Using NPS Chromatography to Monitor Mesylation Reactions

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Using non-porous silica chromatography, mesylation reactions with unhindered and hindered amines were studied as proton scavengers. During reaction monitoring it is important to conduct sensitive and fast analyses. To optimally control the reaction quick feed-back is necessary. The non-porous silica (NPS) proved to be highly suitable. When unhindered amines are used to remove the proton, the SN2 mesylate product was observed to take place followed by the SN1 reaction to form the quaternary salt. The SN1 reaction does not occur when the sterically hindered dicyclohexylamine was employed. LC/MS confirmed this process and was used to identify the final products when various amines were used as proton scavengers. This study confirmed dicyclohexylamine is the preferred proton scavenger if one desires to obtain a stoichometric amount of mesylate.