Why are certain compounds called hydrocarbons



The Hydrocarbons (C.mHn) are a group of compounds that only consist of carbon and hydrogen. The group of substances is quite diverse, there are several subgroups and many compounds in this class, but it is the simplest group of substances in organic chemistry. The hydrocarbons have achieved great technical importance, especially due to their huge deposits as fossil fuels, in many other areas, such as organic synthesis. Methane, an alkane, is the simplest representative of the hydrocarbons and the main component of natural gas.

Systematics

Hydrocarbons one divides into saturated and unsaturated hydrocarbons. In addition, a distinction can be made between chain-shaped and ring-shaped hydrocarbons. Saturated hydrocarbons are systematically referred to as alkanes. These are chemical compounds that only contain C-C single bonds. The simplest and best-known alkanes are methane (CH4), Ethane (C.2H6), and propane (C.3H8). In general, the empirical formula for the homologous series of chain-like alkanes is C.nH2n + 2. They are also known as aliphatics.

Ring-shaped alkanes are known as cycloalkanes. Its general molecular formula is C.nH2n.

Unsaturated hydrocarbons can be divided into alkenes or olefins, alkynes and aromatics or arenes. The alkenes are compounds that contain C = C double bonds. The simplest representative of this group of substances is ethene (also called ethylene) C.2H4. The simplest n-alkenes with only one double bond generally have the empirical formula CnH2n. The polyenes can be in chain form, such as, for example, butadiene, or cyclic, such as, for example, cyclopentadiene. They are a subgroup of the alkenes, they have more than one carbon double bond.

Alkynes are hydrocarbons that contain one or more triple bonds. The best-known representative is ethyne or acetylene with the empirical formula C.2H2. Accordingly, alkynes with a triple bond generally have the empirical formula C.nH2n-2.

The last important group of pure hydrocarbons are the aromatics. These are unsaturated, ring-shaped hydrocarbons, most of which have 6 carbon atoms. The best-known representative is benzene C.6H6. The polycyclic aromatic hydrocarbons are a subgroup of aromatics. They are compounds that consist of several benzene rings attached to one another. A well-known representative is naphthalene C.10H8.

In contrast to the other groups, the substance group of terpenes is not a pure hydrocarbon group; although hydrocarbons belong to it, it also includes many compounds from other substance groups.

links

The most important alkanes are methane and ethane, they are also found in space, among alkenes ethene, the most important cycloalkene is cyclohexene, among alkynes the most important compound is ethyne. The most important cycloalkane is cyclohexane, which occurs in petroleum. Important polyenes are butadiene, isoprene and cyclopentadiene. There are many important arenes, benzene, toluene, xylene and styrene are just a few. The simplest polycyclic aromatic hydrocarbons (PAHs) are biphenyl, naphthalene and anthracene. A list of hydrocarbons can be found here.

properties

Optimal (complete) combustion of hydrocarbons produces water and carbon dioxide, while insufficient (incomplete) combustion can also produce carbon monoxide or carbon (soot) and water. In the case of incomplete combustion, less energy is released, which is why optimal combustion of the hydrocarbons is important. If a hydrocarbon burns with a sooty flame, this can also be an indication of a higher carbon content in the compound (higher chain length, unsaturated hydrocarbons).

Hydrocarbons with the same empirical formula can have different structural formulas (links between the carbon atoms). They are then isomers. They are found in the alkanes from butane and in most other hydrocarbons. A special isomerism, the cis-trans isomerism, sometimes occurs at C = C double bonds.

Hydrocarbons are insoluble in water, but readily soluble in most organic solvents. This means that hydrocarbons are hydrophobic, i.e. also lipophilic.

The reactivity of the alkanes depends on their chain length. Long-chain alkanes are relatively inert (not very reactive). However, in addition to redox reactions during their combustion, they like to enter into substitution reactions, whereby hydrogen atoms can be exchanged for other atoms and groups of atoms, but mainly halogens. Alkenes and alkynes, on the other hand, are very reactive and react with many substances by adding to the C-C multiple bond (addition reaction).

