SYNTHESIS AND CHARACTERIZATION OF SELECTIVELY FLUORINATED STEARIC ACIDS (OCTADECANOIC ACIDS) AND THEIR TRISTEARINS - THE EFFECT OF INTRODUCING ONE AND 2 FLUORINE-ATOMS INTO A HYDROCARBON CHAIN

The synthesis and physical properties of 2,2',2''- and 12,12',12''-tri flubrotristearins 2 and 3 and 12,12,12',12',12'',12''-hexafluorotriste arin 4 are described. NMR, X-ray powder diffraction, melting point and differential scanning calorimetry analyses of these compounds are rep orted and comparisons are drawn with tristearin 1. Analysis of Langmui r film isotherms of the stearic acids gave the average area occupied b y each molecule in a condensed monolayer and was used as a method to p robe disorder in the hydrocarbon chains. Of the compounds studied, 3 p ossesses the closest behaviour to tristearin. The incorporation of a C F2 group into the lipid chain in 4 imparts unique physical properties to the tristearin and a novel thermodynamically stable polymorphic for m (beta'') is observed. This is attributed to a conformational change in the hydrocarbon chain induced by the CF2 groups. Langmuir film anal ysis of the selectively fluorinated stearic acids (octadecanoic acids) 7 and 8 reinforce this conclusion.