Production of 6-<Emphasis Type="Italic">O</Emphasis>-<Emphasis Type="SmallCaps">l</Emphasis>-Ascorbyl Palmitate by Immobilized <Emphasis Type="Italic">Candida antarctica</Emphasis> Lipase B

l-ascorbyl palmitate (ASP) is an oil-soluble derivative of ascorbic acid which is used extensively in food, cosmetics industry, and medical hygiene. Enzymatic synthesis of ascorbyl palmitate in tert-butyl alcohol was carried out using indigenously immobilized lipase preparation PyCal with ascorbic acid and palmitic acid as starting material. The developed batch process under optimized reaction conditions resulted in conversion of 90% with relatively shorter reaction time of 6 h. Continuous process in packed bed reactor gave conversion of 50% with space time yield of 15.46 g/L/h which was found to be higher than the reported literature on enzymatic synthesis of ascorbyl palmitate. The immobilized lipase used in the present work showed good reusability. Characterization of formed ascorbyl palmitate was carried out by FTIR, MS/MS, H¹-NMR, and C¹³-NMR. The enzymatic process resulted in selective synthesis of 6-O-l-ascorbyl palmitate with purity of 98.6% and no side product formation. The use of underivatized starting materials, high space time yield of 15.46 g L^?1 h^?1, high recyclability of catalyst, and no by-product formation make the overall process highly efficient and clean in terms of energy consumption and waste generation, respectively. The optimized reaction parameters for ascorbyl palmitate synthesis in the present study can be used as a useful reference for industrial synthesis of fatty acid esters of ascorbic acid by enzymatic route.     

An Investigation of the Digitized Raman Band Profiles of Aqueous Mg(ClO4)2 - NaSCN Solutions

Abstract

Raman spectra, together with factor analysis and band deconvolution procedure, have been used to study formation of magnesium thiocyanate complexes in aqueous solutions at ambient and elevated temperatures. The total salt concentration in solutions, containing different mole ratio of Mg²⁺ to SCN, varied between 3.4 and 7.5 mol dm^?3. Factor analyses indicated that two linearly independent scattering components in the band envelopes, recorded in the V₁ and v₃ stretching regions of SCN, for all solutions with total salt concentration of 3.4 mol dm^?3. The appearance of a pseudo-isosbestic point in the area normalized spectra supported this result, as well as the baud resolution procedure. The latter revealed the third scattering component in the spectra of solutions with total salt concentration above 3.5 mol dm^?3 Resolved components have been assigned to the free thiocyanate, the 1:1 and 1:2 magnesium thiocyanate complexes. The equilibrium constant K_c of the 1:1 complex is of an order of 10^?1 mol dm^?3.     

Heteroadamantanes and their derivatives. 21. Synthesis of thioureas of the 3,6-diazahomoadamantane series

Unsubstituted and phenyl-substituted thioureas were obtained by the action of benzoyl isothiocyanate and phenyl isothiocyanate on amino-substituted diazahomoadamantanes.For Communication 20 see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 814–817, June, 1993.     

Synthesis and functionalization of poly(ether sulfone)s based on 1,1,1‐tris(4‐hydroxyphenyl)ethane

Branched poly(ether sulfone)s were prepared from 1,1,1‐tris(4‐hydroxyphenyl) ethane and 4,4′‐difluorodiphenyl sulfone (DFDPS) either by polycondensation in dimethyl sulfoxide with the elimination of water or via the silyl method in N‐methylpyrrolidone. With an exact 1/1 stoichiometry, crosslinking was avoidable, but significant fractions of cyclic oligomers and polymers were detected by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry. Furthermore, bridged cycles (bicycles) were detected. For the silyl method, even an excess of DFDPS of 10 mol % did not result in crosslinking. The pendant OH groups were modified by acylation with acetic anhydride, methacrylic anhydride, undecylenoyl chloride, or cinnamoyl chloride. Alkylation was only successful in a one‐pot procedure via the silyl method. Alkylbromide, ethyl bromoacetate, 3‐chloropropionitrile, 4‐nitrobenzyl bromide, and 3,4‐dichlorobenzyl chloride served as alkylating agents. With 1,3‐propane and 1,4‐butane sultone, poly(ether sulfone)s with pendant sulfonate groups were obtained. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2967–2978, 2002     

Heteroadamantanes and their derivatives 26. Synthesis of derivatives of hydroxybenzyldiazahomoadamantane

Summary 1-(4-Hydroxy-3-nitrobenzyl)-3,6-diazahomoadamantan-9-one was obtained by the nitration of hydroxybenzyldiazahomoadamantanone. The behavior of the carbonyl group of this ketone and of its nitro derivative has been studied. The structures of the functional derivatives obtained were confirmed by data of IR, PMR, and mass spectra.For part 25 see [1].M. V. Lomonosov Moscow State Academy of Fine Chemical Technology, Moscow 117571. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 391–394, March, 1995.Original article submitted December 29, 1994.     

