Electrochemical formation of methoxy- and cyano(phenylazo)alkanes from aldehyde and ketone phenylhydrazones

Article abstract of DOI:10.1055/s-2003-41048

Several aldehyde and ketone phenylhydrazones were electrooxidized in MeOH. Electrooxidation in the presence of KI or tetraethylammonium p-toluenesulfonate as the supporting electrolyte afforded the corresponding methoxy(phenylazo)alkanes, whereas electrooxidation in the presence of KI, NaCN, and HOAc afforded the cyano(phenylazo)alkanes.

Full text of DOI:10.1055/s-2003-41048

PAPER
2057
Electrochemical Formation of Methoxy- and Cyano(phenylazo)alkanes from
Aldehyde and Ketone Phenylhydrazones
Electrochemical
F
orm
a
i
tion of
t
Metho
s
xy- and
C
u
yano(pheny
h
s
iro Okimoto,*a Yukio Takahashi,a Toyoji Kakuchib
a
Department of Applied Chemistry and Circumstance Engineering, Kitami Institute of Technology, Koen-cyo165 Kitami 090-8507, Japan
Fax +81(157)247719; E-mail: oki@chem.kitami-it.ac.jp
b
Division of Molecular Chemistry, Graduate School of Engineering, Hokkaido University, W8N13 Kita-Ku, Sapporo 060-8628, Japan
Received 1 April 2003; revised 19 May 2003
Abstract: Several aldehyde and ketone phenylhydrazones were
electrooxidized in MeOH. Electrooxidation in the presence of KI or
tetraethylammonium p-toluenesulfonate as the supporting electro-
lyte afforded the corresponding methoxy(phenylazo)alkanes,
whereas electrooxidation in the presence of KI, NaCN, and HOAc
afforded the cyano(phenylazo)alkanes.
Scheme 2
Hydrazones are considered as one of the already oxidized
products of the corresponding hydrazines, therefore it is
generally understood that they do not readily undergo ox-
idation in the presence of a weak oxidant. In contrast to
previous reports1–4 mentioned above, oxidations of the hy-
drazine derivatives of aldehyde and ketone by means of
electrochemical methods are often straightforward, bring-
ing out valuable results in providing several organic com-
pounds.7
Key words: electrochemical oxidations, azo compounds, hydra-
zones, iodide ion, electron-transfer
The oxidative conversions of aldehyde or ketone phenyl-
hydrazones into the corresponding alkoxy or ace-
toxy(phenylazo)alkanes have been reported in several
studies. The oxidation of acetone phenylhydrazone to the
alkoxyphenylazo derivatives have been reported by
Schantl,1 using iodine as the oxidant, in various alcohols,
with yields of 23–50%, and by Chiusoli2 and co-workers,
using a palladium catalyst, thiourea, and a stream of car-
bon monoxide, with yields of less than 20%. Harrison3
and co-workers have reported on the oxidation of ben-
zophenone phenylhydrazones in dichloromethane, using
lead tetraacetate as the oxidant; however, this application
was only limited to benzophenone phenylhydrazones.
Iffland4 and co-workers have succeeded in the oxidative
conversion of ketone hydrazones into the azoacetate using
lead tetraacetate as the oxidant. We have also reported5 on
a useful synthetic reaction that converted a keto carbonyl
group into a cyano group by the electrooxidation of sever-
al ketone acylhydrazones in the presence of NaCN in
MeOH (Scheme 1).
Herein, we describe our studies on the oxidative conver-
sion of aldehyde and ketone phenylhydrazones 1 into the
corresponding methoxy(phenylazo)alkans 2 and cy-
ano(phenylazo)alkanes 3, by means of the electrochemi-
cal method (Scheme 3). The methodology employed was
based on our previous studies8 on the electrooxidation of
various kinds of hydrazones.
Scheme 3
The first step in our investigation on the electrooxidation
of phenylhydrazones was to optimize the reaction condi-
tions using acetone phenylhydrazone (1c) as the model
substrate. Influences of the electrolyte (KI, NaCN) and
HOAc are shown in Table 1.
Scheme 1
When using only KI as the supporting electrolyte, the cor-
responding methoxy(phenylazo)alkane 2c was produced
in a yield of 74% (Run 1). The presence of both NaCN and
KI resulted also in the formation of corresponding cy-
ano(phenylazo)alkane 3c, however, in lower yields (Runs
2, 3). Increasing amounts of added HOAc into the MeOH
solution resulted in increasing yields of 3c (Runs 4–7).
However, excessive amounts of added KI and HOAc did
not further improve the yield of 3c (Run 9). These results
suggested that the in situ liberation of HCN, from the re-
Furthermore, in our recent study,6 diphenylketene and its
derivatives were obtained by the electrooxidation of ben-
zil monohydrazone through formation of phenylbenzoyl-
diazomethane as the intermediate (Scheme 2).
Synthesis 2003, No. 13, Print: 18 09 2003. Web: 28 08 2003.
Art Id.1437-210X,E;2003,0,13,2057,2063,ftx,en;F02903SS.pdf.
