For adipic acid synthesis

Over iron-phthalocyanine encaged in zeolite Y and using tertiary-butylhydroperoxide (t.-BHP) as oxidant, even cyclohexane can be converted to adipic acid. Selectivities of up to 35 % at conversions around 85 % have been reported. Unfortunately, however, a reaction time of 33 hours at 60 °C was required to achieve this conversion. Although the activity of the latter catalyst is certainly much too low to compete with the conventional catalytic systems for adipic acid synthesis, it provides interesting prospects for further developments. For the near future, we perceive that more and more groups will be working in this interesting field of catalysis by zeolite inclusion compounds. 

Synthesis of adipic acid from DHS utilizes both PCA and catechol as biosynthetic intermediates and requires additional expression of catechol 1,2-dioxgenase in the biocatalytic organism (Figure 1). Since catechol 1,2-dioxygenase is not found in E. coli, the ccuA gene encoding the enzyme has been obtained from Acinetobacter calcoaceticus. Catechol 1,2-dioxygenase catalyzes conversion of catechol to cis, c/.y-muconic acid, which is readily reduced in a separate step to afford adipic acid. Perhaps the most important characteristic of a successful catalyst for adipic acid synthesis will be the avoidance of catechol accumulation. 

Figure 13.5. Ideal plug flow reactor for adipic acid synthesis.

The main use of acrolein is to produce acrylic acid and its esters. Acrolein is also an intermediate in the synthesis of pharmaceuticals and herhicides. It may also he used to produce glycerol hy reaction with isopropanol (discussed later in this chapter). 2-Hexanedial, which could he a precursor for adipic acid and hexamethylene-diamine, may he prepared from acrolein Tail to tail dimenization of acrolein using ruthenium catalyst produces trans-2-hexanedial. The trimer, trans-6-hydroxy-5-formyl-2,7-octadienal is coproduced. Acrolein, may also he a precursor for 1,3-propanediol. Hydrolysis of acrolein produces 3-hydroxypropionalde-hyde which could he hydrogenated to 1,3-propanediol. ... 

Industrial uses of HCN are for synthesis of methyl methacrylate and to form adiponitrile (for adipic acid and nylon) by addition to 1,3-butadiene in the presence of nickel(O) phosphite complexes. Waste HCN is also oxidatively hydrolyzed to give oxamide for use as fertilizer. 

Chemical synthesis at the cost of generating a hazardous byproduct is not unique to adipic acid production. This and other problems characteristic of the chemical industry are illustrated by further examination of adipic acid synthesis. Benzene, the primary starting material in adipic acid manufacture, is a proven carcinogen (9). Benzene is used widely in the chemical industry, particularly as a feedstock ( ). For example, benzene is used to make phenol (4), the starting material from which a small percentage of adipic acid is currently synthesized. The United States alone product over 12 billion pounds of benzene in 1993 (10). Benzene is derived exclusively from petroleum (4,5), a non-renewable fossil fuel. Of the chemicals in the United States which are produced in excess of 10 million pounds per year, 98% are derived from petroleum feedstocks (4). Finally, extreme reaction conditions which are used in adipic acid manufacture include temperatures up to 250°C and pressures which reach 800 psi. Reaction conditions such as these are used routinely by the chemical industry. 

Using chemistry presented in this and previous chapters, propose a synthesis for adipic acid from cyclohexene. 

Thus, the electrochemical route for synthesis of adiponitrile effectively halved the demand for adipic acid. 

Quality Specifications. Because of the extreme sensitivity of polyamide synthesis to impurities ia the iagredients (eg, for molecular-weight control, dye receptivity), adipic acid is one of the purest materials produced on a large scale. In addition to food-additive and polyamide specifications, other special requirements arise from the variety of other appHcations. Table 8 summarizes the more important specifications. Typical impurities iaclude monobasic acids arising from the air oxidation step ia synthesis, and lower dibasic acids and nitrogenous materials from the nitric acid oxidation step. Trace metals, water, color, and oils round out the usual specification Hsts. 

Butadiene is by far the most important monomer for synthetic rubber production. It can be polymerized to polybutadiene or copolymerized with styrene to styrene-butadiene rubber (SBR). Butadiene is an important intermediate for the synthesis of many chemicals such as hexa-methylenediamine and adipic acid. Both are monomers for producing nylon. Chloroprene is another butadiene derivative for the synthesis of neoprene rubber. 

In 1930, DuPont launched the synthetic fiber industry with the discovery of nylon-6,6.2 In 1938, a pilot plant for nylon-6,6 production was put into operation, and in 1939, production was commenced at a large-scale plant in Seaford, Delaware. The classical method for the synthesis of nylon-6,6 involves a two-step process. In the first step, hexamethylene diamine (HMDA) is reacted with adipic acid (AA) to form a nylon salt. Polymerization of the aqueous salt solution is carried out at temperatures in the range of about 210-275°C at a steam pressure of about 1.7 MPa. When 275°C is reached, the pressure is reduced to atmospheric pressure and heating is continued to drive the reaction to completion. 

Reactions of this type are called electrochemical hydrodimerization. They are of great value for the synthesis of various bifunctional compounds. A reaction that has found wide commercial nse is the hydrodimerization of acrylonitrile to adiponitrile (the dinitrile of adipic acid) ... 

Hexamethylenediamine (HMDA), a monomer for the synthesis of polyamide-6,6, is produced by catalytic hydrogenation of adiponitrile. Three processes, each based on a different reactant, produce the latter coimnercially. The original Du Pont process, still used in a few plants, starts with adipic acid made from cyclohexane adipic acid then reacts with ammonia to yield the dinitrile. This process has been replaced in many plants by the catalytic hydrocyanation of butadiene. A third route to adiponitrile is the electrolytic dimerization of acrylonitrile, the latter produced by the ammoxidation of propene. 

