A Paired Electrochemical Method for Synthesis of new

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A Paired Electrochemical Method for Synthesis of new Phenylcarbonimidoyl Dicyanide Dyes Mahdi Jamshidi, Davood Nematollahi, Fatemeh Taheri, and Hojjat Alizadeh ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b04118 • Publication Date (Web): 25 Dec 2018 Downloaded from http://pubs.acs.org on December 26, 2018

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ACS Sustainable Chemistry & Engineering

A Paired Electrochemical Method for Synthesis of new Phenylcarbonimidoyl Dicyanide Dyes Mahdi Jamshidia, Davood Nematollahia*, Fatemeh Taherib and Hojjat Alizadehc a

Faculty of Chemistry, Bu-Ali Sina University, Mahdiyeh Street, Hamedan, Iran. Zip Code

65178-38683. E-mail: [email protected] Fax: 0098 - 813- 8257407, Tel: 0098 - 813- 8282807 b

Isfahan University of Technology, Department of Textile Engineering 8415683111, Khomeyni

Shahr Road, Iran. c

Rooyana veterinary laboratory, Sahely Street, Saqqez, Kurdistan, Iran

ABSTRACT: A paired electrochemical synthesis of new phenylcarbonimidoyl dicyanide dyes was performed by the electrooxidation of fast violet B (FVB) and fast blue BB (FBB) in the presence of malononitrile. Our data show that the reaction of electrogenerated quinone-diimine derived from FVB and FBB with malononitrile to yield the phenylcarbonimidoyl dicyanide derivatives. In addition, the dyed nylon fabrics, showed good to excellent color fastness properties to rubbing and washing. This paper has reported a green and facile catalyst-less method for the synthesis of title compounds.

KEYWORDS: Paired electrochemical synthesis, Phenylcarbonimidoyl dicyanide, Green chemistry, 3-Cyanoindole, Cyclic voltammetry, Reaction pathway.

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INTRODUCTION

It was found that indole-containing compounds showed a wide range of pharmacological properties such as anticancer,1,2 antidepression/anxiety,3 anti-inflammatory,4 antimicrobial,5 antioxidant,6 anticonvulsant,7 antibacterial8 and antirival.9 So a variety of methods by synthetic organic chemists are described for the synthesis of indole derivatives. The most common methods of synthesis of indole derivatives are synthesis via aryl hydrazines, Japp−Klingemann reaction, metal-catalyzed arylation, Larock heteroannulation, cyclization of 2-alkynylaniline derivatives, Leimgruber−Batcho method, reductive cyclizations of dinitrostyrene, o-nitrostyrenes reductive cyclization, cyclization of 2-aminophenethyl aldehydes, hydroformylation of anilines, intramolecular Heck cyclizations, Madelung−Houlihan method and Plieninger method.2,10-16 However, these approaches have some drawbacks such as tedious work-up, heavy metal pollution, the use of environmentally unsafe solvents and reagents, the use of strong acidic or basic media, the use of high temperature and pressure and low yields. One of the synthesized compounds in this study is a new derivative of 3-cyanoindole (3CI). The nitrile group in 3-cyanoindoles can be transformed to a wide series of functional groups, including acids, aldehydes, ketones, heterocycles, amines and amides.17 Therefore, 3-cyanoindoles may be a key building block in drug discovery so that some important drugs for type 2 diabetes, cardiovascular diseases, xanthine−oxidase inhibitors, acetyl-CoA carboxylase inhibitors, antithrombotics factor Xa inhibitors, antiviral hepatitis C virus inhibitors and anticancer agents were synthesized from these compounds.18-23 However, the problems involved in indole derivatives synthesis are also present in 3-cyanoindoles synthesis. Other compounds synthesized in this study are phenylcarbonimidoyl dicyanide derivatives (PCD1 and PCD2). iminoacetonitrile (formimidoyl cyanide) and iminomalononitriles


