Synthesis and cyclisation of 1,4-disubstituted semicarbazides

Article abstract of DOI:10.1080/14786410802435935

Semicarbazides, besides possessing medicinal properties, also find wide applications in agriculture and industry. We report in this article the synthesis of the four 1,4-disubstituted semicarbazides: 1-cinnamoyl-4-phenyl semicarbazide (1), 1-oleyl-4-phenyl semicarbazides (2), 1,1',1''-tricitryl-4,4', 4''-triphenyl semicarbazide (3) and 1-benzoyl-4-phenyl semicarbazide (4), by the condensation of four different hydrazides: cinnamic acid hydrazide (5), oleic acid hydrazide (6), citric acid hydrazide (7) and benzoic acid hydrazide (8). The acid hydrazides were prepared by the condensation of four different acids with phenyl isocyanate. The semicarbazides were also subjected to acid catalysed intramolecular cyclisation. The cyclisation of (1) and (2) afforded substituted 1,3,4-oxadizoles: 2-cinnamoyl-5-aminophenyl 1,3,4-oxadizoles (9) and 2-oleyl-5-aminophenl 1,3,4-oxadizoles (10), respectively, in high yield, while no cyclisation occurred in the cases of (3) and (4). The products in each case have been identified on the basis of melting points and IR spectral studies.

Full text of DOI:10.1080/14786410802435935

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Synthesis and cyclisation of 1,4-
disubstituted semicarbazides
Syeda Farina Asghar a , Khawaja Ansar Yasin a , Habib-ur-Rehman a
& Shahid Aziz a
a Department of Chemistry, University of Azad Jammu and
Kashmir, Muzaffarabad, Pakistan
Version of record first published: 10 Mar 2010.
To cite this article: Syeda Farina Asghar, Khawaja Ansar Yasin, Habib-ur-Rehman & Shahid Aziz
(2010): Synthesis and cyclisation of 1,4-disubstituted semicarbazides, Natural Product Research:
Formerly Natural Product Letters, 24:4, 315-325
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Natural Product Research
Vol. 24, No. 4, 10 March 2010, 315–325
Synthesis and cyclisation of 1,4-disubstituted semicarbazides
*
Syeda Farina Asghar, Khawaja Ansar Yasin, Habib-ur-Rehman and
Shahid Aziz
Department of Chemistry, University of Azad Jammu and Kashmir, Muzaffarabad, Pakistan
(Received 21 August 2007; final version received 15 September 2007)
Semicarbazides, besides possessing medicinal properties, also find wide
applications in agriculture and industry. We report in this article the
synthesis of the four 1,4-disubstituted semicarbazides: 1-cinnamoyl-4-
phenyl semicarbazide (1), 1-oleyl-4-phenyl semicarbazides (2), 1,10,100-
tricitryl-4,40,400-triphenyl semicarbazide (3) and 1-benzoyl-4-phenyl semi-
carbazide (4), by the condensation of four different hydrazides: cinnamic
acid hydrazide (5), oleic acid hydrazide (6), citric acid hydrazide (7) and
benzoic acid hydrazide (8). The acid hydrazides were prepared by the
condensation of four different acids with phenyl isocyanate.
The semicarbazides were also subjected to acid catalysed intramolecular
cyclisation. The cyclisation of (1) and (2) afforded substituted 1,3,4-
oxadizoles: 2-cinnamoyl-5-aminophenyl 1,3,4-oxadizoles (9) and 2-oleyl-5-
aminophenl 1,3,4-oxadizoles (10), respectively, in high yield, while no
cyclisation occurred in the cases of (3) and (4). The products in each case
have been identified on the basis of melting points and IR spectral studies.
Keywords: substituted semicarbazide; acid hyrazides; oxadizoles; synthesis;
physical data
1. Introduction
Semicarbazides are well known for their wide applications in pharmaceutical and
agricultural fields (Konishi & Matsuura, 1982; Renth, Mentrup, Schromm, &
Traunecker, 1985). Most semicarbazides possess herbicidal and fungicidal
(Brantley, 1970; Raman, Surendras, & Steven, 1989), bactericidal (Egrenc¸ , IIhan,
& Otuk, 1992; Foroumadi, Mansouri, Kiani, & Rahmani, 2003; Ram et al., 1990),
antimyobacterial (Rudnicka, Foks, Janowiee, & Zwolska-Kwick, 1986), antituber-
cular (Mir, Siddiqui, & Comrie, 1970) and anticancer (Holla, Verendra, Shivmanda,
& Poojary, 2003) activities. Some of them have shown inhibitory effects on blood
coagulation (Raman et al., 1989). Some others showed anticonvulsant activities and
platelet aggregation (Beregi et al., 1974; Coyne & Cusic, 1968; Gerhard, Rudi,
Walter, & Erich, 1966; Labouta, Hassan, Omainma, Kader, & Montash, 1989). They
are also used for treating ameliorating, neurodegenerative conditions, depression,
and to provide local anaesthesia (Hajipour, Mallakpour, & Khoee, 2000;
*Corresponding author. Email: drhabib56@yahoo.com
ISSN 1478–6419 print/ISSN 1029–2349 online
ß 2010 Taylor & Francis
DOI: 10.1080/14786410802435935
http://www.informaworld.com

