Mechanochemistry or mechanosynthesis is an emerging tool to conduct chemical reactions in a greener and a safer environment. A mechanochemical reaction allows the use of mechanical energy to mix materials together to initiate a chemical reaction. The objective of this study is to understand free-radical based reactions under mechanochemical conditions. Using this novel methodology, we show free-radical reactions are able to be performed under solvent-free conditions, where traditionally harmful solvents such as benzene or carbon tetrachloride are used. Reduction of alkyl halides is one of the reactions that has been studied. Alkyl halides are reduced into their corresponding alkanes in the presence of azobisisobutyronitrile, tris(trimethylsilyl)silane (TTMSS) as the radical initiator and the H atom donor, respectively. The TTMSS-mediated dehalogenation of alkyl halides is believed to occur by radical abstraction/dehalogenation. All the experiments were performed inside the spex 8000m mixer mill at varying temperatures and reaction times. Following initial experiments, TTMSS was identified as the best reducing agent among 1,4-cyclohexadiene, diphenyl phosphite, sodium hypophosphite monohydrate and triethyl silane. Except for tris(trimethylsilyl)silane and triethyl silane, other reducing agents show side reactions with substrates tested. Also triethyl silane acts as a radical scavenger in the presence of radical initiator to inhibit the reaction. This research represents a safe and sustainable alternative to traditional solvent based organic synthesis for radical reductions.

Free radical reactions under mechanochemical conditions

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