DOI: 10.1055/s-2003-41048
© Georg Thieme Verlag Stuttgart · New York

2058
M. Okimoto et al.
PAPER
Table 1 Influence of Electrolytes and HOAc for the Formation of
Table 2 Electrooxidative Methoxylation of Aldehyde and Ketone
Azo Compoundsa
Phenylhydrazonesa
Compound R1
R2
Current Passed Yield of 2
Run
KI
(mmol)
NaCN
(mmol)
HOAc
(mmol)
Yield (%)b
F/mol
(%)b
(52)
(45)
68
2c
74
25
15
12
9
3c
0
1a
1b
1c
1d
1e
1f
Me
H
2.4
1
2
3
4
5
6
7
8
9
10
10
10
10
10
10
10
20
20
0
20
40
40
40
40
40
40
40
0
0
n-Pr
H
3.0
14
16
29
45
63
74
76
71
Me
Me
Me
n-Pr
2.1
0
i-Bu
2.1
71
10
20
30
40
30
40
n-Pr
2.0
73
–(CH2)5-
–(CH2)7-
–(CH2)8-
2.1
74
5
1g
1h
2.2
70
4
3.2
61
3
a 1:10 mmol, Et4NOTs: 6 mmol for 1a, 1b, KI:10 mmol for 1c–1h,
MeOH: 40 mL, reaction temperature: ca. 15 °C.
b Isolated yield. Values in parenthesis were determined by GC analy-
sis.
4
a 1c: 10 mmol, MeOH: 40 mL, constant current: 0.3 A, current passed:
2.1 F/mol, reaction temperature: ca. 15 °C.
b The yields were determined by GC analysis.
of various phenylhydrazones in the presence of KI,
NaCN, and HOAc are shown in Table 3. After passing
2.1–2.5 F/mol of electricity, aldehyde phenylhydrazones
1a and 1b afforded cyano(phenylazo)alkanes 3a and 3b in
32 and 40% yields, respectively, and ketone phenylhydra-
zones, 1c–m afforded corresponding cyano(phenylazo)al-
kanes 3c–m in 57–77% isolated yields. An exception was
the case of cyclopentane phenylhydrazone (1k), which
gave by-products that were difficult to eliminate for spec-
troscopic analysis of 3k. The purity of distilled 3k was
about 80% by GC analysis. In the case of 4-tert-butylcy-
clohexanone phenylhydrazone (1m), the reaction temper-
ature was increased to 35 °C due to the low solubility in
MeOH.
action between NaCN and HOAc in the MeOH solution,
was effective for the formation of 3c as the major product.
For the ketone phenylhydrazones (Table 2, 1c–h), the use
of an equimolar amount of KI as the electrolyte, which
was based on the results shown in Table 1, was found to
be favorable in affording the corresponding methoxy(phe-
nylazo)alkanes 2c–h. However, yields of the correspond-
ing methoxy(phenylazo)alkanes 2a and 2b from the
aldehyde phenylhydrazones 1a and 1b were lower than
20%, and approximately 30% of unreacted hydrazones re-
mained along with considerable amount of tar-like mate-
rials when using KI as the electrolyte. Subsequently, it
was found that methoxy(phenylazo)alkanes 2a and 2b
were produced in nearly 50% yield by using tetraethylam-
monium p-toluenesulfonate (Et4NOTs) as the electrolyte,
and by employing carbon poles instead of platinum net as
the anode.
In both methoxylation (Table 2) and cyanation (Table 3),
after the completion of the electrooxidation of aldehyde
phenylhydrazones 1a and 1b, significant amounts of a tar-
like material were observed during the extraction step.
Although isolated methoxy(phenylazo)alkanes 2 and cy-
ano(phenylazo)alkanes 3 were relatively stable on stand-
ing at room temperature,9 upon heating at temperatures of
nearly 180 °C, the compounds gradually decomposed to
give complex mixtures, accompanied by the evolution of
nitrogen gas. Furthermore, and interestingly, we noticed
that the reactions of the phenylazo compounds upon elec-
tron impact (ionization potential = 70 eV) during mass
spectroscopy were remarkably dependent on both the
structure of the alkane moieties (aldehyde, ketone), and on
the type of the substituents (methoxy, cyano). For exam-
ple, phenylazoalkanes 2a, 2b, 3a and 3b, which were
formed from aldehyde hydrazones clearly indicated their
parent peak (M+), whereas phenylazoalkanes that were
formed from ketone hydrazones did not show their parent
As shown in Table 2, acetaldehyde phenylhydrazone (1a)
and n-butyraldehyde phenylhydrazone (1b) afforded the
corresponding methoxy(phenylazo)alkanes 2a and 2b in
52% and 45% yields, respectively, and ketone phenylhy-
drazones 1c–h afforded the corresponding methoxy(phe-
nylazo)alkanes 2c–h, respectively, in 61–74% isolated
yields after 2.0–3.2 F/mol of electricity had been passed.
In the case of cyano(phenylazo)alkanes 3, we have decid-
ed that the optimal reaction conditions involved the pass-
ing of electricity in the presence of KI (2 equiv), NaCN (4
equiv), and HOAc (3 equiv) for substrates 1 in MeOH.
