Carbon Monooxide (charcoal gas).

Forms at interaction of CO₂ with an incandescent coal:

CO₂ + C Û CO DH^о = 171,5 kJ/mol

The reaction is reversible, its shift to the right is predetermined by an entropy factor, and to the left – by enthalpy. Below 400° reaction is practically fully displaced to the left, and higher than 1000°, to the right. At ordinary conditions, CO is fully stable substance.

Preparation.

In industry: in great scale - in the form of generator and aquatic gases.

Generator gas forms at incomplete combustion of anthracite coal or `coke in large furnaces (generators). It is the mixture of gases: 25% CO, 70% H₂, 4% CO₂, other - N₂, CH₄, O₂.

Water-gas forms at passing of water steam above incandescent carbon:

С + Н₂О = СО + Н₂ DН°₂₉₈ = 117,6 kJ/mol

In a laboratory: at decomposition of formic or oxalic acid or their salts at intearaction with hot concentrated H₂SO₄:

НСООН = СО + Н₂О

Н₂С₂О₄ = СО + СО₂ + Н₂О

Structure.A molecule CO is extraordinarily stable (one of most stable among the known molecules). It sustains heating to 6000°. Energy of bond (1069 kJ/mol) is more than in H₂ (938 kJ/mol) and to the triple bond between atoms:

C O

2s 2p 2s 2p

C O or C O

In accordance with a method of Valence bonds two bonds are formed at coupling of two unpaired electrons of carbon and two - of O and both are displaced toward oxygen; another bond forms according donor-acceptor mechanism: to two-electronic orbital of oxygen is overlapped with a lone electron orbital of carbon. This pair is displaced to carbon, and on the whole the molecule of CO is weakly polar (m = 0,37•10^-29 C^.m).

Properties.Small polarity and capacity for polarizing predetermine low b.p. -191,5° and low solubility in water (3,3 vol. at 100 vol. H₂O).

CO is an extraordinarily toxic gas. Its content in air must not exceed 0,02 mg/l. At slight poisoning, fresh air is an antidote. Qualitatively, the presence of CO in air can be revealed by passing it through a solution of PdCl₂, which darkens:

CO + PdCl₂ + H₂O = Pd¯ + CO₂ + 2HCl

At ordinary conditions, CO is nonsaltforming oxide, it is unreactive with water, acids and alkalis. With alkalis, it reacts only at elevated temperatures, and at the presence of catalysts:

СО + NaOH = HCOONa,

So, CO acts as the anhydride of formic acid.

For CO there are characteristic reactions of addition and oxidation, where it is reduced:

Fe₂O₃ + 3CO = 2Fe + 3CO₂

NiO + CO = Ni + CO₂

CO + Cl₂ = COCl₂ (phosgene)

COCl₂ is slowly decomposed by water, quicker by alkalis and it is a typical chloroanhydride:

COCl₂ + H₂O = CO₂ + 2HCl

Phosgene is very poisonous substance and was used as a chemical weapon.

CO finds wide application in the organic syntheses. It is used as a reagent for preparation of paraffins, petrol, methyl alcohol, aldehydes, a lot of acids (formic, oxalic, vinegar, propionic, adipinic, acrylic), hydrogen cyanide and many other products.

At higher pressures CO reacts with powdered metals with formation of complex metal carbonyls: Fe(CO)₅, Co₂(CO)₈, Ni(CO)₄, Cr(CO)₆ and others. Ligand in these compounds uses unshared electronic pair of carbon. Carbonyls are easily decomposed; they find application for preparation of pure metals.Like CO, all of them are very poisonous.

Date: 2016-01-03; view: 759