Adipic acid route

Adiponitrile is made commercially by several different processes utilizing different feedstocks. The original process, utilizing adipic acid (qv) as a feedstock, was first commercialized by DuPont in the late 1930s and was the basis for a number of adiponitrile plants. However, the adipic acid process was abandoned by DuPont in favor of two processes based on butadiene (qv). During the 1960s, Monsanto and Asahi developed routes to adiponitrile by the electrodimerization of acrylonitrile (qv). 

Adipic acid (qv) has a wide variety of commercial uses besides the manufacture of nylon-6,6, and thus is a common industrial chemical. Many routes to its manufacture have been developed over the years but most processes in commercial use proceed through a two-step oxidation of cyclohexane [110-83-8] or one of its derivatives. In the first step, cyclohexane is oxidized with air at elevated temperatures usually in the presence of a suitable catalyst to produce a mixture of cyclohexanone [108-94-1] and cyclohexanol [108-93-0] commonly abbreviated KA (ketone—alcohol) or KA oil ... 

The manufacture of hexamethylenediamine [124-09-4] a key comonomer in nylon-6,6 production proceeds by a two-step HCN addition reaction to produce adiponittile [111-69-3] NCCH2CH2CH2CH2CN. The adiponittile is then hydrogenated to produce the desired diamine. The other half of nylon-6,6, adipic acid (qv), can also be produced from butadiene by means of either of two similar routes involving the addition of CO. Reaction between the diamine and adipic acid [124-04-5] produces nylon-6,6. 

The first CO route to make adipic acid is a BASF process employing CO and methanol in a two-step process producing dimethyl adipate [627-93-0] which is then hydroly2ed to the acid (43—46). Cobalt carbonyl catalysts such as Co2(CO)g are used. Palladium catalysts can be used to effect the same reactions at lower pressures (47—49). 

The other CO route for adipic acid manufacture involves 1,4-addition of CO and O2 to butadiene to produce an intermediate, which is subsequently hydrogenated and hydroly2ed to adipic acid (50). This is called the oxycarbonylation process. Both the BASF and the oxycarbonylation processes have been intensively investigated. 

Seb cic Acid. Sebacic acid [111-20-6] C QH gO, is an important intermediate in the manufacture of polyamide resins (see Polyamides). It has an estimated demand worldwide of approximately 20,000 t/yr. The alkaline hydrolysis of castor oil (qv), which historically has shown some wide fluctuations in price, is the conventional method of preparation. Because of these price fluctuations, there have been years of considerable interest in an electrochemical route to sebacic acid based on adipic acid [124-04-9] (qv) as the starting material. The electrochemical step involves the Kolbn-type or Brown-Walker reaction where anodic coupling of the monomethyl ester of adipic acid forms dimethyl sebacate [106-79-6]. The three steps in the reaction sequence from adipic acid to sebacic acid are as follows ... 

It is possible to produce adipic acid by a variety of methods from such diverse starting points as benzene, acetylene and waste agricultural products. In practice, however, benzene is the favoured starting point and some of the more important routes for this material are illustrated in Figure 18.4... 

BASF is operating a semicommercial plant for the production of adipic acid via this route.A new route to adipic acid occurs via a sequential carbonylation, isomerization, hydroformylation reactions.The following illustrates these steps ... 

Adipic acid may also be produced from butadiene via a carbonylation route (Chapter 9). 

Obviously, there is a definite need for cleaner, more efficient routes to adipic acid. The question which immediately arises is, naturally, what does the Amoco system do in cyclohexane oxidation In this context it is interesting to compare the relative oxidizabilities of toluene, cyclohexane, cyclohexanol and cyclohexanone (Table 2). 

Hexamethylenediamine is now made by three different routes the original from adipic acid, the electrodimerization of acrylonitrile, and the addition of hydrogen cyanide to butadiene. Thus, the starting material can be cyclohexane, propylene, or butadiene. Currently, the cyclohexane-based route from adipic acid is the most costly and this process is being phased out. The butadiene route is patented by DuPont and requires hydrogen cyanide facilities. Recent new hexamethylenediamine plants, outside DuPont, are based on acrylonitrile from propylene, a readily available commodity. 

Benzene Cyclohexane Scheme 1 Synthetic route to adipic acid... 

Sato, K., Aoki, M., Noyori, R. (1998) A Green Route to Adipic Acid Direct Oxidation of Cyclohexenes with 30 Percent Hydrogen Peroxide. Science, 281, 1646-1647. 

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. 

Figure 1.112 Phosphate groups can be modified with adipic acid dihydrazide in the presence of a carbodi-imide to produce hydrazide derivatives. This is a common modification route for the 5 -phosphate group of oligonucleotides.

Numerous chemical intermediates are oxygen rich. Methanol, acetic acid and ethylene glycol show a O/C atomic ratio of 1, as does biomass. Other major chemicals intermediates show a lower O/C ratio, typically between 1/3 and 2/3. This holds for instance for propene and butene glycols, ethanol, (meth)acrylic acids, adipic acid and many others. The presence of some oxygen atoms is required to confer the desired physical and chemicals properties to the product. Selective and partial deoxygenation of biomass may represent an attractive and competitive route compared with the selective and partial oxidation of hydrocarbon feedstock. 

