Summary
Çalışmamız kapsamında, 3,4-disubstitüe-2,4-dihidro-5H-1,2,4-triazol-5-tiyon türevi bileşiklerin elde edilebilmesi için literatürde kayıtlı bulunan diğer sentez yöntemlerinden farklı olarak aynı tepkime kabında gerçekleştirilen iki basamaklı bir sentez yöntemi geliştirilmiş ve geliştirilen yöntemin üstünlüğü diğer sentez yöntemleriyle karşılaştırılarak ispatlanmıştır. Sübstitüe hidrazitlerin etanollü çözeltilerinin alkil/aril izotiyosiyanatlarla ısıtılmasını takiben tepkime ortamına 4N sodyum hidroksit çözeltisi ilave edilerek ısıtmaya devam edilmiştir. Oluşturulan yeni sentez yönteminde, tepkimenin 6 saat içerisinde tamamlandığı, literatürdeki diğer yöntemlerle kıyaslandığında daha yüksek verim elde edildiği ve daha az çözücü kullanıldığı tespit edilmiştir.Introduction
The chemistry of 1,2,4-triazole-5-thiones has been an interesting field of study for a long time. The synthesis of novel 1,2,4-triazole-5-thione derivatives and investigation of their biological activities have gained more importance in recent years. A survey of literature revealed their potential pharmacological activity profile as antibacterial[1-4], antifungal[5,6], antitubercular[7,8], antiviral[9,10], anticancer[11-13] and anticonvulsant[14,15]. Besides the pharmacological significance of this heterocyclic ring system it is also an attractive scaffold to be constituted for chemical diversity. The current process for preparation of 1,2,4-triazole-5-thiones is achieved via synthesis, isolation and recrystallization of acyl/aroyl substituted thiosemicarbazides[16]. The current process required long reaction times and higher solvent costs. Furthermore, using enviromentally safer solvents especially water has gained prominence in recent years and in our methodology we use water and ethanol to reduce the amount of waste water and waste solvent. Through our new one-pot, two-step synthesis method which was demonstrated to be superior than the current synthesis method; 1,2,4-triazole-5-thione derivatives were synthesized by the addition of alkyl/aryl isothiocyanates to substituted hydrazides in ethanol following the refluxing process of intermeadiate in 4N sodium hydroxide solution.The synthesis of 1,2,4-triazole-5-thione derivatives has been carried out according to the steps shown in Scheme 1. In the initial step, acyl/aroyl substituted thiosemicarbazides were synthesized by the addition of alkyl/aryl isothiocyanates to substituted hydrazides in ethanol. In the second step, 1,2,4-triazole- 5-thione derivatives were synthesized by refluxing the reaction medium in 4N sodium hydroxide solution and then neutralization with hydrochloric acid.
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SCHEME 1: Synthetic route to compounds 1c, 1d, 2a-d, 2a' and 3a-d |
EXPERIMENTAL
Chemistry
All solvents and chemicals used in this study
were supplied from Aldrich, Merck and Fluka
and used without purification. Melting points
(ºC) were measured using Schmelzpunktbestimmer
SMP II melting point apparatus, uncorrected.
The reactions were monitored on Merck
pre-coated aluminium TLC plates 60F–254, using
ethyl acetate and petroleum ether (50:50) as
solvent system and the products were visualized by using UV light. The liquid chromatographic system
consists of an Agilent technologies 1100 series instrument
equipped with a quaternary solvent delivery system and a
model Agilent series G1315 A photodiode array detector. A
Rheodyne syringe loading sample injector with a 50 μl sample
loop was used for the injection of the analytes. Chromatographic
data were collected and processed using Agilent
Chemstation Plus software. The separation of compounds
were performed at ambient temperature by using a reversed
phase Kromasil 100-5C18 (Hichrom, 4.6 x 250 mm) column.