Occurrence and origin

The hydrocarbons are naturally contained in oil, natural gas, coal (or coal tar) and other fossil substances in large quantities. There are three theories about the origin of hydrocarbons: the biogenetic theory, the abiogenetic theory and, according to the latest theory, hydrocarbons are formed during radioactive processes in the earth's mantle.

The hydrocarbons never come in pure form, but always only in mixtures and have to be obtained from them by chemical or physical methods. Even in space, the hydrocarbons, mostly in the form of methane and ethane, can be found on comets, planetary atmospheres and in interstellar matter. Methane was already part of the primordial soup.

The hydrocarbon deposits originated from marine animals that died, sank and were covered by sediment on the sea floor. When the sediments subsided, these organic materials were exposed to high pressure and temperature. Under these conditions, they turned into oil or coal. Natural gas was sometimes produced under similar conditions. Petroleum sediments that have not been exposed to the pressures and temperatures are called petroleum sands. Crude oil is composed differently depending on the location.

use

Alkanes are often used as fossil fuels in mixtures such as biogas, liquid gas, gasoline, diesel fuel, heating oil, kerosene, petroleum and many more.

The hydrocarbons also serve as starting materials for a large number of industrially important chemical synthesis processes, for example for chlorofluorocarbons. In addition, hydrocarbons serve as lipophilic solvents (carbon tetrachloride -> "stain remover"). The polymerization products of the hydrocarbons, such as polystyrene, polyethylene, polypropylene, polyethine, many copolymers and halogenated hydrocarbon polymers such as polyvinyl chloride and polytetrafluoroethylene are also important. The halogen alkanes are also important in medicine as freezing agents (chloroethane) and anesthetics (halothane).

Fire hazard and fire reduction

Hydrocarbons, whether liquid or gaseous, burn very quickly and with a hot flame; the energy released is great. Low boiling point liquid hydrocarbons (gasoline) also evaporate easily and quickly; Due to their low flash point, fires are easy to start. For these reasons, hydrocarbons serve as motor fuels and are therefore extracted, manufactured, transported and stored in large quantities.

In accidents with a fire outbreak z. B. in a refinery, the amount of energy released can lead to disasters, which make special precautions necessary to reduce possible damage. Materials with higher fire rate requirements are used here than are customary in normal structural fire protection. This also applies to tunnel construction in most industrialized countries, because in accidents with fuel transporters in tunnels, leaking fuel can catch fire, causing even the hardest concrete to flake off. For example, a fire in the Eurotunnel reduced the concrete ceiling in the submarine tunnel to a thickness of approx. 50 mm.

Wherever hydrocarbons are used, stored or transported, corresponding laws and regulations apply in order to largely reduce the risk of accidents. There are special containers that are only approved for the transport of hydrocarbons. Special international regulations also apply to petrol stations, such as a smoking ban in the entire petrol station area.

Usually such regulations followed spectacular accidents that historically have caused a great deal of damage. There have also been some tunnel fires that first led to regulations for materials with increased fire rates in this area.

Health significance of hydrocarbon compounds

Some hydrocarbon compounds (aromatic HC) are known to have carcinogenic properties, while others (e.g. some alkanes) are not known to have any harmful properties.

See also

literature

  • Reinhart Schweisfurth:Applied microbiology of hydrocarbons in industry and the environment. ISBN 3-8169-0034-8
  • Silke Wolff:Investigation of reactive intermediate stages of ozonolysis of unsaturated hydrocarbons in the gas phase. Shaker Verlag (1998), ISBN 3-8265-3839-0
  • Andreas Raichle:Production of synthetic steam cracker feed through hydrogenating conversion of cyclic hydrocarbons on zeolite catalysts. Shaker Verlag GmbH, ISBN 3-8322-1109-8
  • Karl Hölemann:Total oxidation of volatile hydrocarbons on catalytically coated microfiber knitted fabrics. Shaker Verlag GmbH (2000), ISBN 3-8265-7255-6

Categories: Hydrocarbons | Substance group