Caprolactam

Caprolactam(CPL) is anorganic compoundwith theformula(CH₂)₅C(O)NH. This colourless solid is alactam(a cyclicamide) ofcaproic acid.Global demand for this compound is approximately five million tons per year, and the vast majority is used to makeNylon 6filament, fiber, and plastics.

Caprolactam

Names
Preferred IUPAC name Azepan-2-one
Other names 1-Aza-2-cycloheptanone 2-Azacycloheptanone ε-Caprolactam Capron PK4 Cyclohexanone iso-oxime Extrom 6N Hexahydro-2-azepinone Hexahydro-2H-azepin-2-one (9CI) Hexanolactam Hexano-6-lactam Aminocaproic lactam
Identifiers
CAS Number	105-60-2Y
3D model (JSmol)	Interactive image
Beilstein Reference	106934
ChEBI	CHEBI:28579Y
ChEMBL	ChEMBL276218Y
ChemSpider	7480Y
ECHA InfoCard	100.003.013
EC Number	203-313-2
Gmelin Reference	101802
KEGG	C06593Y
PubChemCID	7768
UNII	6879X594Z8Y
CompTox Dashboard(EPA)	DTXSID4020240
InChI InChI=1S/C6H11NO/c8-6-4-2-1-3-5-7-6/h1-5H2,(H,7,8)Y Key: JBKVHLHDHHXQEQ-UHFFFAOYSA-NY InChI=1/C6H11NO/c8-6-4-2-1-3-5-7-6/h1-5H2,(H,7,8) Key: JBKVHLHDHHXQEQ-UHFFFAOYAF
SMILES O=C1NCCCCC1
Properties
Chemical formula	C6H11NO
Molar mass	113.160g·mol−1
Appearance	White solid
Density	1.01 g/cm3
Melting point	69.2 °C (156.6 °F; 342.3 K)
Boiling point	270.8 °C (519.4 °F; 544.0 K) at 1013.25 hPa
Solubility in water	866.89 g/l (22 °C)
Vapor pressure	8.10−8mmHg (20°C)
Hazards
GHSlabelling:
Pictograms
Signal word	Warning
Hazard statements	H302,H315,H319,H332,H335
Precautionary statements	P261,P264,P270,P271,P280,P301+P312,P302+P352,P304+P312,P304+P340,P305+P351+P338,P312,P321,P330,P332+P313,P337+P313,P362,P403+P233,P405,P501
Flash point	125 °C (257 °F; 398 K)
Explosive limits	1.4%-8.0%
NIOSH(US health exposure limits):
PEL(Permissible)	none
Except where otherwise noted, data are given for materials in theirstandard state(at 25 °C [77 °F], 100 kPa). Yverify(what isYN?) Infobox references

Synthesis and production

Caprolactam was first described in the late 1800s when it was prepared by the cyclization of ε-aminocaproic acid,the product of the hydrolysis of caprolactam. World demand for caprolactam was estimated to reach five million tons per year for 2015. 90% of caprolactam produced is used to make filament and fiber, 10% for plastics, and a small amount is used as a chemical intermediate.Due to its commercial significance, many methods have been developed for the production of caprolactam. It was estimated that 90% of all caprolactam is synthesised fromcyclohexanone(1), which is first converted to itsoxime(2). Treatment of this oxime with acid induces theBeckmann rearrangementto give caprolactam (3):

The immediate product of the acid-induced rearrangement is the bisulfate salt of caprolactam. This salt is neutralized withammoniato release the free lactam and cogenerateammonium sulfate.In optimizing the industrial practices, much attention is directed toward minimizing the production of ammonium salts.

The other major industrial route involves formation of the oxime fromcyclohexaneusingnitrosyl chloride,and this method accounts for 10% of world production.The advantage of this method is that cyclohexane is less expensive thancyclohexanone.

Other paths to caprolactam include the depolymerization of waste Nylon 6, and the reaction ofcaprolactonewith ammonia.At bench scale, the reaction between cyclohexanone withhydrazoic acidto give caprolactam in theSchmidt reactionhas been reported.

Uses

Almost all caprolactam produced goes into the manufacture ofNylon 6.The conversion entails aring-opening polymerization:

Nylon 6 is widely used infibersandplastics.

In situ anionic polymerization is employed for cast nylon production where conversion from ε-caprolactam to Nylon 6 takes place inside a mold. In conjunction with endless fiber processing the term thermoplastic resin transfer molding (T-RTM) is often used.

Caprolactam is also used in the synthesis of several pharmaceutical drugs includingpentylenetetrazol,meptazinol,andlaurocapram.

Safety

Caprolactam is anirritantand is mildlytoxic,with anLD₅₀of 1.1 g/kg (rat, oral). In 1991, it was included on the list of hazardous air pollutants by the U.S.Clean Air Act of 1990.It was subsequently removed from the list in 1996 at the request of the manufacturers.In water, caprolactam hydrolyzes toaminocaproic acid,which is used medicinally.

As of 2016 caprolactam had the unusual status of being the only chemical in theInternational Agency for Research on Cancer's lowest hazard category, Group 4: "probably not carcinogenic to humans".

Currently, there is no officialpermissible exposure limitset for workers handling caprolactam in the United States. Therecommended exposure limitis set at 1 mg/m³over an eight-hour work shift for caprolactam dusts and vapors. Theshort-term exposure limitis set at 3 mg/m³for caprolactam dusts and vapors.

Climate impact

The production of caprolactam can producenitrous oxideas a by-product, a highly potent greenhouse gas. Emissions differ significantly due to different production processes and inconsistent use of emission abatement technology. A study commissioned by the GermanFederal Ministry for Economic Affairs and Climate Actionestimates emissions between 9 kg of nitrous oxide per ton of caprolactam and almost zero.

Nitrous oxide emissions from caprolactam production are unregulated in most countries. Unlike other chemical production processes, nitrous oxide emissions from caprolactam production are not included in theEuropean Union Emissions Trading System.