Ammonia reaction with polyamides

Ammonolysis. In a reaction closely related to aminolysis, ammonia [7664 1-7] reacts with polyamides, usually under pressure and at elevated temperatures (62). 

Caprolactam [105-60-2] (2-oxohexamethyleiiiiriiQe, liexaliydro-2J -a2epin-2-one) is one of the most widely used chemical intermediates. However, almost all of the aimual production of 3.0 x 10 t is consumed as the monomer for nylon-6 fibers and plastics (see Fibers survey Polyamides, plastics). Cyclohexanone, which is the most common organic precursor of caprolactam, is made from benzene by either phenol hydrogenation or cyclohexane oxidation (see Cyclohexanoland cyclohexanone). Reaction with ammonia-derived hydroxjlamine forms cyclohexanone oxime, which undergoes molecular rearrangement to the seven-membered ring S-caprolactam. 

When the -OH of a carboxylic acid is replaced by an -NH2, the compound produced is an amide. Amides are neutral to mildly basic compounds. They can be made from acids, acid chlorides, acid anhydrides, and esters by reaction with ammonia or primary and secondary amines. The amide linkage is found in polyamide resins such as nylon. 

Type 66 nylon is a polyamide first commercialized by DuPont just prior to World War II. At that time, the needed hexamethylenediamine was made from adipic acid by reaction with ammonia to adiponitrile followed by reaction with hydrogen. The adipic acid then, like now, was made from cyclohexane. The cyclohexane, however, was derived from benzene obtained from coal. The ammonia was made from nitrogen in the air by reaction with hydrogen from water obtained in the water-gas shift reaction with carbon monoxide from the coal. So, in the 1950s, nylon was honestly advertised by DuPont as being based on coal, air, and water. 

Draw a picture in your notebook of the polyamide thin-layer plate exposed under UV light after each of the two or three solvent developments. These pictures should look similar to Figure E2.7. Three fluorescent areas should be evident after solvent 2 however, better separation is achieved by solvent 3. A blue fluorescent area at the bottom of the plate is dansic acid (DNS-OH), which is a hydrolysis product of dansyl chloride. A blue-green fluorescent spot about one-third to one-half up the plate is dansyl amide (DNS-NH2), which is produced by reaction of dansyl chloride with ammonia. A third spot, which usually fluoresces green, is the dansyl derivative of the NH2-terminus amino acid. Note the positions of the standard dansyl amino acids and compare with the unknown. What is the identity of the NH2-terminal amino acid Are any other fluorescent spots evident on the plate Using polarity or nonpolarity, try to explain the position of each molecule on the thin-layer plate. 

The most important method used in the preparation of polyamides is direct amidation, usually through the intermediate formation of a salt of the diamine and dicarboxylic acid, but without it in the case of aminoacids or for pairs of monomers that do not readily form a salt. Esters can react with diamines to form polyamides with liberation of alcohol or phenol. Diamines can be reacted with diamides yielding polyamides and freeing ammonia. Polyamides have been prepared by acidolysis of acyl derivatives of diamines (compare Section 5.4 for acidolysis in polyester preparation). Bis-anhydrides react with diamines to form polyamides and, if reacted further, polyimides. The low-temperature reaction of acid chlorides with diamines has been used, interfacially or as a solution technique, to prepare certain polyamides (compare Section 5.7 for related reactions in polyester synthesis). 

Polyamides have also been prepared by the condensation reaction between a diamine and a diamide with liberation of ammonia... 

Reaction of starch dialdehyde with urea gave a condensation product.442,2633 Carboxyamides,2624 including acrylamide,524,585 were also allowed to react with starch dialdehyde. Condensation can occur between starch dialdehyde and macromolecules containing amido groups, for instance, epichlorohydrin-crosslinked polyamide resin,598 ammonia-diethylamine-epichlorohydrin copolymer,588 dicyanamide-formaldehyde resins,565,566 quaternary alkylam-monium compounds,596,610,611 amino acids,2634,2635 protein,626,2636-2639 and aminoalkylated starch.2515 The reactions are favored by low pH. The guanidino moieties of proteins entered the condensation the most readily. 

Condensation polymers are formed by the reaction of bifunctional or poly functional molecules, with the elimination of some small molecule (such as water, ammonia, or hydrogen chloride) as a by-product. Familiar examples of synthetic condensation polymers include polyesters (Dacron, Mylar), polyamides (nylon), polyurethanes, and epoxy resin. Natural condensation polymers include polyamino acids (protein), cellulose, and starch. The process can be represented as follows ... 

In Section 21.12 you learned that carboxylic acids react with alcohols to form esters and with ammonia and amines to form amides. In each reaction, a molecule of water is split out in a condensation reaction. Polymer chemists use these same reactions to form polyesters and polyamides. However, to form the polymer chain by repeated condensation reactions, you must use a t/tcarboxylic acid (two carboxyl groups), such as terephthalic acid, and a t/talcohol (two hydroxyl groups), such as ethylene glycol, as shown here. 

The polyamide is mixed with gaseous ammonia and the catalyst in the ammonolysis reactor. The main reaction products are caprolactam, hexameth-ylene diamine, aminocapronitrile, and adiponitrile. In addition, there are also... 

---