316
S.F. Asghar et al.
Mallakpour, 1992; Toda, 1995). They also exhibit a stabilising effect on the liquid
crystalline state of chloroplast membrane lipids, and some are known as surfactants
(Brantley, 1970; Konishi & Matsuura, 1982; Renth et al., 1985; Raman et al.,
1989). Another report showed that semicarbazides are also used as stabilising agents
in polymer industry (Coyne & Cusic, 1968). Biological activities of 1, 4-disubstituted
semicarbazides prompted us to synthesise the substituted semicarbazides
1-cinnamoyl-4-phenyl semicarbazide (1), 1-oleyl-4-phenyl semicarbazides (2),
1,10,100-citryol-4,40,400-phenyl semicarbazide (3) and 1-benzoyl-4-phenyl semicarba-
zide (4). The acid hydrazides 5–8 used in the synthesis of the semicarbazides were
also prepared by the condensation of different acids with isocycanate. The
semicarbazides 1–4 were also subjected to cyclisation. The attempted cyclisations
of 1 and 2 have been successful, while 3 and 4 did not cyclise. The identification of
the products was made on the basis of their melting points and their IR spectral data.
2. Results and discussion
The major aim of the present work was to synthesise some 1,4-disubstituted
semicarbazides. The 1,4-disubstituted semicarbazides may be synthesised by refluxing
phenyl isocyanate with the corresponding carboxylic acid hydrazide. The carboxylic
acid hydrazides were obtained by the reaction of hydrazine with carboxylic acid. The
1,4-disubstituted semicarbazides were also subjected to acid catalysed intramolecular
cyclisation on reaction with concentrated sulphuric acid. The four substituted
semicarbazides 1-cinnamoyl-4-phenyl semicarbazide (1), 1-oleoyl-4-phenyl semicar-
bazide (2), 1,10,100-citroyl-4,40,400-phenyl semicarbazide (3) and 1-benzoyl-4-phenyl
semicarbazide (4) were synthesised. The four acid hydrazides, cinnamic acid hydrazide
(5), oleic acid hydrazide (6), citric acid hydrazide (7) and benzoic acid hydrazide (8),
used in the synthesis of semicarbazides, were also synthesised. The semicarbazides were
subjected to acid catalysed intramolecular cyclisation to afford two 2,5-disubstituted
1,3,4-oxadizoles: 2-cinnamoyl-5-aminophenyl 1,3,4-oxadizoles (9) and 2-oleyl-5-
aminophenyl 1,3,4-oxadizoles (10).
1-Cinnamoyl-4-phenyl semicarbazide (1): Compound 1 was obtained with 78.0% yield
by refluxing cinnamic acid hydrazide with phenyl isocyanate. The product was
confirmed by melting point and IR spectral studies. The melting points of cinnamic
acid hydrazide and phenyl isocyanate were 152 and 158ꢀC, respectively, while the
melting point of compound 1 was found to be 45ꢀC. The IR spectrum (KBr) showed
intense ꢀmax absorptions at 3355, 3028, 1708, 1647 and 1068 cmꢁ1, suggesting the
presence of N–H, C–H (sp2), C¼O (urea), C¼O (hydrazide) and C–N functions in
the molecule. The IR spectral data are presented in Table 1. The reaction is presented
in Scheme 1.
1-Oleoyl-4-phenyl semicarbazide (2): Compound 2 was synthesised with yield 100.0%
by refluxing oleic acid hydrazide with phenyl isocyanate. The synthesis of product 2
was confirmed by melting point and IR spectral studies. The melting points of oleic
acid hydrazide and phenyl isocyanate were 93 and 158ꢀC, respectively, while the
melting point of compound 2 was found to be 75ꢀC. The IR spectrum (KBr) showed
intense ꢀmax absorptions at 3353, 3026, 2954, 1708, 1658 and 1068 cmꢁ1, suggesting
the presence of N–H, C–H (sp2), C–H (sp3), C¼O (urea), C¼O (hydrazide) and C–N

