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P.S. Bhadury et al. / Journal of Fluorine Chemistry 116 (2002) 75–80
further stirred for 15 min at room temperature. Gaseous
product could be seen evolving due to the decomposition
of the ylide. The fluorocarbon CF2BrH was collected in the
tedlar bag connected to the reaction system. In order to close
the valve of the tedlar bag, the stem was pulled outward until
it stopped. To disconnect the tubing, it was pulled upward or
was cut off just above the stem. For syringe sampling of the
material in the tedlar bag, the end of the gas tight needle was
inserted through a small hole in the outer valve base flange at
an angle perpendicular to the sloped wall of the swollen
tedlar bag. The needle entered the bag through a larger hole
in the inner valve flange by penetrating through the PTFE/
silicone septum. The opposite wall of the bag while inserting
the needle should not be punctured. For samples for NMR
experiments, the collected gas was bubbled after opening the
valve into an NMR tube containing deuterated acetone and
cooled in a liquid N2/methanol mixture. The isolated yield of
CF2BrH was found to be 4.46 g (71%), b.p. À15 8C.
the volatile gaseous product CF2ClH which was collected
in a tedlar bag. The isolated yield of CF2ClH was 3.2 g
(65%); b.p. À41 8C.
Difluoromethane: As described earlier, a solution of tri-
phenylphosphine (42 g, 0.160 mol) in 100 ml of DMF was
heated to 130 8C; ClCF2CO2Na (8.15 g, 0.053 mol) dis-
solved in 10 ml of DMF was added in one shot. Heating
was discontinued. An exothermic reaction accompanied by
much solid deposition was observed. CF2H2 (isolated yield
1.67 g, 60%) was collected in a tedlar bag; b.p. À52 8C.
CF2ClH from ClCF2CO2Na: Pure sodium chlorodifluor-
oacetate (10 g, 0.065 mol), in the absence of triphenylpho-
sphine, was dissolved in 20 ml of dry DMF. The reaction
mixture was heated up to 100 8C; CF2ClH generated (iso-
lated yield 3.86 g, 68%) was collected in a tedlar bag.
Dichlorofluoromethane: As in the case of other volatile
fluorocarbons, Tris–(dimethylamino) phosphine (HMPT,
10 g, 0.06 mol) was added through a syringe in a nitrogen
atmosphere to a flask of 250 ml capacity containing 30 ml of
dry DMF. Fluorotrichloromethane (8.4 g, 0.06 mol) was
then added in one instalment to the well-stirred solution
when a mildly exothermic reaction occurred due to the
formation of (dichlorofluoromethyl) Tris–(dimethylamino)-
phosphonium chloride. The mixture was stirred for a further
30 min at room temperature; the guard tube was replaced by
an evacuated tedlar bag followed by slow addition of zinc
powder (3.9 g, 0.06 mol) through a solid addition tube. The
gaseous material in the form of CFCl2H (1.3 g, 20%) was
collected in a tedlar bag; b.p. 8–9 8C.
Dibromofluoromethane (CFBr2H): Triphenylphosphine
(8.5 g, 0.032 mol) was dissolved in 30 ml of dry DMF and
the solution was placed in a dried 250 ml three-necked round-
bottom flask, containing a stirring bar and equipped with a
reflux condenser and dry nitrogen inlet, at room temperature.
Fluorotribromomethane (8.8 g, 0.032 mol) was added in one
instalment to the well-stirred solution when an exothermic
reaction occurred due to the formation of (dibromofluoro-
methyl)triphenylphosphonium bromide. After stirring the
mixture for another 30 min, zinc powder (2.1 g, 0.032 mol)
was added slowly as described earlier and the reaction
mixture was stirred for a further 15 min at room temperature.
The course of the reaction was followed by withdrawing a
sample from the mixture and subjecting it to GC/MS analysis.
The reaction mixture was then treated with dichloromethane
followed by filtering off insoluble solid material under suc-
tion. DMF was then removed by repeatedly washing the
dichloromethane extract with excess water. Dichloromethane
was evaporated on a water bath and the product CFBr2H
(b.p. 66–68 8C) was isolated (3.49 g, 56%) by distillation.
Chlorodifluoromethane: Triphenylphosphine (15.0 g,
0.057 mol) was dissolved in 40 ml of dry DMF and the
solution placed in a dried 250 ml three-necked round-bottom
flask, containing a stirring bar and a dry nitrogen inlet, at
room temperature. The middle neck of the flask was con-
nected to a condenser fitted with a CaCl2 guard tube. The
mixture was heated to 100 8C, the nitrogen flow was stopped,
and the guard tube was replaced by an evacuated and
preweighed tedlar bag as described in the case of CF2BrH.
The valve was then opened, heating was stopped and imme-
diately sodium chlorodifluoroacetate (8.7 g, 0.057 mol) dis-
solved in 15 ml of dry DMF was added through a dropping
bulb of the third neck of the round bottom flask in one shot. A
highly exothermic reaction took place with the deposition of
solid material in the reaction flask. The decomposition of
difluoromethylene triphenylphosphonium ylide generated
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