Roy Fields

Thermolysis of low density polyethylene catalysed by zeolites

Plastic wastes, which cause a serious environmental problem in urban areas, can serve as sources of energy. Thermal degradation of low density polyethylene (LDPE) has shown that, under appropriate conditions, polyethylene can yield chemicals in the gasoline range of hydrocarbons as well as those found in jet fuels. In the reactions catalysed by H-mordenite and H-Theta-1, hydrocarbons in the range C11 to C19 are the significant components of the non-volatile fraction, whereas over H-ZSM-5, no hydrocarbon higher that C14 is detected and alkalines are the significant products. H-ZSM-5 catalysed degradation results in a significant amount of aromatics compared with H-mordenite and H-Theta-1 where the yield of aromatics is small.

Preparation of trifluoromethyl-pyrazoles and -pyrazolines by the reaction of 2,2,2-trifluorodiazoethane with carbon-carbon multiple bonds

Abstract 1,3-Dipolar addition of 2,2,2-trifluorodiazoethane to a series of alkenes and alkynes gives good yields of the corresponding pyrazolines and pyrazoles. Chloromethyl and bromomethyl substituents activate the multiple bond more than does a phenyl substituent. A combination of electronics effects and steric hindrance accounts for the reactivity of 3,3,3-trichloropropene, methyl methacrylate, and allyl formate.

Gold(I) complexes derived from secondary phosphines: [{Au(µ-PR2)}n],[(AuBr)2(µ-PPh2)]–, [AuX(PHR2)], and [{Au(PHR2)n}]+. Crystal structure of [AuBr(PHPh2)]

The interaction of secondary phosphines with a variety of gold(I) compounds has been studied. In the presence of bases or polar solvents, polymeric gold(I) phosphides [{Au(µ-PR2)}n] are formed. When these are obtained in the absence of additional ligands they are soluble, presumably with ring structures. More usually, insoluble forms are found, presumably with chain structures. The probable formation of these materials from complexes of the type [AuX(PH R2)] is discussed, and the isolation of the latter complexes (X = Cl or Br, R = Ph or p-tolyl) and of the novel monomeric phosphido-bridged anion [(AuBr)2(µ-PPh2)]– is described. In non-polar solvents a series of secondary phosphine complexes is formed, [Au(PHPh2)n]+(n= 2–4), but that with n= 3 appears to be unstable to disproportionation. The compounds are characterised by 31P n.m.r. and 197Au Mossbauer spectroscopy, and X-ray crystallography in the case of [AuBr(PH Ph2)].

Cyclopropane chemistry. Part 5 [1,2]. Hexafluorocyclopropane as a source of difluorocarbene

Abstract Thermolysis of hexafluorocyclopropane in the presence of ethylene, propene, vinyl chloride, and vinyl bromide gives good yields of the corresponding 1,1-difluorocyclopropanes, formed by addition of difluorocarbene to the olefin. The tetrafluoroethylene formed dimerises to octafluorocyclobutane, co-dimerises with the olefin, or survives, depending on the reaction conditions. With allene, hexafluorocyclopropane gives 1-(difluoromethylene)cyclopropane, 2,2,3,3-tetrafluorospiropentane, and products derived from tetrafluoroethylene and allene.

Reactions of 2,2,2-trifluorodiazoethane with carbon-nitrogen and carbon-oxygen multiple bonds

Abstract 2,2,2-Trifluorodiazoethane reacts with trifluoroacetonitrile in the dark at room temperature to give a 2-(2,2,2-trifluoroethyl)-4, 5-bis(trifluoromethyl)triazole, the 1,2,3-triazole structure being preferred to the 1,2,4-isomer on the basis of the 19F n.m.r. spectrum. The diazoethane reacts more slowly with trichloroacetonitrile, again forming the N-alkylated triazole even in the presence of an excess of the nitrile. No identifiable adduct resulted with acetonitrile. Hexafluoroisopropyl-ideneimine is first N-alkylated and then undergoes addition to form 1-(2,2,2-trifluoro-1-trifluoromethyl)ethyl-4,5-bis(trifluoromethyl)-▵-1,2,3-triazoline, but N-methylhexafluoroisopropylideneimine failed to react. Trifluoroacetaldehyde and trichloroacetaldehyde give mixtures of the ketone (formed by insertion of the CF3CH group into the aldehyde CH bond) and the cis - and trans -oxirans, apparently via a β-hydroxydiazoalkane.

H-ZSM-5 catalysed degradation of low density polyethylene, polypropylene, polyisobutylene and squalane: Influence of polymer structure on aromatic product distribution

Abstract Low density polyethylene, polypropylene and polyisobutylene and a medium molecular weight compound, squalane, were degraded as model compounds for plastics over a H-ZSM-5 zeolite catalyst. These compounds give products that are rich in gasoline-range chemicals, which contain a number of aromatic compounds. Polyisobutylene, (PIB) with dimethyl branching on alternate carbon atoms is shown to produce very little aromatics, whereas polypropylene (PP), with methyl branching and low density polyethylene (LDPE), and with very few branches on the polymer backbone, produces high yields of aromatics, and squalane with methyl branching fairly spaced out produces still higher yields of aromatics compared with PIB. The aromatic distributions obtained from these compounds have been explained in terms of the carbon branching on the polymer and the steric effect resulting from the polymers ingress into the zeolite channels.