Natural Product Research
Table 1. IR spectral data of 1, 4-disubstituted semicarbazides.
IR absorptions in cmꢁ1
ꢀC–H ꢀC–H
317
ꢀC¼O
ꢀC¼O
S. no
Compound
ꢀN–H (Urea) ꢀC¼C (sp2) (sp3) (Hydrazide) ꢀC–N ꢀO–H
1
2
3
4
1-Cinnamoyl-4-phenyl- 3355 1708
1544
1542
1598
1593
3028 2952 1647
3056
3026 2954 1658
3055
3028 2954 1647
3056
1068
–
1-Oleyl-4-phenyl-
3353 1708
3355 1787
3325 1710
1068
–
1,10,100-Tricitryl-4,40,
400-triphenyl-
1-Benzoyl-4-phenyl-
1068 3400
1230
–
2956 1647
–
Table 2. IR spectral data of acid hydrazides.
IR absorptions in cmꢁ1
Carboxylic
acid hydrazide
ꢀC¼O
ꢀC–H ꢀCH
S. no
ꢀN–H (Hydrazide) ꢀC¼C (sp2) (sp3) ꢀC–N ꢀO–H
1
2
3
4
Cinnamic acid hydrazide 3382
1695
1706
1706
1706
1467 3155
1596 3141 2954 1462
1598
1631 3135
–
1461
–
–
Oleic acid hydrazide
Citric acid hydrazide
Benzoic acid hydrazide
3328
3328
3326
–
2954 1461 3400
1461
–
–
functions in the molecule. The melting point and IR spectral data are presented in
Tables 1 and 2, respectively. The reaction is depicted in Scheme 1.
1,19,199-Citroyl-4,49,499-phenyl semicarbazide (3): Compound 3 was obtained with
18.7% yield by refluxing citric acid hydrazide with phenyl isocyanate. The synthesis
of product 3 was confirmed by melting point and IR spectral studies. The melting
points of citric acid hydrazide and phenyl isocyanate were 80 and 158ꢀC,
respectively, while the melting point of compound 3 was 41ꢀC. The IR spectrum
(KBr) showed intense ꢀmax absorptions at 3355, 3028, 2954, 1787, 1647 and
1068 cmꢁ1, suggesting the presence of N–H, C–H (sp2), C–H (sp3), C¼O (urea),
C¼O (hydrazide) and C–N functions in the molecule. The IR spectral data are
presented in Table 1. The reaction is shown in Scheme 1.
1-Benzoyl-4-phenyl semicarbazide (4): Compound 4 was synthesised with yield 10.0%
by refluxing of oleic acid hydrazide with phenyl isocyanate. The synthesis of product
4 was confirmed by melting point and IR spectral studies. The melting points of
benzoic acid hydrazide and phenyl isocyanate were 79 and 158ꢀC, respectively, while
the melting point of compound 4 was 98ꢀC. The IR spectrum (KBr) showed intense
ꢀ
max absorptions at 3325, 3023, 1710, 1647 and 1230 cmꢁ1, suggesting the presence of
N–H, C–H (sp2), C¼O (urea), C¼O (hydrazide) and C–N functions in the molecule.
The IR spectral data are presented in Table 1. The reaction is presented in Scheme 1.