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(carbonimidoyl dicyanide), which are an important class of active imines.24,25 They are interesting compounds for intramolecular [4 + 2] cycloadditions for nitrogen heterocycles synthesis.24-26 Iminomalononitriles are used as intermediates for the synthesis of adenine and 4-amino-1Himidazole-5-carbonitrile.27 These compounds were synthesized from radical reactions in nitrile rich

environment,27

dehydrogenation

of

arylaminoacetonitriles,28

thermolysis

of

the

aminomalononitril,29 addition of some 1,3-diaryltriazenes to tetracyanoethylene30,31 and reaction of tetracyanoethylene with creatinine.32 Further studies show that, in the few papers in which the synthesis of these compounds is studied, often these compounds are referred to as an intermediate, and their spectroscopic information is not available. In addition, the reported methods have the drawbacks of tedious work-up, low yield, multi-step synthesis and unsafe solvent/reagents.27-32 These data encouraged us to develop new synthetic strategies based on electrooxidation of fast violet B (FVB) and fast blue BB (FBB) in the presence of malononitrile (MN) (Scheme 1). The present method is in accordance with the green chemistry principles. It was performed at room temperature and pressure (the energetic aspect). In this methods a mixture of water/ethanol is used instead of toxic solvents (safety) and electron is used instead of chemical reagents (without any catalyst). In addition, the total energy consumption in pair electrochemical synthesis is less than (50%) the common electrochemical methods (the energetic aspect).33,34 From the point of view of novelty, this work has three important implications. (a) The synthesized compounds (3CI, PCD1 and PCD2) are new and their synthesis and structures have not been reported so far. (b) The proposed pathways for the electrooxidation of FVB and FBB in the presence of MN are unique and have not been reported before and (c) the reported protocol for the synthesis of 3CI, PCD1 and PCD2 are quite in accordance with the green chemistry principles.


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Scheme 1. The proposed Scheme for electrooxidation of FBB and FVB in presence of malononitrile.

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MATERIALS AND METHODS Reagents and Apparatus. An Autolab model PGSTAT302N potentiostat/galvanostat was

used for preparative electrolysis, controlled-potential coulometry and cyclic voltammetry. A glassy carbon disc (1.8 mm2 areas) and a platinum wire were used as working and counter electrodes, respectively. An assembly of four graphite rods (30 cm2) and a large stainless steel gauze were used as working and counter electrodes in controlled-potential coulometry and macro scale electrolysis, respectively. The potential of the working electrode was measured against


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Ag/AgCl (AZAR electrode). All chemicals were purchased from commercial sources and used without further purification. Electroorganic synthesis of PCD1 and PCD2. In an undivided electrochrmical cell, a mixture of FBB (0.25 mmol) and MN (0.25 mmol) solved in an aqueous solution (phosphate buffer, c = 0.2 M, pH = 9.0)/ethanol (70:30, v/v) mixture (80 mL) containing FBB (0.25 mmol) and MN (0.25 mmol) was subjected to electrolysis at applied potential 0.45 V versus Ag/AgCl electrode. At the end of synthesis (the decay of current became more than 95%), the electrolyzed solution was extracted with ethyl acetate (three times, 90 mL). The organic phases were dried with anhydrous MgSO4 and evaporated in vacuum. PCD1 and PCD2 were obtained by thin layer chromatography (TLC) on silica gel (n-hexane/ethyl acetate, 1:2 v/v). Electroorganic synthesis of 3CI. Controlled-potential synthesis of 3CI is similar to PCD1 and PCD2 (Eapp = 0.35 V versus Ag/AgCl). When the decay of current became more than 95%, the solution was filtered and the solid washed with distilled water. (4-Benzamido-2,5-diethoxyphenyl) carbonimidoyl dicyanide (PCD1). Isolated yield: 41%. Mp: 158-161 oC (Dec.) 1H NMR (400 MHz, DMSO-d6) δ: 1.45 (t, 3H, CH3), 1.48 (t, 3H, CH3), 4.09 (q, J = 6.9 Hz, 2H), 4.20 (q, J = 6.9 Hz, 2H), 6.41 (s, 1H, aromatic), 7.26 (s, 1H, aromatic), 7.51−7.60 (m, 3H, aromatic), 7.96 (dd, J = 8.3, 1.2 Hz, 2H), 8.07 (s, 1H, NH, disappeared upon the addition of D2O); 13C NMR (100 MHz, DMSO-d6) δ: 13.8, 14.3, 64.2, 65.0, 95.5, 106.4, 110.6, 115.2, 127.4, 128.2, 128.6, 131.2, 131.9, 134.2, 139.8, 151.1, 156.8, 167.8; IR (KBr) v: 3448, 3350, 2986, 2937, 2894, 2207, 1630, 1545, 1446, 1352, 1237, 1039 cm−1; MS (EI, 70 eV) (m/z) (relative intensity %): 362 (2), 331 (3), 306 (4), 275 (9), 248 (12), 223 (9), 129 (11), 105 (21), 73 (28), 43 (100).


