Acetylenic Carbinols and Glycols

Basic supports for the palladium catalyst can also be used to inhibit the hydrogenolysis of allyl alcohols (Eqn. 16.22) and acetates (Eqn. 16.23). The addition of quinoline to the reaction mixture has the same effect (Eqn. 16.24). 5 

While potassium hydroxide is beneficial in catalysts containing palladium loads near 5% with low palladium loads it appears that potassium hydroxide is not always necessary. The semihydrogenation of dehydrolinalool (19) gives 100% of linalool (20) over 0.5% PCI/AI2O3 in alcoholic solvents as shown in Eqn. 16.25. Perhaps with lower palladium-loaded catalysts reactant diffusion is not a factor in the reaction, so the presumed enhanced adsorption of the potassium hydroxide complex is not as important. 

Even though palladium catalysts are generally used for these reactions, Raney nickel has been somewhat effective (Eqn. 16.26) as have Ni/AlP04 catalysts (Eqn. 16.27).  

Selecting the catalyst and reaction conditions for partial reduction of a triple bond situated in a conjugated system is a challenge. Where the hydrogenation of an isolated alkyne can proceed with nearly complete selectivity, the partial saturation of an enyne takes place selectively with much more difficulty. Selectivities of 85-90% in these latter reactions are common and are considered to be reasonable for synthetic applications. 

Dissolving Metal Reductions , in Reductions. Techniques and Applications in Organic Synthesis (R. L. Augustine, Ed.) Deicer, New York, 1968,p95. 

---

Bowden, K., I. M. Heilbron, E. R. H. Jones, and B. C. L. Weedon (1946) Researches on acetylenic compounds. Part I. The preparation of acetylenic ketones by oxidation of acetylenic carbinols and glycols. Journal of the Chemical Society (London), 39-45. 

Toxicoiogy Eye, skin, and resp. tract irritant Precaution Avoid contact with moisture and strong oxidizing agents Hazardous Decomp. Prods. CO , NO , and HCI gas HMIS Health 2, Flammability 0, Reactivity 1 Uses Antioxidant In dietary supplements o-Acetyl-L-camitine hydrochloride. See Acetyl-L-camitine hydrochloride Acetylene carbinol. See Propargyl alcohol Acetylenic glycol. See Tetramethyl decynediol Acetyl ester of lanolin. See Acetylated lanolin N-Acetyl ethanolamine. See Acetamide MEA Achiote. See Annatto (Bbca orellana)... 

---