Hexamethylene diamine Production

Another early example was DuPont s nylon intermediates processes developed in the late 1930s. DuPont chose to commercialize nylon-66 because of the availability of benzene from coal as a feedstock. The benzene had to be hydrogenated to cyclohexane, which was oxidized in two steps to adipic acid. Originally, adipic acid was the precursor for the other intermediate, hexamethylene diamine. Production of nylon and other polymer intermediates would be an important field in homogeneous catalyst innovation in the post-war era (71). 

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. 

Uses. The principal use of adiponitrile is for hydrogenation to hexamethylene diamine leading to nylon-6,6. However, as a result of BASE s new adiponitrile-to-caprolactam process, a significant fraction of ADN produced may find its way into nylon-6 production. Adipoquanamine, which is prepared by the reaction of adiponitrile with dicyandiamide [461-58-5] (cyanoguanidine), may have uses in melamine—urea amino resins (qv) (see "Benzonitrile, Uses"). Its typical Hquid nitrile properties suggest its use as an extractant for aromatic hydrocarbons. 

Bases function in a more complex way than simply by acting as a halogen acceptor, for they cannot always be used interchangeably, and the product may depend on the base used (58,68,69). Diamines, such as ethylene-, propylene-, or hexamethylene diamines may function differently than monoamines. Diamines were thought to function through chelate formation (32). Loven and Speckamp (40) concluded that selectivity in reduction of a... 

The N,N -dibenzyl-N,N -bis-[2-(3, 4 -dihydroxyphenyl)-2-oxoethyl] -hexamethylene-diamine-dichlorohydrate-monohydrate used as the starting material was prepared as follows 2 mols of chloroaceto pyrocatechin were dissolved in 2,000 cc of acetone and heated to boiling with 2 mols of N,N -dibenzylhexamethylene-diamine for 12 hours, almost the theoretical quantity of N,N -dibenzylhexamethylene-diamine-dichlorohydrate being precipitated and removed by suction after cooling. Excess HCI was added to the filtrate, approximately 66% of the theoretically possible quantity of crude dichlorohydrate of the N,N -dibenzyl-N,N -bis-[2-(3, 4 -dihydroxyphenyl)-2-oxoethyl] -hexamethylene-diamine being precipitated. The product was cleaned by recrystallization from water with the addition of animal charcoal. After drying the substance contained water of crystallization at ambient temperature, MP 206° to 209.5°C. 

After separation of the catalyst the product was concentrated until dry, the residue was triturated with acetone, the resulting crystallizate was removed by suction and washed with acetone. The yield of N,N -bis-(2-(3, 4 -dihydroxyphenyl)-2-hydroxyethyl]-hexamethylene-diamine-dichlorohydrate was 3.3 grams, i.e., 92% of the theoretical value. A quantity of 2.8 grams having a melting point of 197,5° to 198°C was obtained by precipitation from a mixture of methanol-ether. 

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

Condensation polymerisation In this case reaction between two groups occurs which leads to the production of a polymer and also a simple molecule, e.g. reaction between adipic acid and hexamethylene diamine yields nylon 66 and water ... 

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. 

On February 28, 1935, Carothers project succeeded beyond anyone s wildest dreams. The cheerful, lively Frenchman Berchet produced a superpolymer made from chemicals derived from cheap benzene, a by-product of coal later they would be made from petroleum. A filament teased from Berchet s polymer was, despite its lowly origins, pearly and lustrous. And when it was tested, it proved to be spinnable. Its code name was 6-6 because both its reactants—hexamethylene diamine and adipic acid—had six carbon atoms. Technically, the filament was polyhexamethylene adipamide, a long-chain polymer similar in structure to proteins. It became world-famous as nylon. 

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. 

The product obtained is known as nylon 6, 6 as there are six carbon atoms in diamine and 6 carbon atoms in diacid. Nylon 6, 10 is obtained by a similar method from hexamethylene diamine and sebacic... 

Calculate the feed ratio of adipic acid and hexamethylene diamine that should be employed to obtain a polyamide of approximately 15,000 molecular weight at 99.5% conversion. What is the identity of the end groups of this product Do the same calculation for a 19,000-molecular-weight polymer. 

Example 2-11 The monomers for nylon are either the amino acid H2N-(CH2)sCOOH, which forms the polymer called Nylon 6 (six carbon atoms in the backbone) or two monomers adipic acid HOOC-(CH2)4COOH and hexamethylene diamine H2N-(CH2)6NH2, which form the polymer called Nylon 66 (six carbon atoms in the backbone of each of the monomers). It is possible to make the 6-carbon atom monomers very easily with high purity, but the production of nylons with five, seven, or other carbons would be very difficult. Why ... 

