Photolysis of cellulose and related compounds by 253.7 nm light. I. Rates of gas production from hydrocellulose

The initial stages of the photolysis of cellulose under vacuum can be followed by the gas production. A photolysis cell is described which allows a rigorous temperature control and gives a reproducible photolysis surface of the solid carbohydrate sample. A mass spectrometer was used to analyze the gases. To measure accurately the small amounts produced in a small volume requires careful calibration of this instrument, together with a fixed routine for the experimental procedure. Using this apparatus, we have photolyzed hydrocellulose under vacuum with 253.7 nm light. Only H₂, CO, and CO₂ were evolved, the rate of H₂ production increasing to a constant value, that of CO increasing more slowly without becoming constant, and that of CO₂ decreasing rapidly to a constant value. No induction periods were observed. The gas evolution was not caused by residual O₂ or CO₂ adsorbed on the polymer, but the rates were altered by leaving the photolyzed sample under vacuum overnight or heating the unphotolyzed sample under vacuum at 100°C. The rates of gas production increased markedly when the light filter was changed to allow a combined photolysis by 253.7 and 184.9 nm light. The results illustrate that stringent precautions must be taken to filter off the latter line in polymer photolyses with Hg arc light if the results are to be meaningfully interpreted in terms of 253.7 nm light photolysis. On photolyzing hydrocellulose previously boiled in NaOH solution, a larger H₂ production rate and a smaller CO₂ rate (compared with untreated hydrocellulose) were observed. It is suggested that this standard alkali treatment is the reason for the differences between our results and the results of the photolysis of cellulose reported in the literature.     

A photoelectrochemical study of the anodic oxidation of lead in alkaline solution

The oxidation of lead in sodium tetraborate and in sulphuric acid solution has been studied. The analysis of photocurrent spectra has shown that tetragonal PbO is formed in both electrolytes. Evidence for photoemission from the metal substrate into the anodic oxide film is presented and discussed. The photocurrent behaviour is related to changes in electrode impedance which accompany the interconvertion of PbO and PbO₂.     

Dinuclear Copper(II) Complexes Incorporating a New Septadentate Polyimidazole Ligand

The dinuclear copper(II) complexes [Cu(2)(tmihpn)(prz)](ClO(4))(2).2CH(3)CN (6) and [Cu(2)(tmihpn)(O(2)CCH(3))](ClO(4))(2).CH(3)CN (7) were prepared, where tmihpn is the deprotonated form of N,N,N',N'-tetrakis[(1-methylimidazol-2-yl)methyl]-1,3-diaminopropan-2-ol and prz is the pyrazolate anion. The crystal structures of 6 and 7 were determined and revealed that both complexes contain bridging alkoxide ligands as well as bridging pyrazolate and acetate ions, respectively. Crystal data: compound 6, triclinic, P&onemacr;, a = 18.089(2) ?, b = 22.948(3) ?, c = 9.597(2) ?, alpha = 93.37(2) degrees, beta = 94.49(2) degrees, gamma = 81.69(2) degrees, V = 3925.1 ?(3), Z = 4; compound 7, triclinic, P&onemacr;, a = 12.417(2) ?, b = 15.012(3) ?, c = 10.699(2) ?, alpha = 104.76(2) degrees, beta = 102.63(2) degrees, gamma = 99.44(2) degrees, V = 1830.1 ?(3), Z = 2. In compound 6, the coordination geometry around both copper centers resembles a distorted square pyramid, while the stereochemistry around the copper centers in 7 is best described as trigonal bipyramidal. Both complexes display well-resolved isotropically shifted (1)H NMR spectra. Selective substitution studies and integration data have been used to definitively assign several signals to specific ligand protons. Results from the solution (1)H NMR studies suggest that the basal and apical imidazole groups do not exchange rapidly on the NMR time scale and the solid state structures of the complexes are retained in solution. In addition, the magnetochemical characteristics of 6 and 7 were determined and provide evidence for "magnetic orbital switching". Antiferromagnetic coupling in 6 (J = -130 cm(-)(1)) is strong, while the copper centers in compound 7 are ferromagnetically coupled (J = +16.4 cm(-1)). Differences in the magnetic behavior of the two copper centers have been rationalized using the "ligand orbital complementary" concept. The ground state magnetic orbitals involved in spin coupling in 6 (d(x)()()2(-)(y)()()2) are different from those in 7 (d(z)()()2).     

The four-jet structure of large transverse momentum events inpp interactions at the ISR

Deep inelastic proton-proton collisions have been recorded with the Split-Field-Magnet Detector (SFM) at the CERN Intersecting Storage Rings (ISR) by triggering on a single particle at high transverse momentum. Full reconstruction of the charged particles in these collisions was performed. In this paper we demonstrate the existence of a structure comprised of four jet-like clusters, two longitudinal and two transverse with respect to the beam, as would be expected from hard scattering of proton constituents.     

Retention of configuration in the opening of 2-arylcyclopropyl bromides by potassium acetate/18-crown-6 in dimethyl sulfoxide

E and Z 2-phenylcyclopropyl bromides react with the title reagents to yield E and Z cinnamyl acetates respectively. No reaction is observed when halide nucleophiles or other aprotic solvents are used suggesting a novel mechanistic role for the acetate ion.