Photodegradation of Hydrophobic Pyridineketoximes in Toluene and Heptane

Article abstract of DOI:10.1111/php.12453

The goal of the research was to study the reactivity of the hydrophobic 2- and 3-pyridineketoximes under exposure to UV-VIS light. The photodegradation was conducted in both toluene and heptane for 10 h under atmosphere of argon. Ten-hour irradiation experiments demonstrated that the pyridineketoximes underwent the facile E-Z photoisomerization, photo-Beckmann rearrangement, and to a lesser extent, the photosubstitution to the pyridine ring. From LC-MS and NMR analysis of the irradiated solutions, it was found that the photosubstitution proceeded to give the corresponding 6-substituted 2- or 3-pyridylketoxime via the replacement of the ring hydrogen by the benzyl or heptyl group. The photo-Beckmann rearrangement led to the formation of the corresponding amides, but also other products formed in the photo-decomposition reaction.

Full text of DOI:10.1111/php.12453

Photochemistry and Photobiology, 2015, 91: 786–796
Photodegradation of Hydrophobic Pyridineketoximes in Toluene and
Heptane
Karolina Wieszczycka*1 and Joanna Zembrzuska2
1Poznan University of Technology, Institute of Chemical Technology and Engineering, Poznan, Poland
2Poznan University of Technology, Institute of Chemistry and Technical Electrochemistry, Poznan, Poland
Received 16 May 2014, accepted 8 March 2015, DOI: 10.1111/php.12453
ABSTRACT
the oxime concentration, type of solvent and the presence of
added species such as salts or mineral acid. The Beckmann rear-
rangement of hydroxyoxime has also been observed, however,
the photodecomposition proceeded to corresponding benzoxaz-
oles. Such rapid degradation of the pyridineketoxime extractants
has not been observed in long-term extraction tests, but in the
case of the 3-pyridineketoximes, a 2-week storage of the com-
pound as a toluene solution caused an increase in a concentra-
tion of (Z)-isomer being a poorly soluble in both aromatic and
aliphatic diluents. The extractant containing the oxime group at
2 position of the pyridine ring appears to be more stable than an
appropriate 3-pyridineketoxime, but even in this case, the (E-Z)
isomerization could change the oxime to an isomer being unable
to form a stable metal complexes. Therefore, the objective of
this study was to evaluate the photochemical reactivity of the
hydrophobic 2- and 3- pyridineketoximes: (Z)-oxime of 1-(2-pyr-
idyl)tridecan-1-one and (E)-oxime of 1-(3-pyridyl)tridecan-1-one
(Fig. 1) and to identify of possible photodegradation products.
The research was carried out in toluene and heptane using UV–
VIS light irradiation. The influence of the presence of com-
plexed copper(II) ions, trace amounts of water and aqueous
solutions of hydrochloric acid on the photostability of the hydro-
phobic pyridineketoximes was also studied.
The goal of the research was to study the reactivity of the
hydrophobic 2- and 3-pyridineketoximes under exposure to
UV-VIS light. The photodegradation was conducted in both
toluene and heptane for 10 h under atmosphere of argon.
Ten-hour irradiation experiments demonstrated that the pyr-
idineketoximes underwent the facile E-Z photoisomerization,
photo-Beckmann rearrangement, and to a lesser extent, the
photosubstitution to the pyridine ring. From LC-MS and
NMR analysis of the irradiated solutions, it was found that
the photosubstitution proceeded to give the corresponding 6-
substituted 2- or 3-pyridylketoxime via the replacement of
the ring hydrogen by the benzyl or heptyl group. The photo-
Beckmann rearrangement led to the formation of the corre-
sponding amides, but also other products formed in the
photo-decomposition reaction.
INTRODUCTION
Oxime ligands containing the pyridyl ring are a very interesting
group of compounds in the chemistry of metal complexes. The
compounds are widely used as analytical reagents (1–3), in
medicinal preparations (4,5) and as components of photody-
namic herbicides (6). The extraction ability of hydrophobic
2- and 3- pyridineketoximes dissolved in aromatic as well as in
aliphatic diluents toward copper(II), zinc(II), cadmium(II), nickel
(II) and iron(III) from aqueous solutions has been broadly inves-
tigated (7–16). The results of our works have shown the possi-
bilities of the pyridineketoximes as extractants for recovery of
metals from industrial processes. The resistance of extractants to
light is also important during industrial operations when extrac-
tion and stripping are carried out with open mixers and settlers
in countries where exposure to light is unavoidable. Even
though in this type of installation the exposure to solar light is
limited, the loss of the extractant due to degradation is still
observed. In particular, hydroxyoxime and organophosphorous
metal extractants have been extensively studied (17–24). These
compounds degraded under exposure to light and the rate of the
photodegradation was influenced by temperature, and the pres-
ence of water, complexed metal and mineral acid. However, in
the case of the hydroxyoxime extractants the studies showed that
E-Z isomerization was the major process and was affected by
MATERIALS AND METHODS
Reagents. Toluene (p.a., Chempur) and heptane (anhydrous, 99%, Sigma-
Aldrich) were used as organic diluents. Tridecanal (95%, Sigma Aldrich)
after a pressure distillation was used as a GC standard. Chloride salts of
metals and other chemicals were of analytical grade. MS-grade methanol
(LC-MS, Sigma Aldrich) with addition of ammonium acetate (p.a., Sigma
OH
N
R
R
N
N
N
Z- (2-oxime)
E- (3-oxime)
HO
Figure 1. Structure of degraded pyridylketoximes: Z-(2-Oxime) – (Z)-1-
(2-pyridyl)tridecan-1-one oxime, E-(3-Oxime) – (E)-1-(3-pyridyl)tridecan-
1-one oxime.
*Corresponding author email: karolina.wieszczycka@put.poznan.pl (Karolina Wie-
szczycka)
© 2015 The American Society of Photobiology
786

Photochemistry and Photobiology, 2015, 91 787
Aldrich) were used as a mobile phase for LC-MS/MS. The LC-grade
water (below 1 [lS cmÀ1]) was prepared by reverse osmosis in a Demi-
wa 5ROI system from Watek (Ledec and Sazavou, Czech Republic), fol-
lowed by double distillation from a quartz apparatus. Only freshly
distilled water was used.
CH2); 0.88 (t., 3H, CH3); 13C NMR (100 MHz; CDCl3) d (ppm): 165.6;
151.7; 148.0; 147.9; 134.9; 130.5; 123.2; 40.1; 31.7; 29.5–29.9; 22.5;
13.9.
