Kinetics of oxidation of acidic amino acids and their monoamides by N-chloroarylsulphonamides in aqueous acidic medium

Article abstract of DOI:10.1002/poc.758

Twelve sodium salts of N-chloroarylsulphonamides were employed as oxidants for studying the kinetics of oxidation of two acidic amino acids (aspartic and glutamic acid) and their monoamides (aspargine and glutamine) in aqueous acidic medium under various conditions, to see how the oxidative strength of these reagents vary with substitution. The sodium salts of N-chloroarylsulphonamides employed are of the general formulae i-X-C₆H₄SO ₂. NaNCl·xH₂O (where i-X = 4-C₂H ₅, 4-F, 4-Cl or 4-Br) and i-X-j-Y-C₆H₃SO ₂NaNCl·xH₂O [where i-X-j-Y = 2,3-(CH ₃)₂, 2,4-(CH₃)₂, 2,5-(CH ₃)₂, 2-CH₃-4-Cl, 2,4-Cl₂ and 3,4-Cl₂]. The reactions show second-order kinetics in [oxidant], fractional order in [amino acid] and an inverse dependence on [H⁺], Addition of the reduced product of the oxidants or variation in ionic strength of the medium has no significant effect on the rates of oxidations. Mechanisms in conformity with the observed kinetics are discussed. The effective oxidizing species of the oxidants is Cl⁺ in different forms. The oxidizing strengths of N-chloroarylsulphonamides depend on the ease with which Cl ⁺ is released from them. The study reveals that the introduction of electron-withdrawing groups such as halides to the benzene ring eases the release of Cl⁺ from the reagent and hence increases the oxidizing strengths of the N-chloroarylsulphonamides. The effect of substituents on E _a of the reactions was analysed by optimising E_a with reference to log A, and log A with reference to E_a of the parent oxidant. Copyright

Full text of DOI:10.1002/poc.758

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY
J. Phys. Org. Chem. 2004; 17: 848–864
Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/poc.758
Kinetics of oxidation of acidic amino acids and their
monoamides by N-chloroarylsulphonamides in
aqueous acidic medium
B. Thimme Gowda* and Mahesha Shetty
Department of Post-Graduate Studies and Research in Chemistry, Mangalore University, Mangalagangothri 574 199, Mangalore, India
Received 12 October 2003; revised 29 January 2004; accepted 29 January 2004
ABSTRACT: Twelve sodium salts of N-chloroarylsulphonamides were employed as oxidants for studying the kinetics
of oxidation of two acidic amino acids (aspartic and glutamic acid) and their monoamides (aspargine and glutamine)
in aqueous acidic medium under various conditions, to see how the oxidative strength of these reagents vary with
substitution. The sodium salts of N-chloroarylsulphonamides employed are of the general formulae i-X-C6H4SO2-
NaNClꢀxH2O (where i-X ¼ 4-C2H5, 4-F, 4-Cl or 4-Br) and i-X-j-Y-C6H3SO2NaNClꢀxH2O [where i-X-j-Y ¼ 2,3-
(CH3)2, 2,4-(CH3)2, 2,5-(CH3)2, 2-CH3-4-Cl, 2,4-Cl2 and 3,4-Cl2]. The reactions show second-order kinetics in
[oxidant], fractional order in [amino acid] and an inverse dependence on [Hþ]. Addition of the reduced product of the
oxidants or variation in ionic strength of the medium has no significant effect on the rates of oxidations. Mechanisms
in conformity with the observed kinetics are discussed. The effective oxidizing species of the oxidants is Clþ in
different forms. The oxidizing strengths of N-chloroarylsulphonamides depend on the ease with which Clþ is released
from them. The study reveals that the introduction of electron-withdrawing groups such as halides to the benzene ring
eases the release of Clþ from the reagent and hence increases the oxidizing strengths of the N-chloroarylsulphona-
mides. The effect of substituents on Ea of the reactions was analysed by optimising Ea with reference to log A, and
log A with reference to Ea of the parent oxidant. Copyright # 2004 John Wiley & Sons, Ltd.
KEYWORDS: N-chloroarylsulphonamides; amino acids; kinetics of oxidation; substituent effect
INTRODUCTION
benzene ring. Thus, N-chloroarylsulphonamides of re-
quired oxidizing capacity may be produced by altering
the electron density on the nitrogen atom of the sulpho-
namide group to obtain Clþ released either at ease or with
difficulty. Hence, in an effort to introduce N-chloroar-
ylsulphonamides of different oxidizing strengths, we have
recently prepared and characterized several mono- and
disubstituted N-chlorobenzenesulphonamides (NCSBS)10,11
of the general formulae i-X-C6H4SO2NaNClꢀxH2O
[where i-X ¼ 4-H (NCBS), 4-CH3 (NC4MBS), 4-C2H5
(NC4EBS), 4-F (NC4FBS), 4-Cl (NC4CBS) or 4-Br
(NC4BBS)] and i-X-j-Y-C6H3SO2NaNClꢀxH2O [where
i - X - j - Y ¼ 2,3-(CH3)2 (NC23DMBS), 2,4 - (CH3)2
(NC24DMBS), 2,5-(CH3)2 (NC25DMBS), 2-CH3-4-Cl
(NC2M4CBS), 2,4-Cl2(NC24DCBS) and 3,4-Cl2
(NC34DCBS)]. Here we employed these 12 reagents as
oxidants for studying the kinetics of oxidation of two
acidic amino acids (AA), aspartic acid (Asp) and gluta-
mic acid (Glu), and their monoamides, aspargine (Asn)
and glutamine (Gln), in aqueous acidic medium. Although
studies with two of the reagents have been partly re-
ported, the kinetics of oxidation of all four amino acids
by these oxidants were also carried out under identical
conditions and are included in the paper for comparison
and completeness of the work.
Many arylsulphonamides and their N-halo compounds
are of fundamental chemical interest owing to their
diverse physical, chemical and biological properties.1–9
They also exhibit fungicidal and herbicidal activities,
due to their oxidizing action in aqueous, partially aqueous
and non-aqueous media. N-Haloarylsulphonamides act
as sources of halonium cations, hypohalite species and
N-anions which behave both as bases and nucleophiles.
Although the various aspects of the prominent members
of this class of reagents, namely N-chlorobenzenesulpho-
namide (NCBS) and N-chloro-4-methylbenzene-sulpho-
namide (NC4MBS) have been studied, there have been
no efforts to alter the electron environment around the
sulphonamide group to obtain Clþ released either at ease
or with difficulty, as the ease with which Clþ is released
from the reagent decides the oxidizing strength of the
oxidant. This in turn depends on the electron density on
the nitrogen atom of the sulphonamide group, which may
be altered by making appropriate substitutions in the
*Correspondence to: B. T. Gowda, Department of Post-Graduate
Studies and Research in Chemistry, Mangalore University, Mangala-
gangothri 574 199, Mangalore, India.
E-mail: gowdabt@yahoo.com
Copyright # 2004 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2004; 17: 848–864

KINETICS OF OXIDATION OF ACIDIC AMINO ACIDS AND AMIDES
849
RESULTS AND DISCUSSION
Kinetic measurements
were linear up to 70% completion of the reactions. The
pseudo-second-order rate constants calculated from the
plots remained unaffected by the changes in [oxidant]0
(Tables 1–8), establishing a second-order dependence of
the rate on [NCSBS]0.
The kinetic studies were carried out in glass-stoppered
Pyrex boiling tubes under pseudo-second-order condi-
tions with [amino acid] ꢁ [NCSBS] (by 5–50-fold). The
reactions were initiated by the rapid addition of known
amounts of oxidant solution (0.0005–0.004 mol dmꢂ3),
pre-equilibrated at a desired temperature, to mixtures
containing the required amounts of amino acid (0.005–
0.04 mol dmꢂ3), perchloric acid (0.01–0.10 mol dmꢂ3),
sodium nitrate and water in the boiling tube, thermostated
at the same temperature. The progress of the reactions
was monitored for at least two half-lives by the iodimetric
determination of unreacted oxidant at regular intervals of
time. The pseudo-second-order rate constants (kobs) were
calculated by graphical methods and the values were
reproducible to within ꢃ3% error.
Effect of varying [AA]0
At constant [NCSBS]0 and [Hþ], the rates increased with
increase in [AA] with fractional order dependences in
[AA] for all the oxidations (Tables 1–9). The plots of kobs
versus [AA] were linear with finite intercepts on the
ordinates (Figs 1 and 2), indicating the operation of a
two-pathway mechanism for the oxidations.
Effect of varying [Hþ]
The kinetic data on the oxidations of Asp, Glu, Asn and
Gln by NCBS, NC4MBS, NC4EBS, NC4FBS, NC4CBS,
NC4BBS, NC23DMBS, NC24DMBS, NC25DMBS,
NC2M4CBS, NC24DCBS and NC34DCBS in aqueous
perchloric acid medium under various conditions of
[NCSBS], [AA], [HClO4] and solution composition of
the medium are shown in Tables 1–9 and Figs 1and 2.
The rates decreased with increase in [Hþ], at fixed
[NCSBS]0 and [AA]0, with varying inverse order depen-
dences in [Hþ] (Tables 1–9).
Effect of varying ionic strength and other
parameters of the medium
Effect of varying [oxidant]0
Variation in either the ionic strength of the medium or
addition of the substituted benzenesulphonamides (SBSA),
the reduced products of the oxidants, to the reaction
mixtures had no significant effect on the rates of
At constant [AA]0 (5–50-fold excess over [oxidant]0) and
[Hþ ], the second-order plots of 1/[oxidant] versus time
Table 1. Pseudo-second-order rate constants (kobs) for the oxidation of aspartic acid (Asp) by the sodium salts of p-substituted
N-chlorobenzenesulphonamides (NCSBS) in aqueous perchloric acid at 303 K(I ¼ 0.30 mol dmꢂ3
)
10 kobs (dm3 molꢂ1 sꢂ1) for 4-X-C6H4SO2NaNCl, where X ¼
103[NCSBS]0
(mol dmꢂ3
102[Asp]0
(mol dmꢂ3
102[HClO4]
)
)
(mol dmꢂ3
)
H
CH3
C2H5
F
Cl
Br
Effect of varying [NCSBS]0
0.5
1.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
3.0
3.0
3.0
3.0
3.0
3.0
2.9
2.7
2.7
2.6
2.6
2.8
2.8
2.7
2.6
2.5
2.6
2.8
2.9
2.9
2.7
2.7
2.8
3.2
4.8
4.6
4.6
4.5
4.5
4.8
6.8
6.7
6.7
6.6
6.5
6.8
8.5
8.4
8.4
8.3
8.3
8.6
4.0
1.0a
1.0b
Effect of varying [Asp]0
1.0
1.0
1.0
1.0
0.5
1.0
2.0
3.0
3.0
3.0
3.0
3.0
1.8
2.2
2.7
3.3
1.8
2.0
2.7
3.4
1.8
2.2
2.9
3.7
3.3
4.0
4.6
6.7
4.1
5.4
6.7
7.6
5.2
7.8
9.7
14.2
Effect of varying [HClO4]
1.0
1.0
1.0
1.0
1.0
2.0
2.0
2.0
2.0
2.0
1.0
2.0
3.0
5.0
7.0
4.0
2.7
1.4
0.6
9.2
4.3
2.7
1.5
0.9
9.7
5.0
2.9
1.7
0.8
19.2
8.4
4.7
3.0
1.6
28.9
13.4
6.6
4.1
2.0
20.8
16.6
9.0
7.6
3.4
10.0
a
I ¼ 0.10 mol dmꢂ3
.
.
b
I ¼ 0.50 mol dmꢂ3
Copyright # 2004 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2004; 17: 848–864

