No abstract

The crystal structure of dibenzyl disulphide, C6Hs-CH2-S-S-CH2-C6Hs, has been determined from three-dimensional X-ray diffraction data. The crystals are monoclinic and belong to the space group Cc.The unit cell has dimensions a= 13.46, b= 8.23, c= 11.29/~, ~= y= 90 °, fl= 99°30 ', and contains four molecules. Difficulty was exl~erienced because of a very strong tendency to twinning of the crystals, often only detected on high-layer line photographs. Positional and temperature factor parameters for sulphur and carbon atoms have been refined by Fourier, block-diagonal least squares and finally by full-matrix least squares. Refinement was unusually difficult because of large correlation coefficients between parameters, associated with a pseudo twofold axis of symmetry in the molecule. In the final stages, hydrogen atoms were included in fixed positions. The final R value based on 867 independent observed reflexions was 7.9%. The precise chemical nature of the S-S bond is examined. ExperimentalA sample of dibenzyl disulphide was recrystaUized from ethanol and gave colourless plate-like crystals, which showed straight extinction parallel to the plate edges when viewed under the polarizing microscope. The density of the crystals was measured by the method of flotation in aqueous solutions of potassium iodide and found to be 1.28 g.cm -3.Considerable difficulty was experienced in selecting a suitable crystal for X-ray analysis since many crystals which appeared suitable after optical and preliminary X-ray examination proved to be twinned when high layer line Weissenberg photographs were taken. A single crystal of dimensions 0.025 x 0.025 x 0.015 cm was eventually used for X-ray analysis, and threedimensional equi-inclination Weissenberg data were collected for the hkO, hkl...hk8, hOl and hll zones.The intensities of 867 independent reflexions were collected photographically, measured visually and converted to [F] 2 and [FI by applying Lorentz and polarization corrections. In view of the small crystal size and the low absorption coefficient, corrections for absorption were considered unnecessary. No correction was made for extinction. Reflexions too weak to be observed were ignored. Crystal data (C6H5. CH2)2S2, M = 246.3 . Monoclinic, a= 13.46, b = 8.23, c = 11.29A_, all + 0.02~ = ), = 90 °, fl = 99 ° 30' + 30'. U= 1233.5~ 3, Z=4, Din= l'28g.cm -3, De= l'32g.cm -3 F000 = 520, Cu K~, 2 = 1.542 A, ~ = 36 cm -1 .Absent reflexions: hkl when h+k is odd, hOl when l is odd (and when h is odd), 0k0 when k is odd.These absences restrict the space group to Cc or C2/c, but the former was confirmed by the pyroelectric test, the statistical test and by the structure refinement. Structure analysisThere are four molecules in the unit cell, and for the space group Cc these must occupy the general positions (x,y,z); (x,-y,½+z); (½+x,½+y,z) and (½+x, ½-Y, ½+z). Patterson summations were performed with hkO and hOl data, but these were not interpreted in terms of a satisfactory trial structure because of the diffuse nature of the peaks. Th...

The crystal structure of 2,2'-diaminodiphenyl disulphide has been determined accurately from threedimensional X-ray diffraction data. Crystals are orthorhombic, and belong to the space group Pbca. The unit cell has dimensions a=8-21, b= 13"14, c=22"77/~,, and contains eight molecules. The positional and anisotropic thermal parameters for the sulphur, carbon and nitrogen atoms have been refined by Fourier and full-matrix least-squares methods on 1313 independent observed reflexions. In the later stages hydrogen atoms were included in fixed positions, and the final agreement factor R = 8"6%. The central part of the molecule C-S-S-C has a skewed non-planar conformation similar to H202, with a dihedral angle of 90.5 °. The S-S bond length is 2.06/~, which is longer than in diphenyl and dibenzyl disulphides. The C-S bond lengths of 1.77 and 1 "75/~ are significantly short. This indicates some double bond character, which may be explained by pzr-dzt bonding. The benzene rings are inclined at an angle of 32"5 ° to each other. ExperimentalA sample of 2,2'-diaminodiphenyl disulphide, H2N-C6H4-S-S-C6H4-NH2, kindly provided by the Clayton Aniline Co. Ltd, was recrystallized from ethanol and gave pale yellow-green platelets elongated along a. These showed straight extinction parallel and perpendicular to a when viewed under the polarizing microscope. The density of the crystals was measured by flotation in aqueous potassium iodide solution, and was found to be 1.33 (5) g.cm -3.Considerable difficulty was experienced in selecting a single crystal for X-ray examination. Many crystals consisted of several parallel platelets, indistinguishable from a single crystal under the polarizing microscope but detectable on higher layer line Weissenberg photographs. Eventually a suitable single crystal of dimensions 0.4 x 0.3 x 0.15 mm was used to obtain oscillation photographs about the a and b axes, and equi-inclination Weissenberg photographs for the Okl-6kl and hOl zones. The relative intensities of 1313 independent reflexions were measured visually and corrected for Lorentz and polarization factors. Absorption corrections were considered unnecessary, in view of the small crystal size compared with the optimum size of 0.50 mm (Buerger, 1958). Reftexions too weak to be observed were omitted. Crystal data C12H12N282

Alkynes can be produced by treating some α-bromo ketones with arylsulfonylhydrazines. The reaction is acid-catalysed and mesitylsulfonylhydrazine was the most efficient hydrazine reagent examined. The mechanism of the reaction has not been elucidated although it is shown not to proceed via an α-bromo mesitylsulfonylhydrazone.

A method is described for the flame-photometric determination of 0 to 60 p.p.m. of calcium in solutions containing 4 per cent. w/w of sodium. Calcium is adsorbed from 100ml of solution on a column of sodium-form Chelex-100 chelating resin ; sodium is selectively eluted with hydrochloric acid at pH 2.4. Adsorbed calcium is eluted with 2 N hydrochloric acid and the resin washed with distilled water. The eluate and washings are diluted to 100m.l and the calcium determined on a Unicam SPQOO flame photometer.Magnesium, zinc, nickel, barium, mercury, manganese, copper and iron, present separately in concentrations of 26 p.p.m. or collectively in concentrations of 5 p.p.m. each, do not interfere. Aluminium depresses the amount of calcium found.The method has been used to determine calcium in simulated sea water.