Laura I. Rossi

An efficient and selective aerobic oxidation of sulfides to sulfoxides catalyzed by Fe(NO3)3–FeBr3

Abstract The binary system Fe(NO 3 ) 3 –FeBr 3 is a very efficient catalyst for the selective air-oxidation of sulfides to sulfoxides. Since the oxidation is selective, it may be applied to any type of dialkyl and alkyl aryl sulfide, as well as to substrates of biological interest. It develops in mild conditions, giving a high yield in the presence of different functional groups on the sulfide. Other binary systems such as Fe(NO 3 ) 3 –FeBr 2 and Cu(NO 3 ) 2 –CuBr 2 are also effective catalysts for sulfoxidation. In contrast to previous oxygenation methods, this oxidation requires neither an aldehyde nor a transition metal complex.

Green synthesis of dimethyl isosorbide.

In the last twenty years, new categories of solvents have been investigated in order to deal with safety and environmental issues; that is, water, supercritical fluids, ionic liquids, solvents derived from CO2 [1b, 4] or from renewables. The advantage of using solvents derived from renewables is that natural products are present in large amounts, although only a small fraction (ca. 4 %) is used for this purpose. d-sorbitol is a good example of biofeedstock and has several applications in food and non-food industries. Besides, its cyclic derivate, isosorbide, is widely used in the pharmaceutical and hygiene industries. The methyl derivative of isosorbide, dimethyl isosorbide (DMI), is also extensively used in cosmetics and as a thinning agent. Furthermore, due to its renewable starting materials and high boiling point (246 8C), DMI is also a suitable substitute of the more toxic currently used solvents, such as dimethylsulfoxide (DMSO), dimethylformamide (DMF), and dimethylacetamide (DMAc). However, currently DMI is synthesized by common methylation reactions, which employ dimethyl sulfate (DMS) or methyl halides. Herein, it is reported an improved green synthesis of DMI by reaction of isosorbide with dimethyl carbonate (DMC) as reagent and solvent, in the presence of a base at reflux temperature of 90 8C. (Scheme 1). DMC, nowadays produced by a clean and halogen-free process, is an environmentally benign substitute of phosgene, DMS, and methyl halides and it is a well-known nontoxic solvent and reagent. 10] In general DMC, as a methylating agent (bimolecular, base-catalyzed, alkyl cleavage, nucleophilic substitution, BAl2, mechanism) [4c] requires temperatures higher than 150 8C in the presence of a base. However, we previously reported that under similar conditions the reaction of hard alkoxides and DMC gave exclusively the transesterified methylcarbonates derivatives (via BAc2 mechanism), also at high temperatures. On the contrary, other softer nucleophiles such as anilines, phenols and methylene-active compounds were easily methylated by DMC via a BAl2 mechanism. [4, 12] Methyl ethers of primary alcohols can be obtained through two steps: a BAc2 transesterification followed by the decarboxylation of the resulting methylcarbonate. However, methylation of secondary alcohols was never obtained quantitatively due to the formation of elimination products. On the other hand, this is not the case in the present work; the secondary hydroxyls groups of isosorbide are efficiently methylated at reflux temperature (90 8C) by reaction with DMC in the presence of a range of bases (Table 1). This is quite surprising, especially in consideration of all the possible products that could be formed by reacting isosorbide with DMC, which include three classes of compounds (Figure 1): carboxymethyl derivates (MC-1, MC-2, dicarboxymethyl isosorbide (DC)), carboxymethyl methyl derivates (MCE-1, MCE-2), and methyl derivates (MMI-1, MMI-2 and DMI). In particular, it was possible to isolate all these isosorbide derivatives as pure compounds except MMI-2 and MC-2 due to their low amount in the reaction mixture. The isolated compounds were identified by GS–MS analysis and NMR spectroscopy (see the Experimental Section). Table 1 shows that the reaction of isosorbide with DMC in the presence of weak bases (entries 1–2), which led mostly to the formation of carboxymethylated products MC-1, MC-2, and DC. However, reactions conducted in the presence of a strong base led to the formation of DMI with yields up to 40 % (Table 1, entries 3–4). Increasing the amount of base (Table 1, entries 5–6), enhanced the yield of DMI. Quantitative conversion to DMI could be achieved using 3 equivalents of sodium methoxide. It is also interesting to point out that the methyl carboxymethyl derivative of isosorbide MCE-1 was formed in higher yields compared to MCE-2 (Table 1, entries 3–5). This result shows that the OH in endo position is more reactive towards methylation compared to the OH in exo position. Scheme 1. Synthesis of dimethyl isosorbide.

The development of an environmentally benign sulfide oxidation procedure and its assessment by green chemistry metrics

Different Iron (III) species were used as catalysts in sulfoxidation reactions giving excellent yields and high chemoselectivity. Among the iron (III) species, the best one was a solid β-cyclodextrin-FeBr3 complex. Sulfoxidation takes place with high chemoselectivity in the presence of other groups such as isothiocyanate. Good results were obtained when these reactions were analyzed using green chemistry metrics.

