organic chemistry Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clayden, J ...

, the Ziegler process (also called the Ziegler-Alfol synthesis) is a method for producing

fatty alcohol Fatty alcohols (or long-chain alcohols) are usually high-molecular-weight, straight-chain primary alcohols, but can also range from as few as 4–6 carbons to as many as 22–26, derived from natural fats and oils. The precise chain length varies ...

s from

ethylene Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds). Ethylene ...

using an

organoaluminium compound Organoaluminium chemistry is the study of compounds containing bonds between carbon and aluminium. It is one of the major themes within organometallic chemistry. Illustrative organoaluminium compounds are the dimer trimethylaluminium, the monomer ...

. The reaction produces linear primary alcohols with an even numbered carbon chain. The process uses an aluminum compound to oligomerize

and allow the resulting

alkyl group In organic chemistry, an alkyl group is an alkane missing one hydrogen. The term ''alkyl'' is intentionally unspecific to include many possible substitutions. An acyclic alkyl has the general formula of . A cycloalkyl is derived from a cycloalk ...

to be oxygenated. The usually targeted products are fatty alcohols, which are otherwise derived from natural fats and oils.

Fatty alcohols Fatty alcohols (or long-chain alcohols) are usually high-molecular-weight, straight-chain primary alcohols, but can also range from as few as 4–6 carbons to as many as 22–26, derived from natural fats and oils. The precise chain length varies ...

are used in food and chemical processing. They are useful due to their amphipathic nature. The synthesis route is named after

Karl Ziegler Karl Waldemar Ziegler (26 November 1898 – 12 August 1973) was a German chemist who won the Nobel Prize in Chemistry in 1963, with Giulio Natta, for work on polymers. The Nobel Committee recognized his "excellent work on organometallic compound ...

, who described the process in 1955.Zerong Wang "Ziegler Alcohol Synthesis (Ziegler Higher Alcohol Synthesis, Alfol Process, Ziegler-Alfol Process, Ziegler-Alfol Synthesis)" in Comprehensive Organic Name Reactions and Reagents, 2010, John Wiley & Sons, Inc. Online

Process details

The Ziegler alcohol synthesis involves

oligomerization In chemistry and biochemistry, an oligomer () is a molecule that consists of a few repeating units which could be derived, actually or conceptually, from smaller molecules, monomers.Quote: ''Oligomer molecule: A molecule of intermediate relat ...

using

triethylaluminium Triethylaluminium is one of the simplest examples of an organoaluminium compound. Despite its name it has the formula Al2( C2H5)6 (abbreviated as Al2Et6 or TEA), as it exists as a dimer. This colorless liquid is pyrophoric. It is an industrially ...

followed by

oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or ...

.¹ The triethylaluminium is produced by action of

aluminium Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It ha ...

, and

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...

gas. In the production process, two-thirds of the triethylaluminium produced is recycled back into the reactor, and only one-third is used to produce the fatty alcohols. The recycling step is used to produce triethylaluminium at a higher yield and with less time. Triethylaluminium reacts with ethylene to form higher molecular weight trialkylaluminium. The number of equivalents of ethylene n equals the total number of monomer units being grown on the initial ethylene chains, where (n = x + y + z), and x, y, and z are the number of ethylene units per chain. Trialkylaluminium is oxidized with air to form aluminum alkoxides, and finally hydrolyzed to aluminum hydroxide and the desired alcohols. # Al+3ethylene+1.5H₂ → Al(C₂H₅)₃
# Al(C₂H₅)₃ n-ethylene → Al((CH₂CH₂)_nCH₂CH₃)₃
# Al((CH₂CH₂)_nCH₂CH₃)₃+ O₂ → Al(O(CH₂CH₂)_nCH₂CH₃)₃
# Al(O(CH₂CH₂)_nCH₂CH₃)₃ → Al(OH)₃ + CH₃CH₂(CH₂C₂)_mOH The temperature of the reaction influences the

molecular weight A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bio ...

of alcohol growth. Temperatures in the range of 60-120°C form higher molecular weight trialkylaluminium while higher temperatures (e.g., 120-150 °C) cause thermal displacement reactions that afford α-olefin chains. Above 150 °C, dimerization of the α-olefins occurs.

Applications

Aluminum hydroxide, the byproduct of the synthesis, can be dehydrated to give aluminium oxide, which, at high purities, has a high commercial value. One modification of the Ziegler process is called the EPAL process. In this process, chain growth is optimized to produce alcohols with narrow molecular weight distribution. Synthesis of other alcohols use Ziegler and the updated EPAL process, such as the transalkylation of

styrene Styrene () is an organic compound with the chemical formula C6H5CH=CH2. This derivative of benzene is a colorless oily liquid, although aged samples can appear yellowish. The compound evaporates easily and has a sweet smell, although high concen ...

to form 2-phenylethanol. Diethylaluminum hydride can be employed in place of triethylaluminium.

References

{{Alcohols Fatty alcohols Chemical processes

Process details

Applications

See also

References