Synthesis of a new thiocarbamate by the reaction of benzyl thiocyanate with camphene, catalyzed by heteropoly acids

Article abstract of DOI:10.1134/S1070427207010338

The reaction of benzyl thiocyanate with camphene in the presence of heteropoly acids, 12-phosphotungstic and 12-silicotungstic, at 65 C was studied. S-Benzyl (1,7,7-trimethylnorbornyl)thiocarbamate was prepared in 66% yield.

Full text of DOI:10.1134/S1070427207010338

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2007, Vol. 80, No. 1, pp. 162 163. Pleiades Publishing, Ltd., 2006.
Original Russian Text
No. 1, pp. 162 163.
A.V. Arkhipova, K.V. Malkova, T.N. Sokolova, V.R. Kartashov, 2007, published in Zhurnal Prikladnoi Khimii, 2007, Vol. 80,
BRIEF
COMMUNICATIONS
Synthesis of a New Thiocarbamate by the Reaction of Benzyl
Thiocyanate with Camphene, Catalyzed by Heteropoly Acids
A. V. Arkhipova, K. V. Malkova, T. N. Sokolova, and V. R. Kartashov
Nizhni Novgorod State Technical University, Nizhni Novgorod, Russia
Received May 30, 2006
Abstract The reaction of benzyl thiocyanate with camphene in the presence of heteropoly acids, 12-phos-
photungstic and 12-silicotungstic, at 65 C was studied. S-Benzyl (1,7,7-trimethylnorbornyl)thiocarbamate was
prepared in 66% yield.
DOI: 10.1134/S1070427207010338
Previously [1] we reported on the reactions of a se-
ries of thiocyanates with a natural terpene, camphene,
in the presence of concentrated sulfuric acid, yielding
the coresponding N-substituted thiocarbamates. We
examined the possibility of using heteropoly acids
(HPAs) for catalyzing this reaction. It is of funda-
mental importance for catalysis that HPAs have high
Brønsted acidity, considerably exceeding that of com-
mon mineral acids and traditional acid catalysts [2].
in the acidity they exceed by 2 5 pK units the tradi-
tional acid catalyst, sulfuric acid [4].
The initial camphene : thiocyanate molar ratio was
1 : 1.48. The reaction was performed with water addi-
tions, because without water the HPA precipitates. It
should also be noted that small amounts of water al-
low the reaction to be performed at a relatively low
temperature.
It is known [5] that camphene can isomerize in
By the reaction of benzyl thiocyanate with cam-
phene in the presence of the most typical tungstic
heteropolyacids, H PW O and H SiW O , we
acid-catalyzed reactions; as a result, several com-
13
pounds are usually formed. Comparison of the
C
3
12 40
4
12 40
NMR spectrum of the purified product with those of
various camphene derivatives [5] allowed identifica-
tion of the compound obtained.
prepared a new camphene derivatives, S-benzyl (1,7,7-
trimethylnorbornyl)thiocarbamate:
Analysis of the mother liquor revealed formation
of small amounts of isobornyl acetate and isoborneol
along with the major product, benzyl (1,7,7-trimethyl-
norbornyl)thiocabamate. These by-products were iden-
tified by GLC using authentic samples.
We optimized the concentrations of the acids used,
reaction temperature, and reactant weight ratio. We
found that the reaction mixture, when heated above
65 C, undergoes tarring (as judged from its color and
amount of the bottoms), which considerably decreases
the yield of the target product.
It should be noted that benzyl thiocyanate does not
react with camphene in the presence of sulfuric acid
as catalyst [1].
The heteropoly acid H SiW O also actively
4
12 40
catalyzes the reaction in question. On the whole, how-
ever, it does not surpass in performance H PW O .
The reaction was performed in acetic acid, taking
into account published data on related syntheses of
N-substituted thiocarbamates [1]. Heteropoly acids of
the Keggin structure in acetic acid are relatively weak
electrolytes dissociating by the first step only [3], but
3
12 40
This fact is consistent with close strength of these
acids. It is known that the strength of heteropolytung-
stic acids depends on the nature of the central atom
insignificantly [2].
162

