Ru(III)-catalyzed oxidation of pyridoxine and albuterol in pharmaceuticals

Article abstract of DOI:10.1016/j.saa.2008.07.035

Ru(III) complexes with coordinated amide were synthesized and characterized by elemental, IR, mass, electronic, ESR spectral analysis, magnetic and conductance measurements and octahedral structures have been proposed. These complexes were used as catalys

Full text of DOI:10.1016/j.saa.2008.07.035

Spectrochimica Acta Part A 72 (2009) 204–208
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Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
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Short communication
Ru(III)-catalyzed oxidation of pyridoxine and albuterol in pharmaceuticals
More Ashok, Adapa V.S.S. Prasad, P. Muralidhar Reddy, Vadde Ravinder∗
Department of Chemistry, Kakatiya University, Warangal 506 009, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Ru(III) complexes with coordinated amide were synthesized and characterized by elemental, IR, mass,
electronic, ESR spectral analysis, magnetic and conductance measurements and octahedral structures
have been proposed. These complexes were used as catalysts for the oxidation of pyridoxine and albuterol
in pharmaceuticals in presence of hydrogen peroxide. The role of co-oxidant and the effect of reaction
time on the yields of oxidation products which were spectrophotometrically determined by condensing
them with sulfanilic acid in acid medium were investigated. Structures of the oxidation products were
established with the help of IR and NMR spectral analysis.
Received 5 November 2007
Received in revised form 20 July 2008
Accepted 23 July 2008
Keywords:
Catalysis
Oxidation
Pyridoxine
Albuterol
© 2008 Elsevier B.V. All rights reserved.
1. Introduction
were condensed with sulfanilic acid (SA) in acid medium [13] for
their spectrophotometric determination.
The development of ruthenium-catalyzed methods [1] for the
oxidation of primary [2] and secondary [3] alcohols to produce
carbonyl derivatives remains an important one in pharmaceutical
products [4]. But, these methods require either the presence of a
co-oxidant [5] or a prolonged oxidation time [6] leading to envi-
ronmental problems. Pyridoxine [7], the first isolated vitamin B6,
is oxidized to pyridoxal in biological system. Albuterol [7] is a beta-
adrenergic stimulant which has a highly selective action on the
receptors in bronchial smooth muscle, there by causing relaxation
of bronchial muscle fibres. In literature, some oxidation methods
of pyridoxine as hydrochloride (5-hydroxy-6-methyl-3,4-pyridine
dimethanol, hydrochloride, PYE) to pyridoxal (3-hydroxy-5-
(hydroxy methyl)2-methyl-4-pyridine carboxaldehyde, PYL) [8]
and albuterol (␣1[(tert-butyl amino)methyl]4-hydroxy m-xylene
␣,␣1-diol sulfate, 2:1 salt, AB) to its oxidation product (5-[(tert-
butyl amino)acetyl]-2-hydroxy benzaldehyde, OPAB) [9] were
reported. Even though some complexes were synthesized using
the [RuCl3(PPh3)3] [10–12], no amide complex of this precursor
was synthesized so far. Hence, Ru(III) complexes with coordinated
amide of the type RuCl2(PPh3)2(L2) (Complex-1–12) were synthe-
sized using the precursor [RuCl3(PPh3)3] and used as catalysts for
the oxidation of pyridoxine and albuterol (in pure form and phar-
maceutical formulations) in presence of hydrogen peroxide with
lesser oxidation times without using a co-oxidant. PYL and OPAB
2. Experimental
2.1. Instruments
The melting points of all the ligands and complexes were
determined on a Buchi-510 melting point apparatus. The per-
centages of carbon, hydrogen, nitrogen were determined using
a PerkinElmer CHN analyzer. The IR spectra were recorded in
KBr pellets on PerkinElmer-283 spectrophotometer. The scanning
rate was 6 min in the range of 4000–200 cm−1. MICROMASS-7070
spectrometer operating at 70 eV using a direct inlet system was
used for mass spectra. UV–visible spectra were recorded with Shi-
madzu UV-160A, a UV–visible double beam spectrophotometer
with matched quartz cells of path length 1 cm. ESR spectra were
recorded on JEOL-JES-FE-3X spectrometer. Gouy balance calibrated
with Hg[Co(NCS)4] was used for the determination of magnetic
susceptibilities of complexes in solid state at room temperature.
