Thermal alkylation of ambidentate lactams with 2-(perfluoroalkyl)-1-iodoalkanes. The effect of reaction conditions and ring size on the synthesis of 2-(perfluoroalkyl)ethanols and the mechanism of reaction

Article abstract of DOI:10.1021/jo00112a029

The perfluoroalkylated long chain alcohols and their derivatives exhibit strong surface activity in solution and novel surface modification properties as adsorbed layers or films. A new, little known synthesis of 2-(perfluoroalkyl)ethanols (R(F)CH₂CH₂OH) employs a lactam, e.g., 2-pyrrolidinone (2), with an iodoalkane, e.g., C₆F₁₃CH₂CH₂I (1). Alkylation of 2 by heating with 1 gives C₆F₁₃CH₂CH₂OH (3) in 83% distilled yield, and treating the residual lactim ether salt (6·HI) with K₂CO₃ gives additional 3, up to 94% yield. Rate of alcohol formation (k(alc)) is unaffected by molar ratio of 2:1, yet rate of 1 reaction (k(iodo)) increases 2.44 times with doubling of 2:1 and side product C₆F₁₃CH = CH₂ (4) decreases from 4 to 2%. For homologous lactams [(CH₂)(n)NHC = O] (n = 3-5), selectivities (mol 3:4) are as follows: 5-membered ring, 18.4; 6-membered ring, 0.73; 7-membered ring, 0.13. Conversions to 3 are as follows: 6-membered ring, 19.4%; and 7-membered ring, 1.75%. A three-stop mechanism is proposed: (1) O-alkylation of the lactam by 1 gives lactim salt I; (2) N-substitution of salt I by another molecule of lactam forms a tetrahedral adduct (II); (3) breakdown of salt II gives 3 and iminolactam salt III. In model experiments, heating of 2 and lactim 6 yields 99% of 3 and iminolactam 5 and 1% of 4. By contrast, 7-membered 14 with 2 gives 45% of 3 and iminolactam 12, besides 4 and -caprolactam 16 (20%). For higher lactams, two competitive reactions can be discerned: (1) the S(N)2 displacement of alcohol by N-attack on salt II and a unimolecular, concerted fragmentation of the lactim, to lactam and alkene.