Electrooxidation under an excessive amount of NaCN and
HOAc prevented the formation of 2 as the by-product of
corresponding 3. The results of electrooxidative cyanation
Synthesis 2003, No. 13, 2057–2063 © Thieme Stuttgart · New York

PAPER
Electrochemical Formation of Methoxy- and Cyano(phenylazo)alkanes
2059
sis. Therefore, the introduction of a methoxy or cyano
group into the phenylhydrazones probably involved the
actual electrochemical process, which subsequently af-
forded the intermediates to give the phenylazo com-
pounds. Based on the observations mentioned above, the
mechanism of the electrooxidation can be described as
follows (Scheme 4).
Table 3 Electrooxidative Cyanation of Aldehyde and Ketone Phe-
nylhydrazonesa
Compound R1
R2
Current Passed Yield of 3
F/mol
2.5
2.3
2.2
2.3
2.4
2.4
2.8
2.1
2.1
2.1
(%)b
1a
1b
1c
1i
Me
H
32
n-Pr
H
40
Me
Me
Me
Me
n-Pr
72
Et
75
1j
n-C5H9
n-Pr
69
1e
1k
1f
70
-(CH2)4-
-(CH2)5-
(43)
77
1l
-(CH2)4CH(CH3)-
76
Scheme 4
1m
-(CH2)2CH(t-C4H9)(CH2)2-
57
At the first stage of the reaction, iodonium ions were
formed from iodide ions through a two-electron oxidation
on the anode surface. Consequently, the lone pair of elec-
trons on the nitrogen atom adjacent to the phenyl group of
hydrazone 1 was attacked by the iodonium ions to give the
corresponding iodide intermediate 1¢ followed by loss of
a proton. The subsequent release of iodide ions resulted in
the conversion of iodide intermediate 1¢ to azo carboca-
tion 1¢¢, which, accordingly, was attacked by a nucleo-
philic group such as a methoxy or cyano ion to produce
substituted phenylazoalkanes 2 and 3. In this oxidation
system, the iodide ions formed as the result of the oxida-
tion of 1 were oxidized again at anode to regenerate iodo-
nium ions.
a Compound 1:10 mmol, KI: 20 mmol, NaCN: 40 mmol, AcOH: 30
mmol, MeOH: 40 mL, reaction temperature: ca. 15 °C except for 1m
(35 °C).
b Isolated yield. The value in parenthesis was determined by GC anal-
ysis.
peaks (M+). Moreover, among the phenylazoalkanes
formed from ketone hydrazones, methoxy(phenylazo)al-
kanes showed the fragment of their alkane moiety (M –
PhN2)+ as the main peak. In contrast, cyano(phenylazo)al-
kanes did not show the fragment of the alkane moieties,
but typically showed the fragment of their phenylazo
group (PhN2)+ as the second largest peak, as described lat-
er in the experimental section.
From the observations that most of the starting phenylhy-
drazones were consumed after the passing of 2.0–2.3 F/
mol of electricity, it was considered that the electrooxida-
tion proceeds through a two-electron oxidation process.
Significant advancement in the yield of the azo com-
pounds was not observed when using KCl, KBr, NaOMe,
NaOAc, or NaClO4 instead of an iodide ion source, such
as KI or NaI as the supporting electrolyte. The results in-
dicate that iodide ions clearly play an important role as an
electron-transfer in the electrooxidative formation of the
substituted phenylazoalkanes.
Unexpectedly, attempts to electrooxidize the phenylhy-
drazones of aromatic carbonyl compounds, such as ben-
zaldehyde or acetophenone in the presence of KI, resulted
in tar-like materials that were troublesome to purify.
In conclusion, we have found that methoxy(phenylazo)al-
kanes can be obtained in reasonable to good yields by the
electrooxidation of aldehyde and ketone phenylhydra-
zones in MeOH using Et4NOTs or KI as the supporting
electrolyte, and similarly, cyano(phenylazo)alkanes can
be obtained using KI, NaCN and HOAc as the supporting
electrolytes. Our investigations on the oxidation of phe-
nylhydrazones by means of the electrochemical method
can be readily accomplished, without the use of special
oxidizing agents under very mild conditions.
In our first estimation, the initial reaction step involves the
addition of a MeOH or an HCN molecule across the car-
bon–nitrogen double bond of the phenylhydrazones to
yield the methoxy- or cyano-substituted hydrazines as the
intermediates.8b However, and surprisingly, allowing the
anolyte to stand overnight, in an attempt to promote the
formation of the MeOH or HCN adducts of phenylhydra-
zone as the intermediate, did not increase the yields of the
corresponding phenylazoalkanes. Moreover, such MeOH
or HCN adducts were not observed during the electroly-
Melting and boiling points are uncorrected. IR spectra were record-
ed neat or as CCl4 solution using a Shimadzu FT-IR 8200 spectro-
1
photometer. H and 13C NMR spectra were recorded with a Jeol
JNM-EX 90A spectrometer, with TMS as the internal standard, and
in CDCl3 or acetone-d6 as the solvent. EI- and CI-MS spectra were
obtained on a Jeol JMS-SX 102A spectrometer. GC analysis were
carried out on a Shimazu GC-8A gas chromatograph using a 2.5 m
Synthesis 2003, No. 13, 2057–2063 © Thieme Stuttgart · New York

2060
M. Okimoto et al.
PAPER
stainless steel column packed with 10% silicone SE-30 on Uniport
B. N2 served as the carrier gas.
HRMS (EI): m/z calcd for C9H12N2O: 164.0950; found: 164.1002
(M+).
