Difluoroacetic acid, methyl ester

Potassium fluoride [7789-23-3], KF, is the most frequently used of the alkaU metal fluorides, although reactivity of the alkaU fluorides is in the order CsF > RbF > KF > NaF > LiF (6). The preference for KF is based on cost and availabiUty traded off against relative reactivity. In its anhydrous form it can be used to convert alkyl haUdes and sulfonyl haUdes to the fluorides. The versatility makes it suitable for halogen exchange in various functional organic compounds like alcohols, acids and esters (7). For example, 2,2-difluoroethanol [359-13-7] can be made as shown in equation 9 and methyl difluoroacetate [433-53 ] as in equation 10. 

Difluoroethanol is prepared by the mercuric oxide cataly2ed hydrolysis of 2-bromo-l,l-difluoroethane with carboxyHc acid esters and alkaH metal hydroxides ia water (27). Its chemical reactions are similar to those of most alcohols. It can be oxidi2ed to difluoroacetic acid [381-73-7] (28) it forms alkoxides with alkaH and alkaline-earth metals (29) with alkoxides of other alcohols it forms mixed ethers such as 2,2-difluoroethyl methyl ether [461-57-4], bp 47°C, or 2,2-difluoroethyl ethyl ether [82907-09-3], bp 66°C (29). 2,2-Difluoroethyl difluoromethyl ether [32778-16-8], made from the alcohol and chlorodifluoromethane ia aqueous base, has been iavestigated as an inhalation anesthetic (30,31) as have several ethers made by addition of the alcohol to various fluoroalkenes (32,33). Methacrylate esters of the alcohol are useful as a sheathing material for polymers ia optical appHcations (34). The alcohol has also been reported to be useful as a working fluid ia heat pumps (35). The alcohol is available ia research quantities for ca 6/g (1992). 

Difluoroacetic acid undergoes reactions typical of a carboxylic acid such as forming an ester when heated with an alcohol and sulfuric acid. Typical esters are methyl difluoroacetate [433-53-4], bp, 85.2°C, and ethyl difluoroacetate [454-31-9], bp, 99.2°C. It can also be photochemicaHy chlorinated to chlorodifluoroacetic acid [76-04-0] or brominated in the presence of iron to bromodifluoroacetic acid [667-27-6] (37,38). 

Tetrafluoroethene has been used as a 2-carbon difluoroacetic acid equivalent, methodology developed by Normanl and co-workers, in the synthesis of inhibitors of Cobra venom phospholipase A2.13 Conversion of the allyl alcohols into the 2,2-difluoropent-4-enoic acids 32 is performed in one pot. The crude acids 32 are then converted into the methyl esters 33. Although esters 33 can be obtained directly from the acyl fluorides 29, as originally described by Normant and co-workers,10 a two-step procedure facilitates the workup after the Claisen rearrangement. 

Yamaki et al. [14-16] investigated the thermal stability of fluorinated esters, which are the same fluorinated esters used as additives to improve the cycling performance reported by Nakajima et al. [12,13] prior to our study. In this study, partially fluorinated carboxylic acid esters (Table 20.1) were used as the electrolyte solvent and LiPFe as the salt. LiPFe was dissolved in methyl difluoroacetate (MEA) and ethyl difluoroacetate (EFA) to a salt concentration of 1 M. In the other fluorinated esters, however, LiPFe salt could be dissolved to a salt concentration of less than 0.2 M. Therefore, the solutions of fluorinated esters (P and 2 ) with 0.2 M of LiPFe were used, and the other fluorinated esters were saturated with LiPFe. For comparison, the solutions of corresponding esters with 0.2 M LiPFe were prepared. Similar measurements were performed employing the conventional electrolyte solution used in lithium batteries 1 M LiPFe/EC + DMC (1 1 by vol). 

From a safety aspect of utilizing lithium-metal anodes, various fluorinated solvents have been studied as the components of electrolyte solutions for Uthium-metal cells. A typical example of these solvents is methyl difluoroacetate (MFA). MFA exhibited better thermal stability and lithium cycling efficiencies among various fluorinated carboxylic acid esters [53]. 

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