Alum [KAl(SO4)2.12H2O] is an inexpensive, efficient, non-toxic and mild catalyst for the preparation of acylals from aromatic and heteroaryl aldehydes with acetic anhydride at room temperature under solvent-free conditions. This method gives remarkable advantages such as excellent chemoselectivity, mild reaction conditions, short reaction times and excellent yields, and offers a green synthetic solution by avoiding toxic catalysts and hazardous solvents.
The synthesis of a series of five novel precursor compounds derived from (R)-(+)-camphor is reported. From these precursors, a further four novel pyridyl alcohol ligands were synthesized. The molecules represent the first reported examples where the pyridyl and hydroxyl moieties are pendant on the C3 position of the camphor skeleton. The regioselective synthesis was investigated and an efficient method was identified. The final ligands were obtained in moderate yield with absolute regio- and stereoselective control. The molecules were screened as catalysts in the alkylation of aldehydes with diethylzinc in order to compare the new arrangement of donor groups with previously reported results obtained with C2 pendant ligands. The results demonstrated a significant improvement for the synthesized C3 pendant ligands over previous C2 examples with moderate yields and up to 85 % ee being obtained.
The evaluation of a series of camphor-derived ligands as catalysts in the asymmetric Henry reaction is reported. The synthesis of two novel derivatives is detailed and these molecules are also screened as catalysts in this reaction. The single crystal X-ray structure of one of the novel compounds is reported. The reaction is catalyzed with moderate to excellent yields and moderate enantioselectivity.
A series of camphor-derived pyridyl ligands were evaluated in the Diels-Alder reaction of 3-acryloyl-2-oxazolidinone 1 with cyclopentadiene 2. High yields with good endo:exo selectivity, but only moderate enantioselectivities (43 % ee), were obtained. The structures of the copper (II) complexes of the ligands were calculated using ONIOM density functional theory and the results suggest that chiral induction to the alkene functional group is indeed lacking. This explains the moderate experimental selectivities obtained.
In the present investigation a novel series of N-(phenyl) chalconyl anthranilic acids containing pyrazolines (4a-j), tetrahydropyrimidines (4k-o), tetrahydrothiopyrimidines (4p-t) and 2-phenylquinazolin-4(3H)-ones containing pyrazolines (8a-f), isoxazolines (8g-l), tetrahydropyrimidines (8m-r) and tetrahydrothiopyrimidines (8s-x) were synthesized and characterized by elemental analysis, FT-IR, 1H NMR and mass spectroscopy. The title compounds (4a-t) and (8a-x) were investigated for their analgesic, anti-inflammatory, antimicrobial and in vitro protein denaturation activities. Compounds 4j and 8x were identified as lead compounds with optimum analgesic, anti-inflammatory and antimicrobial activities.
A range of novel 2-oxo-2H-chromen-7-yl dimethylcarbamates was synthesized containing either an oxygen or sulphur atom in the α-position to the carbonyl or thiocarbonyl group of the amide moiety. The synthesis and spectroscopic data of these compounds are reported. Microwave synthesis was essential for the successful synthesis of some of the sulphur-containing carbamates. The synthesized compounds will be used in a subsequent study on the influence of the α-substituent on the amide rotational barrier.
The binary complexes formed between sulphur dioxide, as electron donor, and the series carbon dioxide, carbonyl sulphide and carbon disulphide, as electron acceptors, have been studied by means of ab initio molecular orbital theory. The optimized structures, the interaction energies and the vibrational spectra have been determined, and the effect of successive substitution of sulphur for oxygen atoms in the electron acceptor molecules has been established. Nitrous oxide, which is isoelectronic with carbon dioxide, has also been included among the electron acceptors, but the properties of the complex formed between sulphur dioxide and nitrous oxide are substantially different from those of the other three complexes.
An easy and convenient route for the synthesis of 2,4-substituted thiazine (3-6) and 2,5-substituted thiazole (16) derivatives from phenacetamidines and glycine methyl ester is reported. To the best of our knowledge, this is the first report in which phenacetamidines have been utilized as precursors for thiazine synthesis. The syntheses of novel cyclic fused 1,3-diazabutadienes 13 and 2-aza-1,3-butadiene 17, and iodocyclization of 17 leading to the formation of thiazole 16a are also reported. In this paper a total of twenty novel compounds are reported.
