On the Adsorption and Reduction of the Herbicide Picloram on Mercury and Carbon Electrodes

At concentrations higher than 2?10^?4 M , and below pH 3, the cyclic voltammograms of picloram (=4‐amino‐3,5,6‐trichloropyridine‐2‐carboxylic acid) on Hg electrodes show two prepeak systems (named I and II attending to the proximity to the main reductions peak), which can be attributed to the weak adsorption of reactant and the strong adsorption of the product at the electrode surface. The system II is due to the uncharged form of picloram, and system I to the picloram protonated at the pyridine N‐atom. Small amounts of the surfactant Triton X‐100 (=α‐[4‐(1,1,3,3‐tetramethylbutyl)phenyl]‐ω‐hydroxypoly(oxyethane‐1,2‐diyl)) cause the disappearance of system I, the shift of system II, and also affect the intensities and widths of anodic and cathodic peaks but not the charge passed in each peak. Thus, the adsorption process responsible for the appearance of system I is inhibited by the presence of Triton; by contrast, the process corresponding to system II is only modified by the surfactant, becoming an electrochemical process occurring at the potentials corresponding to system II, which is more reversible than that observed in the absence of Triton. The addition of Triton permitted the analysis of the main reduction process. Convolution voltammetry of the main reduction peak is consistent with the loss of a Cl‐atom in equilibrium which occurs after a reversible electron transfer and is followed by the reductions of both species present in the equilibrium (Scheme 2). This is also the reduction mechanism on a glassy carbon electrode but the electron transfer on the carbon electrode increases with respect to the mercury electrodes; in addition, the loss of the Cl‐atom does not take place on the electrode surface. From the recording of differential capacity–potential curves, it was concluded that picloram is adsorbed on the carbon electrode; but this adsorption is too weak to induce the appearance of prepeak systems.     

Condensation of Aryl Aldehydes, 2‐naphthol,and Thioacetamide Catalyzed by N‐halo Reagents in Neutral Media

A new three‐component, highly efficient and solvent‐free approach for the synthesis of known and new 1‐thioamido‐alkyl‐2‐naphthol derivatives was investigated. This was achieved via a one‐pot condensation by reacting aryl aldehydes, 2‐naphthol, and thioacetamide in the presence of catalytic amount of 1,3,5‐trichloro‐1,3,5‐triazinane‐2,4,6‐trione (TCCA) and 1,3‐dichloro‐5,5‐dimethylhydantoin (DCDMH). Mechanistically, the in situ generation of Cl⁺ ion from TCCA and DCDMH is proposed to catalyse the reactions in neutral media. In the presented work, most of the products have been reported for the first time.     

Direct Formation of 2,3,5‐Trichloropyridine and its Nucleophilic Displacement Reactions in Ionic Liquid

Abstract

Reaction of trichloroacetaldehyde and acrylonitrile in the presence of a catalytic amount of copper (I) chloride in ionic liquid afforded 2,3,5‐trichloropyridine, fluorination of which with KF and CsF in ionic liquid afforded 3,5‐dichloro‐2‐fluoropyridine and 5‐chloro‐2,3‐dichloropyridine. Reaction of 2,3,5‐trichloropyridine, 3,5‐dichloro‐2‐fluoropyridine, or 5‐chloro‐2,3‐dichloropyride with 2‐(4‐hydroxyphenoxy)propionates in ionic liquid afforded the corresponding 2‐aryloxylpropionates in good yields.     

The synthesis of higher cyclomethylalkylsilazanes

The ammonolysis of dichloro(isobutyl)methylsilane and dichloro(methyl)(nonyl)silane forms triisobutyltrimethylcyclotrisilazane, tetraisobutyltetramethylcyclotetrasilazane, and trimethyltrinonylcyclotrisilazane. The coammonolysis of dichloro(isobutyl)(methyl)silane with trichloro(nonyl)silane gave a cyclic compound with free amino groups-3,7-diamino-1,1,5,5-tetraisobutyl-1,1,5,5-tetramethyl-3, 7-dinonylcyclotetrasilazane- and the coammonolysis of dichloro(isobutyl) (methyl)silane with trichloro-(isobutyl)silane yielded bicyclic products-1,3,5,7-tetraisobutyl-1,5-dimethylbicyclotetrasilazane and 1,3,5,7,9pentaisobutyl-1,5,7-trimethylbicyclopentasilazane.     

