Adipic acid, 2-

Adipic acid (melting point 152.1°C, density 1.344) is manufactured predominantly by the oxidation of cyclohexane followed by oxidation of the cyclohexanol/cyclohexanone mixture with nitric acid (Figs. 1 and 2)  

There is no need to separate the cyclohexanol/cyclohexanone mixture into its individual components oxidation of the mixture is carried out directly. 

Adipic acid can also be 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. 

FIGURE 1 Manufacture of adipic acid by aerial oxidation of cyclohexane. 

FIGURE 2 Adipic acid manufacture by nitric acid oxidation of cyclohexane 

Adipic acid (pKi = 4.43 pK2 = 5.62) is used in powdered fruit juice drinks, for improving the gelUng properties of marmalades and fruit jellies, and for improving cheese texture. It is syn- 

CHEMICAL NAME = hexanedioic acid CAS NUMBER = 124-04-9 MOLECULAR FORMULA = C6H10O4 MOLAR MASS =146.1 g/mol COMPOSITION = C(49.3%) H(6.9%) 0(43.8%) 

Adipic acid is a straight-chain dicarboxylic acid that exists as a white crystalline compound at standard temperature and pressure. Adipic acid is one of the most important industrial chemicals and typically ranks in the top 10 in terms of volume used annually by the chemical industry. Worldwide, approximately 2.5 million tons of adipic acid are produced annually. Adipic acid s main use is in the production of 6,6 nylon. It is also used in resins, plasticizers, lubricants, polyurethanes, and food additives. 

The vast majority of adipic acid production is used to produce nylon, accounting for approximately 90% of its use. Nylon was the first truly synthetic fiber produced and capped a long search for such a material. Throughout human history, a limited number of fibers provided the fabrics used for clothing and other materials wool, leather, cotton, flax, and silk. As early as 1664, Robert Hooke (1635-1703) speculated that production of artificial 

In February 1935, a fiber known in the laboratory as fiber 66 was produced that held promise for commercialization. The 66 refers to the number of carbon atoms in the reactants used to produce it. In the case of fiber 66, the two sixes refer to the six carbon atoms in adipic acid and six carbon atom in hexamethylenediamine, H2N(CH2)6NHr Fiber 66 was the first nylon produced. Like rayon, nylon is a generic term used for a group of synthetically produced polyamides. The name nylon was not introduced until 1938 after an extensive discussion by DuPont on what to call fiber 66. There are several versions of how the name nylon was coined, but one claims that nylon was a modification of norun (no run), which was modified into a unique name that could be used to market the product. DuPont officials had hoped to keep the name secret until the 1939 World s Fair, but leaks and patent preparation forced them to reveal the name early. DuPont did not trademark the name, but promoted the material genetically as nylon. 

Fiber 66 became known as nylon 66. It is produced when adipic acid and hexamethylenediamine are combined under the proper conditions  

The first stage in the production of adipic acid is the oxidation of liquid cyclohexane with air using a cobalt naphthenate catalyst at temperatures in the range at 140°-160°C and pressures about 8-12 bar. A mixed ketone/alcohol oil containing cyclohexanol (CeHnOH) and cyclohexanone (CeHioO) (KA oil) is produced at up to 85% selectivity, with the ketone/alcohol ratio of about 1 1. The conversion is only about 10% and unconverted cyclohexane is recycled. The process was improved by Bashkirov by the additions up to 5% boric acid to the cyclohexane and by restricting the oxygen content of the air to about 4%. The overall yield was increased to more than 90% and conversion to more than 12%. The ketone/alcohol ratio was decreased to 1 9. 

The ketone/alcohol oil was then oxidized further to adipic acid in a 60% nitric acid solution with an ammonium metavanadate/copper nitrate catalyst at 50°-80°C. Selectivity to adipic acid was more than 95%. A second air oxidation process at 80°-85°C and 6 bar has since been developed. By using a copper ace-tate/manganese acetate catalyst in acetic acid solution, the process has the advantage of avoiding the use of the strongly corrosive nitric acid  

Pure cyclohexanol can also be obtained by the hydrogenation of phenol with a palladium catalyst at 150°C and 10 atm although e process is not widely used. Attempts were made by BASF to synthesize adipic acid from butadiene via a two-step caibonylation process in the presence of methanol. The first step of the synthesis operated at 130°C and 600 bar while the second operated at 170°C and a lower pressure of 160 bar. A typical cobalt catalyst with organic ligands was used, but the process was never developed industrially. 

