Hydrocarbons, reduction

The active site similarities listed above belie a remarkable functional diversity, which includes phosphate ester hydrolysis, dioxygen and NO reduction, reversible O2 binding, and O2 activation, the last of which includes enzymes involved in ribonucleotide reduction, hydrocarbon monooxygenation, and fatty acyl desaturation. At the overall protein level, the purple acid phosphatases (PAPs) seem to be completely unrelated, both structurally and functionally, to any of the others in this class. Similarly, the flavo-diiron enzymes form a structurally and probably functionally distinct family of proteins, catalyzing both dioxygen and NO reduction. These last two examples illustrate that attempts to shoehorn all of these enzymes into a single class can sometimes provide a simplistic and misleading view of their chemistry and biochemistry. 

Third, and not least, the mechanistic features of the Fischer-Tropsch hydrocarbon synthesis mirror a plethora of organometallic chemistry. More precisely Molecular models have been invoked that could eventually lead to more product selectivity for eq. (1). Although plausible mechanistic schemes have been considered, there is no way to define precisely the reaction path(s), simply because the catalyst surface reactions escape detection under real process conditions (see Section 3.1.1.4). Nevertheless, the mechanism(s) of reductive hydrocarbon formation from carbon monoxide have strongly driven the organometallic chemistry of species that had previously been unheard of methylene (CH2) [7-9] and formyl (CHO) [10] ligands were discovered as stable metal complexes (Structures 1-3) only in the 1970s [7, 8]. Their chemistry soon explained a number of typical Fischer-Tropsch features [11, 12]. At the same time, it became clear to the catalysis community that molecular models of surface-catalyzed reactions cannot be... 

Other reactions which may generate CAA in the subsurface are the mineral oxidation of dissolved organic material to CAA by such inorganic species as ferric iron (released during clay diagenesis) (24), as well as abiotic sulfate reduction/hydrocarbon oxidation (25) which may take place at temperatures as low as KX>>C (59). 

Reduction of sulfate by hydrocarbons (either biotic or thermal) occurs because their association in the aqueous diagenetic environment is thermodynamically unstable (25). Depending upon the exact reaction (Table II) and the presence or absence of geocatalysts, abiotic or thermal sulfate reduction/hydrocarbon oxidation can occur at temperatures as low as 100-140oC (25). 

The quantity and chemical nature of deposited hydrocarbons from reaction of propane and propene over 1% Cr/Al203 catalysts are substantially different and depend strongly on reaction t emperature a s well a s t he p resence o r absence o f C r p reduced b y h ydrogen reduction. Hydrocarbon deposits are readily formed at temperatures below where propane dehydrogenation is appreciable. Propene does not appear to be a required intermediate in the formation of deposited polyenes under propane dehydrogenation conditions. 

Hydrocarbon reductant Hydrocarbon conversion (%) NO conversion N2 selectivity... 

Iron-containing mesoporous materials have been widely studied due to the unique catalytic performance of selective reduction, hydrocarbon oxidation, and acylation and alkylation reactions (Vinu et al. 2007). Thus, Tanglumlert et al. (2008) were interested in the room temperature synthesis of Fe-SBA-1 using FeCl3 via the sol-gel process. The results illustrated that up to 6 wt% Fe could be contained in the SBA-1 framework without destroying the mesopore order. Nevertheless, extraframework FeOg clusters were also found, as suggested by electron spin resonance (ESR) spectroscopy. The BET surface area was 1062 m /g, with a pore diameter around 2.1 nm. 

Wolff-Kishner reduction—Hydrocarbons from hydrazones—Gope elimination s. 17, 106... 

Potassium terUbutoxide Reaetions in dimethyl sulfoxide Wolff-Kishner reduction Hydrocarbons from hydrazones Cope elimination... 

Clemmensen-Martin-Sherman reduction — Hydrocarbons from a,) -ethyleneketones s. 14, 782... 

Clemmensen reduction Aldehydes and ketones may generally be reduced to the corresponding hydrocarbons by healing with amalgamated zinc and hydrochloric acid. 

