Direct Exploitation of the Ethynyl Moiety in Calcium Carbide Through Sealed Ball Milling

Abstract

Ball milling of calcium carbide (CaC2) enables the reaction of its ethynyl moiety with organic electrophiles. This was realized simply by co‐milling CaC2 with organic substrates in a sealed jar without the need for an additive or a catalyst. Various ketones including those bearing α‐hydrogens were ethynylated in good yields at short reaction times. Aryl halides are also amenable substrates for this protocol as they furnish aryl ethynes through a benzyne intermediate. This method offers a practical and cheap alternative to the established procedures for introducing ethynyl functionalities.

Sustainability Assessment of Mechanochemistry by Using the Twelve Principles of Green Chemistry

“…However, in most cases the reduction in derivatization steps in mechanochemical C−H functionalization reactions is an intrinsic advantage of the general concept of direct C−H activation, rather than the result of the implementation of the mechanochemical approach. This is different from examples such as the previously discussed mechanosynthesis of propargylic diols 4 and 1,4‐diamino‐2‐butynes 9 in which the need for acetylene derivatives (e. g., metal acetylides) [48–50] was avoided by implementing mechanochemistry (Scheme 3).…”

“…In the search for better alternatives, scientists have identified solid CaC 2 as a safer surrogate of acetylene, which not only have exhibited a wide versatility in synthetic chemistry, [46] but which also displays an interesting circular sustainability profile. [47] By mechanochemistry, CaC 2 has enabled the solventfree preparation of cumulenes 6 by: (i) shortening the synthetic route, (ii) avoiding the use of Li-or Mg-acetylide in the synthesis of propargylic alcohols 4, [48,49] and (iii) accomplishing the stannous chloride mediated reductive elimination of 4 without the need for corrosive Brønsted acids such as hydrochloric acid (Scheme 3a). [48] Moreover, the application of CaC 2 as a C 2 synthon has enabled the one-pot mechanosynthesis of 1,4-diamino-2-butynes 9 by copper catalysis.…”

Calcium Carbide: Versatile Synthetic Applications, Green Methodology and Sustainability

“…[ 55d ] Later on, calcium carbide was mechanochemically activated without any additives in solvent free manner. [ 57 ] Alkynylation of various ketones led to the same products with a preference for disubstituted alkynes. Subsequent reductive elimination of the diols in the presence of tin dichloride leads to [3]cumulenes 73 (Scheme 26, D), whereas oxidative coupling of the propargylic alcohols leads to hexa‐2,4‐diyne‐1,6‐diol 74 (Scheme 26, E) followed by reductive elimination to [5]cumulene 75 (Scheme 26, F).…”

Towards Sustainable Carbon Return from Waste to Industry via C2-Type Molecular Unit

“…Hydrolysis of calcium carbide results in gaseous acetylene, which can be easily integrated into industrial processes, providing a wide range of valuable chemicals [ 30 , 31 , 32 , 33 , 34 ]. In addition to the well-established large-scale manufacturing of acetylene, carbide is also used directly, skipping gaseous acetylene, in many fundamental processes [ 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 ]. Currently, calcium carbide is a valuable product of the chemical industry and is produced from natural limestone and fossil carbon [ 52 , 53 , 54 , 55 , 56 , 57 , 58 ].…”