Direct synthesis and applications of solid silylzinc reagents

The increased synthetic utility of organosilanes has motivated researchers to develop milder and more practical synthetic methods. Silylzinc reagents, which are typically the most functional group tolerant, are notoriously difficult to synthesize because they are obtained by a pyrophoric reaction of silyllithium, particularly Me₃SiLi which is itself prepared by the reaction of MeLi and disilane. Furthermore, the dissolved LiCl in silylzinc may have a detrimental effect. A synthetic method that can avoid silyllithium and involves a direct synthesis of silylzinc reagents from silyl halides is arguably the simplest and most economical strategy. We describe, for the first time, the direct synthesis of PhMe₂SiZnI and Me₃SiZnI reagents by employing a coordinating TMEDA ligand, as well as single crystal XRD structures. Importantly, they can be obtained as solids and stored for longer periods at 4 °C. We also demonstrate their significance in cross-coupling of various free alkyl/aryl/alkenyl carboxylic acids with broader functional group tolerance and API derivatives. The general applicability and efficiency of solid Me₃SiZnI are shown in a wide variety of reactions including alkylation, arylation, allylation, 1,4-addition, acylation and more.

The first direct synthesis of PhMe₂SiZnI and Me₃SiZnI reagents from silyl iodides is described. They can be obtained as solids and stored at 4 °C for extended periods. The versatility of solid Me₃SiZnI is demonstrated in a variety of reactions.     

Mössbauer spectroscopy of corrosion products of mild steel due to microbiologically influenced corrosion

Corrosion products of mild steel exposed to four different cultures of sulfur reducing bacteria (SRB) grown in a synthetic medium have been studied by transmission Mössbauer spectroscopy (TMS). Cultures of SRB studied are two hydrogenase positive strains,Desulfovibrio desulfuricans (DD) andDesulfovibrio vulgaris (DV) and two hydrogenase negative strainsDesulfotomaculum orientis orientis (DO) andDesulfotomaculum nigrificans (DN). The corrosion products generated on the coupons as well as in the broth were studied. In all the cases, the corrosion products removed from coupons showed the presence of green rust 2 (GR2), ferrous sulfides, γ-FeOOH and superparamagnetic (SPM) α-FeOOH in different proportions. The corrosion products from the broth showed a symmetrical central doublet, which indicates the presence of γ-FeOOH and SPM α-FeOOH along with ferrous sulfides. The corrosion products from coupons suspended in sewage water also showed the presence of GR 2 and ferrous sulfides together with oxyhydroxides. FTIR spectrum supports the presence of these phases in corrosion products. The formation of GR 2 on coupons seems to be the first step for the SRB induced corrosion. The corrosion rate has been found in the order of DO>DN>DV>DD.     

Copolyesters based on poly(butylene terephthalate)s containing cyclohexyl groups: synthesis,structure and crystallization

Poly(butylene terephthalate-co-cyclohexylene dimethylene terephthalate) copolymers PBTCT, were synthesized by melt condensation with compositions ranging from 94/08 to 23/77. ¹³C NMR spectroscopy was used to study the microstructure of the copolyesters and was found to be completely random. The melting temperature, crystallization temperature on cooling, enthalpy of melting and crystallization followed an eutectic behaviour. Thermal and x-ray diffraction studies indicated that the copolyesters in all composition could crystallize. The XRD studies further indicated that PBT rich copolyesters in the range 75 to 100% BT, crystallized in the PBT lattice while the copolyesters rich in PCT having 38 to 100% CT, crystallized in the PCT lattice.     

Determination of skin friction in strong pressure-gradient equilibrium and near-equilibrium turbulent boundary layers

The conventional Clauser-chart method for determination of local skin friction in zero or weak pressure-gradient turbulent boundary layer flows fails entirely in strong pressure-gradient situations. This failure occurs due to the large departure of the mean velocity profile from the universal logarithmic law upon which the conventional Clauser-chart method is based. It is possible to extend this method, even for strong pressure-gradient situations involving equilibrium or near-equilibrium turbulent boundary layers by making use of the so-called non-universal logarithmic laws. These non-universal log laws depend on the local strength of the pressure gradient and may be regarded as perturbations of the universal log law. The present paper shows that the modified Clauser-chart method, so developed, yields quite satisfactory results in terms of estimation of local skin friction in strongly accelerated or retarded equilibrium and near-equilibrium turbulent boundary layers that are not very close to relaminarization or separation.     

On the Occurrence of Portevin–Le Châtelier Instabilities in Ultrafine-Grained 5083 Aluminum Alloys

The Portevin–Le Châtelier (PLC) instability is commonly observed in Al–Mg alloys and is manifested in serrated flow within the stress–strain response. We investigate the persistence of this instability with reduction in grain size by studying an ultrafine-grained (ufg) aluminum alloy (Al5083) and a conventional grain size Al5083. Micro-scale tensile tests combined with digital image correlation (DIC) reveal strength anisotropy and heterogeneity of the deformation in the three material directions (extrusion, rolled, and transverse). For the same applied displacement rate, the PLC effect in ufg-Al5083 is observed only over a small strain range immediately following the yield, while the coarse-grained Al5083 exhibits serrated flow over nearly the entire plastic strain range. These observations are explained using the stability analysis of Hähner (Acta Mater 45:3695–3707, 1997), and implications for nanocrystalline (nc) alloys are discussed.     

