Fluoro compounds, identification

There is no doubt that these applications will grow in the future and that the range of supercritical fluids used (carbon dioxide and methanol modified carbon dioxide, nitrogen dioxide, ammonia, fluoro-hydrocarbons) will increase as will the combination of this technique with mass spectrometric identification of separated compounds. 

Sanger s reagent (Section 27.11) The compound l-fluoro-2,4-dinitrobenzene, used in N-terminal amino acid identification. 

Ethers can be prepared under mild conditions from aromatic halogen compounds that contain ortho- or para-nitro groups.772"775 Alkyl 2,4-di-nitrophenyl ethers are obtained from 1 -fluoro-2,4-dinitrobenzene and alcohols in the presence of triethylamine,776 a reaction that can be used for identification of alcohols. 

Identification of chloro and bromo compounds is a relatively simple matter because of the unique isotopic pattern. The presence of fluoro and iodo compounds, although not easy, can be inferred from the conspicuously low [M - -1]/[M] ratio, which is due to the fact that F and I are monoisotopic. The molecular ion in aliphatic chlorides is visible only in lower monochlorides. With an increase in the number of chlorine atoms, the abundance of the molecular ion decreases further. The t-cleavage to expel a halogen atom often produces an abundant ion (e.g., the base peak in the mass spectrum of r-butyl chloride is C4H9+). The a-cleavage is of low consequence in alkyl chlorides, but the loss of an alkyl radical can be prominent when the alkyl chain is longer than four carbons the product is a flve-membered ring halonium ion ... 

Organofluorines play an important role in medicinal chemistry, and estimates indicate that 20-30% of the pharmaceutical products on the market contain at least one fluorine atom [57, 58], However, natural organofluorine compounds are exceedingly rare, and the pharmaceutical industry has not yet benefited from a microbial source of such compounds. The soil bacterium Streptomyces cattleya was found to produce fluoro-acetate and 4-fluorothreonine, but the biological scope is limited to a single biological pathway that produces fluoroace-tate [58, 59], Identification of the fluorination enzyme FIA, responsible for C-F bond formation in S. cattleya, enabled the directed manipulation of biosynthetic pathways for the formation of fluorinated natural products. 

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