Solvothermal reactions

The solvothermal reaction between metal halides and polysulfide anions is also a useful method for the synthesis of metal-polysulfide clusters. Hydrothermal reaction of K2PtCl4 with K2S4 (5 eq) at 130 °C in a sealed tube... 

Nanotubes of magnesium hydroxide have been synthesized by a solvothermal reaction from basic magnesium chloride and ethylenediamine solvent.82 These were reported to have diameters of 80-150 nm, a wall thickness of 30-50 nm, and lengths of 5-10 pm. However, their use as polymer fire retardants was not considered. 

It is also possible to carry out reactions in ionic liquids at temperatures much higher than the melting point of the IL. Called ionothermal reactions, these differ from hydrothermal and solvothermal reactions in that they may be carried out at atmospheric pressure, due to the low vapor pressures of ionic liquids. Ionothermal reactions have led to novel materials containing cations with unusual coordination numbers (e.g., four-, five-, and six-coordinate aluminum) and morphologies. 

Demazeau G. Solvothermal reactions an original route for the synthesis of novel materials. Journal of Materials Science. 2008 43(7) 2104—2114. 

Rajamathi M, Seshadri R. Oxide and chalcogenide nanoparticles from hydrothermal/ solvothermal reactions. Current Opinion in Solid State and Materials Science. 2002 6(4) 337-345. 

S. Komarneni, Proceedings of the 2nd International Conference on Solvothermal Reactions, Takamatsu, Japan, 1996, p. 114. 

SELF-ASSEMBLY OF IRON NANOPARTICLES WITH THE ASSISTANCE OF BINARY SURFACTANTS UNDER A SOLVOTHERMAL REACTION... 

In this paper, we report an intriguing finding that binary surfactants helped self -assembly of magnetic particles into spherical aggregates. The self-assembly of magnetic nanometals occurs in a solvothermal reaction through the mortar of trioctylphosphine oxide (TOPO) and oleic acid. 

Zhao et al. obtained NaYE4 nanostructured arrays by solvothermal reaction of NaE, R(NOs)3 and oleic acid. A reverse micelle dissolution-... 

A final TCPP MOF of interest is found in a report that described the synthesis of M + (TCPP) (M +=Cu +, Ni +, and Pd + ) MOFs with dirhodium(II) carboxylate paddlewheel SBUs (110). The compounds were prepared via solvothermal reaction of rhodium acetate and M (TCPP) in methanol. The materials were poly cry stalline, and so structural information was deduced from powder X-ray deffraction (PXRD), elemental analysis, infrared (IR) spectroscopy, and other... 

For the preparation of inorganic materials with well-defined morphologies, liquid phase syntheses are preferred. These synthetic reactions proceed at relatively lower temperatures and therefore require lower energies. The sol-gel (alkoxide) method is one of these methods - however, this method usually gives amorphous products, and calcination of the products is required to obtain crystallized products. In this chapter, solvothermal methods are dealt with, which are convenient for the synthesis of a variety of inorganic materials. General considerations for solvothermal reactions are discussed first and then the solvothermal synthesis of metal oxides is reviewed. 

Various compounds have been prepared by solvothermal reactions metals, metal oxides, chalcogenides, - ° nitrides, - -" phosphides, open-framework structures, - oxometalate clusters, - organic-inorganic hybrid materials, - - and even carbon nanotnbes. - Most of the solvothermal products are nano- or microparticles with well-defined morphologies. The distribution of the particle size of the prodnct is nsnally qnite narrow, and formation of monodispersed particles is freqnently reported. - When the solvent molecules or additives are preferentially adsorbed on (or have a specific interaction with) a certain surface of the products, growth of the surface is prohibited and therefore products with unique morphologies may be formed by the solvothermal reaction. - - Thus nanorods, wires, tnbes, and sheets of various types of products have been obtained solvothermally. 

Water (boiling point [bp], 100°C critical temperature [Tc], 374°C critical pressure [Pc], 218 atm) is the most widely examined reaction medinm for solvothermal reactions. Geochemists first applied this techniqne to explore the formation mechanism of minerals and thus quite long reaction periods were applied to... 

