Carbon monoxide [CO]

Carbon monoxide [CO]:

Preparation:

Carbon monoxide can be prepared by the reaction of carbon with limited amount of oxygen.

2C + O₂ → 2CO

On industrial scale carbon monoxide is produced by the reaction of carbon with air. The carbon monoxide formed will contain nitrogen gas also and the mixture of nitrogen and carbon  monoxide is called producer gas.

2C + O₂/N₂ (air) → 2CO + N₂ ( Producers Gas)

The producer gas is then passed through a solution of copper(I)chloride under pressure which results in the formation of CuCl(CO).2H₂O. At reduced pressures this solution releases the pure carbon monoxide.

Pure carbon monoxide is prepared by warming methanoic acid with concentrated sulphuric acid which acts as a dehydrating agent.

HCOOH + H₂SO₄  → CO + H₂O + H₂SO₄

Properties

It is a colourless, odourless, and poisonous gas. It is slightly soluble in water.

It burns in air with a blue flame forming carbon dioxide.

2CO + O₂ → 2CO₂

When carbon monoxide is treated with chlorine in presence of light or charcoal, it forms a poisonous gas carbonyl chloride, which is also known as phosgene. It is used in the synthesis of isocyanates.

CO + Cl₂ → COCl₂

Carbon monoxide acts as a strong reducing agent.

CO + Fe₂O₃ → 2Fe + 3CO₂

Under high temperature and pressure a mixture of carbon monoxide and hydrogen (synthetic gas or syn gas) gives methanol.

CO + 2H₂ → CH₃OH

In oxo process, ethene is mixed with carbon monoxide and hydrogen gas to produce propanal.

CO + C₂H₄ + H₂ → CH₃CH₂CHO

Fischer Tropsch synthesis:

The reaction of carbon monoxide with hydrogen at a pressure of less than 50 atm using metal catalysts at 500 - 700 K yields saturated and unsaturated hydrocarbons.

nCO + (2n+1)H₂ → C_nH_(2n+2) + nH₂O

nCO + 2nH₂  → C_nH_2n + nH₂O

Carbon monoxide forms numerous complex compounds with transition metals in which the transition meal is in zero oxidation state. These compounds are obtained by heating the metal with carbon monoxide.

Eg. Nickel tetracarbonyl [Ni(CO)₄], Iron pentacarbonyl [Fe(CO)₅], Chromium hexacarbonyl [Cr(CO)₆].

Structure:

It has a linear structure. In carbon monoxide, three electron pairs are shared between carbon and oxygen. The bonding can be explained using molecular orbital theory as discussed in XI standard. The C-O bond distance is 1.128Å. The structure can be considered as the resonance hybrid of the following two canonical forms.

Uses of carbon monoxide:

·           Equimolar mixture of hydrogen and carbon monoxide - water gas and the mixture of carbon monoxide and nitrogen - producer gas are important industrial fuels

·           Carbon monoxide is a good reducing agent and can reduce many metal oxides to metals.

·           Carbon monoixde is an important ligand and forms carbonyl compound with transition metals