850
B. T. GOWDA AND M. SHETTY
Table 2. Pseudo-second-order rate constants (kobs) for the oxidation of aspartic acid (Asp) by the sodium salts of disubstituted
N-chlorobenzenesulphonamides (NCSBS) in aqueous perchloric acid at 303 K (I ¼ 0.30 mol dmꢂ3
)
10 kobs (dm3 molꢂ1 sꢂ1) for i-X-j-Y-C6H3SO2NaNCl, where i-X-j-Y ¼
103[NCSBS]0
(mol dmꢂ3
102[Asp]0 102[HClO4]
(mol dmꢂ3) (mol dmꢂ3
)
)
2,3-(CH3)2 2,4-(CH3)2 2,5-(CH3)2 2-CH3-4-Cl 2,4-Cl2 3,4-Cl2
Effect of varying [NCSBS]0
0.5
1.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
3.0
3.0
3.0
3.0
3.0
3.0
4.0
2.7
2.4
2.2
2.6
3.0
4.4
3.7
3.5
3.3
3.3
3.9
6.4
6.0
5.7
5.6
5.9
6.2
14.0
13.7
13.4
13.3
13.5
13.9
20.6
20.1
19.6
19.5
19.5
20.6
19.8
19.3
19.2
19.0
19.0
19.7
4.0
1.0a
1.0b
Effect of varying[Asp]0
1.0
1.0
1.0
1.0
0.5
1.0
2.0
4.0
3.0
3.0
3.0
3.0
2.1
2.4
2.7
4.4
2.5
2.9
3.7
5.0
3.0
3.7
6.0
7.5
8.6
9.9
13.7
16.4
11.1
13.3
20.1
27.2
13.3
16.4
19.3
25.1
Effect of varying [HClO4]
1.0
1.0
1.0
1.0
1.0
2.0
2.0
2.0
2.0
2.0
1.0
1.0
2.0
3.0
5.0
5.7
4.3
2.7
1.7
1.2
9.5
6.2
3.7
2.7
2.0
13.8
9.2
6.0
4.0
2.7
28.5
16.6
13.7
6.9
42.2
30.8
20.1
15.5
11.4
31.8
24.0
19.3
12.0
6.9
4.1
a
I ¼ 0.10 mol dmꢂ3
.
.
b
I ¼ 0.50 mol dmꢂ3
oxidations (Tables 1–8). The rates were measured at
different temperatures with varying [AA]. The coeffi-
cients of the rate-limiting steps of the considered me-
chanisms were calculated at each temperature as
described later. Activation parameters corresponding to
these constants were also computed.
electrolytes in aqueous solution and they furnish different
reactive species depending on the pH of the medium.1–9
The possible oxidizing species in acidic solutions of
NCSBS are ArSO2NClꢂ, ArSO2NHCl, HOCl and Ar-
SO2NCl2 at low [Hþ] and ArSO2NH2Clþ and H2OClþ at
high [Hþ], where Ar ¼ 4-XC6H4 (X ¼ H, CH3, C2H5, F,
Cl or Br) and i-X-j-Y-C6H3 [i-X-j-Y ¼ 2,3-(CH3)2, 2,4-
(CH3)2, 2,5-(CH3)2, 2-CH3-4-Cl, 2,4-Cl2 and 3,4-Cl2].
Sodium salts of N-chlorobenzenesulphonamide and
its substituted compounds (NCSBS) are fairly strong
Table 3. Pseudo-second-order rate constants (kobs) for the oxidation of glutamic acid (Glu) by the sodium salts of p-substituted
N-chlorobenzenesulphonamides (NCSBS) in aqueous perchloric acid at 303 K (I ¼ 0.30 mol dmꢂ3
)
10 kobs (dm3 molꢂ1 sꢂ1) for 4-X-C6H4SO2NaNCl, where X ¼
103[NCSBS]0
(mol dmꢂ3
102[Glu]0
(mol dmꢂ3
102[HClO4]
)
)
(mol dmꢂ3
)
H
CH3
C2H5
F
Cl
Br
Effect of varying [NCSBS]0
0.5
1.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
3.0
3.0
3.0
3.0
3.0
3.0
2.7
2.4
2.2
2.0
2.3
2.5
3.0
2.7
2.4
2.3
2.7
3.2
2.5
2.4
2.4
2.3
2.5
2.7
3.6
3.5
3.5
3.4
3.3
3.6
4.2
4.0
4.0
4.0
3.8
4.2
8.0
7.9
7.9
7.8
7.8
8.3
4.0
1.0a
1.0b
Effect of varying [Glu]0
1.0
1.0
1.0
1.0
0.5
1.0
2.0
3.0
3.0
3.0
3.0
3.0
1.7
2.0
2.4
2.9
2.3
2.5
2.7
3.9
1.3
1.9
2.4
2.8
2.3
2.7
3.5
4.5
2.9
3.4
4.0
5.0
6.6
7.4
7.9
9.3
Effect of varying [HClO4]
1.0
1.0
1.0
1.0
1.0
2.0
2.0
2.0
2.0
2.0
1.0
2.0
3.0
5.0
7.0
3.9
2.4
1.5
0.7
10.7
5.1
2.7
1.7
0.9
8.0
4.1
2.4
1.6
0.8
11.7
7.4
3.5
2.4
1.2
24.0
13.4
4.0
2.4
1.5
30.8
16.6
7.9
3.7
1.8
10.0
a
I ¼ 0.10 mol dmꢂ3
.
.
b
I ¼ 0.50 mol dmꢂ3
Copyright # 2004 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2004; 17: 848–864

