Neutral media addition-elimination

Chlorination. Electrophilic chlorination of quinoline (66) in neutral medium showed a positional selectivity order of 3 > 6 > 8. The 5- and 8-positions should be sterically hindered to some extent. Hammett cr+ values predict an order for electrophilic substitution of 5 > 8 = 6 > 3. Treatment with chlorine at 160-190°C converted quinoline into a mixture of 3-chloro-, 3,4-dichloro-, 3,4,6- and 3,4,8-trichloro-, 3,4,6,8-tetrachloro-, and 3,4,6,7,8-pentachloro-quinolines. At lower temperatures ( 100°C) the major product was 3-chloroquinoline, albeit in low yield. The 4-substituted species may have arisen from an addition-elimination or radical process (70JHC171). 

Kinetic studies of the nucleophilic reactions of azolides have demonstrated that the aminolyses and alcoholyses proceed via a bimolecular addition-elimination reaction mechanism, as does the neutral hydrolysis of azolides of aromatic carboxylic acids. Aliphatic carboxylic acid azolides which are subject to steric hindrance can be hydrolyzed in aqueous medium by an 5n1 process. There have been many studies of these reactions, and evidence supporting both 5n1 and 5n2 processes leaves the impression that there are features of individual olysis reactions which favour either an initial ionization or a bimolecular process involving a tetrahedral intermediate (80AHC(27)241, B-76MI40701). 

Purification this step features the second innovation of the process which, to eliminate the by-product acrolein, favors the formation of cyanohydrin by means of the hydrogen cyanide which is also present This operation takes place at low temperature (20 Q in agitated reactors, either continuously in the presence of a copper-based catalyst, or semi-continuously with a reaction phase in basic medium (caustic soda addition), followed by a neutralization period (sulfuric acid addition). The cyanohydrin obtained is then removed by vacuum distillation. The withdrawal may be sent to a thin layer evaporator to recover entrained acrylonitrile. These treatments must be conducted in the presence of a polymerization inhibitor and at a temperature below 55 C to prevent the rede-composition of cyanohydrin.... .. ... 

It has already been mentioned that the K, in NCW is several orders of magnitude greater than in water at room temperature. Thus, as shown previously, acid and base catalysis can be facilitated without the use of additional acid. Certainly CO2 reacts with water to form carbonic acid and, as a consequence, the concentration of hydronium ion in NCW can be increased by enriching the medium with CO2. From an environmental point of view this procedure wiU not only facilitate specific acid-catalyzed reactions but will not require neutralization of the acid after the reaction is complete. A simple cooling and depressurization will eliminate the CO2 and phase separates the product(s) of reaction. Thus, Aleman et al. have reported that the conversion of mesitoic acid to mesitylene over a period of 120 min at 250°C increased from 50 to 80% in the presence of 10 bar (rt) of CO2. Hunter and Savage reported the dehydration of cyclohexanol in water at 250 and 275°C and the reaction of p-cresol with tert-butanol in water at 275°C in the absence and presence of CO2. Their results indicated that in the presence of CO2 the rate of dehydration of the cyclohexanol increased by more than a factor of 2 and the rate of formation of 2-tert-butyl-4-methylphenol increased 40-120%. Modest increases in rate were reported for the hydration of cyclohexene to cyclohexanol. 

---