Br J Ind Med: first published as 10.1136/oem.11.1.1 on 1 January 1954. Downloaded from Brit. J. imdstr. Med., 1954, 11, 1. e-CAPROLACTAM BY M. W. GOLDBLATT, MIJRIEL E. FARQUHARSON, GEOFFREY BENNETT, and BERYL M. ASKEW From the Industrial Hygiene Research Laboratories, Imperial Chemical hliduistries, Ltl., The Frythe, Welwyn. Herts. (RECEIVED FOR PUBLICATION JULY 23, 1953) Lactamns are internal amides of amino-acids as Manufacture of s-Caprolactam and its Polymer lactones are internal esters of hydroxy acids. Thus: The general method for the preparation of 8, s, y-Hydroxy butyric acid on losing one molecule of and 4 lactams and their parent amino-acids is the water gives y-butyrolactone formation of the appropriate cyclic ketones from CH20H which, by way of the oximes, the cyclic amide is heat produced by the action of concentrated sulphuric CH2 CH., acid. The last stage is known as the Beckmann < ~~I 0 CH2 CHiC transformation. Thus, starting from phenols, the I hydrolysis intermediate reactions are as follows: COOH CO- OH H OH The formation of lactones is an example of a general tendency of carbon chains to form five or C C more membered rings when the appropriate con- HC CH catalytic H2C CH2 ditions are created. The lactone is readily hydrolysed hlyi(drogenation oxidation 11 http://oem.bmj.com/ to the hydroxy acid. HC CH > H.C CH2 Similar types of change are brought about by heating y, 3, s, and 4 amino-acids to the temperature CH CH2 of fusion, thus: Phenol Cyclohexanol y-amino butyric acid loses one molecule of water 0 N.OH and gives y-butyrolactam 11 11 C C CH2.NH2 CHl,--- heat to fusion H2C/ \CH2 hydroxyl- H,C CH. Conc. on September 28, 2021 by guest. Protected copyright. CH2 CH. amine ,_ NH H.C. CH. HoC CH, H2SO4 CH2 hydrolysis in CH. acid or alkali CH2 CH2 COOH COI Cyclohexanone Oxime The 8-lactam of valeric acid is a six-membered CO-NH ring and the s-lactam of caproic acid is a seven- hydrolysis H.C CH2 COOH NH2 membered ring. in dilute Cyclic amides are foreign to the animal body H2C CH. acid or CH2-CH.-CH.-CH2-CH, although they are readily formed by the conden- alakli sation of amino-acids, e.g. 2-5-dioxo-piperazine CH2 CO-NH Iso-oxime or £-amino Caproic Acid Cyclic Amide from glycine CH2 CH,, by the action s-caprolactam \/ NH-CO This manner of preparation of the lactam from of dehydrating agents. phenol recalls in its earlier stages the first reactions I Br J Ind Med: first published as 10.1136/oem.11.1.1 on 1 January 1954. Downloaded from 2 BRITISH JOURNAL OF INDUSTRIAL MEDICINE in the synthesis of the linear super-polyamide nylon, nitrogen in the Kjeldahl manner). The vapour con- in which the alkaline oxidation of cyclohexanol or tamination consists of lactam at various stages of cyclo-hexanone yields the di-basic adipic acid, polymerization (dimer and trimer mainly), as well which on being melted together with hexamethylene as lactam itself. The vapours condense in the cold diamine gives the polyamide. Since two molecules air and dust deposits on door lintels, window each with six carbons are involved, the polymer is frames, and beams both as a film and in crystalline referred to as " nylon 66 ". form. At the high atmospheric concentrations The " peptide" or amide link -CO-NH- will be given above it is not surprising to find that a bitter familiar. In the nylon synthesis this link arises from taste is experienced. two sources which give rise to the salt. Cross Hohensee (loc. cit.) reports that some workmen linking at the nitrogen atom also occurs. e-Capro- in the spinning section complained that at the end lactam can, by heating its aqueous solution to 260° C. of the shift they were irritable, nervous, uncon- at ordinary pressures, be transformed into a linear trolled, and in some measure mentally confused. polymer thus: The symptoms were alleged to be aggravated when I particularly dusty jobs (e.g. frequent changing of the H 11 spinnerets) were undertaken repeatedly during the CO-NH occurrence -(CHo),5-C-N-(CH2)5-N--N-(CH2)5- day, with the of epistaxis, upper res- H2C CH2 iI H piratory catarrh, with dry and splitting nose and 0 I~~~~~~~~~~~~~~~ lips. Other workers complained of flatulence, H2C CH2 H 11 heartburn, and a heavy feeling in the stomach. All -(CH.,)5-N-C-(CH 2)5-N--C-k(CH2)- these symptoms disappeared after a period in the CH2 ll H fresh air. The epistaxis and respiratory catarrh u 1 were attributed by Hohensee to the local irritant II! action of the lactam dust. This polymer, from which the synthetic fibres are As these were the sole complaints and no other spun, is a German discovery known as " perlon L ". pathological disturbances were reported from the It is unusually