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Tuning the Acidity of Pt/ CNTs Catalysts for Hydrodeoxygenation of Diphenyl Ether
Published on: August 17, 2019
Catalyst-free hydrothiolation of alkynes with dithiocarbamic acids
A Ziyaei Halimehjani1, B Breit
1Faculty of Chemistry, Kharazmi University, P. O. Box 15719-14911, 49 Mofateh Street, Tehran, Iran. ziyaei@khu.ac.ir.
Abstract:
A highly regio- and stereocontrolled procedure for the synthesis of vinyl dithiocarbamates via catalyst-free hydrothiolation of unactivated alkynes with in situ prepared dithiocarbamic acids with total atom economy is reported. While unactivated terminal alkynes afforded the Markovnikov adducts with excellent regioselectivity, ethynyltrimethylsilane furnished the E-selective anti-Markovnikov adducts with excellent regio- and stereoselectivity. In addition, the obtained vinyl dithiocarbamates were applied as efficient precursors for the synthesis of secondary thiols and α-hydroxythioamides.
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Acidity of 1-Alkynes
The acidic strength of hydrocarbons follows the order: Alkynes > Alkenes > Alkanes. The strength of an acid is commonly expressed in units of pKa — the lower the pKa, the stronger the acid. Among the hydrocarbons, terminal alkynes have lower pKa values and are, therefore, more acidic. For example, the pKa values for ethane, ethene, and acetylene are 51, 44, and 25, respectively, as shown here.
Alkynes to Carboxylic Acids: Oxidative Cleavage
Alkynes to Aldehydes and Ketones: Acid-Catalyzed Hydration
Analogous to alkenes, alkynes also undergo acid-catalyzed hydration. While the addition of water to an alkene gives an alcohol, hydration of alkynes produces different products such as aldehydes and ketones.
Nomenclature of Alkynes
Preparation of Alkynes: Dehydrohalogenation
Alkynes can be prepared by dehydrohalogenation of vicinal or geminal dihalides in the presence of a strong base like sodium amide in liquid ammonia. The reaction proceeds with the loss of two equivalents of hydrogen halide (HX) via two successive E2 elimination reactions.
Preparation of Aldehydes and Ketones from Alcohols, Alkenes, and Alkynes

