KINETIC AND MECHANISTIC STUDY OF THE REACTION BETWEEN DITHIOMALONAMIDES AND DIIODINE - CRYSTAL-STRUCTURE OF THE COMPOUNDS 3,5-BIS(ETHYLAMINO)-1,2-DITHIOLYLIUM TRIIODIDE AND 3,5-BIS(MORPHOLINO)-1,2-DITHIOLYLIUM IODIDE MONOHYDRATE

The reaction of N,N'-diethyldithiomalonamide with I2 has been investigated spectrophotometrically. A kinetic study carried out with the stopped-flow technique has shown the transient formation of a 1:1 N,N'-diethyldithiomalonamide.I2 charge-transfer complex having a formation constant K1 = 2.3(3) x 10(3) dm3 mol-1 at 25-degrees-C. This is followed by an oxidation-reduction reaction leading to 3,5-bis(ethylamino)-1,2-dithiolylium iodide and HI(n) (n = 1 or 3), through a first- and a second-order process with respective rate constants at 25-degrees-C k1 = 0.84(7) s-1 and k2 = 2.0(3) x 10(3) dm3 mol-1 s-1, consisting of an unassisted or I2 assisted heterolytic fission of the I-I bond as the slow step. Further associative equilibria of 3,5-bis(ethylamino)-1,2-dithiolylium iodide and HI with free I2 leading to the corresponding triiodides have also been observed, having formation constants, respectively, K2 = 6.2(7) x 10(5) dm3 mol-1 and K3 = 8.9(5) x 10(6) dm3 mol-1. All the kinetic and thermodynamic parameters were obtained by an expressly devised computational method based on nonlinear leastsquares procedures. An X-ray crystal structure analysis of the title compounds, obtained as products of the reaction between I2 and RNR'C(S)CH2C(S)R'NR, showed that the crystals obtained in the RNR' = EtNH and I2 excess case are monoclinic, space group C2/m, with a = 13.643(6), b = 9.749(5), c = 11.879(6) angstrom, beta = 99.76(2)degrees and Z = 4. The structure consists of chains running parallel to [010], where the 3,5-bis(ethylamino)-1,2-dithiolylium cations and triiodide anions are connected through two strong interactions involving the terminal iodide atom of the unsymmetrical I3- (I2 ... 1- anion) and both the sulphur atoms of the disulphide group. In the RNR' = OC4H8N and 1:1 reagents ratio case the crystals are monoclinic, space group P2(1)/c, with a = 9.256(4), b = 20.257(6), c = 8.483(4) angstrom, beta = 90.91 (2)degrees and Z = 4. The structure consists of layers, approximately parallel to (201), determined by contacts involving [OC4H8NC(S)CHC(S)NC4H8O] cations, iodide anions and water molecules.