Calcium Carbide: A Unique Reagent for Organic Synthesis and

DOI: 10.1002/asia.201501323

Focus Review

Synthetic Methods

Calcium Carbide: A Unique Reagent for Organic Synthesis and Nanotechnology Konstantin S. Rodygin,[a] Georg Werner,[a] Fedor A. Kucherov,[b] and Valentine P. Ananikov*[a, b]

Chem. Asian J. 2016, 11, 965 – 976

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Focus Review Abstract: Acetylene, HCCH, is one of the primary building blocks in synthetic organic and industrial chemistry. Several highly valuable processes have been developed based on this simplest alkyne and the development of acetylene chemistry has had a paramount impact on chemical science over the last few decades. However, in spite of numerous useful possible reactions, the application of gaseous acetylene in everyday research practice is rather limited. Moreover, the practical implementation of high-pressure acetylene chemistry can be very challenging, owing to the risk of explosion and the requirement for complex equipment; spe-

cial safety precautions need to be taken to store and handle acetylene under high pressure, which limit its routine use in a standard laboratory setup. Amazingly, recent studies have revealed that calcium carbide, CaC2, can be used as an easyto-handle and efficient source of acetylene for in situ chemical transformations. Thus, calcium carbide is a stable and inexpensive acetylene precursor that is available on the ton scale and it can be handled with standard laboratory equipment. The application of calcium carbide in organic synthesis will bring a new dimension to the powerful acetylene chemistry.

1. Introduction

um carbide, unlike that of acetylene, has been poorly studied and it is a research area full of opportunities. It is worth mentioning that the chemistry of calcium carbide is not confined to its use as a source of acetylene. The possible applications of calcium carbide are not limited to the known reactions of acetylene and may eventually lead to the development of new transformations of the ethynyl moiety. The unique nature of this small molecule has already started to unfold. This review provides a concise description of the topic based on selected references. The main focus is placed on applications in organic chemistry, whilst a brief note is made on the possible use of CaC2 in the preparation of nanoscale systems, because this area is now actively developing.

The chemistry of carbon¢carbon triple bonds has been an inexhaustible source of fundamentally important processes and technologies.[1] Acetylene has been the main industrial source of vinyl chloride, acrylonitrile, vinyl acetate, acetaldehyde, and several other important compounds for many decades. The initial interest in acetylene arose when its transformation into acetaldehyde was first developed in 1916.[1a] The increased industrial use of acetylene caused the demand for calcium carbide. It was not until the late 1950s, after the Wacker process had been implemented, that the total manufacture of calcium carbide decreased, because of lowered demand in acetylene.[1k] Ethylene and propylene turned out to be more-applicable molecules for industrial use. However, the possibility of making acetylene an important industrial source worldwide is discussed again when oil and gas prices change significantly.[2] It may appear that the rules that govern the storage and handling of acetylene are well-known and simple.[3] However, following these rules in a cost-efficient manner can be a challenging technical task as high-pressure equipment, precautions for its transportation and storage, and dedicated materials are required for handling acetylene. Therefore, although acetylene has industrial applications, it does not follow that it can be conveniently used in the laboratory, because working with gaseous acetylene has several difficulties.[3,4] Calcium carbide has a number of advantages over gaseous acetylene. Neither oil nor natural gas is required to synthesize calcium carbide, its transportation does not have the same risks as for acetylene, there is no need to use complicated high-pressure equipment, and working with calcium carbide is safer and more convenient. Surprisingly, the chemistry of calci-

2. Important Processes and Reactions that Involve Acetylene Although acetylene was first described by Davy in 1836,[5] it was not until the Kucherov reaction was discovered in 1881 that this compound started to be used in chemistry.[6] Owing to this reaction, acetylene remained the main source for synthesizing various organic compounds until the middle of the 20th century. In this section, we will briefly mention the key areas of acetylene chemistry to discuss the development of various synthetic methods. Indeed, acetylene is a simple and readily available compound that can be used to access a broad range of valuable products (Scheme 1).[1] Vinyl chloride,[7] acrylonitrile,[8] and vinyl acetate[9] are key raw materials in industrial chemistry and can be produced by the addition of the corresponding acid to acetylene (Scheme 1). The electrophilic addition of a Brønsted acid requires a suitable catalyst (Hg, Cu, Au) and is hindered by sidepolymerization reactions that “poison” the active surface of the metal.[10] Well-known reactions include those of alcohols, thiols, and amines under basic conditions.[11] These reactions provide easy access to an important family of compounds, because vinyl ethers are widely used as co-polymers.[12] The interaction between the acetylenide anion and carbonyl compounds through the Favorsky reaction yields propargyl alcohols.[13] The use of superbasic media makes it possible to produce the corresponding alcohols, even with aryl alkyl ke-

[a] Dr. K. S. Rodygin, Dr. G. Werner, Prof. Dr. V. P. Ananikov Institute of Chemistry Saint Petersburg State University Universitetsky pr. 26 Stary Petergof 198504 (Russia) [b] Dr. F. A. Kucherov, Prof. Dr. V. P. Ananikov Zelinsky Institute of Organic Chemistry Russian Academy of Sciences Leninsky pr. 47 Moscow 119991 (Russia) E-mail: [email protected] Chem. Asian J. 2016, 11, 965 – 976

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Focus Review various cyclic aromatic compounds, including pyridine derivatives.[17] Several catalytic methods for the synthesis of polyacetylene have also been described (Scheme 4).[18]

Scheme 1. Representative examples of the key reactions of acetylene. Adapted with permission from Ref. [1a]. Copyright 2014, American Chemical Society.

Konstantin Rodygin received his doctoral degree in Organic Chemistry from the Institute of Chemistry, Syktyvkar, in 2010. After two years as a Postdoctoral Researcher at St. Petersburg State University, he joined the group of Prof. Ananikov as a Research Associate. His scientific interests include the chemistry of calcium carbide and vinylation reactions.

tones, which are characterized by lower reactivity (Scheme 2).[14] Carbonylation is another method for producing valuable synthons from acetylene as a starting material (Scheme 3). The nickel-catalyzed reaction between acetylene and carbon monoxide in the presence of alcohols, thiols, and amines under high pressure (30 atm) yields the corresponding acrylic acid derivatives.[15]

Georg Werner received his doctoral degree from Hannover University, Germany, in 2011. Currently, he is a Postdoctoral Researcher in the group of Prof. Ananikov at St. Petersburg State University, Russia. His scientific interests include the chemistry of alkynes.

