Sankar P. Dey

Status of groundwater arsenic contamination in Bangladesh: A 14-year study report

Since 1996, 52,202 water samples from hand tubewells were analyzed for arsenic (As) by flow injection hydride generation atomic absorption spectrometry (FI-HG-AAS) from all 64 districts of Bangladesh; 27.2% and 42.1% of the tubewells had As above 50 and 10 μg/l, respectively; 7.5% contained As above 300 μg/l, the concentration predicting overt arsenical skin lesions. The groundwater of 50 districts contained As above the Bangladesh standard for As in drinking water (50 μg/l), and 59 districts had As above the WHO guideline value (10 μg/l). Water analyses from the four principal geomorphological regions of Bangladesh showed that hand tubewells of the Tableland and Hill tract regions are primarily free from As contamination, while the Flood plain and Deltaic region, including the Coastal region, are highly As-contaminated. Arsenic concentration was usually observed to decrease with increasing tubewell depth; however, 16% of tubewells deeper than 100 m, which is often considered to be a safe depth, contained As above 50 μg/l. In tubewells deeper than 350 m, As >50 μg/l has not been found. The estimated number of tubewells in 50 As-affected districts was 4.3 million. Based on the analysis of 52,202 hand tubewell water samples during the last 14 years, we estimate that around 36 million and 22 million people could be drinking As-contaminated water above 10 and 50 μg/l, respectively. However for roughly the last 5 years due to mitigation efforts by the government, non-governmental organizations and international aid agencies, many individuals living in these contaminated areas have been drinking As-safe water. From 50 contaminated districts with tubewell As concentrations >50 μg/l, 52% of sampled hand tubewells contained As <10 μg/l, and these tubewells could be utilized immediately as a source of safe water in these affected regions provided regular monitoring for temporal variation in As concentration. Even in the As-affected Flood plain, sampled tubewells from 22 thanas in 4 districts were almost entirely As-safe. In Bangladesh and West Bengal, India the crisis is not having too little water to satisfy our needs, it is the challenge of managing available water resources. The development of community-specific safe water sources coupled with local participation and education are required to slow the current effects of widespread As poisoning and to prevent this disaster from continuing to plague individuals in the future.

Novel formation of 6-acyl-5-(2-pyrrolyl)-3H-pyrrolizines by base-catalysed condensation of pyrrole-2-aldehyde with methyl ketones

Abstract Pyrrole-2-aldehyde undergoes condensation with methyl ketones in aqueous ethanolic alkali in a 2:1 mole ratio yielding 6-acyl-5-(2-pyrrolyl)-3 H -pyrrolizines as novel products in moderate yield.

Synthesis and the crystal structure of a copper(II) complex dervied from novel tridentate ligand: An unexpected one

A novel tridentate ligand C5H4NCONHCOC5H4N (HL) has been formed by Cannizzaro type reaction of pyridine-2-carboxaldehyde and NaNCO in the presence of copper metal ion and its mononuclear distorted square pyramidal complex [Cu(L)(NCO)(H2O)], 1 has been synthesised and characterised.

Novel conversion of 3-(α-hydroxybenzyl)flavones to 3-benzoylchromones and 3-cyanoflavones with NaN3/TFA

Abstract On treatment with NaN 3 /TFA, 3-(α-hydroxybenzyl)flavones are converted to 3-benzoyl- chromones and 3-cyanoflavones, plausible mechanisms for which have been suggested.

Configuration of the major stereoisomer of Zn/AcOH reduction product of 4 -oxo -4H -chromene -3 -carbaldehyde

Under modified Clemmensen reduction condition 4-oxo-4H-chromene-3-carbaldehyde gave two 1,2-diol products of which the configuration of the major diol was determined by X-ray crystallography

Schmidt Reaction of E-3-Benzylidenechromanones and E-3-Benzylidenethiochromanones

On treatment with NaN3/c. H2SO4-HOAc or NaN3/TFA, E-3-benzylidenechromanones are mostly converted to E-β-aminobenzylidenechromanones while E-3-benzylidenethiochromanones are converted to 3-benzoylthiochromones. A structurally new type of product has been isolated for the reaction of E-3-benzylidene-4′-methoxychromanone with NaN3/TFA. Mechanistic paths have been suggested for formation of the products.

NBS Oxidation of E-3-Benzylidenechromanones to 3-(α-Hydroxybenzyl)chromones and 3-Benzoylchromones

Both natural and synthetic chromones show diverse biological activities,1–7 some being in regular clinical use.8,9 Thus, the chemistry of chromones and related compounds are of interest to organic chemists with the goal of generating new biologically active molecules. We previously reported that E-3-benzylideneflavanones (4) are readily converted to 3-(α-hydroxybenzyl)flavones (5) by oxidation with NBS in CaCl2-dried CCl4 under reflux conditions.10,11 The products were probably formed through the intermediate 3-(α-bromobenzyl)flavones which underwent rapid hydrolysis with adventitious water. However, attempted isolation of such intermediate did not meet with success. In order to assess the scope of this reaction, we undertook the study of the reaction of NBS with E-3benzylidenechromanones (1) in ordinary CCl4 (commercial AR grade, which usually contains trace amount of moisture), particularly because there are very limited number of published reports of synthesis of the expected products 3-(α-hydroxybenzyl)chromones (2).12,13 Thus, when E-3-benzylidenechromanones 1a-g (1 equiv.) were refluxed in CCl4 with NBS (1 equiv.) and benzoyl peroxide (trace), 3-(α-hydroxybenzyl)chromones (2) were formed in very good yields along with 3-benzoylchromones (3) as minor products (Scheme 1, Table 1). Since the formation of 3 indicated that a further oxidation had occurred, this led us to study the reaction of 1 with double the amount of NBS which led to 3 as the major product and 2 the minor one (Table 1). When the 3-(α-hydroxybenzyl)chromones (2) were treated separately with NBS (1 equiv.), they were completely converted to 3benzoylchromones (3) (Table 2). All the new compounds of the series 2 and 3 gave satisfactory combustion analyses and spectral data. This study was extended to E-3-benzylideneflavanones (4) with two molar equivalents of NBS; Scheme 2, Table 3 shows that, except for 4d, all the substrates gave 3benzoylflavones (6), albeit in low yields. Oxidation of 5a-c [NBS (1 equiv.), (PhCOO)2

6-(2-Hydroxybenzoyl)-5-(pyrrol-2-yl)-3H-pyrrolizine.

The title compound, 2-hydroxyphenyl 5-(pyrrol-2-yl)-3H-pyrrolizin-6-yl ketone, C(18)H(14)N(2)O(2), was isolated from the base-catalyzed 1:2 condensation of 2-hydroxyacetophenone with pyrrole-2-carbaldehyde. The pyrrole N-H and hydroxybenzoyl O-H groups are hydrogen bonded to the benzoyl O atom. The allylic C=C double bond of the 3H-pyrrolizine system is located between ring positions 1 and 2, the C atom at position 3 (adjacent to the N atom) being single bonded.