N-(3-pyridine)tridecanoylamide was obtained by a Beckmann rear-
rangement reaction catalyzed by thionyl chloride (30). According to the
reaction’s procedure, a mixture containing chloroform, (E)-oxime of 1-(3-
pyridyl)tridecan-1-one and thionyl chloride was boiled under reflux for
6 h. The liquid obtained after evaporation of chloroform was dissolved in
ethanol and the solution was made alkaline with NaOH. Filtration and
evaporation of ethanol gave N-(3-pyridyl)tridecanoylamide as white crys-
tals (10% yield; m.p. 173.6–174.9°C; 1H NMR (400 MHz; CDCl3), d
(ppm): 9.70 (br., s., 1H, NH), 9.01 (d.,1H, Hpy(2), J = 2.3 Hz) 8.39
(d.d., 1H, Hpy(6), J = 4.7 and 1.6 Hz), 8.28 (d.d.d.,1H, Hpy(4), J = 2.3,
8.2 and 1.6 Hz), 7.47 (t.d, 1H, Hpy(5), J = 8.2 and 4.7 Hz), 1.68 (t., 2H,
CH2-CO), 1.28–1.22 (m., 20H, CH2), 0.87 (t., 3H, CH3); 13C (100 MHz;
CDCl3) d (ppm): 156.5; 139.9; 138.2; 136.9; 132.2; 130.1; 36.1; 32.0;
29.7–25.5; 22.7; 13.9. GC-TOFMS (60 eV) m/z (%): 289 (8.7); 195
(7.1); 153 (8.3); 136 (38.1); 94 (100); 43 (12).
Synthesis of pyridinektoximes. The (E) and (Z)-oxime of 1-(2-pyridyl)
tridecan-1-one and 1-(3-pyridyl)tridecan-1-one were synthesized in the
two-stage process (7,10,25,26): the synthesis of pyridineketones from
pyridinecarbonitryle and alkyl magnesium bromide in diethyl ether as dil-
uent and the oximation reaction of the alkyl-pyridyl ketones by hydroxyl-
amine hydrochloride in ethanol solutions in the presence of Na2CO3 (pH
6–7). 1H and 13C NMR were used to prove the structure of the synthe-
sized oximes (yields: 1-(2-pyridyl)tridecan-1-one oxime – 42%, 1-(3-pyr-
idyl)tridecan-1-one oxime – 68%; purity 99.8%). Oxime of 1-(2-pyridyl)
tridecan-1-one was mainly obtained as a (Z)-stereoisomer and the separa-
tion of (E) from (Z)-stereoisomer (mol fraction 0.01: 0.99) was performed
according to procedure described by Cibulka et al. (27). Oxime of 1-(3-
pyridyl)tridecan-1-one also contained both (Z)- and (E)-stereoisomer (mol
fraction 0.09: 0.91), but the isolation of the isomers was possible by dis-
solution of (E)-isomer of 1-(3-pyridyl)tridecan-1-one oxime in isooctane.
The (Z)-isomer remained as a precipitate and after recrystalization from a
minimum quantity of hot ethanol yielded the (Z)-oxime of 1-(3-pyridyl)
tridecan-1-one.
3-aminopyridine and tridecanoic acids were also observed as the by-
products of the Beckmann rearrangement (3% yield).
3-aminopyridine (31): 1H NMR (400 MHz; CDCl3), d (ppm): 8.05 (s,
1H, Hpyr(2)), 8.01 (d, 1H, Hpyr(6), J = 7.5 Hz), 7.09 (d.d.,2H, Hpyr(5),
J = 6.8 and 7.2 Hz), 6.95 (d., 2H, Hpyr(4), J = 7.0 Hz), 3.71 (br., s., 2H,
N-H); 13C NMR (100 MHz CDCl3) d (ppm): 143.1, 140.1 137.0, 122.9,
121.7.
(E)-oxime of 1-(2-pyridyl)tridecan-1-one: m.p. 61.6–63.1°C (27); 1H
NMR (400 MHz; CDCl3) d(ppm): 8.36 (s., 1H, OH); 8.68 (d, 1H,
Hpy(6), J = 4.2 Hz); 7.78 (d, 1H, Hpy(3), J = 7.9 Hz); 7.72 (t.d., 1H,
Hpy(4), J = 7.5 and 1.7 Hz)); 7.21 (m., 1H, Hpy(5)); 3.28 (t., 2H, CH2);
1.58 (q, 2H, CH2); 1.27–1.29 (m, 18H, CH2); 0.91 (t, 3H, CH3); 13C
Tridecanoic acid m.p. 34.2–36.6°C (CAS No.: 638-53-9); 1H NMR
(400 MHz; CDCl3), d (ppm): 10.98 (br. s.,1H, O-H); 2.34 (t., 2H, CH2);
1.65 (q., 2H, CH2); 1.28–1.22 (m., 18H, CH2); 0.87 (t., 3H, CH3); 13C
NMR (100 MHz; CDCl3) d (ppm): 180.8; 34.3; 32.0; 29.7–29.2; 25.2;
22.8; 13.9.
NMR (100 MHz; CDCl3)
d (ppm): 160.6; 154.0; 149.0; 136.3;
123.4; 120.9; 30.7; 29.3; 29.2; 29.7; 29.8; 29.9; 29.9; 29.9; 29.7; 31.9;
22.7; 14.1
The Beckmann rearrangement reaction catalyzed by thionyl chloride
was also applied to a synthesis of N-(2-pyridyl)tridecanoylamide, but the
expected product degraded immediately to 2-aminopyridine and trideca-
noic acid.
(Z)-oxime of 1-(2-pyridyl)tridecan-1-one: m.p. 56.1–57.4°C (27); 1H
NMR (400 MHz; CDCl3) d(ppm): 9.53 (s., 1H, OH); 8.67 (d.d, 1H,
Hpy(6), J = 4.8 and 1.8 Hz); 7.85 (t, 1H, Hpy(3), J = 7.6 Hz); 7.69 (t.d.,
1H, Hpy(4), J = 7.7 and 1.5 Hz)); 7.35 (d.d., 1H, Hpy(5), J = 4.8 and
7.4 Hz); 3.03 (t., 2H, CH2); 1.62 (q, 2H, CH2); 1.27–1.29 (m, 18H,
CH2); 0.91 (t, 3H, CH3); 13C NMR (100 MHz; CDCl3) d (ppm): 154.0;
160.7; 149.0; 136.3; 123.5; 120.9; 31.9; 29.4; 29.3; 29.7; 29.9; 29.9;
29.9; 29.9; 29.7; 31.9; 22.7; 14.1
2-aminopyridine (31): 1H NMR (400 MHz; CDCl3) d (ppm): 8.11 (d.,
1H, Hpyr(2), J = 4.4 Hz); 7.45 (t., 1H, Hpyr(4), J = 7.0 Hz); 6.66 (t., 1H,
Hpyr(5)), 6.44 (d., 1H, Hpyr(3) J = 7.4 Hz); 4.62 (br. s., 2H, N-H); 13C
NMR (100 MHz; CDCl3), d (ppm): 159.1; 147.8; 138.4; 114.9; 109.2.
