Paulo J. S. Moran

Regioselectivity of the nitration of phenol by acetyl nitrate adsorbed on silica gel

Abstract The reaction of phenol with acetyl nitrate in chloroform gives nitrophenol with an ortho/para ratio of 1.8. This ratio increase to 13.3 when the reaction was carried out with acetyl nitrate pre-adsorbed on dry silica gel. Silica may be acting as a template to bring phenol close to acetyl nitrate by hydrogen bonds forming a ternary complex, which undergoes a six-center rearrangement to o-nitrophenol. The formation of this ternary complex is evaluated by ab initio molecular orbital calculation.

Effect of immobilized cells in calcium alginate beads in alcoholic fermentation

Saccharomyces cerevisiae cells were immobilized in calcium alginate and chitosan-covered calcium alginate beads and studied in the fermentation of glucose and sucrose for ethanol production. The batch fermentations were carried out in an orbital shaker and assessed by monitoring the concentration of substrate and product with HPLC. Cell immobilization in calcium alginate beads and chitosan-covered calcium alginate beads allowed reuse of the beads in eight sequential fermentation cycles of 10 h each. The final concentration of ethanol using free cells was 40 g L-1 and the yields using glucose and sucrose as carbon sources were 78% and 74.3%, respectively. For immobilized cells in calcium alginate beads, the final ethanol concentration from glucose was 32.9 ± 1.7 g L-1 with a 64.5 ± 3.4% yield, while the final ethanol concentration from sucrose was 33.5 ± 4.6 g L-1 with a 64.5 ± 8.6% yield. For immobilized cells in chitosan-covered calcium alginate beads, the ethanol concentration from glucose was 30.7 ± 1.4 g L-1 with a 61.1 ± 2.8% yield, while the final ethanol concentration from sucrose was 31.8 ± 6.9 g L-1 with a 62.1 ± 12.8% yield. The immobilized cells allowed eight 10 h sequential reuse cycles to be carried out with stable final ethanol concentrations. In addition, there was no need to use antibiotics and no contamination was observed. After the eighth cycle, there was a significant rupture of the beads making them inappropriate for reuse.

Acylsilanes and their applications in organic chemistry

Current studies concerning the use of acylsilanes in a variety of organic synthetic routes and the improved methodologies of their preparation have turned organosilanes into important reagents for organic chemistry. This review discusses the recent employment of acylsilanes in organic synthesis and also effective methods for their preparation.

Baker's yeast reduction of α-haloacetophenones

Abstract The fermenting bakers yeast reductions of α-haloacetophenones were carried out by three different procedures. While the α-fluoro-, α-chloro- and α-bromoacetophenones gave the correspondent (−)-halohydrins, the reduction of α-iodoacetophenone gave acetophenone and (−)-1-phenylethanol.

Continuous fermentation of sugar cane syrup using immobilized yeast cells

Several strains of Saccharomyces sp. and commercial Bakers yeast were immobilized by adhesion onto chrysotile, a fibrous magnesium silicate (Mg6Si4O10 (OH)8). The activity of the cells is higher when immobilized, mainly for fermentation of 30 to 50% w/v glucose solutions. In the medium containing 30% w/v glucose, the initial fermentation rate increased 1.2-2.5 times. Yields were in the range of 80.4 to 97.3% for the immobilized cells and 72.7 to 84.5% for the free cells. A packed bed reactor for continuous fermentation was set up using one of the tested strains immobilized onto chrysotile. An average productivity of 20 to 25 g.l(-1).h(-1) was obtained in the first 20 d, and an average of 16 g.l(-1).h(-1) was obtained after 50 d of operation.

Highly efficient extractive biocatalysis in the asymmetric reduction of an acyclic enone by the yeast Pichia stipitis

Abstract A concise highly chemo- and enantioselective preparation of ( S )-2-ethyl-1-phenylprop-2-en-1-ol 6 (65% yield, >99% e.e.) via extractive biocatalysis by the yeast Pichia stipitis CCT 2617-mediated reduction of 2-ethyl-1-phenylprop-2-en-1-one 5 adsorbed on Amberlite™ XAD-7 is reported.

Continuous process for large-scale preparation of chiral alcohols with baker's yeast immobilized on chrysotile fibers

Abstract Bioreductions of prochiral ketones in a continuous process were carried out in a Packed-bed-reactor with bakers yeast ( Saccharomyces cerevisiae ) immobilized on chrysotile fibers (IMBY). The performance of the reactor was observed for 30 days, under a constant dilution rate of 1.7×10 −1 h −1 using ethylbenzoylformate as substrate. The steady state showed 2.9×10 −2 g l −1 h −1 of productivity, 50% chemical yield, and 90% ee (enantiometric excess). Using ethylacetoacetate at the same dilution rate for 8 days, the steady state showed 65% chemical yield and 95% ee. No significant change on the IMBY integrity was observed. The results show that chrysotile is an excellent carrier for immobilization of bakers yeast (BY) cells to be used in the continuous process of bioreduction

Baker's yeast reduction of α-methyleneketones

Abstract The bioreduction of α-methyleneketones, R 1 C(O)C(CH 2 )R 2 (R 1 =Me, Et, Pr, iso- Bu, Ph, CH 2 CH 2 Ph; R 2 =Cl, Me, Et, n- Pr, iso- Pr, n- Bu, n- C 6 H 13 , Ph, CH 2 Ph), was mediated by bakers yeast ( Saccharomyces cerevisiae ) to obtain the corresponding α-methylketones. The R 1 and R 2 groups had a significant influence on the rate and enantioselectivity of the reductions. The rate of CC bond reduction was higher than that of CO bond reduction. Only α-methyleneketones having R 1 =Me yielded α-methylketones in high enantioselectivity with e.e.s of 88–99%.

Aspergillus terreus CCT 3320 immobilized on chrysotile or cellulose/TiO2 for sulfide oxidation

Abstract The increasing interest in applying chiral sulfoxides in asymmetric syntheses requires their preparation on a large scale, which can be obtained by enantioselective enzymatic oxidation of sulfides. We have focused on the preparation of sulfoxides 1 – 6 using Aspergillus terreus CCT 3320 cells to oxidize the precursor sulfides. These biotransformations lead to enantiomeric excesses (ee) better than 95%. In order to improve the biocatalytic process, the cells were immobilized on two supports, chrysotile and on cellulose/TiO 2 . The immobilized cells showed a similar biocatalytic behavior in the conversion rate and in the sulfoxide enantiomeric excess. Scanning electron microscopy (SEM) micrographs show that the cells are intertwined with the fibers of both supports, allowing fast separation from the reaction media and easing the biocatalyst reuse. Supported cells stored for at least 3 months showed no loss of activity.

Synthesis of acylsilanes via oxidative hydrolysis of 2-silyl-1,3-dithianes mediated by N-bromosuccinimide

Abstract The oxidative method for the hydrolysis of 1,3-dithianes was applied to 2-silyl-1,3-dithianes using N -bromosuccinimide providing acylsilanes with good yields under a short reaction period. The oxidation of aroylsilanes to carboxylic acid was prevented by the addition of bases and the lowering of the reaction temperature.