Hydrofluoric acid (bp, 19.5°C Tc, 188°C Pc, 64 atm), nitrogen dioxide (bp, 21°C Tc, 158.2°C Pc, 100 atm in equilibrium with N2O4), sulfuric acid (decomposition at 280°C), and polyphosphoric acid are candidates for solvents in solvothermal reactions, and the reactions of these solvents will produce a variety of products that cannot be prepared by any other methods. For example, Bialowons et al. reported that solvothermal treatment of (02)2Ti7F3o in anhydrous HF at 300°C yielded single crystals of TiF4. Solvothermal reactions in these solvents may produce fruitful results and a new field seems to be awaiting many researchers. 

Carbon nanotubes can be prepared using solvothermal reactions, - however, inherent decomposition of organic compounds into carbon and hydrogen is not yet utilized in the solvothermal synthesis of nanotubes, but hexachlorobenzene was reduced by alkali metal according to the following reaction ... 

Solvothermal reaction (thermal decomposition) of metal aUcoxides in toluene usually yields the corresponding metal oxides (see Section III.B.l). Aromatic hydrocarbons are favored for this reaction over aliphatic hydrocarbons because of the higher solubility of the precursors in the former than those in the latter. Xylenes (dimethylbenzenes) are also suitable solvents for the solvothermal synthesis. 

Solvothermal reactions in alcohols are sometimes called alcohothermal reactions this word is derived from alcoholysis based on the similarity between hydrothermal and hydrolysis. Alcohols are the most common solvents for sol-gel synthesis. Primary alcohols are fairly stable at higher temperatures (up to 360°C) and therefore are widely used for the solvothermal reactions." For example, amorphous gel derived by hydrolysis of metal alkoxides can be crystallized by solvothermal treatment in alcohols. Since lower alcohols (methanol, ethanol, and 1-propanol) are completely miscible with water, water molecules present in the precursor gel may be replaced with the solvent alcohols. Therefore the precursor gel is easily dispersed in the solvent, where crystallization takes place. Detailed mechanisms for the formation of crystals are not yet fully elucidated. Crystallization of metal oxides is usually reported to take place by dissolution-recrystallization mechanisms, but the mechanism seems to depend on the gel structure. Moreover, water molecules dissolved from the gel in the reaction medium may facilitate crystallization of the product. More discussion is given in Section III.D of this chapter. 

Note that the primary alcohols corrode aluminum," and therefore aluminum cannot be used as the sealing material for the autoclave when solvothermal reactions in primary alcohols are performed. 

Dehydration of alcohols proceeds by heterolytic cleavage of the C-O bond, yielding carbocation and hydroxide anion, and the dehydration rate is determined by the stability of the thus-formed carbocation. Therefore tertiary alcohols such as tcrt-butyl alcohol (2-methyl-2-propanol) are more easily dehydrated. When these solvents are used for the solvothermal reaction, the essential nature of the reaction may be identical to that of the hydrothermal reaction. 

All these compounds are thermally stable and therefore are good solvents for solvothermal reactions. Since the amino group also donates its lone-pair electrons to Lewis acid (metal cation), metal cations are stabilized and triethanolamine is a tetradentate hgand. Laine et al. reported that some metal oxides and hydroxides... 

Since these solvents have high affinities to protein, they have a high toxicity to liver. Because of the relative low vapor pressures of these solvents at room temperature, there is relatively low risk when these solvents are used at lower temperatures. However, solvothermal reactions use these solvents at high temperatures, and therefore small leaks from the autoclave can cause severe damage... 

Finally, the author strongly recommends that the reader refer to the material safety data sheet before performing solvothermal reactions in any type of solvent. The material safety data sheet can be obtained from the maker of the chemicals or can be found on the Internet. 

Solvothermal dehydration can avoid this limitation, and dehydration may proceed at a temperature much lower than that required by the hydrothermal reaction. However, thermal dehydration may compete with the solvothermal reaction. When dehydration of hydroxide starts, water formed by dehydration of the starting material may facilitate hydrothermal transformation of the starting material. Therefore complicated reactions may occur simultaneously. As an example, the reaction of gibbsite (a polymorph of aluminum hydroxide, Al(OH)3) in alcohols at 250°C is explained. ... 

Solvothermal reaction of gibbsite in ethanol gives boehmite (AlOOH a polymorph of alnminnm oxyhydroxide), which is also obtained by hydrothermal reaction of the same starting material. The prodnct is comprised of randomly oriented, thin, small crystals of boehmite. This resnlt snggests that a dissolntion-recrystallization mechanism takes place dnring the conversion. 

Dissolution-precipitation mechanisms dissolution of aluminum species in the solvent used for the solvothermal reaction. 

---