Cyclohexane

History

In 1890, Sachse and Mohr discover that the “geometry” of cyclohexane is not plane and describe conformation `chair' by resemblance to a long chair.

In 1942, by studying cyclohexane in a gas state by Diffraction of the electrons, Hassel can establish that the most frequent form in gas phase is the form “chair”. The other shape of the cyclohexane, in which the two opposite carbon atoms are same side of the plan of the molecule is named “boat”. The two forms reciprocally change with facility one and the other: they are in mutual balance. The form boat is less stable.

In 1943, Hassel shows that there exists in cyclohexane two types of CH connections: those which are perpendicular to the average plan of the molecule and those which are parallel to this plan; it is what one will name a little later axial” and “equatorial” connections the “.

Geometry and conformations

Rotation around connections DC makes it possible cyclohexane to adopt an infinity of conformations. When one represents the cyclohexane molecule in 3 dimensions, two conformations can be used: “ chaise ” and “ bateau ”. The passage of a conformation chair to the other known as " inversion of conformation chaise" is done by rotation around the connections carbon-carbon and torsion. From the energy point of view, conformations chairs are most stable indeed with room temperature more than 99% of the cyclohexane molecules are in this conformation. Like shows it the representation, the connections between the atom of carbon and the atom of hydrogen can be of two different types:

the axial connections which are perpendicular to the average plan of the cycle.
the equatorial connections which are more or less located in the average plan of the cycle either a little above or slightly below.

The inversion of conformation chair transforms an equatorial connection into an axial connection and reciprocally. If cyclohexane is substituted by a grouping methyl for example this last will find in equatorial position because the position énergétiquement most favorable (i.e. for which the potential energy is lowest) for a substituent is the equatorial position because it minimizes the interactions with the close hydrogen atoms.

Properties

Cyclohexane is a liquid colorless, mobile, of odor relatively pleasant, insoluble in water, soluble in the solvents organics. As a cyclic Hydrocarbon saturated, cyclohexane is chemically rather inert, with the image of the Paraffine S. It dissociates in Butadiène with the top from 700 °C.

Uses

For its industrial applications, it is oxidized in mixture of Cyclohexanol and Cyclohexanone to lead to the raw materials:

Nylon -6,6 starting from adipic acid and of Hexaméthylène diamine
Nylon-6 via caprolactam.

Synthesis

It is possible to obtain cyclohexane by triple Hydrogénation of the Benzène in the presence of a Catalyseur containing Nickel.

Sentences of risk and the Councils of prudence

R 11 : Easily flammable.

R 38 : Irritating for the skin.

R 50/53 : Very toxic for the watery organizations, can involve harmful effects in the long run for the watery environment.

R 65 : Harmful: can cause an attack of the lungs in the event of ingestion.

R 67 : The vapor inhalation can cause somnolence and giddinesses.

S 2 : To preserve out of the range of the children.

S 9 : To preserve the container in a well broken down place.

S 16 : To preserve well off any flame or source of sparks. Not to smoke.

S 25 : To avoid the contact with the eyes.

S 33 : To avoid the accumulation of electrostatic loads.

S 60 : To eliminate the product and its container like a dangerous waste.

S 61 : To avoid the rejection in the environment. To consult the instructions spéciales/la card of data of safety.

S 62 : In the event of ingestion not to make vomit: to consult a doctor immediately and to show him packing or the label.

See too

Hexane

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