Aromatic acids, production method

The power of green chemistry" is nicely illustrated by reference to the production of aromatic acids. Classical methods using chlorine or nitric acid have been largely displaced by catalytic oxidations with dioxygen (see Fig. 4.48). This leads to high atom utilization, low-salt technology, no chloro- or nitro-compounds as by-products and the use of a very cheap oxidant. 

Ammonium hexanitratocerate(IV) is an efficient catalyst for fast esterification of carboxylic acids and alcohols under mild conditions (Goswami and Chowdhury, 2000). The reaction can be carried out under solventless conditions, or in chloroform. The reaction works with primary and secondary alcohols, and with aliphatic carboxylic acids. No reaction was observed for tertiary alcohols or for aromatic acids. The method is of interest because it is also applicable to the esterification of alcohols based on steroids and on other natural products (scheme 37). Pan and coworkers described the esterification of phenylacetic acids and cis-o cic acid with simple primary and secondary alcohols in presence of an excess of CAN at room temperature (Pan et al., 2003). The alcohol acted as solvent. Ammonium hexanitratocerate(IV) does catalyze not only the esterification of carboxylic acid, but also the transesterification with another alcohol (Stefane et al., 2002). 

By dropping au aromatic acid either alone or mixed with an aliphatic acid into a tube containing a thoria catalyst deposited on pumice and heated to 400-450°. This method is generally employed for the preparation of mixed aromatic - aliphatic ketones. Excess of the aUphatic acid is usually present since this leads to by-products which are easily separated and also tends to increase the yield of the desired ketone at the expense of the symmetrical ketone of the aromatic acid. Thus —... 

The various methods that are used for the production of aromatic acids from the corresponding substituted toluenes are outlined in Figure 1. The first two methods -chlorination/hydrolysis and nitric acid oxidation - have the disadvantage of relatively low atom utilization (ref. 13) with the concomitant inorganic salt production. Catalytic autoxidation, in contrast, has an atom utilization of 87% (for Ar=Ph) and produces no inorganic salts and no chlorinated or nitrated byproducts. It consumes only the cheap raw material, oxygen, and produces water as the only byproduct. 

Route B of this process may be substantially improved in terms of yield and product quality (purity) of the resulting triarylaminoarylcarbonium pigment. To this end, the solution of the free dye base is treated with an excess of aqueous sulfuric acid (20 to 40% ) in a solvent such as chlorobenzene or an aromatic amine. This method produces the sulfate of the basic dye, which is insoluble in this medium, together with the soluble sulfates of the primary aromatic amines, which can therefore easily be separated. The isolated sulfate of the basic dye is then washed and in dry or wet condition monosulfonated with 85 to 100% sulfuric acid. Based on the dye base sulfate, this step affords 96 to 98% yield, compared to only 83 to 89% achieved by the previously described method. The entire synthesis, including the intermediate isolation of the triarylaminoarylmethane sulfate, may also be performed by continuous process [3]. 

Description The common production method of DMT from paraxylene and methanol is through successive oxidations in four major steps oxidation, esterification, distillation and crystallization. A mixture of p-xy-lene and methyl p-toluate (MPT) is oxidized with air using a heavy-metal catalyst. All organics are recovered from the offgas and recycled to the system. The acid mixture from the oxidation is esterified with methanol and produces a mixture of esters. The crude ester mixture is distilled to remove all heavy boilers and residue produced lighter esters are recycled to the oxidation section. Raw DMT is then sent to the crystallization section to remove DMT isomers and aromatic aldehydes. 

The halogen ring-substituted acids are prepared by some one of the general methods of synthesis, depending on whether the desired product is the ortho, meta or para compound. The meta acids are made by direct action of a halogen on the aromatic acid. 

The method to be used is determined by the practicability of the separation of the chloride from the by-products of the reaction, and the excess of the reagent used. Thus, in the laboratory, phosphorus trichloride is used for the lower fatty acids because their chlorides are more volatile than phosphorous acid. The acid, together with 1.5 times the amount of phosphorus trichloride, as indicated in equation (1), is refluxed, and then the acid chloride is distilled from the viscous phosphorous acid and fractionated. Phosphorus pentachloride is used with aromatic acids as shown in equation (2). The dry, finely pulverized potassium or sodium salt of the acid is mixed with a little more than the calculated amount of the pentachloride and heated until the reaction is finished. The resulting oxychloride (POCI3) is removed by distillation. If the boiling points are too close, then the mixture of aryl acid chloride and phosphorus oxychloride is added to finely chopped ice. The oxychloride decomposes instantly, while the aryl acid chloride does not react appreciably at this temperature. The chloride is either separated or extracted with ether, dried, and then fractionated. 

This system has been cited frequently (e.g. [96]) as a method for the production of aromatic acids. Hence, benzoic acid is formed from the hydroiysis of benzoyl chloride, prepared from benzene and an excess of liquid phosgene in the presence of dissolved aluminium(III) chloride [1754]. Toluene or chlorobenzene react similarly to give 4-chloro- or 4-methyIbenzoic acids via the corresponding acid chlorides. 

Heteroatom directed aromatic lithiation reaction is now widely used for the synthesis of condensed heterocyclic compounds. New synthesis of condensed heterocyclic compounds are now known which can provide compounds not readily available by the usual acid catalysed methods. In this chapter these newer methods and their applications to several natural products are presented. Also presented, in some cases, are other non-lithiation methods which can provide comparison with the lithiation method and especially to bring about the latter s superiority in specific cases. 

A soln. of benzaldehyde and 5% SmClj in DMF electrolyzed (apparent current density 0.4-0.5 A/dm ) in a one-compartment cell fitted with a nickel or stainless steel cathode and a sacrificial Mg anode at 20° for 5-18 h, and hydrolyzed with acid - product. Y SOVo. This is the first use of a samarium salt in catalytic amount for pinacol-type coupling the method is applicable to aliphatic and aromatic oxo compds. F.e. inch intramolecular coupling s. E. Leonard et al., J. Chem. Soc. Chem. Commun. 1989, 276-7. 

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