Photostability studies of oximes. 1-(2-pyridyl)tridecan-1-one oxime
and 1-(3-pyridyl)tridecan-1-one oxime dissolved in toluene or heptane
(E)-oxime of 1-(3-pyridyl)tridecan-1-one: m.p. 73.5–75.1°C; 1H NMR
(400 MHz; CDCl3) d(ppm): 10.6 (br. s, 1H, OH); 8.6 (d.d., 1H, Hpy(6),
J = 1.4 and 4.9 Hz); 7.93 (d.d.d., 1H, Hpy(4), J = 2.6; 1.8 and 1.0 Hz);
7.32 (d.d.,1H, Hpy(5), J = 5.1 and 2.0 Hz); 8.9 (d., 1H, Hpy(2)
J = 2.2 Hz,); 2.71 (t., 2H, CH2); 1.54 (q., 2H, CH2); 1.31–1.24 (m.,
18H, CH2); 0.86 (t., 3H, CH3); 13C NMR (100 MHz; CDCl3) d(ppm):
147.2; 132.2; 133.7; 149.3; 122.9; 157.0; 32.8; 31.6; 29.8; 29.6; 29.3;
29.1; 26.2; 25.6; 22.5; 14.0.
and their complexes with copper(II) chloride (1 9 10À3 mol oxime LÀ1
)
dissolved in toluene were irradiated in a Heraeus photoreactor of 120 mL
volume containing a medium pressure mercury lamp TQ 150 W (Herae-
us) and quartz filter (1 mL optical length) (32–35). The lamp was posi-
tioned within the inner part of the photoreactor, and cooling water was
circulated through a Pyrex jacket surrounding the tube. Argon was passed
through the solutions with a stationary flow of 2 mL minÀ1 at 22–23°C
during the irradiation. Agitation of the reaction mixture was provided by
a magnetic stirrer. The photodegradation was repeated two times with a
standard deviation = 5–8%. The photon fluence of the mercury lamp was
determined by chemical actinometry using uridine (254 nm) and potas-
sium ferrioxalate (366 nm), and the lamp radiated the reaction solution
with the intensity of 0.064 9 10À3 einstein LÀ1 minÀ1 at 254 nm and
0.071 9 10À3 einstein/(Lmin) at 366 nm. The samples were collected at
1, 2, 5, 10, 15, 30, 60, 120, 180, 240, 300, 360, 420, 480, 540 and
600 min of UV-Vis exposure. Analyses were performed using the follow-
ing techniques: NMR (1H, 13C), UV-VIS spectroscopy, LC-MS/MS and
GC-TOFMS.
(Z)-oxime of 1-(3-pyridyl)tridecan-1-one: m.p. 103.1–104.7°C; 1H
NMR (400 MHz; CDCl3) d (ppm): 10.7 (br. S.,1H, OH); 8.56 (dd, 1H,
Hpy(6), J = 1.4 and 4.9 Hz); 7.91 (d.d.d., 1H, Hpy(4), J = 2.6; 1.8 and
1.0 Hz); 7.36 (d.d.,1H, Hpy(5), J = 5.0 and 1.9 Hz); 8.72 (d, 1H, Hpy(2)
J = 2.2 Hz,); 2.68 (t, 2H, CH2); 1.54 (q, 2H, CH2); 1.31–1.24 (m, 18H,
CH2); 0.86 (t,3H, CH3); 13C NMR (100 MHz; CDCl3) d (ppm): 157.0;
149.3; 147.2; 133.7; 132.2; 122.9; 32.8; 31.6; 29.8; 29.6; 29.3; 29.1;
26.2; 25.6; 22.5; 14.0.
Synthesis of Beckmann rearrangement products. N-dodecylpyridine-2-
carboxamide and N-dodecylpyridine-3-carboxamide were obtained in a
direct reaction of dodecylamine with picolinic or nicotinic acid, respec-
tively (28,29). The mixtures were heated to reflux (200–215°C) for 12 h,
cooled and extracted with diethyl ether. The extracts were washed with
5% NaHCO3, brine and water. After the solvent removal the amides were
crystalized from an ethanol–water solution.
Isolation of photoproducts. Photosubstitution products were identified
by NMR (1H and 13C) and their structures were elucidated after isolation
by TLC or on a silica column using a mixture of ethyl acetate and di-
chloromethane as a developing solvent.
N-dodecylpyridine-2-carboxamide (28): m.p. 47.1–48.4°C; 1H NMR
(400 MHz; CDCl3) d(ppm): 8.54 (d.d., 1H, Hpy(6), J = 1.7 and 4.6 Hz),
8.21 (d., 1H, Hpy(3), J = 2.4 Hz), 8.06 (s., 1H, NH); 7.85 (t.d.d., 1H,
Hpy(4); J = 2.4, 7.9 and 1.7 Hz); 7.42 (t.d., 1H, Hpy(5); J = 7.9 and
4.6 Hz); 3.47 (q., 2H, -CH2-N); 1.30–1.26 (m., 20H, CH2); 0.88 (t., 3H,
CH3); 13C NMR (100 MHz; CDCl3) d (ppm): 164.3; 150.3; 147.9;
137.4; 126.2; 122.1; 42.1; 31.7; 29.5–29.9; 22.5; 13.9.
1-(6-heptylpyridin-2-yl)tridecan-1-one oxime; 1H NMR (400 MHz;
CDCl3), d (ppm): 9.67 (s., 1H, OH); 7.45 (d, 1H, Hpy(3)); 7.69 (d., 1H,
Hpy(4)); 7.35 (d., 1H, Hpy(5),); 3.20 (t., 2H, CH2); 2.60 (t., 2H, CH2);
1.58–1.62 (q, 4H, CH2); 1.26–1.30 (m, 26H, CH2); 0.89–0.92 (t, 6H,
CH3); 13C NMR (100 MHz; CDCl3) d (ppm): 157.4; 157.1; 153.5;
138.8; 123.0; 118.5; 34.5; 31.3, 32.0; 29.2; 29.1; 29.7; 29.9; 29.9; 29.9;
29.8; 29.5; 31.8; 22.6; 14.0; MS (ESI) (m/z ratio) 389.4 (MH)+.
