Current Organic Chemistry - Volume 20, Issue 12, 2016

Transforming renewable raw materials into biofuels has attracted growing attention due to economic and environmental reasons. The inevitable depletion of fossil fuels, and the increasing generation of greenhouse gas have motivated the development of environmentally friendly processes for biodiesel production. The conversion of acid non-edible vegetal oils using recyclable catalysts has been the goal pursued by research groups around the world. Heteropolyacids are attractive alternative because these are catalysts with acidic properties, which may be easily tunable by structural changes and can be supported on solid with high surface area. Heteropolyacids are oxygen cluster coordinates to addenda atom (i.e. W, Mo, V), which are coordinated to only central atom (i.e. P, Si, As). Biorefinery processes have intensively used this versatile class of catalysts to convert biomass derivative-platform molecules into chemicals and biofuels. Currently, solid supported heteropolyacids have been the catalysts used in various routes to produce biodiesel from vegetable oils and other lipidic feedstock. The combination of renewable and affordable raw materials with efficient solid catalysts (i.e. heteropolyacids) is doubtlessly an industrially strategic route for biodiesel production, and has been widely studied. In this review, the latest research and innovation towards developing processes for biodiesel production based on heteropolyacids will be highlighted. Particular attention was paid to the processes performed in liquid phase under heterogeneous catalysis conditions. Heterogeneous processes have been performed on solid supported heteropolyacids; carbon fibers, silica, zirconia, nanotubes, and niobium are examples of support discussed in this review. In this review, effort was made to describe the advances achieved in the heteropolyacid-catalyzed routes in converting triglycerides and fatty acids into biodiesel. The main synthesis methods and characterization of solid supported heteropolyacids were also addressed.

Owning to its large surface area and atomic thickness, graphene possesses exceptional mechanical, optical and electrical properties. Up to now, graphene and its composites/ hybrids have been widely used in various scientific fields such as drug carriers, electronics, transistors, sensors, conductive materials and so on. Unfortunately, the prospects of more extensive applications of graphene have been impeded by its poor dispersibility, processability and tunability. However, graphene can be chemically modified, and the well-chosen organic molecules with active functional groups would react with graphene to form low-dimensional graphene-organic architectures. The controlled functionalization of organic molecules onto the defective sites of graphene is a very effective route for fabrication of graphenebased composite materials. The aim of this article is to present an overview of the surface functionalization methodologies which are valuable for the selective construction of highly functionalized graphene with controllable properties. The interactions between graphene and organic molecules were discussed in detail. We hope to provide some useful references and enlightened views for scientific research groups.

Pillar[n]arenes, a new star of macrocyclic hosts since it was firstly reported in 2008 by Nakamoto group, have obtained a lot of attention due to their unique and intriguing characteristics and properties. The study of synthetic approaches to design and construct pillar[n]arenes is a significant aspect in pillar[n]arene chemistry. Up to now, routes to prepare pillar[n]arenes or functioned pillar[n]arene derivatives are very mature and diversified. In this review, we summarized the synthesis of pillar[n]arenes and pillar[n]arenes derivatives. With the development of host-guest chemistry, we expect to develop functioned pillar[n]arenes, not only in expanding sophisticated and novel structures like rotaxanes, but also in biological applications such as artificial transmembrane channels, controllable delivery systems and so on.

2-Hydroxy-1,4-naphthoquinone is a synthetically versatile substrate and can be used for the synthesis of a large array of heterocyclic compounds. Advances in the exploitation of 2-hydroxy-1,4-naphthoquinone for organic synthesis are reported in this review.

Disulfides are used in many organic procedures and play a very important role as vulcanizing agents and linkages for controlled drug delivery.As far as we know, no triflate-catalysed coupling of thiols has yet been reported. Metal triflates are classified as very selective catalysts. In view of previous reports on the successful use of Lewis acids in many organic procedures, the aim of this work was to check the activity of those catalysts in the coupling of thiols. A new method has been disovered to obtain symmetric disulfides with yields of up to 97% under mild conditions within a short time. Bismuth(III) triflate demonstrates the highest catalytic activity among all of the tested triflates. This versatile and highly efficient method opens up the way to synthesize aryl disulfides, that play a very important role as further reagents in many organic procedures. Mild conditions, low catalyst loading and the simplicity of the experimental technique are favourable features of this reaction.

Furo(thieno)[3,2-d]pyrimidin-8-ones 1a,b and furo(thieno)[3,2-d]pyrimidine-8-thiones 7a,b have been synthesized and their alkylation with a series of alkyl halides (MeI, EtI, PrI, i-PrI, BuI and BnCl) was carried out to gain information on their lactam-lactim or thiolactam-thiolactim tautomerism and then on their different nucleophilicity. The structure of the obtained compounds has been unambiguously confirmed by using a wide spectrum of physico-chemical methods as well as by an alternative synthesis in some instances. Compounds 1a,b could be able to behave as ambident nucleophiles, in contrast compounds 7a,b were able to behave ‘only’ as nucleophiles at sulphur: the obtained results confirmed the well known nucleophilicity sequence: S N O.