Elemental analyses were performed by the Instrumental Analysis
Laboratories of Hokkaido University. Starting phenylhydrazones
(Tables 1, 1c; Table 2, 1a–h; and Table 3, 1i–m) were prepared by
typical condensation reactions,10 using equimolar amounts of phe-
nylhydrazine and the corresponding carbonyl compounds, in the
presence of catalytic amounts of HOAc in MeOH. Other reagents
were obtained from commercial suppliers and used without further
purification. Since every phenylhydrazones prepared in this study
were relatively unstable,11 even under storage in a refrigerator,
gradually turning to a dark tar-like material within several weeks,
the electrooxidation reactions were carried out immediately. Pre-
parative-scale electrooxidations were carried out in a tall 50 mL
beaker, equipped with a fine frit cup as the cathode compartment
with, either inserting four pieces of carbon poles (diameter, 5 mm;
height, 80 mm) for the formation of methoxylated phenylazo com-
pounds 2a and 2b, or inserting a cylindrical platinum net (diameter,
33 mm; height, 40 mm) for the formation of methoxylated phenyla-
zo compounds 2c–h and the cyanated phenylazo compound 3a–c,
3e, 3f, 3i–m, as the anode, and a nickel coil as the cathode.
1-Methoxy-1-phenylazobutane (2b)
Obtained as crude product; ca. 90% purity; bp 76–78 °C/2.0 mbar.
IR (neat): 2961, 2874, 1466, 1456, 1202, 1121, 1070, 768, 691 cm–1.
1H NMR (CDCl3): d = 0.94 (t, 3 H, J = 7 Hz, CH3), 1.2–2.0 (m, 4 H,
2 × CH2), 3.40 (s, 3 H, CH3O), 4.51 (t, 1 H, J = 7 Hz, CH), 7.4–7.9
(m, 5 H, Ar).
13C NMR (CDCl3): d = 13.97 (CH3), 17.59 (CH2), 35.67 (CH2),
56.72 (CH3O), 105.02 (CH), 122.61 (CH), 129.49 (CH), 131.04
(CH), 151.60 (C).
MS (EI): m/z (%) = 192 (M+, 3), 121(5), 87 ([M – PhN2]+, 60), 77
(27), 54 (16), 44 (100).
HRMS (EI): m/z calcd for C11H16N2O: 192.1263; found: 192.1312
(M+).
2-Methoxy-2-phenylazopropane (2c)
Bp 74–76 °C/1.3 mbar.
IR (neat): 2988, 2937, 1526, 1454, 1371, 1360, 1217, 1074, 764,
691 cm–1.
1H NMR (CDCl3): d = 1.42 (s, 6 H, 2 × CH3), 3.50 (s, 3 H, CH3O),
7.4–7.8 (m, 5 H, Ar).
13C NMR (CDCl3): d = 23.41 (CH3), 50.82 (CH3O), 98.30 (C),
122.37 (CH), 128.96 (CH), 130.75 (CH), 151.89 (C).
MS (EI): m/z (%) = 147 (9), 106 (24), 77 (49), 73([M – PhN2]+,
100), 50 (31), 41 (40), 39 (19).
Electrooxidations of Aldehyde and Ketone Phenyhydrazones;
General Procedures
Methoxy(phenylazo)alkanes (Table 2): A solution of substrate 1a–h
(10 mmol) and Et4NOTs (1.806 g, 6 mmol) for 1a and 1b or KI
(1.66 g, 10 mmol) for 1c–h in MeOH (40 mL) was electrooxidized
under a constant current (0.3 A). For further experimental details
and work-up, see the procedure given below for the preparation of
cyano(phenylazo)alkanes.
MS (CI): m/z = 179 (M + 1) +.
Cyano(phenylazo)alkanes (Table 3): A solution of substrate 1a–c,
1e, 1f, or 1i–m (10 mmol) and KI (3.32 g, 20 mmol), NaCN (1.96
g, 40 mmol), and HOAc (1.8 g, 30 mmol) in MeOH (40 mL) was
electrooxidized under a constant current (0.3 A). During the course
of the electrooxidation, the anolyte was magnetically stirred while
maintaining the temperature of the cell at approximately 15 °C (35
°C in the case of 1m). Upon completion of the electrooxidation, the
reaction mixture was treated with a three-fold amount of the anolyte
solution. After concentrating the combined anolyte solution in vac-
uo at approximately 30 °C to roughly one-fifth of its original vol-
ume, the resulting residue was treated with H2O (50 mL), and the
oily layer was extracted with Et2O (3 × 50 mL). The combined Et2O
extracts were washed with aq Na2S2O3 solution (20% w/w, 50 mL),
and dried (MgSO4). After removal of the solvent, the residue was
purified by distillation under reduced pressures or by silica gel col-
umn chromatography (diameter, 3.5 cm; height, 60 cm) with Et2O
as the eluent. In the cases of 3a, 3b, 3f, and 3m, the residue was pu-
rified by recrystallization from small amounts of EtOH. Products 3a
and 3b were obtained as transparent crystals (needles and scales, re-
spectively), 3f and 3m were obtained as yellow colored crystals
(prisms and fine powder, respectively). The remaining products
were obtained as a viscous liquid with a characteristic orange color.