Chemical investigation of CH2Cl2 and MeOH extracts of Conyza floribunda have led to the isolation of (24S)-ethylcholesta-5, 22E,25-trien-3-O-glucosyl (1"® 4')-rhamnoside (1), (24S)-ethylcholesta-5,25-dien-3-O-β-glucoside (2), cyasterone (3), stigmasta 5, 22-dien-3-acetate (4), stigmasta 5, 22-dien-3-ol (5), spinasta 7, 22-dien-3-ol (6), 3-oxofriedooleanane (7), 3-hydroxyfriedooleanane (8), 3-acetoxyfriedooleanane (9), betullinic acid (10), quercetin 3-O-β-glucoside (11), quercetin (12), myricetin (13) and kaempferol (14). Their structures were determined using spectroscopic and physical methods as well as comparison with data available in the literature.
A glass electrode (GE) can be successfully employed to measure pH in the study of metal-ligand equilibria by voltammetry at extremely low pH (between 0 and 2); two consecutive strong acid-strong base titrations involving different base concentrations (recommended to avoid corrosion of the GE in very basic solutions) are best suited to establish the response parameters of a GE. A novel approach of using a combined linear and binomial GE calibration was developed; this procedure allows measurements between pH 0 and 2 with uncertainty better than ±0.01 pH unit. From an extensive error analysis, it has been established that the uncertainties of about ±0.5 mV in the response slope and ±1.3 mV in E°' might result in an absolute error in pH of about 0.02 which should not generate errors larger than 0.3% in optimized stability constants (as log K values) determined by voltammetry at extremely low pH. A test of GE suitability for the study of metal complexes by voltammetry is also proposed; it should be implemented only for suspect electrodes that show response parameters outside the limits recommended in this work.
Many students' difficulties in learning and applying chemical knowledge are associated with their being incompetent in a few widely applicable intellectual skills and strategies. This paper discusses the results of a study that was done to test first year university students' competence in some types of intellectual skills that are important in chemistry. The skills tested include language skills, mathematical skills, graphical skills, three-dimensional visualization skills, information processing skills and reasoning skills. The study showed that the competence of most students in intellectual skills is very poor. This lack of competence could be expected to lead to negative attitudes and a lack of self-confidence that would seriously handicap their learning, and may also be an important reason for the observed high failure rate of students in science courses. The study also showed a significant correlation between success in first year university courses and competence in intellectual skills and strategies. It is strongly suggested that much greater emphasis should be placed in our courses on the development of students' intellectual skills and strategies. Such training should be integrated with the teaching of subject content.
Some imines were synthesized by the reaction of 5-amino 1-naphthol with substituted aromatic aldehydes in ethanol under reflux conditions. Dialkyl phosphites underwent addition with aromatic imines to give novel α-amino phosphonates. All the title compounds were characterized by elemental analysis, IR, 1H, 13C, 31P NMR and mass spectral data. All the newly-synthesized compounds (4a-j) exhibited moderate antibacterial and antifungal activity.
A series of new pyrazole, thiazole and thiazolinone derivatives incorporated into benzofuran were synthesized by using 3-(benzofuran-2-yl)-1-phenyl-1H-pyrazol-4-carboxaldehyde as starting material. A total of 41 novel compounds were synthesized. Some of these synthesized compounds were evaluated for cytotoxicity activity against HEPG2 (liver carcinoma cell line) and HELA (cervix carcinoma cell line). The tested compounds (1, 2c, 7c, 8b, 9b, 13b and 14b) showed better activities at low concentration against the commonly used human carcinoma cell lines. A detailed synthesis, spectroscopic data and cytotoxicity screening for the new compounds are described.
An extract of Terminalia chebula fruits was investigated as a corrosion inhibitor of mild steel in 0.5 M H2SO4 by means of conventional mass loss, electrochemical polarization, electrochemical impedance spectroscopy and scanning electron microscopy. The mass loss results showed that the extract of Terminalia chebula is an excellent corrosion inhibitor, electrochemical polarization data revealed the mixed mode of inhibition and the results of electrochemical impedance spectroscopy showed that the change in the impedance parameters, charge transfer resistance and double layer capacitance with the change in concentration of the extract is due to the adsorption of active molecules leading to the formation of a protective layer on the surface of mild steel. Scanning electron microscopic studies provided confirmatory evidence of an improved surface condition, due to adsorption, for corrosion protection.