The density of heavy fuels is greater than 0.920 kg/1 at 15°C. The marine diesel consumers focus close attention on the fuel density because of having to centrifuge water out of the fuel. Beyond 0.991 kg/1, the density difference between the two phases —aqueous and hydrocarbon— becomes too small for correct operation of conventional centrifuges technical improvements are possible but costly. In extreme cases of fuels being too heavy, it is possible to rely on water-fuel emulsions, which can have some advantages of better atomization in the injection nozzle and a reduction of pollutant emissions such as smoke and nitrogen oxides. 

Pollution control such as the reduction of nitrogen oxides, halocarbons and hydrocarbons from flue gases [37] is another important field of plasma-assisted chemistry using non-thennal plasmas. The efficiency of plasma chemical reactions can be enhanced by introducing catalysts into the plasma [38, 39]. 

In absolute ethanol solution, the ethyl ether and the corresponding hydrocarbon are formed, the latter by reduction of the diazonium compound by the ethanol, which is itself oxidised to acetaldehyde ... 

With higher alcohols, the formation of the ether becomes negligible, the reaction being limited almost entirely to reduction to the hydrocarbon. 

Note. Hydrocarbons such as ethyl-benzene can also be prepared by the Clemmensen reduction of the corresponding ketone. This is exemplified by the reduction of methylacetophenone (p. 290)]. 

In general, nitro-hydrocarbons are most readily identified by reduction to the corresponding amine (above), which is then identified as its benzoyl or other derivative (p. 374). (M.ps., pp. 550-551.)... 

Metallic sodium. This metal is employed for the drying of ethers and of saturated and aromatic hydrocarbons. The bulk of the water should first be removed from the liquid or solution by a preliminary drying with anhydrous calcium chloride or magnesium sulphate. Sodium is most effective in the form of fine wire, which is forced directly into the liquid by means of a sodium press (see under Ether, Section II,47,i) a large surface is thus presented to the liquid. It cannot be used for any compound with which it reacts or which is affected by alkalis or is easily subject to reduction (due to the hydrogen evolved during the dehydration), viz., alcohols, acids, esters, organic halides, ketones, aldehydes, and some amines. 

Aliphatic hydrocarbons can be prepared by the reduction of the readily accessible ketones with amalgamated zinc and concentrated hydrochloric acid (Clemmensen method of reduction). This procedure is particularly valuable for the prep>aration of hydrocarbons wdth an odd number of carbon atoms where the Wurtz reaction cannot be applied with the higher hydrocarbons some secondary alcohol is produced, which must be removed by repeated distillation from sodium. 

All the products of Clemmensen reductions contain small amounts of un-saturated hydrocarbons. These can be removed by repeated shaking with 10 per cent, of the volume of concentrated sulphuric acid until the acid is colourless or nearly so each shaking should be of about 5 minutes duration. The hydrocarbon is washed with water, 10 per cent, sodium carbonate solution, water (twice), dried with anhydreus magnesium or calcium sulphate, and finally distilled twice from a Claisen flask with fractionating side arm (or a Widmer flask) over sodium. 

Clemmensen reduction of aldehydes and ketones. Upon reducing aldehydes or ketones with amalgamated zinc and concentrated hydrochloric acid, the main products are the hydrocarbons (>C=0 —> >CHj), but variable quantities of the secondary alcohols (in the case of ketones) and unsaturated substances are also formed. Examples are ... 

Wolff - Kishner reduction of aldehydes and ketones. Upon heating the hydrazoiie or semicarbazone of an aldehyde or ketone with potassium hydroxide or with sodium ethoxide solution (sealed tube), the corresponding hydrocarbon is obtained ... 

Unsaturated hydrocarbons are present in nearly all products of the Clemmensen reduction of aromatic ketones and must be removed, if the hydrocarbon is requiral pure, by the above process. Secondary alcohols, often produced m small amount are not appreciably steam-volatile. 

The procedure is to pass purified hydrogen through a hot solution of the pure acid chloride in toluene or xylene in the presence of the catalyst the exit gases are bubbled through water to absorb the hydrogen chloride, and the solution is titrated with standard alkali from time to time so that the reduction may be stopped when the theoretical quantity of hydrogen chloride has been evolved. Further reduction would lead to the corresponding alcohol and hydrocarbon ... 

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