F-Butyl chromate

Oxidation, allylic r-Butyl perbenzoate. f-Butyl chromate. Lead tetraacetate-N-Bromosuc-cinimide. Mercuric acetate. Nickel peroxide. Selenium dioxide. i-amines Cr08-Pyridine. 

In laboratory investigations, hexavalent chromium compounds, such as chromic oxide (CTO3), are often used as the source of chromium, because of their high solubilities in water. Ammonium chromate or ammonium dichromate can also be used, whereby the NH4+ ion is lost during calcination. However, sodium or potassium chromates or dichromates are unsuitable because they leave alkali metal ions on the catalyst that can promote sintering. Other hexavalent chromium compounds that have been used in nonaqueous environments include chromyl chloride and even organic chromates such as bis(f-butyl) chromate. Early Phillips commercial catalysts used aqueous CrOs as the source. 

If the silica is treated with fluoride prior to titanation, which converts many of the silanol groups into Si-F surface groups, the reaction with titanium alkoxide is inhibited and the treatment is less effective. The data in Table 34 illustrate this outcome. Silica samples were treated (or not) with two fluoride compounds in aqueous solution, then they were dried at 260 °C in the normal way prior to titanation. Titanium isopropoxide was added to make the catalyst contain 5 wt% Ti. Each sample was then calcined at 815 °C in air. Chromium was applied (0.5 wt%) as bis(f-butyl) chromate) in hexane solution (two-step activation, see Section 12). After final activation in air at 315 °C, each sample was tested at 102 °C, and the polymer MI values obtained are listed in the table. The change in MI shows that the titanium did not attach well to the carrier in the presence of fluoride. As more fluoride was added, the polymer MI dropped. 

The chromium compound can be impregnated onto the carrier by use of any anhydrous, aprotic solvent. The chromium source can be a hex-avalent chromium compound, such as bis(f-butyl) chromate in pentane,... 

Fluoride ruins the MI enhancement resulting from the two-step activation of Cr/silica-titania catalysts. This tendency probably indicates that fluoride binds to surface titania to displace chromium on the more reactive sites that produce low-MW polymer. An example is shown in Table 42. A silica-titania (5 wt% Ti) was calcined at 820 °C, impregnated with 0.5 wt% Cr as bis(f-butyl) chromate in hexane, and then activated in air at 315 °C. It produced polymer with a MI of 77. It was then dry mixed with 1 wt% ammonium hexafluorosilicate and calcined again at 315 °C. When retested, it produced polymer having a MI of only 0.5, which is comparable to that of Cr/silica activated at 820 °C. This comparison suggests that fluoride displaced chromium from the titania, leaving a catalyst comparable to Cr/silica. 

An experiment is summarized in Table 56 that demonstrates that some even more unusual chromium catalysts can be made by this approach. Bis (f-butyl) chromate, (f-but-0)2CrC>2, is a chromate ester that is soluble in hexane and other hydrocarbons. When deposited onto silica calcined at 600 °C, it has no activity for ethylene polymerization. Dicumenechro-mium(O) is a compound that also dissolves in hydrocarbons, and exhibits no (or marginal) activity when deposited onto calcined silica. However, in the experiments referred to in Table 56, the two compounds were deposited sequentially onto silica, and considerable activity did develop from some unknown redox product formed from the two. In this example, the maximum activity seems to have been obtained when the catalyst contained about 40% Cr(VI) and 60% Cr(0). 

The solution is added dropwise to the mixture in one hour during which time the reaction mixture becomes a muddy brown color (This stage of the reaction is moderately exothermic and the reagent should be added slowly to maintain the temperature below - 70°C.). After the addition is complete, the addition funnel is rinsed with 2 mL of CH2CI2 and the reaction is allowed to warm to room temperature, resulting in an orange solution (-0.2 M) of di-f-butyl chromate. The prepared ester was used directly and isolation was not attempted. 

Butyl cellosolve, see 2-Butoxyethanol tert-Butyl chromate (as CrOj) F (0.8 pm MCEF)... 

Tetra-n-butylammonium acetate, 442 Tetra-n-butylammonium chromate, 443 Tetra-n-butylammonium di-f-butyl phosphate, 443... 

OXIDATION, REAGENTS Acetyl nitrate. Bis(tri-n-butyltin)oxide. Bromine-Hexameth-ylphosphoric triamide. f-Butyl perbenzoate. Ceric ammonium nitrate. N-chlorosuc-cinimide-Dimethyl sulfide. Chromic add. Chromic anhydride. Chromic anhydride-Acetic anhydride. Chromic anhydride-Hexamethylphosphoric triamide. 2,3-Dichloro-5,6-dicyano-l,4-benzoquinone. Dimethyl sulfoxide. Dimethyl sulfoxide-Trifluoro-acetic anhydride. Diphenylseleninlc anhydride. Iodine tris(trifluoroacetate). Lead tetraacetate. N-Methylmorpholine -N-oxide. p-NitrobenzenesulfonyI peroxide. Oxygen, singlet. Palladlumfll) chloride. Peroxybcnzimidic acid. Phenylseleninyl chloride. N-Phenyl-l,2,4-triazoline-3,5-dione. Potassium chromate. Potassium superoxide. Pyri-dinium chlorodiromate. Salcomine. Silver carbonate-Celite. Sodium hypochlorite. Sulfuryl chloridc-Silica gel. Thallium(III) acetate. ThaUium(III) nitrate. Triphenyl phosphite ozonide. Trltyl tetrafluoroborate. Uranium hexafluoride. 

Figure 13.7.1 Variation of the rate of reduction of chromate (0.2 mM) in the presence of different tetra-alkylammonium hydroxides (R4NOH) at —0.75 V vs. SCE and 25°C. (Me, methyl Et, ethyl Pr, propyl Bu, butyl). [From L. Gierst, J. Tondeur, R. Comelissen, and F. Lamy, J. Electroanal Chem., 10, 397 (1965), with permission.]...

CftoH8oClftC0202 6 f /i Bis(2(1H)-tetrahydropyrimidinone)-octakis(2(1H)-tetrahydropyrimidinone)dicobalt(II) perchlorate, 38B, 964 Cft oHg ftCrLiOg, Lithium tetrakis[bis(t-butyl)methoxo]chromate(III) tetrahydrofuran, 46B, 1161... 

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