Current Organic Chemistry - Volume 28, Issue 14, 2024

Important organic reactions require the use of catalysts. The Friedel-Crafts reactions were discovered by Charles Friedel and James Mason Crafts in 1887. They are an essential catalytic process since they are widely applied in different areas such as fuels, cleaning, and pharmacological products. The reaction is usually carried out in the presence of Lewis acids or Brønsted acids in a homogeneous medium, with the nucleophilic aromatic substrate in excess. Although there is still work in the literature on the Friedel- Crafts reaction in a homogeneous medium using metal halides, the tendency is to replace these catalysts, which generate effluents that are harmful to the environment. Heterogeneous catalysts using solid acids show advantages over homogeneous catalysts, especially concerning separating products from the reaction medium, recycling, and reusing. This paper presents a mini-review focusing on the use of solid acids in Friedel-Crafts reactions.

This mini-review reports the current routes used for the production of dimethyl carbonate (DMC), a green and versatile methylating reactant widely used in organic synthesis. The use of DMC in methylation processes is also discussed. The main routes of DMC production, encompassing the reaction between phosgene and methanol and the oxidative carbonylation of methanol with CO and urea methanolysis, are summarised. However, none of them can be considered entirely green, and the drawbacks in terms of green chemistry principles are addressed. The present commercial route to DMC, which involves the initial reaction of CO2 with ethylene oxide to produce ethylene carbonate that further reacts with excess methanol, is also explored regarding the green chemistry principles. Moreover, this review focuses on the direct DMC production from the reaction of methanol and CO2, discussing catalysts and strategies to shift equilibrium. An emphasis is given to heterogeneous catalysts, especially those based on CeO2. A final remark on the production of DMC through the capture of CO2 using chitosan-derived adsorbents and renewable methanol is addressed.

Trihaloisocyanuric acids [1,3,5-trihalo-1,3,5-triazine-2,4,6-(1H,3H,5H)-triones] are commercially available or easily prepared solids. They are highly reactive, stable, easily handled, and have an excellent atom economy, transferring up to three halogen atoms to organic substrates. In these regards, the present review summarizes their synthetic applications as safe and convenient reagents. Therefore, electrophilic halogenation reactions of alkenes, alkynes, arenes, heteroarenes, carbonyl compounds, and heteroatoms, as well as radical halogenation involving saturated substrates and in situ halogenated intermediates for Appel-type reactions are presented and discussed. Remarkably, applications of trihaloisocyanuric acids in processes for the construction of heteroarene scaffolds based on electrophilic halo- and oxidative cyclization, multicomponent reactions, and telescopic reactions are also given.

Flow assurance encompasses the technical challenges of transporting hydrocarbon mixtures from the reservoir to the platform and refineries. Challenges in flow assurance include gas hydrate plugs, deposition of paraffin wax, asphaltenes, naphthenates, scale, and corrosion. Managing these deposits incurs high costs due to production interruptions and remediation operations like pigging, solvent injection, acid dissolutions, and thermal treatments. Therefore, prevention methods, such as the use of chemicals that inhibit deposit formation, are preferred. This review consolidates scientific works highlighting the role of carboxylic acids in the synthesis of chemicals for addressing flow assurance challenges as starting materials or final products for direct use. These organic compounds are already employed for the mild remediation of scale and naphthenate deposits and inhibiting gas hydrate, paraffin wax, asphaltene, scale deposits, and corrosion. Moreover, they play a crucial role in developing green flow assurance challenges inhibitors, given that some, like fatty acids, amino acids, and aromatic carboxylic acids, can be derived from natural sources. The presence of the carboxylic acid group in polymers and biopolymers is also essential for the effectiveness of these products as inhibitors. The literature further suggests that carboxylic acids will play a key role in the future development of simultaneous gas hydrate, corrosion, and scale inhibitors.

An alternative to finding new drugs for the treatment of various diseases is the chemical modification of the structure of compounds of natural origin. Among them, naphthoquinones are very interesting candidates, as they are antibacterial, antifungal, antiparasitic, and anticancer agents. Naphthoquinones are redox compounds that can accept one or two electrons, generating reactive oxygen species in the cell and producing cell apoptosis. Naphthoquinones are unsaturated compounds containing a dicarbonyl sequence in the para position, which is highly reactive. Several studies of the chemical modification of naphthoquinones, either of natural origin (such as lapachol or juglone) or synthetic origin, have demonstrated the great importance and versatility of this type of compound. Polyhydroxylated derivatives, amino, thioethers, and conjugated heterosystems (indole or pyrrole groups) have been synthesized. Depending on the type of derivative, their specific use against certain types of microorganisms or cancer cell lines has been demonstrated.