All experiments were employed in isocratic mode. The mobile
phase was prepared by mixing acetonitrile and 0.1%
phosphoric acid (65:35, v/v) and filtered through a 0.45 μm
membrane and degassed by ultrasonication, prior to use. Solvent
delivery was employed at a flow rate of 1 ml.min-1. Detection
of the analytes were carried out at 254 nm. The Infrared
spectra were recorded on Schimadzu FTIR-8400S Spectrophotometer
and expressed in wavenumber ν (cm-1).
1H-NMR spectra were recorded on Varian Unity Inova Spectrometer
at 500 MHz and Varian Spectrometer at 300 MHz,
using DMSO-d6 as a solvent; tetramethylsilane (TMS) was
used as internal standard. All NMR chemical shifts are reported
as d values in parts per million (ppm) and coupling
constant (J) are given in Hertz (Hz). 1H-NMR and Mass analyses
were provided by Faculty of Pharmacy Center Laboratory
(Ankara University) and the Scientific and Technical Research
Council of Turkey, TÜBİTAK (Ankara).
Ethyl 4-(benzoylamino)benzoate
To the solution of ethyl 4-aminobenzoate (benzocaine; 0.03
mol) in ether benzoyl chloride (0.03 mol) was added dropwise
with stirring. Shortly after the addition was completed the appearing
precipitate was collected and washed with water and
recrystallized from ethanol. Yield 67%, mp: 137°C (17).
4-(Benzoylamino)benzoic acid hydrazide
Ethyl 4-(benzoylamino)benzoate (0.01 mol) and hydrazine
hydrate (9 ml) were heated under reflux for 30 mins. and 15
ml ethanol was added to the reaction medium. The mixture
was heated under reflux for 45 mins. The crude product was
filtered and washed with boiling ethanol. Yield 80%, mp:
235°C (17).
1,4-Disubstituted aroylthiosemicarbazides and
3,4-Disubstituted-2,4-dihydro-5H-1,2,4-triazole-5-thiones
(Method 1)
To the solution of appropriate hydrazide (0.005 mol) in 30 ml
ethanol; ethyl, allyl, phenyl, cyclohexyl isothiocyanates (0.005
mol) and 2N NaOH solution (8 ml) were added respectively
under reflux for 4 h. Acidification of the reaction liquor with
2N HCl solution furnished the precipitate. The crude product
was filtered and washed with distilled water until the filtrate
was no longer acidic and then recrystallized from ethanol.
3,4-Disubstituted-2,4-dihydro-5H-1,2,4-triazole-5-thiones
(Method 2)
After two hours of refluxing appropriate hydrazide (0.005
mol) with ethyl, allyl, phenyl, cyclohexyl isothiocyanates
(0.005 mol) in 30 ml ethanol, 4N NaOH solution (15 ml) were
added and the reaction medium was refluxed for an additional
4 hours. Acidification of the reaction liquor with 2N
HCl solution furnished the precipitate. The crude product
was filtered and washed with distilled water until the filtrate
was no longer acidic and then recrystallized from ethanol.
3-[4-(Benzoylamino)phenyl]-4-allyl-2,4-dihydro-5H-1,2,4-
triazole-5-thione (2a)
The compound was synthesized via method 1 by using 4-(benzoylamino)
benzoic acid hydrazide as the starting compound.
It was recrystallized from ethanol and obtained as yellow crystals. Yield 51%, mp: 191-195°C. FTIR, (cm-1): 3295 (NH str, triazole
and amide), 3100 (=C-H str), 2944 (C-H str), 1653 (amide
C=O str), 1597, 1558, 1512 and 1489 (C=N str and C=C str),
1185 (C=S str). 1H NMR: δ (ppm) 4.72 (s, 2H, N-CH2-), 4.81-
5.16 (m, 2H, =CH2), 5.79- 5.85 (m, 1H,–CH=), 7.50- 7.67 (m, 4H,
Ar-H), 7.89- 7.97 (m, 5H, C6H5), 10.54 (s, 1H, CONH), 13.99 (s,
1H, NH).