(Benzene‐1,3,5‐triyl)tris[phosphine] (C6H3(PH2)3) and (Benzene‐1,3,5‐triyl)tris[phosphonic Acid] (C6H3[P(O)(OH)2]3). Absence of Hydrogen Bonding in Solid Primary Phosphines

The prolonged photo‐Arbuzov reaction (3 weeks, Hg lamp) of 1,3,5‐trichloro‐benzene with a large excess of trimethyl phosphite (as a solvent) at 50° gives moderate yields of dimethyl (3,5‐dichlorophenyl)phosphonate ( 1 ; 14.5%), tetramethyl (5‐chloro‐1,3‐phenylene)bis[phosphonate] ( 2 ; 35.4%), and hexamethyl (benzene‐1,3,5‐triyl)tris[phosphonate] ( 3 ; 30.1%). The products can be separated by fractional distillation. Acid hydrolysis of the esters gives almost quantitative yields of the corresponding phosphonic acids 4 – 6 . Reduction of the esters 1 – 3 by LiAlH₄ in tetrahydrofuran affords the primary phosphines (3,5‐dichlorophenyl)phosphine ( 7 ; 46.5%), (5‐chloro‐1,3‐phenylene)bis[phosphine] ( 8 ; 34.5%) and (benzene‐1,3,5‐triyl)tris[phosphine] ( 9 ; 25.2% yield). In the crude reduction products from 2 (preparation of 8 ) and from 3 (preparation of 9 ), (3‐chlorophenyl)phosphine and (1,3‐phenylene)bis[phosphine], respectively, are observed as by‐products. All compounds are characterized by standard analytical, spectroscopic, and (for 1, 7 , and 8 ) structural techniques. The arrangement of the molecules in the crystal structures of 7 and 8 suggest that H‐bonding between the primary arylphosphines is virtually insignificant for the packing of the components. This is in marked contrast to the importance of H‐bonding for the supramolecular chemistry of arylamines. The new primary polyphosphines and polyphosphonic acids are to be employed in the construction of extended arrays.     

Synthesis and antimicrobial activity of 2,10‐dichloro‐6‐substituted‐4,8‐dinitro‐12H‐dibenzo[d,g][1,3,2]dioxaphosphocin 6‐oxides/sulfides

Novel 2,10‐dichloro‐6‐substituted‐4,8‐dinitro‐12H‐dibenzo[d,g][1,3,2]dioxaphosphocin 6‐oxides ( 4a–h ) were synthesized by reacting 5,5′‐dichloro‐3,3′‐dinitro‐2,2′‐dihydroxydiphenylmethane ( 2 ) with different aryl phosphorodichloridates ( 3a–g ) or bis(2‐chloroethyl)phosphoramidic dichloride ( 3h ) in the presence of triethylamine at 55–60°C, and the compounds 4i–l were prepared by reacting the 2,6,10‐trichloro‐4,8‐dinitro‐12H‐dibenzo[d,g][1,3,2]dioxaphosphocin 6‐sulfide ( 5 ) in situ with substituted phenols and thiophenol 5 was prepared by condensing 2 with thiophosphoryl chloride. IR, ¹H, ¹³C, ³¹P NMR, and mass spectra supported all the proposed structures. Several title compounds exhibited significant activity in the assays against the bacteria Bacillus subtilis and Escherichia coli and fungi Curvularia lunata and Aspergillus niger. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:10–15, 2001     

Studies on pyridazine azide cyclisation reactions

Reaction of sodium azide with 4-methyl-3,5,6-tribromopyridazine results in the formation of 3,5,6-triazide intermediate which could cyclise to give two possible bicyclic products while ab initio calculations show that the formation of a tricyclic compound is extremely energetically unfavourable. However, experimentally, only one major product is isolated. The structure of this unstable product has been conclusively established by X-ray crystallography as 3,5-diazido-4-methyl[1,5-b]tetrazolopyridazine confirming theoretical predictions.     

