168.6; MS m/z: 294 (15%),
272 (100%, MHþ), 230 (59%), 214 (20%); HRMS (ESþ) calcd for
C12H17NO4S [MþHþ] 272.0951, found 272.0955.
(cmꢄ1): 3233, 1654, 1350; 1H NMR (CDCl3, 400 MHz)
d: 3.25 (s, 3H),
7.12e7.39 (m, 4H), 7.43e7.58 (m, 2H), 7.91 (d, 2H, J¼6.4 Hz), 8.38 (d,
6.5.3. o-(Benzanesulfonoxy) acetanilide (8c). The crude product
was purified by column chromatography (30% ethyl acetate/hex-
ane) to give the title compound 8c (91%) as white solid; Rf (25%
ethyl acetate/hexane) 0.40; mp: 120e123 ꢁC; FTIR (KBr) nmax
1H, J¼8.2 Hz), 8.67 (br s, 1H); 13C NMR (CDCl3, 100 MHz)
d: 37.9,
122.9, 124.0, 125.1, 127.2 (2C), 128.3, 128.9 (2C), 131.4, 132.2, 134.1,
138.9, 165.5; MS m/z: 314 (23%, MNaþ), 292 (100%, MHþ), 214 (27%),
157 (25%); HRMS (ESþ) calcd for C14H14NO4S [MþHþ] 292.0638,
found 292.0636.
(cmꢄ1): 3221, 1695, 1366; 1H NMR (CDCl3, 200 MHz)
d: 2.06 (s, 3H),
6.88e7.03 (m, 2H), 7.20 (m, 1H), 7.56 (t, 3H, J¼7.6 Hz), 7.69e7.77 (m,
1H), 7.83e7.87 (m, 2H), 8.16 (d, 1H, 8.2 Hz); 13C NMR (CDCl3,
6.6.2. o-(Butanesulfonoxy) benzanilide (10b). On purification of
crude product by column chromatography (20% ethyl acetate/
hexane) gives the desired compound 10b (80%) as white solid; Rf
(25% ethyl acetate/hexane) 0.45; mp: 95e100 ꢁC; FTIR (KBr) nmax
100 MHz) d: 24.4, 122.6, 122.9, 124.3, 127.8, 128.3 (3C), 129.3 (2C),
131.0, 134.8, 138.8, 168.1; MS m/z: 314 (20%, MNaþ), 292 (100%,
MHþ), 214 (24%), 157 (22%); HRMS (ESþ) calcd for C14H14NO4S
[MþHþ] 292.0638, found 292.0640.
(cmꢄ1): 3221, 1654, 1354; 1H NMR (CDCl3, 200 MHz)
d: 0.79 (t, 3H,
J¼16.2), 1.44e1.47 (m, 2H), 1.89e2.04 (m, 2H), 3.18e3.44 (m, 2H),
7.11e7.25 (m, 3H), 7.30e7.38 (m, 1H), 7.44e7.54 (m, 2H), 7.71e7.78
(m, 2H), 8.61 (d, 1H, J¼5.6 Hz), 8.85 (br s, 1H); 13C NMR (CDCl3,
6.5.4. o-(p-Tolylsulfonoxy) acetanilide (8d). On purification of crude
product by column chromatography (40% ethyl acetate/hexane)
yield the desired compound 8d (90%) as white solid; Rf (30% ethyl
acetate/hexane) 0.45; mp: 120e125 ꢁC; FTIR (KBr) nmax (cmꢄ1):
50 MHz) d: 13.3, 21.3, 25.5, 50.9, 123.2, 123.8,125.0, 127.2 (2C), 128.1,
128.8 (2C), 131.6, 132.1, 134.1, 138.5, 165.4; HRMS (ESþ) calcd for
3235, 1679, 1367; 1H NMR (CDCl3, 400 MHz)
d: 2.07 (s, 3H), 2.46 (s,
C17H20NO4S [MþHþ] 334.1108, found 334.1110.
