R. Stephens

Tooth lead levels in Birmingham children.

The mean lead content of deciduous teeth from children living in the city of Birmingham (U.K.) has been shown to be 11.8 ppm dry weight, irrespective of the sex of the donor. Lead content varies according to type of tooth, and there is a gradient from incisors, with the highest level, to second molars, with the lowest. A relationship was shown between age of donor and lead content of canines and (when lognormalized data were considered) first molars. We were not able to demonstrate a correlation between tooth lead levels and residence near a potential industrial lead source, and we conclude that pollution from a general source is responsible for the body burdens we found.

Polyfluorobicyclo(2.2.1)heptanes—I : 1H-undecafluoro- and 1H,4H-decafluorobicyclo(2.2.1)heptane and a novel elimination process

Abstract The vapour-phase fluorination of bicyclo(2.2.1)heptadiene with cobaltic fluoride gave a complex mixture containing substantial amounts of perfluoro-, 1H-undecafluoro- and 1H,4H-decafluorobicyclo(2.2.1)heptane. The formation of perfluorocarbanions from the latter two compounds has been demonstrated by isotopic exchange in aqueous potassium hydroxide. The undecafluorobicyclo(2.2.1)heptyl anion has been formed also using methyl-lithium in ether at −55°, and trapped by reaction with acetaldehyde, bromine, methyl bromide and deuterium oxide. Near room temperature lithium undecafluorobicyclo(2.2.1)heptyl decomposed in a novel elimination process, thought to involve a transient bridgehead olefin, to give lithium fluoride and either 1-iodo-, or 1-bromo-, nonafluorobicyclo(2.2.1)hept-2-ene, depending on whether the methyl-lithium used to generate the anion was prepared from methyl iodide or methyl bromide, respectively. A similar decomposition in the presence of furan produced a furan adduct.

Polycyclic fluoroaromatic compounds—III : Octafluoroacenaphthylene, and decafluoro-indane, -acenaphthene, -anthracene, and -pyrene

Abstract Perfluoroperhydro-indane, -fluorene, -acenaphthylene, -phenanthrene, -anthracene and -pyrene have been prepared, by fluorination of the aromatic hydrocarbons with cobaltic fluoride. When defluorinated in the vapour phase over heated metal gauze perfluoro-indane, -acenaphthylene, -acenaphthene, -anthracene and -pyrene were obtained.

Polyfluorobicyclo(2,2,1)heptanes Part II. Further derivatives made from 1H-undecafluorobicyclo(2,2,1)heptane

Abstract 1 H -Undecafluorobicyclo(2,2,1)heptane has been lithiated with methyllithium in ether, and thence converted into a range of derivatives including 1-iodo-, 1-hydroxymethyl-, 1-carboxy- and 1-aceto-undecafluorobicyclo(2,2,1)-heptane. The latter reacts further to give α-(undecafluorobicyclo(2,2,1)heptan-1-yl)vinyl acetate. The iodide gave a Grignard reagent, the decomposition of which was studied, and a bis-mercurial. Bridgehead derivatives in this series are easily synthesised. The pyrolytic decarboxylation of anhydrous sodium undecafluorobicyclo(2,2,1)heptane-1-carboxylate and the decomposition of 1-lithio-undecafluorobicyclo(2,2,1)heptane have been studied, and the decomposition products correlated with transient bridgehead olefins.

Polyfluorobicyclo(2,2,1)heptanes Part III. Derivatives from 1H,4H-decafluorobicyclo(2,2,1)heptane

Abstract The title compound was converted via its mono-lithio derivative into the 1,4-disubstituted decafluorobicyclo(2,2,1)heptanes: (1) X -C 7 F 10 - Y (4), where X = H and Y = D, -CH(OH)CH 3 , -Br, -I, -CO 2 H, -CH 3 , -CH(OH)C 6 H 5 , -C(OCOCH 3 ) = CH 2 ; X = Y = D; X = Y = Br; X = Y = I; X = Y = CH 3 ; X = CH 3 , Y = CO 2 H. The lithio derivative decomposed in refluxing ether via a transient bridgehead diradical to give 1,4-disubstituted perfluorobicyclo(2,2,1)hept-2-enes, but related Grignard reagents did not.

Polyfluorobicyclo[2.2.2]octanes-I 1H-tridecafluorobicyclo[2.2.2]octane, and some derived compounds

Abstract A Diels-Alder reaction between 1H-heptafluorocyclohexa-1,3-diene and methyl acrylate gave two carbomethoxy heptafluorobicyclo[2.2.2]oct-5-enes. Cobaltic fluoride fluorination of each isomer in the vapour phase gave a complex mixture containing tetradecafluorobicyclo[2.2.2]octane (3%), 1H-tridecafluorobicyclo[2.2.2]octane (30%), a mixture of 1H,2H- and 1H,3H-dodecafluorobicyclo[2.2.2]octanes (25%) and a liquid mixture of fragmentation products (40%). The formation of a perfluorocarbanion from 1H-tridecafluorobicyclo[2.2.2]octane has been demonstrated by isotopic exchange in aqueous potassium hydroxide. Lithium tridecafluorobicyclo[2.2.2]octyl has been formed using methyl lithium in ether at − 50° and reacted with deuterium oxide, methyl iodide and iodine to give the 1-deutero-, 1-methyl- and 1-iodo-tridecafluorobicyclo[2.2.2]octanes; it was unchanged after 1 hr at 35° and hence represents the most stable perfluoro alkyl lithium so far prepared.

