Caprolactam Aminocaproic acid

Material PA6 2. Formula Made by self condensation of E-caprolactam (aminocaproic acid) Polyamide 6 (Nylon 6)... 

In Europe, 1. G. Earbenindustrie decided to develop nylon-6 that had been synthesized from S-caprolactam using an aminocaproic acid catalyst (1) and commercially introduced as Pedon L in 1940 (11,12). 1. G. Earbenindustrie had evaluated over 3000 polyamide constituents without finding an improvement over nylon-6 and nylon-6,6 (13). In Italy, Societa Rhodiaceta started making nylon-6,6 in 1939. In the United Kingdom, ICl and Courtaulds formed British Nylon Spinners in 1940 and started to manufacture nylon-6,6 in 1941. 

Caprolactam is preferred to w-aminocaproic acid for the manufacture of nylon 6 because it is easier to make and to purify. Over the years many routes for the manufacture of caprolactam itself have been developed and major commercial routes are summarised in Figure 18.6. Of these routes the bulk of manufacture is via cyclohexanone and cyclohexanone oxime. 

The cyclic oligomers are only slightly soluble in water and dilute solutions of caprolactam. They tend to separate out from die extracted waste during die process of concentration and chemical purification of die caprolactam. The cyclic oligomers tend to form on the walls of the equipment used in die process equipment. 6-Aminocaproic acid or sodium 6-aminocaproate may also be found in die oligomeric waste, especially if sodium hydroxide is used to initiate die caprolactam polymerization. 

Continuous Production Process for Caprolactam Production via Nitrocyclohexanone and Aminocaproic Acid... 

The common name caprolactam comes from the original name for the Ce carboxylic acid, caproic acid. Caprolactam is the cyclic amide (lactam) of 6-aminocaproic acid. Its manufacture is from cyclohexanone, made usually from cyclohexane (58%), but also available from phenol (42%). Some of the cyclohexanol in cyclohexanone/cyclohexanol mixtures can be converted to cyclohexanone by a ZnO catalyst at 400°C. Then the cyclohexanone is converted into the oxime with hydroxylamine. The oxime undergoes a very famous acid-catalyzed reaction called the Beckmann rearrangement to give caprolactam. Sulfuric acid at 100-120°C is common but phosphoric acid is also used, since after treatment with ammonia the by-product becomes... 

The polymerization of caprolactam to nylon 6 is an example of a step polymerization that does not lose a molecule of water. Oligomers can be isolated at any time, which is clearly a step reaction. If we recall that it is actually the polymerization of 6-aminocaproic acid, then we can see that it is indeed a step polymerization with loss of water. 

Aminocaproic acid Aminocaproic acid (24.4.1) is synthesized by hydrolyzing e-caprolactam at high temperature [56-62],... 

It should be noted that there is an ambiguity here in that poly(6-aminocaproic acid) and poly(e-caprolactam) are one and the same polymer. The same polymer is produced from two different monomers—a not uncommonly encountered situation. 

Poly(e-caprolactam) orpoly(e-aminocaproic acid) depending on the source of polymer Poly[imino(l-oxohexane-l,6-diyl)]... 

Special terminology based on trade names has been employed for some polymers. Although trade names should be avoided, one must be familiar with those that are firmly established and commonly used. An example of trade-name nomenclature is the use of the name nylon for the polyamides from unsubstituted, nonbranched aliphatic monomers. Two numbers are added onto the word nylon with the first number indicating the number of methylene groups in the diamine portion of the polyamide and the second number the number of carbon atoms in the diacyl portion. Thus poly(hexamethylene adipamide) and polyfhexamethylene sebacamide) are nylon 6,6 and nylon 6,10, respectively. Variants of these names are frequently employed. The literature contains such variations of nylon 6,6 as nylon 66, 66 nylon, nylon 6/6, 6,6 nylon, and 6-6 nylon. Polyamides from single monomers are denoted by a single number to denote the number of carbon atoms in the repeating unit. Poly(e-caprolactam) or poly(6-aminocaproic acid) is nylon 6. 

