Synthesis
Hydrogenolysis of 2,4,6-tribromo-3,5-difluoropyridine occurred rapidly giving
quantitative conversion to 3,5-difluoropyridine (5), with an isolated yield by distillation
of 63%.
Preparation
Synthesis of 3,5-Difluoropyridine: A solution of 2,4,6-tribromo-3,5-difluoropyridine (11) (34.0 g, 97 mmol) in DCM (200 cm3) was washed with activated carbon and filtered. A palladium catalyst (3.4 g of a 5% Pd/C commercially available product) and triethylamine (45 cm3, 31.5 g, 312 mmol) were added to the filtrate and the mixture hydrogenated in a Parr apparatus at 4 Bar for 21 h. The mixture was filtered, water (200 cm3) added and extracted into DCM. Distillation of the DCM solution on Fischer-Spaltrohr apparatus gave 3,5-difluoropyridine (7.0 g, 61 mmol, 63%), b.p. 92.5 ·c (Found: C, 52.2; H, 3.0; N, 12.2. C5H3F2N2 requires C, 52.2; H, 3.0; N, 12.2%);
IR spectrum no. 1; mass spectrum no. 1; nrnr spectrum no. 8.