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(2,5-Diethoxy-4-hydroxyphenyl)carbonimidoyl dicyanide (PCD2). Isolated yield: 48%. Mp: 212-214 oC (Dec.) 1H NMR (400 MHz, DMSO-d6) δ: 1.41 (t, J = 6.9 Hz, 3H), 1.45 (t, J = 6.9 Hz, 3H), 4.03 (q, J = 6.9 Hz, 2H), 4.17 (q, J = 6.9 Hz, 2H), 6.34 (s, 1H, aromatic), 7.08 (s, 1H, aromatic); 13C NMR (100 MHz, DMSO-d6) δ: 13.7, 13.8, 64.6, 64.7, 99.7, 108.5, 110.8, 115.8, 116.7, 125.7, 145.2, 146.2, 155.1; IR (KBr) v: 3445, 2989, 2937, 2883, 2193, 1607, 1536, 1499, 1423, 1274, 1230, 1033, 817, 549 cm−1; MS (EI, 70 eV) (m/z) (relative intensity %): 281 (M+Na), 253(17), 225(51), 199(8), 169(5), 149(100), 105(30), 77(23), 57(18).

N-(2-Amino-3-cyano-7-methoxy-4-methyl-1H-indol-5-yl) benzamide (3CI). Isolated yield: 84%. Mp: 287-289 oC. 1H NMR (400 MHz, DMSO-d6) δ: 2.37 (s, 3H, methyl), 3.89 (s, 3H, methoxy), 6.37 (s, 2H, NH2, disappeared upon the addition of D2O), 6.61 (s, 1H, aromatic), 7.57−7.66 (m, 3H, aromatic), 8.07 (d, J = 7.6 Hz, 2H, aromatic), 9.91 (s, 1H, NH, disappeared upon the addition of D2O), 10.89 (s, 1H, NH, disappeared upon the addition of D2O); 13C NMR (100 MHz, DMSO-d6) δ: 12.47, 55.4, 62.6, 102.3, 115.7, 118.9, 119.3, 126.7, 127.4, 128.5, 128.9, 131.7, 134.0, 142.4, 154.1, 166.5; IR (KBr) v: 3390, 3325, 3227, 2935, 2201, 1641, 1566, 1533, 1479, 1383, 1206, 1095, 810, 681cm−1; MS (EI, 70 eV) (m/z) (relative intensity %): 320 (M, 18),


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215 (32), 150 (7) , 105 (100), 77 (73), 73 (9) , 43 (37); Elemental analysis: Found (%): C, 67.32; H, 5.04; N, 17.31; Calcd. for C18H16N4O2: C, 67.49; H, 5.03; N, 17.49.