318
S.F. Asghar et al.
CH=CH
O
Ph
C
NH
Ph
HN
CH=CH
C
NH
Ph
CONHNH2
Ph–N=C=O
O
+
(1)
(CH2)7
CH=CH
H3C (CH2)7
H3C
HN
CH=CH
(CH2)7
(CH2)7
C
O
H2N HN
C
C
O
HN HN
Ph
O
Ph–N=C=O
+
(2)
O
C
NH NH2
O
HO
H2N
C
C
NH
CH2
CH2
C
O
H2N HN
Ph–N=C=O
+
O
C
O
NH NH
C
NHPh
O
O
C
HO
Ph
C
HN
C
NH
CH2
HN
CH2
C
PhHN
C
O
HN NH
O
(3)
O
C
NH NH
Ph
C
O
NH NH2
Ph
C
O
Ph–N=C=O
Ph HN
+
(4)
Scheme 1. Synthesis of 1,4-disubstituted semicarbazides 1–4.
2.1. Acid hydrazides 5–8
The four different acid hydrazides required for the synthesis were also synthesised by
the condensation of four different carboxylic acids with isocyanate.
Cinnamic acid hydrazide (5): The cinnamic acid was treated with hydrazine to yield
26.1% of cinnamic acid hydrazide (5). The product was confirmed by melting point
and IR spectral studies. The melting points of cinnamic acid and hydrazine were 133
and 202ꢀC, respectively, while the melting point of cinnamic acid hydrazide was

Natural Product Research
319
CH=CH
Ph
C
O
CH=CH
H2N NH2
H2N HN
Ph
COOH
+
(5)
O
C
O
OH
NHNH2
C
(CH2)7
CH=CH
(CH2)7
CH=CH
(CH2)7
(CH2)7
H3C
H2N NH2
H3C
+
(6)
O
C
NH
HO
NH2
NH2
C
HO COOH
C
O
CH2 CH2
C
C
NH
CH2 CH2
H2N
HN
H2N NH2
HOOC
COOH
O
+
(7)
O
H2N NH2
NHNH2
PhC
PhCOOH
+
(8)
Scheme 2. Synthesis of acid hydrazides 5–8.
found to be 152ꢀC. The IR spectrum (KBr) showed intense ꢀmax absorptions at 3382,
3155, 1695, 1467 and 1461 cmꢁ1, suggesting the presence of N–H, C–H (sp2), C¼O
(hydrazide), C¼C and C–N functions in the molecule. The IR spectral data are
presented in Table 2. The reaction is presented in Scheme 2.
Oleic acid hydrazide (6): The oleic acid was treated with hydrazine to yield 96.0% of
oleic acid hydrazide (6). The product was confirmed by melting point and IR spectral
studies. The melting points of oleic acid and of hydrazine were 92 and 202ꢀC, while
the melting point of oleic acid hydrazide was found to be 93ꢀC. The IR spectrum
(KBr) showed intense ꢀmax absorptions at 3328, 3141, 2954, 1706, 1596 and
1462 cmꢁ1, suggesting the presence of N–H, C–H (sp2), C–H (sp3), C¼O (hydrazide),
C¼C and C–N functions in the molecule. The IR spectral data are presented in
Table 2. The reaction is depicted in Scheme 2.
Citric acid hydrazide (7): The citric acid was treated with hydrazine to yield 12.5% of
citric acid hydrazide (7). The product was confirmed by melting point and IR
spectral studies. The melting points of citric acid and hydrazine were 153 and 202ꢀC,
while the melting point of citric acid hydrazide was 80ꢀC. The IR spectrum (KBr)
showed intense ꢀmax absorptions at 3400, 3328, 2954, 1706 and 1461 cmꢁ1, suggesting