Fedor Kucherov received his doctoral degree from Zelinsky Institute of Organic Chemistry, Moscow, in 2004. In 2006, he joined the Chemical Diversity Institute as a Senior Researcher in the medicinal chemistry laboratory. In 2015, he moved back to his alma mater to continue his research work. His scientific interests include organic chemistry and the design and synthesis of conjugates for selective drug delivery.

Scheme 2. Ethynylation of ketones by acetylene.

Valentine Ananikov received his PhD in 1999, his Habilitation in 2003, and, in 2005, he became a Professor and Laboratory Head at the Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences. In 2008, he was elected as a Member of the Russian Academy of Sciences. He has been a recipient of the Russian State Prize for Outstanding Achievements in Science and Technology (2004), an Award of the Science Support Foundation (2005), a Medal of Russian Academy of Sciences (2000), the Liebig Lectureship by the German Chemical Society (2010), the Balandin Prize for outstanding achievements in catalysis (2010), and the Thomson Reuters Highly Cited Researcher—Russia (2015). His scientific interests are focused on molecular complexity and synthetic transformations.

Scheme 3. Carbonylation reactions involving alcohols, amines, and thiols.

The catalytic chemistry of acetylene, developed by Reppe, uses a catalyst to perform selective conversions at relatively low temperatures and pressures (Scheme 4).[16] By varying the catalyst and the solvent, it is possible to direct the reaction towards tetrameric or trimeric products. The nature of the substituent at the triple bond also plays an important role in the outcome of the reaction. These processes are used to produce Chem. Asian J. 2016, 11, 965 – 976

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Focus Review 3. Calcium Carbide in Organic Synthesis Calcium carbide has been used in conventional organic synthesis to irreversibly remove water from reaction mixtures (e.g., during aldol condensation and esterification reactions).[32] However, the use of water-containing solvents to generate acetylene in situ opens up new prospects for alkyne chemistry. A pioneering article on the synthesis of diphenylacetylene chlorides from benzene, calcium carbide, and chlorine was published in 1918.[33] During the early development of calcium carbide chemistry, a number of polyconjugated polymers were synthesized from the reactions of powdered calcium carbide with a,b-dibromoethylbenzene, methyl 2,3-dibromopropanoate, and 2,3-dibromopropanenitrile at 150–300 8C in a pressure-vessel.[34] The reaction of calcium carbide with chlorodimethylsilane in eutectic mixture LiCl/KCl (46 mol % KCl) resulted in the formation of a twelve-membered cyclic product in a low yield (Scheme 5).[35]

Scheme 4. Oligomerization reactions of acetylene[16–18] (the maximum acetylene concentration for safe operation is shown[16]).

The reactions described above have been well-studied and many industrial processes involve these transformations. However, numerous synthetic applications of acetylene are not limited to these possibilities and include several other fundamental transformations.[1] The recent development of alkynes chemistry has led to the emergence of cross-coupling reactions,[19] click chemistry,[20] transition-metal-catalyzed atom-economical transformations,[21] alkyne cyclization,[22] triple-bond metathesis,[23] organocatalytic transformations,[1d] and materials science[24] as attractive directions in acetylene chemistry. When searching for new methods for acetylene conversion, one needs to consider the processes that take place in living organisms. Five anaerobic bacteria[25] and the obligate anaerobe Pelobacter acetylenicus,[26] which use acetylene in its free state as a source of energy and carbon, have been described. The key transformation of acetylene into acetaldehyde in P. acetylenicus is catalyzed by the acetylene hydratase enzyme (Figure 1 A),[27] whose structure contains a cubic iron¢sulfur cluster [4Fe:4S] and a tungsten atom (Figure 1 B).[28] Acetylene biodegradation takes place under strictly anaerobic conditions through a non-redox mechanism,[29] which is not typical of tungsten-based enzymes.[30] The unique structure of acetylene provides two of the most-important factors for living cells, that is, a carbon source and an energy source. Thus, acetylene was considered as a plausible component in the evolution of microbial ecosystems.[31] In this section, we have given a brief overview of the key processes involving acetylene that are commonly used in modern organic chemistry. Many other fascinating reactions that involve alkynes have been described in details in numerous review articles.[1]

Scheme 5. Reaction of calcium carbide with chlorodimethylsilane.

Deuterated bisvinyl sulfide was obtained from calcium carbide, sodium sulfide, and D2O in polar aprotic solvent (Scheme 6) and d10-2,5-dimethyl-4-methylene-1,3-oxythiolane was formed as a byproduct.[36]

Scheme 6. Synthesis of deuterated bisvinyl sulfide from calcium carbide.

When the reaction was performed in a steel autoclave without any solvent (Scheme 7 A), some vinyl ethers were obtained from the alcohols and calcium carbide.[37] The direct use of CaC2 was also possible: 2,5-dimethylhex-3-yne-2,5-diol was synthesized from calcium carbide and acetone under basic conditions followed by acid hydrolysis (Scheme 7 B).[38]

Figure 1. A) Structure of acetylene hydratase from P. acetylenicus; B) structure of the active site of acetylene hydratase. Reproduced with permission from Ref. [28b]. Copyright 2007, National Academy of Sciences. Chem. Asian J. 2016, 11, 965 – 976

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Scheme 7. Reaction of calcium carbide with alcohols (A) and acetone (B).

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Focus Review A number of propargyl alcohols were synthesized from the interaction between acetylene and aliphatic aldehydes and ketones.[39] It should be mentioned that only the a-branched compounds participated in the reaction; no interaction at all was observed for benzaldehyde (Scheme 8 A, C). A seminal recent discovery of Schreiner and co-workers revealed a crucial role of fluoride ions in the reaction between acetylene and ketones (Scheme 8 B).[40] It is possible that fluoride from

Scheme 10. Cross-coupling of aryl- and heteroaryl halides with acetylene. TEA = triethylamine, DBU = 1,8-diazabicyclo[5.4.0]undec-7-ene.

rectly used as an acetylene source to synthesize symmetric diaryl ethynes (Scheme 10 A, B).[45] As expected, the involvement of para-diiodobenzenes in a similar reaction (Scheme 10 C) gave rise to polymerization products.[46] Bis-trialkyl- or bis-triarylstannylacetylenes are also promising synthons that can be produced from the ultrasound-promoted reaction of calcium carbide and an appropriate bis-trialkyl- or bis-triarylstannyl halide.[47] The synthesis of mononuclear triazoles is another important field of acetylene chemistry, because only a limited number of methods for the preparation of these structures are known.[48] Thus, the copper-catalyzed click reaction[49] of acetylene with alkyl- and aryl azides[50] gives rise to unsubstituted aryl triazoles in high yields (Scheme 11 A).[51] Notably, the two-stage one-pot synthesis, in which the initial azide for the click reaction is synthesized from sodium azide and the corresponding aryl boronic acid, is also possible (Scheme 11 B).[52]

Scheme 8. Reactions between CaC2 and aliphatic carbonyl compounds. TBAF = Tetra-n-butylammonium fluoride.