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RESULTS AND DISCUSSION Electrooxidation of FVB in presence of MN. Figure 1a displays a CV recorded for FVB (1.0

mM) in water (phosphate buffer, c = 0.2 M, pH = 9.0)/ethanol mixture (70:30, v/v). The CV displays a pair of anodic/cathodic peaks (A1 and C1) corresponds to quasi-reversible two-electron process of oxidation of FVB to quinonediimine, FVBox and reduction of FVBox to FVB.35 Under the same conditions, electrooxidation of FVB in the presence of MN (nucleophile) was examined. Figures 1b and 1c show the CVs of FVB in the presence of 1.0 and 2.0 mM MN, respectively. Under these conditions, IpC )cathodic peak current) depends on the MN concentration so that decreases with increasing MN concentration. The normalized CVs of FVB in the presence of MN at various potential scan rates are indicated in Fig. 1, curves e-h. As seen, IpC1 increases with increasing potential scan rate. The results reflect the fact that (a) the reaction of MN with FVBox removes FVBox from the surface of the electrode, (b) the reaction rate between FVBox and MN increases with increasing MN concentration and (c) at high scan rates, the time for the reaction of MN with FVBox is not sufficient.36 Fig. 1d shows the CV of MN in the absence of FVB.


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Figure 1. Part I: CV of 1.0 mM FVB: (a) in the absence, (b) in the presence of MN (1.0 mM), (c) in the presence of MN (2.0 mM). (d) CV of 1.0 mM MN. Scan rate: 50 mV s−1. Part II: Normalized CVs of 1.0 mM FVB in the presence of 1.0 mM MN at various potential scan rates (v). v from eh are 10, 25, 50, and 100 mV/s. Working electrode, glassy carbon electrode. Solvent, water (carbonate buffer, c = 0.2 M, pH = 9.0)/ethanol mixture (70/30, v/v). Temperature: 25 ± 1 °C. In an attempt to identify the number of transferred electron (n) and oxidation products, controlled potential coulometry (CPC) of a mixture of FVB and MN was done at a potential of 0.45 V in water (phosphate buffer, c = 0.2 M, pH = 9.0)/ethanol (70:30, v/v). The recorded CVs during the coulometry are shown in Figure 2I. The CVs show that, both anodic (A1) and cathodic (C1) peaks decrease with the progress of coulometry and after passing about 2e− per FVB, the FVB oxidation peak was disappeared. The coulometry was also performed in the constant current mode. To achieve high product yield, the current density effect (from 0.01 to 1.00 mA cm-2) was investigated. These tests are performed while the passed charge was 50 C (theoretical amount). Figure 2II shows that when the applied current is 0.2 mA/cm2, the generated potential is around 0.45 V vs. Ag/AgCl. This potential


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is close to the oxidation potential of FVB (0.41 V) and is appropriate for the selective oxidation of FVB. Consequently, the optimum current density was found to be 0.2 mA/cm2. At higher current densities (1 mA cm-2), the yield becomes lower due to the occurrence of over-oxidation. The yield achieved at current density of 0.2 mA/cm2 was 84% (Figure 2III).

Figure 2. (I) CVs of 0.25 mmol FVB in the presence of 0.25 mmol MN during CPC at 0.45 V when the charge passed is: 0, 20, 31, 41, 51, 63 and 74 C. v: 50 mV s-1. (II) E-t diagram during constant current electrolysis. Rotation rate of electrode: 1000 rpm. (III) Effect of current density on 3CI yield.


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The electrochemical results, along with spectroscopic data revealed the formation of a new derivative of 3-cyanoindole (3CI) (Scheme 2). In the paired electrosynthesis both anodic and cathodic reactions contribute to the formation of the product.34,37-41 Scheme 2. Two-pathway mechanism for the electrochemical oxidation of FVB in the presence of MN.

As seen in Scheme 2, the reaction of anodically generated FVBox with cathodically formed MNto form the intermediate IN1 and the final product (3CI) is then synthesized through two pathways. In path A, IN1 after aromatization and hydrolysis42 leads to IN2. Subsequent cyclization and dehydration reaction afforded 3CI as the final product. In path B, aromatization followed by an