Chlorostannate ionic liquids have been used in hydroformylation reactions [23], Acidic [bmimjCl-SnCb and [l-butyl-4-methylpyridinium]Cl-SnCl2 were prepared from mixing the respective [cation]+ Cl with tin(II)chloride in a ratio of 100 104, much in the same way that the chloroaluminates are made (see Chapter 4). Both these chlorostannate ionic liquids melt below 25 °C. Addition of Pd(PPh3)2Cl2 to these chlorostannate ionic liquids leads to a reaction medium that catalyses the hydroformylation of alkenes such as methyl-3-pentenoate as shown in Scheme 8.9. The ionic liquid-palladium catalyst solution is more effective than the corresponding homogeneous dichloromethane-palladium catalyst solution. The product was readily separated from the ionic liquid by distillation under vacuum. This is an important reaction as it provides a clean route to adipic acid. 

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. ... 

An alternate route to get cyclohexanone is sometimes used— hydrogenating phenol in the liquid phase catalyzed by palladium on carbon. The rest of the process is then the same, except that yields are in the 70% range. Since the by-product yield is so high, the process has had limited acceptance, with only about 5% of the adipic acid being made this way. 

Nylon 66 is made by the condensation polymerization of adipic acid and hexamethylenediamine (HMD). Adipic acid was covered in Chapter 16 (cyclohexane is also the building block for adipic), and HMD shouldn t be such a threatening word to you by now. The hex is six the methylene is —CH2-. The di is two, and amine is the signature group -NH2. Put them all together and they don t spell mother—they spell H2N(CH2)6NH2, which is HMD. The routes to HMD and adipic acid are shown in Figure 24-6. 

A small amount of adipic acid, 2%, is made by hydrogenation of phenol with a palladium or nickel catalyst (150°C, 50 psi) to the mixed oil, then nitric acid oxidation to adipic acid. If palladium is used, more cyclohexanone is formed. Although the phenol route for making adipic acid is not economically advantageous because phenol is more expensive than benzene, the phenol conversion to greater cyclohexanone percentages can be used successfully for caprolactam manufacture (see next section), where cyclohexanone is necessary. 

The synthesis of polyamides follows a different route from that of polyesters. Although several different polymerization reactions are possible, polyamides are usually produced either by direct amidation of a diacid with a diamine or the self-amidation of an amino acid. The polymerization of amino acids is not as useful because of a greater tendency toward cycliza-tion (Sec. 2-5b). Ring-opening polymerization of lactams is also employed to synthesize polyamides (Chap. 7). Poly(hexamethylene adipamde) [IUPAC poly(iminohexanedioylimi-nohexane-l,6-diyl) or poly(iminoadipoyliminohexane-l,6-diyl)], also referred to as nylon 6/6, is synthesized from hexamethylene diamine and adipic acid [Zimmerman, 1988 Zimmerman and Kohan, 2001]. A stoichiometric balance of amine and carboxyl groups is readily obtained by the preliminary formation of a 1 1 ammonium salt (XU ) in aqueous solution at a concentration of 50%. The salt is often referred to as a nylon salt. Stoichiometric... 

One process that capitalizes on butadiene, synthesis gas, and methanol as raw materials is BASF s two-step hydrocarbonylation route to adipic acid(3-7). The butadiene in the C4 cut from an olefin plant steam cracker is transformed by a two-stage carbonylation with carbon monoxide and methanol into adipic acid dimethyl ester. Hydrolysis converts the diester into adipic acid. BASF is now engineering a 130 million pound per year commercial plant based on this technology(8,9). Technology drawbacks include a requirement for severe pressure (>4500 psig) in the first cobalt catalyzed carbonylation step and dimethyl adipate separation from branched diester isomers formed in the second carbonylation step. 

Recently, Monsanto has developed a carbonylation route(50) to prepare adipic acid from butenes. The process is based on dicarbonylation of 1, 4-dimethoxy- -butene with a palladium catalyst containing chloride ligands. This approach could achieve commercial potential if an economically viable 1,4-disubstituted -butene synthesis can be developed. A direct butene carbonylation rout to adipic acid is a desirable research target. 

This significant difference in projected feedstock price is key to a large raw material economic advantage for butadiene oxycarbonylation technology. Recent softening of worldwide oil prices has resulted in 0.85 per gallon benzene and 0.26 per pound butadiene. Butadiene oxycarbonylation economics based on these feedstock prices are less attractive. It may be well into the year 2000 before decreased oil reserves make a synthesis gas route to adipic acid economically attractive. 

When trimethylorthoformate is utilized as the dehydration agent (Equation 8.), heavies due to Aldol condensation are eliminated. Methyl formate can be easily recovered from the reaction products, but synthetic routes to regenerate trimethylorthoformate are very involved and costly. An advancement to improve trimethylorthoformate synthesis would enhance the attractiveness of the homogeneous oxycarbonylation route to adipic acid. 

In Japan the need for new technology was answered by the development of an electrolytic route to sebacic acid(33). The Kolbe type electrolytic process developed by Asahi involves dimerization of adipic acid half methyl ester salt to give dimethyl sebacate(34). The dimerization proceeds in 92% yield with 90% selectivity based on the adipate half ester. The main drawbacks of this process are the cost of energy utilized by the electrolytic process and the cost of adipic acid. A Chem Systems report indicates a small advantage for the Asahi electrolytic process with ample room for new technology development(35). 

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