Xylene oxidised

One industrial example, where there is probably a gross nusmatch between kinetics and mixing rates, is the p-xylene oxidiser used to manufacture terephthalic acid in acetic acid solution. The low solubility of oxygen in the reaction mixture... 

Oxidation of a side chain by alkaline permanganate. Aromatic hydrocarbons containing side chains may be oxidised to the corresponding acids the results are generally satisfactory for compounds with one side chain e.g., toluene or ethylbenzene -> benzoic acid nitrotoluene -> nitrobenzoic acid) or with two side chains e.g., o-xylene -> phthalic acid). 

Oxidation. Acetaldehyde is readily oxidised with oxygen or air to acetic acid, acetic anhydride, and peracetic acid (see Acetic acid and derivatives). The principal product depends on the reaction conditions. Acetic acid [64-19-7] may be produced commercially by the Hquid-phase oxidation of acetaldehyde at 65°C using cobalt or manganese acetate dissolved in acetic acid as a catalyst (34). Liquid-phase oxidation in the presence of mixed acetates of copper and cobalt yields acetic anhydride [108-24-7] (35). Peroxyacetic acid or a perester is beheved to be the precursor in both syntheses. There are two commercial processes for the production of peracetic acid [79-21 -0]. Low temperature oxidation of acetaldehyde in the presence of metal salts, ultraviolet irradiation, or osone yields acetaldehyde monoperacetate, which can be decomposed to peracetic acid and acetaldehyde (36). Peracetic acid can also be formed directiy by Hquid-phase oxidation at 5—50°C with a cobalt salt catalyst (37) (see Peroxides and peroxy compounds). Nitric acid oxidation of acetaldehyde yields glyoxal [107-22-2] (38,39). Oxidations of /)-xylene to terephthaHc acid [100-21-0] and of ethanol to acetic acid are activated by acetaldehyde (40,41). 

These are oxidised by both Fe(III) and Cu(II) octanoates (denoted Oct) in nonpolar solvents at moderate temperatures . 80-90 % yields of the corresponding disulphide are obtained with Fe(III) and this oxidant was selected for kinetic study, the pattern of products with Cu(II) being more complex. The radical nature of the reaction was confirmed by trapping of the thiyi radicals with added olefins. Simple second-order kinetics were observed, for example, with l-dodecane thiol oxidation by Fe(Oct)3 in xylene at 55 °C (fcj = 0.24 l.mole . sec ). Reaction proceeds much more rapidly in more polar solvents such as dimethylformamide. The course of the oxidation is almost certainly... 

Oxidising p-xylene in terephthalic acid is thought to be potentially dangerous. 

Ortho-xylene (A) is oxidised to phthalic anhydride (B) in an ideal, continuous flow tubular reactor. The reaction proceeds via the complex consecutive parallel reaction sequence, shown below. The aim of the reaction is to produce the maximum yield of phthalic anhydride and the minimum production of waste gaseous products (C), which are CO2 and CO. 

The Sandoz company used the dibromoterephthalic acid method. This acid was made from p-xylcnc by brominating it to form 2,5-dibromo-p-xylene and then oxidising this to 2,5-dibromoterephthalic acid. Reaction of one mole of this acid with two moles of an arylamine in the presence of copper(II) acetate gives 2,5-bis(arylamino)terephthalic acid, which can be ring-closed to a linear quinacridone. Unsymmetrical substitution using two different arylamines is possible. 

An alternative route to DMT was introduced in 1953. This was based on air oxidation of y -xylene to /Moluic acid, which was esterified by methanol to form methyl /Moluate, which was oxidised by air to monomethyl terephthalate [40], which in turn was esterified by methanol to make DMT. The two oxidations could be combined so that p-xylene and methyl p-toluate were oxidised in the same vessel, and so could the two esterifications [41], The process was due to Katzschmann of Imhausen, a firm based at Witten and later known as Chemische Werke Witten. This process, known variously by its inventor s name and by various combinations of the names of the companies involved in its development, i.e. Hercules, Imhausen, Witten, and Dynamit Nobel, rapidly replaced the rather unsatisfactory and sometimes hazardous nitric acid oxidation route to DMT. 

