Mercury(II) Chloride

Felipe Fantuzzi was born in Rio de Janeiro, Brazil in 1987. He received his B.Sc. (2011) and M.Sc. (2013) in chemistry from the Universidade Federal do Rio de Janeiro (UFRJ). He won the Sylvio Canuto Award (2010) and the Presentation Prize at the Brazilian Symposium on Theoretical Chemistry (2013). Currently, he is working towards his Ph.D. in theoretical chemistry at UFRJ under the advisory of Professor Marco A. Chaer Nascimento and the co-advisory of Dr. Thiago M. Cardozo. His research interests focus on the nature of the chemical bond from the quantum interference perspective.

Introduction

Organomercurials were among the first prepared organometallic compounds, being known since the second half of the 19^th century.[1] [2] Despite their toxicity, mercury compounds are still used in the chemical and petrochemical industries. For instance, the industrial synthesis of vinyl chloride and acetaldehyde from acetylene is carried out using mercury catalysts.[3] Therefore, the study of environmental and health impacts of mercury and organomercurials, as well as the improvement of safety and handling techniques, are of great importance.

Mercury(II) chloride, HgCl₂, is a commercially available mercury salt, and thus an important mercury(II) source. Besides novel mercuration reactions with organic substrates,[3] [4] [5] [6] [7] HgCl₂ has been extensively used in a variety of cyclization reactions, forming both carbocycles and heterocycles.[8–10] Its use as inorganic thiophile has led to the formation of several new products from organosulfur reactants, especially thiocarbonyl compounds.[11] [12] [13] [14] [15] [16] Finally, the synthesis of mercury(II) alkynyls, mainly from HgCl₂, and their use as building blocks for supramolecular structures has been reviewed.[17]

Abstracts

(A) Preparation of Asymmetrical N,N'-Disubstituted Guanidines Guanidine is a biologically relevant functional group, because it is found in several natural products and in the amino acid arginine. O’Donovan and Rozas reported a simple route to N,N′-asymmetrical disubstituted guanidines from thiourea.[14] The first step is the conversion of thiourea into N-Boc-protected N′-alkyl/aryl substituted thioureas, which are then treated with an amine in the presence of HgCl2 and triethylamine.
(B) Guanylation of N-Iminopyridinium Ylides Cunha et al. reported the synthesis of five pyridinium N-benzoylguanidines in moderate to good yields.[11] The N-aminopyridinium iodide was subjected to modified guanylation reaction conditions, using HgCl2 as inorganic thiophile. Among the two possible stereoisomers (due to the C=N bond), only the E-configuration was detected in the 1H NMR spectra. This study represents the first description of an ylide as the nucleophilic partner in the guanylation reaction.
(C) Synthesis of Trisubstituted Triazines Kaila et al. reported a one-pot synthesis of 1,3,5-trisubstituted triazines from isothiocyanates, N,N-diethylamidines, and carbamidines.[10] An amidinothiourea intermediate is formed from the reaction of the first two materials, which then reacts with the carbamidine in the presence of HgCl2 to generate the desired triazines.
(D) Carbocyclization of Tethered Alkynedithioacetals Biswas et al. reported a general route to five- and six-membered carbo- and heterocycles by HgCl2-mediated cyclization of tethered alkynedithioacetals.[9] If the substrate is a terminal alkyne, the formation of six-membered rings is preferential. On the other hand, substitution at the alkyne terminus leads preferentially to five-membered rings. Moreover, it has been shown that the replacement of HgCl2 by HgI2 interrupts the reaction at the dithioacetal intermediate.
(E) Intramolecular Cyclization of Ethynyl Phenols Atta et al. reported a Hg(II)-specific intramolecular cyclization reaction of ethynyl phenols in semi-aqueous media at room temperature.[8] The use of a malononitrile derivative as an electron-withdrawing group has led to the development of a Hg(II) selective indicator that displays a color change from blue to pale yellow.
(F) Synthesis of α-Heteroatom-Substituted Nitrones The application of nitrones range from biology to polymers and materials chemistry. Voinov and Grigor’ev reported the synthesis of an α-mercurated cyclic aldonitrone with 55% yield.[4] If only 0.5 equivalents of HgCl2 are used in the reaction, a disubstituted mercuric derivative is formed.[5]
(G) Reduction of a Benzo[b]furan Ester Varadaraju and Hwu reported the stereoselective reduction of a benzo[b]furan ester with metallic magnesium, catalytic HgCl2, and methanol as the solvent.[18] The product is a (±)-trans-dihydrobenzo[b]furan. The use of HgCl2 raised the yield from 30% to 82%. It has been proposed that HgCl2 activates the magnesium and thus accelerates the reduction.
(H) Rearrangement of Ketoximes The transformation of ketoximes into amides or lactams, known as the Beckmann rearrangement, usually requires harsh conditions which preclude sensitive oximes to react. Ramaligan and Park reported the use of HgCl2 in acetonitrile to obtain amides and lactams from a variety of acyclic and cyclic ketoximes with good to excellent yields under essentially neutral conditions.[19]

• References

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