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intramolecular cyclization leads to IN3’ and the subsequent aromatization will furnish 3CI as final product. Finally, it should be noted that when the electrochemical oxidation of FVB in presence MN takes place in a divided cell, the yield of 3CI decreased dramatically. In divided cell there is no possibility of the production of malonotrile anion from direct reduction of malononitrile at the cathode and/or by reaction with cathodically produced hydroxide ions. In the next step, fast blue BB (FBB) was investigated. In the structure of FBB two ethoxy groups were replaced with the methoxy and methyl groups in FVB. This change only decreases the half wave potential of FBB (0.22 V) compared to FVB (0.29 V) and has no effect on the voltammetric behavior of FBB (see the Supporting Information). CPC was performed in a solution of 0.25 mmol FBB and 0.25 mmol MN under the conditions mentioned for FVB, at the potential of the FBB oxidation peak (0.36 V). The progress of electrolysis was monitored by recording CV (see the Supporting Information). It is illustrated that, all peaks disappears when the charge passed was about four electrons per FBB. At the end of electrolysis, two compounds (pink, PCD1 and navy blue PCD2 compounds) were separated from the solution by thin layer chromatography (see electroorganic synthesis of PCD1 and PCD2 section). The current density effect on product yield was also studied in the range from 0.01 to 1.75 mA cm−2 (charge passed = 100 C). It is found that, the highest yield of 89% is obtained at 0.1 mA/cm2. The generated potential in this current density (0.1 mA/cm2), is close to the oxidation potential of FBB (0.36 V). The presence of an ethoxy group instead of a methyl group results in a major difference in the product composition (Scheme 3). When the ethoxy group is replaced with the methyl group, as in FBBox, due to more electron donating than methyl group, on the one hand and the higher steric


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energy of the hypothetical product and intermediates originating from the oxidation of FBB in the presence of MN, if the FBB reaction pathway was similar to that of FVB (Fig. 3), on the other hand, causes that the ortho position becomes inactive towards addition reaction (see the Supporting Information).

Figure 3. MM2 results for IN1 and similar hypothetical intermediate (HIN1).

As seen in Scheme 3, the formation of the FBBOX is followed by a Michael type addition reaction of MN- generating the IN4. Oxidation of IN4, followed by the aromatization of IN5, provided PCD1 (pink color) as the final product.


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Scheme 3. The mechanism proposed for the electrooxidation of FBB in the presence of MN.

Another isolated product was identified as PCD2. Our data indicate that hydrolysis of FBBOX to the related Quinoneimine (QI1) was occurred prior to the Michael's reaction. Thus, nucleophilic


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attack of MN- to QI1, oxidation of produced adduct (IN6) followed by the aromatization, produced PCD2 (navy blue color) as the final product. The absorption spectra of PCD1 and PCD2 exhibit three absorption peaks at 313, 356 and 648 nm and two absorption peaks at 314 and 540 nm, respectively (see Supporting Information). In addition, the voltammetric behavior of 3CI, PCD1 and PCD2 was studied (Figure 4). Two significant differences were found between CV of 3CI and those of PCD1,2. The difference in the reversibility of the oxidation process of 3CI and PCD1,2 is the first case and the easier oxidation of 3CI (EpA2 = 0.43 V) compared to PCD1 (EpA3 = 0.89 V) and PCD2 (EpA4 = 1.56 V) is second item, which both are due to the significant difference in structure of the 3CI and PCD1,2.

Figure 4. CVs of saturated solution of 3CI, PCD1 and PCD2. Temperature: 25 ± 1 °C. v: 100 mV s -1. Attachment of an MN group (with electron-withdrawing character) by a double bond to the nitrogen atom in PCD1 and PCD2, is responsible for increasing the oxidation potential and instability of the oxidized molecules. Unlike PCD1-2, 3CI has a somewhat similar chemical structure to FVB. As a result, it has an anodic/cathodic peaks at 0.43 and 0.23 V, respectively, assigned to the 3CI/3CIox redox couple (Scheme 4).


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Scheme 4. Redox behavior of 3CI.

We used the so-called exhaust process for the dyeing of wool, nylon, polyester, cotton, polypropylene and acrylic. The results showed that PCD2 exhibits higher affinity for nylon and wool fabrics (Figure 5), but it was ineffective against other fabrics (see the Supporting Information). Also, fastness properties of PCD2 were tested against external influences. Based on the experimental results, the color fastness to rubbing and washing is very good, however, the color fastness to light was poor (see the Supporting Information).