The overall rate of conversion of e-caprolactam to polymer is higher than the polymerization rate of e-aminocaproic acid by more than an order of magnitude [Hermans et al., 1958, I960]. Step polymerization of e-aminocaproic acid with itself (Eq. 7-57) accounts for only a few percent of the total polymerization of e-caprolactam. Ring-opening polymerization (Eq. 7-58) is the overwhelming route for polymer formation. Polymerization is acid-catalyzed as indicated by the observations that amines and sodium e-aminocaproate are poor initiators in the absence of water and the polymerization rate in the presence of water is first-order in lactam and second-order in COOH end groups [Majury, 1958]. 

It has become the custom to name linear aliphatic polyamides according to the number of carbon atoms of the diamine component (first named) and of the dicarboxylic acid. Thus, the condensation polymer from hexamethylenedi-amine and adipic acid is called polyamide-6,6 (or Nylon-6,6), while the corresponding polymer from hexamethylenediamine and sebacoic acid is called polyamide-6,10 (Nylon-6,10). Polyamides resulting from the polycondensation of an aminocarboxylic acid or from ring-opening polymerization of lactams are indicated by a single number thus polyamide-6 (Nylon-6) is the polymer from c-aminocaproic acid or from e-caprolactam. 

Nylon 6 is also a polyamide, but is made from the monomer e-caprolactam, which is a cyclic amide of e-aminocaproic acid. Heat opens the lactam ring to give the amino acid salt, which forms amide bonds with other molecules by eliminating water. 

Caprolactam (melting point 69.3°C, density 1.02, flash point 125°C, fire point 140°C), so named because it is derived from the original name for the C6 carboxylic acid, caproic acid, is the cyclic amide (lactam) of 6-aminocaproic acid. 

After purification, the lactam is polymerized by heating at elevated temperatures in an inert atmosphere. During self-condensation, the ring structure of the lactam is opened so that the monomer acts as an epsilon-aminocaproic acid radical. Unlike that of nylon 66, the polymerization of caprolactam is reversible the polymer remains in equilibrium with a small amount of monomer. As with nylon 66, nylon 6 is extruded in thin strands, quenched, and cut into chips for subsequent spinning, or the molten polymer is pumped directly to the spinning equipment. 

However, a classification into condensation and addition polymers as originally envisaged by Carothers [2] is no longer appropriate because some polymers can be synthesized by either method. For example, Nylon-6, a polymer with repeating units -NH(CH2)5CO—, can be made either from 6-aminocaproic acid by condensation polymerization or from caprolactam by addition polymerization. 

Cyclization. The two functional end groups of a monomer or polymer molecule might react with one another to form a cyclic compound [15,16]. An example is the formation of caprolactam as a by-product in condensation polymerization of 6-aminocaproic acid to Nylon-6 [5] ... 

Most amino acids are barely soluble in non-aqueous solvents. Nevertheless, their lactams can be prepared by this technique under heterogeneous conditions. For example, when 6-aminocaproic acid and 1 mol % boron catalyst 3,4,5-F3C6H2B(OH)2 are suspended in xylene under reflux the solid slowly dissolves and caprolactam is formed in 93 % yield. 

Fig. 27. Concentration of aminocaproic acid ([Si ]) during hydrolytic polymerization of caprolactam [1]. Initial concentration of water 0.59 ( ) resp. 0.87 mole kg (o) temperature 221.5°C.

Evaluation of the equilibrium concentrations of water, aminocaproic acid, chains and lactam in the hydrolytic polymerization of caprolactam [2, 3, 5, 8, 12, 221, 235, 238] resulted in the following values of Af/j and... 

Hydrolytic polymerization [12,13] of e-caprolactam to form nylon-6 [m = 5 in Eq. (10.48)] is carried out commercially in both batch and continuous processs by heating the monomer in the presence of 5-10% water to temperatures of 250-270°C for periods of 12 hr to more than 24 hr. In the first step, the lactam is hydrolyzed to e-aminocaproic acid ... 

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