Conductance measurements were done on 10−3 M solution of com-
pounds in dichloromethane at room temperature using Digisun
Digital conductivity meter model DL-909.
2.2. Materials and reagents
RuCl3·3H2O (Johnson Matthey & Co. Ltd.), acetone (Qualigens)
and diethyl ether (Qualigens) were used as such. The precursor
RuCl3(PPh3)3 [10] and the 12 amide ligands viz. 2-(anilinocarbonyl)
benzoicacid (ACBA); 4-anilino-4-oxo but-2-enoicacid (AOBEA);
∗
Corresponding author. Tel.: +91 9390100594.
E-mail address: ravichemku@rediffmail.com (V. Ravinder).
1386-1425/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2008.07.035

M. Ashok et al. / Spectrochimica Acta Part A 72 (2009) 204–208
205
Table 1
Physical and analytical data of Ru(III) complexes with coordinated amide
Complex no.
Complex/formula
Mp (◦C)
Color
Yield (g)
Analysesfound(calculated)(%)
C
H
N
Ru
1.
2.
3.
4.
5.
6.
7.
8.
9.
RuCl2(PPh3)2(ACBA), C50H40Cl2NO3P2Ru
RuCl2(PPh3)2(AOBEA), C46H38Cl2NO3P2Ru
RuCl2(PPh3)2(AOBA), C46H40Cl2NO3P2Ru
RuCl2(PPh3)2(NACBA), C54H42Cl2NO3P2Ru
RuCl2(PPh3)2(NAOBEA), C50H40Cl2NO3P2Ru
RuCl2(PPh3)2(NAOBA), C50H42Cl2NO3P2Ru
RuCl2(PPh3)2(BACBA), C51 H40Cl2N3O3P2Ru
RuCl2(PPh3)2(BAOBEA), C47 H38Cl2N3O3P2Ru
RuCl2(PPh3)2(BAOBA), C47 H40Cl2N3O3P2Ru
RuCl2(PPh3)2(PHCBA), C50H41 Cl2N2O3P2Ru
RuCl2(PPh3)2(OPHBEA), C46H39Cl2N2O3P2Ru
RuCl2(PPh3)2(OPHBA), C46H41 Cl2N2O3P2Ru
242
235
231
249
245
243
279
275
271
242
234
231
Green
Green
Green
Brown
Brown
Brown
Black
Black
Black
Green
Green
Green
0.269 (72%)
0.261 (74%)
0.251 (71%)
0.295 (75%)
0.272 (73%)
0.265 (71%)
0.288 (74%)
0.281 (76%)
0.266 (72%)
0.269 (71%)
0.259 (72%)
0.274 (76%)
64.06 (64.10)
62.22 (62.30)
62.11 (62.16)
65.77 (65.72)
64.02 (64.10)
64.01 (63.96)
62.63 (62.70)
60.83 (60.90)
60.71 (60.77)
63.01 (63.09)
61.20 (61.26)
61.05 (61.12)
4.24 (4.27)
4.32 (4.28)
4.55 (4.50)
4.29 (4.25)
4.31 (4.27)
4.51 (4.47)
4.13 (4.09)
4.14 (4.10)
4.34 (4.31)
4.27 (4.31)
4.36 (4.32)
4.57 (4.54)
1.47 (1.49)
1.60 (1.58)
1.59 (1.57)
1.44 (1.41)
1.46 (1.49)
1.49 (1.49)
4.35 (4.30)
4.56 (4.53)
4.56 (4.52)
2.96 (2.94)
3.13 (3.10)
3.13 (3.10)
10.82 (10.79)
11.36 (11.39)
11.33 (11.37)
10.26 (10.24)
10.83 (10.79)
10.72 (10.76)
10.33 (10.34)
10.88 (10.90)
10.91 (10.88)
10.60 (10.62)
11.17 (11.20)
11.15 (11.18)
10.
11.
12.
