Modifications in the Synthesis of Caprolactam and Nylon 6 Recently one of our organic lab sections tried the preparation of caprolactam and Nylon 6 following the procedure of Carraher.' This exoeriment was motivated ~ a , d hv v, the recent ACS recommendation for increased coursework in oolvmer , rhrmistry, and pnrtly by a large supply of cyrlohexanc~ncmimeo n hand, collerted from several years deyrlohrunnone synthesis and drrivarive preparation2 Wesugged mudifivations t u the ('armher pnrrdure, dong with the following rolnrnnents as t o safety and procedure are offered: 1) The Carraher article called for carrying out the Beckman rearrangement of eyelohexanoneoxime with3 M H2SO4. A survey of the literature revealed that 15 M HzSO4 (85%)has been used? this concentration fits the amount of KOH suggested by Carraher for neutralization. This acid concentration . cave much better results. with short ('12 to 1min) heatingtimes. 2) The Beckman rearrangement produced a good quantity of white smoke. Therefore, it seems advisable t o carry out this steo in a fume hood. 3) D~chlommrthanrw ~ used s in place ufthlonkmn for the extmetim of rnlrnhman from rhenqtrrcms rrnction mixture. Rathrr than attempt a vacuum distillstiun un the small quantity of pndurt, the orCanac wlntmn u n d dwolurined w t h Nmitc. the solvent removed on a rotary evaporator, and recrystallization from a 7:l hexaneldichlaromethane mixture carried out: large octahedral crystals of m.p. 67-68T were obtained. 4) Due to the cost of N-acetylcaprolactam4 the compound was prepared from acetic anhydride and eaprola~tam.~ Twenty-five grams of caprolactam (0.22 moles) and 26 gof acetic anhydride (0.25 moles, 24 ml) were refluxed for 2 hr. The brownish solution was added to 100 ml of ice and stirred until the ice melted. The mixture was added to a seoaratorv funnel. % ml of dwhloromethnne were added, and the layers separated. The organic lawr was washed uith SO ml pwtiwv of 5% s d i u m hydrogen enrhunnte aolutlon until agitation prc,dueed nc.gas rvolutim The wgan:c l a y r wa.; dried uvrr anhydnus mncnesium sulfate, and the solvent removed on n n m r y rvnpumtor.'l'hii product was used u,ithout further puriticatiun, and gave satisfactory results in the polymerization of caprolactam. 5) The temperatures used in the preparation of Nylon 6 should he kept as low as possible. Our product had a burned smell, indicating some nylon decomposition.
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LCarraher.C. E.. J. CHEM. EDUC.. 52.51 (19781. , B., and Wingrove, A. S., "Modern Experimental Organic Chemistry", 3rd %herb, R. M.; Gilbert, J. C., ~ o d e w k dL. Ed., Holt, Rinehart and Winston, Inc., New York, 1979, pp. 282-298. 3Blatt, A. H., (Editor), "Organic Syntheses"Col1ective Volume 11, John Wiley & Sons, New York, 1943, p. 77. &AlfaDivision, Ventrom Corporation, was the only supplier. The 1979-80 catalog lists 25 g of N-acetylcaprolactam for sifi an y-"."". 5This procedure is a modification of that of Benson, R. E. and Cairns, T. L., J.Amer. Chem. Soc., 70.2115 (1948). Jon E. Malmin
Luther Coliege Decorah, IA 52101
742 1 Journal of Chemical Education