First sonochemical,simple and solvent-free synthesis of chiral tert-butanesulfinimines using silica supported p-toluenesulfonic acid

A solvent-free, versatile procedure has been developed for the effective synthesis of tert-butanesulfinylimines of a variety of aldehydes using chiral tert-butanesulfinamides under green, sonochemical conditions. This method utilizes silica supported p-toluenesulfonic acid (pTSA·SiO₂) as an efficient, safer and inexpensive catalyst under aerobic conditions. The practicable simplicity, easy preparation of the catalyst from readily available substances, high substrate scope, excellent yields of products in short reaction times and environmentally benign (solvent-free sonochemical) conditions are the exceptional assets of this finding.     

New tetranuclear Cu(II) complexes: synthesis, structure, and magnetic properties

The synthesis, structure, and magnetic properties of two new tetranuclear Cu(II) complexes containing N,N,N',N'-tetraethylpyridine-2,6-dithiocarboxamide (S-dept) of formula [Cu(2)Cl(2)(mu-S-dept)(2)][Cu(2)Cl(4)(mu-Cl)(2)] (1) and [Cu(2)(mu-Cl)(2)(S-dept)(2)][CuCl(3)(EtOH)](2) (2) are reported. Their X-ray crystal structures reveal that the complexes are composed of anionic and cationic dimers, that in both cases contain the metal centers which interact via Coulombic and/or hydrogen bonding interactions. In both cases, the Cu centers in the anionic moieties adopt a slightly distorted tetrahedral geometry whereas for the cationic moieties they adopt a square-pyramidal type of geometry. Magnetic susceptibility data show that compounds 1 and 2 present an overall antiferromagnetic behavior arising from the contribution of both anionic and cationic moieties. For 1, the best fit obtained gave J(1) = -2.62 +/- 0.19 cm(-1), J(2) = -19.54 +/- 0.47 cm(-1), and g(2) = 2.164 +/- 0.004 cm(-1) (R = 8.28 x 10(-5)) whereas for 2 it gave J(1) = 4.48 +/- 2.73 cm(-1), g(1) = 2.20 +/- 0.03, J(2) = -11.26 +/- 2.01 cm(-1), and g(2) = 2.10 +/- 0.03 (R = 1.15 x 10(-4)). The nature of the superexchange pathways in 1 and 2 is discussed on the basis of structural, magnetic, and molecular orbital considerations. Theoretical calculations are performed at the extended Huckel level in order to obtain their molecular orbitals and energies using their crystallographic data.     

Higher-alcohols biorefinery

The concept of a biorefinery for higher-alcohol production is to integrate ethanol and methanol formation via fermentation and biomass gasification, respectively, with, conversion of these simple alcohol intermediates into higher alcohols via the Guerbet reaction. 1-Butanol results from the selfcondensation of ethanol in this multistep reaction occurring on a single catalytic bed. Combining methanol with ethanol gives a mixture of propanol, isobutanol, and 2-methyl-1-butanol. All of these higher alcohols are usefulas solvents, chemical intermediates, and fuel additives and, consequently, have higher market values than the simple alcohol intermediates. Several new catalysts for the condensation of ethanol and alcohol mixtures to higher alcohols were designed and tested under a variety of conditions. Reactions of methanol ethanol mixtures gave as high as 100% conversion of the ethanol to form high yields of isobutanol with smaller amounts of 1-propanol, the amounts in the mixture depending on the starting mixture. The most successful catalysts are multifunctional with basic and hydrogen transfer components.     

Influence of solvent and substituent on excited state characteristics of laser grade coumarin dyes

Absorption and fluorescence emission of 4 and 7 substituted coumarins viz. C 440, C 490, C 485 and C 311 have been studied in various polar and non-polar organic solvents. These coumarin dyes are substituted with alkyl, amine and fluorine groups at 4- and 7-positions. They give different absorption and emission spectra in different solvents. The study leads to a possible assignment of energy level scheme for such coumarins including the effect on ground state and excited state dipole moments due to substitutions. Excited state dipole moments of these dyes are calculated by solvetochromic data experimentally and theoretically these are calculated by PM 3 method. The dipole moments in excited state, for all molecules investigated here, are higher than the corresponding values in the ground state. The increase in dipole moment has been explained in terms of the nature of excited state and resonance structure.     

Novel Synthesis of 1,2,3,4-Tetrahydropyrazino[1,2-a]indoles

Condensation of 2-(3-methyl-1H-indol-1-yl)ethylamine (7) with benzotriazole and formaldehyde gave 2-(1H-1,2,3-benzotriazol-1-ylmethyl)-10-methyl-1,2,3,4-tetrahydropyrazino[1,2-a]indole (8) in 96% yield. Nucleophilic substitutions of the benzotriazolyl group in 8 with NaBH(4), NaCN, triethyl phosphite, allylsilanes, silyl enol ether and Grignard reagents afforded novel 10-methyl-1,2,3,4-tetrahydropyrazino[1,2-a]indoles 9a-i in 78-95% yields.