4-anilino-4-oxobutanoicacid (AOBA); 2-[(1-naphthyl amino)
carbonyl] benzoic acid (NACBA); 4-(1-naphthylamino)4-oxobut-
2-enoicacid (NAOBEA); 4-(1-naphthyl amino)-4-oxobutanoicacid
(NAOBA); 2-[(1H-benzimidazol-2-yl amino)carbonyl]benzoic acid
(BACBA); 4-(1H-benzimidazol-2-ylamino)-4-oxobut-2-enoic acid
(15 min for PYE and 30 min for AB) at 60 ◦C. The contents of the
flask were cooled and transferred separately into 20-ml-calibrated
tubes. Now, sulfanilic acid solution (2 ml for PYL and 4 ml for AB)
was added and the tubes were heated for 5 min in boiling water
bath. Pink color was developed slowly. The tubes were cooled and
the total volumes were made up to 20 ml with double distilled
water. The absorbances of the colored solutions were measured
at 520 nm against their reagent blanks. The amounts of PYL and
OPAB formed during oxidation process were determined from their
respective calibration curves.
(BAOBEA);
4-(1H-benzimidazol-2-ylamino)-4-oxobutanoicacid
(BAOBA); 2-[(2-phenylhydrazino) carbonyl] benzoicacid (PHCBA);
4-oxo-4-(2-phenylhydrazino)but-2-enoic acid (OPHBEA); 4-oxo-
4-(2-phenyl hydrazino)butanoic acid (OPHBA) were synthesized
as previously reported [14]. Hydrogen peroxide solution (Merck,
30%) was used as it is. 0.1N hydrochloric acid solution (Qualigens)
was prepared by diluting 9.1 ml of conc. hydrochloric acid solution
to 1000 ml with double distilled water. 0.1N sulfanilic acid solution
(Merck) was prepared by dissolving 1.071 g in 100 ml of double
distilled water.
3. Results and discussion
3.1. Characterization of Ru(III) complexes with coordinated amide
3.1.1. Physical and analytical data
2.3. Drug solutions
Twelve Ru(III) complexes with coordinated amide were syn-
thesized using the precursor, RuCl3(PPh3)3. The percentages of
carbon, hydrogen and nitrogen were determined experimentally
using CHN analyzer. The percentage of ruthenium in complexes
was determined by literature method [15]. The physical and ana-
lytical data (Table 1) for the newly synthesized Ru(III) complexes
is in good agreement with the proposed molecular formulae viz.
RuCl2(PPh3)2(L2).
Standard stock solutions of pyridoxine hydrochloride or
albuterol sulfate (1 mg/ml) were prepared by dissolving 100 mg
of pure pyridoxine hydrochloride or albuterol sulfate in 100 ml
of double distilled water. The stock solutions were diluted with
double distilled water to get the working pure drug solutions of
100 ␮g/ml. An accurately weighed amount of tablet powder equiv-
alent to 100 mg of pyridoxine hydrochloride or albuterol sulfate was
extracted separately with chloroform (4 × 20 ml) and filtered. The
filtrate was evaporated to dryness and the residue was dissolved
in 100 ml of double distilled water to achieve a concentration of
1 mg/ml. This solution was diluted with double distilled water to
get the working pharmaceutical solutions of 100 ␮g/ml.
3.1.2. Infrared spectral analysis
The infrared spectra of the free amide ligands and precursor are
compared with the Ru(III) complexes to elucidate the binding mode
of the amide ligands to ruthenium. The non-involvement of amide
nitrogen in coordination is confirmed by the consistent stretching
frequencies of amide nitrogen in the range of 3375–3264 cm−1 in
ligand and complexes spectra. However, in the IR spectra of Ru(III)
complexes having ligands derived from benzimidazoles viz. BACBA,
BAOBEA and BOABA, ꢀN-H (benzimidazole) modes are observed at
3360, 3368 and 3365 cm−1, respectively. Similarly, in the IR spec-
tra of complexes having ligands derived from phenylhydrazines
viz. PHCBA, OPHBEA and OPHBA, ꢀN–H (phenylhydrazine) modes
are observed at 3362, 3367 and 3360 cm−1, respectively. Stretching
frequencies of amide oxygen of complexes have undergone neg-
ative shifts by 30–40 cm−1 from 1670 cm−1 of free amide ligands
indicating the coordination of amide oxygen to ruthenium [16]. In
free ligands, strong absorption bands are found around 1710 and
2.4. Recommended procedures
2.4.1. Synthesis of ruthenium(III) catalysts
To RuCl3(PPh3)3 solution (0.4 mmol in 20 ml acetone), lig-
and solution (0.4 mmol in 20 ml acetone) was added and the
reaction mixture was stirred magnetically for 3 h. The resulting
solution was concentrated to 5 ml under reduced pressure and
a few ml of diethylether was added to initiate the crystalliza-
tion. The precipitate formed was separated by suction filtration,
washed with diethylether and dried in vacuum. The crystalline
compound obtained was recrystallized using dichloromethane and
diethylether mixture.