TBAF·3 H2O activates ethynylcalcium hydroxide, which is formed from the reaction of water with solid calcium carbide. The corresponding “ate” complex attacks the carbonyl component to give the propargylic alcohols. The three-component reaction between acetylene and aldehydes (AAA coupling) or haloalkanes[41] (AHA coupling) in the presence of a secondary amine gave rise to a broad variety of aminopropynes (Scheme 9).[42] In the case of coupling reactions with benzaldehydes and bulky secondary amines, the reaction predominantly proceeded through enaminone formation.[43] Propargylamine was only observed among the reaction products in a few cases of a typical AAA reaction. The Sonogashira reaction is one of the key cross-coupling reactions in organic chemistry. A number of methods for obtaining tolane derivatives through the interaction of aryl halides with gaseous acetylene have been described.[44] It is important to mention examples in which calcium carbide was di-

Scheme 11. Synthesis of 1-phenyl-1H-1,2,3-triazoles from CaC2.

The extremely low solubility of CaC2 in organic solvents[53] requires special procedures for its application in chemical processes.[54] One important factor that needs to be tuned for the optimal generation of acetylene is the reaction between CaC2 and water. To tackle this issue, a useful multiphase procedure was proposed for conducting the reactions.[55] In this one-pot system, the bottom layer, which contained calcium carbide, was separated from the water phase by a fluorous solvent (Galden HT135), which acted like a liquid membrane and facilitated water and heat transport in a controllable manner (Figure 2). Gaseous acetylene passed through the fluorous solvent and was applied in situ to the top organic layer to undergo the Sonogashira coupling reaction, Cu-catalyzed azide¢ alkyne cycloaddition, or three-component aldehyde/alkyne/ amine coupling reaction in high yields.

Scheme 9. Reactions of CaC2 with aldehyde/amine and aldehyde/dichloromethane systems. Chem. Asian J. 2016, 11, 965 – 976

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Scheme 14. Synthesis of arylpyrrols from oximes and calcium carbide.

Figure 2. Multiphase system for Sonogashira coupling reactions, “click” reactions, and AAA condensation reactions of calcium carbide. Reproduced with permission from Ref. [55]. Copyright 2015, American Chemical Society. CuAAC = copper(I)-catalyzed azide–alkyne cycloaddition.

To summarize, the development of calcium carbide chemistry has led to the discovery of an impressive number of synthetic reactions that involve the acetylenic CC unit; a brief summary of these transformations is shown in Scheme 15. Indeed, using calcium carbide with the addition of a controlled amount of water opens up a new dimension for acetylene chemistry, that is, the in-flask release of reactive gaseous molecule from an easy-to-handle solid precursor.

Vinyl thioethers, important compounds in materials science, can be easily synthesized by the addition of thiols to CaC2 (Scheme 12).[56] This method can also be used with selenium compounds for the preparation of vinyl selenides. The reaction successfully occurred in a simple and environmentally benign procedure under mild conditions by using a standard laboratory setup. The reaction could also be scaled up to synthesize vinyl sulfides on the gram scale.

Scheme 12. Synthesis of vinyl seleno- and thioethers.

Extension of the scope to the nucleophilic addition of dithiols to the triple bond has recently been reported (Scheme 13 A).[57] This procedure provides a convenient pathway for the synthesis of divinyl thioethers, which are promising monomers for the construction of branched polymers. The same procedure, with DMSO instead of DMF, gave rise to vinyl ethers of heterocyclic thiols (Scheme 13 B).

Scheme 15. Various families of organic compounds that can be synthesized from calcium carbide.

4. Methods for the Preparation of Calcium Carbide In this section and the next section, a brief overview of the methods for the synthesis of calcium carbide and its properties will be discussed to give the necessary background for its synthetic applications. Wçhler first synthesized calcium carbide in 1862 by heating an alloy of zinc and calcium in the presence of coke.[59] Since then, several methods for the preparation of CaC2 have been introduced, almost all of which are based on the high-temperature fusion of a calcium-containing compound (lime, calcium oxide, or metallic calcium) and a source of carbon (coal, coke, biomass, lignin, or graphite). There is also significant interest in the mechanism of the reaction, which is, in fact, rather complicated. The first industrial method for the synthesis of calcium carbide was proposed over a century ago. Calcium oxide and coke granules (diameter: 5–30 mm) were fused in an electric furnace and carbon monoxide was released as a side product.[60] The reaction required heating at about 2200 8C for 1– 2 hours, owing to poor contact between the solid reagents.[61] Pure calcium carbide can be synthesized from the corresponding elemental compounds (Scheme 16 A) or calcium cy-

Scheme 13. Synthesis of divinyl thioethers and thiovinyl ethers that contain a heterocyclic moiety.

A new procedure for the synthesis of arylpyrrols was elaborated based on acetylene that was generated from calcium carbide (Scheme 14).[58] Vinylation products were formed in some cases; however, the yield of these adducts was less than 5 %. Chem. Asian J. 2016, 11, 965 – 976

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Scheme 17. Possible transformations during the synthesis of calcium carbide.

Scheme 16. Thermal synthesis of calcium carbide.

anamide (Scheme 16 B);[62] however, both processes are not suitable for the practical production of CaC2. The production of calcium carbide by the carbothermal reduction of calcium oxide was first described in 1984.[63] The standard process was modified by using rotating furnaces, which provided partial heating by fuel combustion in a flow of oxygen.[64] The reactor could also be completely heated, owing to the combustion of fuel in oxygen.[65] The use of a direct-current plasma-fluidized bed reactor allowed the temperature and reaction time for the carbide synthesis to be decreased.[66] Alternative methods for industrial-scale synthesis that have been elaborated over the past decades have used pit-type electric furnaces fitted with plasma burners (plasmotrons).[61, 66, 67] Technical-grade calcium carbide consists of about 80–85 % CaC2. A mechanochemical approach for obtaining calcium carbide in high yields (up to 98 %) from the corresponding elements was recently proposed.[68] Owing to the high purity of the resulting product, the authors suggested that 11C- and 13C-enriched alkynes could be prepared by using this method. The solidphase synthesis of calcium carbide by the reaction between calcium oxide and carbon was also studied.[69] In the synthesis of calcium carbide, coke can be replaced with biocoal that is produced by the pyrolysis of lignin-containing biomass. Because biocoal is a renewable resource, it is an attractive raw material for large-scale syntheses.[70] In 1975, the null-dimension model for the formation of calcium carbide into solid pellets was proposed.[71] It was assumed that heat energy was transferred through a layer of the product and controlled the propagation rate of the reaction over the entire pellet. A series of studies have been focused on the properties and reactions of calcium oxide and the diffusion of carbon in incandescent lime.[72] As a result, an integrated assessment of the reactions between calcium oxide and carbon in the solid and liquid phases was performed. The available data on the mechanism of formation of calcium carbide are rather contradictory. However, an examination of these data showed that the stages of the process not only depended on the reaction conditions, but also on the ratio of the components.[73] The first stage in the synthesis was the direct interaction between coke and calcium oxide (Scheme 17 A), starting at 1460 8C. The second stage was the reaction between CaC2 and CaO (Scheme 17 B), which began at 1520 8C, only once no more coke was left. The third stage (Scheme 17 C) involved decomposition of the resulting calcium carbide to metallic calcium and carbon, and its rate depended on the speed of calcium evaporation from the surface. The underlying principles in synthesis of calcium carbide have remained unchanged for over a century. However, numerChem. Asian J. 2016, 11, 965 – 976

