Effect of Solvents on the Spectra of Some N′-2-(Substituted Pyridyl)-N-Substituted-Thioureas

Some N′-2-(substituted pyridyl)-N-substituted thiourea (in all 12-substituted pyridyl thioureas) have been examined in ultraviolet region in a series of solvents covering a broad polarity range i. e. from benzene (Z, 54.0) to ethylene glycol (Z, 85.1). Transition energies and oscillator strengths have been calculated and transition energy (E_T) has been plotted against Z-values, a new-empirical measurement of solvent polarity. A linear relationship was observed between the transition energy and Z-value for pyridyl μ→μ* and thiocarbonyl μ→μ* transitions. The effect of substituent present in pyridyl group on λ_max of a compound in the same solvent has been studied. Solvent sensitivites of these ligands have also been calculated.     

Synthesis and Characterization of Nitrobenzoylthiourea Derivatives as Potential Conductive Biodegradable Thin Films

Abstract

The application of thiourea derivatives as conjugated molecular wire candidates in the field of material sciences has attracted great attention recently. To date, conjugated thiourea systems as molecular wires are surprisingly unexplored although the well-known rigid π-systems promise a wide range of electronic properties. Due to this matter, five novel thiourea derivatives A-ArC(O)NHC(S)NHAr-D with polar head and tail groups, namely NO₂ (acceptor A) and alkoxy with varying chain lengths (donor D = OC_nH_2n+1, n = 6, 7, 8, 9, 10), were successfully synthesized and characterized. All compounds were characterized by IR, UV-vis, ¹H and ¹³C NMR spectroscopy, and CHNS elemental microanalysis. The investigation of their potential as dopant systems in polymer conducting films has been accomplished by incorporating of chitosan via the solution casting technique. The conductivity values were obtained using impedance spectroscopy. They show that the ionic conductivities of the N-(4-alkoxyphenyl)-N’-(4-nitrobenzoyl)thioureas increase with increasing chain length of the alkoxy chain. The compounds exhibit great potential for the exploration of future applications as doping systems in conductive materials.     

A convenient one-pot synthesis of thiazol-2-imines: application in the construction of pifithrin analogues

For the first time a reaction intermediate has been isolated giving further insight into the mechanism of thiazol-2-imine formation. The first step of the reaction requires a basic medium, while the second step is an acid mediated E1 elimination reaction. An efficient one-pot synthesis of substituted thiazol-2-imines have been achieved by the condensation of carbonyl compounds with thioureas and 1,3-disubstituted thioureas using 1,1′-(ethane-1,2-diyl)dipyridinium bistribromide (EDPBT). Unsymmetrical 1,3-disubstituted thioureas give regioselective products with symmetrical ketones, which are mainly governed by the pK_as of NH protons of thiourea, whereas symmetrical 1,3-disubstituted thioureas give regioselective products with symmetrical carbonyl compounds owing to the regioselective bromination of ketones. The methodology is extended to access novel neurodegenerative drug candidate pifithrin-α analogues in good yields in shorter reaction time. This method is simple, versatile and is applicable for different 1,3-disubstituted thioureas as well as a range of carbonyl compounds.     

Synthesis and characterization of polymerizable β-diketone-based liquid crystalline metal chelates

Two novel square-planar palladium chelating liquid crystals, bis(p-n-(l-undecenoxyphenyl-3-dodecyloxyphenyl)-propane-1,3-dionato)palladium(II) (Pd-C₁₁-C₁₂) and bis(1,3-di(p-n-tetradecyloxphenyl)-propane-1,3-dionato) palladium (II) (Pd-C₁₄-C₁₄) have been synthesized. Moreover, the copper chelating liquid crystal bis(p-n-(l-undecynoxylphenyl-3-dodecyloxylphenyl)-propane-1,3-dionate)copper (II) (Cu-Cu₁₁-C₁₂) has been synthesized by heterogeneous ligand-exchange reaction. These β-diketone metal chelates have been characterized by elementary analysis, differential scanning calorimetry, polarizing microscopy, X-ray diffraction analysis and temperature-variable IR. It was found that these chelates were discotic lamellar-(D_L) mesophase liquid crystals. In particular, the temperature-variable IR study indicates that the central chelating ring and the surrounding benzene rings would form a co-planar conjugated structure in the liquid crystalline (LC) state.     

