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TRI Programs in Other Countries
Published in Thomas E. Higgins, Jayanti A. Sachdev, Stephen A. Engleman, Toxic Chemicals, 2016
Thomas E. Higgins, Jayanti A. Sachdev, Stephen A. Engleman
For most chemicals, if more than 1 ton of the material is used or manufactured per year, it is considered reportable with the exception of the following 12 substances called specific Class I designated substances, which have a reporting threshold of 0.5 tons per year: AsbestosEthylene oxideCadmiumChromium (VI)Vinyl chlorideDioxinNickelArsenicBerylliumBenzylidyne trichlorideBenzene9-Methoxy-7H-furo[3,2-g][1]benzopyran-7-one; methoxsalen
Microwave-Assisted Synthesis and Functionalization of Six-Membered Oxygen Heterocycles
Published in Banik Bimal Krishna, Bandyopadhyay Debasish, Advances in Microwave Chemistry, 2018
Neha Batra, Rahul Panwar, Ramendra Pratap, Mahendra Nath
Chromenes are benzopyran analogs which form after the fusion of a benzene ring with a six-membered pyran ring. They exist in two isomeric forms such as 2H-chromenes (2H-1-benzopyrans) and 4H-chromenes (4H-1-benzopyrans). Among the chromenes, coumarins (2H-chromen-2-one) have received considerable attention due to their diverse pharmacological profiles such as anticoagulant [98], anticancer [99], anti-HIV [100], antitumor [101], anti-inflammatory [102], anti-Alzheimer′s [103], antileukemic [104], antibacterial [105], antimalarial [106], antitubercular [107], platelet antiaggregator [108], antioxidant [109], anti-HCV [110], hypoglycaemic [111], antifungal [112], and antifilarial agents [113]. The antitumor effect of coumarins is associated with the metabolite 7-hydroxycoumarin [114]. Coumarins are also associated with strong coronary vasodilating effects [115]. The structures of some of the biologically relevant coumarins are presented in Figure 9.2. LG120746 acts as progesterone receptor modulator [116], acolbifene used as estrogen receptor modulator [117], cannabinol exhibited affinity towards the CB1 and CB2 [118, 119] whereas moracin D has demonstrated fungicidal effect [120]. Besides these, coumarins are also used in cosmetics [121] and agrochemicals [122]. They are useful as dyes [123], sensors, and probes due to significant fluorescent properties [124]. Therefore, a large number of synthetic methods have been developed from time to time to construct these molecules for a variety of applications (Figure 5.2).
Green Chemistry and Green Catalysts
Published in Ahindra Nag, Greener Synthesis of Organic Compounds, Drugs and Natural Products, 2022
Ahindra Nag, Himadri Sekhar Maity
In the past decades, most of the scientists have been interested in the synthesis of heterocyclic unit-containing molecules due to their important medicinal and pharmaceutical applications and their use as precursors for the library of natural products and drug or drug-like molecules.40 In organic chemistry, heterocycle units are present in nature more than 70% as promising bioactive and drug molecules which are essential for mankind by boosting the quality of life.41 Among the various heterocycles, much attention is paid to nitrogen and oxygen-containing heterocycles due to their biological significances.42 Heterocyclic compounds can be usefully classified based on their electronic structure. A variety of five- and six-membered heterocyclic compounds such as pyrazole, imidazole, isoxazole, oxazole, pyridazine, phthalazine (benzopyridazine), pyrimidine, pyrazine, uracil, triazole, tetrazole, pyran, benzopyran, triazine and phthalide are present largely in nature owing to the stability of five- and six-member ring systems.43,44 Among the six-membered heterocycles, pyran or oxine with molecular formula C5H6O is a significant class of oxygen-containing heterocyclic compounds. Pyran is non-aromatic due to the presence of five carbon atoms and one oxygen atom along with two double bonds. 2H-pyrans and 4H-pyrans are the two isomers of pyrans which vary by the position of the double bonds. 2H-pyran is named like that due to the presence of the saturated carbon at position 2 whereas, in 4H-pyran, the saturated carbon is present at position 4. The classification of pyran-based heterocyclic molecules is determined by the presence of either 2H- or 4H-pyran scaffold (Figure 1.10).
