PREPARATIVE SYNTHESIS OF VERATRALDEHYDE AND CITRAL OXIME ESTERS
645
1
1
Me2C=CH(CH2)2C(Me)=CHCH=O
characteristic bands at 1535 and 1350 cm . In the H
NMR spectra of VIa VIt, the Me2C=C protons are
manifested as two broadened singlets at 1.60 0.05
and 1.66 0.04 ppm, and the MeC=C protons, as
a broadened singlet at 2.05 0.05 ppm. The HC=C
protons appear as signals at 4.90 6.40 ppm. The sig-
nals of aromatic protons in VIm VIq are observed as
a multiplet at 7.10 9.00 ppm.
Me2C=CH(CH2)2C(Me)=CHCH=NOH
IV
Me2C=CH(CH2)2C(Me)=CHCH=NOC(O)R,
VIa VIt
where R = Me (VIa), Et (VIb), Pr (VIc), Me2CH
(VId), Me2CHCH2 (VIe), Me(CH2)4 (VIf), Me(CH2)5
(VIg), Me(CH2)6 (VIh), Me(CH2)7 (VIi), Me(CH )
(VIj), Me(CH2)16 (VIk), cyclo-C6H11 (VIl), C62H115
(VIm), C6H5(CH2)2 (VIn), cis-C6H5CH=CH (VIo),
C6H5CH=C(C N) (VIp), 3-O2NC6H4 (VIq), MeO
(VIr), EtO (VIs), MeOC(O)(CH2)2C (VIt).
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The H NMR spectra of Va Vs and VIa VIt also
contain the characteristic signals of the ester frag-
ments.
EXPERIMENTAL
The IR spectra were recorded on a Protege-460 IR
Fourier spectrometer (Nicolet) from thin films or KBr
pellets. The H NMR spectra were measured on a BS-
587A spectrometer (100 MHz, Tesla) from 5% solu-
tions in CDCl3; the chemical shifts were determined
relative to internal tetramethylsilane. The molecular
weight M was determined cryoscopically in benzene.
The physicochemcial characteristics of veratraldehyde
II and of oximes of veratraldehyde (III) and citral
(IV) were in agreement with reference data [1, 9, 10].
Oxime esters Va Vs and VIa VIt are colorless
viscous liquids or crystalline compounds crystallizing
from benzene hexane (see table). The esters do not
require additional purification, contain no admixtures
of the starting compounds, benzene, and pyridine,
and can be directly used in fragrance and food indus-
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1
try [3]. According to the H NMR spectra, the com-
pounds were 97 98% pure. Oxime esters Va Vs and
VIa VIt can be well stored at a temperature below
+5 C in the dark under anaerobic conditions. Unsatu-
rated compounds VI VIt were stabilized by adding
0.5% hydroquinone to prevent polymerization.
Veratraldehyde II. A 14-g portion of 90% KOH
was dissolved in 210 ml of water. The solution was
cooled to 20 23 C, and 0.2 mol of vanillin was added
with vigorous stirring. After vanillin fully dissolved,
22 ml of Me2SO4 was added in a single portion.
The mixture was stirred for 6 h at 20 23 C, after
which the stirring was stopped, and the mixture was
cooled to 5 C and left for 10 12 h. The crystalline
precipitate of veratraldehyde II formed in the process
was filtered off on a glass frit, washed with a small
amount of water, and dried in air. Yield 90%.
The compositions and structures of oxime esters
Va Vs and VIa VIt were confirmed by elemental
analysis, cryoscopic determination of the molecular
1
weight (see table), and H NMR and IR spectroscopy.
The IR spectra of veratraldehyde oxime esters Va
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Vs contain the following absorption bands, cm :
CHAr in the range 3100 3000, CHAlk at 3000 2800,
C=O at 1770 1730, C=N at 1675 1665, Ar at 1600
1360, C O at 1300 1000, CHAr at 880 620. In
Veratraldehyde oxime III. A mixture of veratr-
aldehyde II (0.21 mol), hydroxylamine hydrochloride
(0.27 mol), sodium hydrogen carbonate (0.28 mol),
and 96% ethanol (75 ml) was refluxed for 1 h. Then
the mixture was poured into a beaker with 300 ml of
water, cooled to 5 C, and left for 10 12 h. The crys-
talline precipitate of veratraldehyde oxime III formed
in the process was filtered off on a glass frit, washed
with a small amount of water, and dried in air. Yield
92%.
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the H NMR spectra of veratraldehyde oxime esters
Va Vs, the MeO protons give two singlets at 3.90
4.10 ppm. The aromatic protons appear as a multiplet
at 6.70 7.50 ppm. The HC=N proton signal is a sin-
glet at 8.20 8.30 ppm.
The IR spectra of citral oxime esters VIa VIt con-
1
tain the following absorption bands, cm : CHAlk in
the range 3000 2800, =CH at 3050 3020, C=O at
1770 1740, C=C at 1670 1665, C=N at 1645 1635,
CH2 at 1667 1663, C O at 1250 1180. The IR spec-
tra of aromatic carboxylic acid esters VIm VIq also
contain the CHAr absorption bands at 3100 3000 and
707 690, and the Ar absorption bands at 1600 1595,
Veratraldehyde and citral oxime esters Va Vd
and VIa VId (general procedure). Veratraldehyde
oxime III or citral oxime IV (0.01 mol) and appro-
priate acid anhydride (0.011 mol) were dissolved in
20 ml of absolute benzene, and a drop of 47% HClO4
was added. The mixture was shaken and allowed to
stand at 20 23 C for 24 36 h. Then the mixture was
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1455 1450, and 1380 1370 cm . The C N group in
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the IR spectrum of VIp gives a band at 2219 cm ,
and the NO2 group in the spectrum of VIq gives two
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 81 No. 4 2008
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