A novel derivatisation procedure for inorganic mercury(II) for HPLC analysis

Summary A new procedure for derivatisation of inorganic mercury(II) to diphenylethynylmercury with simultaneous extraction into dichloromethane is proposed. The organomercury derivative is effectively analysed by HPLC using UV detection. The calibration curve is linear over three orders of magnitude (0.02–50 mg L^–1 Hg); the detection limit is 0.1 ng Hg. A preliminary study of the effect of potential interfering agents, in particular Cu(II), Zn(II), Cd(II), Pb(II), and cysteine, and applications of the present methodology to real environmental samples are presented.     

1,1-DIANIONS OF ALKYL PHENYL SULPHONES AS SYNTHETIC INTERMEDIATES IN CYCLIZATION REACTIONS

Abstract

α-Sulphonyl carbanions are known to be good nucleophiles both in intermolecular and in intramolecular reactions¹. In the same way gem-dimetalloderivatives of alkyl phenyl sulphones I a,b readily add to aldehydes and ketones to give the (β-hydroxy compounds II in the case of dilithioderivatives Ia, while from dimagnesioderivatives Ib α, β-unsaturated sulphones III are also obtained².     

Migratory aptitudes of simple alkyl groups in the anionotropic rearrangement of quaternary chloromethyl borate species: a combined experimental and theoretical investigation

A combined experimental and theoretical investigation at the DFT and MP2 levels on the boron-to-carbon 1,2-shift in "ate species", coming from the quaternization of boranes (A) and boronate (B), is reported. To discuss the different migratory aptitudes of various alkyl groups, we have examined the migration of primary (R = Me, Et), secondary (R = i-Pr), and tertiary (R = t-Bu) alkyl groups. The effect of the counterion Li(+) and of the solvent (polarized continuous model (PCM) method) has been considered. The following results are relevant: (a) in all cases, the reaction proceeds via a concerted-type mechanism which explains the retention of configuration at the migrating group and the inversion at the migration terminus experimentally observed. (b) The trend of the migration barriers along the direction primary --> secondary --> tertiary alkyl group observed in "ate" species A is reversed in boronate species B, in agreement with the experimental evidences. (c) A simple theoretical model is proposed where the barrier trend is the result of a delicate interplay between two opposite factors: (1) a "steric effect", which favors the most sterically demanding migrating groups, and (2) a "charge effect" associated with the partial carbanionic nature of the migrating carbon atom and which favors the less substituted migrating carbons.     

A modular approach to catalyst hydrophobicity for an asymmetric aldol reaction in a biphasic aqueous environment

Catalyst 5, an ion pair consisting of a hydrophilic cation and a lipophilic anion, fulfils the solubility requirements needed to couple efficiency (enantioselectivities and anti-diastereoselectivities up to > or = 99%) and catalyst recyclability in asymmetric aldol reactions under aqueous biphasic conditions.     

Particulate matter, gas-phase and particle-bound polycyclic aromatic hydrocarbons in an urban environment heavily impacted by vehicular traffic (Bologna, Italy)

A set of 8 polycyclic aromatic hydrocarbons (PAHs) has been analysed in a traffic-limited area in Bologna downtown, both in the gas-phase and in the particulate phase (PM10), and gas-to-particle partitioning has been investigated. From Sep 2002 to May 2003, 28 high volume PM10 samplings were carried out, and in 50 % of the samplings, PM10 concentrations exceeded the limit of 50 microg/m3 established by a 1999 EU directive. A precisely defined sampling strategy was adopted to limit artifacts (8 h sampling in the same time interval) in the 28 samplings carried out in different meteorological conditions. A linear log-log correlation was found between gas-particle partitioning coefficients KBp and the subcooled liquid vapour pressures pB0LB, with rP2P = 0.82 and slope = -0.59. This empirical correlation may be used to anticipate the total (gas + particle-bound) concentration of each PAHs in this urban site, once PM10 and the particle-bound concentration is measured. Parallel samplings of PM10 and of PM2.5 allowed us to ascertain that PM2.5 represents the gross contribution to PM10 and that most of the particle-bound PAHs reside on the finest fraction of particulate matter.     

The hydroboration of propargyl bromide. Simple one-Pot three-component routes to (Z)-1-bromoalk-1-en-4-ols and to anti-homoallylic alcohols

The hydroboration of propargyl bromide with dialkylboranes takes place regioselectively to give 3-bromoprop-1-en-1-yl dialkylboranes 13 which, upon quaternization with bromide ion, undergo a series of transformations into a number of allylic boron species. By a suitable choice of the experimental conditions it is possible to trap the reaction intermediates with aldehydes and to steer the process toward either the synthesis of (Z)-1-bromoalk-1-en-4-ols 6 or anti-homoallylic alcohols 8. Two one-pot three-component processes were developed based on a sequence of four reactions; preparation of dialkylborane and hydroboration of propargyl bromide are the first steps. Then, quaternization with TEBABr may be carried out either in the presence of the aldehyde when (Z)-1-bromoalk-1-en-4-ols 6 are requested, or in the absence of the aldehyde in order to allow the formation of gamma-substituted allyl borane 18 which, successively, adds to the aldehyde affording anti-homoallylic alcohols 8.     

3-Bromo-propenyl acetate in organic synthesis: an expeditious route to 3-alkyl-4-acetoxy-5-iodomethyl isoxazolidines

N-Trimethylsilyloxy-N-benzyl-1-alkyl-2-acetoxy-3-buten-1-amines 13, obtained in good yields and moderate diastereoselectivities by TMSOTf promoted α-acetoxyallylation of nitrones using metallic zinc and 3-bromo-propenyl acetate 11, are exploited in a stereospecific 5-exo-trig iodocyclization reaction to afford 4,5-cis-3-alkyl-4-acetoxy-5-iodomethyl isoxazolidines 14, promising starting materials for the synthesis of pyrrolidine azasugars.     

An efficient diastereoselective route to differentially protected anti-4-amino-1-alken-3-ols

Zinc-promoted hydroxyallylation of alpha-amidoalkyl arylsulfones 4 using 3-bromo-propenyl methyl carbonate 5 proceeds smoothly in DMF at room temperature to afford high yields of differentially protected anti-1,2-amino alcohols 6.