320
Table 3. IR spectral data of 2,5-disubstituted 1,3,4-oxadiazoles.
IR absorptions in cmꢁ1
S.F. Asghar et al.
2,5-Disubstituted
1,3,4-oxadiazoles
ꢀC–H ꢀC–H
ꢀN–H ꢀC–O–C ꢀC¼C/C¼C (sp2) (sp3) ꢀC–N ꢀX¼C¼H ꢀC–H
S. no
1
2
2-Cinnamoyl-5-aminophenyl 3342
1,3,4 -oxadizoles
1193
1178
1708
1704
3022
–
1369
2063
2042
1232
1217
2-Oleyol-5-aminophenyl
1,3,4 -oxadizoles
3319
3006 2954 1377
the presence of O–H, N–H, C–H (sp3), C¼O (hydrazide) and C–N functions in the
molecule. The IR spectral data are presented in Table 2. The reaction is shown in
Scheme 2.
Benzoic acid hydrazide (8): The benzoic acid was treated with hydrazine to yield
42.8% of benzoic acid hydrazide (8). The product was confirmed by melting point
and IR spectral studies. The melting points of benzoic acid and hydrazine were 122
and 202ꢀC, respectively, while the melting point of benzoic acid hydrazide was found
to be 79ꢀC. The IR spectrum (KBr) showed intense ꢀmax absorptions at 3326, 3135,
1706, 1631 and 1461 cmꢁ1, suggesting the presence of N–H, C–H (sp2) C¼O
(hydrazide), C¼C and C–N functions in the molecule. The IR spectral data are
presented in Table 2. The reaction is presented in Scheme 2.
2.2. 2,5-Disubstituted 1,3,4-oxadizoles 9 and 10
The four 1,4-disubstituted semicarbazides were subjected to acid catalysed
intramolecular cyclisation. The cyclisation of 1 and 2 afforded the oxdiazoles 9
and 10, while attempted cyclisation on 3 and 4 was not successful.
2-Cinnamoyl-5-aminophenyl 1,3,4-oxadizoles (9): The acid catalysed intramolecular
cyclisation of 1 with sulphuric acid afforded compound 9. The product was identified
on the basis of its melting point and IR spectral data. The melting point of
1-cinnamoyl-4-phenyl semicarbazide (1) was 45ꢀC, while the melting point of
compound 9 was found to be 81ꢀC. The IR spectrum (KBr) showed intense ꢀmax
absorptions at 3342, 3022, 2063, 1708, 1369, 1232 and 1193 cmꢁ1, suggesting the
presence of N–H, C–H (sp2), X¼C¼O, C¼C/C¼N, C–N, C–O and C–O–C
functions in the molecule. The IR spectral data are presented in Table 3. The
complete reaction is presented in Scheme 3.
2-Oleyol-5-aminophenyl 1,3,4-oxadizoles (10): The acid catalysed intramolecular
cyclisation with sulphuric acid afforded compound 10. The compound was identified
on the basis of its melting point and IR spectral data. The melting point of 1-oleoyl-
4-phenyl semicarbazide (2) was 75ꢀC, while the melting point of compound 10 was
85ꢀC. The IR spectrum (KBr) showed intense ꢀmax absorptions at 3319, 3006, 2042,
2954, 1704, 1377, 1217 and 1178 cmꢁ1, suggesting the presence of N–H, C–H (sp2),

Natural Product Research
321
PhHC=HC
PhHC=HC
O
PhHN
C
O
C
O
HNHN
NHPh
N
N
+ H2SO4
(9)
O
NH
C
CH=CH
(CH2)7
CH3
C
HC=HC (H2C)7
NH
O
N
(H2C)7
H3C
(CH2)7
PhHN
NHPh
N
O
+ H2SO4
(10)
Scheme 3. Intramolecular cyclisation of semicarbazides 1 and 2.
Table 4. Experimental details for the preparation of carboxylic acid hydrazides.
S.
no
Hydrazine
(mL)
Reflux
time (hrs)
Melting
%
Acids (g)
Hydrazide
point (ꢀC) Yield
1
2
3
4
Cinnamic acid (14.816)
Oleic acid (28.230)
Citric acid (19.320)
Benzoic acid (12.212)
50
50
100
50
04
01
25
04
Cinnamic acid hydrazide
Oleic acid hydrazide
Citric acid hydrazide
Benzoic acid hydrazide
152
93
80
79
26
96
12
42
X¼C¼O, C–H (sp3) C¼C/C¼N, C–N, C–O and C–O–C functions in the molecule.
The IR spectral data are presented in Table 3. The reaction is depicted in Scheme 3.
3. Experimental
3.1. Instrumentation/chemicals
The IR spectra were recorded on a FT-IR spectrophotometer 8400S (Shimadzu,
Japan). The melting points were observed on a Gallan Kamp melting point
apparatus. The magnetic stirrer of VELP Italy was used for stirring the reaction
mixture. The chemicals and solvents used were obtained from E. Merck.
3.2. Procedure
The acid hydrazides were synthesised by the reaction of the respective acids with
hydrazine. The acid hydrazides 5, 6, 7 and 8 were refluxed with phenyl isocyanate to
yield the four substituted semicarbazides, 1, 2, 3 and 4. The semicarbazides were
subjected to intramolecular cyclisation with concentrated sulphuric acid. The
cyclisation of 1 and 2 afforded 9 and 10, respectively, while the cyclisation of 3
and 4 could not be achieved. The experimental details for the preparation of the four
carboxylic acid hydrazides, 5–8, the four 1,4-disubsitituted semicarbazides, 1–4, and
the two 2, 5-disubstitued 1,3,4-oxadiazoles, 9 and 10, are given in Tables 4–6,
respectively.