The Photolysis of Tricyclo[4.2.1.02,5]nonadiene: Support of a Doughert ‘type N’ mechanism from photoelectron spectroscopical studies

In earlier work on the photolysis of derivatives of tricyclo[4.2.1.0^2,5]nonadiene (I), the intermediacy of a biallyl-like structure has been postulated which is formed by C₁-C₂ bond cleavage of I in its first excited state. This mechanism is now supported by the results of photoelectron spectroscopical studies on I and its two dihydroderivatives. Further support is gained from the theoretically calculated Ehrenson C₁-C₂-bond indices for the ground and the first excited state of these molecules. While the results for I in principle can be rationalized on the (one-electron) basis of ‘through bond’ interaction between the two π-bonds, the absence of C₁-C₂ photocleavage for a substituted tricyclo[4.2.2.0^2,5]decadiene also requires consideration of an (all-electron) thermochemical driving force.     

Linear polymer of a copper(II) complex and its supramolecular selectivity

The supramolecular framework [Cu₂(TU)₄?·?(TAA)₄] _n (TU?=?thiourea; TAA?=?2-(2-imino-4-oxo-5-thiazolidinylidene)acetic anion) has been synthesized by reaction of CuCl₂?·?2H₂O with meso-2,3-dibromosuccinic acid and thiourea. The one-dimensional supramolecular structure of the title complex is constructed through bridge-linkage of the S atoms on the thioureas between adjacent Cu(II) atoms, forming an infinite chain with lots of positive charges. Around the infinite chain, there are four groups of negatively charged hydrogen-bond tubes constructed by four TAA anions. The hydrogen-bond and ionic interactions between adjacent metal-organic polymeric chains and hydrogen-bond tubes form the three-dimensional supramolecular structure of the complex. Supramolecular selectivity from isomers of 2-(2-imino-4-oxo-5-thiazolidinylidene)acetic anion (TAA) has been studied by quantum calculation.     

Structure Features of 1,3,5-Tris(Diphenylphosphinoxidemethylene)Ben zene in Crystal and Solution on the Base of X-Ray,Dipole Moments and Quantum Chemical Analysis

Abstract

The molecular structure, polarity and conformations in solution of 1,3,5-tris(diphenylphosphinoxidemethy1ene)benzene 1,3,5-[Ph₂P(0)CH₂]₃C₆H₃ have been studied by X-ray, dipole moments and quantum chemistry methods. It have been shown, that in crystal molecule has the conformation in which two diphenylphosphinoxide fragments dispose on one and the same side, but the third - on the other side of central benzene ring plane with torsion angles C_SP2-C_SP2-C_SP3-P 60–80° and C_SP2-C_SP3-P=O about 50–70°. In solution conformational picture is more rich: side by side with the structures realized in crystal, conformations with all three diphenylphosphinoxide fragments disposed on one and the same side of central benzene ring plane with torsion angles C_SP2-C_SP2-C_SP3-P 70-90° and C_SP2-C_SP3-P=O about 70–75° become preferable.     