KINETICS OF OXIDATION OF ACIDIC AMINO ACIDS AND AMIDES
851
Table 4. Pseudo-second-order rate constants (kobs) for the oxidation of glutamic acid (Glu) by the sodium salts of disubstituted
N-chlorobenzenesulphonamides (NCSBS) in aqueous perchloric acid at 303 K (I ¼ 0.30 mol dmꢂ3
)
10 kobs (dm3 molꢂ1 sꢂ1) for i-X-j-Y-C6H3SO2NaNCl, where i-X-j-Y ¼
103[NCSBS]0
(mol dmꢂ3
102[Glu]0 102[HClO4]
(mol dmꢂ3) (mol dmꢂ3
)
)
2,3-(CH3)2 2,4-(CH3)2 2,5-(CH3)2 2-CH3-4-Cl 2,4-Cl2 3,4-Cl2
Effect of varying [NCSBS]0
0.5
1.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
3.0
3.0
3.0
3.0
3.0
3.0
3.2
2.6
2.2
1.9
2.4
2.8
4.1
3.3
3.2
2.5
3.1
3.6
4.9
4.7
4.3
4.2
4.5
4.9
10.8
10.6
10.4
10.3
10.4
10.9
17.9
17.4
17.3
17.1
17.1
17.7
14.3
14.2
13.9
13.6
14.0
14.5
4.0
1.0a
1.0b
Effect of varying[Glu]0
1.0
1.0
1.0
1.0
0.5
1.0
2.0
4.0
3.0
3.0
3.0
3.0
1.9
2.2
2.6
3.5
2.1
2.7
3.3
4.3
2.7
3.1
4.7
6.3
6.9
8.8
10.6
12.7
12.1
13.3
17.4
22.6
8.7
11.7
14.2
18.5
Effect of varying [HClO4]
1.0
1.0
1.0
1.0
1.0
2.0
2.0
2.0
2.0
2.0
1.0
2.0
3.0
5.0
5.8
3.9
2.6
1.9
1.6
9.4
5.9
3.3
2.5
2.0
14.0
7.6
4.7
3.2
2.4
21.1
15.3
10.6
4.3
39.4
27.2
17.4
11.7
7.0
29.7
25.1
14.2
10.2
5.2
10.0
2.6
a
I ¼ 0.10 mol dmꢂ3
.
.
b
I ¼ 0.50 mol dmꢂ3
Amino acids exist in protonation equilibrium in acidic
solutions as
The second-order kinetics in [NCSBS], fractional order
in [AA] and higher inverse order dependence of the rate
on [Hþ] and other effects for the oxidation of Asp, Glu,
Asn and Gln by all the N-chloroarylsulphonamides may
be explained by a two-pathway mechanism as shown in
Scheme 1. It is supported by the fact that the direct plots
of rate constants versus [AA] gave better correlations
(Figs 1 and 2) than the double reciprocal plots
(not shown). Further, in acidic aqueous solutions of the
RCH2CHðNþH3ÞCOOHÐRCH2CHðNþH3ÞCOOꢂþ Hþ
ðSHþÞ
ðSÞ
where R ¼ CH2COOH (Asp), CH2CH2COOH (Glu),
CH2CONH2 (Asn) and CH2CH2CONH2 (Gln).
Table 5. Pseudo-second-order rate constants (kobs) for the oxidation of aspargine (Asn) by the sodium salts of p-substituted
N-chlorobenzenesulphonamides (NCSBS) in aqueous perchloric acid at 303 K (I ¼ 0.30 mol dmꢂ3
)
10 kobs (dm3 molꢂ1 sꢂ1) for 4-X-C6H4SO2NaNCl, where X ¼
103[NCSBS]0
(mol dmꢂ3
102[Asn]0 102[HClO4]
)
(mol dmꢂ3
)
(mol dmꢂ3
)
H
CH3
C2H5
F
Cl
Br
Effect of varying [NCSBS]0
0.5
1.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
3.0
3.0
3.0
3.0
3.0
3.0
4.8
4.3
3.9
3.7
4.2
4.5
4.2
4.0
3.6
3.3
3.4
4.0
4.5
4.3
4.3
4.1
4.1
4.5
6.3
6.2
6.2
6.2
6.1
6.4
7.9
7.8
7.6
7.6
7.6
7.9
12.6
12.5
12.4
12.4
12.4
12.8
4.0
1.0a
1.0b
Effect of varying[Asn]0
1.0
1.0
1.0
1.0
0.5
1.0
2.0
4.0
3.0
3.0
3.0
3.0
2.5
3.2
4.3
6.8
2.3
2.9
4.0
5.3
2.5
3.1
4.3
6.9
4.0
4.7
6.2
8.4
5.8
6.3
7.8
10.5
9.2
10.4
12.5
15.8
Effect of varying [HClO4]
1.0
1.0
1.0
1.0
1.0
2.0
2.0
2.0
2.0
2.0
1.0
2.0
3.0
5.0
14.7
7.0
4.3
2.6
1.8
8.2
4.6
4.0
1.8
0.9
11.4
6.1
4.3
2.2
0.6
11.5
8.9
6.2
4.9
3.4
13.3
10.3
7.8
5.4
3.8
24.0
16.1
12.5
10.2
5.1
10.0
a
I ¼ 0.10 mol dmꢂ1
.
.
b
I ¼ 0.50 mol dmꢂ1
Copyright # 2004 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2004; 17: 848–864

852
B. T. GOWDA AND M. SHETTY
Table 6. Pseudo-second-order rate constants (kobs) for the oxidation of aspargine (Asn) by the sodium salts of disubstituted
N-chlorobenzenesulphonamides (NCSBS) in aqueous perchloric acid at 303 K (I ¼ 0.30 mol dmꢂ3
)
10 kobs (dm3 molꢂ1 sꢂ1) for i-X-j-Y-C6H3SO2NaNCl, where i-X-j-Y ¼
103[NCSBS]0
(mol dmꢂ3
102[Asn]0 102[HClO4]
(mol dmꢂ3) (mol dmꢂ3
)
)
2,3-(CH3)2 2,4-(CH3)2 2,5-(CH3)2 2-CH3 -4Cl 2,4-Cl2 3,4Cl2
Effect of varying [NCSBS]0
0.5
1.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
3.0
3.0
3.0
3.0
3.0
3.0
4.4
3.3
3.2
3.0
3.0
3.5
5.1
4.0
3.5
3.2
3.8
4.4
4.9
4.3
4.2
3.8
4.2
4.5
7.7
7.2
7.1
6.9
7.1
7.5
18.5
18.4
18.1
17.9
18.3
18.7
18.1
17.8
17.4
17.4
17.3
18.4
4.0
1.0a
1.0b
Effect of varying[Asn]0
1.0
1.0
1.0
1.0
0.5
1.0
2.0
4.0
3.0
3.0
3.0
3.0
2.5
2.8
3.2
3.8
2.5
3.2
4.0
4.8
3.2
3.6
4.3
6.3
4.9
5.9
7.2
8.6
12.4
13.7
18.4
28.2
7.7
13.0
17.8
23.5
Effect of varying [HClO4]
1.0
1.0
1.0
1.0
1.0
2.0
2.0
2.0
2.0
2.0
1.0
2.0
3.0
5.0
5.8
4.4
3.2
2.1
1.4
11.2
5.5
4.0
3.2
2.0
12.1
7.9
4.3
2.7
1.5
20.4
12.2
7.2
4.1
2.7
33.3
28.4
18.4
9.7
31.7
22.6
17.8
12.5
6.3
10.0
6.4
a
I ¼ 0.10 mol dmꢂ3
.
.
b
I ¼ 0.50 mol dmꢂ3
N-chloroarylsulphonamides, the corresponding N,N-
dichloro compounds are produced, which are insoluble
in water but soluble in organic solvents.
Applying the steady-state approximation to the inter-
mediate Y in path 1, we have
where [ArSO2NH2Clþ] ¼ [ArSO2NH2Clþ]0 ꢂ [Y] and
[S]0 ꢅ [S]. Since k3 is small and [S] ꢁ [ArSO2NH2Clþ]0,
k3[ArSO2NH2Clþ]0 is negligibly small compared
with other terms in the denominator, hence Eqn (1)
becomes
½Yꢄ ¼ k2½ArSO2NH2Clþꢄ0½Sꢄ=
ð1Þ
½Yꢄ ¼ k2½ArSO2NH2Clþꢄ0½Sꢄ=ðkꢂ2 þ k2½SꢄÞ
ð2Þ
fkꢂ2 þ k3½ArSO2NH2Clþꢄ0 þ k2½Sꢄg
¼ K2½NCSBSꢄ0½Sꢄ=ð1 þ K2½SꢄÞ
Table 7. Pseudo-second-order rate constants (kobs) for the oxidation of glutamine (Gln) by the sodium salts of p-substituted
N-chlorobenzenesulphonamides (NCSBS) in aqueous perchloric acid at 303 K (I ¼ 0.30 mol dmꢂ3
)
10 kobs (dm3 molꢂ1 sꢂ1) for 4-X-C6H4SO2NaNCl, where X ¼
103[NCSBS]0
(mol dmꢂ3
102[Gln]0 102[HClO4]
)
(mol dmꢂ3
)
(mol dmꢂ3
)
H
CH3
C2H5
F
Cl
Br
Effect of varying [NCSBS]0
0.5
1.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
2.7
2.5
2.2
2.2
2.8
2.9
2.9
2.8
2.7
2.8
3.2
3.4
3.1
3.1
3.0
3.2
3.4
4.9
4.8
4.7
4.7
4.6
5.0
7.8
7.6
7.6
7.6
7.5
7.9
9.3
9.2
9.2
9.2
9.0
9.4
4.0
1.0a
1.0b
Effect of varying [Gln]0
1.0
1.0
1.0
1.0
0.5
1.0
2.0
4.0
3.0
3.0
3.0
3.0
1.8
2.1
2.7
3.4
2.2
2.5
2.9
5.0
2.0
2.4
3.1
4.5
3.2
3.9
4.8
6.9
5.3
6.1
7.6
9.8
7.1
8.4
9.2
12.0
Effect of varying [HClO4]
1.0
1.0
1.0
1.0
1.0
2.0
2.0
2.0
2.0
2.0
1.0
2.0
3.0
5.0
8.1
4.2
2.7
1.3
0.8
9.7
4.7
2.9
1.6
0.7
7.7
4.9
3.1
1.6
0.8
20.5
10.4
4.8
2.9
1.2
18.7
11.1
7.6
4.3
2.1
29.3
16.6
9.2
8.7
4.1
10.0
a
I ¼ 0.10 mol dmꢂ3
.
.
b
I ¼ 0.50 mol dmꢂ3
Copyright # 2004 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2004; 17: 848–864

