With chromium salts

Leather is an important material in the world economy, being used in footwear, clothing, luggage and upholstery. It is a complex substrate prepared from animal hides and skins by a long series of treatments. After the removal aU organic material and hairs the material is tanned, usually with chromium salts, which causes the protein chains to cross-link. After treating with oils or fats, to improve its handle, the leather is dyed. 

Metal-Containing Tridentate Formazans. Formazans substituted with OH or COOH in the 2-position of the N1- or Ns-aryl group have the same complexing properties as 2-hydroxy- (or carboxy)-2-aminodiarylazo dyes. Similarly, they also form 1 1 complexes with four-coordinate metals, and 1 2 complexes with six-coordinate metals. Being N ligands formazans react more readily with cobalt salts than with chromium salts. The mostly blue 1 2 cobalt(m) complexes of type 34 [72] and the mostly gray-blue complexes of type 35 [73] are known. 

Chromium-based oxidations aie reliable and well established, but the toxicity associated with chromium salts have meant that they are generally considered the... 

If we take as an example the oxidation of alcohols, chromium salts are in fact selective and have a variety of uses, but the atom efficiency is conceivably bad. [ 13] In this sense, catalytic oxidation with oxygen is far superior to stoichiometric oxidation with chromium salts. [14,15] cf. next page)... 

Chromium/zeolite catalysts have been prepared both by ion-exchange and by impregnation with chromium salts and the activity of the various samples was measured, as a function of time, at various temperatures and pressures. The rate of monomer consumption presented a typical shape, with a sharp increase at the beginning of the run, followed by a decrease that tended to an almost stationary rate. These results are discussed in terms of the possible mechanism for the reaction. 

As already stated, the polyphenols are firmly bormd to the collagen in leathers which have been subjected to vegetable tanning. In the TFG of a leather sample we may therefore expect that this bond will be broken and that fragmentation of both the tannin and the collagen will occur. Fig. 10 ows the TFG of an animal in treated only with chromium salts (chrome-tanned leather). For comparison. Fig. 11 pves the TFG of a chrome leather that has been further tanned with mimosa extract the characteristic, prominent zones of resorcinol (3) and pyrocatechol (2) show up clearly. The typical products of thermolysis of vegetable tanned and unfinished leathers are compiled in Table 5. 

Tannins occur in many plants and are separated by extraction. At present, only quebracho extract is used as a mud thinner in significant quantity in the United States. Quebracho is an acidic material and performs best at high pH. It is an excellent thinner for lime-treated and cement-contaminated muds. However, it is not effective at high salt concentrations. Sulfomethylated tannin products are functional over a wide range of pH and salinity and have either been treated with chromium for good thermal stabiUty (58) or are chrome free. Concentrations of tannin additives are ca 1.5—18 kg/m (0.5—6 lb/bbl). 

Mordant Dyes. MetaUizable azo dyes are appHed to wool by the method used for acid dyes and then treated with metal salts such as sodium chromate [7775-11-5] sodium dichromate [10588-01-9] and chromium fluoride [1488-42-5] to form the metal complex in situ. This treatment usually produces a bathochromic shift ia shade, decreases the solubUity of the coloring matter, and yields dyeiags with improved fastness properties. The chromium salts can be appHed to the substrate before dyeiag (chrome-mordant or chrome-bottom method), together with the dye ia a single bath procedure (metachrome process), or as a treatment after dyeiag (afterchrome process). 

Polyethylene. Low pressure polymerization of ethylene produced in the Phillips process utilizes a catalyst comprised of 0.5—1.0 wt % chromium (VI) on siUca or siUca-alumina with pore diameter in the range 5—20 nanometers. In a typical catalyst preparation, the support in powder form is impregnated with an aqueous solution of a chromium salt and dried, after which it is heated at 500—600°C in fluid-bed-type operation driven with dry air. The activated catalyst is moisture sensitive and usually is stored under dry nitrogen (85). 

Titanate Pigments. When a nickel salt and antimony oxide are calcined with mtile titanium dioxide at just below 1000°C, some of the added metals diffuse into the titanium dioxide crystal lattice and a yellow color results. In a similar manner, a buff may be produced with chromium and antimony a green, with cobalt and nickel and a blue, with cobalt and aluminum. These pigments are relatively weak but have extreme heat resistance and outdoor weatherabihty, eg, the yellow is used where a light cadmium could not be considered. They are compatible with most resins. 

The filtrate is diluted with 140 ml of 50% methanol-water and placed in the refrigerator for 3 days. The thick sheet of crystalline material which forms on the surface is removed by filtration and washed with 75 % acetic acid to yield 32.5 g of crude product. The filtrate is again cooled overnight and an additional 8.7 g of solid is removed. The crops are combined and the material, mp 120-124°, which is highly colored due to chromium salts, is recrystallized twice from methanol to yield 27 g (24 %) of the keto acid (69) mp 127-129° 78° (CHCI3). 

Cephachlor (35) became accessible when methods for the preparation of C-3 methylenecephalosporins became convenient. The allylic C-3-acetoxyl residue characteristic of the natural cephalosporins is activated toward displacement by a number of oxygen- and sulfur-containing nucleophiles. Molecules such as can therefore be prepared readily. Subsequent reduction with chromium(II) salts leads to the desired C-3... 

---