Simon J. Kitchin

Effects of fluorination on the properties of organic pigments

The solid state properties of two fluorinated pigments are compared with their unfluorinated analogues and the influence of fluoro substitution upon the solid state properties is discussed. The effect of fluorination was examined by a range of techniques including UV/visible spectroscopy, solid state NMR spectroscopy and powder X-ray diffraction. Fluorination modified the crystal packing of the molecules and subsequently altered the pigmentary performance of the compounds. In both cases fluorination gave rise to compounds with poorer fastness properties.

Towards molecular sieve inorganic catalysts that are akin to enzymes: studies of a selective cyclo-dimerization over ferrierite at ambient temperature

The solid-acid (Brønsted)-catalyzed cyclo-dimerization of 3-hydroxy-3-methylbutan-2-one (HMB) over a synthetic ferrierite molecular sieve is reported. HMB is a stable liquid at ambient temperatures but in acidic solutions it readily undergoes reaction to generate a variety of products. However, in the acidic molecular sieve catalyst studied here, only one product – the cyclic dimer (proven by in situ solid state 13C NMR and other evidence) – is observed, together with some unreacted HMB. A plausible, proton-catalyzed mechanism is proposed, and prompts comparison between the cyclo-dimerization of HMB within ferrierite and the mode of action of certain enzymes.

Rotary resonance recoupling of 13C−1H dipolar interactions in magic angle spinning 13C NMR of dynamic solids

Abstract Rotary resonance recoupling of heteronuclear 13 C − 1 H dipolar interactions in magic angle spinning solid state 13 C NMR spectra (recorded under conditions of 1 H decoupling at frequency ν 1 and magic angle spinning at frequency ν r ) has been studied for three examples of molecular solids (adamantane, ferrocene and hexamethylbenzene) in which substantial molecular motion is known to occur. It is shown that when rotary resonance conditions are satisfied (i.e. ν 1/ ν r = n , for n =1 or 2), the recoupling can lead to motionally averaged Pake-like powder patterns from which information on 13 C − 1 H internuclear distances and/or molecular motion can be derived.

Topotactic synthesis of α-zirconium phenylphosphonate from α-zirconium phosphate

α-Zirconium phenylphosphonate has been synthesised by a reaction between α-zirconium phosphate and molten phenylphosphonic acid. The reaction produces a physical mixture of the ‘pure’ phases of α-zirconium phenylphosphonate and α-zirconium phosphate, with the ratio dependent on the ratio of phenylphosphonic acid to α-zirconium phosphate in the synthesis mixture. Detailed characterization of the reaction products has been carried out by powder X-ray diffraction, high-resolution solid-state 31P NMR spectroscopy, thermogravimetric analysis and FT-IR spectroscopy, and by considering experiments involving the selective intercalation of n-butylamine.

Porous poly(D,L-lactide) and poly(D,L-lactide-co-glycolide) produced by thermal salt elimination from halogenocarboxylates

Poly(D,L-lactide) has been obtained by thermal elimination of alkali chloride from alkali 2-chloropropionates. Preparative studies and differential scanning calorimetry (DSC) have shown that while the sodium and potassium compounds undergo a clean polymerisation, the lithium analogues decompose on heating without polymerisation. The energetics of the polymerisation reaction have also been investigated by determining the enthalpies of formation of sodium and lithium (S)-2-chloropropionates (from reaction-solution calorimetry), and the enthalpies of formation of poly(L-lactide) and poly(D,L-lactide) (from micro combustion calorimetry). The results suggest that the polymerisation process is thermodynamically favourable for the sodium compounds but not for the lithium compounds, in good agreement with the experimental observations. Copolyesters of glycolic acid (polyglycolide) and lactic acid (polylactide) have been prepared by thermal reaction of crystal mixtures of sodium or potassium chloroacetates and sodium or potassium 2-chloropropionates, which were obtained by co-precipitation of the precursor compounds from methanol solutions. The crystal mixtures and reaction products have been characterised by a number of techniques, including solid state NMR spectroscopy and X-ray powder diffraction. For high contents of glycolide, the reaction occurred entirely in the solid state, whereas for cases with more than 10 mol% lactide, a melt is formed which solidifies on cooling to room temperature. The products are lactide-terminated block copolymers with typical chain lengths of 40 monomer units. Due to the solvent-free nature of the synthesis, all polymers can be obtained with microporous morphology.