KINETICS OF OXIDATION OF ACIDIC AMINO ACIDS AND AMIDES
853
Table 8. Pseudo-second-order rate constants (kobs) for the oxidation of glutamine (Gln) by the sodium salts of disubstituted
N-chlorobenzenesulphonamides (NCSBS) in aqueous perchloric acid at 303 K (I ¼ 0.30 mol dmꢂ3
)
10 kobs (dm3 molꢂ1 sꢂ1) for i-X-j-Y-C6H3SO2NaNCl, where i-X-j-Y ¼
103[NCSBS]0
(mol dmꢂ3
102[Gln]0 102[HClO4]
(mol dmꢂ3) (mol dmꢂ3
)
)
2,3-(CH3)2 2,4-(CH3)2 2,5-(CH3)2 2-CH3-4-Cl 2,4-Cl2 3,4-Cl2
Effect of varying [NCSBS]0
0.5
1.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
3.0
3.0
3.0
3.0
3.0
3.0
4.6
2.8
2.5
1.9
2.6
3.2
4.8
4.0
3.7
3.0
3.6
4.2
5.9
4.7
4.5
4.3
4.6
4.9
6.8
5.4
5.3
5.0
5.2
5.6
15.9
15.5
14.9
14.8
15.2
15.8
14.3
13.7
13.4
13.3
13.3
14.7
4.0
1.0a
1.0b
Effect of varying [Gln]0
1.0
1.0
1.0
1.0
0.5
1.0
2.0
4.0
3.0
3.0
3.0
3.0
2.0
2.3
2.8
3.8
2.6
3.2
4.0
5.5
3.2
3.6
4.7
6.4
4.2
4.6
5.4
8.2
10.4
13.3
15.5
18.9
7.6
9.8
13.7
20.9
Effect of varying [HClO4]
1.0
1.0
1.0
1.0
1.0
2.0
2.0
2.0
2.0
2.0
1.0
2.0
3.0
5.0
7.4
4.9
2.8
2.3
1.7
10.0
6.2
4.0
2.7
1.9
10.6
6.9
4.7
3.0
2.2
11.8
7.9
5.4
4.2
2.8
28.6
21.4
15.5
9.7
28.3
17.1
13.7
9.5
10.0
6.4
6.1
a
I ¼ 0.10 mol dmꢂ3
.
.
b
I ¼ 0.50 mol dmꢂ3
where K2 ¼ k2/kꢂ2. Then the rate of the reaction going
If it is assumed that [NCSB]0 [NCSBS] ꢅ [NCSBS]2,
through path 1 is given by
then the rate law (3) becomes
ꢂd½NCSBSꢄ=dt ¼ k3½NCSBSꢄ½Yꢄ
¼ K2k3½NCSBSꢄ0½NCSBSꢄ½Sꢄ=ð1 þ K2½SꢄÞ
ð3Þ
2
ꢂd½NCSBSꢄ=dt ¼ K2k3½NCSBSꢄ ½Sꢄ=ð1 þ K2½SꢄÞ ð4Þ
Rearranging Eqn (4), we have
Table 9. Kinetic data for the oxidation of amino acids (AA)
by the sodium salts of mono- and disubstituted N-chlorobe-
nzenesulphonamides (NCSBS) in aqueous perchloric acid
(the kinetic order in [NCSBS] was 2 in all the oxidations)
2
ꢂðd½NCSBSꢄ=½NCSBSꢄ Þ=dt ¼ K2k3½Sꢄ=ð1 þ K2½SꢄÞ
ð5Þ
Oxidant
NCBS
Order in
Asp
Glu
Asn
Gln
However, the left-hand side of Eqn (5) may be written as
[AA]
[HClO4]
[AA]
[HClO4]
[AA]
[HClO4]
[AA]
[HClO4]
[AA]
0.3
ꢂ1.2
0.3
0.3
ꢂ1.0
0.3
0.4
ꢂ1.0
0.4
0.2
ꢂ1.1
0.3
2
NC4MBS
NC4EBS
NC4FBS
NC4CBS
NC4BBS
ꢂðd½NCSBSꢄ=½NCSBSꢄ Þ=dt ¼ dð1=½NCSBSꢄÞ=dt ¼ kp1
ꢂ1.1
ꢂ1.1
ꢂ1.0
ꢂ1.1
0.3
ꢂ1.1
0.3
0.4
ꢂ1.0
0.3
0.4
ꢂ1.1
0.3
0.3
ꢂ1.1
0.3
Hence Eqn (5) becomes
ꢂ1.2
ꢂ0.9
ꢂ0.5
ꢂ1.3
kp1 ¼ K2k3½Sꢄ=ð1 þ K2½SꢄÞ
½Sꢄ ¼ K1½SHþꢄ=½Hþꢄ
ð6Þ
0.3
ꢂ1.2
0.4
0.3
ꢂ1.4
0.2
0.2
ꢂ0.6
0.2
0.3
ꢂ1.0
0.2
[HClO4]
[AA]
[HClO4]
We also have
ꢂ0.8
ꢂ1.2
ꢂ0.6
ꢂ0.8
NC23DMBS [AA]
[HClO4]
NC24DMBS [AA]
[HClO4]
NC25DMBS [AA]
[HClO4]
NC2M4CBS [AA]
[HClO4]
[AA]
0.3
ꢂ1.2
0.4
0.3
ꢂ0.9
0.3
0.2
ꢂ0.8
0.3
0.3
ꢂ0.8
0.3
ð7Þ
ð8Þ
ꢂ0.8
ꢂ0.9
ꢂ0.8
ꢂ0.8
Therefore, Eqn (6) takes the form
0.5
ꢂ1.2
0.3
0.4
ꢂ0.9
0.3
0.3
ꢂ0.9
0.3
0.3
ꢂ1.0
0.3
kp1 ¼ K1K2k3½SHþꢄ=ð½Hþꢄ þ K1K2½SHþꢄÞ
ꢂ0.9
ꢂ1.0
ꢂ0.9
ꢂ0.8
NC24DCBS
NC34DCBS
0.4
ꢂ1.0
0.3
0.4
ꢂ1.0
0.3
0.3
ꢂ1.1
0.6
0.3
ꢂ1.0
0.5
If K2 is small, then the rate law (6) will take the form
[HClO4]
[AA]
[HClO4]
kp1 ¼ K2k3½Sꢄ¼ K1K2k3½SHþꢄ=½Hþꢄ
ð9Þ
ꢂ0.9
ꢂ0.8
ꢂ0.8
ꢂ0.8
Copyright # 2004 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2004; 17: 848–864

854
B. T. GOWDA AND M. SHETTY
Figure 1. Plots of kobs versus [AA]. 103[NCSBS] ¼ 33.3[HClO4] ¼ 3.33I ¼ 1.0 mol dmꢂ3; temperature ¼ 303 K. NCSBS: 4-X-
C6H4SO2NaNCl, where X ¼ H, CH3, C2H5, F, Cl, Br
Figure 2. Plots of kobs versus [AA]. 103[NCSBS] ¼ 33.3[HClO4] ¼ 3.33I ¼ 1.0 mol dmꢂ3; temperature ¼ 303 K. NCSBS: i-X-j-Y-
C6H3SO2NaNCl, where i-X-j-Y ¼ 2,3-(CH3)2, 2,4-(CH3)2, 2,5-(CH3)2, 2-CH3-4-Cl, 2,4-Cl2, 3,4-Cl2
Copyright # 2004 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2004; 17: 848–864