1340 cm−1 corresponding to ꢀC
stretching and ␦O–H deforma-
O
tion modes of vibration. In complexes spectra, these bands are not
observed, but new bands are observed in the ranges of 1548–1529
2.4.2. Ruthenium-catalyzed oxidation method
and 1388–1348 cm−1 corresponding to ꢀCOO (asymmetric) and
−
In a 100 ml round bottom flask, 4 ml of pyridoxine hydrochloride
or albuterol sulfate solution (pure or pharmaceutical formulation),
hydrogen peroxide (4 ml for PYE and 6 ml for AB) and 0.01 mmol of
Ru(III) catalyst were taken. The contents of the flask were refluxed
−
ꢀCOO (symmetric) vibrations indicating the participation of oxy-
gen atom of carboxylic group in chelation [12]. Similarly, a strong
absorption band in precursor spectrum as well as complexes

206
M. Ashok et al. / Spectrochimica Acta Part A 72 (2009) 204–208
Table 2
Infrared spectral data of Ru(III) complexes with coordinated amide
Complex no.
Complex
Selected IR bands (cm−1
)
−
−
ꢀN–H (amide)
ꢀC (amide)
ꢀCOO (asy)
ꢀCOO (sy)
ꢀRu–P
ꢀRu–Cl
ꢀRu–Cl
O
1.
2.
3.
4.
5.
6.
7.
8.
9.
RuCl2(PPh3)2(ACBA)
RuCl2(PPh3)2(AOBEA)
RuCl2(PPh3)2(AOBA)
RuCl2(PPh3)2(NACBA)
RuCl2(PPh3)2(NAOBEA)
RuCl2(PPh3)2(NAOBA)
RuCl2(PPh3)2(BACBA)
RuCl2(PPh3)2(BAOBEA)
RuCl2(PPh3)2(BAOBA)
RuCl2(PPh3)2(PHCBA)
RuCl2(PPh3)2(OPHBEA)
RuCl2(PPh3)2(OPHBA)
3375
3354
3373
3264
3268
3272
3360
3368
3365
3362
3367
3360
1658
1660
1662
1669
1667
1652
1653
1659
1661
1662
1661
1652
1546
1548
1531
1547
1529
1553
1545
1541
1542
1541
1542
1541
1371
1378
1384
1383
1382
1383
1388
1386
1382
1386
1388
1348
541
548
541
542
539
538
537
538
540
541
542
539
420
418
440
432
425
415
416
422
430
436
423
417
325, 317
342, 320
330, 321
335, 312
338, 309
339, 311
341, 312
338, 303
337, 302
331, 301
332, 305
343, 306
10.
11.
12.
2
2
spectra was found around 540 cm−1 due to the presence of Ru–P
bond [17]. The coordination of oxygen atom of ligand with ruthe-
nium is indicated by the presence of a band in the range of
440–415 cm−1. Two bands appear around 340 and 320 cm−1 in
complexes spectra indicating the presence of two chlorides in cis
position around ruthenium centre. All other characteristic bands
due to triphenylphosphine are also present in the expected regions
in precursor spectrum and complexes spectra [18] (Table 2). IR
spectrum of RuCl2(PPh3)2(ACBA) is shown in Fig. 1.
doublet levels in the order of increasing energy are A2g and T1g
which arise from the t42ge1 configuration. In most of the Ru(III)
g
complexes the electronic spectra show only charge transfer bands.
Those at 480–540 nm have been assigned to the 2T2g → A2g tran-
2
sition, in conformity with assignments made for similar octahedral
Ru(III) complexes. The other bands in the 220–280 nm region have
been assigned to charge transfer transitions [11].
3.1.5. ESR spectral analysis
The ESR spectra of all the powdered samples of Ru(III) complexes
were recorded at room temperature. They exhibit normal axial dis-
tortion with three g values. The peak high field side is more intense
than the peak at low field side. The g values calculated are in the
range of 1.84–2.40, which are within the literature range [19]. The
average g values of these complexes are very close indicating that
all of them have similar type of distortion [20].
