1. Autocatalytic Cycles in a Copper-Catalyzed Azide-Alkyne Cycloaddition Reaction
Sergey N Semenov, Lee Belding, Brian J Cafferty, Maral P S Mousavi, Anastasiia M Finogenova, Ricardo S Cruz, Ekaterina V Skorb, George M Whitesides J Am Chem Soc. 2018 Aug 15;140(32):10221-10232.doi: 10.1021/jacs.8b05048.Epub 2018 Aug 7.
This work describes the autocatalytic copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction between tripropargylamine and 2-azidoethanol in the presence of Cu(II) salts. The product of this reaction, tris-(hydroxyethyltriazolylmethyl)amine (N(C3N3)3), accelerates the cycloaddition reaction (and thus its own production) by two mechanisms: (i) by coordinating Cu(II) and promoting its reduction to Cu(I) and (ii) by enhancing the catalytic reactivity of Cu(I) in the cycloaddition step. Because of the cooperation of these two processes, a rate enhancement of >400× is observed over the course of the reaction. The kinetic profile of the autocatalysis can be controlled by using different azides and alkynes or ligands (e.g., ammonia) for Cu(II). When carried out in a layer of 1% agarose gel, and initiated by ascorbic acid, this autocatalytic reaction generates an autocatalytic front. This system is prototypical of autocatalytic reactions where the formation of a product, which acts as a ligand for a catalytic metal ion, enhances the production and activity of the catalyst.
2. Intumescent Phosphorus and Triazole-Based Flame-Retardant Polyurethane Foams from Castor Oil
Kesavarao Sykam, Kiran Kumar Reddy Meka, Shailaja Donempudi ACS Omega. 2019 Jan 14;4(1):1086-1094.doi: 10.1021/acsomega.8b02968.eCollection 2019 Jan 31.
Synthesis of a novel phosphorus and triazole-functionalized flame-retardant (FR) monomer (PTFM) using azide-alkyne "click" reaction between triprop-2-ynyl phosphate and 2-azidoethanol that can impart intumescent FR property to polyurethane foams (PUFs) has been reported. Polyurethane triazole foams (PUTFs) were prepared using the as-synthesized PTFM and a hydroxylated castor polyol with a hydroxyl value of ~310 mg KOH/g for application as reactive FR rigid foams. PTFM and the castor polyol were characterized for structural elucidation using Fourier transform infrared and 1H, 13C, and 31P NMR. PUTFs with a varying loading content of PTFM were subjected to the lab-scale flame test, cone calorimetry test, Underwriters Laboratory 94 Vertical burning test (UL 94V), and limiting oxygen index (LOI) test. A significant increase in the char yields, reduction in heat release rates, V-1 rating, and 27% of LOI were observed for PUTFs compared to PUFs and proportional to the percentage loading of PTFM. The cumulative effect of nitrogen and phosphorus in PUTFs on their intumescent behavior was evident from the thermogravimetric analysis and scanning electron microscopy micrographs, which were further supplemented by X-ray photoelectron spectroscopy studies, indicating expulsion of N2 and overall improvement in compression strength as well. Such environment-friendly reactive FRs can be good replacements to the halogenated ones.
3. Ultrasonic assisted Fischer glycosylation: generating diversity for glycochemistry
Nasrin Shaikh, Laura Russo, Laura Cipolla, Francesco Nicotra Mol Divers. 2011 May;15(2):341-5.doi: 10.1007/s11030-010-9281-2.Epub 2010 Oct 8.
In this study ultrasound has been utilised for the Fischer glycosylation using free sugars and sulphuric acid immobilized on silica as catalyst. N-acetyl-D-glucosamine, N-acetyl-D-galactosamine, D-glucose, D-galactose, D-mannose, L-fucose, and lactose were glycosylated with propargyl alcohol or 2-azidoethanol affording the corresponding glycosides, with the production of the α-glycopyranoside as the dominant product. Remarkable acceleration of the glycosylation reactions (15 min-2 h compared to several hours) over reported procedures together with good yields were always observed.
