Correlation of the Rates of Solvolysis of 4-Morpholinecarbonyl Chloride Using the Extended Grunwald-Winstein Equation

Abstract

The rates of solvolysis of 4-morpholinecarbonyl chloride (MPC) have measured at 35.0 o C in water, D2O, CH3OD, and in aqueous binary mixtures of acetone, ethanol, methanol, and 2,2,2-trifluoroethanol. An extended (two-term) Grunwald-Winstein equation correlation gave sensitivities towards changes in solvent nucleophilicity and solvent ionizing power as expected for a dissociative SN2 and/or SN1(ionization) pathway. For nine solvents specific rates were determined at two additional temperatures and higher enthalpies and smaller negative entropies of activation were observed, consistent with the typical dissociative SN2 or SN1(ionization) pathway. The solvent deuterium isotope effect values for the hydrolysis of MPC of kH 2O /kD 2O = 1.27 and for the methanolysis of MPC of kMeOH/kMeOD = 1.22 are typical magnitudes of the SN1 or ionization mechanism.

Use of Linear Free Energy Relationships (LFERs) to Elucidate the Mechanisms of Reaction of a γ-Methyl-β-alkynyl and an ortho-Substituted Aryl Chloroformate Ester

“…The l / m ratio of 1.12 obtained [66], conforms to the expected range of the other carbamoyl esters [12] and implies a strong nucleophilic solvation effect at the developing carbamoyl carbocation [12,66]. The reason that the Koo group [64,65] continue to overlook our work is probably because we named compound 7 as 4-(chloroformyl)morpholine (from the Aldrich catalog); which is a synonym [67] for 4-morpholinecarbonyl chloride.…”

Mechanistic Studies of the Solvolyses of Carbamoyl Chlorides and Related Reactions

“…This was suggested to be consistent with an ionization process with appreciable nucleophilic solvation, as was also suggested for the solvolyses of N , N -dialkylcarbamoyl chlorides [55,58,59]. A consideration of structural, rather than solvent, variations also led to the postulate of an important nucleophilic solvation, which is disrupted by a bulky alkyl group as a substituent on the nitrogen [54].…”

“…Carbamoyl chlorides in which the “two substituents” on the nitrogen are tied back into a ring have been investigated in terms of mechanism [54,58,59]. The behavior of 1-piperidinecarbonyl chloride (V) (Figure 2) was compared to that of 4-morpholinecarbonyl chloride (VI) in 50% acetone, ethanol and cyclohexanol [54] at temperatures ranging from 20–65 °C for the first two solvents and at the one temperature of 90° for the solvolyses in cyclohexanol.…”

“…Some fourteen years later, Koo and coworkers [59] revisted the solvolysies of 4-morpholinecarbonyl chloride. They report data at 35.0 °C in a series of solvents very similar to those used at 25.0 °C in the earlier study and arrived at essentially identical values (Table 1) for l and m of 0.71 ± 0.05 and 0.65 ± 0.02 in an extended Grunwald–Winstein equation treatment and at a value of 0.46 for m with the use of the one-term equation.…”

Positioning solvolyses within the SN2‐SN1 and SN3‐SN2 spectrum of reaction mechanisms

“…Calculated gas phase heterolytic bond dissociation energies (HBDE) show that an adjacent nitrogen atom lowers HBDEs, and so solvolyses of carbamoyl chlorides (R 2 NCOCl) are expected to fit within the S N 2‐S N 1 spectrum. Supporting evidence is provided by KSIE data for the morpholine derivative (1.21 for water/D 2 O) and 1.27 for MeOH), and values of l or l / m (Scheme ). Other examples are summarized in a recent review …”