Imidazolinone herbicides in strongly acidic media: Speciation and electroreduction

From UV-visible measurements and potentiometric titrations it follows that the lowest pK values (pK₁) of imidazolinone herbicides correspond to the simultaneous protonation/dissociation equilibria of both the pyridinic (or quinolinic) nitrogen and the carboxyl group, the following pK (pK₂) to the imminium nitrogen and the basic pK (pK₃) to the dissociation of the imido nitrogen. Below pH 6 and down to pH c.a. 2.5, the dominant form of the herbicide is a double ion having both positive and negative charges, this being important in discussing the effect of pH in the natural dynamics of imidazolinone herbicides, especially in their soil sorption. Electrochemical studies of the reduction of the herbicides were made on mercury and carbon electrodes in strongly acidic media (0.1 to 2.7 M H₂SO₄) as well up to pH 7. The reduction signals were all attributed to the reduction of the imidazolinone ring except the second peak/wave that was found to have originated by the reduction of the pyridine/quinoline ring. A signal observed in strongly acidic media and at highly negative overpotentials was attributed to the reduction of the imidazolinone ring of the product of the previous reduction in a process consisting of two reversible electron transfers followed by a protonation reaction.     

Crystal and molecular structure of bis(imazapyr)diaqua copper(II)

The imidazolinone herbicide imazapyr, 2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)nicotinic acid (H₂imz) interacts with Cu(II) leading to [Cu(Himz)₂(H₂O)₂] which crystallizes in the space group Pbca, with a = 12.5370(3) Å, b = 19.8500(5) Å, c = 22.7720(9) Å, and Z = 8. The Cu(II) atom is octahedrally surrounded by four nitrogen atoms of two Himz^– anions and two water molecules. Each Himz^– acts as a chelating ligand by means of N pyridine and N lactam atoms leading to five-membered chelate rings. The Cu N distances vary from 1.948(4) to 2.299(5) Å while the Cu O are 2.114(5) and 2.256(6) Å. The imidazol N-H are involved in short intramolecular hydrogen bonds with the carboxylate groups. The structure is stabilized by an intermolecular hydrogen-bonded network involving the water molecules and the carboxylate groups.     

新型2-氨基-5-苯亚甲基-4H-咪唑啉-4-酮衍生物的合成及生物活性

通过烯基膦亚胺1与芳基异氰酸酯的aza-Wittig反应得到碳二亚胺2,再用2与亲核试剂的成环反应制得10个新型的2-氨基-5-苯亚甲基-4H-咪唑啉-4-酮衍生物4,探讨了碳二亚胺2与不同亲核试剂反应的活性并分离得到了一个胍中问体3i,初步研究了化合物4的生物活性.     

Efficient Synthesis of 2-(8-Quinolinoxy)-4H-imidazolin-4-ones

IntroductionMany N- heterocycles including 4H - imidazolin-4- ones show bactericidal and fungicidal activities,especially those with a 2 - alkoxyl substituent[1— 5] .The efforts to discover the new biologically activederivatives reflected by the still important numberof publications and patents have been devoted tothe subject[6— 11] .For example,some 2 - amino or 2 -alkylthio substituted 4H- imidazolin- 4- ones showsignificant antifungal and antibacterial activi-ties[7— 9] ,whereas others …     

Determination of imazethapyr and imazapyr residues in soil by coupled-column liquid chromatography

Summary A column-switching method using two separation columns combined with UV detection at 260 or 236 nm has been used to determine the imidazolinone herbicides imazethapyr and imazapyr in soils. The residues were extracted from the soil with 0.1 M aqueous sodium carbonate solution and, after adjusting the pH to 2.0, the solution was partitioned with dichloromethane. Limits of determination for imazethapyr and imazapyr were 3 μg/kg. Recoveries were from 55 to 75% for both imidazolinone herbicides in the range 3–100 μg/kg in soil.     

Imidazolinone and triazine herbicides in soils in relation to the complexes formed with Cu(II) ions

Imidazolinone and triazine herbicides are used in many countries and may have a great impact on metal biocycles in soil. This article deals with the dynamics of imidazolinone and triazine herbicides in soils related to the formation of complexes with Cu(II) ions, which can be very stable. The stability constants of the complexes formed by five imidazolinone herbicides and ten triazine herbicides with Cu(II) ions are determined by means of fast, easy, and inexpensive measurements performed by ultraviolet–visible spectroscopy, for imidazolinones, and voltammetry (cyclic and differential pulse), for triazines. Because of the occurrence of dissociation reactions, the determinations were performed at three pH values for imidazolinones and at one pH value for triazines. In aqueous solutions of 5 < pH < 10 (corresponding to the majority of soils of agricultural use), the herbicides form very stable complexes with the Cu(II) ions, the complexes being integrated by two ligands (herbicides) and one copper ion. In conclusion, crops treated with such herbicides in conjunction with Cu(II) salts experience a decrease in its persistence and effectiveness. In addition, the herbicides and the copper ions may pass to the phreatic layer of the soil, increasing the chance of pollution.     

An efficient synthesis of 3′-quinolinyl substituted imidazole-5-one derivatives catalyzed by zeolite and their antimicrobial activity

A series of some new quinoline based imidazole-5-one derivatives have been synthesized by the fusion of oxazol-5-ones,various p-substituted anilines and zeolite in pyridine.All the derivatives were subjected to an in vitro antimicrobial screening against a representative panel of bacteria and fungi and results worth further investigations.     

A highly diastereoselective synthesis of chroman derivatives bearing spirocyclic N,O-acetals skeleton via a one-pot tandem reaction

A tandem reaction for the synthesis of chroman framework via a one-pot reaction of phenol, paraformaldehyde, and 5-benzylimidazolidin-4-one mediated by p-nitrobenzoic acid is described. The chroman derivatives containing spirocyclic N,O-acetal skeleton can be obtained in moderate to good yields (up to 89%) with good to excellent diastereoselectivities (up to >20:1 dr).     

Improved extraction and clean-up of imidazolinone herbicides from soil solutions using different solid-phase sorbents

Extraction and quantification of herbicide residues from soil are important in understanding the behaviour of persistent herbicides. This research investigated extraction and clean-up methods for imidazolinone herbicides from soil and soil amended with organic material. A series of solvent mixes, pH conditions and sorbents was tested. Across three imidazolinone herbicides: imazapyr, imazethapyr and imazaquin, 0.5 M NaOH extraction gave greater than 90% recovery from soil samples; however, 0.5 M NaOH:MeOH (80:20) resulted in higher recovery for imazaquin, but not for the other two herbicides. Of the sorbents tested, the use of chromatographic mode sequencing using C₁₈ and SCX sorbents provided consistent high (>85%) recovery of all three herbicides from soil and separation of the herbicides from other soil components by high performance liquid chromatography (HPLC). These two methods will allow high recovery of these imidazolinone herbicides from soil and have the ability to detect these herbicides without interference from other soil components.