An Attempt at Enhancing the Regioselective Oxidation of Decane Using Catalysis with Reverse Micelles

Abstract

The regioselective oxidation of linear alkanes to give terminal oxidation products represents a major challenge for catalysis. A number of previous approaches have shown that confinement and encapsulation can offer an experimentally viable way forward. Against this background we have investigated the use of a system comprising gaseous oxygen, a homogenous catalyst (ammonium metavanadate) confined in an aqueous solution within reverse micelles formed in decane using bis (2-ethylhexyl)sulfosuccinate. At low conversion and at short reaction times we show that the approach does lead to a small enhancement in the selectivity to terminal products, but unsurprisingly the surfactant is more readily oxidised than decane and so the small positive effects of the micellar catalyst system are short-lived.

Photocatalytic selective oxidation of the terminal methyl group of dodecane with molecular oxygen over atomically dispersed Ti in a mesoporous SiO2 matrix

“…The bottom spectrum5 for Ti/Si=0.02 almost coincide with that of Ti/Si=0.04.This intense peak indicates that the majority of Ti(IV) occupies a tetrahedral symmetry position forming Ti-O-Si bond in silica lattice. From the sample with Ti/Si=0.33, a weak triplet peak is observed at 4974 eV due to Laporte-forbidden A 1 →T 2 transition 10 as in TiO 2 .…”

“…Catalyst synthesis 5 Titanium (IV) isopropoxide (TTIP, 97%, Sigma-Aldrich), tetraethyl orthosilicate (TEOS, 98%, Acros Organics), tetramethyl ammonium hydroxide solution (TMAOH, 25 wt% solution in methanol, Sigma-Aldrich), 2-propanol (100%, JT baker) were used without further purification. For given amounts 10 of TTIP and TEOS depending on a desired Ti/Si ratio, 3.33 x (TTIP + TEOS) moles of 2-propanol, 0.035 x (TTIP + TEOS) moles of TMAOH, and 3.33 x (TTIP + TEOS) mole of distilled H 2 O were dropped into the Teflon autoclave bottle in this order.…”

“…To increase OHCs selectivity and yield in the series reaction of dodecane partial oxidation (dodecane OHCs CO 2 ), the intermediate OHCs have to be stabilized against total oxidation to CO 2 . Here 5 we propose that dilution of contiguous Ti sites could give better OHC selectivity by employing TiO 2 -SiO 2 mixed oxides as photocatalysts. When pure TiO 2 is used as a photocatalyst, all the carbon atoms of dodecane could contact the surface titanium atoms, so that they are easily oxidized all the way to CO 2 .…”

“…Then, weaker secondary or tertiary C-H 55 bonds are more easily activated than that of the strong primary carbon, hence oxyfunctionalization of the terminal methyl group remains minimal. [4][5][6][7]34,35 In photocatalytic oxidation, hydrocarbon fragments formed from the C-C bond scission are already activated species at the terminal carbons, where subsequent 60 oxyfunctionalization takes place readily to form terminally oxidized products like aldehyde and carboxylic acids. The higher S term value of TiO 2 relative to mixed oxides is also consistent with its higher activity of C-C bond scission.…”

“…For instance, aldehydes and carboxylic acids are intermediates for fatty acids via olefin hydroformylation and subsequent 20 oxidation. [1][2][3] In most oxidation reactions by molecular oxygen, the strength of the involved C-H bonds controls the rate and selectivity [4][5][6] , because the initial step of alkane activation is the hydrogen abstraction to form a reactive intermediate. Hence, preferential oxidation at specific C-H bonds remains a 25 challenging task.…”