Copper(II)‐ and gold(III)‐mediated cyclization of a thiourea to a substituted 2‐aminobenzothiazole

Benzothiazole derivatives are a class of privileged molecules due to their biological activity and pharmaceutical applications. One route to these molecules is via intramolecular cyclization of thioureas to form substituted 2‐aminobenzothiazoles, but this often requires harsh conditions or employs expensive metal catalysts. Herein, the copper(II)‐ and gold(III)‐mediated cyclizations of thioureas to substituted 2‐aminobenzothiazoles are reported. The single‐crystal X‐ray structures of the thiourea N‐(3‐methoxyphenyl)‐N ′‐(pyridin‐2‐yl)thiourea, C₁₃H₁₃N₃OS, and the intermediate metal complexes aquabis[5‐methoxy‐N‐(pyridin‐2‐yl‐κN )‐1,3‐benzothiazol‐2‐amine‐κN ³]copper(II) dinitrate, [Cu(C₁₃H₁₁N₃OS)₂(H₂O)](NO₃)₂, and bis{2‐[(5‐methoxy‐1,3‐benzothiazol‐2‐yl)amino]pyridin‐1‐ium} dichloridogold(I) chloride monohydrate, (C₁₃H₁₂N₃OS)₂[AuCl₂]Cl·H₂O, are reported. The copper complex exhibits a distorted trigonal–bipyramidal geometry, with direct metal‐to‐benzothiazole‐ligand coordination, while the gold complex is a salt containing the protonated uncoordinated benzothiazole, and offers evidence that metal reduction (in this case, Au^III to Au^I) is required for the cyclization to proceed. As such, this study provides further mechanistic insight into the role of the metal cations in these transformations.     

Tandem synthesis of [1,2,4]-triazoles mediated by iodine—a regioselective approach

A tandem regioselective one-pot synthesis of 3-amino-[1,2,4]-triazoles has been achieved from 1,3-disubstituted thioureas using molecular iodine. In this one-pot strategy, the intermediate carbodiimide generated in situ from thiourea upon reaction with HCONHNH₂ gives diaryl/alkylhydrazinecarboximidamide or acylureidrazone, which then undergoes an intramolecular cyclodehydration to afford the corresponding 3-amino-[1,2,4]-triazole. The product regioselectivity for unsymmetrical 1,3-disubstituted thioureas correlate well with the pK_as of the parent amines attached, in which the amine having higher pK_a goes to the ring nitrogen while the other nitrogen remains flanked as an exocyclic nitrogen of the triazole core. This method is milder and environmentally sustainable giving good to excellent yields of the desired products.     

The influence of the type of halogen substituent and its position on the molecular conformation,intermolecular interactions and crystal packing for a series of 1‐benzoyl‐3‐(halogenophenyl)thioureas

By the reaction of benzoyl chloride, potassium isothiocyanate and the appropriate halogenoaniline, i.e. 2/3/4‐(bromo/iodo)aniline, we have obtained five new 1‐benzoyl‐3‐(halogenophenyl)thioureas, namely, 1‐benzoyl‐3‐(2‐bromophenyl)thiourea and 1‐benzoyl‐3‐(3‐bromophenyl)thiourea, C₁₄H₁₁BrN₂OS, and 1‐benzoyl‐3‐(2‐iodophenyl)thiourea, 1‐benzoyl‐3‐(3‐iodophenyl)thiourea and 1‐benzoyl‐3‐(4‐iodophenyl)thiourea, C₁₄H₁₁IN₂OS. Structural and conformational features of the compounds have been analyzed using X‐ray diffraction and theoretical calculations. The novel compounds were characterized by solid‐state IR and ¹H/¹³C NMR spectroscopy. The conformations and intermolecular interactions, such as hydrogen bonds, π–π and S(6)…π stacking, and X…O (X = I or Br), I…S and I…π, have been examined and rationalized, together with four analogous compounds described previously in the literature. The set of nine compounds was chosen to examine how a change of the halogen atom and its position on the phenyl ring affects the molecular and crystal structures.     

Ⅱ conjugation in the butadiene

The π electronic delocalization in trans-C4H6 and cis-C4H6 has been investigated in the frame of ab initio valence bond theory with 6-31G basis set. The result shows that the Csp2-Csp2 single bond length (1.506 A) is only about 0.024 A shorter than the Csp3-Csp3 bond, thus the central bond length shortening would be mainly due to π conjugation. The theoretical resonance energies of the trans-C4H6 and cis-C4H6 are 8.48 and 7.44 kcal/mol, respectively.     