Investigation of template poly condensation kinetics has only been studied within a very narrow scope. Polymerization of dimethyl tartrate with hexamethylene diamine was found to be enhanced by using as a template poly(vinyl pyrrolidone), poly(2-vinyl pyridine), or polysaccharides and poly(vinyl alcohol), poly(4-vinyl pyridine). In this case, the template can be treated as a catalyst. No information exists on the influence of the template on the order of reaction. The increase in molecular weight of the polymerization product by the template can be induced by a shift of equilibrium or by an increase in the reaction rate. A similar increase in the reaction rate was observed when poly(4-vi-nyl pyridine) was used in the synthesis of poly(terephtalamides) activated by triphenyl phosphite.The authors suggested that a high molecular weight template was involved in the increase of the local concentration of the substrate (terephthalic acid) by adsorption and activation via N-phosphonium salt of poly(4- vinyl pyridine). 

Chemical Composition. In polyamide 6 (PA 6, polymerization product of e-caprolactam) and polyamide 66 (PA 66, adipic acid polymerized with hexamethylene-diamine) one chain end consists of an amino group, which can be present in the free state or in the acylated form. Amino groups are of special importance for dyeing because they form ammonium groups in an acidic dyebath by addition of protons. The lower dye uptake in comparison to wool is caused by the comparatively low number of amino groups. The depth of color achieved on PA 6 is somewhat less than that on PA 66. 

Adipic acid [HOjC E COjH], the main product of cyclohexane, is reacted with hexamethylene diamine to produce nylon-6,6, a very strong synthetic fiber. Most carpets are made of nylon, as are many silklike garments, some kinds of rope, and many injection-molded articles. 

Nylon-6,6, poly(hexamethylene adipamide), prepared by reacting substantially equimolar quantities of adipic acid and hexamethylene diamine, has for many years been the world s major wholly synthetic fibre. The rapid rate of growth of polyester production indicates that nylon will soon be supplanted as the major fibre by poly(ethylene terephthalate). 

Suppose we wish to prepare a nylon with an M of 16,000 using adipic acid (H02C(CH2)4C02H) and hexamethylene diamine (H2N(CH2)gNH2), which represents an A-A, B-B type of polycondensation. The common, or trade name of the product, poly(hexamethylene adipamide), H0[0C(CH2)4 CONH(CH2)gNH] H, is nylon 6,6, or nylon 66. The first 6 refers to the number of carbon atoms between amide nitrogens for the amine component, and the second 6 refers to the number of carbon atoms separating nitrogens for the acid component. What monomer feed ratio would be required to achieve this M ... 

Problem 5.20 Consider synthesis of nylon-6,10 from hexamethylene diamine, H2N(CH2)eNH2, and sebacic acid, HOOC(CH2)gCOOH, where the mole ratio (r) of the diacid to the diamine is 9. At 9 conversion of carboxylic acid groups (pa = 0.98) determine (a) M and M , of the product, and (b) the sum of the mole fractions and of the weight fractions of species of degrees of polymerization 1 through 6 inclusive. Compare with the corresponding values calculated as approximations from equations for the stoichiometric case with replaced by... 

In a second step, the esters are hydrogenolysed to 1,6-hexanediol, which is then purified. A third step consists in aminating the diol at 208°C and 23.106 Pa absolute by means of ammonia, and in the presence of Raney nickel as catalyst Hexamethylene-diamine is obtained with a molar yield approaching 90 per cent, and the main by-products are hexamethylene imine and 6-aminohexanoL... 

In the case of nylon-6,6, basic hydrolysis is the preferred treatment. Depolymerization occurs by reaction with sodium hydroxide, hexamethylene diamine and sodium adipate being the initially formed products. In a second step, the latter is converted into adipic acid via acidification with HC1. 

A polycondensation is a series of such reactions, which takes place between bifunctional molecules. For example, the polycondensation of adipic acid with hexamethylene-diamine gives nylon 6-6. In fact, the chemical method of production is not so simple, but we may (naively) write the reaction in the form... 

Problem 5.11 What feed ratio of hexamethylene diamine and adipic acid should be employed in order to obtain a polyamide of M - 10,000 99% conversion Identify the end groups of this product. 

---