KINETICS OF OXIDATION OF ACIDIC AMINO ACIDS AND AMIDES
855
Path 1:
The rate law for the reaction in path 2 was deduced in a
similar way:
K1
Ð
SHþ
S þ Hþ
ðfastÞ
2
2
ꢂðd½NCSBSꢄ=½NCSBSꢄ Þ=dt ¼ K4k5=½Hþꢄ
k2
ðArSO NH ClÞþ þ S
intermediateðYÞ ðfastÞ
Ð
2
2
kꢂ2
or
k3
Y þ ðArSO2NH2ClÞþ ! products
ðslowÞ
2
kp2 ¼ K4k5=½Hþꢄ
ð10Þ
Path 2:
The combined rate law for both the pathways is therefore
given by
K4
Ð
2ðArSO NH ClÞ þ
intermediateðY0Þ þ 2Hþ ðfastÞ
2
2
2
kobs ¼ ðK1K2k3½SHþꢄ=½HþꢄÞ þ ðK4k5=½Hþꢄ Þ
ð11Þ
k5
Y0 ! ArSO2NCl2 þ ArSO2NH2
ðslowÞ
ArSO2NCl2 þ H3Oþ ! H2OClþ þ ArSO2NHCl ðfastÞ
or
H2OClþ þ S ! products
ðfastÞ
ðfastÞ
2
kobs ¼ ðk½SHþꢄ=½HþꢄÞ þ ðk0=½Hþꢄ Þ
ð12Þ
ArSO2NHCl þ Hþ ! ðArSO2NH2ClÞþ
where k ¼ K1K2 k3 and k0 ¼ K4 k5
Scheme 1
Table 10. Calculated constant k for path 1 of the oxidation of amino acids (AA) by the sodium salts of mono- and disubstituted
N-chlorobenzenesulphonamides in aqueous perchloric acid
10 k (dm3 molꢂ1 sꢂ1) for 4-X-C6H4SO2NaNCl, where X ¼
AA
Temperature (K)
H
CH3
C2H5
F
Cl
Br
Asp
298
303
308
313
298
303
308
313
298
303
308
313
298
303
308
313
1.3
1.8
2.2
3.6
1.2
1.5
3.1
3.6
1.5
2.6
5.2
6.4
1.2
1.7
2.4
3.1
1.8
2.1
3.0
4.1
1.4
1.8
3.4
5.1
2.3
2.7
3.4
3.9
2.0
2.2
3.2
3.6
1.1
2.2
3.1
5.2
1.4
1.9
3.3
3.7
1.6
2.2
3.2
3.6
1.3
2.1
2.4
3.4
1.6
3.9
5.3
6.3
1.4
2.5
4.7
5.7
3.3
4.6
6.7
8.4
2.5
3.6
5.7
7.7
2.4
4.4
5.2
8.4
1.6
2.9
5.0
6.2
3.3
5.2
6.6
8.2
2.1
4.8
6.3
8.4
6.3
7.5
9.5
10.4
3.9
6.0
9.0
11.8
5.5
8.0
12.0
16.0
2.9
6.9
8.5
Glu
Asn
Gln
11.2
10 k (dm3 molꢂ1 sꢂ1) for i-X-j-Y-C6H3SO2NaNCl, where i-X-j-Y ¼
2,3-(CH3)2
2,4-(CH3)2
2,5-(CH3)2
2-CH3-4-Cl
2,4-Cl2
3,4-Cl2
Asp
Glu
Asn
Gln
298
303
308
313
298
303
308
313
298
303
308
313
298
303
308
313
1.7
2.0
2.7
4.2
1.3
1.5
2.6
3.5
0.9
1.4
2.0
4.4
2.0
2.3
3.2
4.4
1.6
2.3
4.3
4.7
1.3
1.8
3.0
6.0
1.8
2.3
4.1
6.5
1.6
2.4
4.7
5.8
1.6
3.9
4.3
5.1
2.3
3.3
3.9
5.4
1.5
2.8
4.6
6.2
1.9
2.9
4.6
6.3
4.5
7.3
8.5
9.2
1.9
4.4
5.9
8.4
2.3
3.9
5.1
9.8
3.1
4.1
4.9
10.3
5.6
12.5
21.5
29.8
12.6
14.6
17.6
23.9
10.1
13.8
16.7
22.9
6.0
8.5
10.3
12.2
18.1
4.3
8.2
10.2
15.4
7.0
11.8
15.5
20.2
6.2
8.8
10.2
11.6
8.9
10.4
15.0
Copyright # 2004 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2004; 17: 848–864

856
B. T. GOWDA AND M. SHETTY
Table 11. Calculated constant k0 for path 2 of the oxidation of amino acids (AA) by the sodium salts of mono- and disubstituted
N-chlorobenzenesulphonamides in aqueous perchloric acid
104 k0 (dm3 molꢂ1 sꢂ1) for 4-X-C6H4SO2NaNCl, where X ¼
AA
Temperature (K)
H
CH3
C2H5
F
Cl
Br
Asp
298
303
308
313
298
303
308
313
298
303
308
313
298
303
308
313
0.8
1.4
1.8
2.2
0.9
1.3
1.7
2.5
1.1
1.7
2.0
2.4
0.9
1.4
2.0
2.4
0.9
1.3
2.3
2.7
0.8
1.5
2.1
2.9
0.8
1.4
1.9
2.3
0.7
1.5
2.2
3.0
0.8
1.4
2.0
3.1
0.7
1.1
2.0
2.7
0.7
1.4
1.9
2.6
0.9
1.5
2.2
2.8
1.8
2.2
3.2
4.3
1.3
1.6
2.7
4.0
1.8
2.7
4.0
5.2
1.2
2.2
4.0
5.2
2.1
2.9
4.4
5.4
1.1
2.1
3.0
4.1
2.2
4.1
5.4
7.7
2.3
3.8
4.4
5.8
2.5
3.1
5.0
6.0
3.6
4.6
6.2
9.0
4.7
6.3
7.8
11.5
4.1
5.5
9.0
10.6
Glu
Asn
Gln
104 k0 (dm3 molꢂ1 sꢂ1) for i-X-j-Y-C6H3SO2NaNCl, where i-X-j-Y ¼
2,3-(CH3)2
2,4-(CH3)2
2,5-(CH3)2
2-CH3-4-Cl
2,4-Cl2
3,4-Cl2
Asp
Glu
Asn
Gln
298
303
308
313
298
303
308
313
298
303
308
313
298
303
308
313
1.0
1.5
2.1
2.9
1.1
1.4
2.5
4.1
1.5
2.0
3.1
7.6
1.3
1.5
1.7
3.5
1.5
1.8
3.0
3.9
1.4
1.7
2.3
3.8
1.5
2.2
2.7
4.2
1.7
2.0
2.5
3.4
1.7
2.2
2.9
4.6
1.6
2.0
2.7
3.2
2.1
2.3
2.7
4.0
1.8
2.5
3.1
4.0
4.2
6.2
9.7
13.4
4.1
4.4
5.7
8.5
2.7
3.8
6.0
7.7
2.3
2.7
3.4
5.0
7.2
8.6
16.3
22.9
3.6
7.2
8.4
13.3
18.4
3.6
6.3
9.1
11.7
5.1
6.9
10.2
15.0
4.8
8.6
7.3
13.2
16.8
5.9
9.2
11.3
14.9
13.1
15.6
5.9
6.5
8.7
13.4
The plots of kobs versus [AA] were linear with finite
intercepts on the ordinate (Figs 1 and 2), in conformity
with the rate law (12). The constants k and k0 were
calculated from the slopes and intercepts of the plots,
respectively, by inserting the values of [Hþ]. These
constants were used to recalculate the rate constants
from the rate law (12) as [Hþ] was varied. The recalcu-
lated values agreed reasonably well with the experimen-
tal constants (data not shown), testing the validity of the
rate law and providing support for the suggested mechan-
ism. Further, k and k0 were calculated at different tem-
peratures by varying [AA] at each temperature (Tables 10
and 11). The activation parameters corresponding to
these constants were also calculated from the plots of
log k or log k0 versus 1/T and log (k/T) or log (k0/T) versus
1/T (Tables 12–15).
monosubstituted oxidants. The plots of log ki versus ꢀp
were reasonably linear (Figs 3–6) and the following
relations were found to be valid:
Asp:
Glu:
Asn:
Gln:
log k ¼ ꢂ0.551 þ 1.270ꢀ (r ¼ 0.855)
log k0 ¼ ꢂ3.752 þ 1.011ꢀ (r ¼ 0.947)
log k ¼ ꢂ0.655 þ 1.050ꢀ (r ¼ 0.784)
log k0 ¼ ꢂ3.790 þ 1.123ꢀ (r ¼ 0.817)
log k ¼ ꢂ0.477 þ 1.24ꢀ (r ¼ 0.923)
log k0 ¼ ꢂ3.670 þ 1.607ꢀ (r ¼ 0.957)
log k ¼ ꢂ0.561 þ 1.282ꢀ (r ¼ 0.874)
log k0 ¼ ꢂ 3.702 þ 1.402ꢀ (r ¼ 0.917)
The constancy of the ÁGz values for paths 1 and 2
(Tables 12–15) indicated the operation of similar me-
chanisms in all cases. The formation of more ordered
activated complexes is evident from the negative ÁSz
The applicability of the Hammett equation was tested
for the oxidation of all four amino acids by all of the
Copyright # 2004 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2004; 17: 848–864

