SUERBAEV et al.
586
Esterification of isovaleric acid with L-menthol in the pres-
ence of p-toluenesulfonic acid under microwave irradiation
chromatograph coupled with an HP 5975C mass-selec-
tive detector; HP-FFAP capillary column (30 m×
0.25 mm), stationary phase poly(ethylene glycol)-
modified nitroterephthalic acid; carrier gas helium;
injector temperature 300°C, oven temperature pro-
gramming from 40°C (1 min) at a rate of 5 deg/min to
250°C (1 min); total time 44 min; split ratio 1000:1;
electron impact ionization; retention time of 3
20.4 min. The IR spectra were recorded in KBr on
Reaction time, Yield of 3,
Ratio 1–2–TsOH (mol %)
min
wt %
1:1:5.45×10–5
1:1:5.45×10–5
1:1:5.45×10–5
1:1:5.45×10–5
1:1:4.1×10–5
1:1:6.81×10–5
1:1:8.51×10–5
1:0.9:8.51×10–5
1:1.1:8.51×10–5
1:1.2:8.51×10–5
1:1.3:8.51×10–5
10
11
12
13
12
12
12
12
12
12
12
55.2
63.9
65.7
60.6
55.8
77.7
78.8
81.4
82.5
88.7
81.7
1
a UR-20 spectrometer. The H NMR spectrum was
measured on a Bruker DPX 400 instrument (300 MHz)
using chloroform-d as solvent and tetramethylsilane as
internal standard.
Commercial isovaleric acid and p-toluenesulfonic
acid (Sigma–Aldrich) and reagent grade L-menthol and
concentrated sulfuric acid were used without additional
purification.
optimal 1–2–H2SO4 ratio was 1:1:9.6×10–5 (irradia-
tion time 12 min). Thus the yield of 3 is strongly
determined by the MW power and irradiation duration,
whereas the ratio of the reactants and catalyst is less
significant. The yield of 3 under the optimal conditions
was 59%.
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When the reaction was carried out in the presence
of another acid catalyst, p-toluenesulfonic acid, the
optimal conditions were MW power 560 W, irradiation
time 12 min, and ratio 1–2–TsOH 1:1.2:8.51×10–5.
These conditions ensured 89% yield of 3.
The structure of 3 was confirmed by IR and
1H NMR spectra. The IR spectrum of 3 showed
a strong ester carbonyl stretching band at 1731 cm–1,
and absorption bands at 1050–1300 (C–O–C) and
1
2870–3543 cm–1 (C–H). The H NMR spectrum of 3
was fully consistent with published data [5].
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charged with required amounts of isovaleric acid,
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to microwave irradiation in a Samsung MB 39449G
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gave ester 3 with bp 123°C (6 mm), nD20 = 1.4480;
published data [10]: bp 129°C (10 mm), nD20 = 1.4486.
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(Synthetic Fragrant Subctances), Yerevan: Akad. Nauk
Arm. SSR, 1946.
Gas chromatographic–mass spectrometric analysis
was performed on an Agilent Technologies 7890A gas
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 52 No. 4 2016