Selective Direct Fluorination
Organofluorine chemistry has been flourishing since the middle of the twentieth century, and to serve this demand a number of indirect techniques have been developed to introduce fluorine into an organic compound. These include the Balz-Schiemann reaction, HF diazotisation and the Halex reaction. The use of cobalt fluorides (fluorine reacting with cobalt difluoride to form cobalt trifluoride, which is then used to fluorinate a hydrocarbon) to produce their FLUTEC range of perfluorinated organic fluids. But, until recently, the use of the element, of fluorine itself, was just not credible.
The selective replacement of a hydrogen atom for a fluorine atom was not possible until the positively charged ‘fluoronium’ ion was discovered independently by Barton, Rosen and other. The process still involved a two-stage reaction, firstly between fluorine and a ‘carrier’ to form an F-O or F-N bond, then reaction with an organic substrate. The early reagents were only marginally less reactive and dangerous than fluorine itself, that said however, compounds such as CF OF, FCIO , and N-fluorosulfonylamides have been used extensively as fluorinating agents.
To control fluorination the following factors need to be considered:
1. Heat transfer must exceed mass transfer:
a. Fluorine inventory/rate of feed must be low
b. Heat needs to be transferred from the point of reaction to any cooling surface
2. The F-F bond needs to be polarized to reduce random radical reaction
3. Air must be excluded from the system.
After moderating fluorine sufficiently to allow selective fluorinations. The trifluoromenthyl group has long been used to modify the activity of various biologically active molecules; its higher analogue, the sulfur pentafluoride group is now receiving attention. The group is even more stable to chemical attack, larger in size and would probably have a greater inductive effect than both fluorine and trifluoromethyl.
In conclusion, it can be said that, although fluorine is violently reactive, it is starting to be used as a synthetic reagent. Unpolarised, it is of use for making perfluorinated compounds, while the polarised molecule can act as an electrophile and under the right conditions, can be used selectively. Fluorine is no less heavy-handed than many other reagents, but it does give unusual isomers, and new intermediates, as well as access to the aromatic-SF5 group.
Fluorine is already being used to manufacture aromatic-SF5 compounds, unusual aromatic isomers, beta-diketones and keto-esters. Many are available from stock.
|Species||Bifidobacterium infantis M-63|
|Identification||Identified as B. infantis by the analysis of sugar Fermentation spectrum|
|Viable Cell Count of B. infantis M-63||More than 5.0 x 1010/g (ABCM agar method)|
|General Description||White to slightly brown powder|
|Organoleptic Properties||A unique, slightly sweet taste|
|Moisture||Less than 6%||Drying Method (105+1ºC, 5 hr)|
|Coliform Bacteria||Negative||Violet red bile agar|
|Yeast and Mold||Less than 30/g||Potato Glucose agar|
|Arsenic||Less than 1 ppm||Gutzeit Method|
|Heavy Metals||Less than 10 PPM||Colorimetric Method|
|Packaging Size||1 kg/aluminum bag|
|Storage Conditions||Keep cool below 10ºC|