Generation and Spectroscopic Identification of ClCNS,ClNCS and NCCNS

The photolysis of four chloro‐substituted thiadiazoles (3,4‐dichloro‐, 3‐chloro‐ and 3‐chloro‐4‐fluoro‐1,2,5‐thiadiazole; 3,5‐dichloro‐1,2,4‐thiadiazole) and 3,4‐dicyano‐1,2,5‐thiadiazole was investigated in inert solid‐argon matrices at cryogenic temperatures by means of UV irradiation at selected wavelengths of 254 and 280 nm. The photolysis products were identified by mid‐IR and UV spectroscopy. Evidence for the existence of three novel pseudohalides, namely, chloronitrile sulfide (ClCNS), chlorine isothiocyanate (ClNCS) and cyanogen N‐sulfide (NCCNS), was provided by direct spectroscopic methods supported by quantum chemical calculations. Ground‐state geometries, vibrational frequencies, IR intensities, and UV excitation energies of ClCNS, ClNCS and NCCNS were obtained from calculations using the B3LYP, CCSD(T) and SAC‐CI methods and the aug‐cc‐pV(T+d)Z basis set.     

Solvatomorphism in (E)‐2‐(2,6‐dichloro‐4‐hydroxybenzylidene)hydrazinecarboximidamide

The structures of orthorhombic (E)‐4‐(2‐{[amino(iminio)methyl]amino}vinyl)‐3,5‐dichlorophenolate dihydrate, C₈H₈Cl₂N₄O·2H₂O, (I), triclinic (E)‐4‐(2‐{[amino(iminio)methyl]amino}vinyl)‐3,5‐dichlorophenolate methanol disolvate, C₈H₈Cl₂N₄O·2CH₄O, (II), and orthorhombic (E)‐amino[(2,6‐dichloro‐4‐hydroxystyryl)amino]methaniminium acetate, C₈H₉Cl₂N₄O⁺·C₂H₃O₂⁻, (III), all crystallize with one formula unit in the asymmetric unit, with the molecule in an E configuration and the phenol H atom transferred to the guanidine N atom. Although the molecules of the title compounds form extended chains via hydrogen bonding in all three forms, owing to the presence of different solvent molecules, those chains are connected differently in the individual forms. In (II), the molecules are all coplanar, while in (I) and (III), adjacent molecules are tilted relative to one another to varying degrees. Also, because of the variation in hydrogen‐bond‐formation ability of the solvents, the hydrogen‐bonding arrangements vary in the three forms.     

A facile synthesis and antimicrobial activity of 2,10‐dichloro‐6‐(aryloxy/thiophenoxy)‐4,8‐dinitrodibenzol[d,g][1,3,6,2]‐dioxathiaphosphocin‐ 6‐oxides

Novel 6‐substituted 2,10‐dichloro‐4,8‐dinitrodibenzo[d,g][1,3,6,2]dioxathiaphosphocin‐6‐oxides 4 were synthesized by reacting 5,5′‐dichloro‐3,3′‐dinitro‐2,2′‐dihydroxydiphenyl sulfide ( 2 ) with different aryl phosphorodichloridates, trichloromethylphosphonic dichloride and O‐2‐chloroethyl phosphoryldichloride (3) in the presence of triethylamine at 55–60°. Some of these compounds are prepared by reacting the monochloride, 2,6,10‐trichloro‐4,8‐dinitrodibenzo[d,g][1,3,6,2]dioxathiaphosphoein‐6‐oxide ( 5 ) in situ with substituted phenols and thiols. 5 is prepared by condensing 2 with phosphorus oxychloride. The ¹H nmr chemical shifts of the dibenzodioxathiaphosphocin moiety indicates the presence of more than one conformer in solution. However the presence of more than one conformer in each example cannot be entirely eliminated. Interestingly 4d on oxidation to 12‐sulphone by H₂O₂ in acetic acid medium yielded only 12‐sulphoxide 6a . The ir, ¹H, ¹³C, ³¹P nmr and mass spectral data are discussed. Some of these compounds were screened for antifungal activity against Curvularia lunata and Aspergillus niger and antibacterial activity on Bacillus subtilis and Klebsiella pneumoniae. A few of them possess significant activity.     

