Kinetics of hydrolysis of cyanogen, 1-cyanoformamide and iodine monochloride

Yi Lai Wang, Purdue University

Abstract

The base hydrolysis of cyanogen proceeds by two reaction paths. Only 25% at 5$\sp\circ$C to 33% at 40$\sp\circ$C of the cyanogen reacts directly by C-C bond cleavage to form CN$\sp-$ and OCN$\sp-$ (8.9 $\times$ 10$\sp2$ M$\sp{-1}$ s$\sp{-1}$ at 25.0$\sp\circ$C). The rest of the cyanogen forms 1-cyanoformamide via a second path (2.17 $\times$ 10$\sp3$ M$\sp{-1}$ s$\sp{-1}$ at 25.0$\sp\circ$C). A common reactive intermediate, N$\equiv$C-C(OH)=N$\sp-$, is postulated for the paths. The 1-cyanoformamide that forms also decomposes by C-C bond cleavage, but at a much slower rate than cyanogen. The reaction proceeds by deprotonation of 1-cyanoformamide (pK$\sb{\rm a}$ = 10.8) to give N$\equiv$C-C(=O)-NH$\sp-$, which reacts (0.56 s$\sp{-1}$ at 25$\sp\circ$C) to give CN$\sp-$ and OCN$\sp-$. The hydrolysis of iodine monochloride to form HOI and Cl$\sp-$ is extremely rapid (k$\sb{\rm H\sb2O}$ = 2.4 $\times$ 10$\sp6$ s$\sp{-1}$). The reaction is accelerated by hydroxide ion (k$\sb{\rm OH}$ = 4.5 $\times$ 10$\sp9$ M$\sp{-1}$ s$\sp{-1}$) and phosphate and carbonate buffers (k$\sb{\rm buffer}$ = 1.3 $\times$ 10$\sp9$ M$\sp{-1}$ s$\sp{-1}$). There are two forms of ICl in water, ICl (%18) and H$\sb2$OICl (%82) ($\mu$ = 0.50, 25$\sp\circ$C). Kinetic data indicate that ICl is so reactive that it is unselective and reacts with H$\sb2$PO$\sb4\sp-$, HPO$\sb4\sp{2-}$, HCO$\sb3\sp-$, CO$\sb3\sp{2-}$, and OH$\sp-$ at the diffusion limit. Spectrophotometric measurements of the equilibrium constants at 25.0$\sp\circ$C give ((ICl$\sb{\rm aq}$) (Cl$\sp-$))/((ICl$\sb2\sp-$) = 0.013 M ($\mu$ = 1.0) and ((HOI) (Cl$\sp-$) $\sp2$(H$\sp+$))/(ICl$\sb2\sp-$) = 1.06 $\times$ 10$\sp{-6}$ M$\sp3$ ($\mu$ = 0.5). Oxidation of Ni$\sp{\rm II}$(CN)$\sb4\sp{2-}$ in aqueous solution gives trans-Ni$\sp{\rm III}$(CN)$\sb4$(H$\sb2$O)$\sb2\sp-$. The reduction potential for Ni$\sp{\rm III}$(CN)$\sb4$(H$\sb2$O)$\sb2\sp-$ is 1.15 V (vs NHE). The complex decomposes slower in acid (4.0 $\times$ 10$\sp{-4}$ s$\sp{-1}$, pH 1-3, 25.0$\sp\circ$C, $\mu$ = 0.1) than in base (0.45 s$\sp{-1}$, $-$log(H$\sp+$) = 11.5, 25.0$\sp\circ$C, $\mu$ = 0.1). Nickel(III) oxidizes cyanide to cyanate and the stoichiometry of the decomposition is: 8Ni$\sp{\rm III}$(CN)$\sb4$(H$\sb2$O)$\sb2\sp-$ + 100H$\sp-$ $\to$ 7Ni$\sp{\rm II}$(CN)$\sb4\sp{2-}$ + 40CN$\sp-$ + Ni(OH)$\sb2$ + 20H$\sb2$O. A ball-type mixer-observation cell assembly is designed and fabricated. The cell gives superior performance over the original cell of the Hi-Tech Spectrometer. Design details and performance of the cell are discussed.

Degree

Ph.D.

Advisors

Margerum, Purdue University.

Subject Area

Chemistry

COinS