Synthesis of trifluoromethylthiazoles and their application to azo dyes

3-Bromo-1,1,1-trifluoropropan-2-one ( 2 ) reacted with thiourea and N-monosubstituted thioureas to give the corresponding 4-trifluoromethylthiazoles, respectively. In the reactions with N,N'-diphenylthiourea and thioamides, the considerably stable intermediates, 4-hydroxy-4-trifluoromethylthiazoline derivatives 7 and 8 , were isolated. The reaction of ethyl 2-bromo-4,4,4-trifluoro-3-oxobutanoate ( 4 ) with thiourea was carried out under the gentle conditions to give both thiazole-5-carboxylate 10 and 4-hydroxythiazoline 11 . The thiazole 10 was applied to the azo dye synthesis and the absorption maxima of thus obtained azo dyes were discussed.     

Self- and cross-disproportionation-to-combination rations for cyclopentyl and cyclohexyl radicals and their deuterated analogues

Hydrogen, cycloalkene, and bicycloalkyl were found to be the principal products which account for ≈?97% of all products formed in the gas-phase radiolysis of water vapor containing low concentrations of cycloalkanes. From the ratios of cycloalkene-to-bicycloalkyl yields extrapolated to the zero dose, the self- and cross-disproportionation-to-recombination rate constant ratios Δ = k_d/k_c were determined for the following 12 reactions: Δ(c-C₅H₉, c-C₅H₉) = 0.73; Δ(c-C₅D₉, c-C₅D₉) = 0.58; Δ(c-C₆H₁₁, cC₆H₁₁) = 0.59; Δ(c-C₆D₁₁, c-C₆D₁₁) = 0.46; Δ(c-C₅H₉, c-C₆H₁₁) = 0.28; Δ(c-C₅D₉, c-C₆H₁₁) = 0.28; Δ(c-C₅H₉, c-C₆D₁₁) = 0.24; Δ(c-C₅D₉, c-C₆D₁₁) = 0.24; Δ(c-C₆H₁₁, c-C₅H₉) = 0.33; Δ(c-C₆H₁₁, c-C₅D₉) = 0.25; Δ(c-C₆D₁₁, c-C₅H₉) = 0.35; and Δ(c-C₆D₁₁, c-C₅D₉) = 0.28, where in the case of the cross-disproportionation the symbol Δ(R₁,R₂) is used to represent k_d/k_c for the disproportionation in which radical R₁ captures a hydrogen (deuterium) atom from radial R₂. The geometrical mean rule holds in the cross-combination reactions of cyclopentyl and cyclohexyl radicals. The kinetic isotope effect in the disproportionation reaction was determined as 1.24 ± 0.06.     

Studies in mass spectrometry. IV—Fragmentation of aryltriflates. Substituent effects on [ArO]+ ion abundances: Looking for a best suited electron energy in the steady state approach. Experimental evidence for the ‘through bond’ stabilization of aryl cations by meta electron donor Substituents

The fragmentation patterns of 24 substituted phenyltrifluoromethanesulfonates has been determined by exact mass and metastable transition measurements. The influence of the ring substituent(s) on the abundance of the [ArO]+ ions has been investigated at low energies and a new standard parameter for plotting against Hammett's ó constants is proposed. The direct loss of CF₃SO₃ from the molecular ion of 3,5-(diisopropyl)-phenyl-, 3,5-(dicyclopropyl)phenyl- and 3,5-di(α-methylcyclopropyl)-phenyl-methanesulfonate, and further observations on the fragmentation processes of these compounds are consistent with M.O. calculations on the ‘through bond’ stabilization of the [Ar]+ σ state by meta electron donor substituents.     

