The Zincke–Suhl reaction is a special case of a Friedel-Crafts alkylation and was first described by

Theodor Zincke Ernst Carl Theodor Zincke (19 May 1843 – 17 March 1928) was a German chemist and the academic adviser of Otto Hahn. Life Theodor Zincke was born in Uelzen on 19 May 1843. He became a pharmacist and graduated in Göttingen with his Staatsexame ...

and Suhl in 1906.M Newman. ''A Study of the Zincke and Suhl Reaction'', ''

J. Am. Chem. Soc. The ''Journal of the American Chemical Society'' is a weekly peer-reviewed scientific journal that was established in 1879 by the American Chemical Society. The journal has absorbed two other publications in its history, the ''Journal of Analytic ...

'' 19(6) (1954) p978M Newman. ''The Aluminum Chloride-catalyzed Reaction of Benzotrichloride with p-Cresol'', ''

'' 19(6) (1954) p985 Unlike the traditional Friedel-Crafts reaction, the reduction of the phenyl ring leads to a higher energy final product that can be used as starting material in the dienol–benzene rearrangement, among other reactions. The classic example of this reaction is the conversion of

p-cresol ''para''-Cresol, also 4-methylphenol, is an organic compound with the formula CH3C6H4(OH). It is a colourless solid that is widely used intermediate in the production of other chemicals. It is a derivative of phenol and is an isomer of ''o'' ...

to a cyclohexadienone (with the aid of

aluminium chloride Aluminium chloride, also known as aluminium trichloride, is an inorganic compound with the formula . It forms hexahydrate with the formula , containing six water molecules of hydration. Both are colourless crystals, but samples are often contam ...

as a

catalyst Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

and

tetrachloromethane Carbon tetrachloride, also known by many other names (such as tetrachloromethane, also recognised by the IUPAC, carbon tet in the cleaning industry, Halon-104 in firefighting, and Refrigerant-10 in HVACR) is an organic compound with the chemica ...

as a

solvent A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...

). Melvin Newman, a scientist from the

U.S. The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...

intensively studied the reaction in the 1950s and reported several improved procedures as well as mechanistic studies. Since then, studies investigating the impact of alternate reagents have been conducted by others.

Mechanism

Aluminum chloride plays a range of functions in this reaction, first reacting with p-cresol to form phenoxy aluminum chloride along with a molecule of

hydrogen chloride The compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colourless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hydrogen chloride ga ...

. Additionally, aluminum chloride activates a molecule of tetrachloride that in turn is subjected to a

nucleophilic In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are ...

attack by the phenoxy aluminum chloride. Subsequently, the product interacts with aluminum chloride and tetrachloride again to form a loose complex. Finally, the product is treated with water, resulting in the final product.

Catalysts

During a series of tests, Newman found that utilization of carbon disulfide as a solvent was demonstrated to improve the yield. As an example, addition of a solution of p-cresol and carbon disulfide to a suspension of aluminum chloride and carbon disulfide resulted in a 20% improvement in yield.

Applications

Zincke-Suhl products can be used as starting reagents for the dienol benzene rearrangement. This is an important reaction for artificially producing biologically relevant molecules including the A ring of steroids. Dienol_Benzene_Rearrangement

Perhaps the most intriguing application of the Zincke–Suhl reaction is its potential followin
von Auwers rearrangements
Demeunier and Jaeckh described how such rearrangements may result in the formation of high energy intermediates. For example, reformation of the aromatic ring from the semibenzene (cyclohexadienone) follows an energy drop of just under 36 kcal/mol. Such staunch drops have been experimentally shown to lead to efficient aromatization with high yields. Known_von_Auwers_Rearrangements

Other products including dioxocins and polymers can form depending upon the location of the initial addition of carbon tetrachloride. Furthermore, changes to the reagents such as the use of chloroform instead of carbon tetrachloride can form additional products. Above: Ortho-addition of tetrachloride to phenoxy aluminum chloride can produce 6,12-diphenyl-2,8-dimethyl-6,12-epoxy-6''H'', 12''H''-dibenzo 'b,f''1,5] dioxocin, a high-melting, white polymer.

References

{{DEFAULTSORT:Zincke-Suhl Reaction Substitution reactions Carbon-carbon bond forming reactions Name reactions 1906 in science