Hydrogenolysis

Hydrogenolysis is a chemical reaction whereby a carbon-carbon or carbon-heteroatom single bond is cleaved or undergoes "lysis" by hydrogen.Ralph Connor, Homer Adkins. Hydrogenolysis Of Oxygenated Organic Compounds. J. Am. Chem. Soc.; 1932; 54(12); 4678-4690. DOI: 10.1021/ja01351a026] The heteroatom may vary, but it usually is oxygen, nitrogen, or sulfur. A related reaction is hydrogenation, where hydrogen is added to the molecule, without cleaving bonds. Usually hydrogenolysis is conducted catalytically using hydrogen gas.

History

The term "hydrogenolysis" was coined by Carleton Ellis in reference to hydrogenolysis of carbon-carbon bonds. [Carleton Ellis. Hydrogenation of Organic Substances, 3rd ed., Van Nostrand Company, New York, 1930, p. 564 (as referred by Connor and Adkins).] Earlier, Sabatier had already observed the hydrogenolysis of benzyl alcohol to toluene, [Sabatier and Murat. Ann. Chim. [9] 4, 258, (1915), according to Connor and Adkins.] and as early as 1906, Padoa and Ponti had observed the hydrogenolysis of furfuryl alcohol. [Furfuryl alcohol hydrogenation is accompanied by hydrogenolysis into 2-methylfuran, which gives 2-methyltetrahydrofuran, and further hydrogenolysis opens the ring to give 2-pentanol. Original: Padoa and Ponti. Atti. R. accad. Lincei, 15, [5] 610 (1906); Gazz. chim. ital. 37, [2] 105 (1907), according to Kaufmann: W. E. Kaufmann, Roger Adams. The Use Of Platinum Oxide As A Catalyst In The Reduction Of Organic Compounds. Iv. Reduction Of Furfural And Its Derivatives. J. Am. Chem. Soc.; 1923; 45(12); 3029-3044. DOI: 10.1021/ja01665a033] Adkins and Connors were the first to call the carbon-oxygen bond cleavage "hydrogenolysis".

In the petrochemical industry

In petroleum refineries, catalytic hydrogenolysis of feedstocks is conducted on a large scale to remove sulfur from feedstocks, releasing gaseous hydrogen sulfide (H₂S). The hydrogen sulfide is subsequently recovered in an amine treater and finally converted to elemental sulfur in a Claus process unit. In those industries, desulfurization process units are often referred to as hydrodesulfurizers (HDS) or hydrotreaters (HDT). Catalysts are based on molybdenum sulfide containing smaller amounts of cobalt or nickel. Hydrogenolysis is accompanied by hydrogenation. [Topsøe, H.; Clausen, B. S.; Massoth, F. E., Hydrotreating Catalysis, Science and Technology, Springer-Verlag: Berlin, 1996.]

Another hydrogenolysis reaction of commercial importance is the hydrogenolysis of esters into alcohols by catalysts such as copper chromite.

In the laboratory

In the laboratory, hydrogenolysis is used in organic synthesis. Debenzylation is most common and involves the cleavage of benzyl ethers: [For example Organic Syntheses, Coll. Vol. 7, p.386 (1990); Vol. 60, p.92 (1981). http://orgsynth.org/orgsyn/pdfs/CV7P0386.pdf. For example of C-N scission, see Organic Syntheses, Coll. Vol. 8, p.152 (1993); Vol. 68, p.227 (1990). http://orgsynth.org/orgsyn/pdfs/CV8P0152.pdf] :ROCH₂C₆H₅ + H₂ → ROH + CH₃C₆H₅
Thioketals undergo hydrogenolysis using Raney Nickel, a catalyst that, conveniently, carries its own hydrogen.

References