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ous modifications and new approaches are being proposed as researchers seek to make this rather energy-consuming process less expensive, which also reflects the level of interest in this unique compound. Mechanistic studies have shown the complexity of the processes and the enormous untapped potential of this field.

5. Structure and Properties of Calcium Carbide Structural studies of calcium carbide were stimulated by research endeavors in search for new superconductors and applications of CaC2 in nanoscience. Early structural studies of calcium carbide demonstrated that this compound has a body-centered tetragonal lattice structure,[74] a distorted version of the NaCl lattice in which the dumbbells of the two carbon atoms are oriented along the tetragonal c axis. These findings were later supported by powder neutron diffraction and single-crystal X-ray diffraction studies.[75] The first data on the polymorphism of calcium carbide were inferred from the phase diagram.[76] The following modifications were observed, in addition to the tetragonal structure that is stable at room temperature (I): a cubic high-temperature modification with a NaCltype structure[77] (IV), a low-temperature modification (II), and presumably a metastable modification (III). Calcium ions occupy the lattice sites (like Na ions), whilst the disordered carbon atoms occupy the Cl sites. Single-crystal X-ray diffraction analysis of other polymorphic modifications have also been reported.[77b, 78] Interesting findings were observed in the solid-state magic angle spinning (MAS) NMR data,[79] based on analysis of the chemical shifts: 1) carbon atoms in calcium carbide have an asymmetric environment along the axes; and 2) the “acetylide ion” is not analogous to an alkyne CC triple bond. Analysis of the electronic structure of calcium carbide by using theoretical calculations demonstrated that it is an ionic compound and that a disordered structure in which two carbon atoms lie along the c axis is the most-stable structure (Figure 3).[80] These calculations supported the available data on the stable modification of CaC2. Based on these findings, it was proposed that rotation around the carbon atoms would be almost impossible at low temperatures.[80] Phase diagrams (Figure 4) within the temperature range 10– 823 K confirmed that calcium carbide has four polymorphic modifications and demonstrated the effect of particle size, sample purity, and heating rate on the final structure.[81] It should be mentioned that pure calcium carbide, which can be synthesized from the corresponding elements, was used in the aforementioned study. Compared to technical971


Focus Review the formation of polyanionic carbide at a relatively high pressure (ca. 20 GPa).[87] Polyanionic carbides have semi metallic or metallic character and are promising superconductors. The phase transitions that were induced by changes in pressure were also described.[88] USPEX calculations demonstrated that calcium carbide acted as a superconductor under extremely high pressures. Studies at various pressures made it possible to detect several additional stable forms, two of which were successfully synthesized for the first time. The resulting compounds were identical to previous theoretical calculations. Figure 5 shows that the properties and composition of calcium carbide significantly depended on the pressure; this fact could allow the discovery of new compounds with promising properties by using computational modeling. Figure 3. Crystal structure of tetragonal calcium carbide. Reproduced with permission from Ref. [80]. Copyright 1995, American Chemical Society.

Figure 4. Phase diagram of calcium carbide.[81]

grade or commercial-grade calcium carbide, it was possible to draw a conclusion about the effect of impurities on the phase diagrams. These findings also supported the hypothesis about the metastability of the CaC2 modification, first put forward in 1942.[76c] In 2000, this modification was isolated and characterized in a pure form.[82] After milling, the CaC2 III modification was converted back into CaC2 II. Heating the metastable modification at 460 8C caused a reversible phase-transformation into the cubic modification, CaC2 IV. According to density functional theory analysis, the total energy minimum was attained in the T-shaped singlet state with a very large dipole moment, whilst the transient form was characterized by the linear isomer.[83] Surprisingly, the small calcium carbide clusters, CamCn (m 8, n 12), which have been studied by using theoretical methods, can be used to store hydrogen owing to the weak interactions between calcium atoms (as compared to those in transition metals).[84] Theoretical calculations predicted that there could be additional metastable structures of calcium carbide at high pressures. At a transition pressure of 30 GPa, the six-coordinate NaCl-type structure of CaC2 became an eight-coordinate CsCltype structure.[85] Experimental studies, which focused on the behavior of calcium carbide in a high-pressure diamond anvil cell, also showed that calcium carbide existed in several polymorphic modifications.[86] Ab initio theoretical calculations and the USPEX algorithm were used to predict the possibility of Chem. Asian J. 2016, 11, 965 – 976

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Figure 5. Top) Stability of new calcium carbides. Solid lines denote thermodynamically stable phases; dashed lines denote metastable phases; metallic and semiconductor properties are shown in red and blue, respectively. Bottom) Variation in the composition of the carbide depending on the carbon content. Only thermodynamically stable phases are shown. Reproduced with permission from Ref. [88c]. Copyright 2015, Nature Publishing Group.

The interaction of calcium carbide with transition metal complexes remains an underexplored field. The reaction between a carbide anion (C22¢) and a ruthenium carbonyl cluster was proposed to involve an unusual Ca[Ru10(C)2(CO)24] complex, which was subsequently converted into [ppn]2[Ru10(C)2(CO)24] (Figure 6).[89] 972


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Figure 6. Molecular structure of the anionic part of [ppn]2[Ru10(C)2(CO)24]; ppn = hexaphenyldiphosphazene. Reproduced with permission from Ref. [89]. Copyright 2002, Royal Society of Chemistry. Figure 7. Electron microscopy images: A–C) shallow nanospheres that were prepared by using the AlCl3·6 H2O/CaC2 system; D–F) Carbon nano-onions that were prepared by using the CuCl2·2 H2O/CaC2 system; G–I) nanospheres that were prepared by using the oxalic acid/CaC2 system. Reproduced with permission from Refs. [90, 91, 93]. Copyright 2002, Elsevier; 2011, American Chemical Society; and 2010, Elsevier, respectively.