Phenol produced by the cumene-phenol process is relatively expensive but Solutia has recently claimed a new process developed in Russia.Benzene is oxidized directly to phenol using nitrous oxide. Phenol is then converted to adipic acid by oxidature procedures. Nitrous oxide from the final nitric acid oxidation to adipic acid is recycled to the first stage. This has been reported as the first new commercial technology since DuPont introduced the direct hydrocya-nation of butadiene to adiponitrile in 1971. 

The reaction mixture is poured into a beaker and on cooling the adipic acid crystallizes. It is filtered with suction (Note 5), and the precipitate is washed once with about 200 cc. of cold water and dried in the air. The yield of slightly yellow adipic acid is 375-386 g. (55-56 per cent of the theoretical amount). This product is pure enough for most purposes. However, to remove the yellow color and obtain a purer product, this crude acid may be recrystallized from 700 cc. of concentrated nitric acid (sp. gr. 1.42). The loss in this purification is less than 10 per cent. The recrystallized acid melts at 1530 (Notes 6 and 7). 

If a mechanical stirring device is not available, the reaction may be carried out without stirring. A 5-I. flask should be used, and the mixture must be vigorously boiled to prevent the formation of a layer of cyclohexanol, which might lead to a violent reaction. 

Corks may be used in assembling the apparatus, but they are badly attacked by the hot nitric acid and must be renewed with each run. The asbestos stoppers can be used repeatedly. 

The nitric acid must be boiling hot, so that oxidation will set in as soon as the first drop of cyclohexanol is added. If any considerable amount of cyclohexanol is added before the oxidation starts, a serious explosion may result. 

The cyclohexanol used was the commercial grade, which contains practically no phenol and of which 95 per cent boils between 158-163 °. 

Its name comes from adeps , meaning oil in Latin, due to the fact adipic acid was first obtained from oils. 

Adipic acid is a solid with a melting point of 153 °C. It is produced from the oxidation of cyclohexanol with a nitric acid catalyst. 

Hexamethylene diamine is dissolved in water (bottom layer) and adipic chloride is dissolved in hexane (upper layer). Nylon is formed between these two layers 

If forms long chain polymers upon reaction with diamines and is largely used in the manufacture of nylon. 

An example of the first route is given in the preparation of nylon 66, which is made by reaction of hexamethylenediamine with adipic acid. The first 6 indicates the number of carbon atoms in the diamine and the second the number of carbon atoms in the acid. Thus, as a further example, nylon 6.10 is made by reacting hexamethylenediamine with sebacic acid (HOOC (CH2)g COOH). (In this context the numbers 10,11 and 12 are considered as single numbers the need to use two digits results simply from the limitations of the decimal system.) 

Where the material is denoted by a single number, viz nylon 6 and nylon 11, preparation from either an co-amino acid or a lactam is indicated. The polymer nylon 66/6.10 (60 40) indicates a copolymer using 60 parts of nylon 6.6 salt with 40 parts of nylon 6.10 salt. 

Closely related to the polyamides are the polyimides and derivatives such as polyamide-imides and polyether-imides. These are discussed in Sections 18.13 and 18.14. 

Hexamethylenediamine (1,6-hexanediamine) is a colorless solid, soluble in both water and alcohol. It is the second monomer used to produce nylon 6/6 with adipic acid or its esters. 

The main route for the production of hexamethylene diamine is the liquid-phase catalyzed hydrogenation of adiponitrile  

The reaction conditions are approximately 200°C and 30 atmospheres over a cobalt-based catalyst. 

Adipic acid may be produced by a liquid-phase catalytic carbonylation of butadiene. A catalyst of RhCl2 and CH3I is used at approximately 220°C and 75 atmospheres. Adipic acid yield is about 49%. Both a-gul-taric acid (25%) and valeric acid (26%) are coproduced  

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  

Kirk-Othmer Encyclopedia of Chemical Technology (4th Edition) 

Adipic acid undergoes the usual reactions of carboxylic acids, including esterification, amidation, reduction, halogenation, salt formation, and dehydration. Because of its bifunctional nature, it also undergoes several industrially significant polymerization reactions. 