Ru(03)(N0)(NCS)(PPh3)3 As Ru(O3)(NO)(NCS)(PPh3)3/O3/xylene/80°C this oxidised PPh3 to PPh30. The mechanism may involve the coordinated NO ligand, which can function in effect as a one-electron donor (NO") when the Rn-N-O unit is bent and, as here, a three-electron donor when linear [911]. 

Acetone in conjunction with benzene as a solvent is widely employed. Alternatively cyclohexanone as the hydrogen acceptor, coupled with toluene or xylene as solvent, permits the use of higher reaction temperatures and consequently the reaction time is considerably reduced the excess of cyclohexanone can be easily separated from the reaction product by steam distillation. Usually at least 0.25 mol of aluminium alkoxide per mol of secondary alcohol is employed. However, since an excess of alkoxide has no detrimental effect, the use of 1 to 3 mol of alkoxide is desirable, particularly as water, either present in the reagents or formed during secondary reactions, will remove an equivalent quantity of the reagent. It is recommended that 50 to 200 mol of acetone or 10 to 20 mol of cyclohexanone be employed. Other oxidisable groups are usually unaffected in the Oppenauer oxidation and the reaction has found wide application in the steroid field. 

Two vanadium siiicate moiecular sieves, VS-2 and V-NCL-1 with medium and iarge pore dimensions, respectively, have been synthesised and their cataiytic activity in oxidation reactions evaluated. Isolated vanadium ions, probably in framework positions, possesss unique catalytic activity and shape seiectivity in oxidation reactions. So far, such behaviour has been found oniy in the case of titanium silicaiites. Our studies demonstrate that vanadium siiicates aiso possess such features. The iatter differ from the former in their ability to oxidise even the primary carbon atoms (in paraffins and side chain aikyl groups of aromatic hydrocarbons), and effect further secondary oxidation to a greater extent. V-NCL-1, with its large pore dimensions, enables the oxidation of bulky molecules like o- and m-xylenes and 1,3,5-and 1,2,4-trimethylbenzenes. 

Ce-Cg aromatics show a similar behaviour to C2-C4 olefins. Benzene is easily oxidised and has a limited effect on CO oxidation, while toluene and m-xylene are more difficult to oxidise and more strongly affect CO oxidation. Inhibition of CO oxidation by m-xylene is intermediate between that of 1-butene and 1,3-butadiene. 

Apart from the fact that the photolytic bromine system is more applicable to deactivated, the cobalt system to activated, substrates, another important difference between the systems is their behaviour towards polyalkyl benzenes. For example, with /7-xylene, the photolytic system oxidises the methyl groups evenly, since //-abstraction from the benzyl bromide is more difficult than from the toluene (i.e. the main product of oxidation beyond the first stage is /7-bis-bromomethylbenzene). The cobalt system, on the other hand, gives /7-tolualdehyde and / -toluic acid before the second methyl group is oxidised, since the initially-formed alcohol is oxidised more rapidly than the toluene. Hence, it can be used to prepare 3,5-dimethylbenzoic acid from mesitylene. More recently, a system somewhat similar to the Co system but using cerium instead has been discovered [147],... 

In 1866 Fittig synthesised a trimethylbenzene from acetone, and in 1874 Baeyer argued that the product was 1,3,5-trimethylbenzene in view of its method of preparation (Figure 10.8). Since it was possible to demethylate this trimethylbenzene to give a xylene, it was deduced that this xylene was 1,3-dimethyl-benzene, and the dicarboxylic acid obtained when it was oxidised was benzene-1,3-dicarboxylic acid (isophthalic acid). 

The solvents that are mostly employed include volatile organic solvents (VOCs) like methylene chloride, chloroform, perchloroethylene (PERC) and carbon tetrachloride. Some VOCs like, isopropyl alcohols, xylenes, toluenes and ethylenes have been used as cleaning fluids because of their ability to dissolve oils, waxes and greases. Also, they readily evaporate from the items that they are being used to clean (VOCs readily evaporate or vaporise at room temperature). When VOCs come in contact with sun light and nitrogen oxides (by-products from the combustion of fossil fuels), these are transformed into ozone, nitric acid and partially oxidised organic compounds. 

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