Magali Salas-Reyes

Electrochemical Oxidation of Caffeic and Ferulic Acid Derivatives in Aprotic Medium

O comportamento eletroquimico em funcao da estrutura de uma serie de derivados dos acidos cafeico e ferulico, assim como de seus precursores catecol e guaiacol, eletroquimicamente ativos, foi avaliado por voltametria ciclica. Os resultados revelaram que as condicoes experimentais sao a chave para as mudancas no mecanismo de oxidacao do guaiacol e acido ferulico. A oxidacao eletroquimica dos derivados amida do acido ferulico revelou que o atomo de nitrogenio desempenha um papel importante na derivatizacao da superficie do eletrodo. Alem disso, a atividade sequestradora de radicais dos compostos, avaliada atraves da porcentagem de inibicao do radical 2,2’-difenil-1picril-hidrazila, mostrou uma boa correlacao com os potenciais de oxidacao. We studied the electrochemical behaviour as a function of the structure of a series of caffeic and ferulic acids derivatives as well as their corresponding redox moieties catechol and guaiacol by cyclic voltammetry. Results revealed that the medium is key for changes in the oxidation mechanism of guaiacol and ferulic acid. Electrochemical oxidation of the ferulic acid amide derivatives revealed that the nitrogen atom plays an important role in the derivatization of the electrode surface. In addition, radical scavenging activity of the compounds evaluated through the percentage of inhibition of the 2,2’-diphenyl-1-picrylhidrazyl radical showed a good relationship with the oxidation potentials.

Substituent Effects on 31P NMR Chemical Shifts and 1JP–Se of triarylselenophosphates

The effect of electron-withdrawing (EW) and electron-releasing (ER) substituents on the 31P NMR chemical shifts and the structural parameters of a series of tris-(p-X-aryl)selenophosphates is reported in this article. Similarly to O-aryl phosphates and O-aryl thiophosphates, EW groups attached to aromatic rings induce a shielding effect on the 31P NMR signal. After a detailed experimental and theoretical analysis, we confirmed that the selenium atom is the main part responsible for the charge density transfer toward phosphorus through a back-bonding effect. The obtained 1JP-Se values for the complete series agree with this observation. Supplemental materials are available for this article. Go to the publishers online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.

Crystal structure of eq-2-p-trifluoromethylphenoxy-2-borane-cis-4,6- dimethyl-1,3,2a3-dioxaphosphorinane, C12H17BF3O3P

C12H17BF3O3P, monoclinic, P12i/cl (no. 14), a = 7.0311(6) Â, b = 23.087(2) Â, c = 9.5486(9) k,ß = 92.612(2)°, V = 1548.4 Â, Ζ = 4, Rgt(F) = 0.076, wR^F) = 0.163, Γ =293 Κ. Source of material The title compound was obtained via a two-step synthetic route. 2-chloro-4,6-dimethyl-l,3,2A-dioxaphosphorinane [1] (1.00 g, 5.9 mmol) was reacted with 4-(trifluoromethyl)phenol (0.96 g, 5.9 mmol) and Et3N (0.82 mL, 5.9 mmol) in dry toluene to obtain eg-2-p-trifluoromethylphenoxy cis-4,6-dimethyl-l,3,2A-dioxaphosphorinane as intermediate. The resultant triethylammonium chloride was separated using a filter-tipped cannula. Immediately after filtration, a 1M solution of BH3-THF (7.0 mL) was added to give the desired title compound. The crude product was purified by column chromatography. Crystals suitable for X-ray diffraction were grown from a mixture of hexane and ethyl acetate. Experimental details The structure shows disorder in the trifluoromethyl moiety. The refinement of the disorder converged at the 0.42 : 0.58 ratio. DFIX, SIMU, DELU and ISOR instructions have been used to restraint C—F bond lengths and the anisotropic displacement parameters [2], The B-Η hydrogen atoms were localized by difference Fourier maps, their coordinates have been refined freely, with i/iso(H) = 1.5 t/iso(B). Discussion It is well known that stereoelectronic interactions play an important role in the conformational behaviour of 1,3,2-dioxaphosphorinanes [3], Thus, when the substituent at the phosphorus atom is an electron withdrawing (EW) group, it prefers to occupy the axial position. This behaviour has been attributed to the attractive interaction ηπΟ-σ p-subtìtuent, which takes place only in the axial isomer. Additionally, these compounds are very flexible systems and it has been reported previously that they can adopt more than one conformation, even in the solid state [4]. Despite their importance in synthesis as catalysts [5] and their capacity to stabilize reactive intermediates [6], the conformational behaviour of borane adducts of phosphorus-containing heterocycles has received less attention when compared to their phosphoryl or thiophosphoryl analogues. The anancomeric title compound has an EW substituent at the phosphorus atom that occupies the equatorial position, and was prepared in order to analyse its conformation in the solid state. The dioxaphosphorinane ring adopts a chair conformation with an evident flattening of the 0 1 P 0 3 fragment (<»P-03-C4-C5 = 51.08° and <oP-01-C6-C5 = -^2.56°). This ΟΡΟ ring flattening has been found also in analogous phosphates and thiophosphates [7]. The Ρ—01 and Ρ—03 bond lengths are practically identical [1.568 (3) Â and 1.570 (3) Â], and are veiy similar to the experimental Ρ—O bond lengths of equatorially substituted dioxaphos-phorinanes [4,7]. In the packing, a π-π parallel stacking interaction with an interplanar distance of 3.58 Â is observed. The centroid··-centroid distance of 3.94 Â and the angle formed between the ring normal and the centroid vector (24.8°) corresponds to a horizontal displacement of 1.65 Â, thus indicating a weak interaction [8]. Table 1. Data collection and handling.