Synthesis of pyridyl- and quinolyl-substituted 2-aminothiazoles

Five 2-amino-4-(x-pyridyl)- and 2-amino-4-(x-quinolyl)thiazoles have been synthesized by the condensation of thiourea with bromoacetylpyridines and -quinolines. The reaction of pyridyl pyridylmethyl ketones with thiourea and halogens produced four 2-aminothiazoles possessing pyridyl substituents in 4- and 5-positions on the thiazole ring. Treatment of N-(3-pyridyl)- and N-(3-quinoiyl)thiourea with α-bromoketones gave seven new 2-(3-pyridyl)amino- and 2-(3-quinolyl)aminothiazoles. The ultraviolet spectra of the pyridyl- and quinolyl- substituted 2-aminothiazoles were recorded.     

Synthesis and characterization of tungsten carbonyl complexes containing N-methyl substituted urea and thiourea ligands

Six new mixed-ligand tungsten carbonyl complexes containing N-methyl substituted urea and thiourea of the type W(CO)₄[RCH₂N-(C=X)NH₂] where X?=?O or S and R?=?morpholine, piperidine and diphenylamine are reported. These have been prepared by refluxing hexacarbonyl tungsten(0) with corresponding ligands in THF to produce cis-disubstituted products, [(L-L)W(CO)₄] where L-L?=?a chelating bidentate ligand, morpholinomethyl urea (MMU), morpholinomethyl thiourea (MMTU), piperidinomethyl urea (PMU), piperidinomethyl thiourea (PMTU), diphenylaminomethyl urea (DAMU) and diphenylaminomethyl thiourea (DAMTU). The compounds have been characterized by elemental analysis, IR, electronic and ¹³C NMR spectra, magnetic moments and conductivity measurements. The IR spectra suggests that in all the complexes, the ligands are bidentate chelating, coordinating the metal through carbonyl oxygen or thiocarbonyl sulphur and the ring nitrogen or tert-nitrogen of diphenylamine. The CO force constants and CO–CO interaction constants for these derivatives have also been calculated using Cotton–Kraihanzel secular equations, which indicate poor π-bonding ability of the ligands. ¹³C NMR and electronic spectra reveal loss of cis-carbonyl ligands to produce cis-disubstituted tetracarbonyl derivatives. Molecular modeling studies have been carried out using Hyperchem release 7.52 which suggest a distorted octahedral geometry for these complexes.     

Palladium(II) complexes with 1-allyl-3-(2-pyridyl)thiourea: Synthesis and spectroscopic characterization

New Pd(II) complexes with 1-allyl-3-(2-pyridyl)thiourea (APTU) of the formulas [Pd(C₉H₁₁N₃S)Cl₂] (I) and [Pd(C₉H₁₁N₃S)₂]Cl₂ (II) were obtained and examined by UV-Vis, IR, and 1H NMR spectroscopy. The conditions for the complexation reactions were optimized. The instability constants and molar absorption coefficients of these complexes were calculated. Comparison of the characteristic bands in the UV-Vis and IR spectra of the complexes and free APTU revealed that the ligand in both complexes is coordinated to the metal atom in the thione form in the bidentate chelating mode through the S atom of the thiourea group and the pyridine N atom. In the UV-Vis spectra of the complexes, the charge transfer bands (π → π* Py) and n → π* (C=N_Py), (C=S) experience hypsochromic shifts by 450–470 cm⁻¹ caused by the coordination of APTU to the metal ion, which gives rise to ligand-metal charge-transfer bands (C=N_Py → Pd, n → π* (C=S)) and (SPd). The protons in the 6-, 4-, and 3-positions of the pyridine ring and the thiourea NH proton in the chelate ring are most sensitive to the complexation.     

Organylthiochloroacetylenes: IV. Reaction with Thiourea

Alkylthiochloroacetylenes react with thiourea in acetone to form S-(alkylthioethynyl)isothiuronium chlorides and N-[1-(alkylthio)ethylidene]thioureas; phenylthiochloroacetylene reacts with thiourea to give 4-(phenylthio)-2-imino-1,3(3H)-thiazole hydrochloride.