6. Preparation of Carbon Nanostructures from Calcium Carbide Nanotechnology is one of the key advancement areas of the 21st century, and it continues to develop tremendously quickly. The properties of nanoparticles are mainly caused by their favorable morphology and the ratio of their surface area to volume. Calcium carbide can be used as a source of carbon in this highly promising field. One of the most commonly used methods for preparing nanomaterials from calcium carbide involves heating CaC2 to 100–600 8C in the presence of water-containing compounds, such as the crystal hydrates of inorganic salts. Water is released during heating and interacted with calcium carbide to produce acetylene. Acetylene undergoes polymerization and pyrolysis at high temperatures and pressure, thus giving rise to carbon nanoparticles. The size, shape, and properties of the final material not only depend on the conditions of the process, but also on the water source and the catalyst that were used (Figure 7). To facilitate the formation of shallow nanospheres (diameter: 30 nm), calcium carbide was heated at 500 8C in the presence of AlCl3·6 H2O for 5 hours.[90] Carbon nanoflakes (diameter: 30 nm) were produced in a similar fashion by heating calcium carbide in the presence of CuCl2·2 H2O.[91] Because the reaction that gave rise to acetylene required an acidic proton, compounds such as acids or chloroform (which release HCl when heated) could also be used for this purpose.[92] Organic acids can also act as a source of water molecules: for example, oxalic acid forms calcium oxalate, thus contributing to acetylene release. This approach has been used to produce nanospheres.[93] Another method for producing nanoparticles involves heating calcium carbide in the presence of chlorides of other metals (e.g., Na or Mg) to about 400–900 8C. An anion-exchange reaction takes place under these conditions to afford Chem. Asian J. 2016, 11, 965 – 976

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calcium chloride and the carbide of the corresponding metal, the pyrolysis of which leads to the formation of carbon nanoparticles.[94] The reaction is performed at a lower temperature (250 8C) if titanium chloride (TiCl4) is used.[95] Hollow carbon spheres are manufactured by using the CaC2/CCl4 system in the presence of an FeCl3 catalyst.[96]

7. Other Applications of Calcium Carbide The unique properties of calcium carbide, considered in the previous section, also govern its application as a denitrifying agent.[97] Soil denitrification is the rapid conversion of ammonium nitrogen found in fertilizers into nitrate. This process is possible owing to bacteria in the soil. The resulting nitrates are toxic, but they are rapidly washed out of the soil. When applied together with fertilizers, encapsulated calcium carbide lowers the activity of soil bacteria, thus enhancing the fixation of ammonium nitrogen by plants and increasing the crop. Wax-like materials are usually used as encapsulating agents. Encapsulation slows down the hydrolysis of calcium carbide to several days, even in wet soil. Calcium carbide has higher activity in certain soil types compared to the standard denitrification inhibitors (4-amino-1,2,4-triazole and dicyandiamide). Furthermore, calcium carbide and the products of its hydrolysis are non-toxic to the environment. All of these facts demonstrate that calcium carbide is a promising agent for the inhibition of denitrification. Acetylene released from calcium carbide also inhibits the activity of methane-producing bacteria.[98] This property may be 973


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applied to partially mitigate the problem of the “greenhouse effect”. The use of a small amount of calcium carbide that is encapsulated in wax or paraffin in industrial solid-waste landfills significantly decreases methanogenesis. By varying the carbide/encapsulating-agent ratio or capsule material, an accurately dosed acetylene flow can be obtained that can be released over several days or months. An interesting application concerns the use of encapsulated calcium carbide as an autonomous fuel-free power source.[99] The in-situ-generated acetylene made the carbide-containing capsule move by a distance of up to 37 cm within 16 s at an average speed of 2.3 cm s¢1. Figure 8 shows an image of the capsule and its path.

This work is supported by the RFBR (grant Nos 15-33-20536 and 14-03-01005). G.W. acknowledges Saint Petersburg State University for a postdoctoral fellowship (No. 0.50.1186.2014). Mechanistic studies on the calcium carbide project at Zelinsky Institute were supported by the Russian Science Foundation (RSF; No. 14-50-00126). Keywords: acetylene · calcium carbide · industrial chemistry · nanotechnology · synthetic methods

