Tetrachloroauric acid

Gold colloid with smaller diameter is made by reduction of the tetrachloroauric acid with a citrate/tannic acid reaction mixture given in Table 4.4. 

Formation of dimers is widely observed in the crystal structures of dicoordinated gold (I) mononuclear species. The majority of them are built from [AuXL] units, where X is an anionic ligand and L a neutral one. One type of such species is the well known [ AuX (PR3)] (where PR3 is a tertiary phosphine and X a halogen atom). These species can be mainly synthesized (i) from tetrachloroauric acid (Equation 2.1), or by displacement of a weakly coordinating ligand (Y), such as alkylsulfides or CO, from [AuClY]. 

Sodium citrate trihydrate, tiopronin and 4-mercaptobenzoic acid were purchased from Sigma-Aldrich, sodium borohydride from Merck and acetic acid from Roth. Tetrachloroauric acid [65] and gold-nanoparticles (Table 7.1) were prepared according to the literature (see Table 7.2). After preparation, the nanoparticles were dissolved in water, filtered through syringe filters (PTFE,... 

These hydrophilic nanoparticles were generally prepared by the reduction of tetrachloroauric acid, FIAUCI4, with borohydride in the presence of the ligand. Although this protocol was identical for all of the nanoparticles, their sizes and shapes varied considerably, as could be demonstrated by transmission electron microscopy (TEM, Figure 7.5). 

Selvan and coworkers167168 utilized a block copolymer micelle of polystyrene-block-poly(2-vinylpyridine) in toluene exposed to tetrachloroauric acid that was selectively adsorbed by the micelle structure. On exposure of this solution to pyrrole monomer, doped PPy was obtained concurrently with the formation of metallic gold nanoparticles. The product formed consisted of a monodispersed (7-9 nm) gold core surrounded by a PPy shell. Dendritic nanoaggregate structures were also reported... 

Key words Colloidal gold, Tetrachloroauric acid, Tannic acid, Trisodium citrate, Thiocyanate... 

In this chapter, two new approaches for the synthesis of metal-polymer nanocomposite materials have been described. The first method allows the preparation of contact-free dispersions of passivated gold clusters in polystyrene, and it is based on a traditional technique for the colloidal gold synthesis—that is, the alcoholic reduction of tetrachloroauric acid in presence of poly(vinyl pyrrolidone) as polymeric stabilizer. The primary function of the stabilizer is to avoid cluster sintering, but it also allows us to isolate clusters by co-precipitation. It has been found that the obtained polymer-protected nanometric gold particles can be dissolved in alkane-thiol alcoholic solutions to yield thiol-derivatized gold clusters by thiol absorbtion on the metal surface. Differently from other approaches for thioaurite synthesis available in the literature, this method allows complete control over the passivated gold cluster structure since a number of thiol molecules can be equivalently used and the... 

In a related study, l-en-4-5m-3-ols were treated with tosylamide in the presence of tetrachloroauric acid to yield 1-amino-l-en-3-ynes, which cyclize under the reaction conditions to the corresponding pyrroles (Scheme 4-53). For this tandem amination/intramolecular hy oamination, a rather high catalyst loading of... 

Various transition metals catalyze the aza-Michael addition of carbamates to enones. Among the most efficient are gold(I) and gold(III) salts (Scheme 4-66). The catalyst of the stoichiometry AuCl3-2H20 used by the authors is probably tetrachloroauric acid hydrate (HAuCU X H2O). In the corresponding reaction of... 

The cycloisomerization of a- or (3-hydroxyallenes can also be carried out in water, for example with tetrachloroauric acid as catalyst. This system was used for the first example of a tandem lipase/gold-catalyzed transformation. The one-pot kinetic resolution/cycloisomerization of racemic allenic acetates with Burkholderia cepacia lipase (PS Amano SD Amano Enzyme USA Co., Ltd., Elgin, IL) and HAuCU afforded 2,5-dihydrofurans as well as unreacted starting material with 28-50% isolated yield and 86-98% ee (Scheme 4-96). The mutual tolerance of the Lewis-acidic gold catalyst with the Ixwis-basic lipase is maintained as long as low amounts of the former are used. 

Figure 17.5 Flow rate effect of the mean size of gold nanoparticles prepared in a microflow-through reduction of tetrachloroauric acid with ascorbic acid (measurement of size by centrifugal sedimentation spectroscopy).

Figure 17.8 Cold nanorods obtained by the reduction of tetrachloroauric acid with ascorbic acid in the presence of CTAB at elevated temperature (courtesy of C. Sonnichsen).

Experimental Reagents and Instrumentation. Tetrachloroauric acid (HAUCI4,) tetraoctylammonium bromide (N[CgHj7]4Br,) dodecanethiol, sodium borohydride, and sodium metal were used as received from Sigma Chemical Co. Water and toluene were deoxygenated by reflux and distillation under an inert atmosphere. The monomers phenylmethyldichlorosilane (Gelest,) methyl methacrylate, and styrene (Aldrich) were purified by fractional distillation under vacuum. The initiator, azobisisobutylnitrile (AIBN,) was recrystallized from methanol before use. 

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