Patent GB-844689-A (GB)
Title: Improvements in or relating to the preparation of n-vinyl lactams
Filed: 1956-10-01
Abstract: N-vinyl lactams are prepared by forming a reaction mixture of (1) an organic solvent solution comprising or consisting of acetylene and a lactam having hydrogen on the nitrogen thereof and (2) a strongly alkaline compound of an alkali metal as vinylation catalyst, bringing about a vinylation reaction in such mixture at a temperature between 150 DEG C. and 280 DEG C., while subjecting the mixture to a pressure sufficient to maintain all the acetylene in the liquid phase, wherein the acetylene for the reaction mixture is supplied as a solution prepared by absorbing acetylene in a liquid organic solvent at a temperature not exceeding about 30 DEG C. and under elevated pressure, the resulting solution being maintained under sufficient pressure to maintain all the acetylene in the liquid phase whilst it is being brought up to reaction temperature.  Suitably, the acetylene is absorbed in a liquid starting lactam or an organic liquid solution of starting lactam under pressure at a temperature below 30 DEG C. The catalyst may be present when the acetylene is absorbed at the lower temperatures or at least part of the catalyst may be added subsequently; thus, part of the catalyst may be added in the cold, part during the heating up and the remainder added at or above 200 DEG C. and, if desired, in portions.  The vinylation is preferably effected at 200 DEG -280 DEG C. and under pressures of about 1000-5000 p.s.i.g. suitably in a tubular reactor into which catalyst may be injected at one or more points.  The initial absorption of acetylene may be effected using solely a liquid lactam reagent; a solid lactam reagent may be melted, acetylene absorbed therein, the mixture obtained cooled to below about 30 DEG C. and then absorption of acetylene continued; alternatively liquid or solid lactam reagents may be used dissolved in a solvent such as a C1-5 alkanol, or an N-vinyl lactam.  If desired, auxiliary acetylene solvents may be used and numerous examples are given including various open and cyclic ethers, thio ethers containing ether oxygen and mixtures thereof with one another or with C1-5 alkanols or vinyl lactams.  The absorption of acetylene is generally effected at 0-25 DEG C. under pressure of 100-500 p.s.i.g. until the solution is saturated.  The catalysts are preferably sodium or potassium hydroxide or alkoxide or their salts of lactams.  The preferred lactams contain 4-11 carbon atoms, the carbonyl and -NH- groups being joined by 3-5 carbon atoms; numerous examples are given of unsubstituted and mono-, di or tri, C-alkyl substituted 2-pyrrolidones, piperidones and caprolactams.  In typical examples (1) a mixture of 2-pyrrolidinone and sodium butoxide in butanol is saturated with acetylene at 10 DEG C. under 365 p.s.i.g., and the solution pumped through a tubular reaction zone at 190 DEG C. under 1500 p.s.i., the reaction mixture passing out via a pressure release valve and worked up to recover N-vinyl pyrrolidinone; (3) acetylene is dissolved in 2-pyrrolidinone at 30 DEG -16 DEG C. under pressure from 100-290 p.s.i.g. and the solution is passed through a tubular reactor at 225 DEG C. under 1500 p.s.i.g., a dilute solution of KOH in the lactam being injected into the solution at the entry and mid-way points of the tube; (b) acetylene is dissolved in a mixture of epsilon-caprolactam, dimethoxy ethane and potassium isopropoxide in isopropanol at 30 DEG C. under 300 p.s.i.g. and the solution passed through a tubular reactor at 200 DEG C. and 1500 p.s.i.g., additional catalyst solution being injected at the mid-point of the tube; 3-methyl-, 5:5-dimethyl- and 3:3:5-trimethyl-pyrrolidinone-2 and 2-piperidinone may be reacted similarly; (10) acetylene is dissolved in 2-pyrrolidinone substantially as described in (3) and the solution is pumped through a coil at 250 DEG C. under 1800 p.s.i.g., and a solution of potassium dissolved in excess of the lactam is injected at two points in the coil.