Oxidation of organic sulphides to sulphoxides by nitric acid catalyzed by FeBr3 and (FeBr3)2(DMSO)3

Abstract The selective oxidation of organic sulphides to sulphoxides by 9.5 % (∼1.5 M) nitric acid was catalyzed by FeBr 3 and the coordination compound (FeBr 3 ) 2 (dimethylsulphoxide) 3 .

Possible role of nitrate/nitrite redox cycles in catalytic and selective sulfoxidation reaction. Metallic nitrates and bromides as redox mediators: a comparative study

Abstract Different combinations of metallic nitrates and bromides were used as redox mediators in the conversion of sulfides to sulfoxides. The metal salts were used in catalytic amounts in the oxidation reaction. It is suggested that in the oxidation and oxygenation processes are involved species originated from the nitrate/nitrite redox cycles and/or the dissolved atmospheric dioxygen and/or coordinated water molecules, all in combination with the redox couple 2Br − ⇄Br 2 +2e − . The utilized metallic centers showed distinct reactivity; Fe III appears as the best metallic center.

Mechanism of the Selective Sulfide Oxidation Promoted by HNO3/FeBr3

The oxidation of aryl methyl sulfides containing electron withdrawing and electron donating groups (p-NO(2), p-CHO, p-NCS, p-Br, H, p-CH(3), p-OCH(3)) was carried out in homogeneous solution in acetonitrile in the presence of catalytic amounts of HNO(3) and FeBr(3). The FeBr(3) is required for the reaction to proceed for compounds with strongly electron withdrawing groups (p-NO(2) and p-CHO) but is not necessary in the case of all the other compounds, although in the latter cases the yield decreases considerably. The rate of the reaction was measured as a function of substrate, FeBr(3) and HNO(3) concentration. From the experimental data a mechanism is suggested where there are two reaction pathways, one involving the formation of a ternary complex between the substrate, FeBr(3) and NO(3)(-) and one involving a complex formed between the sulfide and the HNO(3). From these complexes HNO(2) is generated, which then combines with HNO(3) to yield N(2)O(4), initiating a catalytic cycle where the sulfide is oxidized and O(2) from the air is stoichiometrically consumed.

Transition metal halides as catalysts in the oxidation reaction of sulfides into sulfoxides

The oxidation reaction of sulfides into sulfoxides with 10% nitric acid can be catalyzed by several transition metal halides. However, the best results are obtained when the metallic center is iron.

Sedative effect of central administration of Coriandrum sativum essential oil and its major component linalool in neonatal chicks.

Abstract Context Coriandrum sativum L. (Apiaceae) (coriander) is an herb grown throughout the world as a culinary, medicinal or essential crop. In traditional medicine, it is used for the relief of anxiety and insomnia. Systemic hydro-alcoholic and aqueous extract from aerial parts and seeds had anxiolytic and sedative action in rodents, but little is known about its central effect in chicks. Objective To study the effects of intracerebroventricular administration of essential oil from coriander seeds and its major component linalool on locomotor activity and emotionality of neonatal chicks. Materials and methods The chemical composition of coriander essential oil was determined by a gas-chromatographic analysis (> 80% linalool). Behavioural effects of central administration of coriander oil and linalool (both at doses of 0.86, 8.6 and 86 μg/chick) versus saline and a sedative diazepam dose (17.5 μg/chick, standard drug) in an open field test for 10 min were observed. Results Doses of 8.6 and 86 μg from coriander oil and linalool significantly decreased (p < 0.05) squares crossed number, attempted escapes, defecation number and distress calls, and significantly increased (p < 0.05) the sleeping posture on an open field compared with saline and were similar to the diazepam group. Discussion and conclusion The results indicate that intracerebroventricular injection of essential oil from Coriandrum sativum seeds induced a sedative effect at 8.6 and 86 μg doses. This effect may be due to monoterpene linalool, which also induced a similar sedative effect, and, therefore, could be considered as a potential therapeutic agent similar to diazepam.

Fruits of the glossy privet (Ligustrum lucidum—Oleaceae) as biocatalysts for producing chiral aromatic alcohols

Abstract The screening of four invasive plant species for use as biocatalysts in the stereoselective reduction of ketones is reported. Our studies revealed that fruits of Ligustrum lucidum can be used for the bioreduction of acetophenone to (S)-1-phenylethanol (94% conversion, > 99 enantiomeric excess [ee]%). Using this methodology, 13 substituted (S)-phenylethanols were synthesized with good ee values (> 99.9 to 78%) using a technique which is more environmentally friendly than classical reduction of prochiral ketones. The results reveal the fruits of L. lucidum to be promising biocatalysts for the production of key intermediates.

Alternatives to free molecular halogens as chemoselective reactants: Catalysis of organic reactions with reusable complexes of halogen metal salts

Organometallic complexes of halogen metallic salts have been used as catalysts in different organic reactions, mainly the oxidation of organic compounds. Their use has not only allowed the reduction of the amounts of catalyst (since they can be reused) but also a lower generation of byproducts and wastes. The different reaction media developed through the research were analyzed by several green parameters, and the best results were obtained with complexes that have cyclodextrins as organic ligands. The proposed methodology is an alternative to use of molecular halogen as oxidant or catalyst when halogens are significant chemoselective reactants.