Reactions of Methyl Perfluoroalkyl Ethers with Isopropyl Alcohol: Experimental and Theoretical Studies

Abstract

The reaction of an isomeric mixture of the methyl perfluoroalkyl ether, C 4 F 9 OCH 3 (Novec-7100), in the presence of isopropyl alcohol (IPA) and/or water has been studied by measuring the rate of product formation using an ion-selective electrode (ISE) for fluoride ion, Karl Fisher coulometric titrations for water, and 1 H and 19 F NMR spectroscopy for product identification and rate studies. The results showed the methyl perfluoroalkyl ether to be very stable with products forming at the rate of ∼1 ppm per year at a laboratory temperature of 20 °C. Measurements over the temperature range of 6°to 100 °C were made on samples aged for periods up to 1.8 years. Density functional theory calculations (DFT, B3LYP/6-31+G(d)) were employed to investigate different reaction pathways and formulate the probable reaction mechanism. The experimental enthalpy (ΔH ⧧ ) and entropy (ΔS ⧧ ) of activation were determined based on several different kinetic measurements. The ΔH ⧧ values are in the range of 20−25 kcal/mol and the corresponding ΔS ⧧ values range from −32 to −15 cal/(mol K). These are in good agreement with the theoretical values. While the range of ΔH ⧧ values does not change appreciatively, the ΔS ⧧ values are dependent on the proportion of vapor to liquid involved in the reaction of C 4 F 9 OCH 3 with IPA so that the more vapor the more negative the ΔS ⧧ value.

Characterization by NMR of reactants and products of hydrofluoroether isomers, CF3(CF2)3OCH3 and (CF3)2C(F)CF2OCH3, reacting with isopropyl alcohol

“…In general, acyl halides, in the presence of alcohols, react rapidly at ambient temperatures to form esters with rate constants on the order 10 −3 /s. Our measured rate constants for the slow step are between 10 −15 and 10 −12 /s for temperatures of 26 to 90 °C. Thus, the rate constant for the reaction in Eqn , 10 −3 /s, would be between 10 9 and 10 12 times faster than that in Eqn .…”

“…Samples for NMR included both new and aged Novec™ 7100DL and new and aged mixtures of Novec™ 7100DL with IPA. Because IPA is hygroscopic, all samples were prepared in a nitrogen‐purged, dry box . The mixtures ranged from 51.0 to 97.25 wt.% of methoxyperfluorobutane isomers with the remainder being IPA.…”

“…Novec™ 71IPA DL is an isomeric mixture containing the normal ‐isomer, CF 3 (CF 2 ) 3 OCH 3 , the iso‐isomer, (CF 3 ) 2 CFCF 2 OCH 3 in ~40/60 ratio, a chiral isomer (<0.025 wt.%), and IPA at ~4.5 wt.%. Density functional theory calculations for the reaction of the two major isomers with IPA predicted that isomeric acyl fluorides, C 3 F 7 CO(F), isopropylmethyl ether (IME), (CH 3 ) 2 CH–OCH 3 , and HF are produced in the rate‐determining step (Eqn ). Our predicted and measured thermodynamic activation parameters (ΔH ‡ pred.…”

“…= 25 kcal/mol) are indicative of a slow reaction at ambient temperatures. The second, and faster, reaction occurs between acyl fluoride and another molecule of IPA, producing isomeric isopropyl esters and a second molecule of HF (Eqn ) …”

“…Although NMR was used to measure rates at a variety of temperatures and reactant concentrations in our previous study, few spectral details were included. This current paper reports 19 F and 1 H NMR chemical shifts and coupling constants of the two major methoxyperfluorobutane isomers and 4.5 wt.% IPA, and the major products of their reaction at 90 °C in a mixture that was aged for 363 days.…”