1-(6-benzylpyridin-2-yl)tridecan-1-one oxime; 1H NMR (400 MHz;
CDCl3), d (ppm): 13C (100 MHz; CDCl3) d (ppm): 9.67 (s., 1H, OH);
7.45 (d, 1H, Hpy(3)); 7.69 (d., 1H, Hpy(4)); 7.35 (d., 1H, Hpy(5),); 7.31
(t., 2H, Hb(3)); 7.20 (t., 1H, Hb(4)); 7.13 (d., 2H, Hb(2)); 4.17 (s., 2H,
CH2); 2.93 (t., 2H, CH2); 1.62 (q, 2H, CH2); 1.27–1.29 (m, 18H, CH2);
N-dodecylpyridine-3-carboxamide (29): m.p. 76.8–78.1°C; 1H NMR
(400 MHz; CDCl3) d (ppm): 8.89 (d.d.,1H, Hpy(2), J = 2.2 and 0.7 Hz);
8.63 (d.d., 1H, Hpy(6), J = 4.8 and 1.6 Hz); 8.05 (d.d.d.,1H, Hpy(4),
J = 2.2, 8.0 and 1.6 Hz); 7.30 (t.d.d, 1H, Hpy(5), J = 0.7, 8.0 and
4.8 Hz); 6.31 (s., 1H, NH); 3.45 (t., 2H, CH2-N); 1.28–1.26 (m., 20H,

788 Karolina Wieszczycka and Joanna Zembrzuska
0.91 (t, 3H, CH3); 13C NMR (100 MHz; CDCl3) d (ppm): 159.6; 157.1;
153.5; 138.0; 128.8; 128.2; 126.3; 120.6; 46.1; 32.1; 28.9; 29.2; 29.6;
29.8; 29.9; 29.9; 29.9; 29.7; 31.9; 22.7; 14.1. MS (ESI) (m/z ratio) 381.4
(MH)+.
to 250°C; helium flow: 1.2 mL minÀ1; injection ratio 1:4; injection tem-
perature: 250°C.
Mass spectrometric detection. Acquisition rate: 5 Hz; mass range: 30–
400 amu; ion source temperature: 250°C; transfer line temperature:
280°C; electron ionization 70 eV the detector potential À1800 V. Chro-
maTOF software was used for the processing of the collected data.
Spectroscopic analysis. The concentration of the (Z)-oxime of 1-(2-
pyridyl)tridecan-1-one as Cu(II)-oxime complex was performed using V-
750 UV-Vis Spectrophotometer (k = 340 nm, 1 cm cell, methanol as
diluent). Using synthetic solutions containing (Z)-oxime of 1-(2-pyridyl)
tridecan-1-one and by-products of the photodegradation, it was shown
that the proposed techniques had a good agreement with reference the
LC-MS method (signal at tR = 2.21 min) and the obtained regression
equation enabled the (Z)-oxime determination with the precision of
0.4%. Analysis procedure: (i) calibration curve: 1 mL Cu(NO3)2 solution
of 0.01 mol LÀ1 in methanol was added to 10 mL volumetric flask con-
taining a methanolic solution of (Z)-1-(2-pyridyl)tridecan-1-one oxime in
the range of 0.001–1.0 mmol LÀ1. Before measurement, the solutions
were filled to the mark and shaken for 30 min at 25°C; (ii) sample prep-
aration: 1 mL of the degraded solution was evaporated to dryness, next
dissolved in 1 mL of methanol and shaken with 1 mL of 0.01 mol LÀ1
Cu(NO3)2 in methanol. Before measurement, the solution containing Cu
(II)-oxime complex was added to 10 mL volumetric flask and filled to
the mark.
1-(6-heptylpyridin-3-yl)tridecan-1-one oxime; 1H NMR (400 MHz;
CDCl3), d (ppm): 10.3 (s, 1H, OH); 7.49 (d 1H, Hpy(4)); 7.22 (d.,1H,
Hpy(5)); 8.36 (s., 1H, Hpy(2)); 2.71 (t., 2H, CH2); 2.56 (t., 2H, CH2);
1.54–1.58 (q., 4H, CH2); 1.32–1.26 (m., 26H, CH2); 0.86–0.9 (t., 6H,
CH3); 13C NMR (100 MHz; CDCl3) d(ppm): 157.7; 157.1; 148.3; 133.8;
129.8; 120.0; 35.2; 32.8; 31.2; 31.6; 29.8; 29.6; 29.3; 29.1; 26.2; 25.6;
22.5; 14.0; MS (ESI) (m/z ratio) 389.5 (MH)+.
1-(6-benzylpyridin-3-yl)tridecan-1-one oxime; 1H NMR (400 MHz;
CDCl3), d (ppm): 10.1 (s, 1H, OH); 7.49 (d 1H, Hpy(4)); 7.22 (d.,1H,
Hpy(5)); 8.36 (s., 1H, Hpy(2)); 7.33 (t., 2H, Hb(3)); 7.22 (t., 1H, Hb(4));
7.11 (d., 2H, Hb(2)); 4.2 (s., 2H, CH2); 2.69 (t., 2H, CH2); 1.53 (q., 2H,
CH2); 1.31-1.24 (m., 18H, CH2); 0.86 (t., 3H, CH3); 13C NMR
(100 MHz; CDCl3) d(ppm): 158.9; 157.1; 148.9, 134.2; 130.1; 128.7;
128.4; 126.5; 119.9; 45.9; 32.8; 31.6; 29.7; 29.5; 29.3; 29.1; 26.1; 25.6;
22.5; 14.0; MS (ESI) (m/z ratio) 381.6 (MH)+.
Eicosan-8-one was isolated on a silica column using a mixture of
ethyl acetate and hexane (1: 9) as a developing solvent and its structure
was confirmed by 13C NMR in CDCl3 d (ppm): 211.3; 42.9; 42.6; 31.9;
31.8; 29.7; 29.6; 29.4; 29.4; 29.3; 29.2; 26.2; 26.1; 25.5; 24.1; 24.0;
22.7; 22.6; 14.1; 14.0.
Preparation and irradiation of oxime complexes with metal. The tolu-
ene solution containing complex of the oxime with copper(II) chloride
was obtained during extraction process: an aqueous feed solution contain-
ing 0.01 mol LÀ1 of copper(II) chloride and 3 mol LÀ1 NaCl was
mechanically shaken with an organic phase containing 0.01 mol LÀ1 of
the oxime (volume ratio both phases = 1) for 30 min at 22°C in glass se-
paratory funnels, and allowed to stand for the phase separation. The pH
of the aqueous solution was adjusted using 713 pH Meter (Metrohm) to
a desired value of 4.0 by adding 0.02% solutions of HCl. Before and
after extraction the metal concentration in the aqueous phase was ana-
lyzed by atomic absorption spectrometry using Z8200 (Hitachi) instru-
ment. Before irradiation in the Heraeus photoreactor the organic phase
was diluted to 1 9 10À3 mol LÀ1 of the ligand. The photodegradation
was carried out as described above for the uncomplexed oximes. After
the photodegradation the samples were stripped twice for 30 min at 25°C
using 1% succinic acid (copper(II) complexes with the 2-pyri-
dineketoxime) or water (copper(II) complexes with the 3-pyri-
dineketoxime). Next, the samples were washed using 0.2 mol LÀ1
sodium sulphate to pH ~ 7, dried and analyzed, using the LC-MS/MS
method.