KINETICS OF OXIDATION OF ACIDIC AMINO ACIDS AND AMIDES
857
Table 12. Activation parameters for path 1 of the mechanism for the oxidations of amino acids (AA) by the sodium salts of
p-substituted N-chlorobenzenesulphonamides in aqueous perchloric acid
4-X-C6H4SO2NaNCl, where X ¼
AA
Parameter
H
CH3
C2H5
F
Cl
Br
Asp
Ea (kJ molꢂ1
Log A
)
51.3
8.1
40.4
6.2
75.5
12.3
75.0
ꢂ10.5
78.1
55.9
8.9
54.3
ꢂ77.8
78.3
47.9
7.5
46.3
ꢂ89.8
73.4
49.7
7.9
49.0
ꢂ96.1
78.2
62.8
10.5
61.9
ꢂ48.5
76.6
84.1
13.9
82.2
þ14.5
77.7
60.0
10.0
59.6
ꢂ55.7
76.2
56.6
9.3
65.6
11.0
63.4
ꢂ42.5
76.3
75.1
12.4
73.5
ꢂ15.8
77.4
54.9
9.0
54.7
ꢂ75.7
75.6
79.0
13.3
78.6
þ 8.3
76.1
29.9
5.1
ÁHz (kJ molꢂ1
)
48.8
ꢂ98.4
78.6
47.7
7.4
46.8
ꢂ106.3
79.0
70.1
11.5
69.0
ꢂ28.6
78.1
56.6
9.0
38.4
ꢂ130.5
29.3
ꢂ152.9
74.9
59.0
9.8
57.0
ꢂ58.7
75.5
57.9
9.9
55.5
ꢂ63.9
74.9
79.9
13.7
78.0
þ 9.4
75.2
ÁSz (J Kꢂ1 molꢂ1
)
)
)
)
ÁGz (kJ mꢂo1lꢂ1
)
78.0
70.6
Glu
Asn
Gln
Ea (kJ mol
Log A
)
11.5
66.2
ÁHz (kJ molꢂ1
)
ÁSz (J Kꢂ1 molꢂ1
ꢂ40.7
ÁGz (kJ mꢂo1lꢂ1
)
78.5
65.0
Ea (kJ mol
Log A
)
10.6
65.5
ÁHz (kJ molꢂ1
)
ÁSz (J Kꢂ1 molꢂ1
ꢂ39.0
ÁGz (kJ mꢂo1lꢂ1
)
77.5
40.7
Ea (kJ mol
Log A
)
6.5
35.3
ÁHz (kJ molꢂ1
)
54.3
ꢂ80.8
79.0
52.0
ꢂ81.9
76.9
ÁSz (J Kꢂ1 molꢂ1
ꢂ139.2
ÁGz (kJ molꢂ1
)
78.1
values. Further, the enthalpies and entropies of activa-
tions for the oxidations of all the four amino acids by all
the N-chloroarylsulphonamides were correlated. The
plots of ÁHz (kJ molꢂ1) versus ÁSz (J Kꢂ1 molꢂ1) corre-
sponding to both k and k0 were linear (Figs 7–10). The
following relations were found to be valid with isokinetic
temperatures of 297 and 273 K (for Asp), 312 and 293 K
(for Glu), 314 and 303 K (for Asn) and 298 and 311 K (for
Gln), respectively, which are more or less in the tem-
perature ranges employed in the present investigations
(298–313 K):
Asp:
Path 1: ÁHz ¼ 76.17 þ 297ÁSz (r ¼ 0.997)
Path 2: ÁHz ¼ 90.81 þ 273ÁSz (r ¼ 0.966)
Table 13. Activation parameters for path 1 of the mechanism for the oxidations of amino acids (AA) by the sodium salts of
disubstituted N-chlorobenzenesulphonamides in aqueous perchloric acid
i-X-j-Y-C6H3SO2NaNCl, where i-X-j-Y ¼
AA
Parameter
2,3-(CH3)2
2,4-(CH3)2 2,5-(CH3)2
2-CH3-4-Cl
2,4-Cl2
3,4-Cl2
Asp
Ea (kJ molꢂ1
Log A
)
52.8
8.4
62.1
10.1
61.0
ꢂ55.8
77.9
70.9
11.5
67.7
ꢂ35.8
78.6
70.6
11.5
70.5
ꢂ24.5
77.9
80.3
13.2
79.3
þ4.6
77.8
81.6
13.6
43.6
7.4
103.0
17.8
102.4
þ 94.8
73.7
48.7
8.4
ÁHz (kJ molꢂ1
)
50.9
ꢂ90.5
78.3
80.4
13.0
76.3
ꢂ9.0
79.0
78.0
12.6
77.2
ꢂ6.6
79.2
37.7
5.9
78.9
þ 7.7
40.7
ꢂ113.2
44.8
ꢂ96.8
74.1
68.0
11.7
67.4
ꢂ24.6
74.8
64.3
11.1
57.7
ꢂ53.4
73.9
48.2
8.1
ÁSz (J Kꢂ1 molꢂ1
)
)
)
)
ÁGz (kJ mꢂo1lꢂ1
)
76.5
41.4
75.0
86.1
Glu
Asn
Gln
Ea (kJ mol
Log A
)
36.1
6.4
6.7
38.4
14.5
85.1
ÁHz (kJ molꢂ1
)
35.7
ꢂ124.0
ÁSz (J Kꢂ1 molꢂ1
ꢂ127.5
þ29.1
ÁGz (kJ mꢂo1lꢂ1
)
77.0
78.0
76.3
73.6
73.2
42.2
Ea (kJ mol
Log A
)
12.6
77.6
12.1
71.6
7.4
39.4
ÁHz (kJ molꢂ1
)
ÁSz (J Kꢂ1 molꢂ1
þ 0.6
ꢂ16.6
ꢂ112.4
ÁGz (kJ mꢂo1lꢂ1
)
77.4
66.9
76.6
73.9
73.5
48.0
Ea (kJ mol
Log A
)
11.0
64.8
12.3
73.1
8.1
47.9
ÁHz (kJ molꢂ1
)
36.3
ꢂ137.4
77.9
47.9
ꢂ88.2
74.7
ÁSz (J Kꢂ1 molꢂ1
ꢂ41.4
ꢂ10.9
ꢂ87.9
ÁGz (kJ molꢂ1
)
77.3
76.4
74.6
Copyright # 2004 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2004; 17: 848–864

858
B. T. GOWDA AND M. SHETTY
Table 14. Activation parameters for path 2 of the mechanism for the oxidations of amino acids (AA) by the sodium salts of p-
substituted N-chlorobenzenesulphonamides in aqueous perchloric acid
4-X-C6H4SO2NaNCl, where X ¼
AA
Parameter
H
CH3
C2H5
F
Cl
Br
Asp
Ea (kJ molꢂ1
Log A
)
52.7
5.2
54.7
5.5
64.7
7.3
50.5
5.0
47.5
4.7
52.5
5.6
ÁHz (kJ molꢂ1
)
50.3
ꢂ153.5
48.5
ꢂ160.1
62.5
ꢂ112.5
42.3
ꢂ175.2
43.5
ꢂ170.5
94.7
73.6
8.9
73.5
ꢂ73.3
95.7
71.4
8.9
67.4
ꢂ87.8
94.0
54.9
6.1
53.7
ꢂ133.4
94.1
47.9
ꢂ154.5
ÁSz (J Kꢂ1 molꢂ1
)
)
)
)
ÁGz (kJ mꢂo1lꢂ1
)
96.7
50.8
96.9
64.7
96.7
68.2
95.5
54.4
94.4
47.2
Glu
Asn
Gln
Ea (kJ mol
Log A
)
4.9
49.9
7.3
58.0
7.8
65.1
5.6
52.4
4.8
47.1
ÁHz (kJ molꢂ1
)
ÁSz (J Kꢂ1 molꢂ1
ꢂ154.6
ꢂ126.6
ꢂ106.6
ꢂ144.6
ꢂ153.5
ÁGz (kJ mꢂo1lꢂ1
)
96.8
56.9
96.5
53.3
97.4
74.8
96.2
49.8
93.5
42.6
Ea (kJ mol
Log A
)
6.1
55.7
5.4
51.6
9.1
73.0
5.0
47.9
4.1
40.0
ÁHz (kJ molꢂ1
)
ÁSz (J Kꢂ1 molꢂ1
ꢂ134.5
ꢂ149.5
ꢂ78.2
ꢂ155.6
ꢂ174.4
ÁGz (kJ mꢂo1lꢂ1
)
96.2
54.9
96.6
89.7
96.6
65.7
95.0
90.5
92.9
54.1
Ea (kJ mol
Log A
)
5.6
52.9
11.7
84.1
7.5
64.9
11.9
90.4
6.1
48.9
ÁHz (kJ molꢂ1
)
ÁSz (J Kꢂ1 molꢂ1
ꢂ145.0
ꢂ39.0
ꢂ104.0
ꢂ16.8
ꢂ147.0
ÁGz (kJ molꢂ1
)
96.7
96.5
96.5
95.5
93.2
Glu:
Asn:
Gln:
Path 1: ÁHz ¼ 77.52 þ 312ÁSz (r ¼ 0.994)
Path 2: ÁHz ¼ 94.12 þ 293ÁSz (r ¼ 0.993)
Path 1: ÁHz ¼ 78.00 þ 314ÁSz (r ¼ 0.994)
Path 2: ÁHz ¼ 94.78 þ 303ÁSz (r ¼ 0.994)
Path 1: ÁHz ¼ 76.36 þ 298ÁSz (r ¼ 0.996)
Path 2: ÁHz ¼ 95.98 þ 311ÁSz (r ¼ 0.996)
CONCLUSION
The effect of substituents in the benzene ring of the
oxidant on the Ea for the oxidation of amino acids was
analysed by optimizing Ea values with reference to log A
of the parent oxidant (NCSBS) according to the equation
Ea ¼ 2.303RT (log A ꢂ log k). Similarly, log Avalues were
Table 15. Activation parameters for path 2 of the mechanism for the oxidations of amino acids (AA) by the sodium salts of
disubstituted N-chlorobenzenesulphonamides in aqueous perchloric acid
i-X-j-Y-C6H3SO2NaNCl, where i-X-j-Y ¼
AA
Parameter
2,3-(CH3)2
2,4-(CH3)2 2,5-(CH3)2
2-CH3-4-Cl
2,4-Cl2
3,4-Cl2
Asp
Ea (kJ molꢂ1
Log A
)
49.2
4.7
57.2
6.1
54.4
5.7
59.5
7.1
64.4
8.0
49.2
5.4
ÁHz (kJ molꢂ1
)
49.1
ꢂ156.2
57.1
ꢂ128.2
52.1
ꢂ143.0
59.4
ꢂ110.4
57.6
ꢂ113.7
47.2
ꢂ148.2
ÁSz (J Kꢂ1 molꢂ1
)
)
)
)
ÁGz (kJ mꢂo1lꢂ1
)
96.4
73.5
96.0
60.7
95.4
32.5
92.9
49.3
92.0
80.7
92.1
71.0
Glu
Asn
Gln
Ea (kJ mol
Log A
)
8.8
69.8
6.7
60.5
1.9
31.4
5.2
44.7
10.8
76.0
9.1
70.6
ÁHz (kJ molꢂ1
)
ÁSz (J Kꢂ1 molꢂ1
ꢂ88.4
ꢂ118.1
ꢂ212.3
ꢂ161.8
ꢂ53.8
ꢂ73.4
ÁGz (kJ mꢂo1lꢂ1
)
96.6
101.0
13.7
96.3
55.5
95.7
61.4
93.7
56.9
92.1
72.2
92.9
63.8
Ea (kJ mol
Log A
)
5.9
52.8
7.0
56.1
6.4
53.6
9.4
71.8
7.9
59.6
ÁHz (kJ molꢂ1
)
100.9
þ17.1
95.7
68.8
8.0
ÁSz (J Kꢂ1 molꢂ1
ꢂ140.7
ꢂ129.8
ꢂ133.5
ꢂ66.7
ꢂ108.1
ÁGz (kJ mꢂo1lꢂ1
)
95.4
40.8
95.3
44.0
94.0
46.4
92.0
51.6
92.4
50.1
Ea (kJ mol
Log A
)
3.3
40.7
4.0
40.5
4.5
45.1
5.9
49.4
5.5
46.5
ÁHz (kJ molꢂ1
)
63.6
ꢂ108.3
ÁSz (J Kꢂ1 molꢂ1
ꢂ181.7
ꢂ180.3
ꢂ164.6
ꢂ140.1
ꢂ152.6
ÁGz (kJ molꢂ1
)
96.4
95.7
95.1
95.0
91.9
92.7
Copyright # 2004 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2004; 17: 848–864