Figure 5. The results of the dyeing process of PCD2 for different fabrics: (a) nylon (b) wool.

Finally, it should be noted that the antibacterial experiments on PCD1 and PCD2 show that these compounds don’t have any antibacterial activity at 30 μg/mL against Salmonella enteritidis and Escherichia coli (gram negative), Bacillus cereus and Staphylococcus aureus (gram positive) (see the Supporting Information).


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CONCLUSIONS This research indicates that paired electrosynthes is a superior method for the synthesis of dyes. The results show that electrooxidation of FVB in presence of MN leading to the synthesis of a new indole compound (3CI). This compound can be a key building block in drug synthesis. On the other hand, electrooxidation of FBB in presence of MN leads to synthesis of new derivatives of dicyanide dyes (PCD1 and PCD2) which are a novel category of imines24,25 that can be used for the synthesis of nitrogen-containing heterocycles. These compounds are often referred to as synthetic intermediates, and their spectroscopic information are not available. Our results showed that PCD2 exhibits high affinity for nylon and wool fabrics and found that the color fastness of this dye to rubbing and washing is very good. An important feature in the synthesis of 3CI, PCD1 and PCD2 is using electricity instead of chemical reagents. In addition, the synthesis of these compounds were performed at room temperature and pressure in one-pot, using a nontoxic solvent. ASSOCIATED CONTENT Supporting Information. Detailed experimental procedures, antibacterial studies and characterization data for all compounds. FT-IR, 1H NMR,

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C NMR, CHNS and MS spectra of 3CI, PCD1 and PCD2,

electrochemical investigations, CCC and CPC of PCD1 and PCD2, the absorption spectra and dyeing procedure of PCD2. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author


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*E-mail: [email protected]. Notes The authors declare no competing financial interest. ACKNOWLEDGMENT We acknowledge the Bu-Ali Sina University Research Council and Center of Excellence in Development of Environmentally Friendly Methods for Chemical Synthesis (CEDEFMCS) for their support of this work. Thanks Alvansabet Company for performing dyeing experiments. REFERENCES (1) Rao, V. K.; Chhikara, B. S.; Nasrolahi Shirazi, A.; Tiwari, R.; Parang, K.; Kumar, A. 3Substitued indoles: One-pot synthesis and evaluation of anticancer and Src kinase inhibitory activities. Bioorg. Med. Chem. Lett. 2011, 21, 3511–3514, DOI: 10.1016/j.bmcl.2011.05.010. (2) Gribble, G. W. Heterocyclic Scaffolds II: Reactions and Applications of Indoles; Springer, New York, 2010. (3) Kochanowska-Karamyan, A. J.; Hamann, M. T. Marine indole alkaloids: Potential new drug leads for the control of depression and anxiety. Chem. Rev. 2010, 110, 4489–4497, DOI: 10.1021/cr900211p. (4) Radwan, M. A. A.; Ragab, E. A.; Sabrya, N. M.; El-Shenawyc, S. M. Bioorg. Synthesis and biological evaluation of new 3-substituted indole derivatives as potential anti-inflammatory and analgesic agents. Med. Chem. 2007, 15, 3832–3841, DOI: 10.1016/j.bmc.2007.03.024. (5) Rohini, R.; Reddy, P. M.; Shanker, K.; Kanthaiah, K.; Ravinder, V.; Anren, H. Synthesis of mono, bis-2-(2-arylideneaminophenyl) indole azomethines as potential antimicrobial agents. Arch. Pharm. Res. 2011, 34, 1077-1084, DOI: 10.1007/s12272-011-0705-z.


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Graphical Abstract For Table of Contents Use Only A paired electrochemical synthesis of new phenylcarbonimidoyl dicyanide dyes was reported by the electrochemical oxidation of fast violet B and fast blue BB in the presence of malononitrile. Clean synthesis, reagent free, safe solvent, high atom economy, ambient conditions and one-step process are important features of the work.


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A Paired Electrochemical Method for Synthesis of new

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