Pyrrolidines 1- methyl, basicity

It is noteworthy that the kinetics indirectly provided the evaluation of the basicities of these enamines [Eq. (4)]. The pK values for 4-(2-methyl-propenyl)morpholinc, l-(2-methylpropenyl)piperidine, and l-(2-methyl-propenyl)pyrrolidine are 5.47, 8.35, and 8.84, respectively (27). Since the protonation of the j8-carbon atom does not possess the character of a real equilibrium at pH 7 and up [for compound 1 even at pH 1 and up] the basicity must be fully ascribed to the equilibrium between enamine and the corresponding nitrogen-protonated conjugate acid. 

At higher temperatures the mixture of 10 and methyl vinyl ketone yields the 1,4-carbocyclic compound as described previously. Methyl isopropenyl ketone (5), ethyl acetylacrylate (d), 2-cyclohexenone (21), and 1-acetyl-1-cyclohexene (22) also undergo this type of cyclization reaction with enamines at higher temperatures. This cycloalkylation reaction occurs with enamines made of strongly basic amines such as pyrrolidine, but the less reactive morpholine enamine combines with methyl vinyl ketone to give only a simple alkylated product (7). Chlorovinyl ketones yield pyrans when allowed to react with the enamines of either alicyclic ketones or aldehydes (23). 

Cyclization of a,abis(dimethylthiomethylene) ketones by phosphorus pentasulfide leads to 2,5-bis(methylthio)-l,6,6aA4-trithiapentalenes (equation 7) (71AHC(13)161, p. 185). Condensation of carbon disulfide with pyrrolidin-2-one in basic medium, followed by methylation of the reaction product, leads to methyl 3-(dimethylthiomethylene)-2-oxopyrrolidine-l-dithiocarboxylate. This compound, when treated with phosphorus pentasulfide and perchloric acid, yields the 2,5-bis(methylthio)-l,6,6aA4-trithia-2aA5-azacyclopenta[a/]pen-talen-2a-ylium cation. With e- caprolactam similar results are obtained (76BSF1200). 

The term enamine is used mainly for classifications of the functional group as an ensemble, but individual compounds are termed with respect to the parent compound usually as amino substituted olefins, i.e. tertiary enamines as (N,iV-dialkylamino)alkenes. The correct IUPAC nomenclature for tertiary enamines is dialkylalkenylamines, i.e. the basic compound in this case is the amine not the alkene. The difference may be demonstrated for two examples 73 is in the first notation l-iV-methylanilino-2-methyl-propene and, in IUPAC notation, iV-methyl-jV-(2-methyl-l-propenyl)aniline. Correspondingly 74 is usually called 2-methyl- 1-pyrrolidinopropene but in IUPAC notation it is jV-(2-methyl-l-propenyl)pyrrolidine. 

Liquid-liquid extraction provides one of the most important commercial processes for performing group separations between aromatic and aliphatic species in the petrochemical industry. One of the earliest proven processes, the Udex system, is summarized in Fig. 7.8-9. It is based on the use of diethylene gly and water, a polar solvent, which selectively extracts the more polar aromatic conqxxmds fiom the nonpolar aliphatic species. A variety of solvents have been used including diethylene and Iriethylene glycols," N-methyl pyrrolidine, sulfolane, and other polar solvents. The basic process configurations ate similar to those already described, but in some cases a 1 solvent system may be used to remove asphaltic materials simultaneously. More recent studies give further consideration to alternative solvents for this application. 

Aromatization decreases solvent basicity by a factor of 3.5-5.S, as illustrated by the following couples pyrrolidine/pyrrole (0.99/0.18), N-methylpyrroUdine/N-ethylpyrrole (0.92/0.22), tetrahydrofuran/furan (0.59/0.11), 2-meAyltetrahydro-furan/2-methylfuran (0.56/0.16), cyclohexylamine/aniUne (0.%/0.26), N-methyl-cyclohexylamine/N-methylanihne (0.92/0.21), N,N-dimethylcyclohexylainine/ N,N-dimethylanihne (0.99/0.30) and a structurally less similar couple such as piperidine/pyridine (0.93/0.58). 

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