[1] a) I. T. Trotus¸, T. Zimmermann, F. Schìth, Chem. Rev. 2014, 114, 1761 – 1782; b) B. M. Trost, C. J. Li, Modern Alkyne Chemistry: Catalytic and Atom-Economic Transformations, Wiley-VCH, Weinheim, 2015; c) F. Diederich, P. J. Stang, R. R. Tykwinski, Acetylene Chemistry: Chemistry, Biology and Material Science, Wiley-VCH, Weinheim, 2005; d) R. Salvio, M. Moliterno, M. Bella, Asian J. Org. Chem. 2014, 3, 340 – 351; e) W. Wu, H. Jiang, Acc. Chem. Res. 2014, 47, 2483 – 2504; f) R. Chinchilla, C. Njera, Chem. Rev. 2014, 114, 1783 – 1826; g) S. A. Vizer, E. S. Sycheva, A. A. A. Al Quntar, N. B. Kurmankulov, K. B. Yerzhanov, V. M. Dembitsky, Chem. Rev. 2015, 115, 1475 – 1502; h) F. Klappenberger, Y.-Q. Zhang, J. Bjçrk, S. Klyatskaya, M. Ruben, J. V. Barth, Acc. Chem. Res. 2015, 48, 2140 – 2150; i) B. A. Trofimov, E. Y. Schmidt, Russ. Chem. Rev. 2014, 83, 600; j) B. A. Trofimov, N. K. Gusarova, Russ. Chem. Rev. 2007, 76, 507; k) R. Jira, Angew. Chem. Int. Ed. 2009, 48, 9034 – 9037; Angew. Chem. 2009, 121, 9196 – 9199. [2] a) S. Yao, A. Nakayama, E. Suzuki, Catal. Today 2001, 71, 219 – 223; b) K. Feldmann, Chem. Ing. Tech. 1969, 41, 199 – 204; c) C. R. Bozzuto, Acetylene from coal and an electric arc US 4487683, 1984. [3] a) R. J. Tedeschi, Acetylene-Based Chemicals from Coal and Other Natural Resources, Marcel Dekker, New York, 1982; b) J. W. Copenhaver, M. H. Bigelow, Acetylene and Carbon Monoxide Chemistry, Reinhold Publishing Corporation, New York, 1949; c) Technische Regeln fìr Acetylenanlagen und Calciumcarbidlager; Deutscher Acetylenausschuß, B. f. A. u. U., Dortmund, Ed., 1969; d) S. A. Miller, Acetylene: Its Properties, Manufacture and Uses, Vol. 1, Academic Press, New York, 1965; e) State Standard GOST 5457-75; Dissolved Acetylene and Gaseous Acetylene for Technical Purposes: Specifications. [4] a) J. A. Young, Improving Safety in the Chemical Laboratory, Wiley-VCH, Weinheim, 1987; b) Acetylene Praxair Safety Data, Sheet P-4559. [5] E. Davy, Report of the 6th Meeting of the British Association for the Advancement of Science, Vol. 5, 1836, pp.62 – 63. [6] M. Kutscheroff, Ber. Dtsch. Chem. Ges. 1881, 14, 1540 – 1542. [7] J. Zhang, N. Liu, W. Li, B. Dai, Front. Chem. Sci. Eng. 2011, 5, 514 – 520. [8] J. F. Brazdil, Ullmann’s Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2000. [9] G. Roscher, Ullmann’s Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2000. [10] G. J. Hutchings, J. Catal. 1985, 96, 292 – 295. [11] W. Reppe, Liebigs Ann. Chem. 1956, 601, 81 – 138. [12] G. Schrçder in Ullmann’s Encyclopedia of Industrial Chemistry, Vol. 28, Wiley-VCH, Weinheim, 2000, pp. 481 – 485. [13] A. E. Favorsky, Zh. Russ. Fiz.-Khim. O-va. 1905, 37, 643 – 645. [14] E. Y. Shmidt, I. A. Bidusenko, N. I. Protsuk, A. I. Mikhaleva, B. A. Trofimov, Russ. J. Org. Chem. 2013, 49, 8 – 11. [15] W. Reppe, Liebigs Ann. Chem. 1953, 582, 1 – 37. [16] a) W. Reppe, Liebigs Ann. Chem. 1948, 560, 104 – 116; b) W. Reppe, US 2912472, 1959. [17] Y. Wakatsuki, H. Yamazaki, Tetrahedron Lett. 1973, 14, 3383 – 3384. [18] W. J. Feast, J. Tsibouklis, K. L. Pouwer, L. Groenendaal, E. W. Meijer, Polymer 1996, 37, 5017 – 5047. [19] A. de Meijere, F. Diederich, Metal-Catalyzed Cross-Coupling Reactions, Wiley-VCH, Weinheim, 2004. [20] J. E. Hein, V. V. Fokin, Chem. Soc. Rev. 2010, 39, 1302 – 1315.

Figure 8. Left) A capsule with calcium carbide. The white arrow denotes the initial position. Right) The red curve shows the path of the capsule; the black bar denotes the scale (1 cm). Reproduced with permission from Ref. [99]. Copyright 2014, Royal Society of Chemistry.

8. Conclusion Calcium carbide is readily available, easy to handle, and safe for laboratory use, and it has been utilized as a convenient source of in-situ-generated acetylene. In particular, calcium carbide has been successfully applied to various transformations, including Sonogashira reactions, “click” reactions, three-component coupling reactions in alkylamine/aldehyde systems, the production of vinyl thioethers, and the synthesis of heterocyclic substrates. The replacement of gaseous acetylene with an easy-to-handle solid reagent has been of significant benefit to all of these processes. Calcium carbide may also have applications in cutting-edge areas of research, such as the preparation of nanostructures. As representative examples, CaC2 has been used to synthesize a number of nanocarbon structures, that is, nanospheres, nano-onions, and nanoflakes. Calcium carbide has outstanding potential in organic chemistry, because CaC2 can be probed instead of acetylene in many cases. We anticipate that many studies in the near future will explore this fascinating opportunity. The renaissance of calcium carbide chemistry and its corresponding synthetic applications promote the concept of “new life of old molecules”.[100] Demanding synthetic challenges and the requirements of “green” and sustainable development will further stimulate this trend to reconsider the potential of well-known small molecules.

