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Palladium(II) compounds dissolved in 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMI·BF4) ionic liquid are shown to be able to catalyze the hydrodimerization of 1,3-butadiene. In most of the cases, only the 1,3-butadiene dimer 1,3,6-octatriene and the telomer octa-2,7-dien-1-ol have been obtained. The products' selectivity and catalytic activity depend on the reaction conditions. 1,3-Butadiene conversion up to 28%, a turnover frequency (TOF) of 118 h-1, and a selectivity of 94% on telomer were achieved with (BMI)2PdCl4 dissolved in BMI·BF4. The 1,3-butadiene conversion and TOF were significantly increased to 49% and 204 h-1, respectively, by a 5-atm pressure of carbon dioxide. The reactions were performed under homogeneous conditions at 70 °C. However, at temperatures below 5 °C, a two-phase system is formed and the products are easily removed from the reaction mixture by simple decanting. The recovered ionic catalyst solution can be reused several times without any significant changes in the catalytic performance. The structure of the new catalyst precursor (BMI)2PdCl4 has been determined by X-ray diffraction analysis.

The crystal structure of 1-nbutyl-3-methylimidazolium tetraphenylborate molten salt (1) shows C-H ± p interactions between the hydrogens of the imidazolium cation and the phenyl rings of the tetraphenylborate anion. The imidazolium ring is surrounded by three tetraphenylborate anions that are connected with the same cation by C-H ± p (phenyl rings) interactions. The nearest inter-ion interaction is found between the N-CH-N proton of the cation and the B-phenyl centroid (2.349 ) with a nearly T-shaped geometry. The inter-ionic solution structure of 1 has been investigated by the detection of inter-ionic contacts in 1 H NOESY NMR spectra between the protons of the cation and the anion. The 1 H-NMR spectra of molten salt 1 is almost inde-pendent of its concentration in [D 6 ]DMSO solution, the imidazolium proton chemical shifts are in the expected region and there are no observable NOE effects between the protons of the cation with those of the anion, indicating that 1 behaves in [D 6 ]DMSO as a solvent-separated ion pair. In CDCl 3 the 1 H-NMR spectra of 1 are concentration dependent and all the imidazolium protons are shielded as compared with those observed in [D 6 ]DMSO. Moreover, the 1 H NOESY NMR spectra show all the peaks affected by the interaction between the protons of the imidazolium cation and those of the anion, indicating that in CDCl 3 1 possesses a contact ion pair structure. The NCHN proton of the cation exhibits the greatest shielding (up to À 4.5 ppm), an indication of the existence of C-H ± p interactions, even in solution. The calculated distance of this proton to the phenyl centroid is 2.3 for a C-H ± p angle of 1808. The apparent volumes for the cation and anion, calculated from the measured 13 C-NMR relaxation times, increase from 38 and 140 3 in [D 6 ]DMSO to 360 and 600 3 in CDCl 3 , respectively; this indicates the formation of floating aggregates of the type (1) n in CDCl 3 via weak hydrogen bonds, with increasing concentration.

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This is the first report of in situ SER spectra of chemical species adsorbed on a Ag/room temperature ionic liquid (RTIL) interface. We have investigated the dependence of the SERS intensity of the RTIL derived from 1-n-butyl-3-methylimidazolium hexafluorophosfate (BMIPF6) adsorbed on a silver electrode. It has been shown that the BMI+ adsorbs on the silver electrode for potentials more negative than -0.4 V vs a Pt quasireference electrode (PQRE). In the -0.4 to -1.0 V potential range the SER spectra are similar to the Raman spectrum of the RTIL BMIPF6. At potentials more negative than -1.0 V some imidazolium ring vibrational modes and N-CH3 vibrations are enhanced, suggesting that the imidazolium ring is parallel to the surface and for potentials <-2.8 V the BMI+ is reduced to the BMI carbene. The potential dependence of the SERS intensities of Py adsorbed on a silver electrode in BMIPF6 has also been investigated. The results have shown that at potentials less negative than -0.8 V (vs PQRE) Py adsorbs at an end-on configuration forming an Ag-N bond. In the -0.9 to -1.4 V potential range Py molecules lie flat on the electrode surface and at potentials <-1.4 V Py is replaced by the BMI+. The electrochemical and SERS results have shown that Py has the effect of changing the oxidation of silver in that medium as well as the reduction of BMI+ to the BMI carbene. In the presence of Py the BMI+ reduction is observed at potentials near -2.4 V. The Ag electrode has presented SERS activity from 0.0 to -3.0 V.