Ester CAS Registry Number Pressure, kPaa Boiling point, °C 

Salt Formation. Salt-forming reactions of adipic acid are those typical of carboxylic acids. Alkali metal salts and ammonium salts are water soluble alkaline earth metal salts have limited solubility (see Table 5). Salt formation with amines and diamines is discussed in the next section. 

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Colourless liquid with a strong peppermintlike odour b.p. 155" C. Manufactured by passing cyclohexanol vapour over a heated copper catalyst. Volatile in steam. Oxidized to adipic acid. Used in the manufacture of caprolactam. Nylon, adipic acid, nitrocellulose lacquers, celluloid, artificial leather and printing inks. 

C, b.p. 16UC. Manufactured by heating phenol with hydrogen under pressure in the presence of suitable catalysts. Oxidized to adipic acid (main use as intermediate for nylon production) dehydrogenated to cyclohexanone. 

H2N (CH2)a NH2- Colourless solid when pure m.p. 4LC, b.p. 204 C. Manufactured by the electrochemical combination of two molecules of acrylonitrile to adiponitrile followed by catalytic reduction, or by a series of steps from cyclohexanone via adipic acid. Used in the production of Nylon [6, 6]. 

Nylon A class of synthetic fibres and plastics, polyamides. Manufactured by condensation polymerization of ct, oj-aminomonocarboxylic acids or of aliphatic diamines with aliphatic dicarboxylic acids. Also rormed specifically, e.g. from caprolactam. The different Nylons are identified by reference to the carbon numbers of the diacid and diamine (e.g. Nylon 66 is from hexamethylene diamine and adipic acid). Thermoplastic materials with high m.p., insolubility, toughness, impact resistance, low friction. Used in monofilaments, textiles, cables, insulation and in packing materials. U.S. production 1983 11 megatonnes. 

Cyclohexanone, This is readily oxidised by a KjCr 07 - HjSO mixture to the crystalline adipic acid, m.p. 152 , precisely as for cyclohexanol (p. 335). 

By pyrolysis of dibasic acids or their salts to yield cyclic ketones. The slow distillation of adipic acid with about. 5 per cent, of baryta affords cyclo-pentanone in good yield ... 

Mix 200 g. of adipic acid intimately with 10 g. of finely-powdered, crystallised barium hydroxide. Place the mixture in a 1-litre distilling flask, fitted with a thermometer reaching to within 5 mm. of the bottom connect the flask with a condenser and receiver. Heat the mixture gradually in an air bath (1) to 285-295° during about 90 minutes and maintain it at this temperature mitil only a small amount of dry residue remains in the flask this requires a further 2 hours. The temperature must not be allowed to rise above 300°, since at this temperature the adipic acid distils quite rapidly the best working temperature is 290°. The cycZopentanone distils slowly accompanied by a little adipic acid. Separate the ketone from the water in the distillate, and dry it with anhydrous potassium carbonate this treatment simultaneously removes the traces of adipic acid present. Finally distil from a flask of suitable size and collect the cycZopentanone at 128-131°. The yield is 92 g. 

Place 146 g. of adipic acid, 360 ml, (285 g.) of absolute ethyl alcohol 180 ml. of toluene and 1 - 5 g. of concentrated sulphuric acid in a 1-litre round-bottomed flask, attach a short fractionating column connected to a downward condenser, and heat in an oil bath at 115°, When the acid... 

Place 100 g. of adipic acid in a 750 ml. round-bottomed flask and add successively 100 g. (127 ml.) of absolute ethyl alcohol, 250 ml. of sodium-dried benzene and 40 g. (22 ml.) of concentrated sulphuric acid (the last-named cautiously and with gentle swirling of the contents of the flask). Attach a reflux condenser and reflux the mixture gently for 5-6 hours. Pour the reaction mixture into excess of water (2-3 volumes), separate the benzene layer (1), wash it with saturated sodium bicarbonate solution until eflfervescence ceases, then with water, and dry with anhydrous magnesium or calcium sulphate. Remove most of the benzene by distillation under normal pressure until the temperature rises to 100° using the apparatus of Fig. II, 13, 4 but substituting a 250 ml. Claisen flask for the distilling flask then distil under reduced pressure and collect the ethyl adipate at 134-135°/17 mm. The yield is 130 g. 

Adipic acid is conveiiiently prepared by the oxidation of cyc/ohexanol (or cyclohexanone) with concentrated or with 50 per cent, nitric acid ... 