硫代磷酰基硫脲与某些含氯双官能团试剂的成环反应

Ｏ－乙基－Ｎ－异丙基硫代磷酰硫脲衍生物与氯乙酰氯、二氯乙酰氯及三氯乙酰氯，在碱存在下可发生关环反应，得到相应的噻唑啉酮类衍生物，讨论了不同试剂及反应条件对产物结构的影响，而Ｏ－乙基－Ｎ－异丙基硫代磷酰硫脲与氯乙醛关环，则生成相应的噻唑衍生物，所有化合物经元素分析、＾１ＨＮＭＲ、ＩＲ及ＭＳ证实，其中部分化合物显示出一定的除草活性。     

Simultaneous determination of aminopyralid, clopyralid, and picloram residues in vegetables and fruits using ultra-performance liquid chromatography/tandem mass spectrometry

A sensitive and effective method for the simultaneous quantitative determination of aminopyralid, clopyralid, and picloram in vegetables (eggplant, cucumber, and tomato) and fruits (apple and grape) was developed and validated using ultra-performance LC coupled with MS/MS. The three herbicides were successfully separated and independently confirmed in a single run. Different extraction and cleanup methods were used to optimize the pretreatment processes of the residue analysis method. The final method is straightforward and involves extraction with 1% formic acid-acetonitrile, and no complicated cleanup process is needed. Determination of the compounds was achieved within 3.0 min. Respective average recoveries using this method at four concentration levels (0.05, 0.1, 0.5, and 1.0 mg/kg) ranged from 66.5 to 109.4%, with RSDs in the range of 1.1-19.7% (n = 5) for all analytes. The LODs were below 0.010 mg/kg, and the LOQs did not exceed 0.036 mg/kg, which were lower than the maximum residue limits (MRLs) of 0.5-5.0 mg/kg clopyralid in vegetables and fruits samples, as established by the European Union. This study provides a theoretical basis for China to develop MRLs and an analytical method for aminopyralid, clopyralid, and picloram in vegetables and fruits.     

Novel Copolymers of Styrene and Halogen Ring‐Disubstituted 2‐Cyano‐N,N‐Dimethyl‐3‐Phenyl‐2‐Propenamides

Electrophilic trisubstituted ethylene monomers, halogen ring‐disubstituted 2‐cyano‐N,N‐dimethyl‐3‐phenyl‐2‐propenamides, RC₆H₃CH?C(CN)CON(CH₃)₂ (where R is 2,3‐dichloro, 2,4‐dichloro, 2,6‐dichloro, 3,4‐dichloro, 3,5‐dichloro, 2,3‐difluoro, 2,4‐difluoro, 2,6‐difluoro, 3,4‐difluoro, 3,5‐difluoro), were synthesized by potassium hydroxide catalyzed Knoevenagel condensation of ring‐substituted benzaldehydes and N,N‐dimethyl cyanoacetamide, and characterized by CHN elemental analysis, IR, ¹H‐ and ¹³C‐NMR. Novel copolymers of the ethylenes and styrene were prepared at equimolar monomer feed composition by solution copolymerization in the presence of a radical initiator, ABCN at 70°C. The composition of the copolymers was calculated from nitrogen analysis, and the structures were analyzed by IR, ¹H and ¹³C NMR, GPC, DSC, and TGA. High T_g of the copolymers in comparison with that of polystyrene indicates a substantial decrease in chain mobility of the copolymer due to the high dipolar character of the trisubstituted ethylene monomer unit. The gravimetric analysis indicated that the copolymers decompose in the 300–450°C range.     