All electrooxidation products were identified by their physical and
spectral data described as below.
HRMS: m/z calcd for C4H9O: 73.0653; found: 73.0658 (M –
PhN2)+.
Anal. Calcd for C10H14N2O (178.23): C, 67.38; H, 7.92; N, 15.72.
Found: C, 67.02; H, 7.89; N, 15.45.
2-Methoxy-4-methyl-2-phenylazopentane (2d)
Bp 88–90 °C/1.3 mbar.
IR (neat): 2955, 2870, 1526, 1454, 1366, 1225, 1140, 1090, 764,
691 cm–1.
1H NMR (CDCl3): d = 0.90 (d, 3 H, J = 7 Hz, CH3), 0.94 (d, 3 H,
J = 7 Hz, CH3), 1.40 (s, 3 H, CH3), 1.6–2.2 (m, 3 H, CHCH2), 3.48
(s, 3 H, CH3O), 7.3–7.8 (m, 5 H, Ar).
13C NMR (CDCl3): d = 20.93 (CH3), 23.82 (CH3), 24.19 (CH3),
24.60 (CH), 46.83 (CH2), 50.58 (CH3O), 100.42 (C), 122.37 (CH),
128.96 (CH), 130.63 (CH), 151.93 (C).
MS (EI): m/z (%) = 133 (3), 115 ([M – PhN2]+, 100), 77 (32), 73
(50), 58 (57), 41 (27), 39 (23), 31 (16).
MS(CI): m/z = 221 (M + 1)+.
HRMS: m/z calcd for C7H15O: 115.1123; found: 115.1200 (M –
PhN2)+.
Anal. Calcd for C13H20N2O (220.31): C, 70.87; H, 9.15; N, 12.72.
Found: C, 70.62; H, 9.10; N, 12.52.
1-Methoxy-1-phenylazoethane (2a)
Obtained as crude product; ca. 90% purity; bp 81–83 °C/1.3 mbar.
IR (neat): 2988, 2934, 1603, 1522, 1499, 1458, 1217, 1132, 768,
692 cm–1.
1H NMR (CDCl3): d = 1.44 (d, 3 H, J = 6 Hz, CH3), 3.43 (s, 3 H,
CH3O), 4.64 (t, 1 H, J = 7Hz, CH), 7.3–7.8 (m, 5 H, Ar).
13C NMR (CDCl3): d = 19.22 (CH3), 56.52 (CH3O), 101.56 (CH),
122.57 (CH), 129.04 (CH), 131.12 (CH), 151.52 (C).
4-Methoxy-4-phenylazoheptane (2e)
Bp 103–105 °C/1.3 mbar.
IR (neat): 2961, 2874, 1526, 1456, 1310, 1259, 1180, 1086, 764,
692 cm–1.
1H NMR (CDCl3): d = 0.89 (t, 6 H, J = 7 Hz, 2 × CH3), 1.2–1.6 (m,
4 H, 2 × CH2), 1.7–1.9 (m, 4 H, 2 × CH2), 3.45 (s, 3 H, CH3O), 7.4–
7.8 (m, 5 H, Ar).
MS (EI): m/z (%) = 164 (M+, 2), 121 (5), 77 (21), 58 ([M –
PhN2]+,100), 50 (16), 29 (15), 26 (16).
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Electrochemical Formation of Methoxy- and Cyano(phenylazo)alkanes
2061
13C NMR (CDCl3): d = 14.58 (CH3), 16.25 (CH2), 36.81 (CH2),
50.49 (CH3O), 101.19 (C), 122.28 (CH), 128.96 (CH), 130.55 (CH),
152.05 (C).
Anal. Calcd for C16H24N2O (260.37): C, 73.80; H, 9.29; N, 10.76.
Found: C, 73.74; H, 9.23; N, 10.46.
1-Cyano-1-phenylazoethane (3a)
Mp 151–152 °C.
IR (CCl4): 3273, 2216, 1604, 1558, 1495, 1373, 1269, 1234 cm–1.
1H NMR (acetone-d6): d = 2.1 (br s, 3 H, CH3), 6.8–7.5 (m, 5 H, Ar),
9.50 (br s, 1 H, CH).
13C NMR (acetone-d6): d = 15.07 (CH3), 114.43 (CH), 115.73 (CH),
119.19 (CN), 122.53 (CH), 129.66 (CH), 140.07 (C).
MS (EI): m/z (%) = 129 ([M – PhN2]+, 100), 87 (16), 77 (29), 54
(39), 44 (48), 39 (20), 24 (10).
MS(CI): m/z = 235 (M + 1)+.
HRMS: m/z calcd for C8H17O: 129.1279; found: 129.1322 (M –
PhN2)+.
Anal. Calcd for C14H22N2O (234.33): C, 71.75; H, 9.46; N, 11.96.
Found: C, 71.91; H, 9.54; N, 11.97.