KINETICS OF OXIDATION OF ACIDIC AMINO ACIDS AND AMIDES
859
Figure 3. Plots of log k versus ꢀp and log k0 versus ꢀp for oxidation of Asp by NCSBS. NCSBS: 4-X-C6H4SO2NaNCl, where X ¼ H,
CH3, C2H5, F, Cl, Br
optimized with reference to Ea of the parent oxidant
through the equation log A ¼ log k þ Ea/2.303RT. The
optimized values are shown in Tables 16 and 17. It is
evident from the data that the the rates of oxidation and
the Ea values are least affected by the introduction of
electron-donating groups into the benzene ring, whereas
the introduction of electron-withdrawing groups such as
halides into the ring increase the rates of oxidation and
lower Ea. Enthalpies of activation have similar trends.
The log A values have the reverse trend. Hence the
study revealed that the introduction of electron-
withdrawing groups such as halides into the benzene
ring eased the release of Clþ from the reagent and hence
increased the oxidizing strengths of the N-chloroarylsul-
phonamides.
EXPERIMENTAL
Materials and methods
Benzenesulphonamide (BSA) and substituted benzenesul-
phonamides (SBSA), namely 4-methylbenzenesulphona-
mide (4MBSA), 4-ethylbenzenesulphonamide (4EBSA),
Figure 4. Plots of log k versus ꢀp and log k0 versus ꢀp for oxidation of Glu by NCSBS. NCSBS: 4-X-C6H4SO2NaNCl, where X ¼ H,
CH3, C2H5, F, Cl, Br
Copyright # 2004 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2004; 17: 848–864

860
B. T. GOWDA AND M. SHETTY
Figure 5. Plots of log k versus ꢀp and log k0 versus ꢀp for oxidation of Asn by NCSBS. NCSBS: 4-X-C6H4SO2NaNCl, where X ¼ H,
CH3, C2H5, F, Cl, Br
4-fluorobenzenesulphonamide (4FBSA), 4-chlorobenze-
nesulphonamide (4CBSA), 4-bromobenzenesulphonamide
(4BBSA) 2,3-dimethylbenzenesulphonamide (23DMBSA),
2, 4-dimethylbenzenesulphonamide (24DMBSA), 2,5-
dimethylbenzenesulphonamide (25DMBSA), 2-methyl-4-
chlorobenzenesulphonamide (2M4CBSA), 2,4-dichloro-
benzenesulphonamide (24DCBSA) and 3,4-dichloroben-
zenesulphonamide (34DCBSA), were prepared by
chlorosulphonation of the respective substituted benzenes
to the corresponding sulphonyl chlorides and subsequent
conversion of the latter to the respective substituted benze-
nesulphonamides by procedures reported earlier10–13. The
sulphonamides were recrystallized to constant melting-
points from dilute ethanol. The purities of all the sulpho-
namides were further checked by estimating the amount of
sulphur present in them. The observed melting-points ( ꢆC)
Figure 6. Plots of log k versus ꢀp and log k0 versus ꢀp for oxidation of Gln by NCSBS. NCSBS: 4-X-C6H4SO2NaNCl, where X ¼ H,
CH3, C2H5, F, Cl, Br
Copyright # 2004 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2004; 17: 848–864

KINETICS OF OXIDATION OF ACIDIC AMINO ACIDS AND AMIDES
861
¼
¼
Figure 7. Plot of ÁH versus ÁS for oxidation of Asp by NCSBS. NCSBS: i-X-C6H4SO2NaNCl, where i-X ¼ 4-H, 4-CH3,
4-C2H5, 4-F, 4-Cl 4-Br, and i-X-j-Y-C6H3SO2NaNCl, where i-X-j-Y ¼ 2,3-(CH3)2, 2,4-(CH3)2, 2,5-(CH3)2, 2-CH3-4-Cl, 2,4-Cl2,
3,4-Cl2
of the arylsulphonamides and the literature values (in
parentheses) are BSA 152 (150–152), 4MBSA 138 (138–
139), 4EBSA 99 (99–100), 4FBSA 125 (124–127), 4CBSA
145 (145–147), 4BBSA 162 (162), 23DMBSA 138–140,
24DMBSA 140–142, 25DMBSA 149–151, 2M4CBSA
180–182 (184–185), 24DCBSA 178 (179–180) and
34DCBSA 141.
The SBSA were then N-chlorinated as follows to give
sodium salts of substituted N-chlorobenzenesul-
phonamides (NCSBS), namely, the sodium salts of
N-chlorobenzenesulphonamide (NCBS), N-chloro-4-
methylbenzenesulphonamide (NC4MBS), N-chloro-4-
ethylbenzenesulphonamide (NC4EBS), N-chloro-4-fluor-
obenzenesulphonamide (NC4FBS), N-chloro-4-chloro-
¼
¼
Figure 8. Plot of ÁH versus ÁS for oxidation of Glu by NCSBS. NCSBS: i-X-C6H4SO2NaNCl, where i-X ¼ 4-H, 4-CH3,
4-C2H5, 4-F, 4-Cl 4-Br, and i-X-j-Y-C6H3SO2NaNCl, where i-X-j-Y ¼ 2,3-(CH3)2, 2,4-(CH3)2, 2,5-(CH3)2, 2-CH3-4-Cl, 2,4-Cl2, 3,4-
Cl2
Copyright # 2004 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2004; 17: 848–864

862
B. T. GOWDA AND M. SHETTY
¼
¼
Figure 9. Plot of ÁH versus ÁS for oxidation of Asn by NCSBS. NCSBS: i-X-C6H4SO2NaNCl, where i-X ¼ 4-H, 4-CH3,
4-C2H5, 4-F, 4-Cl 4-Br, and i-X-j-Y-C6H3SO2NaNCl, where i-X-j-Y ¼ 2,3-(CH3)2, 2,4-(CH3)2, 2,5-(CH3)2, 2-CH3-4-Cl, 2,4-Cl2,
3,4-Cl2
benzenesulphonamide (NC4CBS), N-chloro-4-bromoben-
zenesulphonamide (NC4BBS), N-choro-2,3-dimethyl-
benzenesulphonamide (NC23DMBS), N-choro-2,4-
dimethylbenzenesulphonamide (NC24DMBS), N-chloro-
2,5-dimethylbenzenesulphonamide (NC25DMBS), N-
chloro-2-methyl-4-chlorobenzenesulphonamide (NC2M4
CBS), N-chloro-2,4-dichlorbenzene-sulphonamide (NC24
DCBS) and N-chloro-3,4-dichlorobenzenesulphonamide
(NC34DCBS). Pure chlorine gas was bubbled through
clear solutions of SBSA in 4 M NaOH at 70 ꢆC for about
1 h. The precipitated sodium salts of NCSBS were filtered,
washed, dried and recrystallized from water. The purity of
¼
¼
Figure 10. Plot of ÁH versus ÁS for oxidation of Gln by NCSBS. NCSBS: i-X-C6H4SO2NaNCl, where i-X ¼ 4-H, 4-CH3,
4-C2H5, 4-F, 4-Cl 4-Br, and i-X-j-Y-C6H3SO2NaNCl, where i-X-j-Y ¼ 2,3-(CH3)2, 2,4-(CH3)2, 2,5-(CH3)2, 2-CH3-4-Cl, 2,4-Cl2,
3,4-Cl2
Copyright # 2004 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2004; 17: 848–864