3H), 6.89 (d,1H, J¼8.4 Hz), 6.98 (t,1H, J¼8.4 Hz), 7.23 (m,1H), 7.34 (d,
2H, J¼8 Hz), 7.54 (m,1H), 7.72 (d, 2H, J¼8.4 Hz), 8.18 (d,1H, J¼8.0 Hz);
6.6.3. o-(Benzanesulfonoxy) benzanilide (10c). The crude product
was purified by column chromatography (30% ethyl acetate/hex-
ane) to give the title compound 10c (91%) as off white solid; mp:
70e72 ꢁC; Rf (25% ethyl acetate/hexane) 0.40; FTIR (KBr) nmax
13C NMR (CDCl3, 100 MHz)
d: 21.3, 24.4, 122.7, 122.8, 124.2, 127.5,
128.4 (2C), 130.0 (2C), 131.0, 131.6, 138.8, 146.2, 168.1; MS m/z: 328
(10%, MNaþ), 306 (100%, MHþ), 264 (52%), 214 (22%); HRMS (ESþ)
calcd for C15H16NO4S [MþHþ] 306.0795, found 306.0798.
(cmꢄ1): 3225, 1683, 1360; 1H NMR (CDCl3, 200 MHz)
d
: 6.90e7.07
(m, 2H), 7.26e7.34 (m, 1H), 7.40e7.65 (m, 6H), 7.81e7.85 (m, 4H),
8.34e8.39 (m, 2H); 13C NMR (CDCl3, 100 MHz)
: 122.9, 123.1, 124.6,
6.5.5. o-(2-Nitrobenzenesulfonoxy) acetanilide (8e). The crude
product on purification by column chromatography (50% ethyl ac-
etate/hexane) gives the title compound 8e (85%) as brown solid; Rf
(40% ethyl acetate/hexane) 0.40; mp: 105e106 ꢁC; FTIR (KBr) nmax
d
127.1(2C),128.0, 128.3 (2C),128.8 (2C),129.4 (2C), 131.2, 132.2, 134.1,
134.5, 134.9, 139.3, 165.1; HRMS (ESþ) calcd for C19H16NO4S [MþHþ]
354.0795, found 354.0797.
(cmꢄ1): 3254, 1699, 1368; 1H NMR (CDCl3, 400 MHz)
d: 2.06 (s, 3H),
7.10 (t, 1H, J¼8 Hz), 7.28e7.30 (1H, m), 7.45 (d, 1H, J¼8.4 Hz),
6.6.4. o-(p-Tolylsulfonoxy) benzanilide (10d). The crude product on
purification by column chromatography (30% ethyl acetate/hexane)
yielded the title compound 10d (90%) white solid; Rf (40% ethyl
7.67e7.71 (m, 1H), 7.85e7.90 (m, 3H), 8.13 (br s, 1H), 8.31 (d, 1H,
J¼8.4 Hz); 13C NMR (CDCl3, 100 MHz)
d: 24.3, 122.0, 122.8, 124.0,

3742
M. Ikbal et al. / Tetrahedron 67 (2011) 3733e3742
acetate/hexane) 0.51; mp: 120e125 ꢁC; FTIR (KBr) nmax (cmꢄ1):
3251, 1678, 1366; 1H NMR (CDCl3, 400 MHz)
: 2.39 (s, 3H),
o-(styrenesulfonoxy) acetanilide (2.36 mmol) and methyl-
methcrylate (MMA 2.37 mmol) or lauryl acrylate (LA 2.36 mmol)
were dissolved in THF in a dry, long glass tube with a magnetic
stirring bar. AIBN was added (molar ratio of monomer: AIBN was
200:1) and stirred till it dissolved. The reaction mixture was
degassed with nitrogen for 20 min. The polymerization was con-
tinued in nitrogen atmosphere at 80 ꢁC in an oil bath for 3 h till it
turned viscous. Reaction was stopped by taking out the tube from
oil bath and placed in cold water. After stopping the reaction the
reaction mixture was dissolved in THF. The solution was concen-
trated and the polymer was precipitated into methanol and was
dried at room temperature for one day followed by drying in
a vacuum oven for another 24 h.
d
6.98e7.04 (m, 2H), 7.19e7.23 (m, 2H), 7.27e7.31 (m, 1H), 7.41e7.59
(m, 3H), 7.69 (d, 2H, J¼8.4 Hz), 7.83(d, 2H, J¼9.4 Hz), 8.35e8.40 (m,
2H); 13C NMR (CDCl3,100 MHz)
d: 21.7,123.0,123.1,124.6,127.1 (2C),
127.8, 128.2 (2C), 128.7 (2C), 130.1 (2C), 131.2, 131.5, 132.1, 134.0,
139.3, 146.2, 164.9; MS m/z: 368 (100%, MHþ), 214 (30%); HRMS
(ESþ) calcd for C20H18NO4S [MþHþ] 368.0951, found 368.0955.