MS (EI): m/z (%) = 159 (M+, 56), 132 (20), 92 (51), 91 (100), 77
1-Methoxy-1-phenylazocyclohexane (2f)
(23), 65 (42), 39 (18), 27 (HCN+, 3).
Bp 110–112 °C/1.3 mbar.
HRMS: m/z calcd for C9H9N3: 159.0794; found: 159.0766 (M+).
IR (neat): 2936, 2858, 1452, 1279, 1259, 1186, 1163, 1146, 1088,
937, 766, 691 cm–1.
1H NMR (CDCl3): d = 1.3–2.0 (m, 10 H, 5 × CH2), 3.45 (s, 3 H,
CH3O), 7.3–7.8 (m, 5 H, Ar).
Anal. Calcd for C9H9N3 (159.19): C, 67.90; H, 5.70; N, 26.40.
Found: C, 67.94; H, 5.81; N, 26.41.
1-Cyano-1-phenylazobutane (3b)
Mp 97–98 °C.
13C NMR (CDCl3): d = 22.19 (CH2), 25.41 (CH2), 32.01 (CH2),
49.92 (CH3O), 98.71 (C), 122.33 (CH), 128.96 (CH), 130.63 (CH),
152.05 (C).
IR (CCl4): 3261, 2966, 2876, 2218, 1605, 1506, 1497, 1234,
1171cm–1.
MS (EI): m/z (%) = 113 ([M – PhN2]+, 100), 81 (78), 77 (31), 71
(14), 50 (16), 44 (32), 39 (18).
MS (CI): m/z = 219 (M + 1)+.
1H NMR (CDCl3): d = 1.07 (t, 3 H, J = 7 Hz, CH3), 1.75 (heptet, 2
H, J = 7 Hz, CH2), 2.2–2.4 (m, 2 H, CH2), 6.7–7.5 (m, 5 H, Ar), 8.26
(br s, 1 H, CH).
13C NMR (CDCl3): d = 13.76 (CH3), 18.85 (CH2), 28.91 (CH2),
114.06 (CH), 117.72 (CH), 120.17 (CN), 122.73 (CH), 129.41
(CH), 142.64 (C).
HRMS: m/z calcd for C7H13O: 113.0966; found: 113.1020 (M –
PhN2)+.
Anal. Calcd for C13H18N2O (218.29): C, 71.52; H, 8.31; N, 12.83.
Found: C, 71.55; H, 8.45; N, 12.77.
MS (EI): m/z (%) = 187 (M+, 84), 158 (28), 105 (30), 92 (48), 91
(100), 77 (85), 65 (43), 39 (20), 27 (HCN+, 8).
1-Methoxy-1-phenylazocyclooctane (2g)
HRMS: m/z calcd for C11H13N3: 187.1109; found: 187.1148 (M+).
Bp 132–134 °C/1.3 mbar.
Anal. Calcd for C11H13N3 (187.24): C, 70.56; H, 7.00; N, 22.44.
Found: C, 70.69; H, 7.16; N, 22.51.
IR (neat): 2926, 2851, 1474, 1457, 1231, 1155, 1136, 1072, 766,
691 cm–1.
2-Cyano-2-phenylazopropane (3c)
Bp 95–97 °C/1.3 mbar.
1H NMR (CDCl3): d = 1.3–2.1 (m, 14 H, 7 × CH2), 3.45 (s, 3 H,
CH3O), 7.3–7.8 (m, 5 H, Ar).
IR (neat): 2990, 2937, 2241, 1524, 1479, 1456, 1364, 1238, 1171,
1150, 768, 689 cm–1.
1H NMR (CDCl3): d = (s, 6 H, 2 × CH3), 7.3–7.8 (m, 5 H, Ar).
13C NMR (CDCl3): d = 21.01 (CH2), 24.43 (CH2), 28.10 (CH2),
30.58 (CH2), 50.25 (CH3O), 101.03 (C), 122.24 (CH), 128.92 (CH),
130.47 (CH), 151.97 (C).
MS (EI): m/z (%) = 141 ([M – PhN2]+, 100), 109 (22), 77 (34), 67
(48), 50 (13), 45 (16), 44 (20), 39 (24).
13C NMR (CDCl3): d = 25.45 (CH3), 67.92 (C), 120.37 (CN),
122.85 (CH), 129.13 (CH), 131.77 (CH), 150.83 (C).
MS(CI): m/z = 247 (M + 1)+.
MS (EI): m/z (%) = 144 (6), 105 (62), 78 (21), 77 (100), 51 (50), 41
(11), 27 (HCN+, 4).
HRMS: m/z calcd for C9H17O: 141.1279; found: 141.1320 (M –
PhN2)+.
MS (CI): m/z = 174 (M + 1)+.
+
Anal. Calcd for C15H22N2O (246.34): C, 73.13; H, 9.00; N, 11.37.
Found: C, 73.05; H, 9.12; N, 11.11.
HRMS: m/z calcd for C6H5N2: 105.0453; found: 105.0443 (PhN2 ).
Anal. Calcd for C10H11N3 (173.21): C, 69.34; H, 6.40; N, 24.26.
Found: C, 69.02; H, 6.58; N, 23.95.
1-Methoxy-1-phenylazocyclononane (2h)
Bp 156–158 °C/2.0 mbar.