3-(4-Aminophenyl)-4-allyl-2,4-dihydro-5H-1,2,4-triazole-5-
thione (2a)
The compound was also synthesized via method 2 by using
4-(benzoylamino)benzoic acid hydrazide as the starting compound.
It was recrystallized from ethanol and obtained as
yellow crystals. Yield 59%, mp: 224°C (5). HPLC tR (min.):
2.72. FTIR, (cm-1): 3454 (NH asymmetric str), 3338 (NH symmetric
str), 3213 (NH str, triazole), 3072 and 3022 (=C-H str),
1608, 1577, 1519 and 1491 (C=N str and C=C str), 1192 (C=S
str).
3-(4-Aminophenyl)-4-ethyl-2,4-dihydro-5H-1,2,4-triazole-5-
thione (2b)
The compound was also synthesized via method 2 by using
4-(benzoylamino)benzoic acid hydrazide as the starting compound.
It was recrystallized from ethanol and obtained as yellow
crystals. Yield 79%, mp: 248-250°C (5). HPLC tR (min.):
2.63. FTIR, (cm-1): 3464 (NH asymmetric str), 3352 (NH symmetric
str), 3093 and 3022 (=C-H str), 1614, 1579, 1519 and 1489
(C=N str and C=C str), 1176 (C=S str).
3-(4-Aminophenyl)-4-phenyl-2,4-dihydro-5H-1,2,4-triazole-
5-thione (2c)
The compound was synthesized via method 2 by using 4-(benzoylamino)
benzoic acid hydrazide as the starting compound.
It was recrystallized from ethanol and obtained as yellow crystals.
Yield 65%, mp: 290°C (5). HPLC tR (min.): 2.82. FTIR, (cm-
1): 3470 (NH asymmetric str), 3335 (NH symmetric str), 3215
(NH str, triazole), 3088 and 3016 (=C-H str), 1604, 1552, 1512
and 1496 (C=N str and C=C str), 1180 (C=S str).
3-[4-(Benzoylamino)phenyl]-4-cyclohexyl-2,4-dihydro-5H-
1,2,4-triazole-5-thione (2d)
The compound was synthesized via method 2 by using
4-(benzoylamino)benzoic acid hydrazide as the starting compound.
It was recrystallized from ethanol and obtained as
yellow crystals. Yield 31%, mp: 200-206°C. HPLC tR (min.):
3.53. FTIR, (cm-1): 3228 (NH str), 3196 (NH str, triazole), 3090
(=C-H str), 2929 and 2852 (C-H asymmetric and symmetric
str), 1672 (C=O str), 1614, 1591, 1512 and 1489 (C=N str and
C=C str), 1170 (C=S str).
3-(4-Hydroxyphenyl)-4-allyl-2,4-dihydro-5H-1,2,4-triazole-
5-thione (3a)
The compound was also synthesized via method 1 by using
4-hydroxybenzoic acid hydrazide as the starting compound. It
was recrystallized from ethanol and obtained as yellow crystals.
Yield 52%, mp: 167-170°C (168-169°C (18), 176-178 (19)).
HPLC tR (min.): 2.71.
3-(4-Hydroxyphenyl)-4-ethyl-2,4-dihydro-5H-1,2,4-triazole-
5-thione (3b)
The compound was synthesized via method 2 by using 4-hydroxybenzoic
acid hydrazide as the starting compound. It
was recrystallized from ethanol and obtained as white crystals.
Yield 86%, mp: 219°C (212-214°C (18)). HPLC tR (min.):
2.63.
3-(4-Hydroxyphenyl)-4-phenyl-2,4-dihydro-5H-1,2,4-
triazole-5-thione (3c)
3-(4-Hydroxyphenyl)-4-cyclohexyl-2,4-dihydro-5H-1,2,4-
triazole-5-thione (3d)
Synthesis method for the 1,4-disubstituted
aroylthiosemicarbazide standarts (lit.17)
Synthesis method for 3,4-disubstituted-2,4-dihydro-5H-
1,2,4-triazole-5-thione standarts (lit. 5)
The compound was synthesized via method 2 by using 4-hydroxybenzoic
acid hydrazide as the starting compound. It was
recrystallized from ethanol and obtained as yellow crystals.