322
S.F. Asghar et al.

Natural Product Research
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324
S.F. Asghar et al.
3.3. 1,4-Disubstituted semicarbazides
1-Cinnamoyl-4-phenyl semicarbazide (1): The 0.25 g of cinnamic acid hydrazide
dissolved in 10 mL of CHCl3 was treated with 2 mL phenyl isocyanate (2 mL of
phenyl isocyanate in 5 mL methanol) in a 250 mL Erlenmeyer flask. The mixture was
refluxed for 1 h, with stirring. This yielded 78.0% of 1-cinnamoyl-4-phenyl
semicarbazide (1), obtained by drying the filtrate at room temperature.
1-Oleoyl-4-phenyl semicarbazide (2): The 3.0 g of oleic acid hydrazide dissolved in
10 mL of CHCl3 was treated with 6 mL phenyl isocyanate in a 250 mL Erlenmeyer
flask. The mixture was refluxed for 1 h with stirring. This yielded 100% of 1-oleoyl-4-
phenyl semicarbazide 2, obtained by drying the filtrate at room temperature.
1,19,199-Citroyl-4,49,499-phenyl semicarbazide (3): The 0.1 g of citric acid hydrazide
dissolved in 10 mL of CHCl3 was treated with 2 mL phenyl isocyanate (2 mL of
phenyl isocyanate in 5 mL methanol) in a 250 mL Erlenmeyer flask. The mixture was
refluxed for 2 h with stirring. This yielded 18.7% of 1,10,100-citroyl-4,40,400-phenyl
semicarbazide 3, obtained by drying the filtrate room temperature.
1-Benzoyl-4-phenyl semicarbazide (4): The 0.3 g of benzoic acid hydrazide dissolved
in 0.5 mL of CHCl3 was treated with 3 mL phenyl isocyanate in a 250 mL Erlenmeyer
flask. The mixture was refluxed for 2 h with stirring yielded 10.0% of 1-benzoyl-4-
phenyl semicarbazide 4, obtained by drying the filtrate at room temperature.
3.4. Acid hydrazides
Cinnamic acid hydrazide (5): The 14.8 g of cinnamic acid was refluxed with 50 mL of
hydrazine for 4 h with stirring. This yielded 26.1% of cinnamic acid hydrazide 5,
obtained by drying the filtered product at room temperature.
Oleic acid hydrazide (6): The 28.2 g of oleic acid was refluxed with 50 mL of
hydrazine for 1 h with stirring. This yielded 96.0% of oleic acid hydrazide 5, obtained
by drying the filtrate room temperature.
Citric acid hydrazide (7): The 19.3 g of citric acid was refluxed with 100 mL of
hydrazine for 25 h with stirring. This yielded 12.5% of citric acid hydrazide 5,
obtained by drying the filtered product at room temperature.
Benzoic acid hydrazide (8): The 12.2 g of benzoic acid was refluxed with 50 mL of
hydrazine for 4 h with stirring, which yielded 42.8% of benzoic acid hydrazide 5,
obtained by drying the filtered product at room temperature.
3.5. 2,5-Disubstituted 1,3,4-oxadizoles
2-Cinnamoyl-5-aminophenyl 1,3,4-oxadizoles (9): The 0.5 g of 1-cinnamoyl-4-phenyl
semicarbazide (1) was refluxed with 26 mL of sulphuric acid for 2 h with stirring. This
yielded 78% of 2-cinnamoyl-5-aminophenyl 1,3,4-oxadizoles (9).

Natural Product Research
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2-Oleyol-5-aminophenyl 1,3,4-oxadizoles (10): The 0.9 g of 1-oleoyl-4-phenyl semi-
carbazide (2) was refluxed with 26 mL of sulphuric acid for 2 h with stirring. This
yielded 89% of 2-oleyol-5-aminophenyl 1,3,4-oxadizoles (10).
References
Beregi et al. (1974). Benzenesulfonyl semicarbazides. US Patent 3,810,914.
Brantley, R.K. (1970). Herbicidal alkylcarbamoyloxy semicarbazides. US Patent 3511875.
Coyne, W.E., & Cusic, J.W. (1968). Anticonvulsant semicarbazides. Journal of Medicinal
Chemistry, 11, 1158–1160.
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