Carbene chemistry. Part 13 [1]. Preparation of sole fluoroallenes by a carbene route, and the reaction of allenes with halogenocarbenes

Abstract Fluoroallene and 1, 3-difluoroallene are prepared in good overall yield by the addition of dichlorocarbene to vinyl fluoride and 1, 2-difluoroethylene respectively, followed by pyrolysis of the dichlorocyclopropanes and treatment of the resulting dichloropropenes with zinc. Pyrolysis of 1, 1-dichloro-2-fluorocyclopropane over zinc gives fluoroallene directly. The reaction of allene with 2, 2, 3-trifluoro-3-trifluoro- methyloxiran at 180°C as a source of difluorocarbene gives both 1, 1-difluoro-2-methylenecyclopropane and its rearrangement product 1-(difluoromethylene)cyclopropane, the latter reacting more readily with a second difluorocarbene to give 2, 2, 3, 3- tetrafluorospiropentane. In an analogous way, fluoroallene reacts with dichlorocarbene, generated from trifluoro(trichloromethyl) silane at 140°C, to give E - and Z -1, 1-dichloro-2- (fluoromethylene)cyclopropane, 1-(dichloromethylene)-2-fluorocyclopropane, and 2, 2, 3, 3-tetrachloro-4-fluorospiropentane.

Gasoline range chemicals from zeolite-catalysed thermal degradation of polypropylene

The thermal degradation of polypropylene over zeolite catalysts (H-ZSM-5, H-mordenite and H-theta-1) has been studied; GC analysis of the product fractions revealed that 70–80% were of the gasoline range hydrocarbons.

Fluorocarbon derivatives of nitrogen. Part 14. Studies on some (CF3)2 no-substituted fluoroaromatics; thermal rearrangement of 4-[bis(trifluoromethyl)amino-oxy]tetrafluoropyridine

Abstract The sodium salt (CF 3 ) 2 NO − Na + (I) [from (CF 3 ) 2 NOH + NaH in Et 2 O], is an alternative bis(trifluoromethyl)amino-oxylating agent to the adduct (CF 3 ) 2 NOH.CsF (III). With pentafluoropyridine it affords 4-X.C 5 F 4 N (II) + 2,4-X 2 .C 5 F 3 N (IV), [X = (CF 3 ) 2 NO]. It has been used to obtain a number of new bis(trifluoromethyl)amino-oxy-compounds; i.e. the following conversions have been effected: perfluoro-(4-isopropylpyridine)→ 2-X.C 5 F 3 N.CF(CF 3 ) 2 -4 (V) + 2,6-X 2 .C 5 F 2 N.CF(CF 3 ) 2 -4 (VI); 3-chlorotetrafluoropyridine → 4-X.C 5 F 3 N.Cl-3 (VII) and 2-X.C 5 F 3 N.Cl-5 (VIII) (not separated) + 2,4-X 2 .C 5 F 2 N.Cl-5 (IX), 3,5-dichlorotrifluoropyridine → 2- (XI) and 4-X.C 5 F 2 N.Cl 2 -3,5 (X) (not separated) + 2,4-X 2 .C 5 FN.Cl 2 -3,5 (XII); and perfluorotoluene → 4-X.C 6 F 4 .CF 3 -1 (XIII). Hexafluorobenzene resisted attack by (CF 3 ) 2 NONa under the conditions used with these aromatic substrates ( ca 20 °C). Static pyrolysis (125 °C) of 4-[bis(trifluoromethyl)amino-oxy]tetrafluoropyridine (II) gave a mixture of 6-bis(trifluoromethyl)amino]tetrafluoro-4-azacyclohexa-2, 4-dienone (XV) and 4-[bis(trifluoromethyl)amino]tetrafluoro-4-azacyclohexa-2,5-dienone (XVI). The 13 C chemical shifts, assigned by analysis of 19 F-coupled and 19 F broad-band decoupled 13 C n.m.r. spectra, are in accord with a +M effect similar to that of fluorine for a (CF 3 ) 2 NO- substituent in the 2- and 4- positions of a polyfluoropyridine and a slightly smaller -I effect; the steric effect of (CF 3 ) 2 NO on the shifts is less than that of chlorine. In contrast, a ring carbon carrying a (CF 3 ) 2 CF- substituent is markedly shielded compared with one carrying fluorine, presumably by a steric effect.

N-halogeno-compounds. Part 9 [1]. Azoxy- and azo-arenes derived from 4-(dichloroamino)tetrafluoropyridine; crystal structure of trans-2,3,5,6-tetrafluoro-4-(2,4,6-trimethylphenyl-onn-azoxy)pyridine

Abstract The nitrosoarenes ArNO (Ar = C6H5, 2-MeC6H4, 2,4,6- Me3C6H2 and C6F5) have been condensed with 4-(dichloroamino)- tetrafluoropyridine to provide the azoxy-compounds pyFN N + ( N - )Ar (pyF = 2,3,5,6-tetrafluoro-4-pyridyl); de-oxygenation of the first three with triphenylphosphine or triethyl phosphite gave the corresponding azo-compounds, and the reverse reaction was achieved in the case of pyFNNC6H2Me3-2,4,6 using peroxytrifluoroacetic acid. Thermolysis of 4-azidotetrafluoropyridine in the presence of pentafluoronitrosobenzene provided the perfluorinated azoxy-compound pyFN N + ( O - )C6F5. X-Ray methods have been used to determine the molecular geometry of pyFN N + ( O - )C6H2Me3-2,4,6.