Calculation. Quantitation and identity confirmation of the degraded
compounds were attained by electrospray positive ionization LC-MS/MS
in multiple reactions monitoring MRM mode. The content of 2- or 3-am-
inopyridine, tridecanal and icosan-8-one isolated from the irradiated solu-
tions and the synthesis were determined using GC-TOFMS from the
calibration curve applying linear regression. The concentration of the (Z)-
1-(2-pyridyl)tridecan-1-one oxime was also determined using UV-VIS
spectroscopy, wherein, an ability of (Z)-1-(2-pyridyl)tridecan-1-one oxime
(not E-oxime) to form a stable complex with Cu(II) ions has been applied
(concentration was also calculated from the calibration curve applying
linear regression).
Before and after the extraction and stripping processes, copper(II) ions
concentration in the aqueous phase was analyzed with atomic absorption
spectrometry. The concentration of the metal ions in the organic phase
was calculated from the difference between the concentrations in the
aqueous phase before and after extraction.
RESULTS AND DISCUSSION
NMR analysis. NMR spectra were recorded at 25°C on a Bruker
Advance DRX 400 spectrometer operating at frequencies 400 MHz (1H),
100 MHz (13C). In all spectra CDCl3 was used as the solvent.
Photodegradation of 2-pyridineketoxime
The irradiation of (Z)-1-(2-pyridyl)tridecan-1-one oxime in tolu-
ene and heptane solutions with the medium pressure mercury
lamp resulted in Z-E photoisomerization and further photodecom-
position of both isomers (photorearrangement and photosubstitu-
tion).
LC-MS/MS analysis. LC analysis was performed using the UltiMate
3000 RSLC chromatographic system from Dionex (Sunnyvale, CA,
USA). Ten microliter samples were injected into a 100 9 2.1 mm I.D.
analytical column packed with 1.9 lm Hypersil Gold C18 RP from
Thermo Scientific (USA). The mobile phase consisted of 5 mmol LÀ1
ammonium acetate in water (A), methanol (B) and at flow rate of
0.25 mL minÀ1. The following gradient was used: 0 min 30% (B),
1.0 min 50% (B), 1.5 min 100% (B), 4.5 min 100% (B).
The LC system was connected to an API 4000 QTRAP triple quadru-
ple mass spectrometer from AB Sciex (Foster City, CA, USA). The
Turbo Ion Spray source operated in a positive ion mode. The dwell time
for mass transition detected in the MS/MS multiple reaction monitoring
mode (MRM) was set at 50 ms. The oximes and the degradation prod-
ucts were detected using the following settings for the ion source and
mass spectrometer: curtain gas 10 psi, nebulizer gas 40 psi, auxiliary gas
40 psi, temperature 450°C, ion spray voltage 5500 V and collision gas
set to medium. The MS/MS parameters used for quantitative determina-
tion of the studied oximes and the by-products are shown in Table 1. In
majority of experiments, protonated molecules [M+H]+ were used as pre-
cursor ions.
In heptane, initially the irradiation causes the photoisomeriza-
tion of the 2-pyridineketoxime. The presence of two isomers was
verified by LC-MS/MS analysis carried out directly after the irra-
diation maintaining under inert storage conditions of the samples.
The isomers had different retention times that were observed at
2.04 and 2.21 min corresponding to (E) and (Z)-oxime, respec-
tively. The intensity of the the (E)- was initially not higher than
2 9 106 and increased to maximum after 15 min of exposure to
UV-VIS light. The second signal had a much lower intensity
(4 9 104) and was fully depleted after 30 min of irradiation.
Spectroscopic analysis of UV-VIS also confirmed that the Z-E
photoisomerization of the oxime occurred under the studied con-
ditions. The decrease in the absorbance intensity of the peak at
340 nm, which corresponded to the (Z)-oxime-copper complex,
resulted from the decrease of the (Z)-isomer concentration with
increasing irradiation time. The results of the spectroscopic
analysis were compared to those obtained with LC-MS/MS
(Fig. 2).
GC–TOF MS analysis. GC–TOF MS analysis was performed using
GC/GC–TOF MS instrument Pegasus 4D (LECO Corp., MI, USA)
consisting of an Agilent 6890N gas chromatograph with split–splitless
injector, 7683 Series autosampler and a Leco Pegasus III high-speed
time-of-flight mass spectrometer (TOF MS). Gas chromatography condi-
tions: capillary column SolGelWax (30 m 9 0.25 mm 9 0.25 lm df)
(Agilent, USA); oven temperature program: 50°C for 2 min, 15°C minÀ1

Photochemistry and Photobiology, 2015, 91 789
Table 1. MS/MS parameters for the analysis of analytes by the MRM positive ionization mode.
MRM
transitions
Precursor ion [M+H]+
Declustering
potential [V]
Collision
energy [V]
Compounds
[m/z]
(precursor ion [m/z] ? product ion [m/z])
E-oxime of 1-(2-pyridyl)tridecan-1-one
Z-oxime of 1-(2-pyridyl)tridecan-1-one
Oxime of 1-(3-pyridyl)tridecan-1-one
291
291
291
291?179
291?161
291?161
291?57
291?120
291?105
291?93
291?105
291?57
291?106
291?93
291?120
291?106
291?95
41
41
26
13
25
25
55
37
57
51
57
55
43
51
37
43
37
N-dodecylpyridine-2-carboxamide
N-dodecylpyridine-3-carboxamide
N-(3-pyridyl)tridecanamide
291
291
291
41
26
26
indicated that in the photochemical synthesis, the sterically hin-
dered isomer is formed and the isomerization can proceed
according to two limiting mechanisms. The first mechanism is a
rotation about C=N bond in conjunction with a reduced bond
order (Scheme 1). In the second mechanism, an in-plane inver-
sion proceeds due to rehybridization of oxime nitrogen without
any significant changes in the bond order (36–38). According to
this mechanism, photoproduct (E)-1-(2-pyridyl)tridecan-1-one
oxime was expected, however, the 1H NMR spectrum of the
oxime isolated from the irradiated solution (Fig. 3) showed sig-
nals indicating the presence of the (E)-isomer, and (Z)-isomer.
These results can be explained by a very fast back isomerization,
especially after exposure to air.
1.0
0.8
0.6
0.4
0.2
0.0
LC-MS
UV-VIS spectroscopy
0
5
10
15
30
Time of irradiation, min
A continuation of UV–VIS exposure over a long period of
time shows (Fig. 4) that a substantial quantity of the oxime ((E)-
and (Z)-isomer) undergoes a photochemical rearrangement into
N-dodecylpyridine-2-carboxamide, 2-aminopyridine, eicosan-8-
one and a photosubstitution to 1-(6-heptylpyridin-2-yl)tridecan-1-
one oxime. Under studied conditions, the photo-Beckmann
rearrangement was found to be the major competing photoreac-
tion of 1-(2-pyridyl)tridecan-1-one oxime. After 10 h of exposure
to UV-VIS light, 57% of the oxime was converted into 2-amino-
Figure 2. Comparison of spectroscopic (UV-VIS spectroscopy) and
chromatographic (LC-MS) analysis of (Z) 1-(2-pyridyl)tridecan-1-one
oxime concentration during UV-VIS irradiation in heptane.
