Zincke–Suhl reaction
The Zincke–Suhl reaction is a special case of a
![Zincke–Suhl reaction](http://upload.wikimedia.org/wikipedia/commons/thumb/a/a8/Zinckesuhl.svg/270px-Zinckesuhl.svg.png)
The classic example of this reaction is the conversion of
Mechanism
Aluminum chloride plays a range of functions in this reaction,[1] first reacting with p-cresol to form phenoxy aluminum chloride along with a molecule of hydrogen chloride. Additionally, aluminum chloride activates a molecule of tetrachloride that in turn is subjected to a nucleophilic 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.[1] 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.
P-cresol (mol) | CCl4 (mol) | AlCl3 (mol) | Solvent | Temperature (C) | Time | Yield |
---|---|---|---|---|---|---|
0.2 | 0.4 | 0.26 | CCl4 | Reflux | 120 | 40.0 |
0.05 | 0.05 | 0.063 | CS2 | 5 | 120 | 56.0 |
0.05 | 0.05 | 0.063 | CS2 | 45 | 120 | 60.3 |
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.[6]
Perhaps the most intriguing application of the Zincke–Suhl reaction is its potential following von Auwers rearrangements. Demeunier and Jaeckh described how such rearrangements may result in the formation of high energy intermediates.[9] 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.
Other products including dioxocins and polymers can form depending upon the location of the initial addition of carbon tetrachloride.[2][4] Furthermore, changes to the reagents such as the use of chloroform instead of carbon tetrachloride can form additional products.[4][5]
Above: Ortho-addition of tetrachloride to phenoxy aluminum chloride can produce 6,12-diphenyl-2,8-dimethyl-6,12-epoxy-6H, 12H-dibenzo[b,f][1,5] dioxocin, a high-melting, white polymer.
References
- ^ J. Am. Chem. Soc.19(6) (1954) p978
- ^ J. Am. Chem. Soc.19(6) (1954) p985
- .
- ^ .
- ^ S2CID 95720919.
- S2CID 197349709.
- ISBN 9780470638859.
- ISSN 0040-4039.
- ^ PMID 25437394.