Fluorine, hydrogenolysis

Catalytic hydrogenation of substituted 2-fluoroprop-2-enoates over palladium at room temperature under atmospheric pressure results in saturation and only partial fluorine hydrogenolysis.100 The replacement of vinylic fluorines with hydrogen by catalytic hydrogenation proceeds more readily in fluoromaleic, fluorofumaric, difluoromaleic, and difluorofumaric acid 10.no It is assumed that fluorine hydrogenolysis occurs before saturation of the C = C bond. Yields of defluorinated products are strongly dependent on the catalyst used.110... 

Tri-, Tetra-, and Pentafluoropyridines. 2,4,6-Trifluoropyridine can be prepared in 75% yield by catalytic hydrogenolysis (paHadium-on-carbon, 280°C) of 3,5-dichloro-2,4,6-trifluoropyridine [1737-93-5] (416). The latter is synthesized by exchange fluorination of pentachloropyridine with potassium fluoride in polar solvents such as /V-methy1pyrro1idinone (417,418). 3,5-Dichloro-2,4,6-trifluoropyridine is used to... 

Catalytic Hydrogenolysis of Carbon-Huonne Bonds it-Bond Participation Mechamsm Hudlicky, M J Fluorine Chem 44, 345-359 58 n o C) S ... 

Reductive removal of fluorme from alk I fluorides requires a potent reducing agent and so is not noimally encountered However, hydrogenolysis of an unacuvated carbon-fluorine bond in, for example, 3 (3-fluorocholestane has been efficiently accomplished in 88% yield with a solution of potassium and dicyclohexyl 18 crown-6 in toluene at 25 C [/] Similarly, sodium naphthaiene in tetrahydrofuran converts 6 tluorohexene-1 and 1-fluorohexane to hydrocarbons in 50% yield at 25 C over a 7-h penod [2]... 

During hydrogenation of vinylic chlorides, both saturation of the double bond and hydrogenolysis of the C-Cl bond take place.433 35 Also, selective hydrogenolysis of chlorine occurs in the presence of fluorine atoms on a Pd/C catalyst (Scheme 4.125).436... 

Selective removal of the iodine from fluorinated compounds was performed by 5% Pd/C catalyzed hydrogenolysis in the presence of triethylamine or sodium acetate.467 Ra-Ni and 1% NaOH were used for the cleavage of the C-I bond.468 The adsorption of chloroiodomethane was studied on a Pt(lll) surface. Dissociation began with C—I bond cleavage at about 150 K. Co-adsorbed deuterium atoms weaken the bonding between the starting compound and the surface and decrease the amount of dissociated molecules.469... 

The conspicuously high speed of hydrogenolysis of allylic and vinylic halogens as compared with those removed further from the multiple bonds or halogens in alkanes implies that the multiple bond participates in a multicenter transition state [63]. Such a mechanism would account even for the surprisingly easy hydrogenolysis of allylic and vinylic fluorine [66, 528, 529, 530]. 

Hydrogenolysis of fluorine and chlorine possible only under exceptionally energetic conditions practically unfeasible. 

Hydrogenolysis (23S) of perchloryl aromatic compounds yields ArH and not ArOH, thus confirming the presence of a —Cl bond. Another useful reaction of FCIO3 involves the replacement of the active hydrogens of methylene compounds by fluorine (145, 262, 284). A typical example is the fluorination of malonic esters ... 

Similarly to alkyl fluorides, fluorocyclohexane is resistant toward catalytic hydrogenolysis. Hydrides and metals appear to be more efficient in the hydrodefluorination of alicyclic fluorine-containing compounds. Butyllithium in refluxing hexane defluorinates fluorocyclohexane to cyclohexane.20 The complete defluorination of fluorocyclohexane (11) is accomplished by activated magnesium in propan-2-ol, but the reaction leads to the predominant formation of cyclohexene.21... 

Catalytic Hydrogenolysis of Carbon-Fluorine Bonds rc-Bond Participation Mechanism Hudlicky, M. J. Fluorine Chem. 1989, 44, 345-359. 

Catalytic hydrogenolysis of 1,1-difluorocyclopropanes occurs at the C2-C3 bond with partial retention of fluorine in the cases studied [49] (equation 38) In contrast, reduction of acetoxy 1,1 difluorocytlopropanes with lithium aluminum hydride occurs with loss of fluoride to give (3-fluoroallyl alcohols, often with high stereose lectivity [50] (equation 39) A further variant involving free radical intermediates produces allylidene difluorides after ring opening [5/] (equation 40)... 

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