Between Ni(mnt)2 and Ni(tfd)2 dithiolene complexes: the unsymmetrical 2-(trifluoromethyl)acrylonitrile-1,2-dithiolate and its nickel complexes

A novel 1,2-dithiolate ligand, that is, the 2-(trifluoromethyl)acrylonitrile-1,2-dithiolate, abbreviated here as tfadt, is prepared from the corresponding cyclic dithiocarbonate. This ligand, substituted with both a CN and a CF(3) group, is compared with the well-known maleonitrile- and bis(trifluoromethyl)ethane-1,2-dithiolates. The preparation, electrochemical properties, and X-ray crystal structures of the square-planar nickel complexes, in both their dianionic diamagnetic [Ni(tfadt)(2)](2)(-) and their monoanionic paramagnetic [Ni(tfadt)(2)](*)(-) forms, are reported, as n-Bu(4)N(+), PPh(4)(+), and (18-crown-6)Na(+) salts, respectively. In the [(18-crown-6)Na](2)[Ni(tfadt)(2)] salt, each CN moiety of the [Ni(tfadt)(2)](2)(-) dianion is coordinated to a (18-crown-6)Na(+) cation through a CN...Na interaction [N...Na = 2.481(3) A], affording an "axle with wheels" model where two MeOH molecules act as axle caps. On the other hand, in [(18-crown-6)Na][Ni(tfadt)(2)], each (18-crown-6)Na(+) cation is coordinated on both sides by the CN groups of two monoanionic [Ni(tfadt)(2)](*)(-) complexes with N...Na(+) distances at 2.434(5) and 2.485(4) A, giving rise to heterobimetallic chains with alternating (18-crown-6)Na(+) and [Ni(tfadt)(2)](*)(-) ions. These two examples demonstrate the attractive ability of the CN moieties in the [Ni(tfadt)(2)](2)(-)(,)(*)(-) complexes to coordinate metallic cationic centers. The paramagnetic salts of the anionic [Ni(tfadt)(2)](*)(-) complex follow Curie-type law in the 2-300 K temperature range, indicating the absence of intermolecular magnetic interactions in the solid state. The complexes are found in their trans form in all crystal structures, while density functional theory calculations establish that both forms have essentially the same energy. A cis-trans interconversion process is observed by variable-temperature NMR on the dianionic [Ni(tfadt)(2)](2)(-) complex with a coalescence temperature T(c) of 260 K and a free energy of activation of 51-53 kJ mol(-)(1).     

Synthesis of trans-(3S,4S)-dibenzyloxycyclopentanone

The 1-cyano-1-thiophenylcyclopentone derivative $\text{1}$, obtained from (R,R)-(+)-tartaric acid, has been converted into a number of derivatives including the important $\text{trans}$-(3S,4S)-dibenzyloxycyclopentanone $\text{2}$ in 45% overall yield.     

Use of medium effects to tune the Delta E(1/2) values of bimetallic and oligometallic compounds

The redox potentials of bis(fulvalene)dinickel, 1, and the tetrakis(ferrocenyl)nickel dithiolene complex 2 have been measured in a variety of nonaqueous electrolytes. The difference in E1/2 values of the two successive one-electron oxidations of 1 (i.e., DeltaE1/2 values) increased from a low of 212 mV in anisole/[NBu4]Cl to a high of 850 mV in CH2Cl2-Na[B(C6H3(CF3)2)4], reflecting an increase of over 1010 in the comproportionation constant (Kcomp = [1+]2/[1][12+]). Six reversible one-electron processes are possible for compound 2, the four oxidations arising from the ferrocenyl substituents, and the two reductions arising from the Ni dithiolene moiety. The E1/2 spreads of the four oxidation waves and the two reduction waves are both highly sensitive to medium effects. For both 1 and 2, the largest DeltaE1/2 values for cationic products are found in solvents of low polarity and donor strength containing electrolyte salts having large anions and small cations. Conversely, the smallest DeltaE1/2 values for anionic products are found under these conditions, culminating in the observation of a single two-electron reduction wave for 2/22- in CH2Cl2-Na[B(C6H3(CF3)2)4]. A combination of solvation and ion-pairing effects must be considered, and may be used to advantage, when using DeltaE1/2 values as a measure of electronic interactions between redox centers in compounds containing two or more electron-transfer sites.     

Covalent modification of graphitic carbon substrates by non-electrochemical methods

New methods for modifying graphitic carbon surfaces without electrochemical assistance, and without the deliberate formation of carbon surface oxygen functionalities, have emerged in the past decade. The approaches rely on spontaneous reactions of aryldiazonium salts, primary amines, ammonia and iodine azide at room temperature, chemical reduction of aryldiazonium salts, reactions of alkenes and alkynes at elevated temperatures and photochemical reactions of alkenes, alkynes, azides and diazirines. This review describes the methodology and scope of these reactions at graphitic carbon materials (excluding carbon nanotubes) and examines mechanistic possibilities and future prospects.