Regioselective synthesis of functional tellanes from tellurium tetrahalides and 1-octene

Proceeding from TeCl₄ and 1-octene a regioselective method was developed of the synthesis of trichloro(2-chlorooctyl)tellane. At adding methanol to this compound chlorine was easily replaced at room temperature by a methoxy group affording trichloro(2-methoxyoctyl)tellane. The reaction of TeBr₄ with 1-octene in methanol resulted in tribromo(2-methoxyoctyl)tellane. A reduction of trichloro- and tribromo(2-methoxyoctyl)tellanes occurs the most selectively in the system NaBH4–water–THF giving 1,2-bis(2-methoxyoctyl)ditellane. The reactions are characterized by a high selectivity and quantitative yields of the products.     

TCT‐DMSO/[bmim]BF4: A novel promoter system for the synthesis of 3,5‐diaryl‐1,2,4‐thiadiazoles at ambient temperature

An efficient and practical procedure for direct synthesis of 3,5‐diaryl‐1,2,4‐thiadiazoles by thioamides with 2,4,6‐trichloro‐1,3,5‐triazine (TCT) and dimethylsulfoxide using 1‐butyl‐3‐methylimidazolium tetrafluoroborate as an eco‐friendly reaction medium under ambient temperature is described. This protocol can be considered as a new procedure for 3,5‐diaryl‐1,2,4‐thiadiazoles synthesis. J. Heterocyclic Chem., (2010).     

Synthesis of new substituted 5‐methyl‐3,5‐diphenylimidazolidine‐2,4‐diones from substituted 1‐(1‐cyanoethyl‐1‐phenyl)‐3‐phenylureas

The reaction of substituted phenyl isocyanates with 2‐amino‐2‐phenylpropanenitrile and 2‐amino‐2‐(4‐nitrophenyl)propanenitrile has been used to prepare substituted 1‐(1‐cyanoethyl‐1‐phenyl)‐3‐phenylureas. In anhydrous phosphoric acid the first products to be formed from 1‐(1‐cyanoethyl‐1‐phenyl)‐3‐phenylureas are phosphates of 4‐methyl‐4‐phenyl‐2‐phenylimino‐5‐imino‐4,5‐dihydro‐1,3‐oxazoles, which on subsequent hydrolysis give the respective ureidocarboxylic acids. On prolongation of the reaction time, the phosphates of 4‐methyl‐4‐phenyl‐2‐phenylimino‐5‐imino‐4,5‐dihydro‐1,3‐oxazoles rearrange to give phosphates of 5‐methyl‐4‐imino‐3,5‐diphenylimidazolidin‐2‐ones, and these are subsequently hydrolysed to the respective substituted 5‐methyl‐3,5‐diphenylimidazolidin‐2,4‐diones. The ureidocarboxylic acids were also prepared by alkaline hydrolysis of 5‐methyl‐3,5‐diphenylimidazolidin‐2,4‐diones. The 5‐methyl‐3,5‐diphenylimidazolidin‐2,4‐diones and ureidocarboxylic acids were characterised by their ¹H and ¹³C NMR spectra. Structure of the 5‐methyl‐5‐(4‐nitrophenyl)‐3‐phenylimidazolidine‐2,4‐dione was verified by X‐ray diffraction. The alkaline hydrolysis of individual imidazolidine‐2,4‐diones was studies spectrophoto‐metrically in sodium hydroxide solutions at 25 °C. The rate‐limiting step of the base catalysed hydrolysis consists in decomposition of the tetrahedral intermediate. The reaction is faster if electron‐acceptor sub‐stituents are present in the 3‐phenyl group of imidazolidine‐2,4‐dione cycle. The pK_a values of individual 5‐methyl‐3,5‐diphenylimidazolidine‐2,4‐diones have been determined kinetically.     