IR (neat): 2926, 2851, 1740, 1663, 1601, 1450, 1094, 764, 691 cm–1.
4-Cyano-4-phenylazoheptane (3e)
Bp 124–126 °C/2.0 mbar.
1H NMR (CDCl3): d = 1.3–2.2 (m, 16 H, 8 × CH2), 3.36 (s, 3 H,
IR (neat): 2963, 2876, 2237, 1524, 1466, 1456, 1144, 770, 691 cm–1.
1H NMR (CDCl3): d = 0.94 (t, 6 H, J = 7 Hz, 2 × CH3), 1.1–1.8 (m,
4 H, 2 × CH2), 1.9–2.3 (m, 4 H, 2 × CH2), 7.3–7.8 (m, 5 H, Ar).
13C NMR (CDCl3): d = 13.93 (CH3), 17.71 (CH2), 39.74 (CH2),
76.96 (C), 118.82 (CN), 122.81 (CH), 129.13 (CH), 131.57 (CH),
150.95 (C).
CH3O), 7.3–7.9 (m, 5 H, Ar).
13C NMR (CDCl3): d = 18.94 (CH2), 22.44 (CH2), 27.57 (CH2),
28.59 (CH2), 50.53 (CH3O), 102.17 (C), 122.28 (CH), 128.92 (CH),
130.51 (CH), 151.97 (C).
MS (EI): m/z (%) = 155 ([M – PhN2]+, 100), 81 (60), 77 (34), 67
(27), 55 (26), 41 (24).
MS (CI): m/z = 261 (M + 1)+.
MS (EI): m/z (%) = 172 (8), 105 (39), 77 (100), 51 (15), 41 (10), 27
(HCN+, 7).
HRMS: m/z calcd for C10H19O: 155.1436; found: 155.1402 (M –
MS (CI): m/z = 230 (M + 1) +.
PhN2)+.
+
HRMS: m/z calcd for C6H5N2: 105.0453; found: 105.0421 (PhN2 ).
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Anal. Calcd for C14H19N3 (229.32): C, 73.32; H, 8.35; N, 18.33.
Found: C, 73.39; H, 8.49; N, 18.19.
IR (neat): 2961, 2874, 2239, 1747, 1602, 1506, 1454, 1258, 1094,
766, 691 cm–1.
1H NMR (CDCl3): d = 1.5–2.6 (m, 8 H, 4 × CH2), 7.3–7.8 (m, 5 H,
1-Cyano-1-phenylazocyclohexane (3f)
Mp 53–55 °C.
Ar).
13C NMR (CDCl3): d = 25.08 (CH2), 38.24 (CH2), 110.35 (C),
120.25 (CN), 122.81 (CH), 129.08 (CH), 131.57 (CH), 150.87 (C).
IR (CCl4): 2941, 2864, 2239, 1522, 1479, 1454, 1312, 1292, 1072,
1020 cm–1.
1H NMR (CDCl3): d = 1.1–2.4 (m, 10 H, 5 × CH2), 7.3–7.8 (m, 5 H,
Ar).
13C NMR (CDCl3): d = 22.27 (CH2), 24.64 (CH2), 34.25 (CH2),
74.15 (C), 119.35 (CN), 122.81 (CH), 129.09 (CH), 131.61 (CH),
151.07 (C).
MS (EI): m/z (%) = 105 (91), 78 (24), 77 (100), 51 (51), 39 (15), 27
(HCN +, 7).
MS (CI): m/z = 200 (M + 1)+.
+
HRMS: m/z calcd for C6H5N2: 105.0453; found: 105.0451 (PhN2 ).
1-Cyano-1-phenylazo-2-methylcyclohexane (3l)
Bp 134–136 °C/1.6 mbar.
MS (EI): m/z (%) = 184 (6), 105 (65), 77 (100), 51 (23), 41 (9), 27
(HCN +, 5).
IR (neat): 2936, 2860, 2237, 1522, 1455, 1381, 1153, 1070, 997
cm–1.
1H NMR (CDCl3): d = 1.0–1.1 (m, 3 H, CH3), 1.2–2.7 (m, 9 H, CH
and 4 × CH2), 7.4–8.0 (m, 5 H, Ar).
13C NMR (CDCl3): d = 16.49 (CH3), 16.78 (CH3), 21.05 (CH2),
22.36 (CH2), 24.72 (CH2), 25.00 (CH2), 29.77 (CH2), 30.99 (CH2),
34.57 (CH2), 36.32 (CH2), 38.16 (CH), 39.95 (CH), 75.01 (C),
79.69 (C), 117.48 (CN), 119.92 (CN), 122.73 (CH), 129.08 (CH),
131.57 (CH), 150.99 (C), 151.28 (C).
MS (CI): m/z = 214 (M + 1)+.
+
HRMS: m/z calcd for C6H5N2: 105.0453; found: 105.0464 (PhN2 ).
Anal. Calcd for C13H15N3 (213.27): C, 73.21; H, 7.09; N, 19.70.
Found: C, 73.41; H, 7.19; N, 19.67.
2-Cyano-2-phenylazobutane (3i)
Bp 108–110 °C/2.0 mbar.
