in their entirety tertiary amine catalysts which are thermally stable under the conditions of the present process and which have a boiling point higher than about 140 u00b0 c are those such as for example 2 or 4 dimethylamino pyridine n methylmorpholine and combinations thereof in another embodiment of this invention the ptc catalysts are imidazole type compounds represented by the following general formula wherein each r 1 r 2 r 3 and r 4 independently is a hydrogen or hydrocarbyl or inertly substituted hydrocarbyl radical containing from 1 to about 16 carbon atoms specifically from 1 to about 6 carbon atoms specific imidazole type phase transfer catalysts are selected from but not limited to the group 1 methylimidazole 2 methyl imidazole 2 ethylimidazole 2 propylimidazole 2 butylimidazole 2 pentylimidazole 2 hexylimidazole 2 cyclohexylimidazole 2 phenylimidazole 2 nonyl imidazole 2 undecylimidazole 2 heptadecylimidazole 2 phenyl 4 methylimidazole 1 benzylimidazole 1 ethyl 2 methylbenzimidazole 2 methyl 5 6 benzimidazole 1 vinylimidazole 1 allyl 2 methylimidazole 2 cyanoimidazole 2 chloroimidazole 2 bromoimidazole 1 2 hydroxypropyl 2 methylimidazole 2 phenyl 4 5 dimethylolimidazole 2 phenyl 4 methyl 5 hydroxymethylimidazole 2 chloromethylbenzimidazole 2 hydroxybenzimidazole 2 ethyl 4 methylimidazole 2 cyclohexyl 4 methylimidazoles 4 butyl 5 ethylimidazole 2 butoxy 4 allylimidazole 2 carboethyoxy butylimidazole 4 methytimidazole 2 octyl 4 hexylimidazole 2 methyl 5 ethylimidazole 2 ethyl 4 2 ethylamino imidazole 2 methyl 4 mercaptoethylimidazole 2 5 chloro 4 ethylimidazole and mixtures thereof phosphine catalysts which are thermally stable under the conditions of the present process and which have a boiling.