Chem. Asian J. 2016, 11, 965 – 976

www.chemasianj.org

974


Focus Review [21] a) X. Zeng, Chem. Rev. 2013, 113, 6864 – 6900; b) M. C. Willis, Chem. Rev. 2010, 110, 725 – 748; c) Top. Organomet. Chem. Vol. 43 (Eds.: V. P. Ananikov, M. Tanaka), Springer, Heidelberg, 2013, pp. 1 – 20. [22] K. Gilmore, I. V. Alabugin, Chem. Rev. 2011, 111, 6513 – 6556. [23] A. Fìrstner, Angew. Chem. Int. Ed. 2013, 52, 2794 – 2819; Angew. Chem. 2013, 125, 2860 – 2887. [24] M. Shiotsuki, F. Sanda, T. Masuda, Polym. Chem. 2011, 2, 1044 – 1058. [25] a) T. Y. Tam, C. I. Mayfield, W. E. Inniss, Curr. Microbiol. 1983, 8, 165 – 168; b) B. M. Rosner, F. A. Rainey, R. M. Kroppenstedt, B. Schink, FEMS Microbiol. Lett. 1997, 148, 175 – 180. [26] B. Schink, Arch. Microbiol. 1985, 142, 295 – 301. [27] B. M. Rosner, B. Schink, J. Bacteriol. 1995, 177, 5767 – 5772. [28] a) R. U. Meckenstock, R. Krieger, S. Ensign, P. M. H. Kroneck, B. Schink, Eur. J. Biochem. 1999, 264, 176 – 182; b) G. B. Seiffert, G. M. Ullmann, A. Messerschmidt, B. Schink, P. M. H. Kroneck, O. Einsle, Proc. Natl. Acad. Sci. USA 2007, 104, 3073 – 3077; c) L. M. Peschel, F. Belaj, N. C. MçschZanetti, Angew. Chem. Int. Ed. 2015, 54, 13018 – 13021; Angew. Chem. 2015, 127, 13210 – 13213. [29] R.-Z. Liao, J.-G. Yu, F. Himo, Proc. Natl. Acad. Sci. USA 2010, 107, 22523 – 22527. [30] R.-Z. Liao, F. Himo, ACS Catal. 2011, 1, 937 – 944. [31] R. S. Oremland, M. A. Voytek, Astrobiology 2008, 8, 45 – 58. [32] a) R. D. Sands, Org. Prep. Proced. Int. 1974, 6, 153 – 156; b) R. V. Oppenauer, Monatsh. Chem. Verw. Teile Anderer Wiss. 1966, 97, 62 – 66. [33] C. Davidson, J. Am. Chem. Soc. 1918, 40, 397 – 400. [34] a) Y. M. Paushkin, Y. Y. Markov, Vysokomol. Soedin. 1965, 7, 1481; b) Y. M. Paushkin, Y. Y. Markov, Vysokomol. Soedin. 1966, 8, 339. [35] M. G. Voronkov, S. F. Pavlov, Zh. Obshch. Khim. 1973, 43, 1408 – 1409. [36] B. A. Trofimov, Zh. Org. Khim. 1982, 18, 451 – 453. [37] B. A. Trofimov, A. S. Atavin, Zh. Prikl. Khim. 1964, 37, 2706 – 2708. [38] a) I. P. Labunsky, Zh. Obshch. Khim. 1977, 47, 728; b) E. Tamate, K. Shoichi, Kogyo Kagaku Zasshi 1957, 60, 729. [39] Y. N. Sum, D. Yu, Y. Zhang, Green Chem. 2013, 15, 2718 – 2721. [40] A. Hosseini, D. Seidel, A. Miska, P. R. Schreiner, Org. Lett. 2015, 17, 2808 – 2811. [41] Y. Zhang, D. Yu, Z. Lin, 006143A1, 2013. [42] Z. Lin, D. Yu, Y. N. Sum, Y. Zhang, ChemSusChem 2012, 5, 625 – 628. [43] D. Yu, Y. N. Sum, A. C. C. Ean, M. P. Chin, Y. Zhang, Angew. Chem. Int. Ed. 2013, 52, 5125 – 5128; Angew. Chem. 2013, 125, 5229 – 5232. [44] S. Menning, M. Krmer, B. A. Coombs, F. Rominger, A. Beeby, A. Dreuw, U. H. F. Bunz, J. Am. Chem. Soc. 2013, 135, 2160 – 2163. [45] a) W. Zhang, H. Wu, Z. Liu, P. Zhong, L. Zhang, X. Huang, J. Cheng, Chem. Commun. 2006, 4826 – 4828; b) P. Chuentragool, K. Vongnam, P. Rashatasakhon, M. Sukwattanasinitt, S. Wacharasindhu, Tetrahedron 2011, 67, 8177 – 8182. [46] N. Thavornsin, M. Sukwattanasinitt, S. Wacharasindhu, Polym. Chem. 2014, 5, 48 – 52. [47] J. C. Cochran, R. P. Lemieux, R. C. Giacobbe, A. Roitstein, Synth. React. Inorg. Met.-Org. Chem. 1990, 20, 251 – 261. [48] Y. Jiang, C. Kuang, Mini-Rev. Med. Chem. 2013, 13, 713 – 719. [49] V. V. Rostovtsev, L. G. Green, V. V. Fokin, K. B. Sharpless, Angew. Chem. Int. Ed. 2002, 41, 2596 – 2599; Angew. Chem. 2002, 114, 2708 – 2711. [50] Y. Jiang, C. Kuang, Q. Yang, Synlett 2009, 3163 – 3166. [51] a) L. Wu, B. Yan, G. Yang, Y. Chen, Heterocycl. Commun. 2013, 19, 397 – 400; b) Z. Gonda, K. Lo˝ rincz, Z. Novk, Tetrahedron Lett. 2010, 51, 6275 – 6277. [52] Q. Yang, Y. Jiang, C. Kuang, Helv. Chim. Acta 2012, 95, 448 – 454. [53] W. A. Barber, C. L. Sloan, J. Phys. Chem. 1961, 65, 2026 – 2028. [54] M. Hamberger, S. Liebig, U. Friedrich, N. Korber, U. Ruschewitz, Angew. Chem. Int. Ed. 2012, 51, 13006 – 13010; Angew. Chem. 2012, 124, 13181 – 13185. [55] R. Matake, Y. Niwa, H. Matsubara, Org. Lett. 2015, 17, 2354 – 2357. [56] K. S. Rodygin, V. P. Ananikov, Green Chem. 2016, 18, 482 – 486. [57] K. S. Rodygin, A. A. Kostin, V. P. Ananikov, Mendeleev Commun. 2015, 25, 415 – 416. [58] N. Kaewchangwat, R. Sukato, V. Vchirawongkwin, T. Vilaivan, M. Sukwattanasinitt, S. Wacharasindhu, Green Chem. 2015, 17, 460 – 465. [59] F. Wçhler, Liebigs Ann. Chem. 1862, 124, 220. [60] J. T. Morehead, G. de Chalmot, J. Am. Chem. Soc. 1896, 18, 311 – 331. Chem. Asian J. 2016, 11, 965 – 976