Generally, the conventional synthesis provides access to a
more stable (E)-isomer, however, in the case of 1-(2-pyridyl)trid-
ecan-1-one oxime the (Z)-isomer is stabilized by intramolecular
hydrogen bridge dominates. Most studies published so far, have
*
hv
R
R
*
N
N
R
N
H
N
C
N
O
OH
HO
N
Π∗, Τ1)
*
(
Π
hv
R
R
N
N
N
N
HO
HO
Scheme 1. Proposed mechanism of photoisomerization of 1-(2-pyridyl)tridecan-1-one oxime.

790 Karolina Wieszczycka and Joanna Zembrzuska
Figure 3. Comparison of H1 NMR spectra of (Z)-oxime of 1-(2-pyridyl)tridecan-1-one (Z-Oxime), (E)-oxime of 1-(2-pyridyl)tridecan-1-one (E-Oxime)
and product isolated from irradiated solution (Product).
1.0
0.8
0.6
0.4
0.2
0.0
pyridine, 7% to N-dodecylpyridine-2-carboxamide and 46% to
eicosan-8-one.
Z-oxime
E-oxime
SubstP
2PNH2
2PA
Mechanism of the photo-Beckmann rearrangement has been
studied extensively. Over the last few years it has been found
that this mechanism includes photochemical isomerization fol-
lowed by the transformation of an excited singlet state of an
oxime (E or Z) into an oxaziridine intermediate. This intermedi-
ate structure is again excited to the singlet state and then reorga-
nizes to give an appropriate amide (38,39). Based on this
knowledge, we can propose the 1-(2-pyridyl)tridecan-1-one
oxime photo-Beckmann rearrangement to the corresponding N-
dodecylpyridine-2-carboxamide (rearrangement product of (Z)-
oxime) or 2-aminopyridine and an appropriate carbonyl
compound – product of the N-(2-pyridyl)tridecanoylamide photo-
decomposition (rearrangement product of the (E)-oxime)
(Scheme 2).
ketone
0
200
400
600
Time of irradiation, min
Figure 4. Changes in concentration of (Z) 1-(2-pyridyl)tridecan-1-one
oxime and its degradation products after UV-VIS irradiation in heptane.
Z-Oxime = (Z)-oxime of 1-(2-pyridyl)tridecan-1-one; E-Oxime = E-
oxime of 1-(2-pyridyl)tridecan-1-one; SubstP – product of photosubstitu-
tion, 2PNH2 = 2-aminopyridine; 2PA = N-dodecylpyridine-2-carboxa-
mide; Ketone – eicosan-8-one.
The photodecomposition of N-(2-pyridyl)tridecanoylamide has
not been yet reported however, it may be assumed that the amide
formed during the irradiation, similar to 3-acetamidopyridine,

Photochemistry and Photobiology, 2015, 91 791
*
R
NH
R
N
N
N
N
R
HN
O
O
N
OH
isomerisation
R
R
*
O
NH
N
R
N
O
NH
N
decomposition
HO
R
C
hydrogen abstraction
from solvent
+
tridecanal
O
NH
N
H2N
N
eicosan-8-on
Scheme 2. Proposed mechanism of photorearrangement of 1-(2-pyridyl)tridecan-1-one oxime.
may undergo a photo-Fries rearrangement (40,41) or, similar to
of the pyridine ring, and the location of the substituent depends
on the structure of pyridine derivatives, polarity of the solvent as
well as pH of the irradiated solution.
2-acetamidopyridine, a photodecomposition (42). The identified
products indicate the photodecomposition to a pyridinamine and
heptyl radicals, which can react with other radicals (eicosan-8-
one formation) or abstract a hydrogen atom from the solvent to
give tridecanal and 2-aminopyridine.
1-(6-heptylpyridin-2-yl)tridecan-1-one oxime is a product of a
photosubstitution reaction, which probably undergoes similarly to
pyridine and derivatives of pyridinecarboxylic acids. The first
stage of the reaction is a hydrogen-atom abstraction from a sol-
vent by the pyridine nitrogen atom. The second stage is a
replacement of a ring hydrogen by strong nucleophilic alkyl radi-
cals (Scheme 3) (33,42–48).
For example, the UV-VIS irradiation in methanol of 2- and 3-
pyridineketoximes leads to the photosubstitution by a methyl,
hydroxymethyl and a methoxy group through different mecha-
nisms. Photosubstitution by the methoxy group is likely to result
from the hydrogen migration favored by the protic solvent, a
methyl substitution proceeds through the reduction of the hy-
droxyalkyl fragment and hydroxyalkyl substitution of 3-pyr-
idylketoxime resulting in radical recombination.Photodegradation
of (Z)-1-(2-pyridyl)tridecan-1-one oxime in toluene
The LC-MS/MS analysis of the samples, collected after
30 min of irradiation demonstrates (Fig. 5) the increase in the
(E)-oxime formation (tR = 2.22) with the simultaneous decrease
in the (Z)-oxime (tR = 2.04), which confirms the photoisomeriza-
tion of the oxime. A continuation of the UV-VIS irradiation
The photosubstitution that has been reported in the literature
occurs without alkyl radical rearrangement, even in the case of a
branched alkyl chain. Furthermore, the selectivity of the reaction
is very high leading to the photosubstitution at position 4, 2 or 6
*
R
hv
N
R
R_H
R
H
N
N
N
N
OH
R
N
H
OH
O
H
R
R
N
H
OH
R
H
N
R-H - solvent
R
-
H
.
N
N
R
-
benzyl or heptyl
radical
OH
Scheme 3. Proposed mechanism of photosubstitution of 1-(2-pyridyl)tridecan-1-one oxime.

792 Karolina Wieszczycka and Joanna Zembrzuska
causes a further photochemical decomposition of the oxime: the
photo-Beckmann rearrangement and the photosubstitution by a
benzyl group. In toluene, the photo-Beckmann rearrangement of
the (Z)-oxime into N-dodecylpyridine-2-carboxamide does not
proceed upon the irradiation and no decay product was detected,
but 60% of the oxime assigned as (E)-isomer degraded to 2-am-
inopyridine and tridecanal – the products of the N-dodecylpyri-
dine-2-carboxamide photodecomposition and next the hydrogen
abstraction by the tridecanoyl radical (Fig. 5).
The irradiated 1-(2-pyridyl)tridecan-1-one oxime also under-
goes the photosubstitution reaction to form 1-(6-benzylpyridin-2-
yl)tridecan-1-one oxime. The mechanism of the photosubstitution
is presumably through the replacement of the ring hydrogen by
the radical generated from the solvent similar to the photoreac-
tion in heptane. However, the photo-product was not stable upon
the UV-VIS irradiation. As shown in Fig. 5, initially, the photo-
product concentration increases achieving maximum (19% yield)
at 3 h of the irradiation and after that it decreases to complete
degradation.
that the photoisomerization is the most rapid reaction within the
first hour of the UV-VIS light exposure (Fig. 7). In the first
15 min of the experiment the concentration of the (E)-oxime
decreases with the simultaneously increase of the (Z)-oxime con-
centration to achieve a maximum at the 15th minute of the irra-
diation. However, prolonged exposure to the light results in a
complete degradation of both isomers, over a 4-h period.
