Rate and product studies with 2-adamantyl fluoroformate under solvolytic conditions

Recent Advances in the Synthesis and Transformation of Carbamoyl Fluorides, Fluoroformates, and Their Analogues

Carbamoyl fluorides, fluoroformates, and their analogues are a class of important compounds and have been evidenced as versatile building blocks for the preparation of useful molecules in organic chemistry. While major achievements were made in the synthesis of carbamoyl fluorides, fluoroformates, and their analogues in the last half of 20th century, an increasing number of reports have focused on using O/S/Se=CF2 species or their equivalents as the fluorocarbonylation reagents for the direct construction of these compounds from the parent heteroatom-nucleophiles in recent years. This review mainly summarizes the advances in the synthesis and typical application of carbamoyl fluorides, fluoroformates, and their analogues by the halide exchanges and fluorocarbonylation reactions since 1980.

Correlation of the rates of solvolysis of i-butyl fluoroformate and a consideration of leaving-group effects

The specific rates of solvolysis of isobutyl fluoroformate (1) have been measured at 40.0 °C in 22 pure and binary solvents. These results correlated well with the extended Grunwald-Winstein (G-W) equation, which incorporated the N(T) solvent nucleophilicity scale and the Y(Cl) solvent ionizing power scale. The sensitivities (l and m-values) to changes in solvent nucleophilicity and solvent ionizing power, and the k(F)/k(Cl) values are very similar to those observed previously for solvolyses of n-octyl fluoroformate, consistent with the additional step of an addition-elimination pathway being rate-determining. The solvent deuterium isotope effect value (k(MeOH)/k(MeOD)) for methanolysis of 1 was determined, and for solvolyses in ethanol, methanol, 80% ethanol, and 70% TFE, the values of the enthalpy and the entropy of activation for the solvolysis of 1 were also determined. The results are compared with those reported earlier for isobutyl chloroformate (2) and other alkyl haloformate esters and mechanistic conclusions are drawn.

Corrrelation of the Specific Rates of Solvolysis of Ethyl Fluoroformate Using the Extended Grunwald-Winstein Equation

The specific rates of solvolysis of ethyl fluoroformate have been measured at 24.2 °C in 21 pure and binary solvents. These give a satisfactory correlation over the full range of solvents when the extended Grunwald-Winstein equation is applied. The sensitivities to changes in the N_T solvent nucleophilicity scale and the Y_Cl solvent ionizing power scale, and the k_F/k_Cl values are very similar to those for solvolyses of n-octyl fluoroformate, consistent with the addition step of an addition-elimination pathway being rate-determining. For methanolysis, a solvent deuterium isotope effect of 3.10 is compatible with the incorporation of general-base catalysis into the substitution process. For five representative solvents, studies were made at several temperatures and activation parameters determined. The results are also compared with those reported earlier for ethyl chloroformate and mechanistic conclusions are drawn.

Correlation of the rates of solvolysis of acetyl chloride and α-substituted derivatives

Additional specific rates of solvolysis have been determined for acetyl chloride and diphenylacetyl chloride. These are combined with literature values to carry out correlation analyses, using the extended Grunwald–Winstein equation with incorporation of literature values for solvent nucleophilicity (NT) and solvent ionizing power (YCl). Parallel analysis are carried out using literature values for the specific rates of solvolysis of trimethylacetyl chloride, chloroacetyl chloride, phenylacetyl chloride, and α-methoxy-α-trifluoromethylphenylacetyl chloride (MTPAC). Chloroacetyl chloride and MTPAC react by an addition-elimination pathway, with the addition step rate-determining, over the full range of solvents. Acetyl chloride reacts over the full range of solvents by an ionization pathway, with considerable nucleophilic solvation. The other three substrates can solvolyze with the domination of either mechanism, depending on the properties of the solvent. Reports concerning the use of product selectivity values, kinetic solvent isotope effects, and computational studies as additional probes of the mechanism of solvolysis are discussed.Key words: Grunwald-Winstein equation, acyl chlorides, mechanism of solvolysis, solvent nucleophilicity.

Sixty Years of the Grunwald–Winstein Equation: Development and Recent Applications

The development of scales of values for solvent nucleophilicity and for the aromatic-ring parameter are described. These are applied to solvolytic addition to carbocations and, together with improved solvent ionising power scales, to solvolyses proceeding with a 1,2-aryl shift and to solvolytic displacements at acyl carbon and at a heteroatom, such as phosphorus or sulfur.