Polyamides from diamines and dibasic acids. The polyamides formed from abphatic diamines (ethylene- to decamethylene-diamine) and abphatic dibasic acids (oxabc to sebacic acid) possess the unusual property of forming strong fibres. By suitable treatment, the fibres may be obtained quite elastic and tough, and retain a high wet strength. These prpperties render them important from the commercial point of view polyamides of this type are cabed nylons The Nylon of commerce (a 66 Nylon, named after number of carbon atoms in the two components) is prepared by heating adipic acid and hexamethylenediamine in an autoclave ... 

Add 40 ml. of ethyl alcohol to 21 -5 g. of 70 per cent, ethylenediamine solution (0 -25 mol) dissolve 36 -5 g. of adipic acid (0 -25 mol) in 50 ml. of a 6 1 mixture of ethyl alcohol and water. Mix the two solutions, stir and cool. Filter off the resulting salt and recrystalliae it from 60 ml. of a 6 1 ethyl alcohol - water mixture, and dry the salt in the air. Heat the salt in an atmosphere of oxygen-free nitrogen or of carbon dioxide in an oil bath until it melts (ca. 160°) the product will sohdify after a short time. Reduce the pressure to 15 mm. of mercury or less and raise the temperature of the oil bath until the product remelts (about 290°) and continue the heating for 4r-5 hours. Upon coohng, a nylon type polymer is obtained. 

X,9. DEPOLYMERISATION OF A HEXAMETHYLENE-DIAMINE-ADIPIC ACID POLYMER (NYLON 66 )... 

Add 10 ml. of concentrated sulphuric acid cautiously to 45 ml. of water contained in a 200 ml. round-bottomed flask, introduce 3 g. of Nylon 66 polymer into the hot solution, and heat under reflux for 6 hours. Allow to stand for 1 hour and cool in ice for a further hour. Filter off the solid and keep the filtrate. Recrystalhse the sohd (adipic acid) from water m.p. 152°. 

Acids. Acetic acid re-Caproic acid Benzoic acid Phenylacetic acid Succinic acid Adipic acid Anthranihc acid. 

The leader of DuPont s effort was Wallace H Carothers who reasoned that he could reproduce the properties of silk by constructing a polymer chain held together as is silk by amide bonds The neces sary amide bonds were formed by heating a dicar boxylic acid with a diamine Hexanedioic acid adipic acid) and 1 6 hexanediamme hexamethylenedi-amine) react to give a salt that when heated gives a polyamide called nylon 66 The amide bonds form by a condensation reaction and nylon 66 is an example of a condensation polymer... 

Figure 5.3 shows the data for the uncatalyzed polymerization of adipic acid and 1,10-decamethylene glycol at 161°C plotted according to Eq. (5.21). The various provisos of the catalyzed case apply here also, so it continues to be appropriate to consider only the final stages of the conversion to polymer. From these results, k is about 4.3 X 10" kg eq min at 161°C. 

Polymerization of AA and BB monomers is illustrated by butane-1,4-diol and adipic acid. The aabb repeat unit in the polymer has an Mq value of 200. If Eq. (5.4) is used to evaluate it gives the number of aa plus bb units therefore = 200(hj )/2. 

As an example of the quantitative testing of Eq. (5.47), consider the polymerization of diethylene glycol (BB) with adipic acid (AA) in the presence of 1,2,3-propane tricarboxylic acid (A3). The critical value of the branching coefficient is 0.50 for this system by Eq. (5.46). For an experiment in which r = 0.800 and p = 0.375, p = 0.953 by Eq. (5.47). The critical extent of reaction, determined by titration, in the polymerizing mixture at the point where bubbles fail to rise through it was found experimentally to be 0.9907. Calculating back from Eq. (5.45), the experimental value of p, is consistent with the value =0.578. 

At 270°C adipic acid decomposesf to the extent of 0.31 mol % after 1.5 hr. Suppose an initially equimolar mixture of adipic acid and diol achieves a value of p = 0.990 after 1.5 hr. Compare the expected and observed values of n in this experiment. Criticize or defend the following proposition The difference between the observed and expected values would be even greater than calculated above if, instead of the extent of reaction being measured analytically, the value of p expected (neglecting decomposition) after 1.5 hr were calculated by an appropriate kinetic equation. 

Adipic acid diester Adipic Acid Salts... 

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