14.12A: Cyanogen and its Derivatives
- Page ID
- 34193
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Compounds with C-N Bonds: Cyanides and Related Compounds
Cyanogen (NºC–CºN) is a poisonous and flammable gas (bp -21 oC. Although its heat of formation is strongly endothermic 297 kJ mol-1 is is fairly stable. Impure cyanogen polymerizes to form "paracyanogen". Cyanogen is prepared by nitrogen dioxide catalyzed oxidation of hydrogen cyanide by oxygen:
\[\ce{2HCN + NO2 -> (CN)2 + NO + H2O}\]
\[\ce{NO + ½O2 -> NO2}\]
It is also formed by oxidation od CN- with Cu2+:
\[\ce{Cu^{2+} + 2CN^{-} -> CuCN + ½(CN)2}\]
Notice the similarity between the above reaction and the one below:
\[\ce{Cu^{2+} + 2I^{-} -> CuI + ½(I)2}\]
The term "pseudo halogen/halide" is often applied to molecules and derived ions such as (CN)2 and CN-. Notice also the existence of HCN which has its parallel in the hydrohalic acids and the reaction of cyanogen with base:
\[\ce{(CN)2 + 2OH^{-} -> CN^{-} + OCN^{-} + H2O}\]
Compare:
\[\ce{(Cl)2 + 2OH^{-} -> Cl^{-} + OCl^{-} + H2O}\]
The reaction of cyanogen with oxygen produces one of the hottest flames known at about 5000 oC.
Hydrogen cyanide boils at 25.6 oC. It is very poisonous and has an odor of almonds which not everyone can smell. It is a very good solvent due to its high dielectric constant, e = 107. It is made on an industrial scale (~300 000 tons in 1980) as follows:
\[\ce{CH4 + 3O2 + 2NH3 -> 2HCN + 6H2O}\]
with Pt/Rh or Pt/Ir catalyst and 800 oC.
or
\[\ce{CH4 + NH3 -> HCN + 3H2}\]
with Pt catalyst and 1200 oC
Cyanides are made industrially via the calcium cyanamide salt by the processes:
\[\ce{CaC2 + N2 ->[1100 degrees] CaNCN + C}\]
\[\ce{CaNCN + C + Na2CO3 -> CaCO3 + 2NaCN}\]
or
\[\ce{NaNH2 + C -> NaCN (500-600 oC)}\]
(NCN2- which yields cyanamide itself, H2NCN, by hydrolysis of the salt, is isoelectronic with CO2.)
Cyanide is important, among other things, as a very good p-acceptor ligand like CO.