Toluates

The catalyst is inactive for the hydrogenation of the (isolated) benzene nucleus and so may bo used for the hydrogenation of aromatic compounds containing aldehyde, keto, carbalkoxy or amide groups to the corresponding alcohols, amines, etc., e.g., ethyl benzoate to benzyl alcohol methyl p-toluate to p-methylbenzyl alcohol ethyl cinnamate to 3 phenyl 1-propanol. 

Various ways of overcoming the PTA oxidation problem have been incorporated into commercial processes. The predominant solution is the use of high concentrations of manganese and cobalt ions (2,248—254), optionally with various cocatalysts (204,255,256), in the presence of an organic or inorganic bromide promoter in acetic acid solvent. Operational temperatures are rather high (ca 200°C). A lesser but significant alternative involves isolation of intermediate PTA, conversion to methyl/)-toluate, and recycle to the reactor. The ester is oxidized to monomethyl terephthalate, which is subsequentiy converted to DMT and purified by distillation (248,257—264). 

Herm/es/Djnamit JS obe/Process. On a worldwide basis, the Hercules Inc./Dynamit Nobel AG process is the dorninant technology for the production of dimethyl terephthalate the chemistry was patented in the 1950s (67—69). Modifications in commercial practice have occurred over the years, with several variations being practiced commercially (70—72). The reaction to dimethyl terephthalate involves four steps, which alternate between liquid-phase oxidation and liquid-phase esterification. Two reactors are used. Eirst, -xylene is oxidized with air to -toluic acid in the oxidation reactor, and the contents are then sent to the second reactor for esterification with methanol to methyl -toluate. The toluate is isolated by distillation and returned to the first reactor where it is further oxidized to monomethyl terephthalate, which is then esterified in the second reactor to dimethyl terephthalate. 

Eigure 3 is a flow diagram which gives an example of the commercial practice of the Dynamit Nobel process (73). -Xylene, air, and catalyst are fed continuously to the oxidation reactor where they are joined with recycle methyl -toluate. Typically, the catalyst is a cobalt salt, but cobalt and manganese are also used in combination. Titanium or other expensive metallurgy is not required because bromine and acetic acid are not used. The oxidation reactor is maintained at 140—180°C and 500—800 kPa (5—8 atm). The heat of reaction is removed by vaporization of water and excess -xylene these are condensed, water is separated, and -xylene is returned continuously (72,74). Cooling coils can also be used (70). 

The oxidation reactor effluent and methanol ate sent to the esterification reactor, which operates at up to 250°C and a pressure sufficient to maintain the Hquid phase. This latter is about 2500 kPa (25 atm). The oxidation products are converted to methyl -toluate and dimethyl terephthalate without a catalyst. Excess methanol is suppHed, and steam and vaporized methanol ate removed and enter a methanol recovery column. The esterification products flow to a cmde ester column, which separates the toluate from the terephthalate. The overhead stream of methyl -toluate is returned to the oxidation reactor, and the bottoms stream of dimethyl terephthalate goes to a primary distillation. The distillate is dissolved in methanol, crystallized, and sohd dimethyl terephthalate is recovered. The dimethyl terephthalate can then be either recrystallized or distilled to yield the highly pure material needed for the polyesterification reaction. 

Methyl esters of short-chain dicarboxylic acids Loss of — OCH2CH2NH2 -C6H10(CO2CH3)2 O-methyl toluates... 

This washing removes potassium />-toluate, which causes difficulty in the distillation of the product if allowed to remain. 

The DuPont patent (US 5866622 A, 1999) describes dissolving the polyester in molten dimethylterephthalate, methyl-/ -toluate or dimethylisophthalate and separating the polyester from non-polyester components. The polyester can subsequently be used as a feedstock for methanolysis to form dimethylterephthalate (DMT) and alkylene glycol. The DMT can be subsequently hydrolysed to recover terephthalic acid. 

Ethyl toluates, e204, e205, e206 Ethyl p-tolyl ether, m3 7 3 Ethyl trimethylacetate, el28 Ethyl vanillin, e46 Ethyne, a41 Ethynylbenzene, p84... 

Solvent Yield (%) Ratio of fi/a Yield of furfuryl toluate (%)... 

ESTERIFICATION OF HINDERED ALCOHOLS tert-BUTYL p-TOLUATE, 51, 96 Esters, from diazoketones and organoboranes, 53, 82 Esters, a-deuterio-, 53, 82 Esters, y [Pg.59]

C=0 group, or sp3 carbon. This last point can perhaps be best appreciated by comparing the rate of-alkaline hydrolysis of methyl p-toluenesulfinate (140) (Bunton and Hendy, 1962) with the rate of alkaline hydrolysis of methyl p-toluate (141) (Jafife, 1953) under the same conditions. One sees that the... 

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. 

Electrolytic reduction, apparatus, 52, 23 Enol acetates, acylation of, 52,1 Enol esters, preparation, 52, 39 Epichlorohydrin, with boron trifluoride diethyl therate and dimethyl ether to give trimethyloxonium tetra-fluoroborate, 51,142 ESTERIFICATION OF HINDERED ALCOHOLS f-BUTYL p-TOLUATE,... 

It now became of interest to determine the biological activity of the individual isomers in AC 222,293 and this required an alternate regio-selective synthesis The synthesis for the m-toluate is shown in Scheme II. 

A similar sequence starting with m-toluic acid then gave the -toluate. 

Table II summarizes these results. Most noticable is the good activity of the m-toluate against wild oats and black grass but poor activity against mustard. On the other hand, mustard is very sensitive to the -toluate, whereas wild oats and black grass are quite tolerant. Careful studies with the more active enantiomer of AC 222,293 showed it to be approximately twice as active as AC 222,293. It should be noted that the selectivity shown by AC 222,293 is dependent on the presence of the methyl ester function. The acids are not selective but studies (2) indicate that it is, in fact, the acid which is the toxicant and this is liberated at different rates from the ester in the sensitive weeds and the crops.

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