6.6.5. o-(2-Nitrobenzenesulfonoxy) benzanilide (10e). Compound
10e (82%) was obtained on purification of the crude product by
column chromatography (40% ethyl acetate/hexane) as off white
solid; Rf (30% ethyl acetate/hexane) 0.40; mp: 122e125 ꢁC; FTIR
(KBr) nmax (cmꢄ1): 3244, 1685, 1377; 1H NMR (CDCl3, 400 MHz)
d
:7.09e7.22 (m, 1H), 7.29e7.42 (m, 5H), 7.42e7.58 (m, 1H),
6.9.1. Polymer SSAIeMMA (19). White solid; FTIR (KBr) nmax
7.59e7.66 (m, 2H), 7.67e7.75 (m, 2H), 7.79e7.82 (m, 1H), 8.25 (d,
(cmꢄ1): 3225, 1650, 1355; 1H NMR (CDCl3, 200 MHz)
d: 1.74e2.01
1H, J¼9.6 Hz), 8.52 (m, 1H); 13C NMR (CDCl3, 100 MHz)
d
: 123.2,
(br m), 2.4e2.6 (br m), 3.12e3.97 (br m), 7.14e7.92 (br m).
123.6, 124.9 (2C), 127.4 (2C), 128.1, 128.4, 128.6 (2C), 130.8, 131.9,
132.3, 132.5, 133.6, 135.7, 139.0, 147.9, 165.3; HRMS (ESþ) calcd for
C19H15N2O6S [MþHþ] 399.0645, found 399.0647.
Acknowledgements
We thank DST (SERC Fast Track Scheme) for financial support,
DST-FIST for 400 MHz NMR and Prof. S. Nanda for HPLC. M. I., R. B.
and A. J. are thankful to CSIR (India) for their research fellowship.
6.7. Photolysis and quantum yield measurements of the
sulfonate esters
Sulfonate ester (0.05 mmol) (8aef and 10aee) was dissolved in
MeOH/H2O (9:1) solvent, and it was irradiated by 125 W medium
pressure Hg lamp using quartz filter. The progress of the reaction
was monitored by 1H NMR analysis. After the completion of the
reaction the solvent was removed under vacuum and the photo-
products (sulfonic acids and o-hydroxyacetanilide or o-hydrox-
ybenzanilide) were separated by column chromatography using
ethyl acetate/hexane as an eluant.
The quantum yield of photogeneration of sulfonic acids was
analyzed by 1H NMR spectroscopy by employing valerophenone as
an actinometer. The percent of acids generated was determined by
calculating the gradual increase in the peak area of the sulfonic
acids using anisole as internal standard.
Supplementary data
Supplementary data related to this article can be found online at
doi:10.1016/j.tet.2011.03.049.
References and notes
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To the mixture of N-acetyl-N-phenylhydroxylamine (2 g,
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6.8.1. o-(Styrenesulfonoxy) acetanilide (SSAI) (16). The monomer
was got without further purification (92%) as yellow liquid, Rf (40%
ethyl acetate/hexane) 0.45; FTIR (neat) nmax (cmꢄ1): 3233, 1654,
1354; 1H NMR (CDCl3, 200 MHz)
d: 2.11e2.15 (s, 3H), 5.50 (d, 1H,
J¼11 Hz), 5.92 (d, 1H, J¼17.6 Hz), 6.68e6.82 (m, 1H), 6.88e7.02 (m,
2H), 7.19e7.26 (m, 2H), 7.54 (d, 2H, J¼8.4 Hz), 7.83 (d, 2H J¼8.6 Hz),
8.15e8.19 (m, 1H); 13C NMR (CDCl3, 50 MHz)
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143.9, 168.5; HRMS (ESþ) calcd for C21H18NO4S [MþHþ] 380.0951,
found 380.0958.
€
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6.9. Preparation of polymers
Polymerization was carried out by free radical method using
AIBN as initiator at 80 ꢁC in THF under N2 atmosphere.