Cross‐Conjugated Hexaphyrins and Their Bis‐Rhodium Complexes

A cross‐conjugated hexaphyrin that carries two meso‐oxacyclohexadienylidenyl (OCH) groups 9 was synthesized from the condensation of 5,10‐bis(pentafluorophenyl)tripyrrane with 3,5‐di‐tert‐butyl‐4‐hydroxybenzaldehyde. The reduction of 9 with NaBH₄ afforded the Möbius aromatic [28]hexaphyrin 10 . Bis‐rhodium complex 11 , prepared from the reaction of 10 with [{RhCl(CO)₂}₂], displays strong Hückel antiaromatic character because of the 28 π electrons that occupy the conjugated circuit on the enforced planar structure. The oxidation of 11 with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) yielded complexes 12 and 13 depending upon the reaction conditions. Both 12 and 13 are planar owing to bis‐rhodium metalation. Although complex 12 bears two meso‐OCH groups at the long sides and is quinonoidal and nonaromatic in nature, complex 13 bears 3,5‐di‐tert‐butyl‐4‐hydroxyphenyl and OCH groups and exhibits a moderate diatropic ring current despite its cross‐conjugated electronic circuit. The diatropic ring current increases upon increasing the solvent polarity, most likely due to an increased contribution of an aromatic zwitterionic resonance hybrid.     

Synthesis of Some New Polyfunctionalized Pyridines

5‐Methyl‐2,4‐dihydro‐3H‐pyrazol‐3‐one and/or 5‐methyl‐2‐phenyl‐2,4‐dihydro‐3H‐pyrazol‐3‐one was reacted with arylidenemalononitrile in the presence of sodium alkoxide to give 2‐amino‐6‐alkoxy‐4‐arylpyridine‐3,5‐dicarbonitrile 4a–e instead of the reported pyrazolo[3,4‐b]pyridine‐5‐carbonitriles. The same products 4a–e were prepared via reaction of arylidenemalononitrile with sodium alkoxide in an appropriative alcohol. However, the new synthetic route for preparation of their positional isomer 4‐amino‐6‐alkoxy‐2‐arylpyridine‐3,5‐dicarbonitrile 7a–j has been achieved via reaction of 2‐aminoprop‐1‐ene‐1,1,3‐tricarbonitrile with different aromatic aldehydes under the same conditions.     

A simple synthesis of 4-amino-6-methyl-1,1,1-trifluoro(trichloro)hepta-3,5-dien-2-ones and 2,2-dimethyl-6-trifluoromethyl-2,3-dihydro-4-pyridone

Treatment of 2,2-dimethyl-6-trifluoro(trichloro)methyl-2,3-dihydro-4-pyrones with ammonia gives 4-amino-1,1,1-trifluoro(trichloro)-6-methylhepta-3,5-dien-2-ones. Under similar conditions 1,1,1-trifluoro-2-hydroxy-6-methylhepta-2,5-dien-4-one and 6-chloro-1, 1,1-trifluoro-2-hydroxy-6-methylhept-2-en-4-one cyclize into 2,2-dimethyl-6-trifluoromethyl-2,3-dihydro-4-pyridone. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2263–2265, December, 1997.     

Stereoselective reductive amination of β-keto esters derived from dipeptides. Stereochemical and mechanistic studies on the formation of 5-carboxymethyl-2-oxopiperazine derivatives

The stereoselective generation of 3,5-disubstituted and 3,5,6-trisubstituted 2-oxopiperazine derivatives can be accomplished by intramolecular reductive amination of β-keto esters derived from Z-Xaa-Gly-OH and Z-Xaa-Yaa- OH dipeptides, respectively. Differences in the stereoselectivity between the use of NaBH₃CN and hydrogen as reducing agents are due to the reduction of different intermediates, as deduced from experiments of isotopic labelling with deuterium.