pure for a technical product, but is factory, in spite of obviously intense exposure to stated to contain normally approximately 1% of dust and vapour of monomer and polymers, it was the monomer. Perlon L possesses a crystalline concluded with some assurance that the toxic pro- structure and in its physico-chemical properties is perties of the materials are not severe. most a readily compared with metal. Its molecular http://oem.bmj.com/ weight is about 20,000 (Gabler, 1948). Perlon U is the polymer derived from the con- Properties of c-Caprolactam densation product of hexamethylene di-isocyanate c-Caprolactam or cyclohexanone iso-oxime and 1-4-butane diol. CH2-CHo--CO\ Grilon is another polymer envisaged which will NH involve the condensation of s-caprolactam by heat CH2-CH2-CH2/ and pressure. is a white crystalline solid and is extremely soluble in water. Recrystallized from ether it yields beautiful on September 28, 2021 by guest. Protected copyright. Working Conditions in the Manufacture of Perlon L transparent rhombs with a melting point of 680 to 700 Experience of the manufacture of " perlon L" is C. The compound tends to take up water in warm, greatest in Germany. Hohensee (1951) has given the humid air. e-Caprolactam is readily hydrolysed to most recent account of the working conditions in £-amino caproic acid by heating in dilute mineral which the polymer is manufactured and the pharma- acid or alkali. It is stable in aqueous solution at cological properties of e-caprolactam. The batch 1000 C. process is carried out in closed autoclaves which --Amino caproic acid was prepared in our are opened only to charge fresh monomer. At the experiments from the lactam by hydrolysis in lower pole of these autoclaves there are the spinneret N.HC1, removal of the Cl by Ag2O, precipitation feeds : the extruded fibres emerge straight into the of excess silver as sulphide and recrystallizing from air, solidify, and are wound on bobbins. the concentrated, aqueous solution by adding The atmosphere in the spinning rooms was found ethanol in which the amino-acid is practically in- to contain 61 mg./m.3 and that of the laboratories soluble. It crystallizes from cold alcohol in trans- 16-17 mg./m.3 as lactam (determination by passage parent, flat, hexagonal prisms. Its melting point is of air into strong acid and estimation of ammonia 2010 to 2020 C. It gives the ninhydrin reaction. Br J Ind Med: first published as 10.1136/oem.11.1.1 on 1 January 1954. Downloaded from s-CAPR OLACTAM 3 Toxicology of e-Caprolactam of a lactam melt (maximum temperature 1800 C.) In the section on lactams Richter (1934-47) without any pathological effects. Application of states that " the amino acids are not poisonous, 5% and 10% solution to the shaven skin of guinea- but that the y and 8 lactams are violent, strychnine- pigs, to the corneae of rabbits, and to the skin of like poisons, affecting the spinal cord and producing human subjects gave no irritant reaction. In the convulsions; e-caprolactam . .. acts, physiologi- rabbit 10 mg./kg. intravenously led to an ephemeral cally, as a nerve poison ". Lactams have weakly rise in blood pressure, and 50 mg./kg. in the cat acid and weakly basic properties. was also pressor (20 mm. Hg), the effects passing The first significant contribution to the toxicology off in 20 to 25 minutes. The pressor effect was not of these compounds seems to have been that by prevented by decapitation or vagotomy or atropine. Jacobj, Hayashi, and Szubinski (1903), although Morphine inhibition of respiration in the rabbit Jacobj had already shown in 1901 that the cyclic was reversed by caprolactam, 500 mg./kg. being iso-oximes are powerful convulsants. Jacobj and equivalent to 50 mg./kg. cardiazol. others, interpreting their physiological results, The conclusions reached by Hohensee (loc. cit.) stated that the effect of introduction of the +NH may be paraphrased thus: acute poisoning of group into the ring of cyclic ketones was to replace human subjects by s-caprolactam is impossible even a motor and central paralysis by a stimulant action in unfavourable industrial conditions; chronic of the " medullary convulsion centre " and later absorption may proceed at high levels for extended paralysis in the medulla. periods without toxic effects: the low volatility of They go on to say that the relatively simple the compound and very high doses required renders cyclic iso-oximes (lactams) (piperidone, hexanone- poisoning by inhalation most improbable. iso-oxime, suberone-iso-oxime, and probably also pyrrolidone) produce convulsions in frogs and mice Toxicological Experiments and must be included in the picrotoxin group.