Polyhalogenated heterocyclic compounds: Part 52. [1] Macrocycles from 3,5-dichloro-2,4,6-trifluoropyridine

Model studies show that displacement of fluorine, rather than chlorine, occurs upon reaction of 3,5-dichloro-2,4,6-trifluoropyridine with sodium methoxide and phenoxide. Subsequent hydro-dechlorination can be achieved by reaction with lithium aluminium hydride whereas reaction of sodium in iso-propanol leads to formation of the tri-iso-propoxy pyridine derivative, via nucleophilic substitution of the methoxy group, rather than the dechlorinated products. Macrocycles can be synthesised by reactions of appropriate difunctional oxygen nucleophiles with 3,5-dichloro-2,4,6-trifluoropyridine, one of which was characterised by X-ray crystallography.     

Mechanisms of reactions of halogenated compounds: Part 7. Effects of fluorine and other groups as substituents on nucleophilic aromatic substitution

The effect of fluorine as a substituent group on nucleophilic aromatic substitution is discussed, where a fluorine atom located ortho to the point of substitution may be of variable activating influence, whereas fluorine located para is slightly deactivating and meta is activating. A rationale of these effects is presented and evidence to support polar influences by ortho fluorine is advanced. The influence of CN, CF₃, CF₂H and CFH₂ is also established by comparison of appropriate measured rate constants and compared with the activation effects of ring nitrogen.     

Fluorinated phosphorus compounds: Part 9. The reactions of bis(fluoroalkyl) phosphorochloridates with oxygen nucleophiles

Twenty nine bis(fluoroalkyl) phosphates (R_FO)₂P(O)OR were prepared in 18-75% yield by treating phosphorochloridates (R_FO)₂P(O)Cl, where R_F was HCF₂CH₂, HCF₂CF₂CH₂, H(CF₂)₄CH₂, C₂F₅CH₂, C₃F₇CH₂, (CF₃)₂CH, (FCH₂)₂CH and (CH₃)₂CF₃C with methanol, ethanol, propanol and isopropanol in diethyl ether in the presence of triethylamine. The bulky chloridate [(CH₃)₂CF₃CO]₂P(O)Cl reacted with methanol, ethanol and propanol, but not with isopropanol - even on heating in the presence of the catalyst 4-dimethylaminopyridine - due to steric hindrance at phosphorus. The relative reactivities of three of the chloridates decreased in the order [(CF₃)₂CHO]₂P(O)Cl > [(FCH₂)₂CHO]₂P(O)Cl > [(CH₃)₂CF₃CO]₂P(O)Cl. Also described is the synthesis of phosphates (CF₃CH₂O)₂P(O)OCH₂R, where R = CH₂Br, CH₂Cl, CH₂F and CHF₂, and diphosphates [H(CF₂)_nCH₂O]₂P(O)OCH₂(CF₂)₂CH₂OP(O)[OCH₂(CF₂)_nH]₂, where n = 1, 2 and 4.     

Fundamentals and applications of needle trap devices: A critical review

The needle trap device (NTD) is an extraction trap that contains a sorbent inside a small needle, through which fluid can be actively drawn into and out of by a gas-tight syringe or pump, or analytes can be introduced passively to the trap by diffusion. The needle trap (NT) is a potentially solventless sampling technique/sample preparation and introduction device. Both fluid-borne analytes and particles can be trapped inside the needle and then adsorbed analytes are desorbed in an inlet of analytical instrument and introduced for identification and quantification. The fluid may be either gaseous or liquid. The objectives of this critical review are to summarize the theory of the sampling process for both active and passive time-average extraction modes in addition to outlining the evolution of the technology and main applications.     

Aminodefluorination of 2-X-pentafluoro-1,4-naphthoquinones (X = NHBu, NEt2, and OMe)

Aminodefluorination of 2-n-butylamino- and 2-diethylaminopentafluoro-1,4-naphthoquinone by alkylamines HNR¹R² (NR¹R² = NHEt, NHⁿBu and NEt₂) occurs at the 6- or 8-position and further, accordingly, at the 8- or at one of the 5- and 6-sites. The isomer ratio changes significantly in favor of a β-replacement product with solvent variation in the sequence: toluene < 1,4-dioxane < DMSO. n-Butylaminodefluorination of 2-methoxypentafluoro-1,4-naphthoquinone gives mixtures of fluorine substitution products both on the benzene and quinone rings.     

Direct di- and triamination of polyfluoropyridines in anhydrous ammonia

Aminodefluorination of polyfluoropyridines (pentafluoro-, 3,5-dichlorotrifluoro-, 3- and 4-chlorotetrafluoro-, 2,3,5,6- and 2,3,4,6-tetrafluoro-, 3-chloro-2,4,6-trifluoro-, and 2,4,6-trifluoropyridine) in anhydrous ammonia has been investigated. Temperatures of the second and third amino group introduction into pyridine ring were shown to increase significantly thus ensuring conditions for selective preparation of mono-, di- and, in the case of perhalopyridines as starting compounds, triaminoderivatives with high yield and purity.     

Organofluorine compounds and fluorinating agents : Part 28. New perfluoroalkyl substituted chiral mesogens

The perfluorohexyl-aryl-thioethers 3 and 4, building blocks for the synthesis of the chiral target mesogens 12-15, were prepared by dithionite-mediated S-perfluoroalkylation of the p-substituted thiophenols 1 and 2. The phenolic HO group of 3 was O-glucosylated with pentaacetyl-d-glucopyranose to 5 followed by deacetylation forming the tetrol 6 and by acetalizing with 4-(4-perfluorohexylsulfanyl-benzoyloxy)-benzaldehyde-dimethylacetal (8) generating the dihydroxy-intermediate 9. The latter contains two perfluorohexylthio chains. Alternatively, the dimethylacetal 8 was linked to p-octylphenyl-β-d-glucopyranoside (10) giving the mixed octyl/perfluorohexyl substituted p-octylphenyl-4,6-O-[4′-(4″-perfluorohexylsulfanyl)-benzoyloxy]-benzylidene-β-d-glucopyranoside (11). Compound 8 was obtained via esterification of 4 with p-hydroxy-benzaldehyde to 4-(4-perfluorohexylsulfanyl-benzoyloxy)-benzaldehyde (7). Finally, the diols 9 and 11 were dehydroxylated to 12 and 13 followed by hydrogenation yielding 14 and 15, respectively. Tetrol 6, diols 9, 11 and the non-amphiphilic compounds 7, 12-15 are thermotropic liquid crystals.