The cleavage of C-S linkages plays a key role in fuel processing and organic geochemistry. Water is known to affect these processes, and several hypotheses have been proposed, but the mechanism has been elusive. Here we use both experiment and theory to demonstrate that supercritical water reacts with intermediates formed during alkyl sulfide decomposition. During hexyl sulfide decomposition in supercritical water, pentane and CO + CO2 were detected in addition to the expected six carbon products. A multi-step reaction sequence for hexyl sulfide reacting with supercritical water is proposed which explains the surprising products, and quantum chemical calculations provide quantitative rates that support the proposed mechanism. The key sequence is cleavage of one C-S bond to form a thioaldehyde via radical reactions, followed by a pericyclic addition of water to the C[double bond, length as m-dash]S bond to form a geminal mercaptoalcohol. The mercaptoalcohol decomposes into an aldehyde and H2S either directly or via a water-catalyzed 6-membered ring transition state. The aldehyde quickly decomposes into CO plus pentane by radical reactions. The time is ripe for quantitative modelling of organosulfur reaction kinetics based on modern quantum chemistry.

In this work, we demonstrated the purification of amoxicillin trihydrate (AMCT) by the formation of 4-hydroxyphenylglycine (4HPG)-coformer complex in solution. Without advanced knowledge of cocrystal formation of 4HPG, a workflow was established to choose the optimal coformer and the amount of coformer to add for a specific target/impurity system. Forty-seven compounds were chosen and screened due to their functional groups having the potential to form heterosynthons with the functional groups on 4HPG. Using solid-state grinding, eleven compounds were selected as coformers for separation experiments because they can form cocrystals with 4HPG but not AMCT. Four compounds, 2-picolinic acid, L-lysine, L-leucine, and L-isoleucine were shown to enhance AMCT purity the most. The purities of the AMCT crystals crystallized from solutions with a 1 : 10 4HPG : AMCT ratio and with these four compounds were significantly greater than that without the addition of coformer and greater than that obtained from a second crystallization from fresh solvent. By varying the coformer-to-4HPG ratio, we can correlate the purification results to the level of complexation in the solution. In addition, the proposed separation method has practical uses and can be applied to expensive products where low yield is unacceptable.