Vera L. Pardini

Electrochemical Oxidation of Thiols to Disulfides

Abstract Disulfides can be easily prepared by electrochemical oxidation of the corresponding thiols in methanol/sodium methoxide solution under constant current conditions.

Anodic cleavage of lignin model dimers in methanol

Abstract The anodic oxidation in methanol of some lignin model compounds, the C17 – C18 compounds ((1) – (5), has been studied to ascertain factors influencing cleavage of Cα  Cβ bonds cf. substitution. Cyclic voltammetric oxidation peak potentials were influenced by structure but not by pH. Preparative-scale electrolyses gave 3,4-dimethoxybenzaldehyde as the major product from compounds (1) – (3), corresponding to cleavage of th Cα  Cβ bonds. In contrast compounds (4) and (5) were not cleaved with significant efficiency. The results are convincingly rationalised in terms of rapid cleavage of the Cα  Cβ bonds in the first-formed radical cations.

Interaction between the carbonyl group and a sulphur atom. Part 9. The relationship between conformation and ground- and excited-state interactions in some α-sulphur-substituted cycloalkanones

The conformations of some α-sulphur-substituted cycloalkanones are estimated approximately from the i.r. spectra. The decrease of the carbonyl stretching frequency in these compounds, by comparison with the corresponding unsubstituted ketones (ΔνCO), is reported and interpreted as due to hyperconjugative σC(2)–S–πCO interaction on the basis of the dependence on the position of C(2)–S bond. Similarly, hyperconjugative interaction in the excited state is proposed to account for the bathochromic shift of the n→π* band, at 300 nm, of the same compounds. The shorter wavelength u.v. absorption band, at 250 nm, is assigned to charge transfer from sulphur to the carbonyl group owing to its dependence on the position of the 3p orbital of sulphur relative to the carbonyl group.

Spectroelectrochemistry and electrocatalytical activity of the bis(2,6-diacetylfurfuryliminepyridine)iron(II) complex

Abstract Reported are the synthesis, spectroelectrochemistry and electrocatalytical properties of the bis(2,6-diacetylfurfuryliminepyridine)iron(II) complex, [Fe(dafipy) 2 ] 2+ . The electrochemical behavior observed for this complex in acetonitrile solutions is typically reversible, exhibiting three characteristic waves at 1.40, −0.86 and −1.12 V vs. she , ascribed to the Fe(III/II) and dafipy 0/−1/−2 redox couples, respectively. The electrocatalytical oxidation of organic substrates, such as N,N -dimethylformamide and 4-substituted-1,2-dimethoxybenzenes, in the presence of the [Fe(dafipy) 2 ] 2+ catalyst proceeds at a lower potential and with great efficiency. The electrocatalytical synthesis of 2,2′-diethyl-4,4′,5,5′-tetra-methoxybiphenyl is discussed.

A Fully Programmable Electronic Coulometer for Charge and Electrolysis Duration.

ABSTRACT A fully programmable, current quantized, electronic coulometer totalizing 6-decades of charge (99,999.9 coulombs) and 6-decades of duration, (99 hours 59 minutes 59 seconds) for electrolysis. On the front panel: two 6-digit 7-segment-LED displays with relevant 12 BCD thumbwheels for monitoring and program setting of charge and duration respectively; charge and time resets and loading-command buttons; current polarity indication; “program-fulfilled”-cutout relay with buzzer. Zero-current detector excludes wrong totalizing due to process interruptions, e.g. electrode cleaning. This coulometer outputs charge and time BCD signals for slave indicators and data processing. It is specially meant for organic electrochemical synthesis. Electrolysis current range: 0.005A to 1.00A of either polarity.

Anodic methoxylation of cinnamate esters

Este trabalho descreve a oxidacao eletroquimica do 4-metoxi-cinamato de metila e de outros esteres metilicos do acido cinâmico di- e tri- metoxilado, em solucao metanolica neutra ou alcalina. Nos estudos eletroquimicos foram empregadas voltametria ciclica, bem como eletrolises preparativas a potencial ou corrente controlados, em celas de um ou dois compartimentos. A influencia de parâmetros tais como densidade de corrente, tipo de cela, material do eletrodo, solvente, concentracao do substrato e base foi investigada para o 4-metoxi-cinamato de metila. Os produtos observados foram resultantes de metoxilacoes nucleares e/ou na cadeia lateral, entretanto com o aumento do numero de metoxilas no anel aromatico foram observados principalmente produtos referentes a metoxilacao no anel aromatico. As estruturas dos produtos tambem dependem do tipo de procedimento empregado no seu isolamento.

The addition of allyltrimethylsilane to cyclic N-acyliminium ions derived from(S)-(+)-mandelic acid and cyclohexyl-based chiral auxiliaries

The TiCl4- promoted addition of allyltrimethylsilane to chiral 5- and 6-membered N-acyliminium ions employing (S)-(+)-mandelic acid, (1R,2S)-trans-2-phenyl-1-cyclohexanol and (1R,2S,5R)-8-phenylmenthol derivatives as chiral auxiliaries occurred with low to moderate diastereoisomeric ratios (1:1-6:1) to afford 2-substituted amides and carbamates in good yields. The best diastereoselection was observed with (1R,2S,5R)-8-phenylmenthol as the chiral auxiliary. The 2-substituted amides and carbamates were converted to the corresponding alkaloids (S)- and (R)-propyl pyrrolidine and coniine with efficient recovery of the chiral auxiliaries.

An Electrochemical Preparation of Methyl Methanethiolsulfonate

Abstract Methyl methanethiolsulfonate is conveniently prepared, in good yields, by electrochemical oxidation of dimethyl disulfide, in aqueous acetonitrile, at constant current.

Electrosynthesis of γ-asarone

Abstract γ-Asarone is synthesised in high yield, and conveniently, by anodic methoxylation of methyl eugenol, at constant current. The method is extremely simple and inexpensive.

Anodic cleavage of carbon–oxygen bonds in diaryl ethers

Diaryl ethers (1), which are model compounds for important linkages in lignins, are cleaved efficiently and conveniently by constant current anodic oxidation in methanol; the bis-acetals (2) are the main products (in 50–80% yield).