Alan M. Forster

A method for stabilising technetium-99m exametazime prepared from a commercial kit

Technetium-99m exametazime (99mTc-d,l-HMPAO), prepared by the reconstitution of the Ceretec kit, is widely used in the investigation of regional cerebral blood flow. The radiochemical purity specification of not less than 80% lipophilic complex requires that the kit is used within 30 min of reconstitution In certain circumstances this imposes restrictions on its clinical availability. A number of approaches to extending the 30-min shelf life have been proposed and these are discussed. A method of stabilising the kit by the addition of 200 μg cobalt chloride hexahydrate (CoCl2 · 6H2O) in 2 ml of water is described. The addition of this solution can extend the shelf life of the reconstituted kit to at least 5 h post reconstitution.

Equilibration of ortho- and para-hydrogen by homogeneous hydrogenation catalysts in solution; A test for the reversibility of hydrogen addition using Raman spectroscopy

Abstract para -Enriched hydrogen is converted into the ortho - para equilibrium mixture by tris(triphenylphosphine)rhodium chloride in toluene solution. The rotational Raman effect can be used to show that this equilibration occurs during the course of hydrogenation of cyclohexene by the above catalyst. The methanol solvate formed by reduction of 1,4-bis(diphenylphosphino)butanebicyclo[2.2.1] heptadienerhodium tetrafluoroborate also catalyses the ortho - para equilibration of hydrogen, in common with related cationic rhodium complexes. No equilibration occurs, however, during the course of hydrogenation of ( Z )-α-benzamidocinnamic acid by cationic chelate rhodium complexes, including that derived from the chiral ligand ( R , R )-1,2-bis( o -methoxyphenylphenyl)ethane (DIPAMP), thus demonstrating that addition of hydrogen to rhodium is irreversible.

Reactions of xenon difluoride: Oxidative fluorination of methyl derivatives of the p-block elements

Abstract A survey has been carried out to determine how xenon difluoride reacts with methyl derivatives of p -block elements, Me n X ( n = 3, X = N, P, As, or Sb; n = 2, X = O, S, or Se; n = 1, X = Cl, Br, or I), on the basis of NMR measurements, tensimetric and IR analysis of the gaseous products, and mass balances. The reaction proceeds smoothly in most cases, although a Freon like CCl 3 F may be needed as a moderator; the rate of the reaction seems to reflect the basicity of the substrate Me n X. The difluoride Me n XF 2 is formed in the cases where X = P, As, Sb, Se, or I. The scope of xenon difluoride in these conditions as a mild selective oxidative fluorinating agent is illustrated by the synthesis of the known compounds (CF 3 ) 2 XF 2 (X = S or Se) and the novel compound Me(CF 3 )SeF 2 . By contrast, cleavage of Cue5f8H bonds, with the formation of CH 2 F derivatives, is the predominant path in the cases where X = N, O, or S, and cleavage of Cue5f8X bonds, with the formation of MeF, occurs in the cases where X = Cl or Br.

Fluorination of dimethyl sulphide. Formation of the fluorodimethylsulphonium cation, [Me2SF]+, and dimethylsulphur difluoride, Me2SF2

The controlled reaction of dimethyl sulphide with xenon difluoride in a non-acidic medium gives rise via CH2FSMe to a product best formulated as [Me2SCH2SMe]+[F(HF)n]–. In HF solution at –23 °C, however, the reaction affords the fluorodimethylsulphonium cation, [Me2SF]+, solid derivatives of which have also been prepared by the reaction of XeF2 with Me2S·A (A = BF3 or AsF5); the species have been characterised by their 1H and 19F n.m.r. and vibrational spectra. With CDCl3 as a diluent, Me2S reacts with an excess of AgF2 at –23 °C to provide the first evidence of the thermally unstable dimethylsulphur difluoride, Me2SF2. The 1H and 19F n.m.r. spectra have served to characterise the new compound and to chart its decomposition (to CH2FSMe) and other reactions.

Synthesis, physical characterisation and chemical properties of methylsulphur trifluoride, CH3SF3

Methylsulphur trifluoride, CH3SF3, has been synthesised by the reaction between AgF2 and a solution of CH3SCl in CCl3F. It is a clear, viscous liquid which attacks glass, is hydrolysed rapidly, and decomposes at ambient temperatures to give CH2FSF3 and CH2FSSCH2F. The compound has been characterised by its 1H and 19F NMR and vibrational spectra, and a partial vibrational assignment is proposed. The chemistry of CH3SF3 is akin to that of SF4. Thus, it functions as a fluoride ion donor much more readily than as a fluoride ion acceptor. It reacts with Pyrex glass to give CH3S(O)F, is hydrolysed to CH3S(O)OH, and effects O–F exchange with acetone to yield 2,2-difluoropropane.

The molecular structure of gaseous bis(trifluoromethyl)selenium difluoride as determined by electron diffraction

The structure of gaseous bis(trifluoromethyl)selenium difluoride has been determined by electron diffraction. Hence the predominant species is shown to be the monomer (CF3)2SeF2 with the CF3 ligands occupying the equatorial sites of a framework derived from a trigonal bipyramid. Salient structural parameters (ra) are: r(Se–F) 182.7(0.5), r(Se–C) 202.2(0.8), and r(C–F) 131.4(0.3) pm; F–Se–F 157.8(3.5), C-Se–C 118.7(1.7), and F–C–Se 108.9(0.4)°. The molecule has C2 symmetry overall, with the CF3 groups twisted 19.8(1.1)° away from the positions in which one C–F bond of each group is anti with respect to an Se–C bond (corresponding to a conformation having C2V symmetry overall). Comparisons with the structures of related molecules show that the switch from SeF4 to (CF3)2SeF2, unlike that from SF4 to (CF3)2SF2, results in an increase in the equatorial bond angle, in keeping with the expectations of the valence shell electron pair repulsion model.