www.chemasianj.org

[61] a) B. Hahne, W. Gordziel, E. Meerbote, Cryst. Res. Technol. 1990, 25, 313 – 324; b) M. H. El-Naas, R. J. Munz, F. Ajersch, Plasma Chem. Plasma Process. 1998, 18, 409 – 427. [62] G. Brauer in Handbook of Preparative Inorganic Chemistry, Vol. 1 (Ed.: R. F. Riley), Academic Press, New York, 1963, pp. 943 – 946. [63] N. N. Greenwood, A. Earnshaw in Chemistry of the Elements, Vol. 1, Butterworth-Heinemann, Woburn, MA, 1984, pp. 319 – 320. [64] J. J. Mu, R. A. Hard, Ind. Eng. Chem. Res. 1987, 26, 2063 – 2069. [65] S. Yue, CN 100513310 C, 2005. [66] C. W. Zhu, G. Y. Zhao, V. Hlavacek, J. Mater. Sci. 1995, 30, 2412 – 2419. [67] M. H. El-Naas, R. J. Munz, F. Ajersch, Can. Metall. Q. 1998, 37, 67 – 74. [68] S. M. Hick, C. Griebel, R. G. Blair, Inorg. Chem. 2009, 48, 2333 – 2338. [69] H. Tagawa, H. Sugawara, Kogyo Kagaku Zasshi 1962, 35, 1276 – 1279. [70] G. Li, Q. Liu, Z. Liu, Z. C. Zhang, C. Li, W. Wu, Angew. Chem. Int. Ed. 2010, 49, 8480 – 8483; Angew. Chem. 2010, 122, 8658 – 8661. [71] C. Brookes, C. E. Gall, R. R. Hudgins, Can. J. Chem. Eng. 1975, 53, 527 – 535. [72] a) M. B. Mìller, Scand. J. Metall. 1990, 19, 64 – 71; b) M. B. Mìller, Scand. J. Metall. 1990, 19, 191 – 200; c) M. B. Mìller, Scand. J. Metall. 1990, 19, 210 – 217. [73] a) G. Li, Q. Liu, Z. Liu, Ind. Eng. Chem. Res. 2012, 51, 10742 – 10747; b) G. Li, Q. Liu, Z. Liu, Ind. Eng. Chem. Res. 2012, 51, 10748 – 10754. [74] a) M. v. Stackelberg, Naturwissenschaften 1930, 18, 305 – 306; b) M. v. Stackelberg, Z. Phys. Chem. 1930, 9, 437. [75] a) M. Atoji, R. C. Medrud, J. Chem. Phys. 1959, 31, 332 – 337; b) O. Reckeweg, A. Baumann, H. A. Mayer, J. Glaser, H. J. Meyer, Z. Anorg. Allg. Chem. 1999, 625, 1686 – 1692. [76] a) H. H. Franck, M. A. Bredig, G. Hoffmann, Z. Anorg. Allg. Chem. 1937, 232, 61 – 74; b) H. H. Franck, M. A. Bredig, K.-H. Kou, Z. Anorg. Allg. Chem. 1937, 232, 75 – 111; c) M. A. Bredig, J. Phys. Chem. 1942, 46, 801 – 819. [77] a) M. Atoji, J. Chem. Phys. 1971, 54, 3514 – 3516; b) N.-G. Vannerberg, Acta Chem. Scand. 1962, 16, 1212. [78] N.-G. Vannerberg, Acta Chem. Scand. 1961, 15, 769. [79] B. Wrackmeyer, K. Horchler, A. Sebald, L. H. Merwin, C. Ross, Angew. Chem. Int. Ed. Engl. 1990, 29, 807 – 809; Angew. Chem. 1990, 102, 821 – 823. [80] E. Ruiz, P. Alemany, J. Phys. Chem. 1995, 99, 3114 – 3119. [81] M. Knapp, U. Ruschewitz, Chem. Eur. J. 2001, 7, 874 – 880. [82] J. Glaser, S. Dill, M. Marzini, H. A. Mayer, H. J. Meyer, Z. Anorg. Allg. Chem. 2001, 627, 1090 – 1094. [83] P. Redondo, C. Barrientos, A. Largo, Chem. Phys. Lett. 2003, 382, 150 – 159. [84] G. Chen, Q. Peng, Y. Kawazoe, Phys. Lett. A 2011, 375, 994 – 999. [85] A. Kulkarni, K. Doll, J. C. Schçn, M. Jansen, J. Phys. Chem. B 2010, 114, 15573 – 15581. [86] J. Nyl¦n, S. Konar, P. Lazor, D. Benson, U. Hussermann, J. Chem. Phys. 2012, 137, 224507. [87] a) D. Benson, Y. Li, W. Luo, R. Ahuja, G. Svensson, U. Hussermann, Inorg. Chem. 2013, 52, 6402 – 6406; b) A. R. Oganov, C. W. Glass, J. Chem. Phys. 2006, 124, 244704; c) C. W. Glass, A. R. Oganov, N. Hansen, Comput. Phys. Commun. 2006, 175, 713 – 720; d) A. O. Lyakhov, A. R. Oganov, M. Valle, Comput. Phys. Commun. 2010, 181, 1623 – 1632. [88] a) L.-N. Jiang, Mod. Phys. Lett. B 2013, 27, 1350221; b) Y.-L. Li, W. Luo, Z. Zeng, H.-Q. Lin, H.-k. Mao, R. Ahuja, Proc. Natl. Acad. Sci. USA 2013, 110, 9289 – 9294; c) Y.-L. Li, S.-N. Wang, A. R. Oganov, H. Gou, J. S. Smith, T. A. Strobel, Nat. Commun. 2015, 6, 6974. [89] M. I. Bruce, N. N. Zaitseva, B. W. Skelton, A. H. White, J. Chem. Soc. Dalton Trans. 2002, 3879 – 3885. [90] H.-L. Zhu, Y.-J. Bai, Y.-X. Qi, N. Lun, Y. Zhu, Carbon 2012, 50, 1871 – 1878. [91] F.-D. Han, B. Yao, Y.-J. Bai, J. Phys. Chem. C 2011, 115, 8923 – 8927. [92] a) Y. Xie, Q. Huang, B. Huang, Carbon 2010, 48, 2023 – 2029; b) C.-l. Yin, G.-f. Wen, Q.-z. Huang, X.-f. Wang, L.-m. He, B.-r. Liu, J. Cent. South Univ. Technol. 2010, 17, 895 – 898; c) L.-L. Pang, J.-Q. Bi, Y.-J. Bai, H.-L. Zhu, Y.-X. Qi, C.-G. Wang, F.-D. Han, S.-J. Li, J. Phys. Chem. C 2008, 112, 12134 – 12137. [93] Y. Xie, Q. Huang, B. Huang, X. Xie, Mater. Chem. Phys. 2010, 124, 482 – 487. [94] C. Dai, X. Wang, Y. Wang, N. Li, J. Wei, Mater. Chem. Phys. 2008, 112, 461 – 465.

975


Focus Review [95] Y. X. Qi, M. S. Li, Y. J. Bai, Mater. Lett. 2007, 61, 1122 – 1124. [96] C. Yin, Q. Huang, B. Liu, X. Wang, Y. Xie, L. He, M. Zhang, X. Yang, Mater. Lett. 2007, 61, 4015 – 4018. [97] a) M. S. Aulakh, S. Kuldip, J. Doran, Biol. Fertil. Soils 2001, 33, 258 – 263; b) R. Mahmood, A. Ali, M. Ahmad, J. Anim. Plant Sci. 2014, 24, 354 – 361; c) Z. Ahmad, M. Abid, F. Azam, S. Tahir, Int. J. Agric. Biol. Eng. 2009, 11, 106 – 109. [98] Z. Tiantao, Z. Youcai, Z. Lijie, C. Haoquan, S. Feng, Z. Haiyan, Waste Manage. Res. 2011, 29, 1197 – 1204.

Chem. Asian J. 2016, 11, 965 – 976

www.chemasianj.org

[99] J. G. S. Moo, H. Wang, M. Pumera, Chem. Commun. 2014, 50, 15849 – 15851. [100] New Life of Old Molecules: Calcium Carbide, EurekAlert! American Association for the Advancement of Science (AAAS), Washington, DC, 2015. http://www.eurekalert.org/pub_releases/2015-08/ioocnlo081215.php. Manuscript received: November 29, 2015 Final Article published: February 22, 2016

976