Yield 73%, mp: 167-170°C (168-169°C (18), 176-178[
The compound was synthesized via method 1 by using 4-hydroxybenzoic
acid hydrazide as the starting compound. It was
recrystallized from ethanol and obtained as white crystals.
Yield 18%. HPLC tR (min.): 2.64. FTIR, (cm-1): 3309 (O-H str),
3161 (NH str, triazole), 3020 (=C-H str), 1610, 1597, 1514, 1487
(C=N str and C=C str), 1411 (O-H bending), 1180 (C=S str).
The compound was synthesized via method 2 by using 4-hydroxybenzoic
acid hydrazide as the starting compound. It was
recrystallized from ethanol and obtained as yellow crystals.
Yield 42%, mp: 260-265°C ( 267-268°C (18)). HPLC tR (min.):
2.79. FTIR, (cm-1): 3440 (O-H str), 3134 (NH str, triazole), 3055
(=C-H str), 1608, 1595, 1512, 1496 (C=N str and C=C str), 1433
(O-H bending), 1176 (C=S str).
The compound was synthesized via method 2 by using 4-hydroxybenzoic
acid hydrazide as the starting compound. It
was recrystallized from ethanol and obtained as white crystals.
Yield 68%, mp: 253-256°C (247-249°C (18)). HPLC tR
(min.): 3.51. FTIR, (cm-1): 3344 (O-H str), 3095 (NH str, triazole),
3014 (=C-H str), 2937 (C-H str), 1614, 1593, 1510, 1487
(C=N str and C=C str), 1386 (O-H bending), 1188 (C=S str).
1H NMR: δ (ppm) 0.92-2.16 (m, 10H, -C6H11), 4.24 (s, 1H,
-C6H11), 6.89 (d, J= 9 Hz, 2H, Ar-H protons in ortho position
due to hydroxyl group), 7.31 (d, J= 9 Hz, 2H, Ar-H protons in
meta position due to hydroxyl group), 10.04 (s, 1H, -OH),
13.71 (s, 1H, NH).
Appropriate hydrazide (0.005 mol) was heated with ethyl, allyl,
phenyl, cyclohexyl isothiocyanates (0.005 mol) under reflux
for 2-2.5 h in ethanol (65 ml). The crude product was filtered
and recrystallized from ethanol.
A mixture of appropriate thiosemicarbazide (0.005 mol) in 2N
NaOH solution (5 ml) were heated under reflux for 4h. The
reaction medium was cooled and acidified by using 2N HCl
solution. The precipitate was washed with distilled water until
the filtrate was no longer acidic and then recrystallized from
ethanol.
Results
To achieve 1,2,4-triazoles, derived from 4-hydroxybenzoic acid hydrazide and 4-benzoyl-aminobenzoic acid hydrazide, the one-pot synthesis method of Shah et al.[18] was employed. Shah et al.[18], reported the synthesis of 3-phenyl-4-n-butyl-5-mercapto- 1,2,4-triazole in yield of 50% by using benzoic acid hydrazide as starting compound. According to the method 1[18]; the ethanolic solutions of the hydrazides, mentioned above, were refluxed with ethyl-, allyl- , cyclohexyl- and phenyl isothiocyanates following 4 hours of heating in 2N NaOH. Administration of this method by using cyclohexyl and phenyl isothiocyanates, 1,4-disubstituted thiosemicarbazides were gained in stead of 3,4-disubstituted-2,4-dihydro-5H-1,2,4-triazole- 5-thiones; consequently the applied method was found workable onyl for reactants ethyl- and allyl isothiocyanates. Our onepot synthesis method (method 2) was developed to gain these failed compounds. In accordance with one-pot two-step reaction procedure; acyl/aroyl substituted thiosemicarbazides were synthesized by the addition of alkyl/aryl isothiocyanates to substituted hydrazides in ethanol and in the second step, 1,2,4-triazole-5-thione derivatives were synthesized by the refluxing the reaction medium in 4N sodium hydroxide solution and then neutralization with hydrochloric acid.The IR spectra of compounds 1c and 1d were characterized by the presence of a C=O absorption bands at 1670 and 1653 cm-1. The signals at 7.69, 10.18 and 10.48 ppm and 7.60, 9.08, 9.98 ppm were attributed –NH- moieties of thiosemicarbazide.