The LC-MS/MS and GC-TOFMS analysis of the samples
taken during the experiment indicated that photoisomerization
takes place under exposure to UV-VIS light, the photo-Beck-
mann rearrangement ((E)-1-(3-pyridyl)tridecan-1-one oxime
decomposes into 3-aminopyridine and eicosan-8-one, and (Z)-1-
(3-pyridyl)tridecan-1-one oxime into N-dodecylpyridine-3-carb-
oxamide), as well as the photosubstitution to the pyridine ring
(1-(6-heptylpyridin-2-yl)tridecan-1-one oxime formation). Fur-
thermore, the analysis of the composition of the degraded prod-
ucts has indicated that the photorearrangement is a dominating
reaction, which occurs in heptane after 10 h of irradiation: 42%
of the oxime degrades to 3-aminopyridine, 47% to eicosan-8-one
and 21% of the oxime degrades to N-dodecylpyridine-3-carboxa-
mide. While the reaction of the photosubstitution by the heptyl
group occurs, the created by-product is not stable. After 4 h UV-
VIS irradiation it gradually degrades to the concentration of
4 9 10À5 mol LÀ1 at 10 h of the experiment.
The photodegradation of (E)-1-(3-pyridyl)tridecan-1-one
oxime in toluene has also led to a reaction of the photoisomeriza-
tion, but the yield of the reaction is slightly higher than in
heptane. Furthermore, in toluene an enhanced photostability of
both isomers is observed (Figs. 7 and 8).
The reaction of the photo-Beckmann rearrangement is also
observed in toluene, but only in the case of (E)-1-(3-pyridyl)trid-
ecan-1-one oxime (Fig. 8). It was indicated that after 10-h expo-
sure to UV-VIS light the oxime converts into 51% to 3-
aminopyridine and in 43% into tridecanal. Toluene does not
enhance the photosubstitution to the pyridine ring. The observed
by-product, 1-(6-benzylpyridin-3-yl)tridecan-1-one oxime, created
in a small amount achieved maximum 4% conversion within the
first 2 h of UV-VIS irradiation.
Photodegradation of 3-pyridineketoxime
The photochemical reactivity of (E)-1-(3-pyridyl)tridecan-1-one
oxime, similar to (Z)-1-(2-pyridyl)tridecan-1-one oxime, was
studied under UV-VIS light exposure in heptane or toluene as a
solvent and under the argon atmosphere. Additionally, in the
case of the toluene solution an influence of trace amounts of
water and an aqueous solutions of hydrochloric acid on the
photostability of the hydrophobic 3-pyridineketoxime were stud-
ied.
The results displayed in Fig. 6 clearly indicate that the reac-
tivity of the oxime depends on the type of solvent and the pres-
ence of additives. The least degree of the photodegradation of
(E)-1-(3-pyridyl)tridecan-1-one oxime is observed in the toluene
solution after shaking with water, the slightly faster photodegra-
dation occurs in toluene after shaking with the aqueous acidic
solution, however, in the heptane the degradation is the highest.
Photodegradation of (E)-1-(3-pyridyl)tridecan-1-one oxime in
heptane. Detailed analysis of the heptane solution of (E)-1-(3-
pyridyl)tridecan-1-one oxime irradiated for period of 10 h shows
Figure 9 shows, that the presence of trace amounts of water
dissolved in the toluene solution does not influence the degree
and the mechanism of the photoisomerization and photodegrada-
1.0
1.0
Toluene
Toluene -Acid
Toluene-Water
Heptane
0.9
Z-oxime
0.8
0.8
0.7
E-oxime
0.6
0.6
0.5
0.4
0.3
0.2
0.1
0.0
SubstP
2PNH2
0.4
0.2
0.0
Tridecanal
0
200
400
600
0
100
200
300
400
500
600
Time of irradiation, min
Time of irradiation, min
Figure 5. Changes in concentration of (Z) 1-(2-pyridyl)tridecan-1-one
oxime and its degradation products after UV-VIS irradiation in toluene.
Z-Oxime = (Z)-oxime of 1-(2-pyridyl)tridecan-1-one; E-Oxime = (E)-
oxime of 1-(2-pyridyl)tridecan-1-one; SubstP – product of photosubstitu-
tion, 2PNH2 = 2-aminopyridine.
Figure 6. Changes in concentration of (E) 1-(3-pyridyl)tridecan-1-one
oxime under UV-VIS irradiation in toluene (Toluene), heptane (Heptane),
in toluene after shaking with water (Toluene-Water) and in toluene after
shaking with 0.2% HCl (Toluene-Acid).

Photochemistry and Photobiology, 2015, 91 793
tion of the oxime. However, the presence of hydrogen and chlo-
ride ions in the toluene solution increases the yield of the photo-
isomerization and plays a protective role against the further
photodegradation of the (E)-isomer. The most important feature
of this experiment is the growth of the yield of the photosubstitu-
tion to the pyridine ring (oxime of 1-(6-benzylpyridin-3-yl)tridec-
an-1-one is created after 3 h irradiation with 17% yield), and
lack of the signals indicating the presence of tridecanal or other
carbonyl compounds in the samples.
The photo-Beckmann rearrangement of the 3-pyridylketoxime
as well as the photosubstitution to the pyridine ring can be
explained by the mechanisms similar to those presented for the
2-pyridylketoxime. In the photo-Beckmann rearrangement the
excited oxime (E or Z-isomer) transforms into an oxaziridine
intermediate, which reorganizes to an appropriate amide. In the
photosubstitution reaction, the first step is probably the pyridyl
radical formation through the hydrogen abstraction from the sol-
vent (43–49) and next, the photosubstitution by the heptyl or
benzyl radicals (Scheme 4).
1.0
0.8
0.6
0.4
0.2
0.0
Z-oxime
E-oxime
SubstP
3PNH2
3PA
Ketone
0
200
400
600
Time of irradiation/min
Figure 7. Changes in concentration of 1-(3-pyridyl)tridecan-1-one oxime
and its degradation products after UV-VIS irradiation in heptane. Z-
Oxime = (Z)-oxime of 1-(3-pyridyl)tridecan-1-one; E-Oxime = (E)-oxime
of 1-(3-pyridyl)tridecan-1-one; SubstP – product of photosubstitution,
3PNH2 = 3-aminopyridine; 3PA = N-dodecylpyridine-3-carboxamide.
Z-oxime
E-oxime
SubstP
3PNH2
Photodegradation of pyridineketoximes in presence of metal.