Copper-assisted synthesis of five-membered O-heterocycles
Published in Inorganic and Nano-Metal Chemistry, 2020
Navjeet Kaur, Yamini Verma, Neha Ahlawat, Pooja Grewal, Pranshu Bhardwaj, Nirmala Kumari Jangid
The 2-(trans-3-pentenyl)-phenol was cyclized in the presence of palladium(II) catalyst and copper acetate/oxygen oxidant to afford 3,4-dihydro-2-vinyl-2H-1-benzopyran readily.[106] The 2-allylphenols by intramolecular oxypalladation afforded benzofurans and their 2,3-dihydro-derivatives in the presence of oxygen in catalytic amounts of palladium chloride or palladium acetate.[107] Products were formed in optically active form through the formation of in situ pinanylpalladium complexes when worked with (1R,5R)-2(10),3-pinadiene or α-pinene. The S-(+)-2,3-dihydro-2-vinylbenzofurans were formed predominantly from 2-(trans-2-butenyl)phenols (Scheme 32), while the (R)-(+)-2,3-dihydro-2-vinylbenzofurans (Scheme 33) were obtained as prevailing enantiomer from cis isomer, although the heterocyclization occurred with a low degree of enantioselectivity (up to 29% ee). The palladium(0) was not formed from palladium(II) with oxygen–copper acetate system or tert-butylhydroperoxide.[108–112] The 2-allylphenols were utilized for the synthesis of substituted 2-methylbenzofurans in the presence of copper acetate/lithium chloride as oxidant system and palladium acetate as catalyst in dimethylformamide as solvent.[113,114]
Thermal, spectroscopic and structural characterization of isostructural phase transition in 4-hydroxybenzaldehyde
Published in Phase Transitions, 2018
Packing (structural) polymorphism is very common in organic compounds arising due to more than one packing motif of the same compound. Thus in packing polymorphism, the same solid shows different crystal packing. An example of an organic polymorph is glycine, which is able to form monoclinic and hexagonal crystals. Studying polymorphs in organic solids is of importance as polymorphs may differ significantly in many important thermodynamic properties such as solubility and melting point, and kinetic properties such as dissolution rate and stability, as well as mechanical properties crucial in pharmaceutical industry [1,2]. 4-hydroxybenzaldehyde(4-HOBAL) an aromatic aldehyde is used in synthesis of various compounds like aldehyde methacrylates, benzopyrans, liquid crystalline compounds, etc. Aldehyde methacrylate has application in manufacturing dental materials as it can form strong and durable bonds with dentin [3]. Benzopyrans have wide applications in the perfume, cosmetic and pharmaceutical industry [4,5]. Two crystal structures of 4-HOBAL, recrystallized from ethylacetate (CCDC no. 676 161) and water (CCDC no. 1232287), respectively have been reported [6,7]. The crystal structure of 4-HOBAL crystallized from ethylacetate is monoclinic, P21/c, a = 6.6992 (8) Ȧ, b = 13.5550 (12) Ȧ, c = 7.1441 (11) Ȧ β = 112.871 (16)o. V = 597.74 (15) Ȧ3, Z = 4 [6]. While the crystal structure of 4-HOBAL crystallized from water is monoclinic, P21/c, a = 6.453 (5) Ȧ, b = 13.810 (8) Ȧ, c = 7.044 (6) Ȧ β = 107.94 (9)o. V = 597.2 Ȧ3, Z = 4 [7]. In both cases, the crystal structure is monoclinic, P21/c, and the crystal packing is stabilized by intermolecular hydrogen bonding (O-H···O) interactions between the hydroxyl and aldlehyde groups. However, noticeable differences are seen in their cell parameters. This communication reports temperature-induced polymorphism (polymorph I to polymorph II) seen in 4-HOBAL using differential scanning calorimeter (DSC). These polymorphs were further characterized using X-ray powder diffraction (XRPD) patterns and Raman spectra.
Facile route for the synthesis and cytotoxic effect of 2-amino-4H-benzo[b]pyran derivatives in aqueous media using copper oxide nanoparticles decorated on cellulose nanocrystals as heterogeneous catalyst
Published in Inorganic and Nano-Metal Chemistry, 2019
Clarina Thanaraj, G.R. Priya Dharsini, Neela Ananthan, Rama Velladurai
Pyrans, an heterocyclic compound constitute the core fragment in variety of natural products, have a broad spectrum of biological properties such as anticoagulants, spasmolytics, diuretic, anticancer and antianaphylactic activities.[1] Benzopyrans as pharmaceutical ingredients used as cognitive enhancers for the treatment of neurodegenerative diseases, including Huntington’s disease, Alzheimer’s disease, AIDS-associated dementia and Down’s syndrome and also used as pigments and photoactive materials.[2] The significant importance of 2-amino-4H-benzo[b]pyrans scaffold in medicinal field draws chemist considerable interest to synthesis these compounds employing the catalysts such as (s)-proline,[3] MgO,[4] nanosized ZnO,[5] LiBr,[6] silica NPs,[7] silica gel-supported polyphosphoric acid,[8] [bmim]OH,[9] infrared irradiation,[10] inorganic-organic hybrid magnetic nanocatalyst,[11] meglumine,[12] hydroxyapatite,[13] per-6-amino-β-cyclodextrin,[14] urea,[15] potassium phthalimide,[16] CoFe2O4 nanoparticles,[17] DABCO,[18] salicyldimine-schiff’s complex of copper (II),[19] CuFe2O4 nanoparticles,[20] lactose,[21] Fe3O4@SiO2-imid-PMAn,[22] poly(4-vinylpyridine)-supported copper iodide nanoparticle,[23] ethylenediamine diacetate,[24] sodium alginate,[25]N,N-dimethylbenzylamine,[26] gold nanoparticles supported on thiol functionalized reduced graphene oxide,[27] glutamic acid,[28] potassium hydrogen phthalate,[29] Fe3O4@GA@lsinglass core/shell magnetic nanoparticles,[30] ammonium hydroxide or ultrasonic irradiation,[31] pyridine-4-carboxylic acid-functionalized Fe3O4 nanoparticles,[32] organocatalyst.[33]