Nylon manufacture

Stereochemistry. Cyclohexane can exist ia two molecular conformations the chair and boat forms. Conversion from one conformation to the other iavolves rotations about carbon—carbon single bonds. Energy barriers associated with this type of rotation are low and transition from one form to the other is rapid. The predominant stereochemistry of cyclohexane has no influence ia its use as a raw material for nylon manufacture or as a solvent. 

Enzymatic hydrolysis is also used for the preparation of L-amino acids. Racemic D- and L-amino acids and their acyl-derivatives obtained chemically can be resolved enzymatically to yield their natural L-forms. Aminoacylases such as that from Pispergillus OTj e specifically hydrolyze L-enantiomers of acyl-DL-amino acids. The resulting L-amino acid can be separated readily from the unchanged acyl-D form which is racemized and subjected to further hydrolysis. Several L-amino acids, eg, methionine [63-68-3], phenylalanine [63-91-2], tryptophan [73-22-3], and valine [72-18-4] have been manufactured by this process in Japan and production costs have been reduced by 40% through the appHcation of immobilized cell technology (75). Cyclohexane chloride, which is a by-product in nylon manufacture, is chemically converted to DL-amino-S-caprolactam [105-60-2] (23) which is resolved and/or racemized to (24)... 

Hydrocarbon Oxidation. The oxidation of hydrocarbons (qv) and hydrocarbon derivatives can be significantly altered by boron compounds. Several large-scale commercial processes, such as the oxidation of cyclohexane to a cyclohexanol—cyclohexanone mixture in nylon manufacture, are based on boron compounds (see Cylcohexanoland cyclohexanone Eibers, polyamide). A number of patents have been issued on the use of borate esters and boroxines in hydrocarbon oxidation reactions, but commercial processes apparently use boric acid as the preferred boron source. The Hterature in this field has been covered through 1967 (47). Since that time the Hterature consists of foreign patents, but no significant appHcations have been reported for borate esters. 

The most important use of cyclohexanone is as a chemical intermediate in nylon manufacture 97% of all cyclohexanone output is used either to make caprolactam for nylon-6, or adipic acid for nylon-6,6. In the caprolactam process cyclohexanone is converted to cyclohexanone oxime (mp,... 

Cyclo-paraffins, also referred to as naphthenes, are mainly produced by dehydrogenation of their equivalent aromatic compounds such as the production of cyclohexane by dehydrogenation of benzene. Cyclohexane is mostly used for the production of adipic acid and nylon manufacturing (Rudd et al., 1981). 

J.F. Mullen (Dorr-Ohver luc.) reports that fluidized bed incinerators have been used for municipal sludge and industrial waste incineration since the early 1960s for a variety of wastes (petroleum tank bottoms, sludge from pharmaceutical, pulp and paper, and nylon manufacturing operations), waste plastics, waste oils, and solvents. Fluid beds were first considered for incinerating hazardous wastes in the 1980s. 

No atoms are lost in the cleavage reaction so that cheap cyclohexene 6 is used to make adipic acid 7 for nylon manufacture. Any of the oxidative cleavage methods from the last chapter could be used Vogel1 has a recipe using concentrated nitric acid on cyclohexanol 8 that presumably goes by dehydration to the alkene 6 followed by oxidation, and other methods are probably used industrially. 

In one process for nylon manufacture, the feedstock is nitration-grade toluene, air, hydrogen, anhydrous ammonia (NH3), and sulfuric acid (H2S04). The toluene is oxidized to yield a 30% solution of benzoic acid, plus intermediates and by-products. Pure benzoic acid, after fractionation, is hydrogenated with a palladium catalyst in stirred reactors operated at about 170°C under a pressure of 147 psi (1013 kPa). The product, cyclohexanecarboxylic acid, is mixed with sulfuric acid and then reacted with nitrosylsulfuric acid to yield caprolactam. 

Intramolecular acylations often go very well indeed when a five- or a six-membered ring is being formed, A classic case is the cyclization of the diethyl ester of adipic acid (diethyl hexanedioate), a component in nylon manufacture. 

Ozonolysis of cyclohexenes is particularly useful as it gives 1,6-dicarbonyl compounds that are Otherwise difficult to make. In the simplest case we get hexane 1,6-dioic acid (adipic acid) a monomer for nylon manufacture. 

Eventually the phenylphosphonothionic dichloride derivative was found to have a large use as an intermediate for the new insecticide, EPN (A), by its inventor (9) and phenylphosphinic acid (B) was shown to be a good stabilizer against yellowing on heating for Nylon 6-6 by Nylon manufacturers (chart I) (70, 77). 

This sequence illustrates the use of enolates from 1,3-dicarbonyl compounds in Michael reactions they are useful too in alkylations, aldol condensations (Knoevenagel conditions), and reactions with epoxides, as in the synthesis3 of 20. Nowadays they tend to be used if they are readily available, or if the disconnections suggest their use, as in the building of 11 into 18. Examples include the diketone 11 and the six-membered equivalent both used in steroid synthesis, acetoacetates 16 and 19 and the keto-lactones 20, malonic acid 21 and its esters, "Meldrum s acid 22, a very enolisable malonate derivative,4 and the keto-ester 25 formed via its stable enolate 24, by the cyclisation of the diester 23, an intermediate in nylon manufacture. The compounds 11,16, 19, 20 R=H, 21, 22, and 25 are all available commercially. 

Many organic syntheses involve HCN, and it is of great industrial importance, a large fraction going into the production of 1,4-dicyanobutane (adiponitrile) for nylon manufacture, and cyanoethene (acrylonitrile) for production of acrylic flbres. 

Cyclohexane is a large volume petrochemical used mainly in nylon manufacture. In 1965 the free-world consumption was 1.1 million tons, and this is expected to double substantially by 1970 (5). Methods for manufacturing cyclohexane are thus of considerable interest. While presently most cyclohexane is made by hydrogenating benzene (I), some is derived from natural sources. A potential method for manufacturing cyclohexane is by the selective hydrodealkylation of methylcyclohexane. Such a process is considerably more direct than the demethanation of toluene, followed by hydrogenation of the resulting benzene. 

Nitrous oxide is produced as a byproduct in multimillion Ib/year quantities in nylon manufacture worldwide. Currently, there is a great interest toward the utilization of NjO due to the environmentally hazardous nature of this gas with respect to the greenhouse effect and ozone layer depletion. In addition to their ability to utilize dioxygen for catalytic hydrocarbon oxidations, ruthenium porphyrins have been shown to activate nitrous oxide which is an extremely inert molecule and a poor ligand. Groves and Roman have found that N O reacted with Ru"(TMP)(THF)2 in toluene to produce Ru (TMP)(0)2 . trans-dioxoRu(VI) complex can in turn epoxidize a suitable substrate such as tra/js-p-methyl styrene. This system was subsequently shown to be catalytic under appropriate conditions . 

The commercial diamines used for nylon manufacture are usually best made by hydrogenation of the corresponding dinitriles. Hexamethylene-diamine is made by hydrogenation of the adiponitrile. Adiponitrile is now commercially produced by several methods. In the oldest method, ammonium adipate was catalytically dehydrated to the dinitrile. In a method developed since World War II, butadiene is treated with chlorine to produce mixture of dichlorobutenes. Reaction with hydrogen cyanide in the prewnce of cuprous halides yields l,4-dicyanobutene-2 exclusively. Hy-dn enation produces adiponitrile. 

Conjugated Alkenes. - By far the largest and best known industrial electro-organic reduction is the hydrodimerization of acrylonitrile to adiponitrile, an important precursor in nylon manufacture. Plants where this process... 

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