The retentive power of graphite towards adipic acid and the catalytic effect of the magnetite, especially present in A, are obvious. TEM examinations of a graphite A sample before and after reaction showed that crystallites of Fe304 appeared to be smaller after the reaction. However, the same graphite sample was reused for three successive reactions without significant loss in yield. When applied to the synthesis of other cyclic ketones (Scheme 7.14), less volatile than 74, it was observed that pressure had an effect on the recovery of product (Tab. 7.9, entries 3 and 4). A slightly reduced pressure (300 mm Hg) was necessary to obtain 3-methylcyclopentanone (75) or cyclohexanone (76) in convenient yield (Tab. 7.9, entries 4 and 5). For the cycliza-tion of suberic acid (73), a less favorable structure, the yield in cycloheptanone (77) remained low (Tab. 7.9, entry 6). 

Pure xylan is not employed in industry. but crude xylan or pentosans are of industrial importance. Xylan has been proposed as a textile size but is not employed as yet for this purpose.130 Perhaps the largest use of pentosans is in their conversion to furfural, which has many applications and serves as the source of other furan derivatives. At the present time, large quantities of furfural are used in the extractive purification of petroleum products, and recently a large plant has been constructed to convert furfural by a series of reactions to adipic acid and hexamethylene-diamine, basic ingredients in the synthesis of nylon. In commercial furfural manufacture, rough ground corn cobs are subjected to steam distillation in the presence of hydrochloric acid. As mentioned above, direct preferential hydrolysis of the pentosan in cobs or other pentosan-bearing products could be used for the commercial manufacture of D-xylose. 

Oxidation is the first step for producing molecules with a very wide range of functional groups because oxygenated compounds are precursors to many other products. For example, alcohols may be converted to ethers, esters, alkenes, and, via nucleophilic substitution, to halogenated or amine products. Ketones and aldehydes may be used in condensation reactions to form new C-C double bonds, epoxides may be ring opened to form diols and polymers, and, finally, carboxylic acids are routinely converted to esters, amides, acid chlorides and acid anhydrides. Oxidation reactions are some of the largest scale industrial processes in synthetic chemistry, and the production of alcohols, ketones, aldehydes, epoxides and carboxylic acids is performed on a mammoth scale. For example, world production of ethylene oxide is estimated at 58 million tonnes, 2 million tonnes of adipic acid are made, mainly as a precursor in the synthesis of nylons, and 8 million tonnes of terephthalic acid are produced each year, mainly for the production of polyethylene terephthalate) [1]. 

Wacker oxidation of styrene has also been performed in [bmim][BF4] and [bmim][PF6], at 60 °C with H2O2 and PdCF as a catalyst [19]. This system gave yields of acetophenone as high as 92 % after 3 h. Hydrogen peroxide may also be used under phase transfer conditions for alkene bond cleavage, to produce adipic acid (an intermediate in the synthesis of nylon-6) from cyclohexene (Scheme 9.9). 

Industry, in fact, has a major interest in these diesters as building blocks for nylon 6,6 and nylon 7,7 in the production of polyesters and polyamides. However, their present synthesis raises an environmental concern. For instance, the oxidation of cyclohexanone by nitric acid (for the preparation of adipic acid), accounts for more than 10% of the total yearly release of N2O, which is among the main gases responsible for the greenhouse effect. The reaction of Scheme 4.14 represents an eco-friendly alternative synthesis of a,(i)-diesters which uses green reagents and, relevantly, has a 100% atom economy. The overall process is mechanistically described as a retro-Claisen condensation. 

One of the best examples of the utility of enzymatic synthesis in catalyzing reactions that cannot be accomplished by any other route is the synthesis of substituted oxazolidine diesters. The oxazolidine ring is extremely water sensitive, the oxazolidine rapidly reverting back to the alkanolamine and aldehyde in the presence of water. Bis-oxazolidines have been used as hardeners for polymer coatings but the diester based on the hydroxyethyl oxazolidine and adipic acid cannot be synthesized directly with chemical catalysis because of the rapid rate of reaction of the oxazolidine ring with either the water from the esterification or the alcohol from transesterification. ... 

Uses Manufacture of adipic acid, hexahydrobenzoic acid, maleic acid, 1,3-butadiene catalyst solvent oil extraction component of coal tar stabilizer for high octane gasoline organic synthesis. 

There are nine chemicals in the top 50 that are manufactured from benzene. These are listed in Table 11.1. Two of these, ethylbenzene and styrene, have already been discussed in Chapter 9, Sections 5 and 6, since they are also derivatives of ethylene. Three others—cumene, acetone, and bisphenol A— were covered in Chapter 10, Sections 3-5, when propylene derivatives were studied. Although the three carbons of acetone do not formally come from benzene, its primary manufacturing method is from cumene, which is made by reaction of benzene and propylene. These compounds need not be discussed further at this point. That leaves phenol, cyclohexane, adipic acid, and nitrobenzene. Figure 11.1 summarizes the synthesis of important chemicals made from benzene. Caprolactam is the monomer for nylon 6 and is included because of it importance. 

For some important groups of polymers, special names and systems of nomenclature were developed. For instance, the nylons were named according to the number of carbons in the diamine and dicarboxylic acid reactants used in their synthesis. The nylon produced by the condensation of 1,6-hexamethylenediamine (6 carbons) and adipic acid (6 carbons) is called nylon-6,6. Even here, there is no set standard as to how nylon-6,6 is to be written with alternatives including nylon-66 and nylon-6,6. 

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