KINETICS OF OXIDATION OF ACIDIC AMINO ACIDS AND AMIDES
863
Table 16. Optimized values of Ea, Log A and ÁSz for path 1 of the mechanism for the oxidation of amino acids (AA) by the
sodium salts of mono- and disubstituted N-chlorobenzenesulphonamides in aqueous perchloric acid
4-X-C6H4SO2NaNCl, where X ¼
Parameter
AA
H
CH3
C2H5
F
Cl
Br
Ea (kJ molꢂ1
)
Asp
Glu
Asn
Gln
Asp
Glu
Asn
Gln
Asp
Glu
Asn
Gln
51.3
47.7
70.1
56.6
8.1
7.4
11.5
9.0
50.9
47.2
70.0
56.0
8.2
7.5
11.5
9.1
50.8
47.1
70.5
56.1
8.2
7.5
11.4
9.1
49.3
46.4
68.7
54.8
8.4
7.6
11.7
9.3
49.0
46.0
68.4
54.1
8.5
7.7
11.8
9.4
47.7
44.2
67.3
53.1
8.7
8.0
12.0
9.6
ꢂ86.3
ꢂ94.8
ꢂ19.3
ꢂ68.3
Log A
ÁSz (JKꢂ1 molꢂ1
)
ꢂ98.4
ꢂ106.3
ꢂ28.6
ꢂ80.8
ꢂ96.2
ꢂ104.8
ꢂ28.3
ꢂ77.7
ꢂ97.0
ꢂ104.4
ꢂ31.7
ꢂ78.3
ꢂ91.9
ꢂ101.8
ꢂ23.9
ꢂ74.0
ꢂ90.5
ꢂ101.2
ꢂ22.7
ꢂ71.7
i-X-j-Y-C6H3SO2NaNCl, where i-X-j-Y ¼
2,3-(CH3)2
2,4-(CH3)2
2,5-(CH3)2
2-CH3-4-Cl
2,4-Cl2
3,4-Cl2
Ea (kJ molꢂ1
)
Asp
Glu
Asn
Gln
Asp
Glu
Asn
Gln
Asp
Glu
Asn
Gln
51.1
47.7
72.2
55.9
8.1
7.4
11.3
9.0
50.6
47.2
70.4
55.8
8.2
7.5
11.5
9.0
49.4
45.7
69.9
55.3
8.4
7.7
11.6
9.1
ꢂ91.9
ꢂ98.6
ꢂ26.5
ꢂ75.6
47.8
45.0
69.2
54.4
8.7
7.9
11.7
9.3
ꢂ86.5
ꢂ95.6
ꢂ23.7
ꢂ72.6
46.5
42.0
65.9
52.5
8.9
8.4
12.3
9.6
ꢂ82.1
ꢂ86.3
ꢂ13.2
ꢂ66.3
46.9
42.4
66.3
52.5
8.8
8.1
12.2
9.6
ꢂ83.6
ꢂ91.1
ꢂ14.5
ꢂ66.3
Log A
ÁSz (JKꢂ1 molꢂ1
)
ꢂ97.4
ꢂ105.2
ꢂ32.2
ꢂ77.5
ꢂ96.1
ꢂ103.5
ꢂ28.1
ꢂ77.4
all the N-chloro compounds was checked by estimating the
amounts of active chlorine present in them and by deter-
mining their melting-points. The observed melting-points
( ꢆC) and the literature values (in parentheses) are NCBS
172–173 (170–173), NC4MBS 168–169 (167–170),
NC4EBS 194, NC4FBS 198, NC4CBS 191 (190),
NC4BBS 179 (178), NC23DMBS 167, NC24DMBS
154, NC25DMBS 192, NC2M4CBS 172, NC24DCBS
210 and NC34DCBS 192. Both the SBSA and
NCSBS were characterized by their infrared and
NMR spectra.10,11 Aqueous stock solutions of these com-
pounds (0.01 mol dmꢂ3) were prepared in doubly distilled
water, standardized by the iodimetric method and pre-
served in dark bottles to prevent their photochemical
deterioration.
Pure samples of amino acids (aspartic acid, glutamic
acid, aspargine and glutamine) (CDH, India) were em-
ployed. They were further assayed by the acetic acid–
perchloric acid method.12 Aqueous stock solutions of
these compounds (0.10 mol dmꢂ3) were used. All other
reagents employed were of the accepted grades of purity.
The ionic strength of the medium was maintained at
0.30 mol dmꢂ3 using a concentrated aqueous solution of
sodium nitrate (Merck).
Stoichiometry and product analysis
The stoichiometry of amino acid–NCSBS oxidations was
determined by equilibrating varying ratios of [NCSBS] to
[AA] in aqueous HClO4 at room temperature. The major
products of the oxidations were the corresponding alde-
hydes. The observed 1:1 stoichiometry may be repre-
sented by the following equation:
ArSO2NClꢂ þ RCHðNH3þÞCOOꢂ þ H2O
! ArSO2NH2 þ RCHO þ Clꢂ þ NH3 þ CO2
where Ar ¼ 4-XC6H4 (X ¼ H, CH3, C2H5, F, Cl or Br)
and i-X-j-Y-C6H3 [i-X-j-Y ¼ 2,3-(CH3)2, 2,4-(CH3)2,
2,5-(CH3)2, 2-CH3-4-Cl, 2,4-Cl2 or 3,4-Cl2] and R ¼
CH2COOH (Asp), CH2CH2COOH (Glu), CH2CONH2
(Asn) or CH2CH2CONH2 (Gln).
In a typical experiment, a mixture of aspartic acid
(0.02 mol dmꢂ3),
N-chloro-4-chlorobenzenesulphona-
(0.001 mol dmꢂ3
) and perchloric acid
mide
(0.03 mol dmꢂ3) was made up to 50 ml with water. The
mixture was allowed to stand for 24 h in the dark to
ensure completion of reaction. It was then treated with an
Copyright # 2004 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2004; 17: 848–864

864
B. T. GOWDA AND M. SHETTY
Table 17. Optimized values of Ea Log A and ÁSz for path 2 of the mechanism for the oxidation of amino acids (AA) by the
sodium salts of mono- and disubstituted N-chlorobenzenesulphonamides in aqueous perchloric acid
4-X-C6H4SO2NaNCl, where X ¼
Parameter
AA
H
CH3
C2H5
F
Cl
Br
Ea (kJ molꢂ1
)
Asp
Glu
Asn
Gln
Asp
Glu
Asn
Gln
Asp
Glu
Asn
Gln
52.7
50.8
56.9
54.9
5.2
4.9
6.1
5.6
52.6
50.4
57.1
54.7
5.1
4.9
5.9
5.7
52.7
51.5
57.1
54.7
5.2
4.7
5.9
5.6
50.9
50.4
55.5
53.7
5.4
5.0
6.2
5.8
50.3
49.7
54.5
52.3
5.5
5.1
6.4
6.0
50.1
47.5
53.4
51.4
5.5
5.4
6.6
6.2
Log A
ÁSz (J Kꢂ1 molꢂ1
)
ꢂ153.5
ꢂ154.6
ꢂ134.6
ꢂ145.0
ꢂ154.1
ꢂ153.5
ꢂ135.7
ꢂ143.8
ꢂ153.5
ꢂ157.0
ꢂ135.7
ꢂ143.8
ꢂ148.5
ꢂ152.9
ꢂ130.4
ꢂ140.5
ꢂ146.6
ꢂ151.2
ꢂ126.9
ꢂ133.5
ꢂ146.2
ꢂ143.9
ꢂ123.3
ꢂ133.0
AA
i-X-j-Y-C6H3SO2NaNCl, where i-X-j-Y ¼
2,3-(CH3)2
2,4-(CH3)2
2,5-(CH3)2
2-CH3-4-Cl
2,4-Cl2
3,4-Cl2
Ea (kJ molꢂ1
)
Asp
Glu
Asn
Gln
Asp
Glu
Asn
Gln
Asp
Glu
Asn
Gln
51.8
50.8
57.4
54.7
5.2
4.9
6.1
5.6
51.3
50.4
56.0
53.9
5.3
5.0
6.1
5.8
50.8
49.8
55.9
53.4
5.4
5.1
6.1
5.9
48.1
47.9
54.7
53.1
5.8
5.4
6.3
5.9
47.3
46.7
52.6
50.1
6.0
5.6
6.7
6.4
47.4
47.0
53.0
50.9
6.0
5.6
6.6
6.3
Log A
ÁSz (JKꢂ1 molꢂ1
)
ꢂ152.2
ꢂ154.1
ꢂ132.8
ꢂ143.6
ꢂ150.6
ꢂ152.9
ꢂ132.8
ꢂ141.5
ꢂ148.9
ꢂ151.2
ꢂ131.7
ꢂ139.5
ꢂ140.3
ꢂ144.5
ꢂ127.5
ꢂ139.0
ꢂ137.6
ꢂ140.8
ꢂ120.6
ꢂ128.6
ꢂ138.0
ꢂ141.7
ꢂ121.9
ꢂ131.5
excess of a saturated solution of 2,4-dinitrophenylhydra-
zine and set aside for 10 h. The precipitated 2,4-dinitro-
phenylhydrazone (DNP) was filtered off, dried and
recrystallized from ethanol. The product was found to
be identical (melting-point) with an authentic sample of
the DNP of formylacetic acid. In similar experiments
with other amino acids, the corresponding carbonyl
compounds were identified as their DNPs of carbonyl
compounds. In all cases, carbon dioxide and ammonia
were detected using baryta water and Nessler’s reagent,
respectively. The presence of aldehydes or ketones were
also confirmed by spot tests. The reduction products,
SBSA, were identified by TLC using light petroleum–
chloroform–butanol (2:2:1, v/v/v) as the solvent system
and iodine as spray reagent.14 The Rf values were
0.88, 0.91, 0.94, 0.93, 0.91, 0.84, 0.91, 0.96, 0.93, 0.95,
0.91 and 0.94 for BSA, 4MBSA, 4EBSA, 4FBSA,
4CBSA, 4BBSA, 23DMBSA, 24DMBSA, 25DMBSA,
2M4CBSA, 24DCBSA and 34DCBSA, respectively.
These Rf values of the reduced SBSA were virtually
identical with the values of the corresponding pure
SBSA.
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Copyright # 2004 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2004; 17: 848–864