SYNTHESIS OF A NEW THIOCARBAMATE
163
EXPERIMENTAL
cyanate and 0.12 g (0.88 mmol) of camphene in 3 ml
of acetic acid was added to 1.34 g (0.46 mol) of
H PW O wetted with water (0.2 ml, 11.11 mmol).
The mixture was heated for 4 h at 65 C. White crys-
tals of benzyl (1,7,7-trimethylnorbornyl)thiocarbamate
were obtained; yield 0.18 g (66% based on the initial
amount of camphene), mp 87 C.
The synthesis was performed for 2 8 h at various
temperatures in a temperature-controlled glass reactor
equipped with a reflux condenser. After the reaction
completion, the mixture was extracted with diethyl
ether in an amount equal to a half of the volume of
the aqueous phase. The organic phase was washed
with 10% NaOH and then with water to neutral reac-
tion of the wash waters, after which it was dried for
24 h over Na SO . The organic layer was analyzed by
3
12 40
Found, %: C 71.9, H 8.5, N 4.3.
C18H25NOS.
Calculated, %: C 71.3, H 8.3, N 4.6.
2
4
GLC. To obtain pure samples of the product, the solv-
ent was removed at reduced pressure. The crystalline
residue was repeatedly recrystallized from n-hexane
until the melting point became constant.
Mass spectrum (electron impact, 70 eV), m/z (I ,
rel
+
%): 303 [M] (20), 212 (11), 180 (14), 137 (16), 124
13
(98), 109 (10), 91 (100), 81 (36), 55 (8), 41(12).
C
NMR spectrum (CDCl , , ppm): 49.3 C(1); 57.3
3
The heteropoly acids of the 12th series H PW O
3
12 40
C(2); 36.2 C(3); 44.5 C(4); 26.1 C(5); 35.4 C(6); 46.2
and H SiW O (pure grade commercial products)
4
12 40
C(7); 19.8, 20.3 [2CH , CH C(7)]; 11.5 [CH C(1)];
3
3
3
were used without additional purification. The starting
127.2, 127.5, 130.0 (C , C , C ); 136.4 (C ); 28.8
22
o
p
m
ipso
optically active camphene {[ ]
+12.5 (c 11.6,
580
(CH , COSCH Ph); 166.8 (CO, COSCH Ph).
2
2
2
CHCl )}, which initially contained 10% tricyclene
3
(GLC data), was brought to 99% purity by recrystalli-
zation from EtOH, mp 50 C (published data [6]: mp
50 C). Acetic acid was purified by distillation of the
ultrapure grade acid on a 0.3-m distillation column.
Commercial chemically pure grade (97% purity) ben-
zyl thiocyanate was used without additional purifica-
tion. Technical-grade isoborneol was brought to 96%
purity (GLC data) by fractional recrystallization from
ethanol. Diethyl ether, ethanol, and n-hexane (chemi-
cally pure grade) were purified by standard procedures
[7]. Isobornyl acetate was prepared by the procedure
described in [8].
CONCLUSIONS
(1) Benzyl (1,7,7-trimethylnorbornyl)thiocarbamate
was prepared in 66% yield by the reaction of benzyl
thiocyanate with camphene in the presence of hetero-
poly acids. With sulfuric acid as catalyst, this com-
pound is not formed at all.
(2) Isoborneol and isobornyl acetate are formed in
this reaction as by-products.
REFERENCES
The purity of the starting substances was checked
and the reaction products analyzed by GLC on a
Chrom 5 chromatograph equipped with a flame ioni-
zation detector and a 30000 10-mm column; sta-
tionary phase polyphenylmethylsiloxane-4 (15%) on
Chromaton N-AW-DMSC (0.20 0.25 mm), column
temperature 180 190 C, carrier gas (nitrogen) pres-
sure 2.5 atm. As internal reference we used N-(1,7,7-
trimethylnorbornyl)propionamide.
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13
The C NMR spectra (32 MHz) were recorded
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(CDCl ) signal as internal reference ( 7.24,
3
C
76.90 ppm).
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A solution of 0.2 g (1.34 mmol) of benzyl thio-
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 80 No. 1 2007