ORIGINAL PAPER Synthesis, Crystal Structure and ab Initio Studies of 5-Phenylamino-3-phenylimino-3H[1, 2]dithiole-4-carboxylic acid ethyl ester Raza Murad Ghalib • Rokiah Hashim • P. S. Pereira Silva • Othman Sulaiman Received: 21 May 2010 / Accepted: 26 September 2011 / Published online: 7 October 2011 Ó Springer Science+Business Media, LLC 2011 Abstract 5-Phenylamino-3-phenylimino-3H[1, 2]dithiole- 4-carboxylic acid ethyl ester, C 18 H 16 N 2 O 2 S 2 , (I), has been synthesized and the structure has been solved by X–ray diffraction. The crystals are triclinic, space group P  1, with a = 5.7127(2) A ˚ , b = 12.1757(5) A ˚ , c = 14.0734(5) A ˚ , a =112.1217(16)°, b = 97.786(2)°, c = 100.694(2)°, Mr = 356.45, V = 868.11(6) A ˚ 3 , Z = 2 and R = 0.0373. In the title compound there is an intramolecular N–HÁÁÁO hydrogen bond. The crystal structure is stabilized only by weak C–HÁÁÁp and pÁÁÁp interactions as well as by van der Waals forces. The geometry of the isolated molecule was optimized by ab initio quantum mechanical calculations, employing both molecular orbital Hartree-Fock (HF) and density functional theory (DFT) methods. In the DFT cal- culation the minimum energy was achieved for a confor- mation very similar to that of the solid-state molecule. Keywords Crystal structure Á 5-Phenylamino-3- phenylimino-3H[1, 2]dithiole-4-carboxylic acid ethyl ester Á DFT calculations Á Molecular orbital Hartree-Fock calculations Introduction Phenyl isothiocynate is a useful reagent for the synthesis several heterocyclic molecules such as thiophenes, pyrroles, pyrimidines and imidazoles [1, 2]. Phenyl isothiocynate reacts with 1, 3 dicarbonyl compounds in basic media to give substituted thiophenes [3]. Here in this reaction when phenyl isothiocynate reacts with diethyl malonate in basic medium it gives unexpected title compound 5-phenylamino-3-phe- nylimino-3H[1, 2]dithiole-4-carboxylic acid ethyl ester. Experimental Methods Preparation of the Title Compound A mixture of phenylisothiocyanate (1.19 mL, 10 mmol) and diethylmalonate (1.51 mL, 10 mmol) in molar ratio 1:1 were refluxed in THF on water bath for 6 h in presence of Na 2 CO 3 (Scheme 1). The reaction mixture was dried on rotary evaporator at low pressure and further fractionated with chloroform. The chloroform soluble part was further dried on rotary evaporator and chromatographed over silica gel (Merck, 0.04–0.063 mm, 230–400 mesh ASTM) column loaded in light petroleum ether. The column was eluted successively with light petroleum ether and light petroleum ether–diethylether (9:1–1:1). The elutants obtained in solvent system light petroleum ether–diethyl- ether (8:2–7:3), on crystallization with chloroform–dry ethanol (1:1) gave the yellowish crystals of 5-phenylamino- 3-phenylimino-3H[1, 2]dithiole-4-carboxylic acid ethyl ester (800 mg) (mp 138 °C). The melting point was deter- mined on a Thermo Fisher digital melting point apparatus of IA9000 series and is uncorrected. Crystal Structure Determination A crystal of (I) with a thick plate shape and having approximate dimensions of 0.42 9 0.36 9 0.21 mm was R. M. Ghalib (&) Á R. Hashim Á O. Sulaiman School of Industrial Technology, Universiti Sains Malaysia, Pulau Pinang 11800, Malaysia e-mail: raza2005communications@gmail.com P. S. P. Silva CEMDRX, Physics Department, University of Coimbra, P-3004-516 Coimbra, Portugal 123 J Chem Crystallogr (2011) 41:1889–1893 DOI 10.1007/s10870-011-0196-2