In the IR spectra of compound 2a, which was gained through method 1, absorption bands attributable to aromatic primary amine –NH2- was not observed moreover the presence of C=O absorption band at 1653 cm-1 clarifying existence of 4-benzoylamino moiety. The signal at 10.54 ppm attributable to –NH- proton of 4-benzoylamino moiety provided confirmatory evidence for unhydrolyzed amide. Compounds 2b-d were synthesized via method 2 with the yield range 31-79%. Melting points of compounds 2a-c were found in accordance with literatüre[5,20,21]. Consequential check of IR spectra of compounds 2a and 2c revealed absence of bands between 1650-1700 cm-1 appertaining C=O groups and existence of bands at 3213 and 3215 cm-1 attributable to triazole –NH .
Compounds 2b and 2c were also synthesized by using standart synthesis method[5]; their retention times (Comparative retention times for compounds synthesized by method 1 and 2 were given in Table 1.) and UV spectra were matched with the compunds that were gained through our one-pot two step reaction procedure. (Overlaid UV spectra of compounds 2b and 2c that were gained through method 1 and 2 were given in Figure 1.). Gathering data from IR bands at 1672 and 3228 cm-1 corresponding to C=O and triazole N-H group of compound 2d convinced us about cyclization of thiosemicarbazide to form triazole ring.
TABLE 1: Comparative retention times of compounds gained by different methods
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FIGURE 1: Overlaid UV spectra of compounds 2b and 2c. (For compounds 2b and 2c; dotted lines belong to the products achieved by standart synthesis method and continous lines belong to the products achieved by using method 2) |
Compounds 3a-d were synthesized by using 4-hydroxybenzoic acid hydrazide as starting compound in accordance with method 2 and their yields were detected between 42-86%. Absence of C=O strecthing bands between 1650-1700 cm-1 and existence of N-H strecthing bands between 3376-3095 cm-1 were also substantive content relating to triazole ring closure. (Overlaid UV spectra of compounds 3a, 3b and 3d that were gained through method 1 and 2 were given in Figure 2.). Compound 3a were synthesized by using procedures of both methods. The 1HNMR spectra of products gained by using method 1 and method 2 were evaluated and –NH- signals of both products were detected at 13.86 ppm.
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FIGURE 2: Overlaid UV spectra of compounds 3a, 3b and 3d. (For compound 3a; dotted line belongs to the product achieved by employing method 1 and continous line belongs to the product achieved by using method 2. For compound 3b; dotted line belongs to the product achieved by employing method 2 and continous line belongs to the product achieved by using method 3. For compound 3d; dotted line belongs to the product achieved by employing method 2 and continous line belongs to the product achieved by standart synthesis method. ) |
Conclusion
Consequently, a new method was developed for the synthesis of 3,4-disubstituted-1,2,4-triazole-5-thione derivatives from 4-hydroxybenzoic acid hydrazide and 4-benzoyl-aminobenzoic acid hydrazide. The current processes for preparation of 1,2,4-triazole-5-thiones involve synthesis, isolation and recrystallization of acyl/aroyl substituted thiosemicarbazides requiring long reaction times and higher solvent costs. Our new onepot, two-step synthesis method was demonstrated to be superior than the current synthesis methods by means of leading desired products by higher yields within only 4 or 6 hours. The developed method has no notable advantage to current methods in terms of each reaction time but diminished experimental procedure is easily appreciable. The products of our method were compared to the products of current literature methods through experimental data gathered from high performance liquid chromatography, IR and 1H-NMR spectroscopy.Reference
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