Understanding the fundamental mechanisms of chemical reactions is of particular interest to many fields of science as it enables the rationalization, prediction, and design of experiments. Many chemical processes involve the formation of short-lived reaction intermediates, most of which cannot be isolated and are challenging to detect. One such an intermediate is the tetrahedral intermediate proposed to be generated upon the nucleophilic substitution of the chlorine atom by a simple alcohol in acetyl chloride. Therefore, the formation of this tetrahedral intermediate is still a subject of controversy as it has not been detected. In the present investigation, a 266 nm pulsed Nd:YAG laser was used to evaporate and ionize reactants, reaction intermediates, and products in microdroplets of acetyl chloride and ethanol. A linear quadrupole ion trap mass spectrometer was used to detect the ions and collision-activated dissociation (CAD) experiments were employed for their structural characterization. The mass spectra measured indicate the presence of the protonated tetrahedral intermediate of <i>m/z</i> of 125 and 127, corresponding to the two isotopes of chlorine. Ions of each <i>m/z</i> were isolated and subjected to CAD, resulting in the loss of water and ethylene. These results demonstrate that the ethanolysis of acetyl chloride proceeds via an addition-elimination mechanism involving a tetrahedral reaction intermediate.

Detection of the tetrahedral reaction intermediate of acetyl chloride in solution via drop-on-drop laser desorption/Ionization mass spectrometry

ACS Spring 2022

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