IR (neat): 2976, 2939, 2239, 1524, 1454, 1312, 1150, 1072, 766,
691 cm–1.
1H NMR (CDCl3): d = 1.06 (t, 3 H, J = 8 Hz, CH3), 1.72 (s, 3 H,
CH3), 1.8–2.3 (m, 2 H, CH2), 7.3–7.8 (5 H, m, Ar).
13C NMR (CDCl3): d = 8.80 (CH3), 23.74 (CH3), 32.05 (CH2),
72.97 (C), 119.39 (CN), 122.81 (CH2), 129.13 (CH2), 131.69 (CH2),
150.91 (C).
MS (EI): m/z (%) = 184 (6), 105 (47), 77 (100), 51 (13), 41 (6), 27
(HCN+, 3).
MS (CI): m/z = 228(M+1)+.
+
HRMS: m/z calcd for C6H5N2: 105.0453; found: 105.0441 (PhN2 ).
Anal. Calcd for C14H17N3 (227.30): C, 73.97; H, 7.54; N, 18.49.
Found: C, 74.24; H, 7.63; N, 18.30.
MS (EI): m/z (%) = 144 (14), 105 (92), 78 (28), 77 (100), 51 (57),
39 (9), 27 (HCN+, 12).
4-tert-Butyl-1-cyano-1-phenylazocyclohexane (3m)
Mp 144–145 °C.
MS (CI): m/z = 188 (M + 1)+.
+
HRMS: m/z calcd for C6H5N2: 105.0453; found: 105.0458 (PhN2 ).
IR (CCl4): 2957, 2868, 2239, 1479, 1454, 1396, 1367, 1240, 1153,
930 cm–1.
Anal. Calcd for C11H13N3 (187.24): C, 70.56; H, 7.00; N, 22.44.
Found: C, 70.47; H, 7.11; N, 22.19.
1H NMR (CDCl3): d = 0.94 (s, 9 H, t-C4H9), 1.24–2.4 (m, 9 H, CH
and 4 × CH2), 7.3–7.8 (m, 5 H, Ar).
13C NMR (CDCl3): d = 23.54 (CH2), 27.49 (CH3), 32.41 (C), 34.45
(CH2), 46.79 (CH), 74.76 (C), 119.19 (CN), 122.81 (CH), 129.09
(CH), 131.61 (CH), 151.07 (C).
2-Cyano-2-phenylazoheptane (3j)
Bp 128–130 °C/1.6 mbar.
IR (neat): 2957, 2932, 2239, 1603, 1522, 1454, 1377, 1148, 1070,
768, 691 cm–1.
1H NMR (CDCl3): d = 0.87 (t, 3 H, J = 8 Hz, CH3), 1.1–1.6 (m, 6 H,
3 × CH2), 1.73 (s, 3 H, CH3), 1.8–2.3 (m, 2 H, CH2), 7.3–7.8 (m, 5
H, Ar).
13C NMR (CDCl3): d = 13.89 (CH3), 22.32 (CH2), 24.07 (CH2),
24.15 (CH3), 31.52 (CH2), 38.73 (CH2), 72.48 (C), 119.60 (CN),
122.81 (CH2), 129.13 (CH2), 131.65 (CH2), 150.91 (C).
MS (EI): m/z (%) = 184 (3), 105 (76), 77 (100), 57 (18), 51 (9), 41
(15), 27 (2, HCN+).
MS (CI): m/z = 270 (M + 1)+.
+
HRMS: m/z calcd for C6H5N2: 105.0453; found: 105.0413 (PhN2 ).
Anal. Calcd for C17H23N3 (269.38): C, 75.79; H, 8.61; N, 15.60.
found: C, 76.00; H, 8.71; N, 15.60.
MS (EI): m/z (%) = 144 (10), 105 (41), 78 (8), 77 (100), 51 (11), 41
(7), 27 (HCN+, 4).
MS (CI): m/z = 230 (M + 1)+.
References
(1) Schantl, J. Tetrahedron Lett. 1970, 3785.
(2) Chiusoli, G. P.; Venturello, C. Organometal. Chem. Synth.
1971, 1, 203.
HRMS: m/z calcd for C6H5N2 (229.32): 105.0453; found: 105.0456
(PhN2 ).
+
(3) Harrison, M. J.; Norman, R. O. C.; Gladstone, W. A. F. J.
Chem. Soc. C 1967, 735.
(4) Iffland, D. C.; Salisbury, L.; Schafer, W. R. J. Am. Chem.
Soc. 1961, 83, 747.
(5) Okimoto, M.; Chiba, T. J. Org. Chem. 1990, 55, 1070.
(6) Okimoto, M.; Takahashi, Y. Bull. Chem. Soc. Jpn. 2002, 75,
2059.
Anal. Calcd for C14H19N3: C, 73.32; H, 8.35; N, 18.33. Found: C,
73.38; H, 8.40; N, 17.96.
1-Cyano-1-phenylazocyclopentane (3k)
Obtained as crude product; ca. 80% purity; bp 118–123 °C/1.6
mbar.
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PAPER
Electrochemical Formation of Methoxy- and Cyano(phenylazo)alkanes
2063
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Synthesis 2003, No. 13, 2057–2063 © Thieme Stuttgart · New York