Polyfluoro-compounds based on the cycloheptane ring system. Part 5. Octafluordcyclohepta-1,3,5-triene and hexafluorotropone

Abstract Decafluorocyclohepta-l,3-diene underwent reductive addition-elimination with sodium borohydride to give mainly 1H-nonafluorocyclohepta -1,3-diene, together with minor products, the 1H,4H-octafluoro-analogue and, most significantly, 5H-nonafluorocyclohepta-l,3-diene. Decafluorocyclohepta -l,4-diene similarly gave mainly a mixture of 1H- and 2H-nonafluorocyclohepta -l,4-diene, together with some 6H-nonafluorocyclohepta-l,4-diene and a trace of the 5H-1,3-diene. These last two dienes were important products, having hydrogen on allylic carbons. They could be dehydrofluorinated, either by bubbling through molten potassium hydroxide or, better, with powdered alkali in an inert medium. Unless special precautions were taken, such reactions yielded hexafluorotropone. With care however the primary product, octafluorocyclohepta-l,3,5-triene, could be isolated, but it was hydrolysed rapidly, even by water, to give the tropone. Isomerisations and pyrolytic dehydrofluorinations of the major reduction products were carried out, but none yielded the triene or the tropone. It seemed that the triene was probably formed but decomposed to give perfluoroarenes. An interesting defluorination pathway was also operating, to give pentafluorobenzene. 2H-Nonafluorocyclohepta-1,3-diene was an isomerisation product. Hexafluorotropone reacted with sodium methoxide in methanol to give 3,6-dimethoxytetrafluorotropone.

Reductive coupling of polyfluorovinyl halides in the presence of copper-bronze

Abstract 1-Chloro-1,2-difluoroiodoethylene, 1-bromononafluorocyclohexeneand 1-bromoheptafluorocyclopentene undergo reductive coupling reactions when heated with copper bronze to give 1,4-dichlorotetrafluorobuta-1,3-diene and perfluorobicyclo-hex-1,1′-enyl and -pent-1,1′-enyl, respectively. The same olefins undergo crossed coupling reactions with phenyl and pentafluorophenyl halides and, in the first case, with 1-iodoheptafluoropropane.

Polyfluoro-compounds based on the cycloheptane ring system. Part 2. The 1H,3H- and 1H,4H-dodecafluorocyclophetanes, derived undecafluorocycloheptenes and decafluorocyclohepta-1,4- and 1,3-diene

Abstract From the mixture obtained by reaction of cycloheptane with cobalt(III) fluoride at 180–190°, the cis- and trans- 1H,3H- and 1H,4H- dodecafluorocycloheptanes were isolated. Each 1H,3H- compound was dehydrofluorinated by aqueous potash to 3H- and 4H-undecafluorocyclohept-1-ene, and thence decafluorocyclohepta-1,4- and 1,3-diene. The 1H,4H-isomers each gave 4H- and 5H-undecafluorocyclohept-1-ene and thence the two dienes on dehydrofluorination. The dichloro-adduct of the 5H-ene was reduced by lithium aluminium hydride, and the three possible 1H,2H,5H-undecafluorocycloheptanes were isolated. Likewise, the 4H-ene gave the 4 possible 1H,2H,4H-undecafluorides. All were identified by further fluorination with cobalt(III) fluoride at 160°, to appropriate dodecafluorocycloheptanes.

Tristrifluoromethylmethane takes up deuterium from a neutral medium faster than do 1H-perfluorobicyclo-[2,2,2]octane and -[2,2,1]heptane: Are inductive effects still a sufficient explanation or is a concept such as negative hyperconjugation necessary after all?

Abstract Mixtures of tristrifluoromethylmethane(I) and 1H-undecafluoro- bicyclo[2,2,1]heptane(II), and of I and 1H-tridecafluorobicyclo- [2,2,2]octane(III) were kept for approximately 19 days in hexadeuteroacetone/deuterium oxide (9:1) at 50°C. Uptakes of deuterium as measured by mass spectrometry were ca. 70% into I, not detectable with II, and ca. 12% into III. If this reaction is mechanistically similar to base-catalysed proton exchange, the acyclic system(I) is much more acidic than the bridgehead species (II). This result revives again the possibility that fluorine hyperconjugation (no-bond resonance) could be significant in aliphatic organofluorine chemistry.