Recebido em 7/4/06; aceito em 3/7/06; publicado na web em 26/3/07 TRANSFORMATION OF TRIGLYCERIDES INTO FUELS, POLYMERS AND CHEMICALS: SOME APPLICATIONS OF CATALYSIS IN OLEOCHEMISTRY. The use of biomass as raw-material for obtaining chemicals, polymers and fuels is emerging as a clever alternative solution for the increasing energy demand, environmental awareness and petroleum shortage. In this work, some attempts in order to develop catalytic systems suitable for triglyceride transformation into fuels, polymers and intermediates are reviewed.Keywords: oleochemistry; catalysis; biofuels. INTRODUÇÃOHistoricamente a biomassa foi largamente empregada como fonte de obtenção de diversos materiais, tais como fibras, polímeros e combustíveis, e este interesse pode ser atribuído ao seu caráter renovável e sua ampla disponibilidade 1 . Com a expansão da indús-tria do petróleo, a biomassa perdeu sua importância devido à obtenção e desenvolvimento de materiais com propriedades diferenciadas, a custos competitivos 1,2 . Cabe salientar que em alguns segmentos, a biomassa manteve sua posição em razão da sua natureza renovável, ampla disponibilidade, biodegradabilidade ou baixo custo, como no caso das fibras de algodão e lã, da borracha natural, do etanol combustível e das tintas à base de resinas alquídicas. No entanto, o constante aumento na demanda por fontes de energia, a ampliação da consciência ecológica e o esgotamento das reservas de petróleo de fácil extração, aliado a um possível desenvolvimento econômico-social, têm incentivado pesquisas no sentido de desenvolver novos insumos básicos, de caráter renovável, para diversas áreas de interesse industrial 3,4 . Neste contexto, os óleos e as gorduras animais e vegetais (triglicerídeos), in natura ou modificados, têm tido um papel importante em muitos segmentos, tais como materiais poliméricos, lubrificantes, biocombustíveis, revestimentos, adesivos estruturais, entre outros.Devido às diferentes funcionalidades presentes em sua estrutura química (Esquema 1), os triglicerídeos, que são derivados de ácidos graxos, exibem uma grande versatilidade reacional 5 . Este potencial químico pode ser aproveitado para preparação de vários materiais com inúmeras aplicações comerciais, sendo que muitos dos processos químicos de transformação dos triglicerídeos ocorrem na presença de espécies químicas em quantidades catalíticas e, em muitos casos, quasi-estequiométricas. Estas espécies, por não estarem associadas ao produto final, são consideradas como catalisadores.O objetivo deste trabalho é apresentar uma revisão bibliográfi-ca de alguns processos de transformação de óleos vegetais mediados por catalisadores. Não se pretende aqui abranger toda a ampla contribuição da catálise para a oleoquímica, mas abordar os principais aspectos que envolvem o uso de catalisadores, mesmo quando empregados em teores não-catalíticos, em alguns processos de grande interesse da área, tais como aqueles envolvendo a obtenção de biocombustíveis, insumos químicos e macromoléculas. BIOCOMBUSTÍVEISO uso de óleos...

BiocomBustíveis a partir de óleos e gorduras: desafios tecnológicos para viaBilizá-los paulo a. z. suarez*, andré l. f. santos, Juliana p. rodrigues e melquizedeque B. alves Instituto de Química, Universidade de Brasília, CP 4478, Brasil Recebido em 28/1/09; aceito em 3/3/09; publicado na web em 17/3/09 OILS AND FATS BASED BIOFUELS: TECHNOLOGICAL CHALENDGES. Periodically, during petroleum shortage, fatty acids and their derivatives have been used as alternative fuels to those derived from petroleum. Different approaches have been proposed, including the use of neat fats and oils or their derivatives. Indeed, the utilization of biodiesel produced by alcoholysis of triacilglycerides or esterification of fatty acids, or hydrocarbons obtained from cracking of fatty materials were studied and used in several countries. Increasing concerns about energy security and climate changes have lead several countries, including Brazil, to start up biofuels programs. Different technologies are currently being developed in order to produce biofuels with economical feasibility. In this work are discussed alternative fatty raw-materials and processing technologies that are currently being studied in order to produce fuels suitable to sustainable substitute diesel fuel.