3.1.3. Mass spectral analysis
The proposed molecular formula of Ru(III) complex was con-
firmed by the mass spectral analysis by comparing its molecular
formula weight with m/z value. The mass spectra contain molecu-
lar ion peaks at m/z (M+) 936 (Complex-1), 886 (Complex-2), 888
(Complex-3), 987 (Complex-4), 936 (Complex-5), 938 (Complex-
6), 976 (Complex-7), 927 (Complex-8), 928 (Complex-9), 951
(Complex-10), 902 (Complex-11) and 903 (Complex-12). This data
is in good agreement with the respective molecular formulae. Mass
spectrum of RuCl2(PPh3)2(ACBA) is presented in Fig. 2.
3.1.6. Magnetic and conductance measurements
The magnetic susceptibility measurements have been carried
out for Ru(III) complexes and the values lie between 1.7 and 1.9 BM
indicating t5 configuration and a low spin 3+ oxidation state for
2g
3.1.4. Electronic spectral analysis
ruthenium in all these complexes. Hence, the compounds are para-
magnetic in nature [11]. Molar conductance measurements made
for all the Ru(III) complexes in dichloromethane reveals that all the
compounds are non-electrolytes.
Electronic spectra of all the complexes in dichloromethane
showed two to four bands in the 240–560 nm region. The ground
state of Ru(III) (t5 configuration) is T2g and the first excited
2
2g
Fig. 1. IR spectrum of RuCl2(PPh3)2(ACBA).

M. Ashok et al. / Spectrochimica Acta Part A 72 (2009) 204–208
207
Fig. 2. Mass spectrum of RuCl2(PPh3)2(ACBA).
On the basis of analytical and spectral data, octahedral struc-
tures (Scheme 1) have been proposed for all the Ru(III) complexes
with coordinated amide.
the oxidation was stated at about 15 min and completed within
30 min and the percent yield of the product was found to be 98.18%.
Almost similar tendencies were observed with the remaining 11
Ru(III) catalysts (Complex-2–12). 0.01 mmol of ruthenium cata-
lyst is found to be sufficient for the reaction. The Ru(III) catalyst
can be used three times after its recovery. The best results were
obtained when the temperatures of reaction mixtures were set to
60 ◦C. The role of co-oxidant, i.e. N-methyl morpholine-N-oxide,
which was generally used in the oxidation of benzyl alcohol [2],
was also investigated. The yields of oxidation products in the pres-
ence as well as in the absence of co-oxidant were found to be one
and the same. Hence, presence of co-oxidant was not necessary
when present catalysts are used for oxidation. After completion
of the oxidation of drugs, the mixtures were cooled. The residual
hydrogen peroxide after competition of oxidation is removed by
adding 1 ml of 0.01 M potassium permanganate solution. The con-
densation of oxidation products of pyridoxine and albuterol were
carried out with five amino group compounds viz. sulfanilic acid
[13], 2-thio barbituric acid [21], thiosemicarbazide [22], o-toluidine
[23] and diphenylamine [24]. Since, sulfanilic acid produces either
high molar absorptivity it was chosen for condensation of oxida-
tion products. The adequate volumes of sulfanilic acid required for
condensation are found to be 2 ml for pyridoxal and 4 ml for the oxi-
dation product albuterol. Maximum wavelength of both the colored
products were found to be 520 nm and were stable up to 1 h.