Hydrophobic 2-pyridineketoxime, which is a strong extractant,
can extract copper(II) as a stable chelate efficiently even at low
concentration of chloride ions. In this complex copper ion is
coordinated by the pyridine nitrogen and the deprotonted oxygen
atom of the hydroxyimine group (50). High stability of the com-
plexes was also observed during exposure to UV-VIS light, and
even 10 h irradiation did not decompose the structure of the
complexes and the structure of the uncomplexed 2-pyr-
idineketoxime.
1.0
0.8
Tridecanal
0.6
0.4
0.2
0.0
The location of oxime substituent at position 3 of the pyri-
dine ring has enabled a metal coordination through a solvating
mechanism forming a centrosymmetric binuclear macrocylic
complex (only pyridine nitrogen atom is involved in coordina-
tion of the metal ion) with stabilization by double anion
bridges (8,51). Unfortunately, even the creation of additional
interactions as the intermolecular hydrogen bond does not pre-
vent the complex destruction under both UV and VIS light irra-
diation. It has been noted that after 15 min of light exposure,
the whole complex decomposes releasing free molecules of the
oxime and copper as copper oxide in the precipitate. Thus, as
was shown in Fig. 10, the continuation of the free (E)-1-(3-pyr-
idyl)tridecan-1-one oxime irradiation also causes the photoiso-
merization (1 h irradiation causes a change of 10% of (E)-
stereoisomer into (Z)-oxime) and next photodegradation. How-
ever, the products of the photo-Beckmann rearrangement to cor-
responding amido-, keto- and cyano-derivatives, and the
photosubstitution to the pyridine ring are not observed. It is dif-
ficult to determine how the presence of the coordinated metal
ion influences the mechanism of the photodegradation, but CuO
precipitate suggests a photolysis of released cupric chloride spe-
cies, which also leads to form a long lived free radical-metal
complex (52,53). Finally, when copper ions were irradiated
together with 1-(3-pyridyl)tridecan-1-one oxime, the less effi-
cient photoisomerization and the further decomposition can take
place in toluene solutions.
0
200
400
600
Time of irradiation, min
Figure 8. Changes in concentration of 1-(3-pyridyl)tridecan-1-one oxime
and its degradation products after UV-VIS irradiation in toluene. Z-
Oxime = (Z)-oxime of 1-(3-pyridyl)tridecan-1-one; E-Oxime = (E)-oxime
of 1-(3-pyridyl)tridecan-1-one; SubstP – product of photosubstitution,
3PNH2 = 3-aminopyridine, Ketone – eicosan-8-one.
E-oxime
Z-oxime
3PNH2
SubstP
1.0
0.8
0.6
0.4
0.2
0.0
0
200
400
600
Time of irradiation, min
Figure 9. Changes in concentration of 1-(3-pyridyl)tridecan-1-one oxime
and its degradation products after UV-VIS irradiation in toluene after
shaking with 0.2% HCl. Z-Oxime = (Z)-oxime of 1-(3-pyridyl)tridecan-
1-one; E-Oxime = (E)-oxime of 1-(3-pyridyl)tridecan-1-one; SubstP –
product of photosubstitution, 3PNH2 = 3-aminopyridine.
CONCLUSION
The irradiation of (Z)-oxime of 1-(2-pyridyl)tridecan-1-one and
(E)-oxime of 1-(3-pyridyl)tridecan-1-one in toluene and heptane

794 Karolina Wieszczycka and Joanna Zembrzuska
R
R
*
R
hv
R-H
N
N
H
N
OH
OH
N
N
H
N
H
OH
R
R
H
R
R
H
N
N
R
N
H
OH
OH
R
N
.
R - benzyl or heptyl
radical
Scheme 4. Proposed mechanism of photosubstitution of 1-(3-pyridyl)tridecan-1-one oxime.
the photo-Beckmann rearrangement with lower yield the photo-
substitution to the pyridine ring. In the case of the photodegrada-
tion of (Z)-1-(2-pyridyl)tridecan-1-one oxime in toluene as the
diluent the photo-Beckmann rearrangement of the (Z)-oxime was
not observed, however, (E)-oxime degraded to 2-aminopyridine
and tridecanal. In heptane, the photo-Beckmann rearrangement
led to the formation of 2-aminopyridine (rearrangement of the
(E)-oxime), eicosan-8-one (product of the recombination of trid-
ecanolyl and heptyl radicals) and N-dodecylpyridine-2-carboxa-
mide (rearrangement of the (Z)-oxime). In the case of (E)-oxime
of 1-(3-pyridyl)tridecan-1-one in heptane the photodegradation
led to formation of N-dodecylpyridine-3-carboxamide, 3-amino-
pyridine and eicosan-8-one, however, the photodegradation
conducted in toluene as diluent led only to the formation of
3-aminopyridine and tridecanal.
1.0
0.8
0.6
0.4
0.2
0.0
E-oxime T-Cu
Z-oxime T-Cu
E-oxime T
Z-oxime T
0
200
400
600
Time of irradiation, min
The reaction of the photosubstitution of the oxime of 1-(3-
pyridyl)tridecan-1-one by the heptyl or benzyl groups also took
place with average yield between 6% and 14%. The by-products
were not stable upon exposure to light they gradually degraded,
to full depletion. A comparison of the photodegradation of the
copper complexes with (Z)-oxime of 1-(2-pyridyl)tridecan-1-one
and (E)-oxime of 1-(3-pyridyl)tridecan-1-one indicated that the
chelating character of copper complexes and 2-pyridineketoxime
protected against UV-VIS light more than the complex created
through a solvating mechanism.
Figure 10. Changes in concentration of 1-(3-pyridyl)tridecan-1-one
oxime and its degradation products after UV-VIS irradiation in toluene T
and toluene in presence of copper(II) ions T-Cu. Z-Oxime = (Z)-oxime
of 1-(3-pyridyl)tridecan-1-one; E-Oxime = (E)-oxime of 1-(3-pyridyl)trid-
ecan-1-one.
caused the photodegradation of the compounds and the degree of
the photodegradation depended mainly on the type of solvent
and the position of the oxime group at the pyridine ring. The
compound with the oxime group at position 3 had a higher resis-
tance to UV-VIS light than the 2-pyridineketoxime and the pho-
todegradation of the oximes was much slower in toluene than in
heptane. The differences between the photodegradation in tolu-
ene and heptane as diluents can also be a result of the oxime-dil-
uent interaction (e.g. solvent-solute energy transfer, promotion)
as well as a reactivity of the diluent under irradiation condition
(excited toluene can undergo an isomerization and dissociation
with a proton release).
Acknowledgements—This work was supported by grants: 03/32/DS-PB/
0500 DS PB and 03/31/DS-PB/0293 DS PB. NMR analyses were carried
out at the Institute of Bioorganic Chemistry Polish Academy of Sciences
in Poznan, Poland.
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