3.2. Catalytic applications
3.2.1. Development of catalytic oxidation method
The oxidation of pyridoxine and albuterol using hydrogen per-
oxide was carried out in the presence of ruthenium catalyst. To
produce a high yield of oxidation products, a continuous feed of
hydrogen peroxide was employed. 4 ml of hydrogen peroxide for
pyridoxine and 6 ml of hydrogen peroxide for albuterol were found
to be optimum for oxidation. To assess whether any direct oxida-
tion occurred upon addition of hydrogen peroxide, it was added to
pyridoxine and albuterol separately in the absence of ruthenium
catalyst at 60 ◦C. The oxidation of pyridoxine was started at about
30 min, completed after 2 h. The yield of oxidation product, i.e. pyri-
doxal was found to be 82.62%. But, in the presence of ruthenium
catalyst (Complex-1), the oxidation was started at about 10 min,
completed within 20 min and the yield of the oxidation product was
found to be 96.66%. Similarly, the oxidation of albuterol was started
at about 45 min, completed after 3 h and the percent yield of oxida-
tion product was found to be 85.83% in the absence of ruthenium
catalyst. But, in the presence of ruthenium catalyst (Complex-1),
3.2.2. Product analysis
In order to establish the structures of oxidation products, IR and
NMR spectra of pyridoxine and albuterol were compared with the
spectra of their oxidation products. The infrared spectra of pyridox-
ine and albuterol show a broad peak around 3455 cm−1 due to O–H
stretching. They do not show any peak around 1680 cm−1 indicating
the absence of carbonyl group. The appearance strong absorption
band in PYL and OPAB around 1680 cm−1 indicates the presence
of carbonyl group due to C O stretching after oxidation. This sup-
ports the oxidation of primary alcoholic group to aldehyde group
in PYL and oxidation of primary and secondary alcoholic groups to
aldehyde and ketone groups, respectively, in OPAB. This fact was
further supported by the disappearance of the broad peak around
3055 cm−1 due to O–H stretching in OPAB. However, the broad peak
at 3500 cm−1 was retained in PYL, since the alcoholic group at meta
position of the pyridine ring does not undergo oxidation. Hence, in
PYE, the alcoholic group at para position to pyridine ring which has
relatively less steric hindrance when compared to alcoholic group
Scheme 1. Structures of Ru(III) complexes with coordinated amide.

208
M. Ashok et al. / Spectrochimica Acta Part A 72 (2009) 204–208
Scheme 2. Colored products formed between PYL or OPAB and SA.
Table 3
when compared to PYL (Table 3), which may be due to the presence
of two alcoholic groups in AB.
Yields of PYL and OPAB formed by using Ru(III) complexes with coordinated amide
Complex no.
Complex
Yield (%)
PYL
4. Conclusions
OPAB
1.
2.
3.
4.
5.
6.
7.
8.
9.
RuCl2(PPh3)2(ACBA)
RuCl2(PPh3)2(AOBEA)
RuCl2(PPh3)2(AOBA)
RuCl2(PPh3)2(NACBA)
RuCl2(PPh3)2(NAOBEA)
RuCl2(PPh3)2(NAOBA)
RuCl2(PPh3)2(BACBA)
RuCl2(PPh3)2(BAOBEA)
RuCl2(PPh3)2(BAOBA)
RuCl2(PPh3)2(PHCBA)
RuCl2(PPh3)2(OPHBEA)
RuCl2(PPh3)2(OPHBA)
96.66
97.27
96.02
97.29
97.82
95.03
97.54
98.25
98.15
96.54
97.85
96.35
98.18
98.84
97.58
98.55
98.95
96.78
98.88
99.65
98.85
97.90
98.54
97.85
Ru(III) complexes with coordinated amide ligands were syn-
thesized from RuCl3(PPh3)3. Octahedral structures were assigned
to these complexes based on elemental and spectral data. These
complexes were found to be efficient for the oxidation of alcoholic
drugs. This catalytic method is environmentally friendly, simple to
set-up, requires short reaction times and produces high product
yields.
10.
11.
12.
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at meta position may be oxidized to aldehyde [25]. Oxidation of
alcoholic groups to carbonyl groups is further confirmed by NMR
spectral analysis. The NMR spectra of pyridoxine show peaks at 8.37,
5.94, 5.13 and 2.86 ␦ corresponding to aromatic, methylene, alco-
holic and alkyl protons, respectively, where as its oxidation product
shows one additional peak at 9.50 ␦. The NMR spectra of albuterol
shows peaks at 6.55, 5.83, 4.66, 3.61 and 1.12 ␦ corresponding to
aromatic, alcoholic, imino, methylene and methyl protons, respec-
tively, where as its oxidation product show one additional peak at
9.60 ␦. The peak at 5.83 was not shown in the spectra of OPAB, indi-
cating the absence of alcoholic proton. The appearance of peaks at
9.50 or 9.60 ␦ in both the spectra of oxidation products, indicates the
presence of aldehyde protons in the oxidation products and there
by confirms the oxidation of alcoholic groups to aldehyde groups.
3.2.3. Chemistry of colored species and yields of oxidation
products
The pink colored products are formed due to the condensation
between the newly formed carbonyl groups in PYL and OPAB and
amino group of sulfanilic acid in acid medium with the elimination
of water molecule(s) (Scheme 2). The yields of oxidation products of
pyridoxine and albuterol with all the 12 ruthenium catalysts were
determined spectrophotometrically. The yields of OPAB are high